mafic and felsic magma interaction in granites the hercynian karkonosze pluton sudetes bohemian massif the hercynian post collisional karkonosze pluton contains several lithologies equigranular and porphyritic granites hybrid quartz diorites and granodiorites microgranular magmatic enclaves and composite and lamprophyre dykes field relationships mineralogy and majorand trace element geochemistry show that 1 the equigranular granite is differentiated and evolved by small degrees of fractional crystallization and that it is free of contamination by mafic magma 2 all other components are affected by mixing the end members of the mixing process were a porphyritic granite and a mafic lamprophyre the degree of mixing varied widely depending on both place and time all of the processes involved are assessed quantitatively with the following conclusions most of the pluton was affected by mixing implying that huge volumes 475 km of mafic magma were available this mafic magma probably supplied the additional heat necessary to initiate crustal melting part of this heat could have also been released as latent heat of crystallization only a very small part of the karkonosze granite escaped interaction with mafic magma specifically the equigranular granite and a subordinate part of the porphyritic granite minerals from these facies are compositionally homogeneous and or normally zoned which together with geochemical modelling indicates that they evolved by small degrees of fractional crystallization 520 accessory minerals played an important role during magmatic differentiation and thus the fractional crystallization history is better recorded by trace rather than by major elements the interactions between mafic and felsic magmas reflect their viscosity contrast with increasing viscosity contrast the magmatic relationships change from homogeneous hybrid quartz diorites granodiorites to rounded magmatic enclaves to composite dykes and finally to dykes with chilled margins these relationships indicate that injection of mafic magma into the granite took place over the whole crystallization history consequently a long lived mafic source coexisted together with the granite magma mafic magmas were derived either directly from the mantle or via one or more crustal storage reservoirs compatible element abundances e g ni show that the mafic magmas that interacted with the granite were progressively poorer in ni in the order hybrid quartz dioritescgranodioritescenclavesccomposite dykes this indicates that the felsic and mafic magmas evolved independently which in the case of the karkonosze granite favours a deep seated magma chamber rather than a continuous flux from mantle two magma sources mantle and crust coexisted and melted almost contemporaneously the two reservoirs evolved independently by fractional crystallization however mafic magma was continuously being intruded into the crystallizing granite with more or less complete mixing several lines of evidence e g magmatic flux structures incorporation of granite feldspars into mafic magma feldspar zoning with fluctuating trace element patterns reflecting rapid changes in magma composition indicate that during its emplacement and crystallization the granite body was affected by strong internal movements these would favour more complete and efficient mixing the systematic spatial temporal association of lamprophyres with crustal magmas is interpreted as indicating that their mantle source is a fertile peridotite possibly enriched metasomatized by earlier subduction processes

site investigations to evaluate flow liquefaction slides at sand heads fraser river delta l ecoulement par liquefaction spontanee est un processus recurrent dans la progradation du delta du fleuve fraser une portion du delta a ete etudiee au moyen d essais de penetration au cone sismique et de resistivite et au moyen de l analyse spectrale de la methode des ondes de surface et de l echantiollonage de sol et de vapeur dans un effort pour determiner la stratigraphie du site l etat in situ et le degre de saturation afin explorer l enigme de l ecoulement par liquefaction spontanee un ensemble de capteur de pression interstitielle et d inclinaison a ete installe comme partie de l etude pour mesurer les effets de la vidange resultant du reflux de la maree les resultats ont indique que le lit de la mer a faible profondeur etait partiellement sature contenant un volume significatif de gaz methane qui affectait la reponse dynamique de la pression interstitielle durant le jusant une reduction de la contrainte effective atteignant 16 5 kpa a ete mesuree de meme qu un delai de 50 min entre le reflux de la maree et la reaction de la pression interstitielle ceci suggere que les effets de tampon sont un facteur significatif dans le declenchement de la liquefaction spontanee des sables l ches non viellis la ou ils reposent sur des pentes sous marines les resultats des essais in situ montrent que les sables nouvellement deposes du fleuve fraser ont une forte susceptibilite a l ecoulement par liquefaction

crustal extension ag pb zn veins in the xiong ershan district southern north china craton constraints from the shagou deposit the shagou vein type ag pb zn deposit in the xiong ershan district southern margin of the north china craton is hosted within amphibolite facies metamorphic rocks of the late archean to early paleoproterozoic taihua group the ag pb zn veins are localized in ne to nne trending brittle faults and typically display symmetrical zoning consisting of siderite quartz sphalerite galena and quartz calcite from the margin toward the center of each vein ore related hydrothermal alteration is well developed on both sides of the veins dominated by silicification sericitization chloritization and carbonatization sericite separates extracted from a major ag pb zn vein yield a 40 ar 39 ar plateau age of 140 0 1 0 ma 1 and isochron age of 141 1 1 6 ma 1 indicating that mineralization occurred at the beginning of early cretaceous field and textural relationships indicate four hydrothermal stages marked by assemblages of quartz siderite stage i quartz sphalerite ankerite stage ii quartz galena silver minerals ankerite stage iii and quartz calcite stage iv respectively silver minerals are abundant in all veins and are composed of in paragenetic order argentiferous tetrahedrite polybasite jalpaite argentite and native silver these silver minerals commonly occur as replacements of galena chalcopyrite and other sulfides or as fillings of microfractures in sulfides and quartz microthermometric measurements of primary fluid inclusions in quartz carbonates and sphalerite from various hydrothermal stages indicate that ore minerals were deposited at intermediate temperatures 267 157 c from aqueous carbonic to aqueous fluids with moderate salinities 7 2 15 9 wt nacl equiv coexisting galena sphalerite pair yields sulfur isotope equilibrium temperatures of 205 to 267 c consistent with the overall homogenization temperatures of fluid inclusions the microthermometric data also indicate that both fluid mixing and fluid rock interaction were important mechanisms for ore precipitation carbonate minerals siderite ankerite calcite spanning the entire mineralization history have 13 c v pdb values of 5 2 to 1 4 and 18 o v smow of 10 9 to 15 0 corresponding to calculated values for the ore fluids of 6 5 to 1 8 and 1 4 to 5 4 respectively 34 s v cdt values of sulfide minerals pyrite sphalerite galena range from 1 1 to 5 5 consistent with a deep seated sulfur source galena separates have 206 pb 204 pb ratios of 17 472 to 17 813 207 pb 204 pb ratios of 15 411 to 15 498 and 208 pb 204 pb ratios of 38 178 to 38 506 the isotope data together with geological and geochronological evidence favor a primary metamorphic source for sulfur and other components in the ore fluids a synthesis of available data suggests that the shagou deposit is a typical vein type ag pb zn deposit that formed under an extensional geodynamic setting associated with tectonic reactivation of the north china craton during the late mesozoic a time period that is manifested by pervasive magmatism widespread formation of metamorphic core complexes and development of faulted basins throughout the eastern part of the craton metamorphic devolatilization of the meso neoproterozoic marine sedimentary rocks previously subducted beneath the xiong ershan district facilitated by extensive magmatism and elevated heat flow due to lithospheric extension could have provided large amounts of ore fluids responsible for the ag pb zn mineralization the ne to nne trending faults affiliated with the transcrustal machaoying fault may have acted as pathways for the upward migration of deep seated metamorphic fluids mixing of the metamorphically derived fluids with meteoric waters ultimately resulted in deposition of the ag pb zn veins in brittle extensional structures

mafic magmatic enclaves and mafic rocks associated with some granitoids of the central sierra nevada batholith california nature origin and relations with the hosts abstract the calc alkaline granitoids of the central sierra nevada batholith are associated with abundant mafic rocks these include both country rock xenoliths and mafic magmatic enclaves mme that commonly have fine grained and less commonly cumulate textures scarce composite enclaves consist of either xenoliths enclosed in mme or of mme enclosed in other mme with different grain size and texture enclaves are often enclosed in mafic aggregates and form meter size polygenic swarms mostly in the margins of normally zoned plutons enclaves may locally divert schlieren layering mafic dikes which also occur in swarms are undisturbed composite or largely hybridized in central sierra nevada with the exception of xenoliths that completely differ from the other rocks host granitoids mafic aggregates mme and some composite dikes exhibit a bulk compositional diversity and at the same time important mineralogical and geochemical including isotopic similarities mme and host granitoids display distinct major and trace element compositions however strong correlations between mme host granitoid pairs indicate interactions and parallel evolution of mme and enclosing granitoid in each pluton identical mafic mineral compositions and isotopic features are the result of these interactions and parallel evolution mafic dikes have broadly the same major and trace element compositions as the mme although variations are large between the different dikes that are at distinctly different stages of hybridization and digestion by the host granitoids the composition of the granitoids and various mafic rocks reflects three distinct stages of hybridization that occurred respectively at depth during ascent and emplacement and after emplacement the occurrence and succession of hybridization processes were tightly controlled by the physical properties of the magmas the sequential thorough or partial mixing and mingling were commonly followed by differentiation and segregation processes unusual mme that contain abundant large crystals of hornblende resulted from disruption of early cumulates at depth whereas those richer in large crystals of biotite were formed by disruption of late mafic aggregates or schlieren layerings at the level of emplacement mme and host granitoids are considered cogenetic because both are hybrid rocks that were produced by the mixing of the same two components in different proportions the felsic component was produced by partial melting of preexisting crustal materials whereas the dominant mafic component was probably derived from the upper mantle however in the lack of a clear mantle signature the origin of the mafic component remains questionable

chronology and geochemistry of mesozoic granitoids in the bengbu area central china constraints on the tectonic evolution of the eastern north china craton abstract we performed zircon u pb dating and analyses of major and trace elements and sr nd pb isotopes for granitoids in the bengbu area central china with the aim of constraining the magma sources and tectonic evolution of the eastern north china craton ncc the analyzed zircons show typical fine scale oscillatory zoning indicating a magmatic origin zircon u pb dating reveals granitoids of two ages late jurassic and early cretaceous 206pb 238u ages of 160 ma and 130 110 ma respectively the late jurassic rocks jingshan intrusion consist of biotite syenogranite whereas the early cretaceous rocks huaiguang xilushan nushan and caoshan intrusions are granodiorite syenogranite and monzogranite the late jurassic biotite syenogranites and early cretaceous granitoids have the following common geochemical characteristics sio2 70 35 74 56 wt k2o na2o 0 66 1 27 mainly the occurrence of neoproterozoic magmatic zircons 850 ma and inherited early mesozoic 208 228 ma metamorphic zircons within the late jurassic biotite syenogranites together with the occurrence of neoproterozoic magmatic zircons 657 and 759 ma and inherited early mesozoic 206 231 ma metamorphic zircons within the early cretaceous nushan and xilushan granitoids suggests that the primary magmas were derived from partial melting of the yangtze craton yc basement in contrast the occurrence of paleoproterozoic and paleoarchean inherited zircons within the huaiguang granitoids indicates that their primary magmas mainly originated from partial melting of the ncc basement the occurrence of yc basement within the lower continental crust of the eastern ncc indicates that the yc was subducted to the northwest beneath the ncc along the tan lu fault zone during the early mesozoic

u pb ages and morphologies of zircon in microgranitoid enclaves and peraluminous host granite evidence for magma mingling granites of the s type wilson s promontory batholith lachlan fold belt australia contain zircons which are euhedral and relatively large their age is 395 ma which can be considered as the best available estimate of the crystallysation age of the granites contrary to their dominance in other s type granites of the lachlan fold belt very few zircon cores give inherited ages varying between 500 and 1700 ma microgranitoid enclaves contained within the granites contain a zircon population that is dominated by relatively small anhedral or elongated crystals these give ages that are indistinguishable from the crystallisation age of the granite some enclaves which are characterised by the presence of megacrysts contain a proportion of larger euhedral zircons these zircons give inherited ages similar to the zircons from the granitic host rocks the data are in agreement with a magma mingling origin for the microgranitoid enclaves the large euhedral zircons are interpreted to have been introduced into the enclave magma during a hybridisation event which also introduced quartz and plagioclase megacrysts into the magma the relatively high proportion of inherited cores within the large zircon population of the enclaves is related to the timing of mixing between enclave and host magma this mixing event took place before the majority of the magmatic zircons crystallised in the granitic magma the small anhedral zircons within the enclaves crystallised during quenching of the globules of enclave magma against the cooler granitic magma

origin of the xiaohekou skarn copper deposit and related granitoids in the zha shan ore cluster area south qinling china abstract the xiaohekou copper deposit is one of the few typical skarn type commercial deposits in the zha shan ore cluster area in the eastern part of south qinling the ore related granitoids in the xiaohekou mining district include a number of small plutons of granodiorite porphyry and granite porphyry as well as numerous dykes they are characterized by relatively low sio2 65 9 73 3 wt and mgo 0 26 1 72 wt contents variable mg 29 4 64 0 values high k2o 3 11 5 75 wt content and negligible eu 1 00 1 15 values the samples also exhibit depletion in cr ni nb ta and ti content and high sr y 46 6 64 7 and la yb 17 0 25 0 ratios these features are similar to those of high k calc alkaline adakite like magma formed by partial melting of thickened lower crust in continental collision zones or intracontinental settings the majority of the samples have tdm2 hf of 1 5 1 2 ga corresponding to weakly negative ehf t values 4 75 to 0 13 typical of crustal material but more than one quarter have tdm1 hf of 0 80 0 71 ga corresponding to positive ehf t values of 0 07 to 2 45 indicating that the granitoids resulted from partial melting of mesoproterozoic lower crustal rocks with significant input from enriched lithospheric mantle derived magmas zircons from the xiaohekou granitoids have fmq values concentrated around 0 62 to 5 54 most of which show the magma fo2 of fmq to hm in accordance with the widespread occurrence of magnetite hematite and specularite in the xiaohekou skarn system which is an indicator of relatively high fo2 for a magmatic hydrothermal system the granitoids exhibit similar or even higher ce4 ce3 average of 452 and eu eu average of 0 72 values in comparison with those of fertile cu deposits worldwide indicating that the xiaohekou granitoids may possess the potential to form a large magmatic hydrothermal cu deposit zircons of the granitoids show obvious positive correlations between oxidation indices ce and eu anomalies ce4 ce3 ratios and fmq values and ehf t values implying the involvement of an oxidized mantle component which might have caused the fo2 elevation and played an important role in the formation of cu deposits the zircon u pb ages 141 3 1 3 and 138 1 2 0 ma of the xiaohekou ore related granitoids obtained in this study are similar to the zircon u pb and molybdenite re os ages yielded from porphyry mo mineralization at the chigou and lengshuigou deposits in the zha shan ore district indicating that they are possibly part of a single tectonic magmatic and metallogenic event in the yanshan orogeny the ore related granitoids in the xiaohekou area were formed in a post collisional compression extension transition regime during the early cretaceous qinling intracontinental orogeny the orogeny can be attributed to the far field effect of a switch from pre mesozoic tethyan tectonics to late mesozoic pacific tectonics this triggered a stress field transition from n s to e w trending and from intracontinental subduction thickening to large scale lithospheric delamination and thinning

la icp ms zircon u pb dating trace element and hf isotope geochemistry of the heyu granite batholith eastern qinling central china implications for mesozoic tectono magmatic evolution article i nfo mesozoic granitoids are widespread in the southern margin of the north china craton and of particular geo logical interests because of their indication for lithospheric evolution and close association with porphyry mo mineralization in this contribution in situ la icp ms u pb hf isotope and trace element analyses of zircon crystals have been combined to constrain the emplacement time and petrogenesis of the heyu granitic bath olith which hosts the yuchiling porphyry mo system henan province china as inferred from field investiga tions the concentrically zoned heyu batholith mainly consists of four texturally distinguishable phases and displays a pattern of monotonically decreasing u pb age from 143 0 1 6 ma for phase 1 through 138 4 1 5 ma for phase 2 through to ca 135 ma for phase 3 and to 133 6 1 3 ma for the mo mineralized yuchiling granite porphyry phase 4 the ehf t values 27 7 to 3 4 and the two stage hf model ages 1403 to 2924 ma of zircon grains together with the ages of local strata suggest that the magmas forming the heyu batholith were dominantly sourced from the crust with input of a mantle component the higher ce ce ratios of the zircon crystals in the mineralized yuchiling porphyry compared to those in the mo barren phases suggests that fluids exsolved from oxidic magmas might be more favorable for mo enrichment a regional synthesis suggests that intensive lithospheric thinning in the southern margin of the north china craton should not be earlier than 130 ma

hf isotopes in zircon reveal contrasting sources and crystallization histories for alkaline to peralkaline granites of temora southeastern australia peralkaline granites exhibit the hallmark features of a type igneous rocks but strongly differentiated chemistry and intense hydrothermal alteration camouflage their ultimate origins we present the first in situ hf isotope data from zircons of peralkaline granites aimed at clarifying the protoliths of these plutons and their genetic relationship to associated metaluminous weakly peraluminous granites this study used rocks of the devonian narraburra complex in southeastern australia and found that correlations between hf isotopes and trace element ratios reveal fundamentally different origins for the nonperalkaline and peralkaline granites the latter have a depleted mantle like ancestry whereas a weakly peraluminous rock formed from melts of older arc crust that were modified by interaction with juvenile probably alkaline magmas juxtaposition of crust and mantle derived magmas reflects the high heat flow and lithosphere scale faults associated with continental extension and explains the diversity of a type granites

the early cretaceous yangzhaiyu lode gold deposit north china craton a link between craton reactivation and gold veining the yangzhaiyu gold deposit is one of numerous lode gold deposits in the xiaoqinling district southern margin of the north china craton gold mineralization is hosted in neoarchean to early paleoproterozoic amphibolite facies metamorphic rocks and consists of auriferous quartz veins and subordinate disseminated ores in the vein proximal alteration zone ore related hydrothermal alteration is dominated by sericite quartz sulfide assemblages close to gold veins and biotite quartz pyrite chlorite epidote alteration generally distal from mineralization pyrite is the predominant sulfide mineral locally coexisting with minor amounts of chalcopyrite sphalerite and galena gold occurs mostly as free gold enclosed in or filling microfractures of pyrite and quartz and is also present in equilibrium with au bearing tellurides mainly petzite and calaverite coexisting with hessite tellurobismuthite and altaite fluid inclusion studies suggest that gold veins were deposited at intermediate temperatures 175 313 c from aqueous or aqueous carbonic fluids with moderate salinity 5 14 wt nacl equiv 34s values of sulfide minerals range mainly from 2 0 to 4 4 whereas auriferous quartz vein samples have 18o values of 12 4 to 9 6 with calculated 18oh2o values of 6 0 to 3 2 gold related pyrite grains yield elevated 3he 4he ratios 1 51 0 32 ra relative to crustal reservoirs and mantle like 20ne 22ne and 21ne 22ne ratios 9 90 9 68 and 0 029 respectively the stable and noble gas isotopes thus suggest deep seated most likely magmatic and mantle derived sources for the ore fluids sulfur and by inference other components in the ore system 40ar 39ar dating of ore related sericite and biotite separates indicates two episodes of gold genesis at 134 5 to 132 3 and 124 3 to 123 7 ma the mineralization ages overlap zircon u pb ages of 141 0 1 6 to 125 8 1 4 ma 2 for the wenyu and niangniangshan monzogranite plutons and a number of mafic to intermediate dikes intruding these plutons all being proximal to the yangzhaiyu gold deposit the synchronism of gold genesis and magmatism provides additional weights of evidence for a magmatic derivation of ore fluids and sulfur the geochronologic data also suggest that gold veining took place billions of years after the stabilization of the north china craton and associated metamorphism in the late archean to early paleoproterozoic this contrasts sharply to lode gold deposits in other precambrian cratons that formed predominantly in late archean to paleoproterozoic temporarily and genetically related to regional high grade metamorphism and compressional or transpressional tectonism available data have demonstrated that the north china craton was reactivated in the late mesozoic as marked by voluminous igneous rocks faulted basin formation high crustal heat flow and widespread metamorphic core complexes in the eastern part of the craton it is thus suggested that the yangzhaiyu gold deposit together with other deposits of similar ages in the xiaoqinling district were products of this craton reactivation event lithospheric extension and extensive magmatism related to the craton reactivation may have provided sufficient heat energy fluid and sulfur required for the formation of the gold deposits

multiple sources for the origin of granites geochemical and nd sr isotopic evidence from the gudaoling granite and its mafic enclaves northeast china geochemical and sr and nd isotopic data have been determined for mafic to intermediate microgranular enclaves and host granitoids from the early cretaceous gudaoling batholith in the liaodong peninsula ne china the rocks include monzogranite porphyric granodiorite and quartz diorite monzogranites have relatively high 87rb 86sr ratios 0 672 0 853 low initial 87sr 86sr ratios 0 7052 0 7086 and e nd t values 18 5 to 20 9 indicating that they were mainly derived from a newly underplated crustal source with a short crustal residence time quartz diorites have high initial 87sr 86sr ratios 0 7118 0 7120 and negative e nd t values 13 2 to 18 1 coupled with high al2o3 and mgo contents indicating they were derived from enriched lithospheric mantle with contributions of radiogenic sr from plagioclase rich metagreywackes or meta igneous rocks i e ancient lower crust two groups of enclaves with igneous textures and abundant acicular apatites are distinguished dioritic enclaves and biotite monzonitic enclaves dioritic enclaves have low al2o3 13 5 16 4 wt and high mgo mg 72 3 concentrations low initial 87sr 86sr ratios 0 7058 0 7073 and negative e nd t values 7 2 and are enriched in liles and lrees and depleted in hfses suggesting they were derived from an enriched lithospheric mantle source biotite monzonitic enclaves have sr and nd isotopic compositions similar to the monzogranites indicating they were crystal cumulates of the parental magmas of these monzogranites granodiorites have transitional geochemistry and nd and sr isotopic compositions intermediate between the monzogranites quartz diorites and the enclaves geochemical and sr and nd 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 mafic mantle derived and juvenile crustal derived magmas coupled with crystal fractionation and assimilation of ancient lower crust is compatible with the data this example shows that at least some calc alkaline granitoids are not produced by pure intracrustal melting but formed through a complex multi stage hybridization process involving mantle and crustal derived magmas and several concomitant magmatic processes crystal fractionation crustal assimilation and crustal anatexis

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

multi element geochemical modelling of crust mantle interactions during late archaean crustal growth the closepet granite south india the closepet granite in the dharwar craton of south india is a large late archaean magmatic body its composition can be explained as a result of interactions between mantle derived melts and pre existing continental crust ttg gneisses using geochemical modelling based upon major and trace element compositions the following petrogenetic model is proposed for the formation of the batholith i an enriched mantle garnet and amphibole bearing lherzolite melts to produce a basaltic liquid ii the basaltic liquid undergoes limited fractional crystallization of biotite and amphibole f 0 9 iii the differentiated liquid rises into the old continental crust and induces water saturated anatexis of the ttg gneisses k feldspar qtz plagioclase melt iv both mantle derived and anatectic liquid mix and give rise to magma compositions ranging from quartz monzonite to granite the origin of the mantle enrichment is discussed in the context of the regional geological setting the most likely possibility seems to be metasomatism by slab melts the metasomatism of a mantle wedge by slab melts this suggests a two stage evolution for the dharwar craton during the late archaean i a subduction related event with the formation of ttgs sanukitoids and with associated mantle metasomatism and ii re melting of the metasomatized mantle this evolutionary history implies that at least some of the k rich late archaean granites are juvenile rather than products of intracrustal reworking as frequently assumed

zircon texture and chemical composition as a guide to magmatic processes and mixing in a granitic environment and coeval volcanic system this study documents the chemical and textural responses of zircon in the elba igneous complex with particular reference to the 7 to 7 8 ma old monte capanne pluton in relation to its coeval volcanic counterpart capraia using bse imaging and quantitative electron microprobe analyses the monte capanne pluton displays multiple field and geochemical evidence for magma mixing the samples we have investigated including monzogranitic mafic enclave and dyke samples display similar zircon textures and are associated with an extremely large range of trace and minor element hf y hree th u compositions which contrast with relatively simple textures and zoning patterns in zircons from a capraia dacite we have used a relatively simple textural classification patchy zoning homogenous cores oscillatory zoning and unzoned zircon as the basis for discussing the chemical composition and chemical variation within zircons from the monte capanne pluton based on these data and other works dini et al 2004 in lithos 78 101 118 2004 it is inferred that mixing between metaluminous and peraluminous melts occurred early in the evolution of the monte capanne magma chamber in particular mixing was responsible for the development of the patchy zoning texture in the zircon cores which was associated with reactions between other accessory phases including monazite apatite allanite which we infer to have significantly affected the th distribution in zircon zircons from the mc pluton displaying homogeneous cores have chemical affinities with zircons in the coeval capraia volcanic system consistent with the participation of a capraia like mantle end member during mixing further zircon growth in the mc pluton produced the oscillatory zoning texture which records both long term crystal fractionation and transient recharge with both silicic and mafic magmas events in a hybrid magma chamber it is inferred that hf and the th u ratio cannot be used alone to infer magmatic processes due to their dependency on temperature nor are they a diagnostic feature of xenocrystic grains this study shows that zircon chemistry coupled with detailed textural analysis can provide a powerful tool to elucidate the complex evolution of a magma system

destruction of the eastern north china craton in a backarc setting evidence from crustal deformation kinematics abstract the eastern north china craton ncc west of the pacific ocean has a long history of rifting from early cretaceous to the end of paleogene when the craton experienced destruction and significant thinning of the lithosphere the cause and geotectonic environment for this destruction remain controversial we use a set of field observation including basin patterns fault geometry and kinematics fault plane slip data dike distribution and fabric data from metamorphic core complexes to determine the kinematic evolution of the deformation in the eastern ncc during this period we show that the principal extension direction in the eastern ncc evolved from wnw ese in the earliest middle early cretaceous via nw se in the latest early cretaceous to nearly n s in the late cretaceous paleogene the movement history from late mesozoic to early cenozoic of the oceanic plates in the pacific ocean with respect to the eastern ncc is available from previous studies the izanagi plate first subducted nearly orthogonally wnw wards during earliest middle early cretaceous time and then moved obliquely nnw wards in the latest early cretaceous while the relaying pacific plate moved generally northwards from the late cretaceous to paleogene both the movement direction of oceanic plates and the principal extension direction of the continental deformation rotated clockwise we suggest that such a correlation can be explained by the eastern ncc being in a backarc setting in the cretaceous paleogene period the results support the backarc extensional model for the destruction and significant lithospheric thinning of the eastern ncc

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

geochemical evidence for origin of magma mixing for the triassic monzonitic granite and its enclaves at mishuling in the qinling orogen central china abstract whole rock major trace elements and sr nd isotopes mineral chemistry and zircon u pb and lu hf isotope compositions are reported for i type monzogranite and its mafic microgranular enclaves from the triassic mishuling granite in the qinling orogen central china zircon u pb dating yields an age of 212 5 ma for the mafic enclaves and 213 3 ma for the host monzogranite whole rock major trace elements sr nd isotopes and zircon hf isotopes preclude simple crystal fractionation or restite unmixing for a genetic link between the enclaves and the monzogranite mixing between mafic and felsic magmas is compatible with the geochemical data the monzogranite displays an enriched lile and lree pattern high 87sr 86sr i ratios of 0 7068 to 0 7071 and low end t values of 9 2 to 5 7 suggesting a crustal origin its high mg 47 6 to 50 7 cr and ni contents clearly indicate its derivation from mafic refractory lower crust most of the zircons in the monzogranite have negative ehf t values of 12 5 to 0 1 and two stage hf model ages of 1049 to 1683 ma and some zircons in the host monzogranite have positive ehf t values of 0 3 to 4 8 and single stage hf model ages of 665 to 845 ma this indicates that the monzogranite is most likely to be formed by partial melting of a proterozoic lower continental crust the mafic enclaves have fine grained igneous textures and contain abundant acicular apatite that indicates rapid cooling they also have a high 87sr 86sr i ratio of 0 7071 and a low end t value of 6 5 suggesting a derivation from ancient subcontinental lithosphere mantle sclm zircons in the mafic microgranular enclaves have ehf t values of 1 6 to 5 1 and single stage hf model ages of 700 to 910 ma suggesting a possible origin from partial melting of the neoproterozoic sclm that may form in association with contemporaneously supercontinental rifting in the south china block therefore the mishuling i type granite may form by anatexis of meso neoproterozoic lower crust with mixing between the mafic and felsic magmas in particular we interpret the positive ehf t values as being derived from reworking of neoproterozoic juvenile lithosphere in response to tectonic extension in the late stage of the triassic continental collision between the south china block and the north china block

magma mixing origin for the post collisional adakitic monzogranite of the triassic yangba pluton northwestern margin of the south china block geochemistry sr nd isotopic zircon u pb dating and hf isotopic evidences petrogenesis of high mg adakitic rocks in intracontinental settings is still a matter of debate this paper reports major and trace element whole rock sr nd isotope zircon u pb and hf isotope data for a suite of adakitic monzogranite and its mafic microgranular enclaves mmes at yangba in the northwestern margin of the south china block these geochemical data suggest that magma mixing between felsic adakitic magma derived from thickened lower continental crust and mafic magma derived from subcontinental lithospheric mantle sclm may account for the origin of high mg adakitic rocks in the intracontinental setting the host monzogranite and mmes from the yangba pluton have zircon u pb ages of 207 2 and 208 2 ma respectively the mmes show igneous textures and contain abundant acicular apatite that suggests quenching process their trace element and evolved sr nd isotopic compositions 87sr 86sr i 0 707069 0 707138 and end t 6 5 indicate an origin from sclm some zircon grains from the mmes have positive ehf t values of 2 3 8 2 with single stage hf model ages of 531 764 ma thus the mmes would be derived from partial melts of the neoproterozoic sclm that formed during rift magmatism in response to breakup of supercontinent rodinia and experience subsequent fractional crystallization and magma mixing process the host monzogranite exhibits typical geochemical characteristics of adakite i e high la yb and sr y ratios low contents of y 9 5 14 5 ppm and yb no significant eu anomalies eu eu 0 81 0 90 suggesting that garnet was stable in their source during partial melting its evolved sr nd isotopic compositions 87sr 86sr i 0 7041 0 7061 and end t 3 1 to 4 3 and high contents of k2o 3 22 3 84 and th 13 7 19 0 ppm clearly indicate an origin from the continental crust in addition its high mg 51 55 cr and ni contents may result from mixing with the sclm derived mafic magma most of the zircon grains from the adakitic monzogranite show negative ehf t values of 9 4 to 0 1 with two stage hf model ages of 1 043 1 517 ma some zircon grains display positive ehf t of 0 1 3 9 with single stage hf ages of 704 856 ma these indicate that the source region of adakitic monzogranite contains the neoproterozoic juvenile crust that has the positive ehf t values in the triassic thus the high mg adakitic granites in the intracontinental setting would form by mixing between the crustal derived adakitic magma and the sclm derived mafic magma the mafic and adakitic magmas were generated coevally at late triassic temporally consistent with the exhumation of deeply subducted continental crust in the northern margin of the south china block this bimodal magmatism postdates slab breakoff at mantle depths and therefore is suggested as a geodynamic response to lithospheric extension subsequent to the continental collision between the south china and north china blocks

giant mesozoic gold provinces related to the destruction of the north china craton abstract lode gold deposits in precambrian cratons represent the world s major gold source and were mostly generated during formation and stabilization of the cratons however there is an extraordinary exception in the north china craton ncc where lode gold deposits formed after prolonged stabilization of the craton molybdenite re os and hydrothermal sericite and biotite 40 ar 39 ar dating of major gold deposits from the xiaoqinling district southern ncc bracket their emplacement in the range of 154 1 1 1 to 118 9 1 2 ma n 23 postdating formation of the craton by more than 1 7 billion years fluid inclusions extracted from gold bearing pyrite have elevated 3 he 4 he ratios 1 52 0 22 ra and mantle like ne isotopes 20 ne 22 ne 10 02 9 22 and 21 ne 22 ne 0 033 0 027 indicating presence of mantle derived fluids in the ore system measured 34 s of pyrite and d and 18 o of hydrothermal micas and fluid inclusion waters in auriferous quartz further confirm a magmatic mantle source for sulfur and ore fluids gold deposits of similar ages also widely occur in the eastern and northern margins of the ncc which together with those in the xiaoqinling district have a total reserve of 2500 t gold forming the only known giant late mesozoic gold province in the world s precambrian cratons these deposits formed coevally with extensive felsic to mafic magmatism development of intracontinental rift basins and exhumation of metamorphic core complexes across the eastern ncc events interpreted as indicating thinning and destruction of the lithosphere beneath the craton rising of asthenosphere coupled with destruction of the lithosphere has generated voluminous mafic and felsic magmas that provided sufficient fluids sulfur and by inference other ore components to form the giant gold provinces

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

crust mantle interaction in the central north china craton during the mesozoic evidence from zircon u pb chronology hf isotope and geochemistry of syenitic monzonitic intrusions from shanxi province abstract in situ zircon u pb ages hf isotopic compositions and whole rock geochemical and sr nd isotopic compositions are presented for three mesozoic syenitic monzonitic intrusions from shanxi province central north china craton zircons from these intrusions all show core rim structures in that the oscillatory rims recorded their intrusive ages whereas the cores are interpreted as xenocrysts the u pb age data reveal that the northernmost dishuiyan monzonite was emplaced at 241 ma while the huyanshan and erfengshan syenitic monzonitic complexes were emplaced at 130 ma and 128 134 ma respectively the dishuiyan monzonite is petrologically and geochemically uniform it shows lree enrichment and hfse depletion and exhibits enriched sr and nd isotopic compositions with 87 sr 86 sr i 0 7065 and end t 8 3 7 9 the zircon rims in the dishuiyan monzonite show highly varied hf isotopic compositions with ehf t 27 8 6 4 the varied hf isotopic compositions and enriched sr nd isotopic compositions together with the ubiquitous xenocrystic zircon cores suggest the dishuiyan monzonite was produced by the mixing of melts from enriched lithospheric mantle and lower crust the monzonite and syenite from the huyanshan complexes exhibit different geochemical features the end t values of syenite which are higher than those of monzonite resemble the enriched lithospheric mantle and together with the absence of zircon in the syenite we propose that it was originated by partial melting of enriched lithospheric mantle monzonites from huyanshan and erfengshan share similar petrological and geochemical characteristics being enriched in lree and depleted in hfse and they show low end t values between 18 2 and 13 9 similar to zircon rims in the dishuiyan monzonite those in the huyanshan and erfengshan monzonites also exhibit highly varied hf isotopic compositions the consistent ages between the xenocrystic zircons in monzonites and the lower crustal basement rocks of the ncc reveal a significant contribution from the lower crust in the formation of the monzonites we propose that the monzonites from huyanshan and erfengshan were formed through hybridization of enriched lithospheric mantle derived and lower crust derived magmas the mesozoic syenitic monzonitic intrusions in shanxi province were produced under extensional environments which linked to different geodynamic settings the triassic dishuiyan monzonite is a product of post collisional lithospheric extension related to the subduction of the paleo asian oceanic plate under the ncc and subsequent slab break off in the north while the cretaceous huyanshan and erfengshan syenite monzonite was produced under a back arc extensional regime linked to the subduction of the paleo pacific slab beneath east asia

tracing magma mixing in granite genesis in situ u pb dating and hf isotope analysis of zircons in situ zircon u pb and hf isotopic data have been determined for mafic microgranular enclaves and host granitoids from the early cretaceous gudaoling batholith in the liaodong peninsula ne china in order to constrain the sources and petrogenesis of granites the zircon u pb age of the enclaves 120 1 ma is identical to that of the host monzogranite 120 1 ma establishing that the mafic and felsic magmas were coeval the hf isotopic composition of the enclaves ehf t 4 5 to 6 2 is distinct from the host monzogranite ehf t 15 1 to 25 4 indicating that both depleted mantle and crustal sources contributed to their origin the depleted mantle component was not previously revealed by geochemical and nd and sr isotopic studies showing that zircon hf isotopic data can be a powerful geochemical tracer with the potential to provide unique petrogenetic information some wall rock contamination is indicated by inherited zircons with considerably older u pb ages and low initial hf isotopic compositions hafnium isotopic variations in early cretaceous zircons rule out simple crystal liquid fractionation or restite unmixing as the major genetic link between enclaves and host rocks instead mixing of mantle derived mafic magmas with crustal derived felsic magmas coupled with assimilation of wall rocks is compatible with the data

application of the restite model to the deddick granodiorite and its enclaves a reinterpretation of the observations and data of maas et al 1997 mafic s type granites of the lachlan fold belt always contain a introduction distinctive suite of enclaves dominated by schists and gneisses of high maas et al 1997 have proposed complex models of metamorphic grade generally with lesser numbers of microgranular crustal melting and magma mixing to account for the enclaves maas et al 1997 journal of petrology 38 chemical and isotopic features of several kinds of enclaves 815 841 recently described enclaves from the s type deddick in the s type deddick granodiorite of the lachlan fold granodiorite they concluded that the metasedimentary enclaves belt lfb exposed at mckillops bridge that grancould be either source lithologies or accidental xenoliths and that odiorite is a member of the bullenbalong suite area the most common microgranular enclaves formed as globules of 3100 km white chappell 1988 itself part of the hybrid magma that mingled with the host magma all features of very extensive and slightly more diverse bullenbalong the metasedimentary enclaves are consistent with an origin as lithic supersuite total area 8750 km plus 4000 km of restite fragments from the source and their ubiquity in the mafic svolcanic rocks it occurs near the southern extremity of type granites and their rarity in both felsic varieties and in i type those granites these are the rocks that have been used granites conform with such an origin the argument that these as primary examples of restite and of the restite model enclaves are not in chemical equilibrium with the host granite in s type granites hine et al 1976 white chappell because they do not complement its composition is not valid as they 1977 chappell et al 1987 chappell 1996b and the represent less fertile parts of the source that did not melt to the point enclosed enclaves have been regarded by us as lithic of disaggregation unaltered cores of microgranular enclaves in the restite white chappell 1988 chen et al 1989 s type granites have compositions that do not match those of any chappell white 1991 white et al 1991 wyborn known igneous rock and an origin by metamorphism of a calcareous et al 1991 sediment is probable partial melting during that metamorphism maas et al 1997 mostly reject the presence of restite accounts for the pseudo igneous textures seen in these enclaves enclaves in the deddick granodiorite however the

the shanggong gold deposit eastern qinling orogen china isotope geochemistry and implications for ore genesis abstract the shanggong au deposit in the xiong er terrane east qinling china has resources of about 30 ton au making it one of the largest orogenic mesothermal au deposits hosted in volcanic rocks of the mesoproterozoic xiong er group three stages of hydrothermal activity are recognized early middle and late of which two early and middle were ore producing and characterized by quartz pyrite and polymetallic sulfides respectively the third and late stage is represented by a carbonate quartz assemblage hydrogen oxygen and carbon isotope systematics of the shanggong deposit from a previous work suggest that the early stage fluids were derived from magmatic and or metamorphic devolatilization of sedimentary rocks at depth this is supported by new c s and published sr and pb isotopic data presented in this paper these new data 13c values ranging from 1 5 for early stage ankerite to 2 2 for late stage ankerite negative 34s values for sulfides from the middle stage 19 2 to 6 3 suggest a contribution from organic matter and that the ore fluid evolved from deeply sourced to shallowly sourced with those of the middle stage representing a mixture of these two fluid systems the comparison of the hydrogen oxygen carbon sulfur lead strontium isotope systematics between the shanggong deposit and the main lithologies in the xiong er terrane shows that neither these nor the underlying lower crust and mantle or combinations thereof could be considered as the source of ore fluids for the shanggong au deposit a likely source was a carbonaceous carbonate sandstone shale chert sequence in the underthrusted guandaokou and luanchuan groups exposed south of the xiong er terrane ar ar and rb sr isochron ages for mineral phases of the early middle and late stages together with geological field data constrain the timing of the hydrothermal activity and au metallogenesis at 242 10 167 7 and 112 7 ma respectively this metallogenesis and associated granitic magmatism can be related to the continental collision between the yangtze and north china cratons that resulted in the formation of the qinling orogen led to the different hydrothermal systems that were responsible for the three stages that formed the shanggong au deposit over a period of about 130 myrs

the source of granitic gneisses and migmatites in the antarctic peninsula a combined u pb shrimp and laser ablation hf isotope study of complex zircons zircons gneisses and migmatites collected from the antarctic peninsula have different core rim hafnium isotope ratio relationships depending on whether evidence for zircon dissolution is present or absent two samples contain inherited zircon that is partially dissolved in these samples the 176hf 177hf rations of the inherited zircon and new magmatic zircon rims are on average indistinguishable and consistent with in situ melting in such cases the hafnium isotopic composition of the melt was probably strongly influenced by the dissolved zircon component at the source variation in 176hf 177hf within the magmatic zircon rims from grain to grain suggests that hf isotopes were only partially homogenized during melt migration alternatively zircon growth may have taken place within small volumes of partial melt other samples do not preserve textural evidence for zircon dissolution during melt generation in these samples the 176hf 177hf values of the inherited zircon and new magmatic zircon rims are different the zircon rims apparently suggest a source of less evolved hafnium than that contained within the inherited zircon whether this relates to a separate juvenile source or alternatively is derived from minerals other than zircon at the source cannot be resolved inherited zircon irrespective of age has been strongly influenced by the reworking of a juvenile late mesoproterozoic source suggesting that such crust underlies the antarctic peninsula our results therefore suggest that hf isotope analyses provide great potential for future studies investigating the source and processes involved in the generation of crustal melts

petrogenesis of late triassic granitoids and their enclaves with implications for post collisional lithospheric thinning of the liaodong peninsula north china craton abstract major and trace element sr nd and hf isotope zircon u pb and hf isotope data are reported for mafic microgranular enclaves and host granitoids from the xiuyan pluton in the liaodong peninsula of the eastern north china craton in order to investigate their sources petrogenesis and tectonic implications the zircon u pb age of the enclaves 211 1 ma is identical to that of the host granite 210 1 ma establishing that the mafic and felsic magmas were coeval the enclaves have high mgo concentrations at low silica contents and positive ehf t values they are enriched in large ion lithophile and light rare earth elements and depleted in high field strength elements which can be explained as melts derived from a depleted asthenospheric mantle with some crustal contamination the host granitoids have high sio2 contents variable initial 87sr 86sr ratios and highly negative end t and ehf t values suggesting they were mainly derived from an ancient crustal source heated by the input of asthenospheric mantle derived magmas field observations geochronology geochemistry sr and nd isotopic and zircon hf isotopic compositions point to a complex petrogenesis where asthenospheric mantle and crust derived magma mixing was coupled with crystal fractionation thus explaining the genetic link between enclaves and host rocks identification of an asthenospheric mantle component in the xiuyan granitoids suggests asthenospheric mantle upwelling and decompressional melting of the mantle indicating that post collisional lithospheric thinning in the liaodong peninsula was initiated in the late triassic

magma mixing revealed from in situ zircon u pb hf isotope analysis of the muhuguan granitoid pluton eastern qinling orogen china implications for late mesozoic tectonic evolution in this paper we present zircon u pb age and hf isotope data to document the significance of magma mixing in the formation of late jurassic granitoid intrusions in the eastern qinling orogen china the muhuguan granitoid pluton from this orogen consists of monzogranite and lesser biotite granite and granodiorite all containing abundant hornblende rich cumulates dioritic xenoliths and mafic magmatic enclaves mmes the monzogranite and granodiorite are intruded by a number of lamprophyre dykes both a cumulate and a dioritic xenolith samples have concordant zircon u pb ages of ca 161 1 ma but possess contrasting hf isotopic compositions the cumulate has more radiogenic zircon hf isotopes with negative ehf t values 7 9 to 2 5 and tdm1 ages of 0 9 1 1 ga indicating its derivation likely from basaltic rocks of the neoproterozoic to early paleozoic kuanping group in the area the dioritic xenolith has much lower zircon ehf t values of 19 5 to 8 8 and tdm2 ages of 2 4 1 7 ga consistent with a juvenile paleoproterozoic crust source presumably represented by the metabasic rocks of the qinling group in the area individual samples of the monzogranite mme and a lamprophyre dyke have u pb ages of 150 1 152 1 and 152 1 ma respectively demonstrating coeval mafic and felsic magmatism in the late jurassic the lamprophyre dyke has homogeneous highly negative zircon ehf t values 29 8 to 24 8 and archean tdm2 ages 3 0 2 7 ga and its genesis is interpreted as partial melting of an ancient enriched subcontinental mantle source zircons from the fine grained mme show a large range of ehf t between 29 1 and 9 8 overlapping values of the monzogranite and lamprophyre dyke samples zircon u pb age and hf isotopes of the mmes are consistent with their formation by mixing of crustal and enriched mantle derived magmas the main group of zircons from the monzogranite has ehf t values 17 9 to 9 3 and tdm2 ages 2 3 1 8 ga that are compatible with the dioritic xenoliths indicating that the former was produced by partial melting of paleoproterozoic crustal source with involvement of mantle derived magmas mafic magmatism revealed from the muhuguan pluton indicates that the eastern qinling orogen was dominated by lithospheric extension during the late jurassic compilation of existing geological and geochronological data suggests that this extensional event started in late jurassic ca 160 ma and persisted into the early cretaceous until ca 110 ma the jura cretaceous extension may have resulted from the late mesozoic westward subduction of the pacific plate beneath the east asian continental margin

in situ zircon u pb oxygen and hafnium isotopic evidence for magma mixing and mantle metasomatism in the tuscan magmatic province italy in this study we have used in situ u pb hf and o isotopic analyses of zircon grains to gain insights into both magmatic processes and duration of magmatism in igneous rocks from the tuscan magmatic province 0 1 9 ma italy three plutonic centres have been investigated monte capanne and porto azzuro monzogranites in elba and the giglio monzogranite as well as capraia the only volcanic centre in the tuscan archipelago new ion microprobe zircon u pb data reveal a continuum of plutonic activity in elba over 2 ma 8 3 6 3 ma with coeval volcanic activity in capraia 7 1 7 6 ma and plutonic activity resuming in giglio 5 5 ma after a gap of 1 ma from these zircon data we also show that construction of the monte capanne pluton elba may have occurred over a period of c 0 5 ma a significant range of both 176hf 177hf determined by la mc icpms and 18o determined by ion microprobe in zircon 7 epsilon hf units and 5 respectively is present which together with zircon morphology and trace element data gagnevin et al 2010 emphasises the importance of mixing and replenishment involving magma batches with both metaluminous and peraluminous affinities inherited and xenocrystic zircons also occur but are scarce these have a wide range of 176hf 177hf and 18o values further emphasising that a variety of crustal components has contributed to the genesis of the tuscan magmas either as contaminants or magma sources while mixing undoubtedly occurred between mafic metaluminous and felsic peraluminous magmas the range of hf and o isotopic data suggests a diversity within the peraluminous component the unradiogenic hf composition ehf t 6 of the inferred mantle derived component represented by capraia volcanism and at least in part lamproitic in composition strongly supports the idea that the mantle source involved in tuscan magmatism was severely modified by subduction related crustal derived metasomatic fluids

geochemistry of late mesozoic lamprophyre dykes from the taihang mountains north china and implications for the sub continental lithospheric mantle many late mesozoic lamprophyre dykes occur in the taihang mountains north china these lamprophyres are rich in large ion lithophile elements e g rb sr ba and k and light ree and have highly differentiated ree patterns they show large but regular variations in chemical and nd sr isotopic compositions all these suggest that the lamprophyres were produced from differentiation of a parental magma coupled with contamination by lower crust the parental magma was derived from melting of a long term enriched sub continental lithospheric mantle source as is indicated by the highly enriched isotopic signatures of the lamprophyres mantle enrichment in the area was probably produced by interaction of volatile rich melts released from the asthenosphere with the above lithosphere in middle proterozoic times

preface of special issue of applications of modern analytical techniques in the study of mineral deposits by rucheng wang and mei fu zhou guest editors

mantle dynamics of western pacific and east asia insight from seismic tomography and mineral physics abstract recent results of high resolution seismic tomography and mineral physics experiments are used to study mantle dynamics of western pacific and east asia the most important processes in subduction zones are the shallow and deep slab dehydration and the convective circulation corner flow processes in the mantle wedge the combination of the two processes may have caused the back arc spreading in the lau basin affected the morphology of the subducting philippine sea slab and its seismicity under southwest japan and contributed to the formation of the continental rift system and intraplate volcanism in northeast asia which are clearly visible in our tomographic images slow anomalies are also found in the mantle under the subducting pacific slab which may represent a small mantle plumes b upwellings associated with the slab collapsing down to the lower mantle or c sub slab dehydration associated with deep earthquakes caused by the reactivation of large faults preserved in the slab combining tomographic images and earthquake hypocenters with phase diagrams in the systems of peridotite water we proposed a petrologic model for arc volcanism arc magmas are caused by the dehydration reactions of hydrated slab peridotite that supply water rich fluids to the mantle wedge and cause partial melting of the convecting mantle wedge a large amount of fluids can be released from hydrated morb at depths shallower than 55 km which move upwards to hydrate the wedge corner under the fore arc and never drag down to the deeper mantle along the slab surface slab dehydration reactions at 120 km depth are the antigorite related 5 reactions which supply water rich fluids for forming the volcanic front phase a and mg surssasite breakdown reactions at 200 and 300 km depths below 700 c cause the second and third arcs respectively moreover the dehydration reactions of super hydrous phase b phases d and e at 500 660 km depths cause the fluid transportation to the mantle boundary layer mbl 410 660 km depth the stagnant slabs extend from japan to beijing china for over 1000 km long indicating that the arc trench system covers the entire region from the japan trench to east asia we propose a big mantle wedge bmw model herein where hydrous plumes originating from 410 km depth cause a series of intra continental hot regions fluids derived from mbl accumulated by the double sided subduction zones rather than the india asia collision and the subsequent indentation into asia are the major cause for the active tectonics and mantle dynamics in this broad region

deep slab subduction and dehydration and their geodynamic consequences evidence from seismology and mineral physics abstract we present new pieces of evidence from seismology and mineral physics for the existence of low velocity zones in the deep part of the upper mantle wedge and the mantle transition zone that are caused by fluids from the deep subduction and deep dehydration of the pacific and philippine sea slabs under western pacific and east asia the pacific slab is subducting beneath the japan islands and japan sea with intermediate depth and deep earthquakes down to 600 km depth under the east asia margin and the slab becomes stagnant in the mantle transition zone under east china the western edge of the stagnant pacific slab is roughly coincident with the ne sw daxing anling taihangshan gravity lineament located west of beijing approximately 2000 km away from the japan trench the upper mantle above the stagnant slab under east asia forms a big mantle wedge bmw corner flow in the bmw and deep slab dehydration may have caused asthenospheric upwelling lithospheric thinning continental rift systems and intraplate volcanism in northeast asia the philippine sea slab has subducted down to the mantle transition zone depth under western japan and ryukyu back arc though the seismicity within the slab occurs only down to 200 300 km depths combining with the corner flow in the mantle wedge deep dehydration of the subducting pacific slab has affected the morphology of the subducting philippine sea slab and its seismicity under southwest japan slow anomalies are also found in the mantle under the subducting pacific slab which may represent small mantle plumes or hot upwelling associated with the deep slab subduction slab dehydration may also take place after a continental plate subducts into the mantle

timing and genesis of the adakitic and shoshonitic intrusions in the laoniushan complex southern margin of the north china craton implications for post collisional magmatism associated with the qinling orogen abstract the nww striking qinling orogen formed in the triassic by collision between the north china and yangtze cratons triassic granitoid intrusions mostly middle to high k calc alkaline are widespread in this orogen but contemporaneous intrusions are rare in the southern margin of the north china craton an area commonly considered as the hinterland belt of the orogen in this paper we report zircon u pb ages elemental geochemistry and sr nd hf isotope data for the laoniushan granitoid complex that was emplaced in the southern margin of the north china craton zircon u pb dating shows that the complex was emplaced in the late triassic 228 1 to 215 4 ma indicating that it is part of the post collisional magmatism in the qinling orogen the complex consists of from early to late biotite monzogranite quartz diorite quartz monzonite and hornblende monzonite which span a wide compositional range e g sio2 55 9 70 6 wt k2o na2o 6 6 10 2 wt and mg of 24 to 54 the biotite monzogranite has high al2o3 15 5 17 4 wt sr 396 1398 ppm and ba 1284 3993 ppm contents and relatively high la yb mostly 14 30 and sr y mostly 40 97 ratios but low yb mostly 1 3 1 6 ppm and y mostly14 19 ppm contents features typical of adakitic rocks the quartz monzonite hornblende monzonite and quartz diorite have a shoshonitic affinity with k2o up to 5 58 wt and k2o na2o ratios averaging 1 4 the rocks are characterized by strong lree hree fractionation in chondrite normalized ree pattern without obvious eu anomalies and show enrichment in large ion lithophile elements but depletion in high field strength elements nb ta ti the biotite monzogranite 228 ma has initial 87sr 86sr ratios of 0 7061 to 0 7067 end t values of 9 2 to 12 6 and ehf t values of 9 0 to 15 1 whereas the shoshonitic granitoids mainly 217 215 ma have similar initial 87sr 86sr ratios 0 7065 to 0 7075 but more radiogenic end t 12 4 to 17 0 and ehf t 14 1 to 17 0 the sr nd hf isotope data indicate that the rocks were likely generated by partial melting of an ancient lower continental crust with heterogeneous compositions as partly confirmed by the widespread presence of early paleoproterozoic inherited zircons mafic microgranular enclaves mmes characterized by fine grained igneous textures and an abundance of acicular apatites are common in the laoniushan complex compared with the host rocks they have lower sio2 48 6 53 7 wt and higher mg 51 56 cr 122 393 ppm and ni 24 79 ppm but equivalent sr nd isotope compositions indicating that the mmes likely originated from an ancient enriched lithospheric mantle the abundance of mmes in the granitoid intrusions suggest that magma mixing plays an important role in the generation of the laoniushan complex collectively it is suggested that the laoniushan complex was a product of post collisional magmatism related to lithospheric extension following slab break off formation of the adakitic and shoshonitic intrusions in the laoniushan complex indicates that the qinling orogen had evolved into a post collisional setting by about 230 210 ma