zircon u pb hf isotopic and whole rock geochemical studies of paleoproterozoic metasedimentary rocks in the northern segment of the jiao liao ji belt china implications for provenance and regional tectonic evolution abstract this study examines the original nature tectonic setting and evolution of paleoproterozoic metasedimentary rocks of the north liaohe and laoling groups of the northern segment of the jiao liao ji belt in the northeastern margin of the eastern block of the north china craton using new petrological whole rock geochemical geochronological and lu hf isotope data zircons in the metasediments are magmatic and metamorphic in origin yielding peak ages of 2 03 ga for the deposition of the protoliths of the metasedimentary rocks and 1 90 and 1 85 ga for their metamorphism geochemical analyses indicate the protoliths contained sandy wacke and claystone material with minor shale derived from paleoproterozoic granites coeval acidic meta volcanic rocks meso and neo archean basement granites and paleoproterozoic meta mafic rocks using regional geological and new lu hf isotopic data we propose that the protoliths of the metasedimentary rocks of the north liaohe and laoling groups in the northern segment of the jiao liao ji belt were deposited in a back arc basin setting this region experienced two crustal growth events at 2 57 2 46 and 2 28 2 08 ga as well as two metamorphic events at ca 1 90 and 1 85 ga

deformation history of the paleoproterozoic liaohe assemblage in the eastern block of the north china craton the paleoproterozoic liaohe assemblage and associated liaoji granitoids represent the youngest basement in the eastern block of the north china craton various structural elements and metamorphic reaction relations indicate that the liaohe assemblage has experienced three distinct deformational events d1 to d3 and four episodes of metamorphism m1 to m4 the earliest greenschist facies event m1 is recognized in undeformed or weakly deformed domains wrapped by the s1 schistosity suggesting that m1 occurred before d1 the d1 deformation produced small mostly meter scale isoclinal and recumbent folds f1 an associated penetrative axial planar schistosity s1 a mineral stretching lineation l1 and regional scale ductile shear zones concurrent with d1 was m2 metamorphism which occurred before d2 and produced low to medium pressure amphibolite facies assemblages regionally divergent motion senses reflected by the asymmetric f1 folds and other sense of shear indicators together with the radial distribution of the l1 lineation surrounding the liaoji granitoids imply that d1 represents an extensional event the d2 deformation produced open to tight f2 folds of varying scales s2 axial crenulation cleavages and ene ne striking thrust faults involving broadly nw se compression following d2 was m3 metamorphism that led to the formation of sillimanite and cordierite in low pressure type rocks and kyanite in medium pressure rocks the last deformational event d3 formed nw wnw trending folds f3 axial planar kink bands spaced cleavages s3 and strike slip and thrust faults which deflect the earlier d1 and d2 structures d3 occurred at a shallow crustal level and was associated with or followed by a greenschist facies retrograde metamorphic event m4 the liaohe assemblage and associated liaoji granitoids are considered to have formed in a paleoproterozoic rift the late spreading of which led to the occurrence of the early extensional deformation d1 and the m1 and m2 metamorphism and the final closing of which was associated with the d2 and d3 phases of deformation and m3 and m4 metamorphism

shear zone model for the origin of metamorphic core complexes core complex tectonite results from simple shear rotational strain within regional ductile shear zones that have accommodated a tertiary crustal stretching the emplacement of younger and or upper level nontectonite rocks on older and or deeper level tectonites is the ordinary and predictable result of normal slip translation along shear zones that cut upward through the local geologic column progressive deformation produces a structural stratigraphy marked from bottom to top by normal country rock protolith mylonitic gneiss tectonite carapace microbrecciated tectonite microbreccia decollement and upper plate detachment rocks as young as mid miocene the reconstructions suggest that local regional crustal stretching locally exceeded 100

scale invariant sheath folds in salt sediments and shear zones abstract sheath folds are developed in a broad spectrum of geological environments in which material flow occurs including gravity driven surficial deformation in ignimbrites unconsolidated sediments and salt together with deeper level ductile shear zones in metamorphic rocks this study represents the first geometric comparison of sheath folds in these different settings across a wide range of scales elliptical closures defining eye folds represent y z cross sections through highly curvilinear sheath folds our analysis of the published literature coupled with field observations reveals remarkably similar ellipticities r yz for sheath folds in metamorphic shear zones r yz 4 23 salt r yz 4 29 sediment slumps r yz 4 34 glaciotectonites r yz 4 48 and ignimbrites r yz 4 34 nested eye folds across this range of materials n 1800 reveal distinct and consistent differences in ellipticity from the outer r yz to the inner most r y z elliptical rings of individual sheath folds the variation in ratios from outer to inner rings r r yz r y z in gravity driven surficial flows typically displays a relative increase in ellipticity to define cats eye folds r r yz that are remarkably constant r 2 0 99 across 9 orders of magnitude sheath y axes range from 0 1 mm to 75 km our findings lead us to conclude that the geometric properties of sheath folds are scale invariant and primarily controlled by the type and amount of strain with r also reflecting the rheological significance of layering associated with original buckle fold mechanisms the scaling pattern of sheath folds reflects the length scales of the precursor buckle folds and width of deformation zones across a broad range of materials and environments with continued deformation the layering marking the original folds may become increasingly passive to define sheath folds these empirical relationships suggest sheath folding is a fundamental mode of viscous response across a broad spectrum of materials strain rates and scales encompassing a variety of deformation settings

pbsl dating of garnet and staurolite constraints on the paleoproterozoic crustal evolution of the eastern block north china craton abstract it is well accepted that the north china craton formed by assembly of the eastern and western blocks along the trans north china orogen with cratonization in the paleoproterozoic 1 85 ma however there is controversy about the formation of the eastern and western blocks themselves especially the timing of cratonization of the eastern block the jiao liao ji orogenic belt is the most important paleoproterozoic orogenic belt in the eastern block and consists mainly of the north and south liaohe groups and the liaoji granitoids the timing of metamorphism of the liaohe group is the key to understanding the evolution of the eastern block of the north china craton because the isotope systematics of metamorphic minerals can be used to date parts of the prograde thermal histories of metamorphic belts dating of minerals such as garnet and staurolite has the distinct advantage that time information can be related directly to the pressure temperature deformation history recorded by the same mineral in this paper we present results of precise 207pb 206pb stepwise leaching pbsl dating of garnet and staurolite from the metasedimentary rocks of the south liaohe group the primitive pb and radiogenic pb are selectively extracted from garnet and straurolite by leach steps and determined by multiple collector mc icp ms the garnet and staurolite record two groups of 207pb 206pb ages at 1 93 1 91 ga and 1 86 ga respectively these constrain the time of peak metamorphism of the liaohe group during collision between the longgang block in the north and the liaonan nangrim block in the south and a subsequent post collisional event respectively our data for the south liaohe group and previously published data for the liaoji granite combined with key lithological structural and metamorphic information indicate that the cratonization of the eastern block of the north china craton occurred at 1 93 1 91 ga

fold fault relationships in low angle detachment systems a close kinematic and timing relationship between low angle extensional faulting and upright to moderately inclined folding with fold axes parallel to the extension direction is established for two well exposed neogene detachment systems in the simplon region of the alps and in the death valley region of california fold amplitude is largest in the oldest mylonitic foliation of the footwall these folds are transected by younger mylonitic foliation s and cataclastic detachment faults which are themselves folded about similar axes in general the amplitude decreases and the wavelength increases for progressively younger fold structures consistent with a history of progressive folding during faulting the interplay between folding and faulting in the footwall reflects a component of shortening perpendicular to fold axial surfaces during extension parallel to fold axes this strain pattern can develop in regions with a transcurrent component or during lateral extrusion and does not necessarily require overall crustal thinning

geochronological and geochemical constraints on the petrogenesis of the early paleoproterozoic potassic granite in the lushan area southern margin of the north china craton abstract we conducted a geochronological and geochemical study on the paleoproterozoic potassic granites in the lushan area southern margin of the north china craton ncc to understand the tectonic regime of the ncc at 2 2 2 1 ga this rock suite formed at 2194 29 ma the rocks are rich in sio2 76 10 77 73 wt and k2o 5 94 6 90 wt with high k2o na2o contents from 7 56 wt to 8 48 wt but poor in cao 0 10 0 28 wt p2o5 0 02 0 05 wt and mgo 0 01 0 30 wt mg 1 08 27 3 indicating they experienced fractional crystallization major element compositions suggest the potassic granites share an affinity with high k calc alkaline granite even though the lushan potassic granitic rocks have high a cnk ratios 1 11 1 25 which can reach peraluminous feature the very low p2o5 contents and negative correlation of p2o5 and sio2 ruling out they are s type granites different from peralkaline a type granites the lushan potassic granites have variable zr concentrations 160 344 ppm 226 ppm on average and 10 000 ga al ratios 1 76 3 00 together with high zircon saturation temperatures tzr 826 885 c indicating they are fractionated aluminous a type granites enriched lree la yb n 9 72 81 8 negative eu anomalies and low sr y with no correlations in sr y and sr zr versus cao suggest the possible presence of ca rich plagioclase and absence of garnet in the residual magmatic zircon grains have variable ehf t values 2 4 to 7 3 with zircon two stage hf model ages tdmc varying from 2848 ma to 2306 ma mostly around ca 2 5 ga and are plotted in the evolution line of crustal felsic rock we propose that the rocks mainly formed by partial melting of ca 2 50 ga tonalitic granodioritic crust as a result of upwelling mantle derived magmas which provided thermal flux and source materials in an intra continent rifting the ca 2 2 ga magmatism suggests that intra continental rifting occurred at 2 35 1 97 ga at least in the southern margin of the ncc after its final cratonization in the late neoarchean

palaeoproterozoic metasedimentary rocks of the ji an group and their significance for the tectonic evolution of the northern segment of the jiao liao ji belt north china craton in this paper we present new petrological and whole rock geochemical data for the palaeoproterozoic metasedimentary rocks in the upper part of the ji an group within the jiao liao ji belt china as well as zircon u pb age dates and in situ lu hf isotope data the new data improve our understanding of the original nature of the metasedimentary rocks further providing insights into their tectonic setting and the evolutionary history of the northern segment of the jiao liao ji belt the zircons can be divided into two groups viz one of magmatic origin and the other of metamorphic origin zircon u pb dating gave mean or statistical peak ages for the magmatic zircons at 2035 2082 2178 2343 2421 2451 2545 2643 2814 and 2923 3446 ma and mean peak ages for the metamorphic zircons at 1855 and 1912 ma which indicate a maximum depositional age of 2 03 ga and two stage metamorphic events at c 1 91 and 1 85 ga for the metasedimentary rocks geochemical data show that 1 the protoliths of these rocks were mainly sandstones greywackes and claystones together with some shales 2 the main sources of the sedimentary material were palaeoproterozoic granites and acid volcanic rocks with minor contributions from archaean granitic rocks and 3 the sediments were deposited in an active continental margin setting moreover along the northeastern margin of the eastern block of the north china craton there is evidence of ancient crustal materials as old as 3 76 ga and multiple crustal growth events at 3 23 3 05 2 80 2 65 2 54 2 45 and 2 28 2 08 ga

the liaonan wanfu metamorphic core complexes in the liaodong peninsula two stages of exhumation and constraints on the destruction of the north china craton 1 the liaodong peninsula early cretaceous extension province lep located in the eastern part of the north china craton ncc was highly extended in early cretaceous the liaonan and the wanfu metamorphic core complexes mccs are two most important elements in the province both are typical cordilleran type core complexes that are composed of a general three layered structure but show various differences shearing along the jinzhou detachment fault zone in the liaonan mcc generated ductile to brittle tectonites various deformation microstructures and several types of quartz c axis fabrics implying that the mcc has a complicated progressive exhumation history however medium temperature microstructures and fabrics are superimposed by low temperature features along the wanfu detachment fault zone suggesting a relatively short and simple exhumation history of the wanfu mcc magmatic zircon u pb geochronological dating reveals that the early cretaceous extension of the lep began with the initiation of shearing along the jinzhou detachment fault zone and exhumation of the liaonan mcc before ca 134 ma subsequently relatively slow cooling and exhumation of the lower plate accompanied a giant magmatic event from 130 ma to 120 ma exhumation of a new mcc i e the wanfu mcc was triggered by progressive extension after ca 120 ma rapid cooling and exhumation of the metamorphic lower plate of the two mccs are attributed to coeval detachment faulting along both the jinzhou and wanfu faults from 120 ma to 113 ma the extension ended at ca 107 ma these data provide reliable evidence that the two mccs were exhumed progressively and sequentially during two stages of crustal extension of the lep our results indicates that heterogeneous lithosphere extension and upper middle crust upper mantle detachment possibly due to the interaction between the paleo pacific and eurasian plates are among the most important processes during the early cretaceous thinning of the lithosphere tectonic extension may have led to the detachment in east asia which contributed to the thinning of the lithosphere and the destruction of the ncc a phase of uniform and consistent wnw ese extension was responsible for the generation of the extensional structures in the eastern asia continent and the destruction of the ncc

mid late triassic metamorphic event for changhai meta sedimentary rocks from the se jiao liao ji belt north china craton evidence from monazite u th pb and muscovite ar ar dating abstract the precise constraints on the timing of metamorphism of the changhai metamorphic complex is of great importance considering the prolonged controversial issue of the north margin and the extension of the sulu dabie hp uhp belt while the monazite u th pb and muscovite 40 ar 39 ar techniques are widely accepted as two of the most powerful dating tools for revealing the thermal histories of medium low grade metamorphic rocks and precisely constraining the timing of metamorphism the changhai metamorphic complex at the se jiao liao ji belt north china craton consists of a variety of pelitic schist and grt ky bearing paragneiss and minor quartzite and marble analyses of mineral inclusions and back scattered electric bse images of monazites combined with la icp ms u th pb ages for monazites and 40 ar 39 ar ages for muscovites provide evidence of the origin and metamorphic age of the changhai metamorphic complex monazites separates from various grt mus schists and grt ky st mus paragneisses exhibit homogeneous bse images from cores to rims and contain inclusion assemblages of grt mus qtz ctd ky in schist and grt ky st mus pl kfs qtz inclusions in paragneiss these inclusion assemblages are very similar to matrix minerals of host rocks indicating they are metamorphic rather than inherited or detrital in origin la icp ms u th pb dating reveals that monazites of schist and paragneiss have consistent 206 pb 238 u ages ranging from 228 1 3 8 to 218 2 3 7 ma in contrast muscovites from various schists show slightly older 40 ar 39 ar plateau ages of 236 1 1 5 to 230 2 1 2 ma these geochronological and petrological data conclude that the pelitic sediments have experienced a metamorphic event at the mid late triassic 236 1 218 2 ma rather than the paleoproterozoic 1950 1850 ma commonly regarded as the precambrian basement for the jiao liao ji belt hence the changhai metamorphic complex should be considered as a discrete lithotectonic group this newly recognized mid late triassic metamorphic event 236 1 218 2 ma for the changhai metamorphic complex is coeval with the hp uhp metamorphic event 235 220 ma for sulu dabie rocks this leads us to speculate that the metamorphism of the changhai complex belt along the se margin of the north china craton was genetically related to the mid late triassic collision of the north china and south china cratons by the same token the sulu dabie hp uhp belt may have extended through yantai and the southern yellow sea and to the southern side of the changhai metamorphic complex

in situ zircon u pb dating and whole rock geochemistry of metasedimentary rocks from south liaohe group jiao liao ji orogenic belt constraints on the depositional and metamorphic ages and implications for tectonic setting abstract the liaohe group is an important paleoproterozoic lithostratigraphic unit of the jiao liao ji orogenic belt and traditionally subdivided into the north and south liaohe groups however their tectonic setting and evolution are still a matter of debate the precise depositional and metamorphic data of the studied metasedimentary rocks from the south liaohe group provide important information on the controversial discussion of the tectonic setting and evolution based on cathodoluminescence cl imaging and connecting la icp ms u pb geochronology zircon grains separated from metasedimentary rocks of different formations of the south liaohe group were subdivided into detrital and metamorphic zircons or zircon domains igneous zircon cores of detrital zircons of the li eryu gaojiayu dashiqiao and gaixian formations yield u pb age peaks at 2130 ma 2520 ma 2160 ma 2500 ma and 2040 ma indicating that their sediments were transported from the liaoji granitoids the archean basement rocks of the adjacent complex in addition deposition age of the sedimentary precursors was investigated which must have taken place at some time after 2 05 ga 2 07 ga 2 04 ga and 1 92 ga respectively these new geochronological data can be well explained by 1 a continent arc collision model which suggests that the south liaohe group formed an intervening island arc and foreland basin sandwiched between the longgang and nangrim complexes and 2 a northward subduction of the nangrim complex source rocks of the south liaohe group these source rocks were successively deposited along the margin of the two complexes

are the south and north liaohe groups of north china craton different exotic terranes nd isotope constraints abstract the liaohe group is an important paleoproterozoic stratigraphic unit in the northeastern part of the north china craton and is traditionally subdivided into the north and south liaohe groups associated with both the north and south liaohe groups are voluminous paleoproterozoic granitoid rocks named the liaoji granitoids different tectonic models including terrane amalgamation continent arc collision and rift closure have been proposed to interpret the tectonic setting and evolution of the north and south liaohe groups and associated liaoji granitoids at the centre of the controversy between these models is whether or not the north and south liaohe groups developed on the same archean basement nd isotopic geochemistry of the liaoji granitoids provides important constraints on this controversial issue the liaoji granitoids associated with the north and south liaohe groups display similar e nd values restricted to a narrow range from 0 to 2 implying that these granitoid rocks were derived from the same or a similar magma source moreover the liaoji granitoids associated with the north and south liaohe groups have similar nd model ages t dm ranging from 2 4 to 2 6 ga suggesting that the protoliths of the liaoji granitoids associated with both groups may have formed simultaneously and that the basement rocks underneath the liaoji granitoids and associated north and south liaohe groups belong to the same continental block rather than two different blocks combining lithological structural and geochronological considerations we interpret the north and south liaohe groups as having developed on a single late archean basement that underwent paleoproterozoic rifting associated with the intrusion of the liaoji granitoids and the formation of the liaohe group and closed upon itself in the paleoproterozoic

emplacement kinematics of a granite diapir the chindamora batholith zimbabwe the geometric features of a large 50 40 km granitic batholith and its surrounding greenstone belt envelope are described the batholith is made up of several intrusive components and an intrusion sequence based on contact relations and xenoliths has been established the igneous rocks show a local foliation s fabric and preferred orientation of minerals the intensity of this fabric accords with the finite strain determined from xenolith shape analysis when the strain variations are analysed in detail it appears that the batholith was built up by a succession of magmatic pulses each of which led to a stretching of the previously consolidated igneous material so called balloon tectonics evidence is presented that xenolith deformation commences only when the surrounding igneous material has crystallized and a method is suggested whereby the position of the surface separating crystal supported phase plastic behaviour from melt supported phase liquid behaviour at different stages in the plutonic history can be determined ductile shear zones are present and their geometry accords well with the shape changes necessary to allow the outer parts of the pluton to stretch

la icp ms u pb zircon ages of the liaohe group in the eastern block of the north china craton constraints on the evolution of the jiao liao ji belt abstract as a major lithostratigraphic unit of the palaeoproterozoic jiao liao ji belt in the eastern block of the north china craton the liaohe group consists of an assemblage that is transitional from a lower arkose and volcanic rich sequence langzishan li eryu and gaojiayu formations through a middle carbonate rich sequence dashiqiao formation to an upper argillaceous sequence gaixian formation tectonically associated with the liaohe group are large volumes of granitoid rocks named the liaoji granite whose emplacement age has been dated at about 2 1 2 2 ga regionally the liaohe group and the associated liaoji granite extend along a nee trending belt that is flanked by 2 45 2 55 ga basement gneisses u pb zircon data and cathodoluminescence cl imaging are used to constrain the maximum depositional and metamorphic ages of the liaohe group which are critical in understanding the tectonic setting and history of the jiao liao ji belt cathodoluminescence images reveal that most detrital zircon grains from the liaohe group are characterized by concentric oscillatory zoning with comparatively low luminescence and high th u ratios suggesting magmatic origin but minor zircon grains have structureless overgrowth or recrystallization rims that are characterized by low th u ratio indicating metamorphic origin results of this study show that the detrital zircon grains of the langzishan formation the lowest sequence of the liaohe group have concordant u pb ages ranging from 2 05 to 2 24 ga suggesting that the liaohe group was deposited at some time after 2 05 ga although most overgrowth or recrystallization rims are too narrow to be analyzed some rims yield concordant or upper intercept ages around 1 93 ga interpreted as the peak metamorphic age of the liaohe group detrital zircon grains from the dashiqiao formation in the middle sequence of the liaohe group have concordant u pb ages ranging from 2 25 to 2 53 ga some of which are similar to those of the basement gneisses in the area this study indicates that the liaohe group was deposited after the emplacement of the liaoji granite and the latter may be a major component of the provenance for the langzishan formation in contrast the protoliths of the middle sequence of the liaohe group were most probably derived from the basement gneisses these new zircon ages for the liaohe group and recent data for the liaoji granite combined with lithological structural and metamorphic considerations support a rifting model for the evolution of the jiao liao ji belt

shrimp u pb zircon geochronology of the liaoji granitoids constraints on the evolution of the paleoproterozoic jiao liao ji belt in the eastern block of the north china craton abstract the paleoproterozoic jiao liao ji belt lies at the eastern margin of the eastern block of the north china craton and is composed mainly of the liaohe group and the liaoji granitoids the liaoji granitoids are divisible into pre tectonic magnetite and hornblende biotite monzogranitic gneisses and post tectonic or anorogenic porphyritic monzogranites and alkaline syenites shrimp u pb zircon geochronology combined with cathodoluminescence cl imaging has enabled for resolution of magmatic and metamorphic events that can be directed towards understanding the history of the paleoproterozoic jiao liao ji belt shrimp u pb zircon analyses reveal that the pre tectonic magnetite monzogranitic gneisses were emplaced in the period 2176 2166 ma and metamorphosed at 1914 ma and the pre tectonic hornblende biotite monzogranitic gneisses were emplaced at 2150 2143 ma these data demonstrate that the pre tectonic monzogranitic gneisses of the liaoji granitoids were not younger than the deposition of the liaohe group as previously considered since the latter contains a large amount of 2100 2000 ma detrital zircons in contrast the pre tectonic monzogranitic gneisses of the liaoji granitoids or similar aged granitoids may have been an important component of the provenance for the liaohe group shrimp u pb zircon analyses also reveal that the post tectonic porphyritic monzogranites and granites in the jiao liao ji belt were emplaced at 1875 10 and 1856 31 ma respectively simultaneously with the emplacement of the alkaline syenites that was dated at 1857 20 and 1843 23 ma similar post tecotnic or anorogenic granites are not only limited to the jiao liao ji belt but are also found in the north and south korea suggesting that the 1 85 ga post tectonic or anorogenic granitic magmatic event may have occurred in both the korean peninsula and the eastern block of the north china craton the shrimp zircon ages of this study combined with lithological structural metamorphic and geochemical data is consistent with a rift closure model which suggests that the archean complexes on the northern and southern sides of the jiao liao ji belt were originally situated on a single continental block that underwent paleoproterozoic rifting associated with the formation of the liaohe group and liaoji granitoids and closed upon itself at 1 9 ga

historical relative gravity observations and the time rate of change of gravity due to postglacial rebound and other tectonic movements in canada 1 a major re adjustment of the primary canadian gravity standardization network cgsn is carried out based on relative gravity measurements spanning over 40 years anticipating that secular variations of gravity dominated primarily by the continuing process of glacial isostatic adjustment could be detected we parameterize the time rate of change of gravity into the observation equation and estimate it directly from a generalised least squares solution time rates of change of gravity from repeated absolute gravity observations as well as absolute gravity values at selected sites are used as weighted constraints the results are presented in form of a map and demonstrate that the primary cgsn with its over 40 year long history can provide us with useful constraints for the evaluation verification and refinement of post glacial rebound models

petrogenesis of the 2 1 ga lushan garnet bearing quartz monzonite on the southern margin of the north china craton and its tectonic implications abstract the lushan garnet bearing quartz monzonite was emplaced into the western taihua complex at 2134 17 ma on the southern margin of the north china craton ncc the rocks contain sio 2 contents of 56 98 59 05 wt with high k 2 o na 2 o 7 46 9 14 wt and al 2 o 3 15 87 17 58 wt and low cao 2 38 2 77 wt and mgo 1 18 1 50 wt contents and belong to an intermediate shoshonitic series magmatic garnet grains in the rocks are chemically homogeneous with relatively high cao 6 36 7 92 wt but low mno 1 45 1 94 wt and mgo 2 47 3 45 wt contents and high fe mn ratios they contain 61 94 66 39 mol almandine 18 60 23 40 mol grossular 10 06 15 11 mol pyrope and 1 09 4 32 mol spessartine similar to high pressure garnets formed from m type magma but different from those found in s type granites and metapelites phase equilibrium diagrams in combination with trace element distribution coefficients between zircon and garnet suggest whole rock zircon saturation temperatures varying from 891 c to 951 c and the mineral assemblage of garnet plagioclase amphibole or biotite in these rocks is stable at 15 kbar and 890 950 c with h 2 o t 800 c all of the rocks are enriched in lile and lree with low nb la ratios 0 24 0 61 similar to those of lithospheric mantle which has a nb la ratio of 0 5 therefore the garnet and whole rock chemical compositions indicate that the lushan quartz monzonite possibly formed by small degrees of partial melting of a phlogopite bearing lithospheric mantle the variable zircon hf t values 3 5 to 4 1 with t dm c from 2 34 ga to 2 51 ga suggest involvement of crustal materials the rocks have slightly negative nb and ta anomalies characteristics of island arc basalts iab however their high zr 598 926 ppm and zr y ratios 17 1 21 8 suggest an affinity with ocean island basalt oib hence the mixed iab and oib like geochemical signatures are indicative of continental intra plate rifting possibly related to extension and thinning of the lithosphere and upwelling of asthenosphere our study proposes that an intra continental rifting event occurred at 2 2 2 0 ga on the southern margin of the ncc after the final amalgamation of ncc

the location and evolution of the tectonic boundary between the paleoproterozoic jiao liao ji belt and the longgang block northeast china abstract in this paper we discuss the location nature and evolution of the tectonic boundary between the jiao liao ji belt and the longgang block northeast china the boundary in terms of paleogeography which involves a study of the liaohe group or tectonics employing non seismic geophysical data e g gravity data and magnetotelluric soundings existing geological data and the differences in physical properties between the jiao liao ji belt and the longgang block we clarified the spatial distribution of the tectonic boundary and characterized the geological bodies at different depths on either side of the boundary we analyzed the most recently updated bouguer gravity anomaly gravity magnetic and electrical profile data as well as comprehensive data on the physical properties of the rocks in the research area thus providing information on the geological nature of the boundary at deep levels the results indicate that during the early period of formation of the jiao liao ji belt a basin controlling boundary fault developed that constituted the original tectonic boundary between the jiao liao ji belt and the longgang block this fault extended from shuangtaling to sandaoling lian shanguan dawanggou balidianzi and erhulai to guaimozi following a roughly east west trend most previous studies have considered that the liaohe group which extends from benxi city to benxi county and huanren county is the paleo geographic boundary of the jiao liao ji belt

the inner zone of the liaoji paleorift its early structural styles and structural evolution abstract a suite of eugeosynclinal formations together with common occurrence of extensional granitic rocks constitutes the major part of the inner zone of the liaoji paleorift in liaodong peninsula china two characteristic associations of deformation structures formed under different crustal conditions have been recognized in the liaoji paleorift zone from macro meso and micro structural studies and tectono thermal analyses magmatic core complex mcc a special structural style of extensional regime inherited from early rifting is constituted by the spatial temporal and genetic associations of magmatic cores bedding parallel ductile shear zones and extensional nappes such complexes are widely developed in the rift zone superposed on the mccs thrust nappes and thrusting related brittle ductile shear zones dominate a compressional event in the later evolution of the rift zone early structures were strongly deformed and transformed by later structures and meanwhile also exerted control on the latter e g the thrust nappes are often related to early folds and represented by fold nappes with extensive reactivation and reemplacement of granitic rocks in the cores a schematic evolutionary model for the early structural evolution of the early proterozoic in the inner zone is presented which indicates a different evolution of early rift zones from those of younger ones

paleoproterozoic metavolcanic rocks in the ji an group and constraints on the formation and evolution of the northern segment of the jiao liao ji belt china abstract in this paper we present new petrological and whole rock geochemical data for the paleoproterozoic metavolcanic rocks in the lower part of the ji an group within the northern segment of the jiao liao ji belt china as well as u pb dates and lu hf isotope data for the zircons in these rocks the new data help in understanding the original nature of these volcanic rocks as well as their tectonic setting and the formation and evolution of the belt the zircons can be divided into two groups of which one is of a typical magmatic origin whereas the other shows a metamorphic origin zircon u pb dating and lu hf isotopic results show that the magmatic zircons have peak ages at 2184 2365 2503 and 2710 ma with ehf t values ranging from 1 40 to 8 95 10 86 to 1 48 14 68 to 7 53 and 1 05 and with corresponding model ages of 2 18 2 69 2 80 3 57 2 54 3 83 and 3 22 ga respectively the metamorphic zircons show two peak ages at 1857 and 1914 ma geochemical data show that the protolith of the metavolcanic rocks consists mainly of basaltic andesite andesite and dacite along with minor basalt and rhyolite and that these rocks formed a continuous calc alkaline magmatic sequence in this sequence the intermediate basic rocks have relatively low sio2 contents are enriched in mgo feot the light rare earth elements lrees cr co and ni and depleted in heavy rare earth elements hrees and high field strength elements hfses such as nb ta and ti indicating derivation by partial melting of a depleted lithospheric mantle that had been metasomatized by fluids or melts derived from a subducted slab on the other hand the acidic rocks have high contents of sio2 and low contents of mgo and feot are enriched in alkalis ba th u and k and depleted in nb ta p and ti these geochemical characteristics together with their hf isotope data indicate the acidic rocks could have been derived from the partial melting of juvenile crust and a small amount of ancient crustal material possibly as old as late archean we consider therefore that the metavolcanic rocks in the lower part of the ji an group were formed at ca 2 18 ga as an assemblage of volcanic rocks typical of an active continental margin and that they were affected by two stage metamorphic events at 1 90 and 1 85 ga taking into account the regional geological data we consider that the evolution of the northern segment of the jiao liao ji belt was related to an arc continent collision before the middle paleoproterozoic

early proterozoic tectonic styles and associated mineral deposits of the north china platform abstract the remarkable change in tectonic style from archean granite greenstone belts and high grade terrains to linear sedimentary basins marks the beginning of the early proterozoic in china the different evolutionary histories of and accumulations in the early proterozoic basins result in different archean early proterozoic boundaries two time limits 2 8 and 2 5 ga are significant for the boundary in eastern china early proterozoic basins displaying different tectonic styles contain different mineral deposits the liaodong peninsula type of early proterozoic basin contains the most abundant mineral resources and deposit types including stratabound b fe and pb zn deposits in the eugeosynclinal facies of the liaojitite suite and pyrite p and magnesite deposits in miogeosynclinal facies rocks the magnesite deposits in liaodong peninsula are the largest in the world and were formed in a unique geological setting

a computer model of sheath nappes formed during crustal shear in the western gneiss region central norwegian caledonides abstract the eastern western gneiss region of central norway is part of the deepest exposed norwegian caledonides where basement gneisses and an overlying thrust nappe sequence have been folded into large fold nappes structural analysis of a fold nappe within the central part of the district the grovudal area suggests that it has a strongly sheath like form and that other fold nappes of the western gneiss region may also have sheath like forms the structural history within the grovudal area is dominated by intense east directed subhorizontal shear in an overthrust sense followed by asymmetric refolding with an easterly vergence a computer generated kinematic model was developed to test whether the regional interference patterns could be explained by sheath fold development during this type of deformation the computer model shows that the major regional interference patterns could have been formed by such a kinematic history but does not rule out other possibile histories the proposed kinematic history is however compatible with the regional tectonic history of the main caledonian nappe pile suggesting that the complex nappe interference patterns typical of the region were formed in a kinematically simple but intense ductile deformation associated with caledonian continental imbrication

epma u th pb monazite and shrimp u pb zircon geochronology of high pressure pelitic granulites in the jiaobei massif of the north china craton the jiaobei massif constitutes the southern segment of the paleoproterozoic jiao liao ji belt in the eastern block of the north china craton and contains high pressure hp mafic and pelitic granulites the hp pelitic granulites contain four distinct mineral assemblages garnet kyanite biotite muscovite rutile m1 garnet kyanite ternary feldspar biotite muscovite rutile m2 garnet sillimanite biotite perthite anti perthite m3 and biotite muscovite sillimanite plagioclase m4 of which m2 is a typical hp pelitic assemblage the origin of these hp granulites is important for understanding the tectonic evolution of the jiao liao ji belt but the timing of the hp event still remains unknown this study applied the epma u th pb monazite and shrimp u pb zircon dating techniques to determine the metamorphic ages of the hp pelitic granulites in the jiaobei massif cl images and th u ratios show that all monazite and zircon grains in the analyzed samples are of metamorphic origin eighty two epma analyses on 16 monazite grains from two samples yielded three age groups at 1895 to 1882 ma 1814 to 1813 ma and 1706 to 1692 ma and the ages of 16 shrimp analyses on 14 zircon grains from one sample range from 1864 to 1803 ma the oldest ages of 1895 to 1882 ma were yielded from high y monazite grains enclosed in garnet and sillimanite pseudomorph after kyanite and thus interpreted as the time of the hp m2 granulite facies metamorphism the epma monazite ages of 1814 to 1813 ma and shrimp zircon ages of 1864 to 1803 ma are interpreted as the approximate ages of the post hp granulite facies metamorphism m3 most probably resulting from the exhumation of the hp granulites to the medium pressure granulite facies levels the youngest age group of 1706 to 1692 ma obtained from low y monazite grains in the matrix can be interpreted as the age of late cooling and retrograde metamorphism m4 that occurred when the hp pelitic granulites were exhumed to the upper crust the presence of paleoproterozoic hp mafic and pelitic granulites in the southern segment of the jiao liao ji belt suggests that the evolution of the jiao liao ji belt in the eastern block of the north china craton must have been involved in subduction or collision related tectonic processes

zircon u pb and lu hf isotopic constraints on archean crustal evolution in the liaonan complex of northeast china abstract the changhai area is located in the southeastern part of the liaonan complex within the eastern block of the north china craton ncc in china early precambrian rocks in this area consist mainly of various types of gneisses and schists we present cathodoluminescence images u pb dates and trace element and hf isotope data for zircons from these rocks in order to constrain the formation and evolution of continental crust in the liaonan complex our results show that the magmatic precursors of the biotite monzonitic gneiss granitic gneiss garnet bearing monzogranitic gneiss and biotite granodioritic gneiss that is relatively sodium rich gneisses in the area were emplaced at ca 2543 ma muscovite bearing granitic gneiss monzogranitic gneiss and biotite granitic gneiss that is relatively potassium rich gneisses in the area were emplaced at ca 2516 ma whereas the sedimentary protolith s of the associated schists along the gneissose fabric of the gneisses were deposited after 2518 ma and metamorphosed at ca 1885 ma the latter age may represent the time of metamorphism of the south liaohe group in the jiao liao ji belt large numbers of inherited zircons with ages of 2596 2842 ma coupled with the results of previous studies suggest that multiple meso to neoarchean magmatic events took place in the liaonan complex at ca 2 84 2 75 2 67 2 61 2 54 and 2 51 ga lu hf isotopic results for magmatic zircon grains with ages of 2 61 2 84 ga have positive e hf values 2 4 to 11 3 and average continental crust model ages tc dm of 2 63 3 05 ga with a peak at 2 76 2 98 ga of the zircons with ages of ca 2 54 ga and 2 51 ga 94 have positive e hf values 0 13 to 8 57 average 3 1 and tc dm model ages of 2 53 3 06 ga similar to those of zircons with ages of ca 2 61 2 84 ga suggesting that both sets of zircons were derived from partial melting of juvenile crust however the remaining zircons 6 with ages of 2 54 2 51 ga and all metamorphic zircon grains with ages of ca 1885 ma have negative e hf values of 0 12 to 3 00 and 8 8 to 15 9 respectively and similar older tc dm model ages of 3 11 3 56 ga and 3 08 3 23 ga respectively these data combined with those from previous studies of the ncc indicate that the basement rocks of the liaonan complex underwent two significant juvenile crustal growth events at ca 2 71 2 99 ga and 2 54 2 51 ga a local reworking event at ca 2 51 ga and a major reworking event at 1 88 ga

a review of criteria for the identification of magmatic and tectonic foliations in granitoids abstract foliations in granitoids can form by magmatic flow submagmatic flow high temperature solid state deformation and moderate to low temperature solid state deformation a review of previous work suggests that no single criterion can consistently distinguish foliations in granitoids formed by flow during ascent diapiric emplacement and expansion emplacement during regional deformation or regional deformation post dating emplacement however a magmatic origin is favoured for foliations defined by the alignment of igneous commonly euhedral minerals particularly where the foliation is parallel to internal or external pluton contacts foliations formed during expansion or ballooning of diapirs may be strictly magmatic in origin although some studies suggest that solid state deformation also may occur if so we would hope to find evidence of deformation of crystal melt systems and that the solid state deformation occurred at high temperatures the inference of syntectonic foliations is most convincing where magmatic and high temperature solid state foliations are subparallel these foliations are continuous with regionally developed foliations in the wall rocks synkinematic porphyroblasts are present in the wallrocks and igneous minerals have the same age as metamorphic minerals associated with the regional cleavage a strictly tectonic origin for foliations in granitoids is favoured when the foliation is defined by metamorphic minerals no alignment of igneous minerals occurs the foliation is locally at high angles to pluton wallrock contacts and the foliation is continuous with a regionally developed cleavage

polyphase structural deformation of low to medium grade metamorphic rocks of the liaohe group in the jiao liao ji orogenic belt north china craton correlations with tectonic evolution abstract the paleoproterozoic jiao liao ji orogenic belt in the eastern north china craton provides evidence of the evolution from the early rifting and ocean opening to the final collision of the longgang and nangrim blocks however it is still open to debate and thus controversial as to whether the jiao liao ji orogenic belt formed by closure of a rift without subduction or from an ocean with subduction based on detailed field mapping and structural analysis on a micro meso scale of the liaohe group in the center of the orogenic belt we define at least four phases of deformation and metamorphism s 0 is bedding formed during deposition of the lower liaohe sediments in the liaohe back arc basin during d 1 deformation an early greenschist facies event m 1 was associated with a bedding parallel s 1 metamorphic foliation penetrative axial planar foliation micro to meso scale folds f 1 and an l 1 lineation all formed during accretion probably in a trench subduction setting an m 2 metamorphism took place during medium pressure barrovian type amphibolite facies conditions and associated d 2 deformation that gave rise to major thrusts open isoclinal folds and a well developed crenulation cleavage during exhumation of high pressure and high temperature rocks and collision of the longgang and nangrim blocks m 3 metamorphism at sillimanite m 3 1 and cordierite m 3 2 grade was associated with d 3 deformation that produced regional gentle re folds related to post collisional exhumation of the orogenic belt an m 4 retrograde metamorphism and d 4 deformation gave rise to a weak foliation that can be correlated with late cretaceous extension that affected the whole eastern north china craton we present new isotopic ages la icpms u pb zircon of a granitic vein 2162 ma a pegmatite 1840 ma and a very late granite 114 ma that are integrated with relevant published data accordingly the formation age of deformation and metamorphism was set up and at last a modified tectonic model was presented

multi stage paleoproterozoic structural evolution of the southern liaodong orogenic belt a case study of the hadabei granite gneiss dome abstract a group of paleoproterozoic gneiss domes are well preserved in the southern liaodong segment of the jiao liao ji orogenic belt jljob eastern north china craton similar to the domes in many other orogenic belts they may provide important clues to our understanding of the orogenic processes and related middle lower crustal mass flow during the tectonic evolution of the orogenic belt this paper conducted detailed structural analysis of the hadabei dome a typical example in the dome group to unravel the paleoproterozoic structural styles and deformation history of the southern liaodong orogenic belt three stages of deformation d1 d3 are reconstructed for the structural evolution of the dome the d1 deformation is characterized by meso to micro scale intrafolia folds f1 penetrative foliations s1 and mineral lineations l1 in the metamorphosed volcanic sedimentary rocks the d2 deformation intensively transformed s1 foliations to form asymmetrical folds f2 and crenulation cleavages s2 the d3 deformation is mainly evidenced by occurrence of open folds f3 at various scales u pb zircon geochronological dating of syn tectonic leucogranitic dykes shows that the d2 deformation occurred from 1860 ma to 1822 ma it is also shown that the d2 deformation is the peak stage of deformation that contributed to the formation of the overall tectonic framework of the hadabei dome and therefore the orogenic belt at this stage subhorizontal mass flow contributed to the widely developed shear structures the formation of the hadabei dome was ascribed to early diapirism d1 subhorizontal shearing and doming d2 and fold superposition d3 the multi stage structural evolution was resulted from successive e w oriented rifting extension and contraction and subsequent superimposition by n s shortening in the southern liaodong paleoproterozoic orogenic belt these conclusions provide a better understanding of the mechanisms of doming regional structural deformation and tectonic evolution of the jljob

a comparison of u pb and hf isotopic compositions of detrital zircons from the north and south liaohe groups constraints on the evolution of the jiao liao ji belt north china craton the jiao liao ji orogenic belt is one of the important paleoproterozoic mobile belts in the north china craton ncc and its central segment consists of the north and south liaohe groups and the liaoji granitoids the north and south liaohe groups consist of sedimentary and volcanic successions metamorphosed from greenschist to lower amphibolite facies and the liaoji granitoids are divisible into 2 2 2 1 ga pre tectonic monzogranitic gneisses and 1 88 1 85 ga post tectonic porphyritic monzogranites and alkaline syenites combined with cathodoluminescence cl imaging we report la icp ms laser ablation inductively coupled plasma mass spectrometry u pb and hf isotopic data for detrital zircons from the north and south liaohe groups zircons grains from both groups have igneous zircon cores that yielded two u pb age populations at 2 0 2 2 ga major and 2 5 ga minor indicating that their provenances were similarly dominated by paleoproterozoic liaoji granitoids and late archean basement rocks some structureless zircon rims in both groups yield concordant or upper intercept ages 1 9 ga interpreted as the peak metamorphic age of the two groups these results suggest that both groups were deposited in the period 2 0 1 9 ga shortly after the emplacement of the liaoji granitoids moreover zircons from both groups have similar hf model age peaks t c dm peaks at 2 66 2 75 ga and 2 80 3 00 ga

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

zircon u pb and lu hf isotopic and whole rock geochemical constraints on the protolith and tectonic history of the changhai metamorphic supracrustal sequence in the jiao liao ji belt southeast liaoning province northeast china abstract the changhai metamorphic supracrustal rocks located in the eastern central part of the jiao li ji belt in the north china craton ncc are composed mainly of various garnet mica schists along with minor quartzites and marbles this study presents whole rock major and trace element data zircon u pb dates and hf isotope data for these rocks in order to constrain their protolith age and provenance and discuss the tectonic implications geochemical results indicate that the source rocks were mainly granitoids with a possible minor contribution from clastic sediments with an active continental margin signature detrital zircons have u pb age peaks at approximately 1887 2174 2552 2765 and 3212 ma hf values of 11 1 to 13 0 and three major time windows of average continent crustal model ages t dm c of 2 04 2 33 2 48 2 56 and 2 72 2 93 ga besides these units also contain significant numbers of concordant metamorphic zircons that yielded a peak age of ca 248 ma indicating that the region was modified by an early triassic tectono thermal event these results suggest that sediments of the changhai metamorphic supracrustal rocks were mainly sourced from nearby basement granitoid rocks and to a lesser extent from paleoproterozoic metamorphosed strata such as the north and south liaohe groups furthermore the source rocks of the magmatic zircons analyzed in this study appear to have originated from interaction between old continental crust and juvenile material the youngest concordant zircon age peak at 1879 ma coincides with the timing of formation of regionally widespread granitoids mafic igneous rocks and metamorphism of the south liaohe and ji an groups in the jiao liao ji belt and suggest that the sedimentary protoliths of the changhai metamorphic supracrustal rocks were deposited after this time the results indicate that the archean liaobei jinan complex in the north and the liaonan nangrim complex in the south were already a single continental block by 1887 ma and that the changhai metamorphic supracrustal rocks were deposited at an active continental margin

withdrawn detrital zircon u pb ages and hf isotopes of the metasedimentary rocks from the jiaodong group jiaobei terrane provenance and implications for the crustal evolution in the north china craton

influence of the meridional overturning circulation on tropical subtropical pathways abstract an ocean gcm is used for idealized studies of the atlantic circulation in a square basin the subtropical the tropical and the equatorial gyres are produced by forcing the model with a wind stress profile having only latitudinal dependence the goal is to understand the effect of the meridional overturning circulation moc on the atlantic intergyre exchanges the moc is imposed by prescribing an inflow all along the southern boundary and an outflow at the northern boundary the results indicate that the northward flow of the moc has a crucial effect on the subtropical tropical pathways in this idealized configuration the north atlantic wind field creates a basinwide potential vorticity barrier therefore the water subducted in the north atlantic has to flow to the western boundary before turning equatorward this is shown by the trajectories of floats injected in a band of northern latitudes the warm water return flow of the moc inhibits this pathway and reduces the inflow of north atlantic