boundary fault linkage and its effect on upper jurassic to lower cretaceous sedimentation in the gudian half graben songliao basin northeastern china abstract the songliao basin northeastern china is one of the few ultra large petroleum basins in the world fault superposition linkage and stratigraphic architecture have produced a complicated basin evolutionary history in this study we report the boundary fault linkage and associated upper jurassic and lower cretaceous stratigraphic record using 3d seismic reflection data and well data our results show that the geometry of the boundary gudian fault was originally controlled by six shorter fault segments which grew and were linked during a syn rift stage then frictionally weakened and inverted in a post rift stage this boundary fault has variably controlled coeval syn rift sedimentation fault segments in the middle section controlled the development of the limited but thickest huoshiling and the first member of shahezi formations in the early syn rift stage ca 150 133 9 ma later that control gradually weakened and vanished on succeeding the second member of shahezi and yingcheng formations in the late syn rift stage ca 133 9 105 ma the processes and the diverse syn rift sedimentation response to gudian fault growth and linkage have further implications for graben evolution and can guide hydrocarbon exploration in the songliao basin this study will help elucidate the different controls of boundary fault linkage on associated sedimentation as well as rift basins development in eastern china and similar areas throughout the world

gis based landslide susceptibility mapping using bivariate statistical analysis in devrek zonguldak turkey devrek town with increasing population is located in a hillslope area where some landslides exist therefore landslide susceptibility map of the area is required the purpose of this study was to generate a landslide susceptibility map using a bivariate statistical index and evaluate and compare the results of the statistical analysis conducted with three different approaches in seed cell concept resulting in different data sets in geographical information systems gis based landslide susceptibility mapping applied to the devrek region the data sets are created from the seed cells of a crowns and flanks b only crowns and c only flanks of the landslides by using ten different causative parameters of the study area to increase the data dependency of the analysis all parameter maps are classified into equal frequency classes based directly on the percentile divisions of each corresponding seed cell data set the resultant maps of the landslide susceptibility analysis indicate that all data sets produce fairly acceptable results in each data set analysis elevation lithology slope aspect and drainage density parameters are found to be the most contributing factors in landslide occurrences the results of the three data sets are compared using seed cell area indexes scai this comparison shows that the crown data set produces the most accurate and successful landslide susceptibility map of the study area

palaeoenvironmental reconstruction and biostratinomic analysis of the jurassic yanliao lagerstatte in northeastern china abstract the middle upper jurassic yanliao lagerstatte contains numerous exceptionally preserved fossils of aquatic and land organisms including insects salamanders dinosaurs pterosaurs and mammaliaforms despite extensive study of the diversity and evolutionary implications of the biota the palaeoenvironmental setting and taphonomy of the fossils remain poorly understood we reconstruct both the palaeoenvironment of the daohugou area one of the most famous yanliao fossil areas and the biostratinomy of the fossils we use high resolution stratigraphic data from field investigation and excavations to document in detail the stratigraphic succession lithofacies facies associations and biostratinomic features of the lagerstatte our results show that frequent volcanic eruptions generated an extensive volcaniclastic apron and lake s in the studied area the frequent alternation of thin lacustrine deposits and thick volcaniclastic apron deposits indicates either that the studied area was located in the marginal regions of a single lake where the frequent influx of volcaniclastic apron material caused substantial fluctuations in lake area and thus the frequent lateral alternation of the two facies or that many short lived lakes developed on the volcaniclastic apron most terrestrial insects were preserved in the laminated normally graded siltstone claystone and tuff facies that form many thin intervals with deposits of graded sandstone siltstone and tuff in between within each interval the terrestrial insects occur in many laminae associated with abundant aquatic organisms but are particularly abundant in some laminae that directly underlie tuff of fallout origin most of these terrestrial insects are interpreted to have been killed in the area adjacent to the studied palaeolake s during volcanic eruptions their carcasses were transported by influxes of fresh volcaniclastic material primarily meteoric runoff and possibly minor distal pyroclastic flow into the palaeolake s and were buried in palaeolake deposits prior to extended decay probably due to a combination of rapid vertical settling ash fall and water turbulence

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

early mesozoic tectonics of the south china block insights from the xuefengshan intracontinental orogen abstract intracontinental orogens remain less understood than accretionary or collisional orogens that are related to plate margin interactions in the center of the south china block the xuefengshan belt provides a well exposed example of such an intracontinental orogen of early mesozoic age detailed field tectonic observations indicate that the xuefengshan belt can be divided into a western outer zone characterized by km scale box fold structures and an eastern zone separated from the western outer zone by the se dipping main xuefengshan thrust in the eastern zone nw verging folds coeval with a pervasive slaty cleavage and a nw se trending lineation are the dominant structures from west to east the dip of the cleavage surface exhibits a fan like pattern the bulk architecture of the xuefengshan belt results from polyphase deformation d 1 is characterized by a top to the nw ductile shearing d 2 corresponds to se directed back thrusting and folding d 3 consists of upright folds with vertical cleavage and lineation at depth a high strain zone characterized by greenschist facies metamorphic rocks and a top to the nw ductile shearing corresponds to a ductile decollement zone that accommodated the deformation of the neoproterozoic to early triassic sedimentary series kinematic compatibility suggests that the synmetamorphic ductile shearing was coeval with the d 1 event in the sedimentary cover the xuefengshan belt is interpreted as an early mesozoic intracontinental orogen which possibly originated from the se directed continental subduction of a piece of the south china block in response to northwestwards subduction of the pacific plate

multistage structural deformations of a superimposed basin system and its tectonic response to regional geological evolution a case study from the late jurassic early cretaceous tanan depression hailar tamtsag basin abstract the spatial temporal extent and influence of the mongol okhotsk and paleo pacific tectonic regimes in northeast ne china and adjacent areas during late mesozoic times have long been controversial as a superimposed rift system which formed due to extensive intracontinental extension during the late jurassic to early cretaceous periods the hailar tamtsag basin is a key area to study the relationship between the mongol okhotsk and paleo pacific tectonic regimes and their superposition with the aim of constraining the evolution of those two regimes in this paper the tanan depression which is a second order structural unit in the western part of the hailar tamtsag basin has been chosen as the research object on the basis of structural analysis of three dimensional 3d seismic data in the tanan depression and taking into account the controlling effect and influence of the pre existing facies on the basin evolution the deformation events in the early cretaceous can be subdivided into four periods 1 a nw se trending extension during the deposition of the tongbomiao formation to the upper part of the second member of the nantun formation 2 a nw se trending compression during the deposition of the upper part of the second member of the nantun formation to the first member of the yimin formation 3 a near ew trending extension during the deposition of the second member to the lower part of third member of the yimin formation 4 a near ew trending compression during the deposition of the upper part of the third member of the yimin formation additionally we identify compressional structures in the basement in the southeast part of the depression which is a key study that resulted from the mongol okhotsk collisional orogeny during the late jurassic the above five major deformational events make up a relatively complete tectonic deformation sequence of the hailar tamtsag basin moreover the deformation sequence together with other available information from the literature in ne china and adjacent areas including petrology geochemistry and geochronology data also record the whole process from the orogenic stage after the closure of the mongol okhotsk ocean over the post orogenic collapse of the mongol okhotsk orogen to the weakening of the influence of the mongol okhotsk regime and eventually to be replaced by the paleo pacific tectonic regime considering that the superposition and transformation of the two tectonic regimes involves almost all the geological process in ne china and adjacent area during the late mesozoic the complete geological record in the tanan depression during this period provides new constraints on the research of regional tectonic evolution and the model of multiphase deformation is also expected to have useful implications for future studies of complex basin systems

the xiaoqinling metamorphic core complex a record of early cretaceous backarc extension along the southern part of the north china craton

jurassic earliest cretaceous tectonostratigraphic evolution of the erlian basin northeast china records of polyphase intracontinental deformation in northeast asia abstract the erlian basin is an important part of the late mesozoic extensional basin system in northeast asia the basin contains thick jurassic lower cretaceous rocks and provides excellent opportunities to understand intracontinental deformation in northeast asia during the late mesozoic however the jurassic early cretaceous evolution of the basin and associated driving mechanisms remain disputed based on 13 new zircon u pb ages for the jurassic lowest cretaceous strata in the erlian basin the correlation of jurassic lowest cretaceous strata between the erlian basin and the yan shan is reestablished and a high precision chronostratigraphic framework is presented the aqitu qiha formations are ascribed to the aalenian early bathonian ca 174 167 ma the xing anling group to the oxfordian early kimmeridgian ca 163 153 ma the hugejiletu formation to the tithonian early valanginian ca 151 139 ma and the aershan formation to the valanginian ca 138 ma combined with seismic reflection profiles the jurassic earliest cretaceous tectonostratigraphic evolution of the erlian basin is reconstructed and five major phases of deformation are revealed these deformation phases include aalenian early bathonian initial extension late bathonian callovian compression oxfordian early kimmeridgian extension late kimmeridgian earliest valanginian compression and valanginian extension integrated with geological evidences from peripheral regions of the erlian basin potential driving mechanisms related to far field tectonic events along asian margins are suggested for each of these deformation phases

holocene landscape evolution along the andean piedmont bolivian chaco abstract as part of the gran chaco the andean piedmont in eastern bolivia is characterized by a highly seasonal climate and large rainfall variability it receives sediments from small drainage basins in the subandean ranges therefore it should constitute a suitable sedimentary and geomorphic archive for the detection of past environmental changes this study reconstructs holocene landscape evolution along the andean piedmont in the bolivian chaco by combining large scale geomorphological analysis and the investigation of sedimentary sequences fluvial aggradation and channel avulsions are the dominant processes of piedmont construction and were particularly pronounced during the mid holocene this is interpreted to reflect a generally active landscape characterized by reduced forest cover as result of increased aridity widespread soil formation and landscape stability in all investigated catchments start after 4 cal ka bp indicating the onset of wetter conditions and successively denser forest cover in the bolivian chaco renewed sedimentation during the last millennium could imply a shift to more arid environmental conditions probably in relation to larger scale climatic phenomena such as the little ice age lia particularly during the last centuries the fluvial system of the study area has undergone the most profound changes of the entire holocene with sedimentation of very coarse sediments and subsequent incision this reflects important changes both in discharge and sediment supply and might be the result of either shorter term climate changes or increasing human impact

structure of the crust and uppermost mantle of the yanshan belt and adjacent regions at the northeastern boundary of the north china craton from rayleigh wave dispersion analysis abstract we have used rayleigh wave dispersion analysis and inversion to produce a high resolution s wave velocity imaging profile of the crust and uppermost mantle structure beneath the northeastern boundary regions of the north china craton ncc using waveform data from 45 broadband ncisp stations rayleigh wave phase velocities were measured at periods from 10 to 48 s and utilized in subsequent inversions to solve for the s wave velocity structure from 15 km down to 120 km depth the inverted lower crust and uppermost mantle velocities about 3 75 km s and 4 3 km s on average are low compared with the global average the moho was constrained in the depth range of 30 40 km indicating a typical crustal thickness along the profile however a thin lithosphere of no more than 100 km was imaged under a large part of the profile decreasing to only 60 km under the inner mongolian axis ima where an abnormally slow anomaly was observed below 60 km depth the overall structural features of the study region resemble those of typical continental rift zones and are probably associated with the lithospheric reactivation and tectonic extension widespread in the eastern ncc during mesozoic cenozoic time distinctly high velocities up to 4 6 km s were found immediately to the south of the ima beneath the northern yanshan belt ysb extending down to 100 km depth the anomalous velocities are interpreted as the cratonic lithospheric lid of the region which may have not been affected by the mesozoic cenozoic deformation process as strongly as other regions in the eastern ncc based on our s wave velocity structural image and other geophysical observations we propose a possible lithosphere asthenosphere interaction scenario at the northeastern boundary of the ncc we speculate that significant undulations of the base of the lithosphere which might have resulted from the uneven mesozoic cenozoic lithospheric thinning may induce mantle flows concentrating beneath the weak ima zone the relatively thick lithospheric lid in the northern ysb may serve as a tectonic barrier separating the on craton and off craton regions into different upper mantle convection systems at the present time

crustal structure of the northern margin of the north china craton and adjacent region from sinoprobe02 north china seismic war r experiment abstract the sinoprobe02 north china seismic experiment consisted of three seismic recording efforts along a 450 km long profile the profile extended from northwest of beijing across the northern margin of the north china craton ncc and across the southeastern portion of the central asian orogenic belt caob to the solonker suture zone we processed analyzed and modeled the data collected during a wide angle reflection and refraction effort the recording of seismic waves from 8 explosions was conducted in 4 deployments of 300 texan recorders with station spacings of 1 1 5 km the p wave field provided good quality data for most of the profile arrivals of refracted and reflected waves from sediments and basement pg intracrustal phases pcp plp and the moho pmp pn were typically observed travel time modeling was done layer by layer using the top to bottom approach and was constrained by a coincident deep reflection seismic profile the initial velocity model was altered by trial and error and the forward model was updated by damped least squares inversion in our modeling calculated travel times fit observed arrivals for all 1439 traces with an average rms error of 0 113 s the final 2 d p wave velocity model contains many features of tectonic significance 1 the velocity structure varies significantly from the ncc to the caob 2 thicker crust appears beneath the yinshan yanshan belt and was probably generated by compression in the early jurassic and modified during the craton s destabilization and extension the flat and relatively shallow moho in the caob may be attributed to the extension 3 strong velocity variations beneath the bainaimiao arc and ondor sum subduction accretion complex indicate that multiple pulses of magmatism occurred during the complex tectonic evolution of this area

early mesozoic deformations of the eastern yanshan thrust belt northern china the yanshan thrust belt ytb is located at the northern edge of the north china plate because of the intense thicking and subsequent delamination of the lithosphere in north china geologists have been focused on the late mesozoic deformation in the yanshan belt the yanshan belt has been regarded as part of a stable craton from the proterozoic to the early mesozoic in this paper the authors present that the yanshan area was deformed during the early mesozoic this deformation could be related to ocean basin closure along the northern margin of north china or related to the collision between the north china and yangtze plates along the qinling dabie ultrahigh pressure belt three stages of early mesozoic deformation are identified in the eastern yanshan at lingyuan county the first stage is characterized by westward thrusting d1 the second stage comprises a top to east thrust system d2 and the third stage comprises extensional gravity induced collapse and landsliding d3 the timing of these evens is constrained by both the crosscutting relationships of faults and the isotopic dating of volcanic rocks and gravels the d1 and d2 events took place in the late triassic and early jurassic whereas d3 event occurred at the end of the middle jurassic the dengzhangzi formation was deposited during the d1 d2 period and recorded a rapid uplift erosion and deposition sequence these early mesozoic contractional deformations in the ytb were probably related to the closure of ancient asian ocean and ancient qinling ocean the later crustal extension was caused by gravitational collapse of the eastern china plateau during early mesozoic

out of sequence thrusting in polycyclic thrust belts an example from the mesozoic yanshan belt north china craton the ew trending yanshan belt an intraplate fold thrust belt located in the northern north china craton that has experienced several episodes of deformation widely separated in time is characterized by out of sequence thrusts according to detailed mapping in the central yanshan belt five geometric and stratigraphic criteria used to aid in determining whether a thrust has an out of sequence geometry or not can be recognized they are 1 unconformable relationships 2 inclination of fault surfaces 3 irregular changes in apparent offset along strike 4 short fault length relative to apparent offset and 5 in sequence geometry with the help of these criteria two generations of out of sequence thrusts that postdate the original in sequence thrusting in the central yanshan belt are recognized the ancestral southward verging fold and thrust belt that formed prior to 180 ma was deformed and cut by two younger generations of faults that are probably more deeply rooted and are constrained to between 172 165 ma and 152 135 ma a series of thrusts with opposite vergence formed during the last period resulting in abundant abnormal field relationships such as younger on older thrust relations fold truncation and cutting down section the nature and occurrence of faults in the yanshan belt implies that superimposed deformation a common feature in polycyclic orogenic belts is a mechanism for the generation of out of sequence thrusting this adds to mechanisms already described in the literature such as maintaining constant critical taper at an orogenic scale inhibition of the deformation front and lateral changes in the nature of the decollement horizons

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

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

lower crustal processes leading to mesozoic lithospheric thinning beneath eastern north china underplating replacement and delamination abstract our recent studies show that the lower crust and lithospheric mantle in the eastern north china craton ncc was thinned in the mesozoic the lower crust played a key role in the tectonic mechanism that led to lithospheric thinning geochemical data from volcanic rocks and xenoliths support the idea that delamination of the lower crust and lithospheric mantle took place only along the northern and perhaps the southern margins of the ncc and this was linked to post collisional orogenic processes however it is difficult for the delamination process to act on the whole eastern ncc and remove 80 120 km of the lithosphere lower crustal xenoliths in mesozoic and cenozoic basalts within the ncc are of two kinds one is granulite facies metamorphosed two pyroxene gabbros and eclogite facies metamorphosed garnet pyroxenites formed at 140 120 ma the other is precambrian granulites that were strongly overprinted by mesozoic metamorphism large scale lower crustal replacement took place in the mesozoic beneath the ncc in other words some or perhaps most part of the present lower crust of the ncc is not precambrian the present lowermost crust is mostly composed of mesozoic meta gabbros and pyroxenites abundant late jurassic high sr granites in the ncc which are compositionally similar to a dakite probably formed by partial melting of the lowermost crust leaving a residue of eclogite or garnet amphibolite a hot upwelling mantle was necessary to partially melt the pre existing lowermost crust and underplate magma in order to form the present lower crust although eclogites could sink into the mantle it is hard to imagine that there was a thick enough eclogite layer that could drag 80 120 km of the lithosphere into the asthenosphere beneath the ncc magmatic underplating seems to be a better alternative mechanism thus the formation of the present lower crust through the underplating and replacement of the pre existing one was closely related to lithospheric thinning and represented a continuation of the same geodynamic process

mesozoic faults in the ne tarim western china and the implications on collisions in the southern eurasian margin abstract paleozoic and cenozoic deformation events responding to the continental growth in the southern eurasian margin since the paleozoic have been well documented in surface and subsurface geology in contrast mesozoic deformation remains poorly known based on interpretation of numerous seismic profiles carried out for oil and gas exploration a mesozoic transpressional linked fault system has been identified in the ne tarim which is composed of 1 the nw se trending longkou ying s ying n and tienan strike slip faults to the west 2 the ne sw trending and nw dipping ying e 1 and ying e 2 thrust faults as well as their branches to the southeast and 3 to the north the weimak fault which can be divided into nw se trending dextral strike slip segments and ne sw trending se verging segments the unconformity and growth strata related to activity of these faults occurred from the jurassic to the cretaceous this transpressional linked fault system in the ne tarim block is a kind of intracontinental deformation attributed to the collisions of the qiangtang and lhasa blocks to the southern eurasian margin from the jurassic through the cretaceous

mesozoic cenozoic evolution of the xining minhe and dangchang basins northeastern tibetan plateau magnetostratigraphic and biostratigraphic results 1 accurate stratigraphic ages are crucial to understanding the deformation history of the tibetan plateau prior to and during the indo asian collision efforts to quantify mesozoiccenozoic ages are hindered by limited fossils and a paucity of volcanic horizons and regionally correlative strata magnetostratigraphic and biostratigraphic results from the xining minhe longzhong basin complex and dangchang basin provide an improved chronology of nonmarine basin development over a large region of the northeastern tibetan plateau 34 37 n 101 105 e analyses of 171 magnetostratigraphic levels and 24 palynological assemblages 120 species indicate late jurassic early cretaceous to mid tertiary deposition although magnetic polarity zonation is incomplete independent palynological age control partially restricts possible correlations to the geomagnetic polarity timescale the sediment accumulation record basin provenance structural geology and published thermochronological data support a history of jurassic exhumation late jurassic early cretaceous fault related basin initiation and cretaceous paleogene reduced accumulation these patterns which are compatible with late jurassic early cretaceous extension and cretaceous paleogene postrift thermal subsidence were disrupted at about 40 30 ma when shortening related to the indo asian collision induced localized range uplift vertical axis rotation and amplified subsidence indexterms 1520 geomagnetism and paleomagnetism magnetostratigraphy 8102 tectonophysics continental contractional orogenic belts 9320 information related to geographic region asia 9604 information related to geologic time cenozoic 9609 information related to geologic time mesozoic keywords tectonics magnetostratigraphy tibetan plateau cenozoic mesozoic sedimentary basins

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

a palaeomagnetic study from the mongol okhotsk region rotated early cretaceous volcanics and remagnetized mesozoic sediments we collected 47 sites of upper triassic to middle jurassic siltstones and sandstones and two sites of lower cretaceous andesites in a large basin located south of the mongol okhotsk suture the suture separates the siberian craton to the north from the mongolian and chinese blocks to the south laboratory treatment and analyses identify the same post folding direction in all rocks the mean direction with a corresponding palaeopole at 76 8on 152 2oe a95d 4 2o of the overprint component nd 49 sites is significantly different at the 95 confidence level from the expected time averaged brunhes or present day field directions the lower cretaceous andesites possess a stable remanent direction at high temperatures that is distinct at 95 confidence limits from the overprint direction the corresponding pole 58 3on 51 0oe dp dm d 3 8o 4 6o based on only fourteen samples is significantly rotated 78 4o 5 3o counterclockwise and insignificantly displaced 2 7o 3 4o north with respect to the early cretaceous reference pole for siberia we argue that the rotation is likely tectonic in nature and not due to a chance reading of the palaeosecular variation of the earth s magnetic field both the palaeomagnetic data and the folding patterns we observed in the field suggest that deformation associated with the suture continued after the early cretaceous and involved sinistral shear 1998 elsevier science b v all rights reserved

characteristics of hydrothermal chlorite from the niujuan ag au pb zn deposit in the north margin of ncc and implications for exploration tools for ore deposits abstract the niujuan ag au pb zn deposit is located in the northern hebei province of north china which is hosted by permian coarse grained granite the orebodies are controlled by a ne striking fault chloritization is the most extensive alteration with increasing alteration intensity from the distal to proximal end of the orebody chlorite and biotite from twenty one altered samples from different depths of four drill holes were analyzed using electron microprobe empa and laser ablation inductively coupled plasma mass spectrometry la icpms empirical geothermometry shows that chlorite formed at 206 340 c through comparing with compositions of unaltered biotite two biotite converted to one chlorite 2bt 1chl is the main chloritization mechanism in weakly and moderately altered granites during the hydrothermal alteration in the niujuan deposit during the alteration hydrothermal fluid mainly brought in fe sr th pb and co2 and took out mg ti si f k li zn sc ga co from the biotite which was accompanied by the formation of quartz rutile calcite and fluorite during the chloritization chlorite in quartz chlorite veins was precipitated directly from the hydrothermal fluids veined chlorite in intensely altered granites formed by the dissolution transport precipitation mechanism under the high fluid rock conditions veined chlorite has nearly the same compositions as chlorite in quartz chlorite veins according to the compositions of chlorite from intensely altered granites and quartz chlorite veins we infer that the hydrothermal fluid had low hfses and transition elements such as ti ga sc and v and low fo2 from weak to intense chloritization granites feo sr th and pb contents of chlorite increase while mgo tio2 li zn sc ga v co and nb contents decrease the composition variations of chlorite are controlled by the composition of biotite the compositions of fluids and the intensity of fluid rock interaction during alteration this indicates that the chemical variations of chlorite could be as a tool for mineral exploration in the moderate low temperature ag au pb zn deposit comparison with chlorite of different genesis shows that compositions of chlorite mainly differ in mg fe and aliv which are mainly controlled by the composition of host rocks and the formation temperature

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

late jurassic to early cretaceous sedimentary tectonic development in the chengde basin yanshan fold thrust belt north china craton abstract the chengde basin is located in the central part of the yanshan fold thrust belt in the northern north china craton the sediments in the upper jurassic to lower cretaceous tuchengzi formation in the chengde basin provide a detrital record of basin dynamics and uplift of the basin margins during that time we analyzed the sedimentary facies paleocurrents and provenance of the tuchengzi formation in the chengde basin for the period of the late jurassic and early cretaceous shortening in the yanshan fold thrust belt four sedimentary facies associations have been identified in the tuchengzi formation corresponding to proximal fan mid fan distal alluvial fan and fluvial facies the transport and distribution of the upper jurassic to lower cretaceous sediments in the chengde basin was controlled by the faults bounding the basin paleocurrent indicators and provenance data of conglomerate clasts reveal that the sediments of the tuchengzi formation in the northern part of the chengde basin were delivered from source regions to the north of the basin the early sediments of the tuchengzi formation in the southern part of the basin comprise a suite of fluvial deposits similar to the fluvial sediments in the northern part of the basin and their paleocurrent data and the compositions of conglomerate clasts also suggest a northern source however the subsequent sedimentation in the tuchengzi formation in the southern part of the basin changed markedly to proximal fan facies with sediments being derived from the south of the basin according to the paleocurrent data and conglomerate clast lithology the sandaohe sheet which is located in the southeast limb of the chengde syncline is not a klippe formed as a result of long distance northward thrusting but an autochthonous pop up tectonic wedge generated by n s shortening during the early cretaceous sedimentation of the tuchengzi formation the sedimentation ended before the onset of the early cretaceous volcanic eruption recorded by the zhangjiakou formation which unconformably overlies the tuchengzi formation

petrology structural setting timing and geochemistry of cretaceous volcanic rocks in eastern mongolia constraints on their tectonic origin abstract cretaceous volcanism occurred over a wide region of eastern asia hypotheses for its development include intra continental rifting continental arc magmatism plume activities and delamination of a previously thickened mantle lithosphere one of the major obstacles in differentiating the above model is the lack of systematic studies of cretaceous volcanic rocks in eastern mongolia and far east russia in this study we address this issue by examining the timing and geochemistry of cretaceous volcanic rocks in eastern mongolia our 40 ar 39 ar dating of volcanic rocks together with the existing k ar ages of volcanic rocks indicate that cretaceous volcanism in our study area occurred between 120 ma and 104 ma our field investigation and geochemical analysis reveal three types of volcanic rocks in the study area 1 a bimodal series 2 a shoshonite series and 3 a basanite series geochemical analysis of the volcanic rocks indicates a highly heterogeneous source which is characterized by a mixture of depleted enriched and metasomatized mantle at least three models may explain the timing geochemistry and regional tectonic setting of cretaceous volcanism in eastern mongolia 1 partial delamination of a previously thickened mantle lithosphere generated by arc magmatism and collision tectonics 2 back arc extension and its related mantle upwelling due to rapid collapse of a flat subduction slab and 3 mantle avalanche of a thick pile of cold subducted paleo asian oceanic plates initially trapped at the 670 km endothermic phase transition triggered by westward pacific subduction causing mixing of several mantle sources testing the above models require further studies on the spatial and temporal relationships between cretaceous volcanism and structural history of ne asia in addition a careful restoration of the position and history of past subducted slabs of the paleo asian oceans may help differentiate the above competing models in the future

gold deposits of the northern margin of the north china craton multiple late paleozoic mesozoic mineralizing events the northern margin of the north china craton is well endowed with lode gold deposits hosting a resource of approximately 900 tonnes t of gold the 1 500 km long region is characterized by east trending blocks of metamorphosed archean and proterozoic strata that were episodically uplifted during variscan indosinian and yanshanian deformational and magmatic events at least 12 gold deposits from the daqinshan yan liao includes the zhangjiakou yanshan and chifeng gold districts and changbaishan gold provinces contain resources of 20 100 t au each most deposits are hosted in uplifted blocks of precambrian metamorphic rocks although felsic paleozoic and mesozoic plutons are typically proximal and host 30 of the deposits the lodes are characterized by sulfide poor quartz veins in brittle structures with low base metal values and high au ag ratios although phyllic alteration is most common intensive alkali feldspar metasomatism characterizes the wulashan dongping and zhongshangou deposits but is apparently coeval with variscan alkalic magmatism only at wulashan stepwise 40ar 39ar geochronology on 16 samples from gangue and alteration phases combined with unpublished shrimp u pb dates on associated granitoids suggest that gold mineralizing events occurred during variscan indosinian and yanshanian orogenies at circa 350 250 200 180 150 and 129 ma however widespread permo triassic 250 ma and early jurassic 180 ma thermal events caused variable resetting of most of the white mica and k feldspar argon spectra as well as previously reported k ar determinations compiled and new stable isotope and fluid inclusion data show that most 18o values for ore stage veins range from 8 to 14 indicating a fluid in equilibrium with the precambrian metamorphic basement rocks d values from fluid inclusions range widely from 64 to 154 which is indicative of a local meteoric component in some veins and highly variable 34s data 7 to 17 even within individual deposits indicate various local country rock sources for sulfur fluid inclusions from all districts show variable homogenization temperatures between 240 and 400 c and are consistently characterized by low salinity h2o co2 ch4 n2 solutions although the data are largely consistent with that from orogenic gold veins intrusion related veins and epithermal veins are also recognized the multiple episodes of mineralization are coincident with episodic tectonic reactivations and associated magmatism along the northern margin of the north china craton electronic supplementary material to this paper can be obtained by using the springer link server located at http dx doi org 10 1007 s00126 001 0239 2

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

numerical investigation of the geodynamic mechanism for the late jurassic deformation of the ordos block and surrounding orogenic belts abstract orogenic belts have developed along the edges of the stable ordos block in northern china three main geodynamic models have been proposed to explain the formation of these orogenic belts they have included the collision between the north china and south china blocks subduction of the pacific plate and stresses transmitted over long distances from the closure of the mongolia okhotsk ocean however these explanations are still controversial and not universally accepted leaving the mechanisms that formed the orogenic belts poorly understood to address these fundamental questions we developed a 3d numerical model using the finite element method to explore the geodynamic mechanism for the late jurassic deformation of the ordos block and its surrounding orogenic belts we investigated the effect of different dynamic regimes on the late jurassic deformation of this region our primary results suggest that strong and stable ordos block remains undeformed despite its location at the center of a region of deformation east west trending fold and thrust belts would have developed along the north and south edges of the ordos block during the closure of the mongolia okhotsk ocean or the collision between the north china and south china blocks north south trending fold and thrust belts would have developed along the east and west edges of the ordos block due to subduction of the pacific plate however the paleo stress field in the late jurassic indicates that the orientations of the maximum compressive principle stress were nearly perpendicular to the edge of the ordos block and the compressive deformation around it was coeval it is difficult to explain the distribution of belts of deformation with a single stress regime our numerical model reveals that multi direction convergence pattern with time during the transformation of these three regimes can be used to interpret the formation and deformation styles of ringed mountains around the ordos block during the late jurassic this proposed mechanism results in many insights into the mesozoic tectonic deformation and mountain building of this region

structural evolution and 40ar 39ar dating of the zanhuang metamorphic domain in the north china craton constraints on paleoproterozoic tectonothermal overprinting abstract the zanhuang domain in the hinterland of the north china craton consists of archaean paleoproterozoic mesoproterozoic and palaeozoic rocks and was previously considered a mesozoic metamorphic core complex our reappraisal of regional structural history and mineral 40 ar 39 ar geochronology shows that the domain was subjected to a number of deformation events and had a heterogeneous uplift cooling history during the paleoproterozoic four primary deformation events have been recognized in the domain the first event reflects the earliest deformation in the region however only closed and rootless folds are preserved d2 was dominated by wnw ese shortening and top to ese thrusting in a collisional environment d3 was a divergent extensional and ductile shearing event driven by the post collisional extensional collapse and exhumation of the thickened crust in the domain d4 was characterized by localized ductile shearing with the development of three nne trending ductile shear zones the 40 ar 39 ar plateau ages derived from the thermochronology analyses of the biotite concentrates from the metamorphic rocks are interpreted as cooling ages through biotite 40 ar 39 ar closure temperature 300 c and this allows us to constrain the timing of deformation events in conjunction with the evidence from structural analyses and previous geochronological data we conclude that 1870 and 1870 1826 ma define the timing of d1 and d2 events respectively while 1826 1793 ma represents the age of d3 the last event d4 occurred at 1689 1633 ma as constrained by 40 ar 39 ar plateau ages of biotite concentrates from the mylonites within the ductile shear zones these data together with k feldspar 40 ar 39 ar geochronology allows us to depict the cooling history of the region during the paleoproterozoic and mesoproterozoic it appears that the uplift cooling rate varies temporally and spatially in the region

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

timing and processes of late mesozoic mid lower crustal extension in continental ne asia and implications for the tectonic setting of the destruction of the north china craton mainly constrained by zircon u pb ages from metamorphic core complexes abstract late mesozoic large scale crustal extension occurred across the northeastern section of continental asia and metamorphic core complexes mccs are the major features in this region this paper presents new zircon u pb and ar ar ages of biotite and hornblende for pre or syn mylonitized and post kinematic unmylonitized intrusions from these mccs and attempts to determine the timing of initiation duration and termination of the mid lower crustal ductile extension by integrating with geochronological data from previous studies these mccs have similar 40 ar 39 ar biotite and hornblende ages 130 to 110 ma mainly from 130 to 120 ma which are interpreted as the cooling ages and represent the timing of the late stage formation of the mccs zircon u pb ages for syn to post kinematic intrusions from some mccs suggest that the mid lower crustal extension probably initiated at ca 150 145 ma with a peak occurring 145 130 ma and continued to 130 120 ma which is older than that suggested by 40 ar 39 ar ages by 10 20 ma the early ductile extension most likely initiated in mongolia and northern china during the late jurassic 150 145 ma at a deeper level then propagated southwards 140 130 ma and finally developed throughout the entire continental ne asia 130 120 ma based on the timing and processes of the extension a geodynamic model and tectonic setting of the destruction of the north china craton ncc are proposed

u pb dating of single detrital zircon grains from mesozoic sandstone in the beipiao basin in the eastern yan liao orogenic belt china provenance and correlation of tectonic evolution single grain u pb ages of sediments from the beipiao basin northeast china were conducted to determine the evolution of basin provenance zircons from a sandstone in the upper triassic laohugou formation yield a wide range of ages and according to their u pb ages fall into four groups 209 3 4 0 304 2 4 9 1565 5 71 2154 50 2400 35 2499 9 2512 11 2557 74 ma these ages indicate that the zircons were principally derived from late archean proterozoic and late paleozoic plutonic rocks intrusions in the mongolian accretion belt and the northern margin of the north china block ncb were probably the main source of the sediments in the basin but the easterly liaodong block also provided minor detrital material with lower u pb ages during the late triassic most of the u pb ages from zircons collected from a sandstone in the lower jurassic beipiao formation range from 194 3 2 9 to 233 8 4 2 ma reflecting the major sediment source during the early jurassic zircons derived from late indosinian plutonic rocks increased which suggests that the detritus was supplied mainly from the interior of the yan liao orogenic belt especially from the liaodong block late indosinian zircons 200 230 ma were eroded and deposited in the lower jurassic beipiao formation and this implies that intensive tectonic activation and uplift of the yan liao orogenic belt in the mesozoic commenced in the late indosinian c 2005 elsevier ltd all rights reserved

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

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

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

geology geochronology and sulphur isotope geochemistry of the black schist hosted haoyaoerhudong gold deposit of inner mongolia china implications for ore genesis abstract the haoyaoerhudong gold deposit is located in the urad middle banner area of inner mongolia in china and is hosted by black schist of the bilute formation in the mesoproterozoic bayan obo group the gold mineralization is within a 4500 m long and 100 m wide zone associated with sulphide quartz veins following the schistosity and crosscutting fractures in the host rocks locally as disseminated sulphide in altered black schist the sulphide mineral assemblage is pyrrhotite pyrite arsenopyrite chalcopyrite sphalerite and is associated with a weak hydrothermal alteration characterized by a silica halo with variable amounts of biotite sericite and carbonate the bilute formation was intruded by multi stage dykes these include metamorphosed porphyritic diorite that pre dates mineralization unmetamorphosed amphibole olivine gabbro that pre dates mineralization and tourmaline bearing pegmatite that post dates mineralization in order to constrain the timing of the gold mineralization and host rocks zircons from the porphyritic diorite amphibole olivine gabbro and tourmaline bearing pegmatite were extracted for u pb dating gold bearing pyrite samples were analysed for 34 s to help determine the possible source of s in the mineral zones a weighted mean 206 pb 238 u age date of 288 3 ma mswd 2 4 was obtained for the porphyritic diorite a weighted mean 206 pb 238 u age date of 282 1 ma mswd 0 58 was obtained from the amphibole olivine gabbro and a weighted mean 206 pb 238 u age date of 182 1 ma mswd 1 04 was obtained from the tourmaline bearing pegmatite these dates constrain the timing of gold mineralization to between 282 1 and 182 1 ma and are consistent with the hydrothermal alteration ages of ca 267 246 ma reported from the literature these new zircon dates indicate that the regional metamorphism of the bayan obo group ceased by the time the haoyaoerhudong gold mineralization was deposited and the genesis of mineralization is not related to the regional metamorphic event the gold bearing pyrites gave positive 34 s v cdt values between 6 8 and 13 4 and are different from the 34 s widely distributed values for the typical black rocks indicating that the sulphur is not derived from the black bilute formation but sourced from some other relatively uniform reservoir widespread contemporaneous granitic magmatism is developed in the haoyaoerhudong area and we suggest that the sulphur forming the gold bearing sulphides is probably sourced from a carbonate contaminated granitic magma reservoir the new zircon dates for the dykes and the 34 s data for gold bearing sulphides indicate that the gold mineralization did not form from metamorphosed black schist in the bayan obo group but is associated with magmatic hydrothermal activity

seismic evidence for significant lateral variations in lithospheric thickness beneath the central and western north china craton abstract we have migrated teleseismic s receiver functions to construct detailed lithospheric structure images that cover the three constituent parts of the north china craton ncc our images show that in contrast to the eastern ncc where significantly thinned lithosphere 60 100 km is widespread the central and western ncc are characterized by the coexistence of both preserved thick and dramatically thinned lithosphere the thick lithosphere 200 km is present beneath the stable ordos plateau and the thinned lithosphere up to 80 km is found in the late cenozoic yinchuan hetao and shaanxi shanxi rift areas with sharp changes occurring over a lateral distance of

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

early cretaceous tectonostratigraphic evolution of the erlian basin ne china a record of late mesozoic intraplate deformation in east asia abstract the erlian basin is one of the largest intracontinental meso cenozoic basins in northeast china the basin is filled with extra thick cretaceous sediments and offers unique opportunities to untangle the late mesozoic intraplate deformation in east asia however despite decades of petroleum exploration in the basin the early cretaceous chronostratigraphy and structural evolution of the erlian basin have been poorly studied based on newly obtained zircon u pb geochronological data well lithological logs and seismic reflection profiles the present study carries out a detailed analysis of the tectonostratigraphic evolution of the erlian basin during the early cretaceous the depositional ages of the lower cretaceous strata in the basin are refined and the early cretaceous evolution of the basin is reestablished the lower aershan upper aershan lower tenggeer upper tenggeer and saihan formations are constrained to the middle valanginian ca 138 135 ma late valanginian ca 135 133 ma hauterivian early aptian ca 133 121 ma middle aptian ca 119 115 ma and latest aptian albian post ca 115 ma respectively the early cretaceous syn rift subsidence of the basin was intermittent rather than continuous and was punctuated by multiphase contractional deformation during the earliest cretaceous prior to ca 138 ma middle valanginian ca 135 ma latest valanginian ca 133 ma middle aptian ca 120 ma late aptian ca 115 ma and early late cretaceous boundary we tentatively attribute the extensional and contractional deformation in the erlian basin to a series of continental collisions along asian margins karakoram lhasa qiangtang collision kolyma omolon siberia collision siberia amuria collision chukotka kolyma omolon collision west philippines south china collision and okhotomorsk east asia collision

late jurassic fluvial eolian deposits from the tianchihe formation ningwu jingle basin shanxi province china abstract eolian systems were widespread in china in the cretaceous however the reports of pre cretaceous eolian and its related systems are scarce which prohibits studying the construction accumulation and preservation of eolian systems as well as its allogenic and autogenic controlling factors in this paper we report on fluvial eolian successions from the late jurassic tianchihe formation in the ningwu jingle basin these successions represent the oldest reported inland fluvial eolian systems in china fourteen lithofacies types are recognized in the tianchihe formation and have been grouped into six facies associations including meandering fluvial channel levee and overbank in the lower part and eolian sandsheet eolian dune ephemeral fluvial channel and floodplain in the upper part the fluvial system comprises a series of wetting upward cycles which indicate humid climate culminating in high precipitation and shallow water table level eolian dune deposits composed of grainflow grainfall wind ripple strata and pin stripe laminations currently implies that all deposits types are internally bounded by reactivation surface and superimposition surface suggesting compound dunes or draas eolian sandsheet deposits consist dominantly of subcritical climbing translatent strata and pin stripe lamination the association of eolian dune and eolian sandsheet is development of a dry eolian system twelve drying upward cycles mainly composed of eolian sandsheet eolian dune successions and four wetting upward cycles consisting of eolian sandsheet dune ephemeral fluvial channel floodplain successions occur in the eolian system these repeated cycles likely reflect an evolving erg system directly controlled by sediment supply sediment availability and relative water table the vertical transition from fluvial to eolian systems indicate a local climatic oscillation from relatively humid to arid conditions which may be related with the uplift of the east china plateau in the late jurassic

structure of crust and upper mantle beneath the ordos block and the yinshan mountains revealed by receiver function analysis a temporary seismological network of broadband three component stations has been deployed n s to investigate the crust and upper mantle structure across the ordos block and the yinshan mountains p wave receiver functions reveal the moho depth to be about 41 km beneath the central ordos block and down to 45 km beneath the northern ordos block a slight uplifting to 42 43 km beneath the hetao graben increasing to 47 48 km beneath the yinshan mountains and then decreasing to 44 km beneath the northern yinshan mountains along the profile in the ordos block the crustal vp vs ratio about 1 80 south to the hetao graben differs from that about 1 75 beneath the center ordos block the crustal vp vs ratio is significantly lower about 1 65 1 70 beneath the yinshan mountains the p wave receiver function migration imaging suggests relatively flat discontinuities at 410 and 660 km indicating the lack of a strong thermal anomaly beneath this profile at these depths and a low s wave velocity anomaly in the upper mantle beneath the hetao graben we suggest that the low s wave velocity anomaly may be attributable to heat and that the thermal softening advances the evolution of the hetao graben while the lower crustal ductile flows transfer from the hetao graben to the northern ordos block resulting in crustal thickening

late mesozoic compressional to extensional tectonics in the yiwulushan massif ne china and their bearing on the yinshan yanshan orogenic belt part ii anisotropy of magnetic susceptibility and gravity modeling abstract granitoids play an important role in deciphering both crustal growth and tectonic evolution of earth in the eastern end of the yinshan yanshan belt of north china craton the yiwulushan massif is a typical region that presents the tectonic evolution features of this belt our field work on the host rocks has demonstrated two phases of opposite tectonics compressional and extensional however the deformation is almost invisible in the intrusive rocks to improve the understanding of the tectonic evolution of the yiwulushan massif and the late mesozoic tectonics of east asia a multidisciplinary study has been carried out in this study anisotropy of magnetic susceptibility ams and gravity modeling have been applied on these jurassic plutons lushan jishilazi and guanyindong which intrude into the yiwulushan massif according to laboratory measurements and microscopic observations on thin sections the ams of the yiwulushan massif is characterized by secondary fabrics indicating that the intensive post solidus deformation has reset the primary magmatic magnetic fabrics a relatively gentle nw dipping magnetic foliation has been identified with two distinct groups of magnetic lineations of n34 e and n335 e orientations namely lm1 and lm2 relatively gravity modeling reveals a southward thinning of the massif with a possible feeding zone rooted in the northern part of the massif integrating all results from structural observation geochronological investigation ams measurement and gravity modeling two tectonic phases have been identified in the yiwulushan massif posterior to the jurassic 180 160 ma magmatism in the yinshan yanshan area the early one concerns a late jurassic early cretaceous 141 ma compressional event with a top to the south to southwest sense of shear the second one shows an early cretaceous 126 ma nw se ductile extensional shearing at that time sedimentary basins widened and jurassic plutons started to be deformed under post solidus conditions in fact the nw se trend of the maximum stretching direction is a general feature of east asian continent during late mesozoic

the jiashan syenite in northern hebei a record of lithospheric thinning in the yanshan intracontinental orogenic belt abstract the early cretaceous jiashan syenite is located in a region of late jurassic crustal thickening the jiashan syenite can be divided into three concentrically arranged units the jiangjiawan longtangou and longtannangou units which were intruded sequentially geochemically the jiashan syenite has a high ga al ratio 3 is enriched in silica alkalis fe ree th ga nb zr and hf is depleted in mg ba sr and ti and in transition elements such as cr co ni and v the three units of the jiashan syenite have ce pb ratios ranging from 6 12 to 13 41 and are enriched in light ree lree with a moderate eu negative anomaly the 87sr 86sr initial ratios range from 0 701409 to 0 707405 with a mean of 0 70379 the end t values of 2 27 to 5 58 indicate that the magma was probably derived from enriched mantle the jiashan syenite is a post orogenic intrusion and can be considered to be an a type granite it was emplaced in an environment of lithospheric extension during asthenospheric mantle upwelling this suggests that the regional compressional shortening and crustal thickening tectonic regime in the yanshan orogenic belt during the late jurassic ca 135 ma changed to lithospheric extension and thinning in the early cretaceous

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

sr nd isotopic and geochemical constraints on provenance of late paleozoic to early cretaceous sedimentary rocks in the western hills of beijing north china implications for the uplift of the northern north china craton late paleozoic to mesozoic strata which were deposited in the western hills of beijing north china recorded the contemporary tectonic evolution of the northern part of the north china craton ncc fine grained sandstones and siltstones of these strata were analyzed for their major and trace element concentrations and sr nd isotope compositions their la sc th sc la co th co and cr th ratios are similar to those of sediments derived from felsic source rocks indicating that the original source materials were mostly intermediate to acidic rocks their end 0 values show dramatic shifts implying changes in provenances from the late paleozoic to the early cretaceous the end 0 values of the late paleozoic and the late jurassic to early cretaceous formations are very low whereas the end 0 values of the xingshikou and the xiaoyaopo formations are much higher indicating that a juvenile component has been added into their sources based on the sr nd isotope compositions the late paleozoic and the late jurassic to early cretaceous samples fall in the paleozoic to mesozoic magmatic rocks distributed in the northern part of the ncc however the sr nd isotope compositions of the xingshikou and the xiayaopo formations vary between the xing meng orogenic belt xmob and the north part of the ncc components these changes can be interpreted by the complex uplift and exhumation history of the northern ncc from the late paleozoic to the early cretaceous during the late carboniferous the uplift of the inner mongolia paleo uplift impu which probably commenced at the late carboniferous might supply detrital materials to the late paleozoic strata in the late triassic the uplift of the xmob and impu was responsible for the mixing source of the xingshikou formation after that the northern xmob became the main source of the xiayaopo formation resulting from the uplift of the xmob due to the collision of siberia and north china mongolia plates during the middle to late jurassic finally the uplift of the yftb which occurred from the late jurassic to early cretaceous provided the source materials and blocked the input of the xmob components

a short lived but significant mongol okhotsk collisional orogeny in latest jurassic earliest cretaceous abstract the central asian orogenic belt caob is one of the largest orogenic collages on earth which records a long history of accretionary orogenesis from the late proterozoic to the mesozoic although paleomagnetic studies have unanimously suggested that the major mongol okhotsk ocean in the eastern caob closed mainly during the late jurassic early cretaceous few conclusive and self consistent geological studies in central asia and east asia have confirmed the occurrence of this significant collisional orogeny based mainly on basin evolution in the caob tarim block north china block and qaidam qialian block during the late jurassic early cretaceous the present study proposes that a short lived but significant mongol okhotsk collisional event occurred in the latest jurassic earliest cretaceous the rapid closure of the mongol okhotsk ocean was possibly related to the clockwise rotation of siberia which was driven by the continental collision between the siberia craton and the kolyma omolon microcontinent in northeast russia in the late jurassic owing to the clockwise rotation of siberia and the subsequent closure of the mongol okhotsk ocean a number of areas to both the east and the west of the mongol okhotsk suture underwent uplift and erosion including lake baikal transbaikalia sayan ranges altai shan junggar basin turfan basin tarim basin tian shan mohe basin great xing an ranges hailar tamsag basin erlian basin songliao basin east gobi basin yingen basin bei shan yin shan yan shan belt ordos basin chaoshui yabulai basin and northern qaidam basin forming a giant fold and thrust belt in northern china and mongolia the collision probably caused a prominent gap between late jurassic and early cretaceous magmatic episodes in the eastern caob and north china block after lasting for about 10 million years the main portion of the mongol okhotsk ocean closed forming a northeast trending suture during the early cretaceous a remnant ocean still remained in the easternmost part of the mongol okhotsk ocean and the regional compressional setting in east asia related to the closure of the mongol okhotsk ocean changed to escape tectonics driven by the collision of the lhasa block at the southern margin of asia strike slip faulting triggered gravitational collapse of upper crust and delamination of lower crust and mantle lithosphere that was thickened during the mongol okhotsk collision resulting in the development of a continental scale extensional setting in east asia associated with rift basins metamorphic core complexes and igneous rocks

early jurassic extensional basin formation in the daqing shan segment of the yinshan belt northern north china block inner mongolia abstract structural and stratigraphic studies of the western daqing shan segment of the yinshan belt have recognized an early jurassic extensional episode supported by several lines of evidence first normal faults cut the lowermost jurassic sequence and are overlapped by younger lower jurassic rocks second lower jurassic rocks include growth strata in small scale graben at the base of the jurassic basin third rapid lateral facies changes are mapped from boulder conglomerates along the basin bounding faults to lacustrine and meandering fluvial rocks in the basin center fourth paleodrainage systems provided sediment input from three sides of the basin two transverse and one axial finally there is a strongly asymmetric distribution of coarse proximal and fine distal facies within the basin the early jurassic extensional episode was responsible for formation of an east trending half graben basin in the western daqing shan in which at least 1800 m of syn extensional nonmarine sediments accumulated and are preserved previous studies in the triassic and jurassic of other parts of northwest and north central china have concluded that the early mesozoic was a time of continental amalgamation and contractile deformation the recognition of an early jurassic extensional episode along the northern margin of the north china block is problematic in this context at least superficially we propose two possible explanations for the early jurassic extension transtension associated with strike slip tectonics or gravitational collapse of a pre existing late paleozoic early mesozoic contractile orogenic belt the first possibility transtensional deformation is problematic because specific strike slip faults have not been identified that could control extension in the western daqing shan however several lines of evidence allow the possibility of such a driving mechanism including documented early jurassic transtensional systems in the southwestern north china block several candidate strike slip faults along the china mongolia border region structural discontinuity between the daqing shan and southern mongolia and along strike changes in structural style within the yinshan belt the second possibility orogenic collapse is similarly difficult to establish because of the limited amount of data concerning the regional distribution and orientation of pre jurassic contractile structures and early jurassic extensional structures however documented late paleozoic triassic contractile deformation as well as the close temporal and spatial association and parallelism between early jurassic extensional structures and older contractile structures in the western daqing shan requires consideration of gravitational collapse as a driving mechanism for early jurassic extension in the yinshan belt

rapid change from compression to extension in the north china craton during the early cretaceous evidence from the yunmengshan metamorphic core complex abstract the yunmengshan metamorphic core complex ymmcc is situated in the northern part of the eastern north china craton ncc the main structures in the ymmcc area include the arcuate sihetang shear zone shtsz and the ne striking shuiyu shear zone sysz we present structural and geochronological evidence to show that the shtsz was a top to the ssw thrusting zone formed between 140 and 137 ma the sysz is an extensional top to the se shear zone developed between 131 and 114 ma in association with intense magmatism and the development of the huairou rifted basin in the hanging wall ductile shearing on the sysz was followed by isostatic rebound from 114 ma to the end of the early cretaceous and then was replaced by brittle normal faulting the normal displacement on the sysz and subsequent isostatic rebound led to the formation of the ymmcc the mechanism of formation is consistent with a rolling hinge model of detachment faulting and core complex formation the structural evolution of the yunmengshan area in common with the whole eastern ncc thus records a rapid switch from a nne ssw shortening regime to a nw se extension one in the earliest cretaceous the intense nw se extension of the early cretaceous as recorded by the ymmcc was associated with peak lithospheric thinning in the eastern ncc we attribute the shortening to the final closure of the mongol okhotsk ocean between the siberian craton and the north china south mongol block and the extension to the back arc deformation related to the subduction of the izanagi plate in the pacific ocean we suggest that the yunmengshan area illustrates how back arc compression can be driven by the overriding plate motion while connection of the overriding plate to a larger continent favors subduction related back arc extension

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

discussion on mesozoic extensional structures of the fangshan tectonic dome and their subsequent reworking during collisional accretion of the north china blockjournal vol 163 2006 127 142 yu wang writes on the basis of descriptions of the stratigraphic sequences and structural features in the field and interpretations of published data yan et al 2006 a reach the surprising conclusion that early mesozoic early middle triassic ese oriented extension resulted in formation of the fangshan metamorphic core complex if correct the authors have made an important contribution to understanding of the tectonic evolution of north china however the way in which they cite previously published work to support their model and discrepancies between their findings in the field and those of other workers raise a number of problems that will be discussed below citing of published work yan et al 2006 a cited many references e g lei et al 1994 niu et al 1994 yu zhang 1996 chen 1999 fu 1999 meng et al 2003 in support of their conclusions about early triassic extension and formation of metamorphic core complexes as well as late cretaceous normal faulting in many cases however the cited references do not lend support to their interpretations for example the du shan granite and surrounding archaean and proterozoic metamorphic rocks yu zhang 1996 contain no evidence for extension or development of metamorphic core complex features but instead record ne trending strike slip ductile shearing not top to the se extension the malanyu dome is an old metamorphic sequence chen 1999 and no one has previously interpreted it as an extensional dome associated with se directed extensional shear zhang et al 1991 did not examine any aspect of the geology in the area of the so called yuerya metamorphic core complex furthermore no dome has been identified here by any previous geologists instead it is a c 175 174 ma u pb sensitive high resolution ion microprobe ages luo et al 2001 granitic sheet like

is the jurassic yanshanian intraplate tectonics of north china due to westward indentation of the north china block terra nova 24 333 338 2012 abstract the northern mountains of beijing are the type locality of the mesozoic yanshanian orogen our structural study emphasizes the importance of dextral strike slip for the formation of this intracontinental belt the south and north directed thrusts are positive flower structures rooted in strike slip faults this transpressional tectonics developed from late triassic to late jurassic early cretaceous through three deformation phases coeval with syntectonic sedimentation separated by two transtensional episodes coeval with magmatism the late jurassic early cretaceous tectonic event is also recognized in several places of north china strike slip faulting controls the deformation of the northern border of the north china block in the yanshan yinshan belt simultaneously east directed thrusts and folds develop along n s elongated ranges in helanshan shanxi highlands and taihangshan the jurassic tectonics of the north china block is interpreted in a unitary way as the result of the westward underthrusting of the north china block below the alashan block

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

the yingba shear zone on the sino mongolian border southwestern extension of the zuunbayan fault from mongolia to china and implications for late mesozoic intracontinental extension in eastern asia abstract major strike slip and normal faults are prominent features of eastern asia during the meso cenozoic and they are critical to understanding the intracontinental deformation among others the northeast striking zuunbayan fault in southeastern mongolia is usually documented as a strike slip fault but it may be a normal fault during the late mesozoic however its southwestern extension from mongolia to china is still uncertain the northeast striking yingba shear zone in western inner mongolia china just lies in the place where the zuunbayan fault probably strikes through southwestward the gentle northwest dipping foliation and lineation and top to the northwest shear sense in the granitic mylonite indicate that the yingba shear zone is a northwest dipping low angle normal fault the mylonitization occurred mainly at 400 500 c as a result of the early cretaceous intracontinental extension as bounded by the zircon u pb ages of 145 ma from two deformed pre tectonic pegmatite veins and of 134 ma from one undeformed post tectonic pegmatite vein all of which definitely crosscut the shear zone the yingba normal faulting was coeval with the late mesozoic extensional phase of the zuunbayan fault in southeastern mongolia which is characterized by northwest dip and nw se extension from at least 155 to 126 ma therefore the yingba shear zone is considered as the southwestern segment of the zuunbayan fault in china the late mesozoic intracontinental extension which was possibly triggered by the jurassic thrusting in the south gobi area of mongolia generated the yingba shear zone and the yagan metamorphic core complex on the sino mongolian border

sedimentary record and tectonic implications of mesozoic rifting in southeast mongolia the east gobi basin of mongolia is a poorly described late jurassic early cretaceous extensional province that holds great importance for reconstructions of mesozoic tectonics and paleogeography of eastern asia extension is especially well recorded in the structure and stratigraphy of the unegt and zuunbayan subbasins southwest of saynshand mongolia where outcrop and subsurface relationships permit recognition of prerift synrift and postrift mesozoic stratigraphic megasequences within the synrift megasequence three sequences developed in response to climatic and rift related structural controls on sedimentation where best exposed along the northern margin of the unegt subbasin each of the synrift sequences is bounded by unconformities and generally fines upward from basal alluvial and fluvial conglomerate to fluvial and lacustrine sandstone and mudstone resedimented ashes and basalt flows punctuate the synrift megasequence rifting began in the unegt subbasin prior to 155 ma with coarse alluvial filling of local fault depressions subsidence generally outstripped sediment supply and fresh to saline lacustrine environments expanding southward with time dominated the unegt zuunbayan landscape for much of latest jurassic early cretaceous time episodic faulting and volcanism characterized the basin system for the balance of the early cretaceous a brief period of compressional and or transpressional basin inversion occurred at the end of the early cretaceous prior to deposition of a widespread upper cretaceous overlap sequence the driver s of late jurassic early cretaceous extension remain uncertain because southeast mongolia occupied an intraplate position by the beginning of the cretaceous extension in the east gobi basin was coeval with collapse and extension of early mesozoic contractional orogenic belts along the northern and southern borders of mongolia and probably was a linked phenomenon strike slip faulting associated with collisions on the southern asian and mongol okhotsk margins likely also played a role in late mesozoic deformation of the east gobi region perhaps partitioning the gobi from apparently coeval large magnitude contractional deformation in the yinshan yanshan orogenic belt south of the study area in inner mongolia

permian geodynamic setting of northeast china and adjacent regions closure of the paleo asian ocean and subduction of the paleo pacific plate abstract northeast china and adjacent regions are located in the central east asian continent and consist tectonically of both the paleo asian and paleo pacific orogens between the siberian platform and sino korean north china block this paper discusses some hotly debated issues concerning the permian geodynamic setting of these regions based on a comprehensive analysis of available geological geochemical paleobiogeographical and paleomagnetic data spatial and temporal distribution of ophiolites and associated continental marginal sequences permian sedimentary sequences spatial distribution and geochemistry of permian magmatic rocks and the evolution of paleobiogeographical realms imply 1 that the permian marine basins in northeast china and adjacent regions include remnants of the paleo asian ocean in southeastern inner mongolia and central jilin province and active continental margins of the paleo pacific ocean 2 that the suture between the siberian and sino korean paleoplates was finally emplaced in the permian and is located in areas from suolunshan solonker eastwards through regions north to the xar moron river in southeastern inner mongolia and then central jilin province to the yanji area and 3 that the permian crustal evolution of northeast china and adjacent regions as well as parts of the siberian paleoplate was influenced by subduction of the paleo pacific oceanic plate finally the permian tectonic framework and paleogeography of northeast china and adjacent regions in central east asia are discussed briefly and early and late permian palinspastic reconstruction maps are provided

first report of sauropod tracks from the upper jurassic tianchihe formation of guxian county shanxi province china abstract this paper presents the first report of sauropod tracks from the upper jurassic of shanxi province china dinosaur tracks appear concentrated in five trackways in different stratigraphic levels of the late jurassic tianchihe formation tracks are dominantly small and medium size sauropod tracks and are tentatively assigned to brontopodus based on preserved track morphology trackway pattern and statistical analysis the tianchihe formation in which the tracks appear shows a gradual change from meandering fluvial to sandy braided fluvial depositional systems developed in a seasonally arid environment comparisons of the evaluated speed of bipedal to quadruped trackways indicate that the slower walk more easily produces pes dominated overprints trackways in the guxian tracksite appear following different orientations suggesting that these trackways were produced by different sauropods at different times an unusual trackway following a curved pattern has been identified in the site and could represent a special locomotion character or a social behavior the presence of eolian deposits in central shanxi province could have acted as a paleogeographic and paleoenvironmental barrier for the dispersion of the yanliao biota that survived in northern hebei western liaoning and northestern shanxi province to the ordos basin during the late jurassic

significant zn pb cu remobilization of a syngenetic stratabound deposit during regional metamorphism a case study in the giant dongshengmiao deposit northern china abstract the giant dongshengmiao zn pb cu deposit is located in the langshan district northern china the ores are hosted within a proterozoic rift sequence which underwent lower greenschist facies metamorphism and shear deformation during development of early cretaceous intraplate orogenic belt northwest dipping thrust faults which share similar orientations and dip angles with the orebodies are well developed in the mining area syngenetic stratabound sulfides were formed during the proterozoic rifting event but syngenetic ore textures have seldom been preserved except for some pretectonic fine grained pyrite petrological observation 39 ar 40 ar geochronology combined with previous isotopic and fluid inclusion studies indicates that significant zn pb cu remobilization took place as a result of thrust faulting associated with metamorphic devolatilization of ore hosting rocks at ca 136 ma coeval with the intraplate orogeny and regional crustal shortening sulfides were redistributed in shear structures or along grain boundaries of ore hosting carbonates and fe rich carbonates were ideal sites for zn pb cu precipitation

joint development and tectonic stress field evolution in the southeastern mesozoic ordos basin west part of north china abstract major joint sets trending e w j1 ene wsw j2 ne sw j3 n s j4 nnw sse j5 nne ssw j6 nw se j7 and wnw ese j8 respectively are recognized in mesozoic strata within the southeast of ordos basin among them the j1 j2 and j3 joint sets are systematic joints while the other five joint sets j4 j5 j6 j7 j8 are nonsystematic joints there are three groups of orthogonal joint systems i e j1 and j4 sets j2 and j5 sets and j6 and j8 sets and two groups of conjugate shear fractures ene wsw and nne ssw ene wsw and ese wnw in the study area joint spacing analysis indicates that 1 layer thickness has an effect on the joint spacing but the correlation of joint spacing and layer thickness is low 2 joint density of systematic joints is greater than nonsystematic joints and the joint density of a thin layer is also greater than that of a thick layer and 3 the joints of mesozoic strata in the basin are the result of tectonic events affected by multiple stress fields all these joints in the mesozoic strata are formed in the two main tectonic events since late mesozoic times one is the westward subduction of the pacific plate beneath the eurasia plate which formed the approximately e w trending compressive stress field in the china continent the trends of the j1 joint set e w and the bisector of conjugate shear fractures composed of ene wsw and ese wnw fractures are all parallel to the trend of maximum compressive stress e w the other stress field is related to the collision of the indian and eurasian plates which formed the ne sw trending compressive stress field in the china continent the trends of the j3 joint set and bisector of conjugate shear fractures composed of ene wsw and nne ssw fractures are all parallel to the trend of maximum compressive stress ne sw finally we conclude that the j1 and j4 sets are formed in the e w trending compressive stress field and the j2 j3 j5 j6 j7 and j8 sets are formed in the ne sw trending stress field

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

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

two phases of mesozoic north south extension in the eastern altyn tagh range northern tibetan plateau 1 the 300 km long east striking lapeiquan fault lies in the eastern altyn tagh range along the northern margin of the tibetan plateau and was interpreted as a north dipping thrust in early studies however our mapping shows that the fault is a south dipping normal fault juxtaposing archean proterozoic gneisses beneath an early paleozoic volcanic and sedimentary sequence its dip angle varies from 30 to 60 the central fault segment is expressed as a 30 50 m thick ductile shear zone with well developed mylonitic fabrics and stretching mineral lineations where the eastern and western segments are characterized by cataclastic deformation kinematic indicators such as asymmetric boudinage asymmetric folds and minor brittle and ductile faults within the fault zone consistently indicate a top south normal slip sense of shear the age of the lapeiquan fault is constrained by two types of information first a sequence of early middle jurassic sediments is locally present in the hanging wall of the lapeiquan fault the clasts of the jurassic strata particularly the stromatolite bearing cherty limestone and purple quartzite can be correlated uniquely with those in the footwall of the fault we interpret that the early middle jurassic strata were deposited in an extensional basin related to motion along the lapeiquan fault second 40ar 39ar thermochronologic analyses indicate two prominent cooling events in the lapeiquan footwall the older event occurred in the latest triassic earliest jurassic between 220 and 187 ma while the younger event occurred in the latest early cretaceous at 100 ma because the 220 187 ma cooling ages are widespread in the lapeiquan footwall we suggest it to represent the main stage of faulting we interpreted the younger phase of fault motion at 100 ma to have been related to fault reactivation the deformation was aided by motion along the south dipping qiashikan normal fault that merges with the eastern lapeiqaun fault from the regional tectonic setting it appears that mesozoic extension in northern tibet to have occurred in a back arc setting during northward subduction of the tethyan oceanic plate the findings of mesozoic extensional structures in northern tibet suggest that compressive stress induced by collision of the qiangtang and lhasa terranes with asia was not transmitted beyond northern tibet this in turn implies that the popularly inferred contractional setting for mesozoic evolution of the tian shan north of tibet needs a reevaluation based on a combination of both structural and sedimentological observations

revisiting of the yanshanian basins in western and northern beijing north china abstract we present new laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb ages and provenance data for the yanshanian basins in western and northern beijing north china with the aims of demonstrating the relationship between basin evolution and yanshanian tectonism and constraining the late jurassic early cretaceous tectonic evolution of the region the inherited yanshanian basin in western beijing has a late jurassic early cretaceous tectonic history similar to that of typical yanshanian basins in the yanshan fold thrust belt yftb and it became inactive at 138 ma the qianjiadian basin qjb in northern beijing is only infilled by the sediments of the tuchengzi formation our new zircon u pb ages 160 156 ma for the pyroclastic and volcanic rocks of the tuchengzi formation suggest that formation of the qjb commenced at 160 ma consistent with the main episode of yanshanian tectonism the qjb developed in the footwall of the pingquan gubeikou thrust fault pgf and records the syn tectonic unroofing and erosion of the hanging wall of that fault it was later reformed by the post depositional qianjiadian thrust fault qjf along the western margin the formation and development of the qjb in northern beijing and the inherited yanshanian basin in western beijing were related to the yanshanian tectonism especially at ca 160 ma when the intense deformation and large scale magmatism occurred the tectonic transition from n s to nw se shortening is attributed to the northwest ward subduction of the paleo pacific plate and is constrained to 156 135 ma in the yftb and eastern china

post cratonization deformation processes and tectonic evolution of the north china craton abstract the timing of events during the tectonic evolution of the north china craton ncc and the east china region is debated extension compression transpression and shearing occurred throughout the ncc since 320 ma these main structural stages and the temporal evolution of the structural framework and kinematics are summarized we present here data from multiple structural and magmatic stages related to temporally varying kinematics and deformation mechanisms during the evolution of the post cratonization of the ncc the timing of each stage is constrained using isotopic dating along with the timing of magmatic intrusion dyke intrusion and basin formation associated with tectonic transformation of the ncc age data indicate distinct structural and magmatic stages at 1600 1500 1300 1100 445 315 270 200 170 155 130 110 75 65 and 25 20 ma relating to basin formation and continental uplift or collapse these stages define the tectonic evolution and structural transformation of the ncc and associated de rooting reactivation reworking and orogenic growth the tectonic setting and movement direction of adjacent plates changed multiple times during the various stages the stages are as follows separation of the ncc from the gondwana supercontinent and northwards drift formation of the central asian orogenic belt caob and northwards subduction of the yangtze plate resulting in closure of the qinling ocean the rapid initial formation of the western pacific plate and subsequent subduction and final closure of the mongol okhotsk ocean combined with closure of the bangong nujiang suture zone and southwards movement of the siberian continent as well as thinning of the north china cratonic lithosphere moreover temporal and spatial changes in deformation magmatism and basin formation as well as kinematic and mechanical transformations occurred in response to the changing tectonic setting and movement direction of surrounding plates these various factors resulted in a complex structural evolution of the ncc since 1 8 ga

the 40ar 39ar dating of the early jehol biota from fengning hebei province northern china the bird fossil bearing deposits at the jiecaigou section correlative to the dabeigou formation in fengning hebei province northern china is well known for yielding a fossil assemblage representing the earliest evolutionary stage of the jehol biota the precise age of the fossil bearing deposits however is unknown the ar 40 ar 39 age spectrum obtained on bulk k feldspars from the tuff layer about 2 m below the bird fossil bearing layer gave a plateau age of 129 0 1 3 ma 2 sigma full external error and an isochron age of 132 3 4 5 ma 2 sigma full external error seventeen total fusion ar 40 ar 39 ages on k feldspars from the interbedded tuff about 6 m below the fossil bearing layer resulted in a weighted mean of 130 7 1 4 ma 2 sigma full external error these dates suggest an age of similar to 131 ma for the early jehol biota and combined with previous dating indicate that this biota lasted at least from 131 ma to 120 ma late hauterivian to aptian these dates also represent the earliest absolute age for known enantiornithine birds in the world

regional geologic setting and metallogenesis of central inner mongolia china guides for exploration of mesothermal gold deposits abstract the central inner mongolia district forms one of the most important metallogenic provinces in china because the district has been influenced by repeated distinct tectonomagmatic activity the genetic relationships and spatial temporal evolution of ancient tectonism and associated geologic structures and metallogeny are discussed in this paper an integrated genetic model for gold metallogeny is proposed during the late archean to paleozoic repeated north southward accretional tectonics between the paleo mongolia oceanic plate and the north china paleoplate led to the formation of not only the e w trending deep crustal faults but also a series of sedimentary volcanic and metamorphic events numerous stratiform fe cu au pb zn and ree ores formed in association with sedimentation and volcanism within the platform environments at this time during the late paleozoic to early mesozoic the central inner mongolia district was largely influenced by northwestward subduction of the circum pacific plate beneath the eurasia plate a series of ne sw trending faults together with s type granitoid intrusions formed as a result of this subduction mesothermal type gold deposits e g the saiyingwusu laoyanghao shibaqin wulashan and donghuofang deposits formed during the permian to jurassic 158 5 to 275 4 ma preferentially at or near the intersections between ne sw trending and e w trending fault systems at these intersections the areas of not only late paleozoic to early mesozoic granitoids but also late archean to early proterozoic metamorphic rocks especially the gold rich seertengshan wulashan and bayan obo group rocks may be promising exploration targets for mesothermal gold deposits

new u pb and re os age data and the geodynamic setting of the xiaojiayingzi mo fe deposit western liaoning province northeastern china abstract the xiaojiayingzi deposit located in the western liaoning province in northeastern china is a skarn type mo fe deposit with an average mo grade of 0 23 wt the deposit is temporally and spatially associated with fine grained diorite mo fe mineralization is present mainly as veins lenses and layers that are hosted by skarn new shrimp u pb zircon and re os molybdenite age determinations yielded a crystallization age for the diorite of 169 9 1 4 ma and a molybdenite re os isochron age of 165 5 4 6 ma the u pb and re os ages are identical within error the mineralization is therefore considered to be genetically related to diorite emplacement in the middle jurassic a high re content of 21 75 to 163 0 ppm with an average of 64 31 ppm in the molybdenite together with 34 s values between 3 3 and 8 0 of sulfides in the ores indicates that the metal source was a mixed crust mantle system from these geochronological data and previously presented regional geological relationships we propose that diorite emplacement and mo fe mineralization in the xiaojiayingzi mine resulted from an early stage of the subduction of the paleo pacific plate beneath the eurasian block