behavior of alkalies during diffusive interaction of granitic xenoliths with basaltic magma a series of three experiments was made at 125 c and 10 kbar in which a 1 gram reservoir of molten oceanic tholeiite was maintained in contact with one end of a 6 5 mm diameter cylinder of partially molten fine grained granite detailed microprobe analysis 450 spots total of the quenched samples revealed progressive basalt granite interaction as run duration increased from 0 75 to 8 to 24 hours interdiffusion of melt components is limited for structure controlling species such as si 4 and al 3 and for divalent cations which all mix over a zone less than 0 5 mm wide in 24 hours at run conditions in contrast k and na are extremely mobile resulting in considerable uptake of k by the basalt melt and eventual loss of na from the basalt to the granite by uphill diffusion the chemical diffusivity of k in the basalt can be accurately estimated at 3 times 10 18 cm 2 sec for the specific experimental conditions used although this value is somewhat lower than previous estimates k o

evolution of the archean and paleoproterozoic lower crust beneath the trans north china orogen and the western block of the north china craton abstract we report u pb ages and hf isotopes of zircons in granulites from two continental suture zones in the north china craton ncc from granulite xenoliths entrained in the cenozoic hannuoba basalts within the trans north china orogen tnco that amalgamates the western and eastern blocks and from a mafic granulite associated with ultrahigh temperature uht granulites within the inner mongolia suture zone imsz that welds the yinshan and ordos blocks the zircons in these rocks together with the inherited zircons from mesozoic subalkalic intrusives of these regions show several distinct u pb age populations and provide constraints on the evolution of the lower crust beneath the ncc parts of the older zircons from the tnco yield discordant data that project to ages of about 2 5 to 2 7 ga these old zircons show hf tdm model ages of 2 6 2 9 ga suggesting the existence of archean lower crust beneath the tnco which is coupled with the neoarchean metamorphic basement and greenstone belt a major zircon population grew at 1 75 2 0 ga consistent with the timing of the paleoproterozoic collision between the various crustal blocks within the ncc suggesting that this event had a significant effect on the archean lower crust the older inherited zircons from the western block also yield discordant data that project to younger ages of about 1 8 to 1 9 ga this age is consistent with the timing of intrusion of the mafic magmatic protoliths of the granulites associated with the uht rocks in the khondalite belt within the imsz these older zircons yield hf tdm model ages of 2 0 2 5 ga suggesting that the lower crust beneath the western block in the ncc to be dominantly paleoproterozoic and decoupled with the archean metamorphic basement of the region yet another population of zircons from the hannuoba banded granulite xenoliths garnet bearing pyroxenite cumulate and dark pyroxenite xenoliths yield a large spread of phanerozoic concordant ages ranging from 470 ma to 40 ma with peaks at 315 ma 220 230 ma 120 ma and 46 ma the late paleozoic zircons predominantly occur in the garnet bearing pyroxenite xenoliths and yield variable ehf t values of 24 to 18 triassic cretaceous zircons mainly occur in the banded granulite xenoliths and yield highly variable ehf t values ranging from 48 to 16 the tertiary zircons occur only in the dark pyroxenite xenoliths and show a restricted ehf t with a dominant range from 0 to 18 these data suggest episodic magmatic underplating in the ancient lower crust of the ncc lasting continuously throughout phanerozoic producing zircons from the underplated magmas or providing the heat source for the recrystallization of zircons from the ancient crust our data clearly demonstrate the important events of phanerozoic magmatic underplating beneath the neoarchean paleoproterozoic crust of the ncc

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

mineralogy and geochemistry of microgranular enclaves in palaeoproterozoic malanjkhand granitoids central india evidence of magma mixing mingling and chemical equilibration palaeoproterozoic ca 2 480 ma felsic magmatism of malanjkhand region of central indian precambrian shield referred to as malanjkhand granitoids mg contain xenoliths of country rocks and mesocratic to melanocratic fine grained porphyritic microgranular enclaves me the shape of me is spheroidal ellipsoidal discoidal elongated and lenticular varying in size from a few centimeters to about 2 m across the contact of me with the host mg is commonly sharp crenulate and occasionally diffuse which we attribute to the undercooling and disaggregation of me globules within the cooler host mg the me as well as mg show hypidiomorphic texture with common mineral hbl bt kfs pl qtz assemblage but differ in modal proportions the variation in minerals composition presence of apatite needles elongated biotites resorbed plagiclase ocellar quartz and other mafic felsic xenocrysts strongly oppose the restite and cognate origins of me compositions of plagioclases an3 an29 amphiboles mg mg fe2 0 55 0 69 and biotites mg mg fe2 0 46 0 60 of me are slightly distinct or similar to those of mg which suggest partial to complete equilibration during mafic felsic magma interactions al in amphibole estimates the mg pluton emplacement at ca 3 4 0 5 kbar and therefore magma mixing and mingling must have occurred at or below this level the hbox fe rightleftharpoons hbox mg substitution in biotites of me and mg largely suggests subduction related calc alkaline metaluminous i type nature of felsic melts most major and trace elements against sio2 produce near linear variation trends for me and mg probably generated by the mixing of mafic and felsic magmas in various proportions trace including rare earth elements patterns of me mg pairs however show partial to complete equilibration most likely governed by different degrees of elemental diffusion the available evidence supports the model of me origin that coeval mafic enclave and felsic mg magmas produced a hybrid me magma layer which injected into cooler partly crystalline mg and dispersed mingled and undercooled as me globules in a convectively dynamic magma chamber

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

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

origin of a mesozoic granite with a type characteristics from the north china craton highly fractionated from i type magmas we report geochronological geochemical and isotopic data for the mesozoic shangshuiquan granite from the northern margin of the north china craton the granite is highly fractionated with sio2 74 occurrence of annitic biotite high contents of alkalis k2o na2o rb y nb and heavy rare earth elements high feot mgo low contents of cao al2o3 ba and sr and large negative eu anomalies makes it indistinguishable from typical a type granites a mantle derived origin for the rocks of the granite is not favored because their high initial 87sr 86sr 0 706 and low end t 15 are completely different from either those of the lithospheric or asthenospheric mantle in fact their sr nd isotopes fall within the range of sr nd isotopic compositions of the archean granulite terrains and are comparable to those of mesozoic crustal derived i type granitoids in the region therefore the shangshuiquan granite is considered to be dominantly derived from partial melting of the ancient lower crust its parental magmas prove to be similar to i type magmas and to have undergone extensive fractionation during its ascent this is supported by the fact that some of the nearby hannuoba feldspar rich granulite xenoliths can be indeed regarded as the early cumulates in terms of their mineralogy chemistry sr nd isotopes and zircon u pb ages and hf isotopes it is furthermore argued that some of highly fractionated granites worldwide especially those with a type characteristics and lacking close relationship with unfractionated rocks may in fact be fractionated i type granites this suggestion can explain their close temporal and spatial associations as well as similar sr nd isotopes with i type granites our study also sheds new light on the petrogenesis of deep crustal xenoliths

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

geochemistry and u pb shrimp zircon chronology of granitoids and microgranular enclaves from jhirgadandi pluton of mahakoshal belt central india tectonic zone india abstract the northern part of central india tectonic zone citz is delineated by an arc shaped supracrustal belt commonly referred to as mahakoshal belt which is considered as a product of intense rifting of sialic crust that occurred at ca 2400 2600 ma several granitoid plutons intrude the parsoi formation of mahakoshal belt among these an elliptical small stock like granitoid body trending e w is exposed in and around jhirgadandi region of mahakoshal belt referred herein as jhirgadandi pluton it is composed of minor amount of mafic rocks diorite and predominant granitoids country rock pelitic xenoliths and microgranular enclaves me are commonly hosted in granitoids but are absent in diorite the me exhibit typical magmatic texture with a bt cpx hbl pl kf qtz mag ap assemblage similar to that in host granitoids but with contrasting mineral proportions whole rock molar al 2 o 3 cao na 2 o k 2 o a cnk ratios of diorite 0 63 0 72 me 0 69 1 21 and granitoids 0 83 1 05 suggest their nature largely metaluminous i type to rarely peraluminous s type granitoids on most binary plots involving silica two distinct compositional paths can be recognized one formed by an array of differentiating diorite and me and another by fractionating granitoids gradually depleting in compatible elements it is most likely that me were generated by progressive and concurrent mixing of coeval pristine mafic diorite and granitoid magmas and fractionation processes however coherent and identical trace elements except for sr th y and ni and ree patterns for me granitoid pairs most likely suggest partial to near complete chemical equilibration through varying degrees of diffusion process across the me partly crystalline host granitoid boundary high precision u pb shrimp zircon 206 pb 238 u ages for me 1758 19 ma and host granitoid 1753 9 1 ma from jhirgadandi pluton further support the notion that they were coeval the obtained age 1750 ma of jhirgadandi pluton also points to the existence and role of super columbian continental component in the evolution of mahakoshal belt of the citz

radiation damage in sulfides radioactive galena from burning heaps after coal mining in the lower silesian basin czech republic the isotopic composition of lead 207 pb 206 pb 208 pb 206 pb and 210 pb in a recently formed galena from burning heaps after coal mining in radvanice markousovice and rybnicek the lower silesian basin czech republic was studied in detail 210 pb activity in galena varied from 135 9 to 714 22 bq g and calculated integral doses ranged from 2 21 10 11 to 6 11 10 11 g the radioactivity of the galena causes micro deformations in its crystal structure as indicated by the williamson hall graphs showing that the level of micro strain depends on the length of time that galena samples were exposed to the radiation however the crystal structure of galena is affected very inhomogenously according to tem investigations there are domains of fully crystalline polycrystalline and fully metamict galena within one crystal inductively coupled plasma mass spectrometry icp ms was used to determine the isotopic composition of the studied galena the stable isotope ratios of pb varied for 207 pb 206 pb from 0 8402 to 0 8435 and for 208 pb 206 pb from 2 0663 to 2 0836 the average ratios 207 pb 206 pb 0 8312 and 208 pb 206 pb 2 0421 were obtained for coal from the same localities these isotope ratios show that there is no isotopic fractionation taking place during the coal burning and subsequent galena crystallization from hot gases

evolving magma sources during continental lithospheric extension insights from the liaonan metamorphic core complex eastern north china craton abstract the relation between magmatic activity and detachment faulting during continental lithospheric extension remains a persistent question this paper takes the liaonan metamorphic core complex mcc in the eastern north china craton as an example to explore how magma generation relates to detachment faulting in response to continental lithospheric extension due to the subduction of the paleopacific plate beneath the eurasian continent in the early cretaceous dating of lower plate granitic intrusions and trachy dacitic volcanic rocks in the supradetachment basin constrains a progressive exhumation of the mcc between ca 134 ma and 113 ma syn tectonic magmatism is grouped into three types i e early syn kinematic late syn kinematic and post kinematic magmatism in reference to detachment faulting the magmatic rocks exhibit obvious differences in whole rock sr nd isotopes implying varying sources e g lithospheric mantle juvenile and ancient lower crusts evolving magma sources during the progressive exhumation of the mcc are shown from one with a lithospheric mantle signature for the early syn kinematic intrusions to one with mixed derivations from both juvenile and ancient lower crust for the late syn kinematic plutons and volcanics and finally to a juvenile lower crust source for the post kinematic intrusions the source evolution of magmatism during the continental lithospheric extension implies that both crustal and mantle processes may have been involved in the magma generation the parallel extension tectonics model is applied to explain both the tectonic faulting and magmatic activities in the model the evolving magma sources accompanying the mcc exhumation were attributed to thinning of the cratonic lithosphere as a consequence of coupled crust mantle detachment faulting during tectonic extension the model can be applied to the variably extended provinces in the north china craton but integrated structural geochronological and geochemical studies are needed to present a comprehensive tectono thermal magmatic history of these provinces

hannuoba intermediate mafic granulite xenoliths revisited assessment of a mesozoic underplating model abstract the intermediate mafic granulite xenoliths from tertiary hannuoba alkali basalts at the northern margin of the north china craton have been commonly considered to be formed by mesozoic basaltic underplating due to their abundant mesozoic zircons and compositionally higher mg molecular mg mg fe than rocks of the adjourning archean granulite terrain however such a mesozoic underplating model cannot account for the presence of precambrian zircons in the xenoliths and their evolved sr nd isotopic compositions which are dissimilar to expected basaltic melts from both the lithospheric and asthenospheric mantle instead their sr nd isotopic compositions resemble those of the granulite terrain and of the mesozoic low mg granitoids here newly acquired data and published data are combined to assess the mesozoic basaltic underplating model and to discuss the origin of the hannuoba intermediate mafic granulite xenoliths in terms of their relationships with the mesozoic magmatism and the granulite terrain zircons from a mafic granulite xenolith jn0724 which has geochemical and sr nd isotopic compositions indistinguishable from other mafic granulite xenoliths yield 2 5 ga u pb ages providing unambiguous evidence that the mafic xenoliths represent portions of ancient lower crust combined data reveals that the pyroxene rich granulite xenoliths can be best explained as restites left after partial melting of the ancient lower crust to produce the mesozoic low mg granitoids hf isotope analysis on mesozoic zircons from the hannuoba feldspar rich granulite xenoliths demonstrates that the zircons crystallized from mesozoic granitic magmas that were derived from ancient lower crust rather than from mesozoic underplated magmas the proposed scenarios successfully explain the age and compositional differences between granulite xenoliths and the granulite terrain and also provide new insights into derivation and evolution of granitic magmas it is concluded that most of the hannuoba intermediate mafic granulite xenoliths and the mesozoic granitoids reflect reworking of ancient lower crust rather than juvenile crust addition it provides strong evidence that crustal anatexis may be one of the major processes controlling the chemical differentiation of the continental crust our data imply that whether younger zircon ages in granulite xenoliths from many other archean cratons register post archean basaltic underplating could be tested by integrated analysis of u pb age and hf isotopes

pattern and kinematic polarity of late mesozoic extension in continental ne asia perspectives from metamorphic core complexes 1 late mesozoic extension in ne asia resulted in the development of a large extensional province metamorphic core complexes mccs are the major features in this province and have 40ar 39ar ages of 130 110 ma for the mylonites and u pb zircon ages of 150 110 ma for the integral granitic intrusions based on this and previous studies this paper summarizes major characteristics of these mccs and recognizes a regional kinematic shear sense most mccs in the transbaikalia region sino mongolia border tract and the northwest central portion of the north china craton ncc show a top to the southeast se shear whereas those in the eastern and southern ncc locally underwent top to the northwest nw shear the three largest basins songliao huabei and ordos in north china are located in the transitional zone between domains of opposing shear sense we interpret the extension in the transbaikalia sino mongolia tract and northwestern part of the ncc to reflect late orogenic collapse of thickened crust following middle late jurassic collision along the okhotsk suture the southeastward extension is probably controlled by crustal scale top to the se tangential shear the transition from contraction to extension is marked by detachment faults that nucleated as extensional crenulation cleavage ecc i e c in sub horizontal ductile shear zones late in orogenic crustal thickening the combined effect of gravitational loading and thermal uplifting is considered to be the origin of the late or post orogenic collapse the top to the nw extension in the ne of the ncc might reflect antithetic sub extensional zones or mesozoic back arc extension as a far field effect of cretaceous pacific plate subduction

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

the cretaceous duimiangou adakite like intrusion from the chifeng region northern north china craton crustal contamination of basaltic magma in an intracontinental extensional environment abstract zircon u pb ages major and trace element and sr nd and pb isotope compositions of the duimiangou dmg quartz monzonite from the chifeng region on the northern north china craton ncc were studied to investigate its derivation evolution and geodynamic significance laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating yields an emplacement age of 128 1 ma for this intrusion with numerous mesozoic inherited zircons clustering at 219 12 ma and 161 3 ma along with some ancient zircons with ages of 2 5 ga 1 77 ga and 324 ma bulk rock analyses show that this intrusion is characterized by variable sio 2 63 4 69 4 wt al 2 o 3 14 5 16 3 wt na 2 o k 2 o 8 01 8 95 wt and mg 41 3 48 0 they are enriched in large ion lithophile elements and light rare earth elements without significant eu anomalies mostly between 0 89 1 10 and depleted in heavy rare earth elements and high field strength elements with high sr y 63 7 101 7 and la yb n 20 5 31 0 ratios the dmg intrusion formed in an intracontinental extensional setting contemporaneous with the formation of pull apart basins metamorphic core complexes and intense magmatism rather than in a convergent margin it has homogeneous sr 87 sr 86 sr i 0 7059 0 7066 nd e nd t 6 2 to 7 2 and pb 206 pb 204 pb i 17 289 17 375 207 pb 204 pb i 15 359 15 463 208 pb 204 pb i 37 130 37 472 isotope compositions sr nd isotope modeling results plus relatively young nd model ages 1522 1618 ma and the presence of relict zircons suggest that this intrusion could have originated from crustal contamination of newly formed basaltic melts derived from asthenospheric mantle accompanied by fractional crystallization of k feldspar biotite apatite fe ti oxides and minor hornblende and plagioclase thus the dmg adakite like intrusion may record the magmatic event associated with underplating of asthenospheric magma in an intracontinental extensional environment and both asthenospheric magma underplating and lithospheric delamination may have played important roles in the lithospheric thinning of the northern ncc

mafic felsic magma mixing limited by reactive processes a case study of biotite rich rinds on mafic enclaves article history mafic enclaves in felsic plutons are often used to argue that intermediate magmas are formed by mafic felsic magma mixing but the extent and nature of mixing remains unclear here we examine biotite rich rinds on mafic enclaves from the cretaceous bernasconi hills pluton in the peninsular ranges batholith of southern california to gain insight into magma mixing processes rinds differ from the enclave interior and the host monzogranite in being more fine grained and more mafic and potassic rinds are also 2 5 times more enriched in rare earth elements than the host monzogranite and up to 3 times more enriched than enclave interiors these observations indicate that the rinds were not generated by isochemical quenching binary mixing between enclave and host monzogranite or in situ magmatic differentiation instead rinds appear to have been formed by chemical reaction between the solidified enclave and a hydrous k rich residual melt or fluid formed after progressive crystallization and cooling of the host magma body transforming amphibole in the enclave into biotite rich rinds field observations show snapshots of biotite rich rinds being eroded away and new rinds simultaneously forming on freshly eroded surfaces of enclaves consistent with rinds being formed by chemical reaction instead of as quenching products deformation of enclaves is accommodated primarily by ductile attenuation of the thin rind while the enclave as a whole tends to rotate as a rigid body with minimal internal deformation other than localized brittle failure a comparison of the aspect ratios and cross sectional areas of mafic bodies in the pluton shows that those with high aspect ratios indicating greater accumulated strain are systematically more biotite rich and have smaller cross sectional areas than those with lower aspect ratios which are amphibole rich these relationships not only confirm that biotite rich lithologies are more deformable but also indicate that the high aspect ratio biotite rich bodies also known as schlieren derive from small parent bodies consistent with a derivation from eroding enclave rinds rather than from the enclave itself finally geochemical and thermodynamic modeling indicates that the biotite rich rinds formed when the host felsic magma had cooled to a low melt fraction state f 0 15 0 3 700 760 c suggesting that such reactions occur late in the lifespan of a magma body thus mafic felsic mixing may not be an efficient process for making intermediate magmas unless the magma body can reside at this low temperature range long enough to permit rind formation and subsequent deformation

late mesozoic compressional to extensional tectonics in the yiwulushan massif ne china and its bearing on the evolution of the yinshan yanshan orogenic belt part i structural analyses and geochronological constraints abstract with a cratonic nucleus the north china craton ncc experienced a complex tectonic evolution with multiphase compressional and extensional events during mesozoic times along the northern part of the ncc the yinshan yanshan fold and thrust belt was a typical intraplate orogen jurassic and cretaceous continental sedimentation magmatism widespread intraplate characterize the yinshan yanshan orogenic belt the geodynamic significance of these tectonic events is still in dispute in the western part of the liaoning province the yiwulushan massif crops out at the eastern end of the yinshan yanshan orogenic belt the yiwulushan massif presents an elliptical domal shape with a ne sw striking long axis the structural evolution of this massif brings new insights for the understanding of the mesozoic plutonic tectonic history of the ncc a multidisciplinary study involving structural geology geochronology anisotropy of magnetic susceptibility ams and gravity modeling have been carried out the presentation of the new results splits into two parts part i this paper deals with field and laboratory structural observations and presents the main geochronological results the ams gravity modeling data will be provided in a companion paper part ii the early compressional deformation d1 corresponds to a late jurassic to early cretaceous southward thrusting the subsequent deformation is related to the early cretaceous exhumation of the yiwulushan massif a detailed structural analysis allows us to distinguish several deformation events d2 d3 and d4 the cretaceous extensional structures such as syntectonic plutons bounded by ductile normal faults metamorphic core complexes and half graben basins are recognized in many places in east asia these new data from the yiwulushan massif constitute a link between transbaikalia mongolia north china and south china indicating that nw se extensional mesozoic tectonics occurred throughout the entire region

paleoproterozoic arc magmatism in the north china craton no siderian global plate tectonic shutdown abstract arc magmatism in convergent plate margins has been a major contributor to continental growth following arc arc and arc continent collisions in the archean leading to the amalgamation of micro blocks the north china craton ncc witnessed major pulses of continental arc magmatism during the paleoproterozoic in this study we present geochemistry zircon u pb geochronology and lu hf isotope data from a suite of magmatic rocks sampled from the region of confluence of two major paleoproterozoic suture zones in the ncc the inner mongolia suture zone imsz and the trans north china orogen tnco our zircon u pb geochronological data indicate new zircon growth during multiple tectonothermal events as displayed in the 207pb 206pb weighted mean ages of 2410 41 ma for metagranite 2480 12 ma 2125 18 ma 1946 8 ma 1900 15 ma and 1879 12 ma from metagabbros 2446 11 ma from charnockite and 1904 6 ma and 1901 9 ma from metatuffs the 207pb 206pb upper intercept age of zircons in the khondalite shows 2102 76 ma which is identical to the age obtained from the magmatic zircons in one of the metagabbros the khondalites also carry a group of concordant metamorphic zircons with 207pb 206pb mean age of 1881 20 ma metamorphic zircons in the gabbros and charnockites also yield similar ages of 1890 14 ma and 1852 19 ma respectively the age data suggest prolonged arc magmatism in a convergent margin setting during ca 2 48 to 1 9 ga followed by metamorphism at ca 1 89 1 85 ga associated with the final collision lu hf analyses reveal that the dominant populations of zircons from all the rock types are characterized by positive ehf values 1 9 to 6 8 mean 1 8 the ehf and tdmc data suggest that the magmas were mostly derived from neoarchean and paleoproterozoic juvenile components the salient geochemical features of these rocks attest to magma generation from heterogeneous sources involving subduction derived arc components with minor input from continental crust the results presented in this study together with those from previous investigations in different domains of the imsz and tnco suggest major paleoproterozoic arc magmatic events in the ncc lasting for nearly 600 million years associated with the final assembly of the crustal blocks into a coherent craton construction of the final cratonic architecture of the ncc thus witnessed not only the arc continent amalgamations at 2 7 2 5 ga but also major crust building events in the paleoproterozoic through melts generated from juvenile and recycled components in continental magmatic arc systems along an active convergent margin followed by intense deformation and metamorphism during the final collision at 1 85 1 80 ga the prominent paleoproterozoic magmatic records in the ncc do not support the proposal of global plate tectonic shutdown in the siderian and confirm vigorous convergent margin magmatism and crust building processes throughout the paleoproterozoic

nature and evolution of the lower crust in the eastern north china craton a review abstract in this paper published data for granulite terrain rocks exposed at the surface lower crustal xenoliths and mesozoic intermediate felsic igneous rocks from the eastern north china craton ncc are integrated to constrain the nature and evolution of the lower crust in this area u pb zircon dating shows that the protolith ages for most of the granulite terrain rocks are 2500 to 2600 ma and that many of them experienced 1800 1900 ma metamorphism lower crustal xenoliths entrained in volcanic rocks with ages varying from 460 to 10 ma suggest that the lower crust is dominated by neoarchean rocks although there may be minor rocks with ages of meso to paleoarchean 3000 ma 45 ma and possibly 1900 ma locally the mesozoic intrusive rocks although varying from diorite to granite and spanning from triassic to cretaceous contain 2500 ma inherited zircons and have magmatic zircons with hf crust model ages t dm hf c ages of 2500 2700 ma and whole rock sr nd isotopic compositions falling within the field of the granulite terrain rocks pointing to their derivation by the melting of neoarchean lower crust the combined data for the granulite terrain rocks lower crustal xenoliths and mesozoic intermediate felsic igneous rocks indicate that the present lower crust is dominated by rocks with neoarchean ages and is intermediate to mafic in composition i e sio 2 87 sr 86 sr i e nd t and e hf t of the lower crust at 130 ma are considered to be 0 705 to 0 716 10 to 28 and 13 to 28 respectively the e nd t range is very different from that proposed previously 32 to 44 the large range of e hf t for the lower crust implies that significant e hf t variations for magmatic zircons from the mesozoic intermediate felsic igneous rocks do not necessarily reflect mixing of mantle and crustal magmas as commonly thought instead they may reflect heterogeneity in the ancient lower crust given that the voluminous mesozoic intermediate to felsic igneous rocks in the eastern ncc are derived dominantly by partial melting of the archean lower crust it requires that a large amount of archean lower crust be restitic a restite origin can explain some of the hannuoba granulite xenoliths having higher mg than the granulite terrains it may be applicable to other parts of the world

the relationship between gold mineralization exhumation of metamorphic core complex and magma cooling formation of the anjiayingzi au deposit northern north china craton abstract the anjiayingzi gold deposit is hosted by the jiguanzi quartz monzonite in the footwall of the kalaqin metamorphic core complex mcc at chifeng in the northern part of the north china craton ncc an earlier ca 135 125 ma top to the ne ductile brittle shear and a later ca 121 ma top to the nw and se brittle detachment normal faulting are recognized around the kalaqin mcc the jiguanzi quartz monzonite intruded the footwall of the kalaqin mcc at ca 133 1 ma with crystallization temperatures of 640 691 c pressures of 167 271 mpa and an average depth of 8 6 km gold veins in the anjiayingzi gold deposit are hosted by the monzonite and controlled by the ne trending brittle ductile and brittle fault zones these ore bearing faults are products of a regional sinistral shearing event coinciding with the earlier top to the ne ductile brittle shear at the kalaqin mcc the ore of the anjiayingzi deposit is characterised by its low au ag ratio 2 o co 2 nacl fluid system with salinities of 1 3 15 6 wt nacl equiv trapping pressures of ore fluids were 50 110 mpa corresponding to an average depth of 2 5 km under a lithostatic load and 7 5 km under a hydrostatic load fluid mixing and immiscibility are potential causes for the rapid precipitation of sulphides carrying au the stable isotope d 80 3 to 96 5 and 18 o h 2 o 3 7 to 5 5 of the ore fluids the consistent pb isotope compositions between the ore bearing sulphides and k feldspar from the jiguanzi quartz monzonite and a 2 billion year time gap between the gold mineralization and metamorphism of the basement all indicate that the mineralizing fluids and metals are derived from a concealed intrusion near the major eastern louzidian fault in the kalaqin mcc this proposal is supported by the presence of mafic magmatic enclaves and rhyolite dykes in the jiguanzi quartz monzonite and higher average th total 322 c and 34 s 2 4 of eastern veins than those of western veins with a th total of 287 c and 34 s value of 0 3 the ca 133 126 ma gold mineralization at anjiayingzi was formed during rapid cooling of ca 133 126 ma jiguanzi quartz monzonite at a cooling rate of 42 71 c ma and fast exhumation and cooling of the kalaqin mcc between ca 135 and 121 ma at a cooling rate of 30 c ma this process was accompanied by fluid immiscibility and mixing within the structural transition from ductile brittle to brittle deformation with resultant fluid pressure fluctuations between the supra hydrostatic and hydrostatic regimes

magma mixing in the kalaqin core complex northern north china craton linking deep lithospheric destruction and shallow extension abstract the widespread mesozoic magmatism in the north china craton ncc has received considerable attention as a trigger for large scale lithospheric destruction here we investigate the early cretaceous jiguanzi adamellite from the northern part of the ncc which is contemporaneous with shallow extensional deformation and deep lithospheric destruction this intrusion emplaced at ca 133 ma is located in the foot wall of the kalaqin metamorphic core complex mcc and occurs as a synextensional ring complex with numerous magmatic equigranular group 1 and porphyritic group 2 enclaves hornblende and plagioclase from the host adamellite and xenocrysts of group 2 enclaves show distinct inverse zoning with mg and ca rich mantle the group 2 enclaves are characterized by plagioclase xenocrysts hosting hornblende biotite and apatite inclusions quartz ocelli with fine grained rim enriched in biotite and hornblende and poikilitic biotite surrounded by hornblende geochemically the host intrusion is calc alkaline to alkaline and metaluminous with variable contents of sio 2 60 70 72 20 wt al 2 o 3 14 19 17 22 wt na 2 o k 2 o 6 16 9 42 wt and mg values 28 0 47 7 whereas the group 2 enclaves exhibit low sio 2 54 05 55 55 wt high fe 2 o 3 8 18 8 64 wt and tio 2 2 08 2 28 wt and moderate mg 44 0 44 1 both the host intrusion and group 2 enclaves are enriched in large ion lithophile and light rare earth elements and depleted in high field strength elements and heavy rare earth elements except that the latter has lower ba and high nb ta and ti contents the major and trace element contents of the group 1 enclaves are broadly similar to those of the host intrusion analyses of sr nd hf isotopes in the host intrusion and in group 1 and group 2 enclaves show 87 sr 86 sr i host 0 70600 0 70618 e nd t host 8 2 to 9 6 t 2dm nd host 1592 1706 ma e hf t host 9 2 to 12 0 87 sr 86 sr i group 1 0 70590 0 70635 e nd t group 1 9 6 to 10 4 t 2dm nd group 1 1705 1775 ma 87 sr 86 sr i group 2 0 70586 0 70587 e nd t group 2 0 6 to 0 7 t 2dm nd group 2 971 978 ma and e hf t group 2 4 5 to 10 0 the mineralogical and geochemical features suggest that the host jiguanzi adamellite and group 2 enclaves were generated through synchronous mixing and fractional crystallization accompanied by mechanical and chemical exchanges the group 1 enclaves showing cogenetic affinity with their felsic host represent the mechanical concentrations of mafic minerals and accessory phases from evolved hybrid host magma magma sources of the host jiguanzi adamellite and its group 1 enclaves are dominated by lower crust lcc components whereas those for the group 2 enclaves are dominated by metasomatized lithospheric mantle the magma genesis involved complex multi stage crust mantle interaction processes including 1 lithospheric mantle modification induced by triassic subduction of the paleo asian ocean slab and or triassic cretaceous asthenospheric melt underplating and 2 melting of the ancient lcc and lithospheric mantle and hybridization of mantle and crust derived melts in conjunction with regional geological and geochemical data we argue that the late jurassic early cretaceous shallow extension events represented by the kalaqin mcc triggered deep seated multi stage magmatism and lithospheric destruction and the continuous generation of magma further strengthened the extension and result in more extensive lithospheric thinning

metamorphic core complexes vs synkinematic plutons in continental extension setting insights from key structures shandong province eastern china abstract continental extension is an important geodynamical process mostly diagnostic of a peculiar behaviour of the crust accommodated by geological structures that highlight these specific conditions in the crust though a metamorphic core complex mcc reveals a much stronger crustal extension than a synkinematic pluton the nature of those two structures implies different implications in terms of crustal extension mechanisms and geodynamic significations in eastern asia a major continental extensional event occurred during mesozoic and early cenozoic times the resulting various extensional events described in previous studies consist in large intracontinental basins important volcanism emplacement of plutons in the upper crust and exhumation of mccs an efficient description of mccs and plutons in eastern asia is essential to discriminate important differences of those two structures in terms of strain amount undergone by continental crust and geodynamic significations in that way an integrated structural and geophysical study has been realized to precisely discriminate the structure in the jiaodong peninsula shandong province eastern china previously regarded as simple sheared plutons a succession of three main stages have been identified all pertaining to a nw se extensional setting 1 the exhumation of the late jurassic early cretaceous linglong mcc below the se dipping linglong detachment fault 2 the emplacement of the guojialing syntectonic pluton below the n dipping extensional guojialing intracrustal shear zone 130 124 ma and 3 a penetrative brittle normal faulting associated with gold mineralizations 120 ma as a result the maximum amount of extension in jiaodong peninsula characterized by partially melted lower to middle crust upward into the linglong mcc should be revised to late jurassic early cretaceous period

evolution of the yiwulushan metamorphic core complex from distributed to localized deformation and its tectonic implications 1 the yiwulushan metamorphic core complex ysmcc is situated in the northern part of the eastern north china craton ncc that experienced significant lithospheric thinning in an extensional regime during the late mesozoic we present structural and geochronological evidence to show that the ysmcc underwent nne ssw extension in the late jurassic and wnw ese extension in the early cretaceous we show that the ysmcc started with a sub horizontal shear zone referred to as the yiwulushan detachment shear zone ydsz in the late jurassic between 157 and 147 ma with a top to the ssw shear sense the ydsz was subjected to limited doming probably toward the end of its formation the nne striking wnw dipping waziyu normal shear zone wzysz was formed along the western margin of the core complex during the early cretaceous and truncates the earlier ydsz the whole core complex underwent doming in a rolling hinge manner in the end of the latest early cretaceous thereafter the ysmcc was overprinted by brittle normal faults along its western margin in the late cretaceous development of the initially flat lying ydsz is associated with diffuse mid crustal flow whereas the formation of the rolling hinge type wzysz is characterized by localized deformation the late jurassic more diffuse deformation has a rather constant top to the ssw shearing and produced a variety of shear related structures such as recumbent isoclinal folds and transposition foliation the ysmcc evolution also demonstrates that the late mesozoic extension along the northern part of the eastern ncc started as early as the late jurassic rather than the previously proposed early cretaceous

temporal and spatial variations of mesozoic magmatism and deformation in the north china craton implications for lithospheric thinning and decratonization abstract mesozoic triassic cretaceous magmatic rocks and structural deformation are widely distributed in the north china craton ncc and are crucial to understanding the timing location and geodynamic mechanisms of lithospheric thinning and decratonization of the ncc our new geochronological geochemical and structural data combined with previously published results on mesozoic magmatic rocks and deformational structures in the ncc indicate a temporal and spatial migration of magmatism and deformation from its margins to its cratonal interior triassic and early jurassic igneous rocks are only distributed along the northern southern and eastern margins of the ncc in contrast cretaceous magmatic rocks are widely distributed in whole eastern and central parts of the ncc there is a younging trend for mesozoic magmatic rocks from the northern and eastern parts yanshan jiaodong peninsula and liaodong to the central part of the ncc taihangshan mesozoic deformation in the ncc exhibits a similar migration trend from craton margins to its inland areas triassic early jurassic deformation mainly occurred in the margins of the ncc and transformed from compression during the early middle triassic to extension during the late triassic to early jurassic in its northern margin middle late jurassic to earliest cretaceous deformation is widely distributed in the ncc and exhibited non unique contractional directions usually perpendicular to boundaries of the ncc and its ordos block indicating that it was likely controlled by multiple tectonic regimes during the middle late jurassic to earliest cretaceous early cretaceous deformation was characterized by near unique nw se extension that was likely controlled by unique geodynamic regime that probably related to the far field effect of cretaceous paleo pacific plate subduction the above mentioned temporal and spatial migrations of mesozoic magmatic rocks and deformation indicate that lithospheric thinning and decratonization of the ncc was diachronous and complex the lithospheric thinning and decratonization of the ncc initially started from its northern and eastern margins as a result of post collisional post orogenic lithospheric delamination during the middle late triassic and then spread to the interior of the craton during the late mesozoic interactions of the surrounding orogenesis and the small size of the ncc may have played important roles on its late mesozoic lithospheric thinning and decratonization

the first record of the mosasaur hainosaurus reptilia lacertilia from north america hainosaurus pembinensis a new species of tylosaurine mosasaur is described from the pembina member of the pierre shale campanian late cretaceous of manitoba hainosaurus differs from tylosaurus in having a larger number of vertebrae anterior to the chevron bearing caudals a greater length of the femur relative to the humerus and a greater length of the external nares hainosaurus pembinensis is distinguished from other species of this genus by its long supratemporal fenestra and homodont dentition this is the first record of hainosaurus from north america and represents both a geographic and stratigraphic range extension for the genus