early devonian alkaline intrusive complex from the northern north china craton a petrological monitor of post collisional tectonics abstract laser ablation inductively coupled plasma mass spectrometry zircon u pb dating and geochemical data document the early devonian sandaogou alkaline complex 409 ma from the northern margin of the north china craton the rock suite includes pyroxene syenite quartz syenite and monzonite these rocks exhibit high contents of k 2 o 5 13 wt strong enrichments in large ion lithophile elements and light ree slightly negative eu anomalies and pronounced depletions in high field strength elements they are characterized by moderate 87 sr 86 sr i ratios of 0 7052 0 7071 low e nd t values of 12 7 to 17 9 and zircon e hf t values from 27 8 to 32 3 these geochemical features and quantitative isotopic modelling suggest that they might have been formed through simultaneous fractional crystallization and lower crustal assimilation of a metasomatized mantle derived alkali basaltic magma these trachytic rocks together with the middle devonian alkaline rocks and mafic ultramafic complex from neighbouring regions constitute a linear post collisional magmatic belt along the northern north china craton possibly formed under a tectonic regime of slab breakoff they serve not only as a magmatic milestone for marking the termination of early palaeozoic orogenic cycle around the northern north china craton but also as a spatial tracer for locating the position of the potential ancient slab breakoff at the surface supplementary material analytical methods mineral composition data field and zircon cathodoluminescence cl photographs are available at http www geolsoc org uk sup18403

geochemistry of miocene trachytes in bugasi lhasa block tibetan plateau mixing products between mantle and crust derived melts abstract it is generally believed that cenozoic potassic and ultrapotassic volcanic rocks of the tibetan plateau were generated by partial melting of an enriched mantle region or lower crustal materials the miocene bugasi volcanic rocks bvr in the western part of the lhasa block are composed mainly of trachyandesites and trachytes both of which belong to the shoshonite series the trachytes show somewhat transitional compositions between the mantle derived trachyandesites of the bvr and the crust derived potassic rocks of konglongxiang most evident in their sr ba and ni concentrations nb ta rb sr th nb zr nb and ba rb trace element ratios and sr and nd isotopic compositions these features coupled with the relatively high cr and ni concentrations and mg suggest that the trachytes are the product of mixing between mantle derived and lower crust derived melts

structural and rheological features of the western liaoning metamorphic core complex corridor indications for late mesozoic extension of the eastern north china craton abstract the xingcheng taili ductile shear zone and yiwulushan metamorphic core complex formed during crustal extension of the eastern north china craton the ene trending xingchegn taili sinistral ductile shear zone developed along the margins of the western liaoning metamorphic core complex corridor within upper greenschist to lower amphibolite facies grade metamorphic conditions shearing was associated with two different ductile deformation events in the yiwulushan metamorphic core complex i e 1 an earlier dextral shearing and 2 later sinistral shearing the earlier dextral ductile shear zone is mainly characterized by simple shear dominated general shear with l s and ls tectonites under upper greenschist to lower amphibolite facies conditions the orientation and fabrics of l s tectonites indicate that the later ductile deformation consists of almost equally simple and pure shear and constrains a low middle temperature sinistral shear within upper greenschist facies grade conditions the estimation of rock rheological parameters from dynamically recrystallized grain sizes of quartz indicates that the high temperature shear zone has formed under lower stress conditions and higher strain rates while opposite features exist in the lower temperature shear zone the initiation of deformation of the western liaoning metamorphic core complex corridor might have started between 136 ma and 120 ma and its termination time was at ca 100 ma the ne ene strike slip ductile deformation in the western liaoning metamorphic core complex corridor within the eastern block of the north china craton was resulted from roll back of the subducting pacific plate beneath the north china craton along the eastern asian margin during early cretaceous times

oxygen and neodymium isotope evidence for recycling of juvenile crust in northeast china it has been long recognized from nd and sr isotopes that depleted mantle sources consist of recycled oceanic materials but difficulty was encountered in identifying this signature by means of oxygen isotopes because of significant postemplacement hydrother mal alteration zircon is expected to preserve this signature because it is resistant to high temperature hydrothermal alteration this effect is illustrated by a combined sm nd and oxygen isotope study of whole rock and mineral samples from a mesozoic a type granite at nianzishan in northeastern china the sm nd isotope results show positive nd t val ues of 10 86 to 14 27 with young nd model ages of 569 846 ma manifesting a significant input of newly mantle derived material the zircon d 18 o values of 3 12 4 19 are significantly lower than the d 18 o value of 5 3 6 0 3 for the normal mantle zircon and thus appear to require remelting of hydrothermally altered oceanic crust the combined nd o isotope studies not only provide compelling evidence for geochemical recycling of young juvenile crust by plate subduction but also demonstrate that the granitic magmas can result from partial melting of mantle derived rocks that were subjected to seawater hydrothermal alteration before magma generation disequilibrium oxygen isotope frac tionations are observed between common rock forming minerals with significantly lower d 18 o values for alkali feldspar than seawater corresponding to meteoric hydrothermal alteration after magma crystallization

columbite group minerals and mica of peraluminous granite record the magmatic hydrothermal processes that formed the zhaojinggou tanb deposit in the north china craton abstract the newly discovered zhaojinggou ta nb deposit in the northern margin of the north china craton contains ore reserves of more than 38 mt at an average grade of 0 013 wt ta2o5 and 0 012 wt nb2o5 the ta nb mineralization is mainly hosted in a peraluminous albite granite body which is about 400 m long and 20 to 100 m wide with a surface exposure of 0 05 km2 granitic pegmatites and greisen veins that range from several centimeters to meters in width occur in the margin of the granite body and wolframite quartz veins intrude the wall rocks up to tens of meters away from the granite contact la icp ms u pb dating for columbite of the granite yields the lower intercept ages between 131 8 1 0 ma and 134 6 2 1 ma on the tera wasserburg concordia diagram indicating that the mineralization occurred in the early cretaceous coeval with the peak stage of lithospheric thinning and destruction of the north china craton the columbite grains in the granite are commonly euhedral and are surrounded or penetrated by irregular tantalite patches rims containing ta2o5 as high as 59 5 wt the ta concentrations within single columbite crystals commonly increase slightly from the center outwards consistent with a systematic decrease of nb ta caused by crystallization of columbite from the silicic magma mica in the granite shows disordered bright and dark domains in their bse images bright domains are f rich zinnwaldite crystallized from highly evolved melts that were relatively enriched in fe li rb nb and ta whereas the dark domains are f poor muscovite crystallized from later hydrothermal fluids that were relatively enriched in al mn ba sn and w it is thus likely that the tantalite patches rims around the columbite grains crystallized from a ta and f rich hydrosilicate melt in a magmatic hydrothermal transitional stage the wolframite quartz veins adjacent to the granite body likely formed from a w rich hydrothermal fluid

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

tracing magma mixing and crystal melt segregation in the genesis of syenite with mafic enclaves evidence from in situ zircon hf o and apatite sr nd isotopes abstract alkaline rocks contain essential information on post collisional intraplate extensional magmatic processes within the continental lithosphere the erhulai syenitic pluton in the liaodong peninsula north china craton consists of quartz syenite mafic enclaves and porphyritic k feldspar granite field observations and zircon u pb dating reveal that the quartz syenite and the hosted mafic enclaves were coeval with identical emplacement ages of 129 126 ma and slightly older than the porphyritic k feldspar granite ca 123 ma the mafic enclaves have relatively low sio2 and high mgo contents up to 3 0 and lack ba or eu anomalies whole rock analyses of the mafic enclaves and accessory minerals in the enclaves show relatively low initial 87sr 86sr ratios 0 7056 to 0 7078 and variable end t 11 2 to 2 0 and ehf t 15 8 to 5 5 values large proportion of zircons from the mafic enclaves possess mantle like 18o values these geochemical features suggest an enriched mantle source with the addition of crustal material the quartz syenites have relatively high sio2 and low cao and mgo contents as well as significantly positive k ba and eu anomalies all the quartz syenites show variable 87sr 86sr i ratios 0 7073 to 0 7081 and end t values 10 4 to 8 6 for the whole rocks and apatites ehf t values of 12 4 to 3 6 for the zircons and zircon 18o values of 4 4 to 7 0 mainly greater than 5 3 all these features can be isotopically produced by the partial melting of ancient crustal material with the involvement of mantle derived magma crystal fractionation process such as k feldspar crystallization and accumulation played an important role in the formation of the quartz syenite the porphyritic k feldspar granites possess relatively evolved geochemical compositions with high silica contents sio2 69 wt and remarkable negative ba and eu anomalies which are chemically complementary to the quartz syenite a crystal mush model was employed to establish the genetic link between the porphyritic k feldspar granite and the quartz syenite with the granite representing the interstitial melt extracted from the crystal mush and the quartz syenite representing the residual accumulation of crystals the variable isotopic compositions of the quartz syenite and the porphyritic granite were mainly the result of extensive interaction of isotopes between mantle and crust derived magmas during magma mixing in situ analyses of the sr nd hf and o isotopes of accessory minerals coupled with field observations and whole rock geochemical data for the erhulai syenitic pluton indicate a complex multi stage magmatic process involving magma mixing crystal melt segregation and wall rock assimilation our study also shows that in situ isotopic analyses of accessory minerals provide unique information on and are powerful geochemical tracers of mantle crust interactions and magmatic processes

geochemical transition shown by cretaceous granitoids in southeastern china implications for continental crustal reworking and growth abstract zircon u pb ages and in situ trace elements and hf o isotope compositions together with whole rock geochemical and sr nd hf isotopic data are presented for cretaceous granitoids in southeastern se china in order to establish their origin and the evolution of the underlying lithosphere during the late mesozoic two stages of cretaceous magmatism with contrasting geochemical features have been identified an earlier adakite like biotite granite as represented by the shangying pluton and a later enclave bearing monzogranite as represented by the zaoshan pluton the shangying biotite granites have a zircon u pb age of 99 1 ma they have relatively low y and yb contents with high la yb and sr y ratios showing geochemical features of adakite their sr nd hf isotope compositions are similar to those of early cretaceous mafic rocks in the same area indicating that they were generated by partial melting of juvenile granulitic crust at a depth of about 40 km the source was formed by underplating of enriched lithosphere mantle derived magmas in contrast the zaoshan calc alkaline monzogranites their enclaves and associated dolerite dykes from the zaoshan pluton have an emplacement age of 88 1 ma the dolerites have high mgo contents relatively low sio 2 concentrations and low la yb ratios and depleted hf isotope compositions all these geochemical features suggest that they were derived from a depleted spinel iherzolite mantle source the enclaves have high sio 2 contents indicating that they were derived from a crustal source they have variable zircon hf and o isotope compositions suggesting that two components i e a high e hf t and a low 18 o component and a low e hf t and high 18 o component were involved in their origin the high zircon e hf t values and low 18 o values are similar to those of the dolerites indicating a common source thus we suggest that the enclaves were generated by partial melting of newly underplated depleted mantle derived materials the monzogranites have distinctly different zircon hf and o isotope compositions from the enclaves indicating that the parental magmas were mainly derived from ancient crust that interacted with underplated depleted mantle derived magmas the monzogranites have relatively high hree contents suggesting a garnet free source

the age isotopic signature and significance of the youngest mesozoic granitoids in the jiaodong terrane shandong province north china craton abstract most cretaceous granitoids in the jiaodong terrane of shandong province north china craton were intruded between 130 and 122 ma however four granitoid batholiths are significantly younger with an average zircon u pb shrimp emplacement age of 116 2 ma these are the sanfoshan batholith 118 1 ma the aishan batholith 116 1 ma the yashan pluton 113 2 ma and the laoshan batholith 115 2 ma these granitoids post date proposed delamination that occurred prior to 125 ma in the eastern ncc and their geochemistry thus provides information about the nature of the continental crust at this time the rocks are mostly monzogranites and syenogranites of i type affinity with local alkali feldspar granite of a type affinity in addition a monzogranite sample from the aishan batholith records an age of 125 3 ma indicating a direct association with the slightly older granitoids in the area indeed they all contain inherited zircons with ages of 125 120 ma indicating interaction with these earlier granitoids most samples are metaluminous enriched in light rare earth elements and depleted in high field strength elements paleo to neoarchean t dm2 model ages ranging from 3900 ma to 2491 ma and negative e hf t values imply the involvement of archean basement and older recycled continental crustal material in the magma source region they were likely derived from partial melting of the lower or middle crust due to mafic magma underplating followed by various degrees of interaction between mantle derived mafic magma and felsic crustal magma accompanied by fractional crystallization we propose that lithospheric thinning and extension in the early cretaceous due to roll back of the pacific plate beneath the eastern north china craton led to asthenospheric upwelling and basaltic magmatism this underplating in turn led to crustal melting and evolution of the granitic intrusions described here

temporal changes in the subduction of the paleo pacific plate beneath eurasia during the late mesozoic geochronological and geochemical evidence from cretaceous volcanic rocks in eastern ne china abstract subduction of the paleo pacific plate played an important role in the evolution of the eastern margin of the eurasian continent however the details of the processes of subduction during the late mesozoic remain poorly constrained here we examine the geochronology and geochemistry of cretaceous volcanic rocks from eastern ne china with the aim of understanding the variation of subduction process cretaceous volcanism in the region mainly occurs in the raohe mishan suifenhe wangqing and jiamusi jixi areas in eastern jilin and heilongjiang provinces as well as in the lesser xing an range where volcanism extends from the continental margin farther inland the cretaceous volcanic rocks in the raohe mishan suifenhe wangqing rmsw area are composed of basalts basaltic andesites andesites dacites and rhyolites with late early cretaceous 122 106 ma ages and dacites that yield early late cretaceous 96 93 ma ages a mixed source of compositionally heterogeneous mantle and crustal rocks is assumed based on the compositional range of volcanic rocks adakitic andesites 114 110 ma were derived from a mantle source modified by slab derived melt that infiltrated the mantle wedge adakitic dacites 122 106 and 96 93 ma were produced by partial melting of thickened lower crust that formed in response to earlier subduction of the paleo pacific plate beneath eurasia the rhyolites and dacites that lack adakitic signatures were derived from partial melting of a depleted lower crustal block that was accreted during the neoproterozoic in particular the late early cretaceous 106 ma basalt was derived from a depleted lithospheric mantle that was metasomatized by slab derived fluids and subsequently by asthenospheric melts at a relatively shallow depths implying rollrback of the subducted paleo pacific plate the cretaceous volcanism in the jiamusi jixi area formed during the late early cretaceous 124 110 ma and shows a bimodal distribution of compositions with a prominent daly gap the mafic members were generated by re melting of depleted lithospheric mantle that was modified by subduction related fluids and underwent fractional crystallization the coeval felsic end members with or without a type characteristics were generated by partial melting of juvenile crustal material consistent with an extensional environment related to subduction of the paleo pacific plate cretaceous volcanism in the lesser xing an range shows a bimodal compositional distribution of volcanic rocks with a daly gap and a period without volcanism at 108 97 ma andesites with and without adakitic signatures were derived from partial melting of mantle that was hybridized by slab derived melts and metasomatized by a fluid rich subduction component in contrast the coeval a type rhyolites were generated by partial melting of juvenile crust implying the migration of the extensional environment the formation of and spatio temporal relationships between cretaceous volcanic rocks in ne china combined with the regional geological data suggest a transition from low angle subduction to slab rollback and subsequent changes in the direction of motion of the paleo pacific plate during the late early cretaceous to the late cretaceous

origin of cretaceous aluminous and peralkaline a type granitoids in northeastern fujian coastal region of southeastern china abstract in this work we report the geochemical whole rock sr nd and hf isotopes and zircon u pb age and hf o isotopic compositions for six granitic intrusions in northeastern fujian coastal region of southeastern china to elucidate the petrogenesis of aluminous and peralkaline a type granites in this region zircon u pb dating of these rocks including porphyritic syenites porphyritic granites alkali feldspar granites and arfvedsonite granites yielded late cretaceous ages of 94 98 ma mineral assemblage and geochemical features suggested that the arfvedsonite granites were peralkaline a type but the porphyritic syenites porphyritic granites and alkali feldspar granites were aluminous a type geochemical data whole rock nd hf isotopes end t 5 5 to 4 0 ehf t 3 6 to 0 and the zircon hf o isotopes ehf t 3 0 to 1 4 18o 5 4 6 0 indicated that the porphyritic syenites were produced by partial melting of crustal rocks in the lower crust the porphyritic granites and alkali feldspar granites had similar geochemical features and zircon hf o isotopic composition with the porphyritic syenites suggesting that they were formed by feldspar dominant crystal fractionation of deep crust derived syenitic magma under shallow crustal level compared with the aluminous a type granites the peralkaline a type granites had lower abundance of al2o3 mgo cao ba and sr higher abundance of sio2 and hfse as well as higher ratio of total feo mgo ga al and rb sr however the whole rock nd hf and zircon hf o isotopic compositions of the peralkaline and aluminous a type granites were similar it could be inferred that the peralkaline a type granites were formed by crystal fractionation of aluminous a type granitic magmas since the studied a type granitic intrusions were coeval with the bimodal volcanic rocks and the extensional basins in the coastal region of southeastern china they were likely produced in an extensional setting possibly during lithospheric thinning that resulted from the subduction of the paleo pacific plate beneath southeastern china

coastal and inland karst morphologies driven by sea level stands a gis based method for their evaluation sea level is the base level for groundwater circulation in coastal aquifers the evolution of karst surface landforms and subsurface drainage systems in these aquifers has been conditioned in geological time by tectonics and glacio eustatic sea level changes present morpho structural settings and the type distribution of karst surface and subsurface forms have developed in different carbonate formations according to differences in lithology climate and exposure time all driving the intensity of morphologic and karst processes the repeated and significant changes of groundwater level linked to sea level changes have had the most important role in driving the continuous evolution of karstic drainage systems and has resulted in most cases in a multiphase karst this study aims at defining a general method for identifying in karst coastal settings the elevations of flat or low topographic gradient surfaces using morphometric analysis of digital elevation models dems and geographical information systems giss and their comparison with elevations of distinctive karstic levels passages lateral solution cavities observed in vertical shafts and horizontal caves of the elevations of flat or low topographic gradient surfaces only those agreeing within 10 m or 20 m with elevation ranges marked by the high frequency of distinctive karst levels were considered as representative of the more probable past sea level stands the method is applied to a regional coastal carbonate formation in southern italy by using a 10 m dem and information on 140 complex caves and 85 shafts of the 15 elevations indicated by dem analysis 620 600 470 450 425 385 355 315 270 250 205 180 150 110 and 70 m above sea level a s l 13 match clearly those highlighted by significant frequencies of distinctive karstic levels these elevations are validated by comparison to the elevation of terraces and karst plains indicated in the literature copyright 2012 john wiley sons ltd

nd isotopic variation of paleozoic mesozoic granitoids from the da hinggan mountains and adjacent areas ne asia implications for the architecture and growth of continental crust abstract there is a long standing controversy regarding the tectonic division composition and structure of the continental crust in the da hinggan mountains and adjacent areas which are mainly part of the southeastern central asian orogenic belt caob this paper approaches these issues via neodymium isotopic mapping of paleozoic mesozoic 480 to 100 ma granitoids on the basis of 943 published and 8 new whole rock nd isotopic data the study area can be divided into four nd isotopic provinces i ii iii and iv province i the youngest crust nd model ages tdm 0 8 0 2 ga is a remarkable region of phanerozoic crustal growth which may reflect a major zone for closures of the paleo asian ocean province ii slightly juvenile crust tdm 1 0 0 8 ga the largest nd isotopic province in the southeastern caob is considered to reflect the recycling of the initial crustal material produced during the early stage early neoproterozoic evolution of the paleo asian ocean province iii slightly old crust tdm 1 6 1 1 ga is characterized by ancient crustal blocks such as the central mongolian erguna dariganga and hutag uul xilinhot blocks which represent micro continents and precambrian basements in the southeastern caob several parts of province iii are located along the northern margin of the north china craton ncc which is interpreted as a destroyed cratonic margin during the paleozoic and mesozoic province iv the oldest crust tdm 2 9 1 6 ga mainly occurs within the ncc and reflects its typical precambrian nature these mapping results indicate that the boundary between provinces ii and iii the northern margin of the ncc along the solonker xar moron fault can be regarded as the lithospheric boundary between the caob and ncc provinces i and ii account for 20 and 44 of the area of the southeastern caob respectively and therefore the ratio of continental growth is 64 from the neoproterozoic to the mesozoic which is typical for this part of the caob and distinguishes the caob from other phanerozoic orogens in the world

timing of destruction of the north china craton abstract the north china craton ncc is the typical example of destruction of an ancient craton however the destruction mechanism and geodynamic controlling factors still remain enigmatic due to controversy on the timing of destruction which is the key to understanding the destruction processes based on temporal and spatial distributions of the igneous rocks and their sources and tectonic settings it is recognized that six stages of tectono magmatism occurred in the ncc during the phanerozoic i e carboniferous to early permian late permian to middle triassic late triassic jurassic early cretaceous and cenozoic among them cenozoic magmatism mainly consists of alkali basalts and is found only occasionally in the eastern ncc the first four stages of magmatism and tectonism related to the southward subduction of the paleo asian plate and the assembly of sino korean and yangtze cratons are locally distributed in limited parts of the ncc reflecting a multiple stage modification of the ncc from the late carboniferous to jurassic however the intensive development of early cretaceous magmatism extensional deformation and associated gold mineralization with significant continental crustal growth indicate that the eastern ncc was destroyed during this time period this destruction was the result of paleo pacific subduction beneath the eastern asian continent with lithospheric removal and or replacement of an ancient cratonic lithosphere by a juvenile oceanic lithosphere

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

geochemistry geochronology and zircon hf isotopic study of peralkaline alkaline intrusions along the northern margin of the north china craton and its tectonic implication for the southeastern central asian orogenic belt abstract a giant permian alkaline magmatic belt has recently been identified in southern inner mongolia along the northern margin of the north china craton ncc this belt is mainly composed of syenite quartz syenite alkaline granite and mafic microgranular enclaves mme bearing granodiorite in order to study the petrogenesis and tectonic implications of these rocks we undertook zircon u pb dating and geochemical analysis of two permian alkaline plutons the first guangxingyuan pluton occurs in the hexigten area and is composed of mme bearing tonalite k feldspar granite and syenite the second durenwuliji pluton located in the xianghuangqi area comprises syenite quartz syenite and k feldspar granite zircon u pb dating on tonalite k feldspar granite syenite and quartz syenite from the two plutons yielded a tight range of ages from 259 to 267 ma the peralkaline alkaline rocks show high abundance of total alkalis k2o na2o 7 9 12 9 and k2o contents 3 9 8 0 enrichment in large ion lithophile elements lile and light rare earth element lree and depletion of high field strength elements hfse the associated tonalite and mmes display i type granitic geochemical affinity with less total abundance of trace elements than the peralkaline alkaline rocks zircon hf isotopic analysis of the guangxingyuan pluton yielded a large range of ehf t values from 15 5 to 6 7 and model ages tdmc from 781 to 2012 ma by contrast the hf isotopic data of the durenwuliji pluton shows a small range of ehf t from 6 2 to 8 9 and tdmc from 667 to 816 ma the geochemical and hf isotopic characteristics indicate that the parental magma was derived from a mixing of metasomatic mantle derived mafic magma with different amount of crust derived felsic magma and followed by fractional crystallization considering previous tectonic studies in inner mongolia a permian post orogenic extension was proposed to account for these peralkaline alkaline intrusions following the amalgamation of ncc and its northern blocks in the southeastern part of central asian orogenic belt

the enigmatic yinshan fold and thrust belt of northern china new views on its intraplate contractional styles the east to east northeast trending yinshan belt lies within north china extending westward at least 1100 km from china s eastern coast to inner mongolia this intraplate jurassic cretaceous belt underwent contractional and normal faulting folding and contemporaneous terrestrial sedimentation and magmatism current views on its contractional deformational style favor relatively limited thick skinned faulting of archean basement and cover units these views are challenged however by recent discoveries in the eastern part of the belt of south directed ductile nappe formation and large displacement 40 45 km thin skinned northward thrust faulting both involving archean and younger rock units collision of the siberian and north china plates upon closure of a jurassic and early cretaceous mongolo okhotsk ocean more than 800 1100 km to the north may have been responsible for yinshan north south contraction some patterns of contraction e g jurassic cretaceous ductile nappe formation appear to have been influenced by a superposed magmatic regime related to westward subduction of a pacific basin plate beneath the north china plate

petrogenesis and tectonic implications of a type granites in the dabie orogenic belt china geochronological and geochemical constraints the dabie orogenic belt is characterized by the presence of large volumes of intrusive and volcanic rocks that formed in late mesozoic times most of the intrusive bodies are i type granites but it is still unclear whether there are contemporary a type granites here we report the first unambiguous discovery of a type granite from baiyashan in the north dabie tectonic belt the crystallization age of the body has been fixed as 120 4 1 2 ma using u pb analysis of zircons by la icpms the baiyashan granite is enriched in si k na rb and ree has elevated feo tot feo tot mgo and ga al ratios and is depleted in mg ca mn ba sr p and ti the ree composition shows highly fractionated patterns with la yb n 6 95 16 68 and eu eu 0 33 0 59 its crystallization age field relationships petrographic and geochemical data show beyond doubt that the baiyashan granite is an early cretaceous a type granite sr nd isotope systematics are characterized by a high i sr of 0 708 0 714 and a low nd of 7 5 to 19 4 with t dm2 1 5 2 5 ga and these data indicate that the magmas were dominantly sourced from partial melting of middle to lower crustal intermediate felsic igneous rocks and mingling with mafic to intermediate magmas during rift related magmatism associated with subduction of the palaeo pacific plate beneath eastern china in early cretaceous times

rapid exhumation and cooling of the liaonan metamorphic core complex inferences from 40ar 39ar thermochronology and implications for late mesozoic extension in the eastern north china craton the liaonan metamorphic core complex formed during crustal extension in the liaodong peninsula eastern north china craton and consists of the jinzhou detachment fault proterozoic paleozoic sedimentary rocks in its upper plate and exhumed high grade archean metamorphic rocks and early cretaceous granitic plutons in the lower plate exhumation of its footwall from mid crustal levels is evidenced in the detachment fault zone by the temporal transition from amphibolite facies mylonitization at depth through retrograde chloritic shearing and brecciation to brittle faulting during final uplift the footwall mylonite zone is 2 5 3 5 km thick and includes early cretaceous 128 118 ma granitic rocks together with older metamorphic rocks the 40ar 39ar ages of muscovite hornblende biotite and k feldspar from the mylonitic rocks record that the core complex cooled between ca 120 and 107 ma from the time of initial crystallization of zircons 122 118 ma at 700 800 c in syntectonic leucocratic dikes and granitic rocks to closure of argon diffusion in hornblende micas and k feldspar at 500 to 200 c throughout the eastern north china craton the synchroneity of cooling and exhumation of metamorphic core complexes the formation of pull apart basins and regional alkaline igneous activity reflects regional extensional tectonics in the early cretaceous this accompanied lithospheric thinning possibly resulting from the rollback of the subducted pacific plate along the eastern asian margin during the early cretaceous

multi phase cooling of early cretaceous granites on the jiaodong peninsula east china evidence from 40 ar 39 ar and u th he thermochronology abstract the jiaodong peninsula at the southeastern periphery of the north china craton ncc has undergone complex changes since the mesozoic a striking feature of the ncc is the widespread distribution of late mesozoic magmatic rocks predominantly characterized by granitic intrusions these igneous plutons are economically important due to their polymetallic mineralization and significant as geodynamic tracers of the regional tectonic evolution two representative early cretaceous granites the yashan and yuangezhuang plutons on the jiaodong peninsula were selected for multiple thermochronometer studies to constrain a complete thermal history from their emplacement to near surface conditions we obtained biotite 40ar 39ar ages of two granites on the new generation argus vi noble gas mass spectrometer two biotites registered identical 40ar 39ar plateau ages of 117 ma which are consistent within the error with their zircon u pb ages this suggested that the two granites were emplaced at the same time and cooled rapidly to about 300 c the single crystal zircon u th he zhe dating for the two samples gave weighted mean ages of 93 5 4 5 ma and 93 3 5 0 ma combined with previously published geochronological data and the thermal inversion of the zircon low temperature thermochronological data three phases of rapid cooling were identified for the two studied plutons 1 the early cretaceous 117 110 ma 2 the late cretaceous 100 90 ma and 3 the early tertiary 65 50 ma the early cretaceous phase of cooling occurred in a regional extensional regime on the ncc characterized by various extensional structures the late cretaceous cooling is consistent with the third episode of the yanshan movement which caused a regional basin inversion event on the ncc in comparison to the first two phases of rapid cooling the early tertiary cooling was more gradual this phase corresponded to a widely developed eocene rift on the ncc and the reactivation of major boundary faults such as the giant tan lu fault zone and the taihangshan fault

partial melting of apatite bearing charnockite granulite and diorite melt compositions restite mineralogy and petrologic implications melting experiments p 6 9 kbar t 850 950 c nno 02 hm were done on mafic to felsic charnockites a dioritic gneiss and a felsic garnet granulite all common rock types in the grenville basement of eastern north america a graphite bearing granulite gneiss did not melt water h2o 0 60 to 2 0 wt is bound in low grade retrograde metamorphic minerals and is consumed during the earliest stages of melting most melts are water undersaturated melt compositions range from metaluminous silicic granodiorite diorite starting composition to peraluminous or weakly metaluminous granites all others in general liquids become more feldspathic less silicic and less peraluminous and are enriched in feo mgo and tio2 with increasing temperature residual feldspar mineralogy controls the cao k2o and na2o contents of the partial melts and the behavior of these elements can be used particularly if the degree of source melting can be ascertained to infer some aspects of the feldspar mineralogy of the source k feldspar a common restite phase in the charnockite and granulite but not the diorite should control the behavior of ba and possibly eu in these systems and yield signatures of these elements that can distinguish source regions and in some cases bulk versus melt assimilation apatite a common restite phase is enriched in rare earth elements ree especially middle ree retention of apatite in the restite will result in steep light ree enriched patterns for melts derived from the diorite and charnockites

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

development of the north china craton during the late archaean and its final amalgamation at 1 8 ga some speculations on its position within a global palaeoproterozoic supercontinent abstract new data obtained over the past few years indicate that by the end of the archaean the north china craton consisted of two major crustal entities identified as the eastern and western blocks the formation of island and magmatic arcs along the western margin of the eastern block record the latest archaean events so far identified the location of the western block at this time is unknown however the occurrence of palaeoproterozoic passive margin sediments similar in age to those occurring in the eastern block indicates essentially similar conditions and possible separation by an ocean of unknown dimensions re initiation of east dipping subduction beneath the western margin of the eastern block resulted in closure of this palaeoproterozoic ocean bringing the western block into close proximity continued subduction resulted in a major continental continental collision and the western margin of the eastern block was again reactivated leading to extensive thrusting high pressure metamorphism and the generation of crustal melts this occurred between 1 88 and 1 79 ga ago resulting in the formation of the trans north china orogen and final amalgamation of the north china craton although information is sparse to non existent we have reviewed the possible location of the north china craton at the time of collision and note a similarity in terms of age lithology and distribution of major crustal components between the north china craton and baltica although speculative we present this model in the hope that it will stimulate debate and lead to further research in these areas

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

mesozoic crust mantle interaction beneath the north china craton a consequence of the dispersal of gondwanaland and accretion of asia we present evidence from zircons entrained within lower crustal xenoliths in the cenozoic hannuoba basalt of multiple melting events beneath the north china craton in the late mesozoic peak activity was between 180 and 80 ma the upper crustal signature of which was the generation of voluminous granitoids and related volcanic rocks emplacement of dioritic and lamprophyric dikes and widespread gold mineralization the process involved partial loss of mantle lithosphere accompanied by wholesale rising of asthenospheric mantle beneath eastern china we correlate these events with lithospheric thinning resulting from the breakup and dispersal of gondwanaland accompanied by a major mantle overturn fueled by the destruction of oceanic lithosphere and triggered by its sinking into the lower mantle during the subsequent accretion of asia

constraints on the timing of uplift of the yanshan fold and thrust belt north china this paper reports in situ u pb ages and hf isotopic data on detrital zircons from paleozoic to late mesozoic strata in the xishan area near beijing that provide important constraints on the evolution and paleogeography of the northern part of the north china craton ncc zircons from carboniferous to late mesozoic sandstones are characterized by three major groups of u pb ages 2 5 2 3 ga 1 9 1 7 ga and late phanerozoic ages the neoarchean and paleoproterozoic zircons and some phanerozoic zircons have negative ehf t values similar to igneous zircons from intrusive rocks known from the ncc indicating that the source of the sandstones was locally derived however late triassic to late jurassic 205 158 ma sandstones contain a group of phanerozoic zircons with positive ehf t values distinct from known igneous zircons in the ncc suggesting an exotic source the nearest potential source is the xing meng orogenic belt xmob to the north of the ncc where considerable amounts of juvenile crustal materials exist it is concluded that there are two sudden shifts in source provenances of the xishan sediments from the ncc before the late triassic to a mixed source from the ncc and xmob during the late triassic to late jurassic and then from the ncc again during the late jurassic 158 ma the first shift in source resulted from the exhumation and denudation of rocks due to uplift of the xmob which coincided with post collisional extension in the late triassic and intraplate extension of the ncc in the middle to late jurassic the second source shift resulted from the uplift of the yanshan fold and thrust belt thus constraining the timing of this to the late jurassic

crust mantle interaction beneath the luxi block eastern north china craton evidence from coexisting mantle and crust derived enclaves in a quartz monzonite pluton abstract the laiwu quartz monzonite in the luxi block of eastern north china craton ncc is characterized by the presence of abundant plagioclase amphibolite and gabbro diorite enclaves here we present la icpms zircon u pb ages which show that the host quartz monzonite was emplaced at 129 8 1 0 ma whereas the protolith of the plagioclase amphibolite enclaves formed during early paleoproterozoic the gabbro diorite enclaves were produced simultaneously with or slightly earlier than the formation of the host quartz monzonite combined with the archean and paleoproterozoic zircons as well as the low e nd 0 values 18 4 to 18 0 in the plagioclase amphibolite enclaves the equilibrium temperature and pressure conditions 645 670 c and 4 8 6 5 kb suggest that the plagioclase amphibolite enclaves are fragments of the middle crust the gabbro diorite enclaves mainly originated from an enriched lithospheric mantle metasomatized by melts fluids derived from the continental crust as indicated by their low sio 2 54 4 54 7 wt and high mgo 10 9 11 1 wt contents as well as the negative e nd t values 13 5 to 10 7 and enrichment of liles e g ba and sr and depletion of hfses e g nb ta p and ti compared with the ancient crustal rocks and the mafic plutons considered to have been derived from lithospheric mantle in the luxi block the moderate e nd t 15 7 to 15 1 and e hf t 20 7 to 13 0 values of the quartz monzonite in our study suggest that both mantle and crust derived melts were involved in the magma generation thus we propose a model involving magma mixing between mantle and crust derived melts for the formation of the quartz monzonite since significant crust mantle interaction is recorded not only in the quartz monzonite and its enclaves in the luxi block but also in the other granitoids widespread in the ncc it is considered that large scale crust mantle interaction and magmatic underplating were associated with the mesozoic lithospheric mantle thinning and crustal reactivation in the eastern ncc

silicic magma formation in overthickened crust melting of charnockite and leucogranite at 15 20 and 25 kbar 50 60 vol accompanied by settling of residualof crustal source rocks at depths 50 km 2 production of syenite crystals would lead to a magma of restricted compositional rangemagma by partial melting of quartzofeldspathic rocks at pressures with a heavy rare earth element depleted pattern overall the granitic 15 kbar melting experiments at 15 20 and 25 kbar were melt composition obtained in the experiments divers from that ofperformed on archaean biotite bearing charnockite of opx bearing a type granite however at degrees of melting below

petrogenesis of the dengzhazi a type pluton from the taihang yanshan mesozoic orogenic belts north china craton abstract the voluminous mesozoic monzonitic to monzogranitic rocks in the north china craton ncc mostly show high k calc alkaline and i type granitoids features the dengzhazi granitic pluton however shows features typical of a type granites the a type pluton was emplaced in the taihang yanshan orogenic belts of the northern margin of the ncc with zircon u pb ages of around 140 ma the dengzhazi a type granites are characterized by high sio 2 70 2 77 7 wt k 2 o na 2 o zr nb ga zn and y contents as well as high ga al ratios and extremely low cao ba sr in addition they show high zircon saturation temperatures 870 950 c low water and low oxygen fugacity all these features are consistent with the a type affinity of the pluton in situ hf isotopic analyses for the dated zircons show relatively small range of e hf t 13 to 17 they also have homogeneous initial nd isotopic compositions with e nd t ranging from 15 1 to 16 3 the hf and nd isotopic data suggest that the dengzhazi a type granites originated from a homogeneous crustal source probably the archean mafic intermediate granulites taking into account the high temperatures the low h 2 o and f o 2 of the magma system we believe that partial melting of the granulites should have been triggered by underplating of mantle derived magmas at the base of the mafic lower crust in an extensional regime the dengzhazi a type granite is the oldest pluton of the taihang yanshan mesozoic magma belts signifying the commencement of extensive underplating of mafic magmas and thus of lithospheric thinning in the northern ncc

establishing sediment budgets for two small lowland agricultural catchments in the uk sediment budgets have been established for two small 4 km2 lowland agricultural catchments by using 137cs measurements sediment source fingerprinting and more traditional monitoring techniques to quantify the individual components of the budget the gross and net erosion rates for the fields on the catchment slopes were estimated using 137cs measurements within selected fields which encompassed a representative range of slope angles slope lengths and land use these estimates were extrapolated over the entire catchment using a simple topographically driven soil erosion model terrain based gis tbgis superimposed on a dem to derive catchment average gross and net erosion rates suspended sediment yields were measured at the catchment outlets and sediment source fingerprinting techniques were used to establish the relative contributions from the catchment surface subsurface tile drains and eroding channel banks to the sediment yields in channel and wetland storage were quantified using both direct measurements and 137cs measurements the sediment budgets established for the catchments highlighted the importance of subsurface tile drains as a pathway for sediment transfer accounting for ca 60 and 30 of the sediment output from the two catchments erosion from channel banks contributed ca 10 and 6 of the sediment output from the two catchments although the suspended sediment yields from these catchments were considered high by uk standards ca 90 t km 2 year 1 the sediment delivery ratios ranged between 14 and 27 indicating that a major proportion of the mobilised sediment was stored within the catchments in field and field to channel storage were shown to be of similar magnitude but storage of sediment in the channel system and associated wetlands was relatively small representing 5 of the annual suspended sediment yield

multi chronometric ages and origin of archaean tonalitic gneisses in finnish lapland a case for long crustal residence time the tojottamanselka gneisses of the koitelainen region northern finland have been dated by the sm nd and the common pb methods the sm nd data of seven samples from a small area 100 m 100 m define an isochron oft 3 06 0 12 2 ga with correspondingind 0 50848 9 2 orend t 3 7 1 8 this age is in good agreement with the zircon u pb discordia age 3 1 ga reported by kroner et al 1981 and is interpreted as the time of magmatic emplacement the distinctly negativeend t value is found for the first time for archean tonalitic gneisses and implies derivation of these magmas by remelting of continental material with a long 200 500 ma crustal residence time a few samples on the other hand possessend t values close to zero hence they are thought to be derived by partial melting of basaltic sources with nearchondritic ree distribution patterns

nd isotope evidence for crust mantle interaction in the generation of a type granitoid suites in labrador canada early proterozoic a type granite suites in labrador northeastern canada have initial nd isotopic compositions that lie between those of a depleted mantle reservoir and the local basement rocks one of these a type granite suites consists of a linear array of discrete plutons that crosses the boundary between an archean craton and an adjoining early proterozoic crustal block the nd of these granites at formation t 1720 ma changes from 8 to 4 across this boundary reflecting changes in the nature and antiquity of the continental crust however in both domains the granites cannot be derived entirely by anatexis of the local basement rocks and apparently require significant amounts of juvenile mantle derived material a type granites have been widely interpreted as anatectic derivatives of lower crustal rocks that were depleted by previous melt extraction the nd isotopic data suggest that these labrador examples were instead mixtures of mantle derived magmas and overlying lower crustal rocks and that new material may have been the volumetrically dominant component 50 90 in most cases as an alternative to the prevalent residual source model it is proposed that the distinctive geochemical characteristics of these a type granites are a function of the high liquidus temperatures and primitive mg rich character of subcrustal magma fluxes in post orogenic and anorogenic environments where such magmas are emplaced into stabilized continental crust further nd isotope studies of other a type granite suites are required to ascertain if models invoking crust mantle interaction are more widely applicable

early mesozoic alkaline complexes in the northern north china craton implications for cratonic lithospheric destruction abstract early mesozoic alkaline intrusive complexes are widespread in the northern north china craton ncc and constitute an e w trending alkaline magmatic belt that is more than 1500 km long along the northern sino korean craton our new zircon and baddeleyite u pb dating results of the yongfucun yaojiazhuang and sungezhuang alkaline complexes combined with previous geochronological data indicate emplacement of the e w trending alkaline belt in the northern ncc during the middle late triassic at around 235 220 ma geochemical and sr nd hf isotopic data suggest a common source region for the syenites pyroxene syenites and mafic rocks within the complexes they were mainly derived from a metasomatized enriched lithospheric mantle however some materials from depleted asthenospheric mantle have been involved during formation of these alkaline complexes involvement of depleted asthenospheric mantle materials indicates upwelling of the asthenospheric mantle and asthenosphere lithospheric mantle interaction in northern ncc during the early mesozoic initiation of lithospheric thinning and destruction of the northern ncc occurred in the middle late triassic which is much earlier than in other parts of the ncc during the late mesozoic delamination at the root of the subduction induced thick lithospheric mantle is likely main mechanism for the early mesozoic lithospheric thinning and destruction of the northern ncc multiple subduction of oceanic plates beneath the northern southern and eastern parts of the ncc and interactions of the surrounding orogenesis during the late paleozoic to mesozoic may play important roles on the late mesozoic lithospheric destruction of the ncc

petrogenesis and geodynamic implications of the gejiu igneous complex in the western cathaysia block south china abstract the gejiu tin district in western cathaysia block comprises a series of igneous rocks including equigranular and porphyritic granites gabbro and nepheline syenite systematic shrimp or la icp ms zircon u pb analyses of 15 representative samples from various phases of the gejiu complex yielded late cretaceous ages of 78 85 ma based on their mineralogical geochemical and sr nd hf isotope characteristics these rocks are categorized into three groups felsic rocks alkaline rocks and mafic rocks the felsic rock group includes the equigranular and porphyritic granites geochemical characteristics include high sio 2 contents enrichment in rb th u nb ta nd and hf and depletion in ba k sr p eu and ti compared to primitive mantle ree patterns feature slight lree enrichment with pronounced negative eu anomalies geochemical data and sr nd and hf isotopic compositions indicate that the felsic rocks were probably generated by partial melting of crustal source rocks with a minor input from mantle materials the mafic rocks gabbro and mafic microgranular enclaves have distinct geochemical and isotopic features consistent with derivation from an enriched mantle source with variable degrees of mixing with crustal derived magmas strontium nd and hf isotopic compositions of the alkaline rocks are similar with those of the mafic rocks suggesting that they have a similar source nevertheless petrological and geochemical characteristics of these rocks indicate that they experienced extensive crystal fractionation and limited crustal contamination based on the emplacement of the gabbro mafic microgranular enclaves syenite granites in the gejiu district together with contemporaneous geological events in other parts of the western cathaysia block we suggest that a widespread extension related magmatic episode affected the entire region in the late cretaceous possibly as a result of lithospheric thinning basaltic underplating and associated crustal melting

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

numerical analysis of morphology in relation to coastline variations and karstic phenomena in the southeastern murge apulia italy abstract in the coastal karstic area of the southeastern murge apulia italy changes in sea level due to vertical tectonic movement and or global climatic phenomena generated morphological effects both at the surface marine terraces and underground variations of karstic base level so by integrating and comparing observations of surface and subsurface morphology a more reliable picture of the structural and palaeogeographical evolution was obtained the calculation of topographic gradients and spectral analysis of the topographic surface was applied in order to identify the morphological remnants left by coastal terraces corresponding to palaeo coastlines using these methods it is possible to recognize small morphological scarps which otherwise would be masked by major structures the results obtained were compared with the altimetric distribution of karstic cave bottom surfaces which were examined in order to determine karstic base levels some discrepancies between the two kinds of observations can be explained in terms of rate of sea level variation produced by the tectonic tilting of the apulian foreland in some periods this rate was probably compatible with the rate of the surface processes but not with that of underground processes

the petrogenesis of a type magmas from the amram massif southern israel the 550 530ma alkaline magmatic suite of the amram massif southern israel was emplaced during the transition from an orogenic to an intra plate tectonic setting in the northeastern arabian nubian shield ans the suite ranges from 45 6t o 788 wt sio2 and consists of rhyolites alkali quartz syenites quartz syenites monzonites and co magmatic mafic to felsic alkaline dikes these rocks define a continuous chemical evolutionary trend and reveal a correlation between decreasing stratigraphic age and increasing silica content the felsic members of the suite display a type characteristics and are genetically linked through fractionation to the more mafic ones moderately positive initial end values a2 05 low initial 87 sr 86 sr values 07036 2 high mgo and fe2o3 concentrations 410 895 and 100 125 wt respectively and relatively flat rare earth element patterns la yb na 64 09 in the amram mafic dikes 456 495 wt sio2 suggest their derivation from the sub continental lithospheric mantle above the garnet stability zone the melts program was used to quantitatively model the chemical evolution of the suite extensive anhydrous fractionation 490 of plagioclase alkali feldspar clinopyroxene olivine and minor timagnetite and apatite from parental mafic magmas represented by the amram mafic dikes produced the rhyolitic compositions as well as the intermediate members of the suite this suggests the presence of a large unexposed body of cumulate rocks at depth as well as fusion of a large source region equivalent to an 5km layer in the lithospheric mantle regarded as a representative example for similar a type outcrops in this region this petrogenetic model further suggests that neoproterozoic early cambrian a type magmatism in the northeastern ans represents a significant post orogenic addition of mantlederived material to the juvenile crust this magmatic episode was of a similar magnitude to that of the cenozoic extensionrelated alkaline volcanism of the arabian plate

1700 ma shachang complex northeast china proterozoic rapakivi granite not associated with paleoproterozoic orogenic crust proterozoic rapakivi granites are found on all continents and are characteristically associated with paleoproterozoic crustal domains that predate the granites by

effect of terrace forms on water and tillage erosion on a hilly landscape in the yangtze river basin china in long term agricultural practices cultivated land on long slopes in hilly areas is sometimes terraced to diminish soil loss caused by water and facilitate farming operations in the upper yangtze river basin the forms of the terraces vary with the landform soil resources and traditional techniques used in different areas this study assessed the pattern of soil redistribution and soil particle size redistribution for two major types of terraces with and without embankments samples of cs 137 and soil texture were collected at the upper and lower parts of terraces and at an interval of 5 m along the transect of the toposequence of individual terraces the non embankment terrace net landscape showed increasing cs 137 downslope whereas the embankment terrace et landscape exhibited an abrupt change in cs 137 at the embankment tillage erosion dominated the soil redistribution with smaller contributions made by water erosion in the et landscape in addition to tillage erosion water erosion played an important role in the soil redistribution in the net landscape resulting in a net soil loss at both the upper and lower parts of the terrace soil fine particle fractions exhibited a trend of gradual increase along the transect of the toposequence in the net landscape and a similar fraction of fine particles was found at the upper and lower parts of the terrace the establishment of embankments at the lower end of the terrace obstructed the formation and development of overland water flow thereby creating a line of null downslope soil transport leading to tillage induced soil accumulation on the upslope side of the embankment with little granulometric sorting in the net landscape soil loss seemed to increase as a result of tillage erosion an important delivery mechanism for water erosion accelerating the on site soil loss the embankments at the lower end of the sloping terrace played a crucial role in the soil redistribution patterns of the toposequence resulting in a shift from a water dominated erosion process to a tillage dominated process and a distinct pattern of soil particle size distribution c 2014 elsevier b v all rights reserved

gold mineralization in the northern margin of the north china craton influence of alkaline magmatism and regional tectonic during middle paleozoic mesozoic abstract the northern margin of north china craton nncc has undergone multiple tectonic and magmatic episodes associated with numerous gold mineralization during devonian to cretaceous the origin of gold mineralization is a subject of debate in the nncc but there is a consensus on a metamorphic hydrothermal origin and a magmatic hydrothermal origin for this study we focused on four gold districts including the daqingshan zhangjiakou west liaoning and changbaishan from west to east we specifically constrain the link between the hadamengou dongping jinchanggouliang erdaogou and haigou gold deposits and their magmatic episodes the dahuabei and haigou granites and dongping syenite rocks have an alkaline affinity in contrast the xitaizi jinchanggouliang and xiaoxigou granites as well as the duimiangou quartz monzonites are calc alkaline with high alkaline rocks they are predominantly metaluminous and high fractionated i type granites except the xiaoxigou granite which is a type granites with peraluminous nature this indicates a variable mixing between depleted mantle derived mafic magma and ancient crust derived magma the magmatic events overlap the gold mineralization episodes in the nncc we have identified four magmatic episodes during middle paleozoic to mesozoic at 400 320 ma 245 221 ma 199 161 ma and 143 125 ma on the other hand gold mineralization was emplaced from carboniferous to cretaceous 390 110 ma with a peak in the middle jurassic 170 160 ma the available sulfur oxygen and carbon isotopic data from the studied nncc gold deposits suggest that the ore forming fluids were derived from a mixture of magmatic fluids and meteoric waters that flow in the wall rocks except for the hadamengou and jinchanggouliang gold deposits both late deposits present a multi source involving organic matter and other regional crustal rocks as shown by their positive 34s values 0 6 18 5 the intrusive rocks and sulfides in the nncc display similar lead isotope data suggesting that the lead isotopes might have similar origin the gold forming materials resulting from the mixing of these fluids are the product of several alkaline magmatism activities in this region hence this study has proved that gold mineralization is spatially and temporally related to the alkaline magmatism in the nncc the dominant tectonic events in the nncc are marked by post collisional or anorogenic geodynamical setting which is characterized by high alkaline features and andean type arc related to subduction geodynamical setting and characterized by calc alkaline features of the studied rocks both tectonic events are controlled by 1 the collision between the ncc and the bainaimiao arc 2 the subduction of the paleo asian ocean plate beneath the ncc 3 the collision between the siberian craton and the ncc and 4 the subduction of the western paleo pacific beneath the ncc these tectonic regimes are expressed by a transitional regime changing from compression to extension at western and an extensional regime at western and eastern parts of the nncc respectively

jurassic magmatism related pb zn w mo polymetallic mineralization in the central nanling range south china geochronologic geochemical and isotopic evidence from the huangshaping deposit abstract the nanling range in south china is characterized by extensive mesozoic magmatism and coeval nonferrous and rare metal mineralization huangshaping is a world class pb zn w mo polymetallic skarn deposit in the central nanling range magmatic rocks occurring in this ore district include quartz porphyry granite porphyry granophyre dacite porphyry and aplite with only the first three granitoids genetically associated with polymetallic mineralization most of the orebodies are constrained within the contact zones as skarn and veins between these granitic stocks and the carbonate wall rocks since the age of the quartz porphyry is still controversial and studies of the dacite porphyry and aplite are absent we focus on these magmatic rocks first la icp ms zircon u pb dating suggests that the crystallization ages of the quartz porphyry dacite porphyry and aplite are 154 3 1 9 ma 158 1 0 8 ma and 148 4 3 4 ma respectively combined with previously published age data we infer the evolutionary sequence of magmatic rocks should be dacite porphyry quartz porphyry granite porphyry granophyre aplite the quartz porphyry dacite porphyry and aplite yield high contents of high field strength elements zr nb ce y 255 440 ppm high ratios of 10 000 ga al 2 6 3 2 and prominent depletions in ba sr eu p and ti indicating their crustal affinities to a type granites they have negative end t values 9 4 to 7 0 and high initial pb isotopic ratios 206pb 204pbi 18 307 18 644 207pb 204pbi 15 689 15 742 208pb 204pbi 38 589 38 986 suggesting that they were probably derived by partial melting of ancient granulitic crustal materials the sulfide minerals exhibit a wide range of 34sv cdt values from 22 6 to 24 2 with 206pb 204pb of 17 669 19 708 207pb 204pb of 15 492 15 714 and 208pb 204pb of 37 880 39 789 indicating that sulfur lead and other associated metals were derived from a mixture of magmatic components and the carboniferous wall rocks fluid inclusions in pyrrhotite sphalerite and marmatite samples have 3he 4he ratios of 0 12 to 1 53 ra with calculated mantle helium proportions of 1 3 to 18 9 indicating a predominantly crustal origin for the ore fluids with minor inputs from the mantle the huangshaping deposit is a typical example of the genetic relationship both spatially and temporally between jurassic magmatism and polymetallic metallogeny in the nanling range

cretaceous exhumation of proterozoic carbonatite on the northern margin of the north china craton constrained by apatite fission track and u th he geochronology abstractsome carbonatites related to proterozoic rift activities developed on the northern margin of the north china craton and have a close genetic relationship with certain types of mineralization we obtained new fission track and u th he geochronological data from fragments of pegmatitic apatite that coexists with proterozoic igneous carbonatite along the border of three provinces hebei shanxi and inner mongolia twenty fragments yielded a fission track central age of 124 1 6 5 ma 1 thermal history inversion and track length distribution suggest rapid early cretaceous cooling through the apatite partial annealing zone sixteen single fragment apatite u th he ages range between 82 2 1 8 and 109 6 2 3 ma with the age variation much larger than the analytical uncertainty several reasons could account for this dispersion while alpha particle redistribution resulted from u and th inhomogeneties chemical variations and radiation damage are the most probable causes we calculated the me

petrogenesis of an alkali syenite granite rhyolite suite in the yanshan fold and thrust belt eastern north china craton geochronological geochemical and nd sr hf isotopic evidence for lithospheric thinning the yanshan fold and thrust belt in eastern china has been intruded by a series of alkalic igneous rocks ranging in composition from granite and rhyolite to syenite and trachyte laser ablation inductively coupled plasma mass spectrometry u pb analyses of zircon from three alkaline suites yield early cretaceous ages of 130 117ma three groups of rocks have been identified based on their mineralogical geochemical and sr nd hf isotope characteristics the alkali granites and rhyolites are ferroan and have low al2o3 mgo cao sr ba and eu concentrations and high sio2 total fe2o3 k2o nb ga ta th and heavy rare earth element abundances and ga al ratios geochemical data and sr ndand zircon hf isotopic compositions sr sr i1 4 0 7050 0 7164 end t 1 4 8 4 to 13 6 and ehf t 1 4 5 7 to 16 8 indicate that they were probably generated by shallow dehydration melting of biotiteor hornblende bearing granitoid crustal source rocks and then mixed with contemporaneous magma from a mantle and or lower crustal source ferroan syenites have distinct geochemical features from those of the alkaline granites and rhyolites suggesting that they were produced by clinopyroxene and plagioclase fractionation of melt derived from an enriched mantle source mixed with lower and upper crustal derived magmas the magnesian syenites and trachytes have sr ndand zircon hf isotopic compositions that are distinct from those of the ferroan syenites they were mainly derived from partial melting of lower crustal materials mixed with enriched mantle derived alkali basaltic magma the emplacement of an alkali syenite granite rhyolite suite coeval with the formation of metamorphic core complexes and pull apart basins in eastern china indicates they formed in an extensional setting possibly as a result of lithospheric thinning

crust mantle interaction and craton destruction evidence from late mesozoic plutons in the north china craton late mesozoic granitoids widely distributed in the yanshan belt of the north china craton ncc are important markers of cratonic destruction and lithospheric thinning we report new petrological geochemical zircon u pb and lu hf isotopic data on two late mesozoic granitic plutons from the central ncc near the trans north china orogen we report zircon u pb emplacement ages of 162 156 ma and 132 ma from the siganding and fangshan plutons respectively indicating late jurassic early cretaceous magmatism the presence of a dusty zone and discontinuous zoning in plagioclase phenocrysts and the occurrence of mafic microgranular enclaves in both granitoid plutons suggest mingling and mixing of felsic and basic magmas the rocks investigated in this study show high na 2 o k 2 o and high mg mg mg fe mg and are metaluminous with enrichment in light rare earth elements and large ion lithophile elements rb ba u and sr and depletion in high strength field elements th u nb ta p and ti they also display negative ehf t values and high sr y ratios comparable with adakitic rocks suggesting that the felsic magmas of these intrusions were probably derived from the partial melting of the palaeoproterozoic two stage zircon hf depleted model ages between 2 5 and 1 9 ga thickened lower crust of the ncc whereas the mafic magma was probably derived from subcontinental lithospheric mantle we correlate the magmatism with lithospheric thinning beneath the ncc and associated crust mantle interaction it is inferred that lithospheric thinning was of limited extent in late jurassic 162 156 ma times the magma flare up at around 130 ma was produced by large scale melting of the enriched subcontinental lithospheric mantle with development of extensive intracontinental adakitic magmatic rocks derived from thickened ancient lower continental crust with variable involvement of subcontinental lithospheric mantle supplementary material mineral assemblages and abundance representative electron microprobe analyses la icp ms zircon u pb age data and la mc icp ms lu hf isotopic data are available at https doi org 10 6084 m9 figshare c 3815308

rapid cooling of the yanshan belt northern china constraints from 40ar 39ar thermochronology and implications for cratonic lithospheric thinning abstract the yanshan orogenic belt is located in the northern part of the north china craton ncc which lost 120 km of lithospheric mantle during phanerozoic tectonic reactivation mesozoic magmatism in the yanshan fold and thrust belt began at 195 185 ma early jurassic with most of the granitic plutons being cretaceous in age 138 113 ma along with this magmatism multi phase deformational structures including multiple generations of folds thrust and reverse faults extensional faults and strike slip faults are present in this belt previous investigations have mostly focused on geochemical and isotopic studies of these magmatic rocks but not on the thermal history of the mesozoic plutons we have applied 40ar 39ar thermochronology to biotites and k feldspars from several lower cretaceous granitic plutons to decipher the cooling and uplift history of the yanshan region the biotite 40ar 39ar ages of these plutons range from 107 to 123 ma indicating that they cooled through about 350 c at that time all the k feldspar step heating results modeled using multiple diffusion domain theory yield similarly rapid cooling trends although beginning at different times two rapid cooling phases have been identified at ca 120 105 and 100 90 ma the first phase of rapid cooling occurred synchronously with widespread extensional deformation characterized by the formation of metamorphic core complexes a type magmatism large scale normal faults and the development of half graben basins this suggests rapid exhumation took place in an extensional regime and was a shallow crustal level response to lithospheric thinning of the ncc the second phase of rapid cooling was probably related to the regional uplift and unroofing of the yanshan belt which is consistent with the lack of upper cretaceous sediments in most of the yanshan region

rb sr geochronology of chalcopyrite from the chehugou porphyry mo cu deposit northeast china and geochemical constraints on the origin of hosting granites the chehugou porphyry mo cu deposit is located ca 300 km north of beijing in the boundary zone between the archean north china craton and the neoproterozoic mesozoic central asian orogenic belt using hydrothermal chalcopyrite from this deposit we are able to show for the first time that the rb sr isotope system in massive nonfractured chalcopyrite grains can provide reliable age constraints for mo cu deposits we analyzed two chalcopyrite samples from slightly different petrogenetic environments showing contrasting texture and deformation history five 2 to 5 mg fragments of a single nonfractured chalcopyrite grain containing spatially isolated inclusions of k mica k feldspar and quartz yielded an rb sr isochron age of 256 7 ma 2 including uncertainty for this sample the dense chalcopyrite matrix apparently inhibited diffusion of rb and sr after chalcopyrite crystallization and the age should therefore reflect the time of crystallization of chalcopyrite from the mo cu mineralizing fluids the evidence for mo cu mineralization during the late permian requires a revision of the previous notion that the chehugou deposit was formed during the yanshanian orogeny lasting from 200 to 60 ma fragments of a second chalcopyrite sample that in contrast to the first had experienced deformation as indicated by intragranular fractures and alignment of k mica and k feldspar inclusions along these fractures this sample yielded a clearly younger rb sr isochron age of 207 15 ma 2 this age obviously reflects an isotopically open system due to fluid movement and or prolonged diffusion of rb and sr along the fractures single biotite crystals from an associated monzogranite yielded an rb sr isochron age of 250 ma which is interpreted as a lower age limit for the mo cu mineralization and the time when the granite cooled below 400 to 300 c considering the field evidence for a broadly contemporaneous origin of the mo cu mineralization and the hosting granitoids we suggest that the granitoids are not much older than ca 260 ma the mo cu hosting granitoids range in composition from monzogranite to highly evolved syenogranite with high la yb and sr y ratios initial end values of ca 21 to 23 nd crustal residence times of the sources 1 9 to 2 7 ga indicate melting of the predominantly archean north china craton and a subordinate juvenile mantlederived component much older u depleted lower crustal sources for the granitoids are supported by high initial 208pb 204pb ratios lithospheric delamination and underplating of hot mantle derived material may have facilitated crustal melting in a late orogenic to postcollision

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

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

vapor absent melting at 10 kbar of a biotite and amphibole bearing tonalitic gneiss implications for the generation of a type granites vapor absent melting experiments on a biotite and amphibole bearing archean tonalitic gneiss agc150 at 10 kbar and 875 to 1050 c show that amphibole breaks down from 900 to 950 c producing garnet orthopyroxene and granitic melt biotite dehydration melting produces 10 wt melt up to 950 c via incongruent melting reactions that produce garnet orthopyroxene and titanomagnetite widespread biotite dehydration melting occurs between 950 and 975 c and produces orthopyroxene magnetite titanomagnetite and 20 wt fluorine rich melt up to 0 31 wt f minor f rich 2 7 wt biotite is present even at 1000 c our experiments show that under vapor absent conditions intrusion of hot mantle derived magmas into the lower crust is necessary to initiate widespread biotite dehydration melting in rocks with compositions like agc150 we propose that the high thermal stability of biotite in agc150 suggests that this rock is residual after a previous episode of partial dehydroxylation that left behind somewhat f enriched biotite we show that dehydration melting of such f enriched biotite produces f rich granitic liquids with compositions within the range of a type granite and leaves behind a granulitic residue consisting of orthopyroxene plagioclase quartz titanomagnetite and magnetite

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

meso cenozoic uplift of the taihang mountains north china evidence from zircon and apatite thermochronology the taihangshan mountain belt in the central north china craton represents an important crustal and tectonic boundary to explore the complex tectonic evolution of this area during the mesozoic cenozoic we gathered zircon and apatite u th he thermochronology data along a vertical transect elevation of 630 1584 m of the northern part of the taihang mountain belt from our data we observed three separate rapid cooling phases that occurred at 100 ma 50 40 ma and 27 ma combined with previously published geochronological ages we suggest that the uplift of the taihang mountain belt initiated during the jurassic and experienced multiphase rapid uplift from the cretaceous to the cenozoic the early cretaceous rapid cooling uplifting events are widespread in the north china craton and are caused by the collision between the okhotomorsk block and the east asian continental margin the eocene and oligocene rapid cooling events correspond to the initial rifting and thermal subsidence of the bohai bay basin indicating a coupling between the creation of basins and mountains

contrasting triassic ferroan granitoids from northwestern liaoning north china magmatic monitor of mesozoic decratonization and a craton orogen boundary article i nfo the diversity exhibited by ferroan granitoids testifies to multiple distinct crustal and mantle processes generally within extensional environments and thus holds the key to monitoring important geodynamic and crustal evolutionary processes and calibrating terrane tectonic affinity this study documents three middle to late triassic ferroan granitoid suites from northwestern liaoning north china and proposes distinct petrogenetic scenarios for each the middle triassic ca 238 ma ping andi pad granites are mainly calc alkali and peraluminous their radiogenic whole rock nd and zircon hf isotopic signatures argue for an origin consistent with partial melting of a juvenile quartzofeldspathic crust formed by prior mantle derived magmatic underplating and their differentiations by contrast the late triassic ca 220 ma dashaoleng dsl and sijiazi sjz suites show an evolved character from alkali calcic to alkali and from metaluminous to peraluminous their variably evolved whole rock sr nd and mixed zircon hf isotopic compositions suggest that both suites were formed by variable mixing between depleted mantle derived mafic magma and old crust derived felsic magma with distinctively higher input from juvenile components in the dsl suite these contrasting ferroan granitoid suites not only provide a spatial marker for monitoring juxtaposition of the north china craton ncc and the central asian orogenic belt caob along a lithospheric scale boundary fault in the region but also present a temporal snapshot that records a southwardly progressing crustal growth scenario possibly in response to lithospheric dripping within a post orogenic extensional regime the cratonic scale synthesis further indicates that diachronous decratonization pattern of the ncc might record episodic response of the craton to evolved plate tectonic processes with two contrasting phanerozoic orogenic systems

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

structural characteristics and la icp ms u pb zircon geochronology of the deformed granitic rocks from the mesozoic xingcheng taili ductile shear zone in the north china craton abstract we describe the recently detected ene trending xingcheng taili ductile strike slip shear zone which is an important mesozoic low to middle grade tectonic element formed during the reactivation of the north china craton ncc at the eastern termination of the yanshanian orogenic belt within the xingcheng taili ductile shear zone the degree of deformation weakens gradually from nw to se three main types of banded granitic gneisses represent low to middle grade metamorphic tectonites new u pb zircon dating gives a wide range of protolith ages neoarchean granitic rocks with an emplacement age of 2498 4 6 3 ma have obvious e w trending banded structures upper triassic granitic rocks with u pb zircon ages of 219 7 1 1 ma 218 74 0 61 ma 212 1 1 6 ma and 212 3 1 9 ma are considered to relate to the collision of the ncc and yangtze craton in early mesozoic times the emplacement of biotite adamellite bodies with ages of 159 0 0 8 ma and 152 4 1 9 ma is related to the thinning of the ncc s continental crust an ene trending sinistral ductile shear zone developed within these granites the strongly deformed biotite adamellite bodies bear a gneissosity with s c fabrics ene trending sinistral shear zones and show the deformation characteristics of a shallow crustal level reflecting decratonization of the ncc crystal lattice preferred orientations lpo of quartz determined by electron back scatter diffraction suggest sinistral strike slip shear and a deformation temperature at about 400 to 500 c quartz mainly shows low temperature fabrics with a dominant 0001 slip system similar to the temperature estimated by the micro structural characteristics of quartz and feldspar this deformation event might have occurred in early cretaceous times and is related to the lithospheric thinning and extension of the north china craton triggered by an ongoing roll back of the pacific plate beneath the eastern north china craton

what drove late mesozoic extension of the northern china mongolia tract the northern china mongolia tract exhibited a tectonic transition from contractional to extensional deformation in late mesozoic time late middle to early late jurassic crustal shortening is widely thought to have resulted from collision of an amalgamated north china mongolia block and the siberian plate but widespread late late jurassic early cretaceous extension has not been satisfactorily explained by existing models some prominent features of the extensional tectonics of the northern china mongolia tract are 1 late jurassic voluminous volcanism prior to early cretaceous large magnitude rapid extension 2 overlapping in time of contractional deformation in the yinshan yanshan belt with development of extensionrelated basins in the interior of the northern china mongolia tract and 3 widespread occurrence of alkali granitic plutonism extensional basins and metamorphic core complexes in the early cretaceous a new explanation is advanced in this study for this sequence of events the collision of amalgamated north china mongolia with siberia led to crustal overthickening of the northern china mongolia tract and formation of a high standing plateau subsequent breakoff at depth of the north dipping mongol okhotsk oceanic slab is suggested as the main trigger for late mesozoic lithospheric extension of that tract slab breakoff resulted in mantle lithospheric stretching of the adjacent northern china mongolia tract with subsequent ascent of hot asthenosphere and magmatic underplating at the base of the crust collectively these phenomena triggered gravitational collapse of the previously thickened crust leading to late late jurassic early cretaceous crustal extension and importantly coeval contraction along the southern margin of the plateau in the yinshan yanshan belt the proposed model provides a framework for interpreting the spatial and temporal relationships of distinct processes and reconciling some seemingly contradictory phenomena such as the synchronous extension of northerly terranes during major contraction in the neighboring yanshan yinshan belt d 2003 elsevier b v all rights reserved

reduced rapakivi type granites the tholeiite connection reduced rapakivi type granites are the most iron enriched and reduced i e least oxidized of the anorogenic granite association the low oxygen fugacity and chemical composition of these granites severely limit their sources in this paper we argue that reduced rapakivi type granites and their eruptive equivalents high potassium fayalite rhyolites are derived from mafic sources because tholeiitic magmas and their derivatives have the required low oxygen fugacity reduced rapakivi type granites are produced either by extreme differentiation of basaltic melts or by partial melting of underplated basalts and their differentiated equivalents they form in extensional environments where the asthenosphere is present at shallow depths we envision three stages in the origin of these rocks 1 tholeiitic melts are emplaced at the base of the crust 2 continued introduction of heat partially remelts these tholeiitic rocks and 3 the hot dry melts so produced migrate into the middle crust to produce rapakivi batholiths or erupt as rhyolites partial melting of felsic continental crust may accompany the intrusion of rapakivi type magmas thereby producing the other metaluminous and peraluminous granite compositions of the anorogenic suite

structures kinematic analysis rheological parameters and temperature pressure estimate of the mesozoic xingcheng taili ductile shear zone in the north china craton abstract the ne to ene trending mesozoic xingcheng taili ductile shear zone of the northeastern north china craton was shaped by three phases of deformation deformation phase d 1 is characterized by a steep generally e w striking gneissosity it was then overprinted by deformation phase d 2 with ne sinistral shear with k feldspar porphyroclasts forming a subhorizontal low angle stretching lineation on a steep foliation during deformation phase d 3 lateral motion accommodated by ene sinistral strike slip shear zones dominated associated fabrics developed at upper greenschist metamorphic facies conditions and show the deformation characteristics of middle to shallow crustal levels in some parts the older structures have been in turn overprinted by late stage sinistral d 3 shearing finite strain and kinematic vorticity in all deformed granitic rocks indicate a prolate ellipsoid l s tectonites near plane strain simple shear dominated general shear during d 3 deformation is probably of general significance the quartz c axis textures indicate prism gliding with a dominant rhomb slip and basal slip system formed mainly at low middle temperatures mineral deformation behavior quartz c axis textures quartz grain size and the kruhl thermometer demonstrate that the ductile shear zone developed under greenschist facies metamorphic conditions at deformation temperatures ranging from 400 to 500 c dislocation creep is the main deformation mechanism at a shallow crustal level fractal analysis showed that the boundaries of recrystallized quartz grains had statistically self similarities differential stresses deduced from dynamically recrystallized quartz grain size are at around 20 39 mpa and strain rates in the order of 10 12 to 10 14 s 1 this indicates deformation of granitic rocks in the xingcheng taili ductile shear zone at low strain rates which is consistent with most other ductile shear zones hornblende plagioclase thermometer and white mica barometer indicate metamorphic conditions of medium pressures at around ca 3 5 kbar and temperatures of 400 500 c within greenschist facies conditions the main d 3 deformation of the ene trending sinistral strike slip ductile shearing is related to the roll back of the subducting pacific plate beneath the north china craton

on the formation of dissolution pipes in quaternary coastal calcareous arenites in mediterranean settings a large number of uniform cone shaped dissolution pipes has been observed and studied in quaternary coastal calcareous arenites in apulia and sardinia italy and tunisia these cylindrical tubes have a mean diameter of 52 8 cm and are up to 970 cm deep mean depth for sediment free pipes is 1 38 m they generally have smooth walls along their length are perfectly vertical and taper out towards their bottoms their development is not influenced by bedding nor fractures sometimes their walls are coated by a calcrete crust their morphology has been studied in detail and their relationships with the surrounding rocks and with the environment have been analysed the perfectly vertical development is a clear evidence of their genesis controlled by gravity the depth of the dissolution pipes can be described by an exponential distribution law the milanovic distribution strongly suggesting they developed by a diffusion mechanism from the surface vertically downward we believe dissolution pipes preferentially form in a covered karst setting local patches of soil and vegetation cause infiltration water to be enriched in carbon dioxide enhancing dissolution of carbonate cement and local small scale subsidence this process causes the formation of a depression cone that guides infiltrating waters towards these spots giving rise to the downward growth of gravity controlled dissolution pipes a change of climate from wetter phases to drier and hotter ones causes the formation of a calcrete lining fossilizing the pipes when the pipes become exposed to surface agents by erosion of the sediment cover or are laterally breached the loose quartz sand filling them may be transported elsewhere copyright 2010 john wiley sons ltd

a review of the geodynamic setting of large scale late mesozoic gold mineralization in the north china craton an association with lithospheric thinning abstract abundant gold deposits are distributed along the margins of the north china craton ncc occurring throughout the precambrian basement and located in or proximal to mesozoic granitoids these deposits show a consistent spatial temporal association with late jurassic early cretaceous magmatism and are characterized by quartz lode or disseminated styles of mineralization with extensive alteration of wall rock their ages are mainly early cretaceous 130 110 ma and constrain a very short period of metallogenesis sr nd pb isotopic tracers of ores minerals and associated rocks indicate that gold and associated metals mainly were derived from multi sources i e the wall rocks precambrian basement and mesozoic granites and associated mafic rocks previous studies including high surface heat flow uplift and later basin development slow seismic wave speeds in the upper mantle and a change in the character of mantle xenoliths sampled by paleozoic to cenozoic magmas have been used to suggest that ancient cratonic mantle lithosphere was removed from the base of the ncc some time after the ordovician and replaced by younger less refractory lithospheric mantle the geochemistry and isotopic compositions of the mafic rocks associated with gold mineralization 130 110 ma indicate that they were derived from an ancient enriched lithospheric mantle source whereas the mafic dikes and volcanic rocks younger than 110 ma were derived from a relatively depleted mantle source i e asthenospheric mantle according to their age and sources relation to magmatism and geodynamic framework the gold deposits were formed during lithospheric thinning the removal of lithospheric mantle and the upwelling of new asthenospheric mantle induced partial melting and dehydration of the lithospheric mantle and lower crust due to an increase of temperature the fluids derived from the lower crust were mixed with magmatic and meteoric waters and resulted in the deposition of gold and associated metals

a type granites in northeastern china age and geochemical constraints on their petrogenesis abstract a type granites are widely distributed in northeastern china ne china they were emplaced during three major episodes the permian late triassic to early jurassic and early cretaceous and evolved in different tectonic regimes according to their mineralogical and geochemical characteristics two subgroups of a type granites aluminous and peralkaline can be recognized the peralkaline subgroup contains alkali mafic minerals such as riebeckite arfvedsonite and sodic pyroxene while the aluminous subgroup contains annite and fe rich calcic or sodic calcic amphibole with respect to the aluminous subgroup the peralkaline granites contain higher rb ga and total rare earth elements ree but lower mgo cao al 2 o 3 ba and sr based on the discrimination criteria of eby geology 20 1992 641 the permian and late triassic to early jurassic a type granites belong to the a 2 post orogenic type whereas the early cretaceous granites are of the a 1 anorogenic type nd isotopic compositions of these a type granites indicate their derivation from a dominantly juvenile crustal source their origin is thought to have involved partial melting of an underplated lower crustal source because the generation of a type granites requires high melting temperature we propose models involving slab break off lithospheric delamination and extension the permian a type granites have the same age range as those in eastern junggar southern mongolia and central inner mongolia they occur along a major suture and form a narrow belt between the north china and siberian cratons we suggest that their formation was associated with post collisional slab break off the late triassic to early jurassic a type granites are likely to be the product of lithospheric delamination after the final collision of the major crustal blocks in the late paleozoic to early triassic the early cretaceous a type granites have an anorogenic affinity and were possibly associated with rifting in eastern china at this time associated with the onset of paleo pacific subduction consequently we conclude that the a type granites in ne china were generated at three different times involving multiple processes operative in different tectonic environments

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

geochronology of the guilaizhuang gold deposit luxi block eastern north china craton constraints from zircon u pb and fluorite calcite sm nd dating abstract the guilaizhuang deposit is the largest gold producer in the southwestern shandong province with a unique au te mineralization feature different from the other gold deposits in the adjacent jiaodong peninsula the tongshi alkaline intrusive complex which is composed of syenites and monzonites with a crystallization age of 180 ma is the main magmatic unit in this area and considered to represent post collisional magmatism the syenite intruded into the sedimentary carbonate sequence in the guilaizhuang district cryptoexploded and was altered by fluorine rich fluid the intensely mineralized cryptoexplosive breccias along the ew trending fault are extensively cemented by fluorite and calcite minerals the intrusive age of the syenite should mark the lower limit of the gold mineralization age whereas the formation age of the fluorite and calcite would represent the upper limit in this study we analyzed zircons from the altered syenite in the open pit and the results show u pb ages of 179 180 ma consistent with those of the tongshi intrusive complex we also present a sm nd isochron age from the fluorite calcite mineral pair that shows 181 ma based on those results we infer the timing of gold mineralization to be approximately 180 ma coeval with the intrusion of the tongshi complex a correlation with the regional tectonic milieu shows that the guilaizhuang gold deposit was located in a post collision setting at this time following the amalgamation between the north china craton and the yangtze craton thus the guilaizhuang deposit should mark an important alkaline rock related gold forming event within the eastern margin of the north china craton in a post collisional setting associated with the collision of the north china craton and yangtze craton during late triassic to early jurassic and is obviously different from the early cretaceous intensive gold mineralization in the adjacent jiaodong peninsula

petrogenesis of syenite granite suites from the bryansky complex transbaikalia russia implications for the origin of a type granitoid magmas abstract two syenite granite suites metaluminous and peralkaline that form the bryansky complex in transbaikalia russia have been studied with the aim to constrain the existing models of a type granitoid magma generation the bryansky complex is a large intrusive body of about 1600 km2 emplaced in the central part of the mongolian transbaikalian granitoid belt which extends for more than 2000 km and is 200 300 km wide the belt comprises about 350 a type granitoid plutons and numerous volcanic fields u pb and rb sr isotope dating revealed that all the intrusive rocks of the complex and closely associated comendites were emplaced within a narrow time span 279 285 ma the isotope characteristics are rather similar for all main rock types the metaluminous suite has a 87sr 86sr t value of 0 7050 0 001 end t from 1 9 to 3 0 and the peralkaline suite has 87sr 86sr t 0 7053 0 0008 end t 2 1 and 2 4 comendites and trachyandesites have similar end t values from 2 2 to 3 5 but a slightly higher 87sr 86sr t value of 0 7062 0 0002 the systematic change in chemical and mineralogical composition from syenitic to granitic rocks in both suites and the similar isotopic ratios suggest that the granites were formed by fractional crystallization of the syenite magmas several lines of evidence suggest that metaluminous syenite is the parental magma for the whole bryansky complex study of melt inclusions in quartz phenocrysts from the peralkaline granite and in pyroxene from the nordmarkite indicates that fractional crystallization has resulted in significant f enrichment in the granitic magma up to 1 5 1 7 wt the syenite magmas crystallized at rather high temperature 940 c whereas the near liquidus temperature of the peralkaline granite was lower 760 790 c very high homogenization temperatures of the melt inclusions in quartz phenocrysts from comendites 1000 1100 c suggest that the alkali rich silicic magma formed at a depth of 50 60 km far exceeding the normal crust thickness the sr nd isotope data advocate the main role of mantle derived material in the source region from which the alkali rich syenitic and granitic magmas were produced

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

tectonic uplift sea level changes and plio pleistocene evolution of a coastal karst system the mount saint paul palawan philippines the st paul karst palawan philippines is a tropical coastal karst consisting of towers cones huge depressions and large caves this area hosts the puerto princesa subterranean river ppsr 24 km long whose main entrance is a large spring along the coast and which is one of the largest cave complexes in eastern asia a geomorphological study performed by several field surveys and a morphometric analysis of the digital terrain model dtm and 3d cave models allowed formulation of a first evolutionary framework of the karst system the dtm was extracted from maps and aerial photographs in order to find different generations of relict landforms through the morphometric analysis of topographic surface and karst landforms several features suggest a long and multi stage evolution of the karst whose age ranges from pliocene to present the southern and northern sectors of the area differ in their altimetric distribution of caves in the southern sector some large caves lie between 300 and 400 m asl and were part of an ancient system that developed at the base level of a past river network in the northern sector some mainly vadose caves occur with a phreatic level at 120 130 m asl an important phase of base level cave development is well documented in the inactive passages of ppsr at 50 80 m asl morphological features such as horizontal solution passages and terraced deposits suggest a phase of stillstand of the base level which is recorded in the topography as low relief surfaces at 40 50 m asl the age of this phase is probably early pleistocene on the basis of assumed uplift rates the more recent caves are still active being located at the current sea level but they show more than one cycle of flooding and dewatering with calcite deposition in the ppsr several morphologic features such as two main water level notches at 12 4 and 7 7 m asl and terraced alluvial deposits suggest that the lower and active level passed through more than two high stands of sea level and so it could have formed throughout most of the middle late pleistocene copyright 2010 john wiley sons ltd