lithospheric processes and products in the southern canadian cordillera a lithoprobe perspective analyses of lithoprobe and other data from southwestern canada provide new insights on how this portion of the cordillera formed during plate convergence along the western margin of north america crustal rocks are detached from their mantle lithosphere which must have been consumed during subduction detachment occurred at or near the base of the crust beneath the intermontane and or omineca belts probably along the tips of tectonic wedges while the rocks were still outboard of the relatively cool mechanically rigid north american craton during the late cretaceous and early tertiary rotation of detached rocks caught between the north american craton and the oceanic plates accounts for some apparently conflicting results between paleomagnetic data that indicate large northward translation of rocks in the western cordillera and regional geological features that appear to preclude comparable amounts of translation of rocks in the eastern cordillera during the same time interval transpression assoc

late pleistocene and holocene sedimentary facies on the ebro continental shelf abstract late pleistocene holocene history of the ebro continental shelf of northeastern spain is recorded in two main sedimentary units 1 a lower transgressive unit that covers the shelf and is exposed on the outer shelf south of 40 40 n and 2 an upper progradational prodeltaic unit that borders the ebro delta and extends southward along the inner shelf the lower transgressive unit includes a large linear shoal found at a water depth of 90 m and hardground mounds at water depths of 70 80 m some patches of earlier pleistocene prodelta mud remain also exposed or covered by a thin veneer of transgressive sand on the northern outer shelf this relict sand sheet is 2 3 m thick and contains 9000 12 500 yr old oyster and other shells at water depths of 78 88 m the upper prodelta unit covers most of the inner shelf from water depths of 20 80 m and extends from the present ebro river delta to an area to the southwest where the unit progressively thins and narrows interpretation of high resolution seismic reflection data shows the following facies occurring progressively offshore 1 a thick stratified facies with thin progradational foresets beds 2 a faintly laminated facies with sparse reflectors of low continuity and 3 a thin transparent bottomset facies underlain by a prominent flat lying reflector deposition in the northern half of the prodelta began as soon as the shoreline transgressed over the mid shelf but progradation of the southern half did not begin until about 1000 3000 yrs after the transgression a classic deltaic progradational sequence is shown in the ebro prodelta mud by 1 gradation of seismic facies away from the delta 2 coarsening upward sequences near the delta and fining upward sequences in the distal mud belt deposits and 3 thin storm sand layers and shell lags in the nearshore stratified facies the boundaries of the prodeltaic unit are controlled by increased current speeds on the outer shelf where the shelf narrows and by development of the shoreface sand body resulting from shoaling waves on the inner shelf

an exotic mesoarchean microcontinent the coorg block southern india abstract sandwiched between the dharwar craton in the north and the neoarchean proterozoic crustal blocks to the south the coorg block in southern india is composed dominantly of a suite of arc magmatic rocks including charnockites ttg tonalite trondhjemite granodiorite related granitoid suite and felsic volcanic tuffs together with minor accreted oceanic remnants along the periphery of the block coeval mafic and felsic magmatism with magma mixing and mingling in an arc setting is well represented in the block here we present the petrology geochemistry zircon u pb geochronology and lu hf isotopes of all the major lithologies from this block computation of metamorphic p t conditions from mineral chemical data shows consistent granulite facies p t conditions of 820 870 c and up to 6 kbar our geochemical data from major trace and ree on representative samples of the dominant rock types from the coorg block corroborate an arc related signature with magma generation in a convergent margin setting the zircon data yield weighted mean 207pb 206pb ages of 3153 4 9 to 3184 0 5 5 ma for syenogranites 3170 3 6 8 ma for biotite granite 3275 5 1 ma for trondhjemite 3133 12 to 3163 8 6 9 ma for charnockites 3156 10 to 3158 3 8 2 for mafic enclaves 3161 16 ma for diorite and 3173 16 ma for felsic volcanic tuff an upper intercept age of 3363 59 ma and a lower intercept age of 2896 130 ma on zircons from a charnockite as well as an evaluation of the th u values of the zircon domains against respective 207pb 206pb ages suggest that the mesoarchean magma emplacement which probably ranged from 3 3 to 3 1 ga was immediately followed by metamorphism at ca 3 0 to 2 9 ga the ages of magmatic zircons from the charnockites and their mafic granulite enclaves as well as those from the volcanic tuff and biotite granite are all remarkably consistent and concordant marking ca 3 1 ga as the peak of subduction related crust building in this block within the tectonic milieu of an active convergent margin the majority of zircons from the coorg rocks show hf isotope features typical of crystallization from magmas derived from juvenile sources their hf crustal model ages suggest that the crust building might have also involved partial recycling of basement rocks as old as ca 3 8 ga the crustal blocks in the southern granulite terrane in india preserve strong imprints of major tectonothermal events at 2 5 ga 2 0 ga 0 8 ga and 0 55 ga associated with various subduction accretion collision or rifting events however the coorg block is exceptional with our data suggesting that none of the above events affected this block importantly there is also no record in the coorg block for the 2 5 ga pervasive regional metamorphism that affected all the other blocks in this region the geochronological data raise the intriguing possibility that this block is an exotic entity within the dominantly neoarchean collage in the northern domain of the southern granulite terrane of india the mesoarchean arc related rocks in the coorg block suggest that the magma factories and their tectonic architecture in the early earth were not markedly different from those associated with the modern style plate tectonics

geological and isotopic geochemical constraints on the evolution of the fuping complex north china craton abstract the neoarchean to paleoproterozoic fuping complex together with the adjacent hengshan and wutaishan complexes form the middle part of the central zone that separates the north china craton into the eastern and western archean continental blocks the fuping complex comprises three major lithological assemblages the 2 50 ga fuping trondhjemite tonalite granodiorite ttg gneisses the wanzi paragneisses and the 2 08 and 2 02 ga nanying granitic gneisses the ttg gneisses contain abundant enclaves of highly metamorphosed supracrustal rocks including 2 70 ga mafic granulites and amphibolites with endt of 3 29 to 3 96 and tdm of 2 72 2 82 ga and are characterized by tdm of 2 76 3 04 ga and a linear correlation between endt 1 64 to 0 96 and 1 nd indicative of mixing of melts derived from the 2 70 ga metabasic rocks and 3 0 ga crustal materials mafic dikes along the chengnanzhuang shear zone were most likely emplaced at 2 31 ga and have endt of 2 24 to 4 78 and tdm of 2 34 2 59 ga the nanying granitic gneisses with endt of 4 04 to 5 24 were most likely related to partial melting of the 2 70 ga supracrustal rocks and or the 2 50 ga ttg gneisses these geological relationships and isotopic data suggest that the fuping complex probably formed from the following five major tectonomagmatic events 1 mafic magmatism and early crustal growth at 2 7 ga with the possible existence of older 3 0 ga crust s 2 collision related crustal thickening underplating of basaltic magma high grade metamorphism crustal anatexis and ttg magmatism at 2 5 ga 3 extensional deformation and emplacement of the mafic dikes and the nanying granitic plutons along the chengnanzhuang shear zone 2 5 to 2 0 ga 4 s type granitic magmatism and associated amphibolite facies metamorphism 2 0 to 1 80 ga and 5 emplacement of granitic pegmatite dikes at 1 80 ga

late paleoproterozoic 1900 1800ma nappe stacking and polyphase deformation in the hengshan wutaishan area implications for the understanding of the trans north china belt north china craton abstract the hengshan wutaishan area forms part of the trans north china belt developed in response to the final amalgamation of the north china craton the hengshan wutaishan domain and the adjacent fuping massif constitute the largest and the most representative rock exposure of the belt a structural study allows us to redefine the lithological and tectonic units that compose the architecture of the hengshan wutaishan domain and to propose that the trans north china belt was built up through a polyphase tectonic evolution within the period 1900 1800 ma the first event d1 corresponds to the emplacement of lower and upper nappes herein called the orthogneiss and volcanites unit ovu and the low grade mafic unit lgmu respectively the ovu mainly consists of rocks formed in an arc system and metamorphosed under amphibolite facies conditions whereas the lgmu represents oceanic crust rocks with an arc component that underwent greenschist facies metamorphism the syn metamorphic d1 deformation is characterized by a nw se stretching and mineral lineation with a top to the se sense of shear that corresponds to the sense of nappe motion u th pb epm chemical dating on monazite from three metapelites of the ovu gives isochron ages of 1884 11 ma 1886 5 ma and 1887 4 ma interpreted as the age of the prograde amphibolite facies metamorphism coeval with nappe stacking during the d1 event the d2 event corresponds to a widespread crustal melting of the ovu and underlying basement rocks in hengshan related to the exhumation of deep structures about 20 30 ma after nappe emplacement the migmatite contains blocks of retrograded eclogite or hp granulitic restites and is characterized by the development of a pervasive foliation and lineation a late d2 event represents the folding stage of the migmatitic foliation during the completion of a dome the orthogneiss and volcanics unit and the low grade mafic unit are unconformably covered by weakly metamorphosed to unmetamorphosed sediments belonging to the hutuo supergroup these rocks were deformed by a ductile d3 event characterized by a nw se trending stretching lineation south verging folds associated with an axial planar slaty cleavage and an e w crenulation lineation lastly a left lateral wrenching along the zhujiafang shear zone separates the northern and southern parts of hengshan our structural study shows that there is no significant difference between the southern part of hengshan and the lower part of wutaishan both areas belong to ovu and show a structural continuity we suggest that this polyphase deformation developed in response to a north westward subduction of an old ocean named the luliang ocean beneath the western block followed by collision with a micro continent named the fuping block at 1890 1880 ma

anomalous paleomagnetism of the crowsnest formation of the rocky mountains the volcanic crowsnest formation of albian age late early cretaceous from the rocky mountain fold and thrust belt of alberta has a stable remanent magnetization with a mean direction of 349 59 95 5 and paleopole at 78 n 108 e dm 7 dp 5 the inclination is lower than and the declination clockwise of the expected mid cretaceous paleogeomagnetic field for cratonic north america taken at face value the result indicates that the crowsnest formation and the thrust sheet in which it occurs have been transported from the south relative to cratonic north america by 17 6 about 1800 km and rotated 24 10 clockwise it is also possible that flattening of inclination is caused by magnetic anistropy but tests show this to be unlikely a third possibility is that the magnetization is secondary and of latest cretaceous age but there are good reasons for believing this is not so lastly it is possible that the unit could have been formed close to its present position relative to the craton

the neoarchean paleoproterozoic volcanic sedimentary rocks in the zanhuang complex north china craton petrogenesis and implications for tectonic evolution abstract the zanhuang complex is located in central section of the trans north china orogen tnco in the north china craton ncc with complicated tectonic history the formation timing neoarchean or paleoproterozoic of the guandu group or central zanhuang domain czd is still under debate while this question is critical for understanding the tectonic evolution of the zanhuang complex and the tnco the mafic rocks in the guandu group or czd can be subdivided into three different types by petrological geochronological structural and petrogenetic differences type 1 consists of pillow epidosites and amphibolites located at the west part of the guandu group type 2 dominated by amphibolites and interbedding with various sedimentary rocks located at the east part and type 3 consists of mafic dikes beyond the scope of this paper type 1 mafic rock yielded zircon u pb age of 2501 12 ma which constrains it formed at neoarchean with older nd tdm ages 2 8 3 0 ga interbedded sedimentary rocks with younger than 2 1 ga detrital zircon ages and the much younger nd tdm model ages 2 2 2 3 ga of the amphibolites from type 2 together suggest that the type 2 mafic rocks and associated sedimentary rocks may have formed at paleoproterozoic thus we propose that the so called guandu group is not a single and unitary tectonic lithological unit but consists of at least two different volcanic sedimentary successions formed at different times and pieced together by later tectonic event s a new two period tectonic events model is proposed here before 2 5 ga the western margin of the eastern block deposited a series of volcanic sedimentary rocks type 1 at 2 5 ga the fuping arc including the western zanhuang domain amalgamated with the eastern block by arc continent collision after a quiescent period it underwent 2 1 ga extension and rifting later the rift evolved into a small ocean basin with the deposition of volcanic sedimentary sequences type 2 then closed through west dipping subduction and collision at 1 9 1 85 ga resulting in the final amalgamation of the ncc and the widespread deformation and metamorphism in the zanhuang complex as well as the whole tnco

reply to comment by wang et al on paleoproterozoic arc continent collision in the north china craton evidence from the zanhuang complex by li et al 2016 precambrian research 286 281 305

the ebro continental shelf quaternary seismic stratigraphy and growth patterns abstract single channel seismic reflection profiles on the ebro shelf and upper slope between cap salou and the columbretes islands have been interpreted to outline the quarternary shelf evolution in this deltaic area three types of unconformity surfaces can be differentiated in the seismic records type 1 and 2 unconformities and toplap surfaces these surfaces are the stratigraphic expression of the difference between rate of eustatic sea level fall and subsidence on the outer shelf a type 1 unconformity forms if the rate of eustatic sea level fall is the more rapid a type 2 unconformity forms if subsidence is faster and toplap forms if subsidence and eustatic sea level fall are equal thirteen stratigraphic units can be differentiated on the basis of unconformities based on their relative location on the shelf these units are subdivided into inner and outer units the inner units occur on the inner and middle shelf and are characterized by an underlying transgressive surface while the outer units extend onto the middle to outer shelf and upper slope and show unconformities at their bases the inner units are interpreted to be stacked transgressive and highstand systems tracts bounded by a maximum flooding surface the outer units correspond to shelf deltas and shelf margin deltas that prograded southward and seaward over an unconformity in relatively stable water depths when sea level fall was compensated for by subsidence the progradation of these units ends with an episode of generalized erosion of the shelf and canyon cutting across the new shelf edge the growth pattern of the northern ebro shelf is characterized by important hiatuses condensed stratigraphic sections and units which are older than those on the southern shelf the depositional processes were mainly controlled by eustatic sea level oscillations subsidence and changes in sediment supply the subsidence during the late pleistocene was sufficient to compensate for the sea level falls and allow the development of shelf deltas and shelf margin deltas on the middle and outer shelf during low sea level stands

eustatic sea level changes interpreted from seismic stratigraphy a critique of the methodology with particular reference to the north sea jurassic record seismic stratigraphic methods for interpreting eustatic sea level change are based on generalized stratigraphic models and chronostratigraphic interpretations that have not been substantiated by publication of the necessary basic supportive data chronostratigraphic correlations of sea level change curves between basins are based partly on circular reasoning onlap and offlap seismic models may not indicate sea level change but flexural subsidence facies shifts or changes in sea level in the opposite direction to that proposed resolution of some of these problems may be achieved by publication of basic data now in confidential industry files the widely acclaimed vail curves should not be used as templates for basin correlation until such data have been provided and such use should be supported by appropriate conventional lithostratigraphic and biostratigraphic documentation from each new basin where such data have been made available as with the north sea jurassic serious questions of interpretation are raised

paleoproterozoic arc continent collision in the north china craton evidence from the zanhuang complex abstract the trans north china orogen tnco marks the major ca 300 km wide paleoproterozoic collisional suture between the eastern and western blocks of the north china craton ncc which also incorporates several microblocks or complexes here we investigate the zanhuang complex along the eastern margin of tnco we present petrological geochemical zircon u pb and lu hf data on a suite of quartz mica schist metavolcanics and diorite from the central zanhuang domain czd as well as granitoids and amphibolite that constitute the basement rocks of the western zanhuang domian wzd and eastern zanhuang domain ezd our study represents a cross section across two continental margins and covers the paleo ocean tract in between the metavolcanics show calc alkaline to tholeiitic affinity and negative correlations of la sm n vs p nd ti ti ce ce and positive with nb nb the granitoids fall within the vag field the iab and morb features of the volcanic suite are consistent with magma derivation in arc to back arc environment from an enrichment source the magmatic suite also displays lree enrichment positive rb k la pb nd anomalies and negative ta nb ce ti anomalies la cipms u pb geochronology of detrital zircon grains shows two age populations in the quartz mica schist with 207pb 206pb mean ages of 2499 14 ma and 2252 22 2216 39 ma and the timing of deposition is estimated as ca 2 3 2 2 ga zircons from the granodioritic gneiss yield 207pb 206pb mean age of 2508 14 ma representing neoarchean continental basement the metavolcanics and two diorite samples yield ages of 2302 30 ma 2089 63 ma marking the timing of an active arc the metamorphic zircons from these rocks show an age of 1882 15 ma the zircon lu hf data yield both positive and negative ehf t values suggesting depleted mantle source mixed with crustal components their crustal residence ages t dm c range from 3875 to 2224 ma and depleted model ages t dm range from 3415 to 2092 ma suggesting mixed juvenile and reworked crustal components and possible vestiges of mesoarchean basement we propose that the zanhuang complex is one of the paleoproterozoic arcs within the tnco which was accreted to the neoarchean continent along the eastern block of the ncc during the suturing along the tnco the tectonics associated with crustal growth and recycling in the tnco and the arc continent collision broadly coincided with the building of the columbia supercontinent

shrimp u pb zircon geochronology of the fuping complex implications for formation and assembly of the north china craton abstract the fuping complex located within the central zone of the north china craton is composed of amphibolite to granulite facies orthogneisses interleaved with minor supracrustal rocks at similar metamorphic grade the oldest components recognised are hornblende gneiss enclaves within the predominant biotite orthogneiss which have a shrimp u pb zircon age of 2708 8 ma we consider these enclaves to represent fragments of 2 7 ga continental materials incorporated in the biotite gneiss the biotite gneiss has a shrimp u pb zircon age of 2513 12 ma interpreted to be time of magmatic crystallisation of the igneous precursor based on the igneous characteristics of the zircons this indicates a major magmatic episode at 2 52 ga in the fuping complex identical to the age of felsic volcanism within the low grade wutai complex which crops out immediately to the west a gneissic granite that intrudes the biotite gneisses has a poorly defined 207pb 206pb age of 2045 64 ma this is within error of the age of 2097 46 ma obtained from a fine grained gneiss interlayered with amphibolite of the wanzi supracrustal suite wss interpreted to be volcanic in origin zircons from both these samples have strong oscillatory zoning and provide the first indication of a palaeoproterozoic magmatic event in the area again similar in age to magmatic events recently recognised in the adjacent wutai complex these data indicate a comparable history for the fuping and wutai complexes and support geochemical evidence that they had a common origin and formed part of a late archaean arc affected by later palaeoproterozoic re activation low uranium zircons without oscillatory zoning separated from a sample of biotite gneiss yield data clustered at 1817 26 ma which is interpreted to reflect a period of new zircon growth during a major metamorphic event these data support the recently proposed tectonic model that amalgamation of the north china craton occurred due to collision of the eastern and western blocks along the central zone at 1 8 ga ago

the gulf of valencia continental shelf extensional tectonics in neogene and quaternary sediments abstract seismic reflection profiles obtained with mud penetrator 3 5 khz sparker 3000 j uniboom 300 j and side scan sonar 100 khz enabled us to map recent morphostructural features extensional structures in neogene and quaternary sediments of the gulf of valencia shelf these structures are dominated by a group of normal faults trending subparallel to the coast the faults produced a series of steps in the neogene quaternary depositional series these sedimentary formations are very thick throughout the area decreasing southward in the direction of the betic system this distensive regime is still active today producing structures which affect the morphology of the shelf

petrogenesis and tectonic implications of the 2 1 2 0 ga granitoids in fuping complex north china craton constraints from petrology geochemistry and zircon u pb hf isotopes abstract mid paleoproterozoic 2 2 2 0 ga magmatism in the trans north china orogen tnco is of great significance for the paleoproterozoic geological evolution of the entire north china craton ncc in this paper we present geochemical shrimp zircon u pb and hf isotopic data on the 2 1 2 0 ga granitoids in the fuping complex of the tnco these include the nanying granitic gneiss which yielded ages of 2075 13 ma 2079 9 ma and 2073 10 ma the gangnan granitic gneiss dated at 2081 8 ma 2082 14 ma and 2063 7 ma the baiyangling granite with ages of 2077 6 ma 2070 19 ma and 2069 12 ma and the shangzhuang granite which yielded ages of 2072 12 ma and 2070 12 ma the 2 1 2 0 ga granitic rocks in fuping complex are enriched in sio2 k2o na2o rare earth elements rees except eu high field strength elements like zr nb ga and y and depleted in cao al2o3 and sr their ga al ratios and absolute zr nb y ce contents are high and their average zr saturation temperatures are as high as 890 c all of which are consistent with the features of a type granite the ehf t values of zircon in all samples are much lower than that of the depleted mantle at the same stage while hf model tdm1 tdmc ages have ranges of 2 3 2 7 ga and 2 4 2 9 ga respectively which are much older than the age of the granitoids these zircon hf model ages are similar to those of the neoarchean ttg tonalite trondhjemite granodiorite gneisses in the fuping complex therefore based on a combination of petrology geochemistry and isotopic characteristics we infer that these four 2 1 2 0 ga granitic plutons in the fuping complex are partial melts of the neoarchean ttg gneiss generated in an extensional environment based on extensive data the 2 1 2 0 ga a type granites and the mafic dikes in the fuping complex represent a bimodal magma association considering the sedimentary rocks of the gantaohe group deposited in the same period we deduce that the 2 1 2 0 ga a type granite in the tnco fuping complex was emplaced in an intra continental rift setting in the ncc this evidence indicates that the north china craton was initially stabilized at the end of the neoarchean

magmatic affinity of modern and ancient subalkaline volcanic rocks determined from trace element discriminant diagrams when dealing with ancient subalkaline volcanic rocks the alkali total iron magnesium afm diagram is of limited use in assigning a tholeiitic versus calc alkaline affinity because these eleme

structural pattern of the wutai complex and its constraints on the tectonic framework of the trans north china orogen abstract wutai complex is a key to test controversial models for the tectonic evolution of the trans north china orogen tnco along which the eastern and western blocks amalgamated to form the north china craton three stages of deformation d 1 to d 3 were identified in the wutai complex d 1 is characterized by ne sw trending foliations s 1 and nw se orientated lineations l 1 indicating an initial nw se directed compression associated with d 1 was prograde metamorphism m 1 d 2 progressively overprinted d 1 and generated z shaped folds and nee sww trending ductile shear zones d 2 resulted in a fan shaped structural pattern of the complex with top to the nw thrusting in the northwestern part and opposite top to the se thrusting in the southeastern part during d 2 the crust was doubled through thickening leading to peak metamorphism m 2 d 3 developed during post collision exhumation and deformed the early fabrics to be open folds resulting in near isothermal decompression m 3 and late cooling metamorphism m 4 the overall structure of the wutai complex is characterized by a fan shaped pattern with structural divergence structural features of the wutai complex combined with those of the adjacent hengshan and fuping complexes indicate that the tnco is characterized by a fan shaped orogenic wedge with opposite senses of thrust this orogenic wedge could have resulted from an eastward subduction and collision between the western and eastern blocks to finally form the tnco at 1 85 ga

neoarchean paleoproterozoic crustal growth and tectonic evolution of the trans north china orogen north china craton evidence from granite greenstone successions in the dengfeng complex granite greenstone successions and associated tonalite trondhjemite granodiorite ttg suites constitute dominant components of precambrian cratons here we present petrology geochemistry zircon u pb geochronology and lu hf isotopes on monzonite granodiorite granite and amphibolite from the dengfeng complex in the southern part of the north china craton ncc zircon u pb data yield weighted mean 207pb 206pb ages of 2498 6 ma for monzonite 2481 16 ma for granodiorite and 2475 21 ma for granite lu hf isotope systematics show ehf t values ranging from 1 3 to 6 7 and crustal model ages t text dm text c in the range of 2584 2934 ma for the rocks the monzonite granodiorite and granite show moderate total rare earth element ree contents enrichment in light rees lree and depletion in heavy rees hree negative nb ta and ti anomalies high al2o3 sr y and la yb n ratios with low cr and ni indicating that the magma was possibly sourced from partial melting of the lower crust the geochemical features of amphibolites are characterized by low sio2 na2o k2o sr y la yb n and high feo low total rees values limited lree hree fractionation and absence of obvious ce anomaly showing similarity to island arc magmatic rocks our results are consistent with the model of subduction and arc continent collision in the trans north china orogen during the neoarchean to paleoproterozoic

sea level changes an integrated approach sea level changes an integrated approach in october 1985 sepm sponsored a four day conference entitled sea level changes an integrated approach the purpose of the conference was to provide a forum for an interdisciplinary exchange of ideas on sea level changes and to provide an opportunity for integrating various types of evidence in approaching unresolved issues the conference was successful in bringing together scientists from industry academia and government representing all of the major geosciences disciplines presentations of many new papers plus significant releases of data that were previously held proprietary provided fertile ground for discussion this much cited volume represents the best of the material presented at the conference includes the early vail chart

geochronological and geochemical constraints on the luliang group in the luliang complex implications for the tectonic evolution of the trans north china orogen abstract the luliang complex is located at the western margin of the middle segment of the trans north china orogen along which the western and eastern blocks amalgamated to form the basement of the north china craton the complex consists of the late neoarchean to paleoproterozoic granitic plutons and meta supracrustal rocks of which the latter are subdivided into the jiehekou luliang yejishan and heichashan lanhe groups the luliang group is composed mainly of siliciclastic rocks in the lower part and volcanic rocks in the upper part all of which have been metamorphosed from greenschist to amphibolite facies u pb ages of detrital zircons from meta sedimentary rocks in the luliang group yield four populations of 3061 2920 ma 2790 2600 ma 2599 2280 ma and 2211 2202 ma suggesting that their provenances were derived mainly from the luliang and taihua complexes in the trans north china orogen the meta volcanic rocks give igneous zircon u pb ages of 2209 2178 ma and e hf t values of 0 8 to 3 6 geochemically they are subalkaline basalts and andesites that can be classified into two groups of which one group has flat lrees weak enrichment in lrees relative to hrees and flat hrees and displays e morb like spider diagrams with the exception of insignificantly negative nb ta zr hf and ti anomalies in contrast the other group displays stronger lree fractionation stronger enrichment in lrees relative to hrees and mildly fractionated hrees and is characterized by spiky spider diagrams similar to arc volcanic rocks the first group is interpreted to have originated from a neoarchean e morb source whereas the second group shows inputs of newly subduction derived fluids in the mantle source these geochronological and geochemical signatures indicate the existence of an 2 2 2 1 ga continental back arc system in the luliang complex of the trans north china orogen which is consistent with the model that the collision between the eastern and western blocks to form the coherent basement of the north china craton in the paleoproterozoic not at the end of neoarchean

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

cordilleria revisited with a three dimensional model for cretaceous tectonics in british columbia the cordilleria microcontinent theory for the tectonics of british columbia in the cretaceous and early tertiary and for the origin of the canadian rocky mountains and related features is reviewed new isotopic geological and paleomagnetic data support the hypothesis that the amalgamated superterranes of british columbia and alaska were not attached to the mainland of north america in the early cretaceous and were probably well south of their present relative position consideration of that evidence together with sedimentological evidence from the albian leads to a slightly earlier best estimate 115 ma for the time of initial collision in the yukon new geophysical data for southeastern british columbia and idaho lead to a comparison with the iapetus suture in northern england it is suggested that the cordilleria suture dips west from the present purcell thrust and related structures and should cut the moho a new model for regional deformation in se british columbia is proposed involving a flake

discovery of neoarchean suprasubduction zone ophiolite suite from yishui complex in the north china craton abstract the archean tectonic realm of the north china craton ncc is considered in recent models as a collage of several microblocks which were amalgamated along zones of ocean closure during late neoarchean here we report the finding of a dismembered ophiolite suite from the southern margin of the jiaoliao microblock in the interior of the unified eastern block of the ncc the suite is composed of lherzolite pyroxenite noritic and hornblende gabbro and hornblendite intruded by veins and sheets of leuco granite together with transposed layers and bands of metavolcanics and amphibolites banded iron formation bif and diabase dykes in the adjacent locations the yishui complex corresponds well with a dismembered suprasubduction zone ophiolite suite clinopyroxene in the pyroxenite and gabbroic rocks is mg rich and range in composition from augite to diopside among orthopyroxenes those in lherzolite show the highest xmg of 0 84 0 85 plagioclase in hornblende gabbro shows high anorthite content an50 64 calcic amphiboles in the gabbroic rocks range in composition from ferropargasite to ferro edenite edenite and pargasite spinel inclusions in lherzolite are cr rich magnesiospinel geochemically the mafic rocks from yishui complex show subalkaline basaltic source whereas the granitoids show volcanic arc affinity the hornblende gabbro and gabbro lherzolite and hornblendite show compositional similarity to e morb and n morb respectively the lherzolite and hornblendite possess arc related ultramafic cumulate nature with overall features straddling the fields of iat and iat morb the geochemical features are consistent with evolution in a suprasubduction regime with no significant crustal contamination the majority of zircon grains in the yishui suite exhibit magmatic texture and high th u ratios zircon grains from hornblendite define 207pb 206pb upper intercept age of 2538 30 ma zircons from the granite show ages of 2538 16 ma and 2503 21 ma and those from the gabbros yield ages of 2503 16 ma and 2495 10 ma the well defined major age peak at 2500 ma is broadly coeval with neoarchean ages reported from the microblocks in the north china craton the zircon lu hf data from the yishui suite display ehf t values between 2 5 and 5 0 with corresponding model ages suggesting magma derivation from neoarchean juvenile sources together with limited reworked paleo mesoarchean crustal components our study is the first report of neoarchean suprasubduction type ophiolites from a locality far from the margins of the major crustal blocks and suture zones in the ncc and strengthens the concept that the craton is a mosaic of several microblocks with intervening oceans that closed along multiple subduction zones we envisage that the amalgamation between the xuhuai and the jiaoliao microblocks resulted in the accretion of the yishui suprasubduction zone ophiolitic assemblages onto the southern margin of the jiaoliao microblock the neoarchean microblock amalgamation in the north china craton provides new insights into continental growth in the early earth and confirms that modern style plate tectonics might have been initiated early in the history of our planet

a long lived tectono metamorphic event in the late paleoproterozoic evidence from sims u th pb dating of monazite from metapelite in central south trans north china orogen abstract as a key accessory mineral in metapelite monazite forms in the metamorphic event and therefore places important direct constraint on the timing of the tectono metamorphic event in this study we investigate four representative metapelites from different metamorphic terranes in the central south trans north china orogen tnco applying secondary ion mass spectrometry sims u th pb dating on monazite the dating results reveal that monazite collected from the huashan luoning zanhuang and wutai metamorphic complexes record the metamorphic ages of 1 83 ga 1 95 ga 1 85 ga and 1 91 to 1 83 ga respectively combined with the literature data of metamorphic geochronology on the discrete terranes within the tnco it is suggested that the amalgamation between the western and eastern blocks of the north china craton along the nearly ns trending tnco stared as earlier as 1 97 ga and continued to as late as 1 80 ga which was in fact a long lived tectono metamorphic event

tectonic evolution of the hengshan wutai fuping complexes and its implication for the trans north china orogen abstract the hengshan wutai fuping complexes comprise the central segment of the trans north china orogen tnco in the north china craton ncc the tectonic evolution of these complexes is regarded as representative for the entire tnco although the timing of the events has been controvesial on the basis of new nd isotope and structural data and a re appraisal of published geochemical and geochronological data a refined model for the tectonic evolution in the neoarchean to paleoproterozoic has been proposed a major ocean named the proto north china ocean developed between the western and eastern blocks prior to 2565 ma northwest ward intra oceanic subduction resulted in the formation of a proto arc as represented by the 2565 2540 ma wutai granitoids the proto arc was rifted and a back arc basin propagated and extended to form an intra oceanic arc basin system at about 2540 2525 ma the main products during the development of this system were a morb arc back arc basalt adakite association in the wutai greenstone belt and synchronous granitoids in the wutai complex the main subduction accretion process involving multiple subduction zones occurred at 2525 2475 ma resulting in closure of the wutai back arc basin and the formation of diverse arc magmas although the tectonic history between 2 5 and 1 8 ga remains uncertain final collision between the eastern and western blocks and the buildup of the tnco most likely took place at 1 9 1 8 ga the tectonic evolution of the tnco is characterized by subduction accretion processes and the development of arc basin systems thus it is more likely a cordilleran type orogen than a simple continent continent collisional orogen

geometry and structure associated to gas charged sediments and recent growth faults in the ebro delta spain abstract in the ebro delta ne spain small to large scale synsedimentary deformation has been observed by means of high and low resolution seismics correlated with a network of wells lithoseismic units involved are middle upper pleistocene clays and gravels and holocene deltaic sequence gassy sediments and large river floor pockmarks are identified from seismic profiles along the ebro delta gas charged sediments are identified by zones of acoustic turbidity and other acoustic anomalies on seismic profiles most of the gas is believed to be biogenic in origin resulting from the decay of organic matter contained within rapidly developing shelf margin deltas a group of large symmetric river floor pockmarks also occurs along the inner delta plain both on the river floor surface and buried in the sediment column listric fault geometry is a typical scope shaped plane with a steep upper surface 40 60 that passes downward into a horizontal shear plane the shear plane appears seismically as chaotic and convoluted high amplitude reflectors and is correlated with well data showing layers that include gravel sand and clays associated structural features include reverse drag of reflectors antithetic faults and fluid escapes methane water the growth faulting along the ebro delta includes a break away and thin near surface layer created by overstepping of a sandy holocene delta slope the over steeping lies down dip from growth faults along the shelf break the overall growth faults province appears to represent a deeper seated general movement of the delta mass involving differential loading overpressure of fluids diapiric movements and extensional tectonics that cause listric faults and associated structures at different scales the recent growth faults are regularly spaced with the distance between successive faults controlled by the depth to the detachment layer three main fault systems have been identified a first or primary system spaced 5 2 10 5 km above a detachment layer at 55 95 m deep a second system spaced 3 5 6 km and a third system spaced 1 5 2 5 km above a detachment layer at 25 30 m the slope angle calculated by empirical equations ranges between 0 5 and 1 0 for the three systems

geological framework of the ebro continental margin and surrounding areas abstract the eastern and southeastern margins of iberia were affected during neogene time by a rifting tectonic process superimposed on the alpine structures the valencia trough situated off the northeastern coast of iberia has been defined as a rift system that began its activity in late oligocene early miocene time the opening of the valencia trough produced a series of tectonic grabens created by fractures which strike parallel to the coastline as a consequence of the rifting subsidence occurred and depositional sequences of miocene age were subsequently deposited over the triassic and mesozoic basement some of the mesozoic faults were reactivated and affected the tertiary deposits the depositional history was controlled mainly by extensional faulting during the late paleocene early miocene and by rapid subsidence during the late pliocene a second extensional period occurred in the iberian chain resulting in the present configuration of the continental margin in the study area the pliocene quaternary evolution of the margin was largely controlled by fluctuation of the ebro river sediment supply and sea level oscillations

shrimp u pb zircon geochronology of the huai an complex constraints on late archean to paleoproterozoic magmatic and metamorphic events in the trans north china orogen the huai9an complex is situated in the northern segment of the trans north china orogen tnco a continent continent collisional belt along which the discrete archean eastern and western blocks amalgamated to form the basement of the north china craton the complex consists of six distinct lithologic units the huai9an ttg gneisses the manjinggou high pressure mafic granulites the khondalite series the dongjiagou granitic gneiss the huai9an charnockite and the dapinggou k feldspar granite shrimp u pb geochronology combined with th and u data and cathodoluminescence cl imaging of zircons enables resolution of magmatic and metamorphic events that can be directed towards understanding the late archean to paleoproterozoic history of the tnco cl images reveal the coexistence of magmatic and metamorphic zircons in most lithologies of the huai9an complex of which the metamorphic zircons occur as either single grains or overgrowth rims surrounding and truncating oscillatory zoned magmatic zircon cores shrimp u pb analyses on magmatic zircons reveal that the tonalitic trondhjemitic and granodioritic protoliths of the huai9an ttg gneisses were emplaced at 2515 20 ma 2499 19 ma and 2440 26 ma respectively much earlier than the emplacement of the dongjiagou granitic gneiss dated at 2036 16 ma however their metamorphic zircons yield similar concordant 207pb 206pb ages of 1847 17 ma 1842 10 ma and 1847 11 ma for the tonalitic trondhjemitic and granodioritic gneisses respectively and 1839 46 ma for the dongjia granitic gneiss these ages demonstrate that the huai9an complex underwent a regional metamorphic event at 1850 ma which is further supported by a mean 207pb 206pb age of 1848 19 ma for metamorphic zircons in the manjinggou high pressure mafic granulite and 1849 10 ma and 1850 17 ma for igneous zircons in the anatectic huai9an charnockite and dapinggou garnet bearing s type granite respectively the timing of late archean to paleoproterozoic magmatism and regional metamorphism in the huai9an complex is in general agreement with recent shrimp zircon data for other metamorphic complexes in the tnco these data prove that the high grade gneiss complexes were not the basement to the low grade granite greenstone terranes in the tnco furthermore the lithologies of the orogen are considered to have developed as a long lived magmatic arc that was subsequently tectonically disrupted and juxtaposed during the collision of the eastern and western blocks at 1 85 ga leading to final assembly of the north china craton

comments on paleoproterozoic arc continent collision in the north china craton evidence from the zanhuang complex by li et al 2016 precambrian research 286 281 305

shrimp u pb zircon ages of the fuping complex implications for late archean to paleoproterozoic accretion and assembly of the north china craton the fuping complex is situated in the central part of the north china craton and consists of four major lithological assemblages fuping tonalitic trondhjemitic granodioritic gneisses longquanguan augen gneisses wanzi supracrustal assemblage and nanying granitic gneisses shrimp u pb geochronology combined with u th and cathodoluminescence cl imaging of zircon enables resolution of magmatic and metamorphic events that can be directed towards understanding the late archean to paleoproterozoic history of the fuping complex cl images reveal the coexistence of magmatic and metamorphic zircons in nearly all rock types of the fuping complex the metamorphic zircons occur as either single grains or overgrowth or recrystallization rims surrounding and truncating oscillatory zoned magmatic zircon cores and are all characterized by nebulous zoning or being structureless with extremely high luminescence and very low th contents these features make them distinct from magmatic zircons that are characterized by concentric oscillatory zoning comparatively low luminescence and high th and u contents shrimp u pb analyses on magmatic zircons reveal that the tonalitic trondhjemitic and granodioritic plutons of the fuping gneisses were emplaced at 2523 14 ma 2499 10 ma and 2486 8 ma respectively whereas the monzogranitic and granitic plutons of the longquanguan augen gneisses were intruded respectively at 2510 22 ma and 2507 11 ma prismatic and oscillatory zoned zircons dominate in the pelitic rocks of the wanzi supracrustal assemblage and are interpreted as detritus from igneous source rocks the concordant and discordant u pb ages of 2502 5 ma and 2507 14 ma obtained from two pelitic rock samples indicate these rocks must have been deposited no earlier than 2507 ma ago in addition a zoned zircon grain in one pelitic rock sample has a near concordant age of 2109 5 1 ma which may provide a maximum depositional age for the wanzi supracrustal rocks shrimp results also reveal that granitic magmatism assigned to the nanying granitic gneisses occurred over a protracted interval from 2077 13 ma to 2024 21 ma the nebulously zoned zircon grains and overgrowth recrystallization zircon rims from different rocks yielded similar concordant 207pb 206pb ages in the range 1875 to 1802 ma interpreted as approximating the age of regional metamorphism of the fuping complex timing of primary zircon crystallization and regional metamorphism of the fuping complex is in general agreement with recent u pb zircon ion probe results for the wutai and hengshan complexes that bound the fuping complex to the northwest these areas are characterized by the emplacement of major granitoid bodies at around 2 50 ga to 2 48 ga ago deposition of supracrustal rocks in the paleoproterozoic intrusion of paleoproterozoic granitic bodies at 2 1 to 2 0 ga and regional metamorphism at 1 875 to 1 802 ga these data indicate that the fuping and hengshan complexes do not represent an older crystalline basement to the wutai complex as suggested in previous tectonic models but together with the wutai complex represent elements of a single late archean to paleoproterozoic magmatic arc system that has been subsequently tectonically disrupted and juxtaposed during the collision of the eastern and western north china blocks at 1 85 ga which resulted in the final assembly of the north china craton

geochemistry of neoarchean mafic volcanic rocks and late mafic dikes in the zanhuang complex central orogenic belt north china craton implications for geodynamic setting abstract an archean melange belt has been recognized in the zanhuang complex central orogenic belt cob north china craton ncc all units of the melange belt are intruded by a ca 2 5 ga granite pluton and cross cut by undeformed 2 5 ga pegmatites which constrains the archean formation age of the melange some exotic mafic ultramafic blocks are tectonically dispersed in the metasedimentary matrix to the melange and mainly consist of metabasaltic rocks deformed pillow lavas with epidosite cores gabbros and ultramafic rocks both metabasalts and epidosites are characterized by enrichment in light rare earth elements lree and pronounced negative nb and zr anomalies on chondrite and primitive mantle normalized diagrams these geochemical characteristics are consistent with supra subduction zone geochemical signatures based on the pillow structures and seafloor hydrothermal alteration combined with the geochemical characteristics an intra oceanic arc forearc setting is proposed for the formation of these exotic blocks furthermore a west dipping intra oceanic subduction zone is proposed to have formed in an ocean between the eastern block and an arc terrane prior to 2 5 ga the collision between the arc and the eastern block of the ncc happened at ca 2 5 ga resulting in the formation of the archean melange belt in the zanhuang complex all of the units of the melange belt were intruded by late mafic dikes which are present as boudinaged or lenticular shapes in the melange and surrounding gneisses and are intruded by younger ca 2 5 ga pegmatites geochemical characteristics of the late mafic dikes are consistent with an arc related mantle source region rather than an oib like source accordingly pending determination of their precise age an arc polarity reversal event is proposed to have occurred following the arc continent collision resulting in east dipping subduction beneath the newly accreted arc and eastern block forming the swarm of arc affinity mafic dikes the new subduction zone further resulted in ponded magma below the accreted arc block which induced the partial melting of thickened crust and the intrusion of ca 2 5 ga granitic and pegmatitic melts into the melange and the mafic dikes the mafic dikes were then deformed and metamorphosed when the remaining open part of the ocean between the arc collision modified margin of the eastern block collided with the western block of the ncc

sm nd and shrimp u pb zircon geochronology of high pressure granulites in the sanggan area north china craton timing of paleoproterozoic continental collision abstract high pressure hp mafic granulites are widely distributed as sheet like and lenticular bodies within highly deformed tonalitic gneisses in the sanggan area north china craton they have clockwise isothermal decompression and isobaric cooling p t paths implying continental collision tectonics whole rock analyses of 15 samples define a sm nd isochron yielding an age of 2547 87 ma with e nd t 2 7 corresponding nd depleted mantle model ages show a similar range and are interpreted as the age of the magmatic protolith to the high pressure granulites a combined sm nd mineral whole rock isochron from one of these samples yields an age of 1813 23 ma taken to represent the metamorphic age at an early stage on the cooling path shrimp u pb zircon analyses of three hp mafic granulite samples give uniform weighted mean 207 pb 206 pb ages of 1817 12 1817 12 and 1819 16 ma these ages are interpreted to date metamorphism of the hp granulites and with the sm nd mineral whole rock result strongly suggest that the time of continental collision was at ca 1 82 ga an additional sample records two age populations one at 1803 9 ma and an older one at 1872 16 ma the latter may indicate the timing of either an earlier metamorphic event or possibly the earliest stage of a single prolonged metamorphic episode that peaked at 1 82 ga these results confirm the paleoproterozoic age for assembly of the north china craton

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

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

paleomagnetic evidence for motions of parts of the canadian cordillera abstract paleomagnetic evidence from major terranes of the western cordillera in canada referred to collectively as baja british columbia indicates that they have moved as a whole about 2300 km from the south and rotated 60 clockwise relative to north america in the late cretaceous and earliest tertiary 85 50 ma sometime between the early jurassic and the mid cretaceous 190 100 ma these same terranes moved south over 1000 km and underwent irregular but where well constrained counter clockwise rotations the terranes amongst themselves seem to have shared much the same paleolatitude during and since the late triassic although they may have undergone relative rotations in the later jurassic and early cretaceous these motions are now known to be broadly consistent with the motions of oceanic plates to the west as calculated by independent procedures and indicate that the terranes of the western cordillera were for part of their existence coupled to oceanic plates first to the farallon plate during the late jurassic and early cretaceous and then to the kula plate during the late cretaceous and early tertiary it was this change of allegiance from farallon to kula that caused first the southerly and then the northerly motion the paleomagnetic evidence despite claims to the contrary is consistent with geologically inferred displacements along major faults in the canadian cordillera when due account is taken of the age constraints on those motions

genesis of the hanwang fe deposit in neoarchean granite greenstone succession of the eastern north china craton abstract research on history of the earth s continents and the genesis of mineral deposits has been one of the hotspots in geology but only limited studies have been completed on iron deposits hosted by banded iron formations bifs such as the large hanwang iron deposit located in the eastern north china craton ncc in this contribution we present the petrology zircon u pb geochronology lu hf isotopes and whole rock geochemistry on hanwang iron deposit hosted by the metamorphosed neoarchean to early paleoproterozoic taishan group and orthogneiss derived from tonalite trondhjemite granodiorite ttgs magnetite bearing amphibolite magnetite bearing quartz amphibolite and gneiss host the hanwang iron deposit which is characterised by subhedral to euhedral magnetite pyrite with minor galena and bif laminations gangue minerals include hornblende plagioclase and quartz with minor amounts of biotite chlorite epidote and microcline this mineral assemblage is indicative of amphibolite facies metamorphism with regression to greenschist facies the deposit is located in a transition zone between metamorphosed mafic to felsic volcanic rocks the age of the hanwang bif hosted iron deposit is late neoarchean lu hf isotope systematics indicate that the protolith for the biotite amphibolite is derived from a neoarchean mantle contaminated by the crust and orthogneiss is derived from the neoarchean crust the biotite amphibolite is characterised by high na fe and low k assays enrichment in light rare earth elements lree and relatively depletion in heavy rees hree without an obvious ce anomaly the geochemistry of the orthogneiss is characteristic of a volcanic arc granite although this must be accepted with caution given that the orthogneiss is metamorphosed and deformed at amphibolite facies it is proposed that hanwang iron deposit was deposited in a marine volcanic arc environment and derived from hydrothermally leached volcanic units and similar to the algoma type iron deposit most bifs occurring in neoarchean granite greenstone succession of the eastern ncc belong to the algoma type iron deposits globally this sequence appears to be coeval with the yilgarn craton in western australia

tectonics and surface effects of the supercontinent columbia abstract assembly of the supercontinent columbia at about 1 85 1 90 ga coincided with several events that affected the entire earth the oldest worldwide network of orogenic belts formed at the same time although some granite granodiorite gg suites had formed earlier the gg suites became common in the 1 8 1 9 ga orogenic belts these suites succeeded the older tonalite trondhjemite granodiorite ttg suites which were not produced after 1 8 ga changes on the earth s surface at 1 8 1 9 ga include rapid increase in the concentration of oxygen in the atmosphere and oceans and probably the evolution of eukaryotes all of these surface changes occurred as columbia accreted and the assembly of columbia may have contributed to the drastic changes in the earth s surface environment as well as to the evolution of primitive life forms

sedimentary evolution of the pliocene and pleistocene ebro margin northeastern spain abstract the pliocene and pleistocene deposits of the spanish ebro margin overlie a regional unconformity and contain a major disconformity these unconformities named reflector m and reflector g mark the bases of two seismic sequences except for close to the upper boundary where a few small channel deposits are recognized the lower sequence lacks channels the upper sequence contains nine channel levee complexes as well as base of slope aprons that represent the proximal part of the valencia turbidite system diverse geometries and variations in seismic units distinguish shelf slope base of slope and basin floor facies four events characterize the late miocene to pleistocene evolution of the ebro margin a formation of a paleodrainage system and an extensive erosion to depositional surface during the latest miocene messinian b deposition of hemipelagic units during the early pliocene c development of canyons during the late pliocene to early pleistocene and d deposition of slope wedges channel levee complexes and base of slope aprons alternating with hemipelagic deposition during the pleistocene sea level fluctuations influenced the evolution of the sedimentary sequences of the ebro margin but the major control was the sediment supply from the ebro river

new insights into neoarchean paleoproterozoic crustal evolution in the north china craton evidence from zircon u pb geochronology lu hf isotopes and geochemistry of ttgs and greenstones from the luxi terrane abstract tonalite trondhjemite granodiorite ttg suites constitute dominant components of precambrian continental crust and provide important insights into the crustal evolution history of the early earth here we investigate a suite of ttgs and associated greenstones from the luxi terrane in the south eastern part of the north china craton ncc we present data from petrology geochemistry zircon u pb geochronology and lu hf isotopes to characterize these rocks and understand their genesis mineral assemblage in the greenstones and ttgs suggests that the rocks have undergone amphibolite facies metamorphism with regression under greenschist facies zircon u pb data from the magmatic grains yield upper intercept ages of 2753 37 and 2582 40 ma for greenstone 2552 13 ma for ttg gneiss and 2476 18 ma for tonalite and weighted mean 207pb 206pb age of 2507 22 ma for granodiorite lu hf isotope systematics show ehf t values ranging from 2 13 to 7 29 and crustal model ages tcdm in the range of 2603 3125 ma for the ttgs whereas the ehf t values are up to 8 53 with tcdm ages of 2644 3006 ma for the greenstone the results suggest that the protolith for the greenstone was derived from a meso to neoarchean mantle contaminated by the crust source whereas the ttgs were mostly sourced from juvenile crustal sources with reworking of older basement the geochemical features of greenstone are similar to island arc basalt with low na2o k2o and tio2 low total rare earth elements rees values relative enrichment in light rees and depletion in heavy rees absence of obvious ce anomaly and negative nb ta and ti anomalies the ttgs show similar features except for the high k2o content and moderate total rees values we propose that the greenstone likely represent a part of the early and initial crustal growth at ca 2750 2600 ma and the ttgs were generated subsequently at ca 2550 2450 ma our results are consistent with the previous models on the crustal growth models in the ncc and provide further insights into the neoarchean to paleoproterozoic tectonic history of the craton

on determining paleohorizontal and latitudinal shifts paleomagnetism of spences bridge group british columbia the spences bridge group of late albian age palynology and u pb zircon date of 104 5 ma is situated in the intermontane belt of the southern canadian cordillera zeolite grade andesite lavas and interbedded volcaniclastic rocks have been sampled through a thickness of about 2900 m sampling has been confined to localities whose bedding attitudes are well defined and to rocks that have not undergone internal deformation of the 27 sites studied 25 gave single component magnetizations with well grouped directions high coercivities and high unblocking temperatures applying corrections for geological tilt to all 25 sites yielded minimum dispersion after 65 untilting analysis indicates that this is a consequence of the interaction of two modes of behavior one exhibited by y magnetizations at 8 sites in which minimum dispersion occurs after 35 untilting and one x magnetizations at 17 sites in which minimum dispersion occurs after 100 correction actually the dispersion is essentially constant in the range 88 to 100 correction the y magnetizations are uninterpretable in terms of the paleofield because no estimate of paleohorizontal can be made because of their positive response to the tilt test the x magnetizations were acquired before tilting and it is argued that geologically determined bedding planes are good estimators of paleohorizontal at the time of remanence aquisition there may be errors because of paleoslope but arguments are presented for believing that these are small on this basis the best estimate of the mean direction of the paleofield in spences bridge time is estimated to be d i declination inclination 38 7 63 9 17 sites k 44 compared with k 11 in situ 95 5 4 with a paleopole at 64 4 n 321 0 e k 24 compared with k 5 in situ a95 7 5 when compared with the cratonic reference field for mid cretaceous time this pretilting magnetization indicates a clockwise rotation of the study area of 66 3 11 8 p 0 05 and an apparent displacement from the south of 15 5 7 1 1725 790 km when these and other data previously obtained from cretaceous rocks of the pacific northwest are compiled they show an increase in apparent displacement from east to west across the cordillera this result is discussed in terms of three hypotheses 1 no translation but systematic tilts of about 30 to the southwest 2 translation of a substantial part of the pacific northwest referred to as baja british columbia and is defined more exactly in the text by variable amounts up to more than 2000 km from the south together with clockwise rotations and 3 lesser translation of baja british columbia by about 1500 km combined with variable tilting predominantly to the south it is concluded that paleomagnetic data as they are presently known are consistent with hypotheses 2 and 3 but unless serious sources of error are present are not consistent with hypothesis 1 the most likely candidate for such errors is the uncertainty in estimating initial dip of beds paleoslope in volcanic rock units

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

high pressure granulites in the sanggan area north china craton metamorphic evolution p t paths and geotectonic significance high pressure basic granulites are widely distributed as enclaves and sheet like blocks in the huaian ttg gneiss terrane in the sanggan area of the central zone of the north china craton four stages of the metamorphic history have been recognised in mineral assemblages based on inclusion exsolution and reaction textures integrated with garnet zonation patterns as revealed by compositional maps and compositional profiles the p t conditions for each metamorphic stage were obtained using thermodynamically and experimentally calibrated geothermobarometers the low ca core of growth zoned garnet along with inclusion minerals defines a prograde assemblage m1 of garnet clinopyroxene plagioclase quartz yielding 700 c and 10 kbar the peak of metamorphism at about 750 870 c and 11 14 5 kbar m2 is defined by high ca domains in garnet interiors and inclusion minerals of clinopyroxene plagioclase and quartz kelyphites or coronas of orthopyroxene plagioclase magnetite around garnet porphyroblasts indicate garnet breakdown reactions m3 at conditions around 770 830 c and 8 5 10 5 kbar garnet exsolution lamellae in clinopyroxene and kelyphites of amphibole plagioclase around garnet formed during the cooling process at about 500 650 c and 5 5 8 kbar m4 these results help define a sequential p t path containing prograde near isothermal decompression itd and near isobaric cooling ibc stages the clockwise hybrid itd and ibc p t paths of the hp granulites in the sanggan area imply a model of thickening followed by extension in a collisional environment furthermore the relatively high pressures 6 14 5 kbar of the four metamorphic stages and the geometry of the p t paths suggest that the hp granulites together with their host huaian ttg gneisses represent the lower plate in a crust thickened during collision the corresponding upper plate might be the tectonically overlying khondalite series which was subjected to medium to low pressure mp lp 7 4 kbar granulite facies metamorphism with a clockwise p t path including an itd segment both the hp and the mp lp granulite facies events occurred contemporaneously at c 1 90 1 85 ga in a collisional environment created by the assembly process of the north china craton

geotechnical characteristics and slope stability on the ebro margin western mediterranean abstract sedimentological and geotechnical analyses of core samples from the ebro continental slope define two distinct areas on the basis of sediment type physical properties and geotechnical behavior the first area is the upper slope area water depths of 200 500 m which consists of upper pleistocene prodeltaic silty clay with a low water content 34 dry weight average low plasticity and high overconsolidation near the seafloor the second area the middle and lower slope water depths greater than 500 m contains clay and silt size hemipelagic deposits with a high water content 90 average high plasticity and a low to moderate degree of overconsolidation near the sediment surface results from geotechnical tests show that the upper slope has a relatively high degree of stability under relatively rapid undrained static loading conditions compared with the middle and lower slopes which have a higher degree of stability under long term drained static loading conditions under cyclic loading which occurs during earthquakes the upper slope has a higher degree of stability than the middle and lower slopes for the surface of the seafloor calculated critical earthquake accelerations that can trigger slope failures range from 0 73 g on the upper slope to 0 23 g on the lower slope sediment buried well below the seafloor may have a critical acceleration as low as 0 09 g on the upper slope and 0 17 g on the lower slope seismically induced instability of most of the ebro slope seems unlikely given that an earthquake shaking of at least intensity vi would be needed and such strong intensities have never been recorded in the last 70 years other cyclic loading events such as storms or internal waves do not appear to be direct causes of instability at present infrequent particularly strong earthquakes could cause landslides on the ebro margin slope the columbretes slide on the southwestern ebro margin may have been caused by intense earthquake shaking associated with volcanic emplacement of the columbretes islands localized sediment slides on steep canyon and levee slopes could have been caused by less intense shaking in general the slope is stable under present environmental loading conditions and is fundamentally constructional nevertheless rapid progradation caused by high sedimentation rates and other processes acting during low sea level periods such as more intense wave loading near the shelfbreak may have caused major instability in the past

morphosedimentary features and recent depositional architectural model of the cantabrian continental margin abstract multibeam bathymetry high sleeve airguns and very high resolution parametric system topas seismic records were used to define the morphosedimentary features and investigate the depositional architecture of the cantabrian continental margin the outer shelf down to 180 245 m water depth displays an intensively eroded seafloor surface that truncates consolidated ancient folded and fractured deposits recent deposits are only locally present as lowstand shelf margin deposits and a transparent drape with bedforms the continental slope is affected by sedimentary processes that have combined to create the morphosedimentary features seen today the upper down to 2000 m water depth and lower down to 3700 4600 m water depth slopes are mostly subject to different types of slope failures such as slides mass transport deposits a mix of slumping and mass flows and turbidity currents the upper slope is also subject to the action of bottom currents the mediterranean water mw that interact with the le danois bank favouring the reworking of the sediment and the sculpting of a contourite system the continental rise is a bypass region of debris flows and turbidity currents where a complex channel lobe transition zone cltz of the cap ferret fan develops the recent architecture depositional model is complex and results from the remaining structural template and the great variability of interconnected sedimentary systems and processes this margin can be considered as starved due to the great sediment evacuation over a relatively steep entire depositional profile sediment is eroded mostly from the cantabrian and also the pyrenees mountains source and transported by small stream river mountains to the sea it bypasses the continental shelf and when sediment arrives at the slope it is transported through a major submarine drainage system large submarine valleys and mass movement processes down to the continental rise and adjacent biscay abyssal plain sink factors controlling this architecture are tectonism and sediment source dispersal which are closely interrelated whereas sea level changes and oceanography have played a minor role on a long term scale

zircon u pb geochronology of the zanhuang metamorphic complex reappraisal of the palaeoproterozoic amalgamation of the trans north china orogen amphibolites and metapelites exposed in the zanhuang metamorphic complex situated in the south middle section of the trans north china orogen tnco underwent upper amphibolite facies metamorphism and record clockwise p t paths including retrograde isothermal decompression high resolution zircon u pb geochronological analyses indicate that the metamorphic peak occurred during 1840 1860 ma which is in accordance with the ubiquitous metamorphic ages of 1850 ma retrieved by miscellaneous geochronologic methods throughout the metamorphic terranes of the northern tnco confirming that the south middle section of the tnco was involved in the amalgamation of the eastern and western blocks of the north china craton during the palaeoproterozoic

sea valleys and related depositional systems in the gulf of lion and ebro continental margins 1 four main types of sea valleys submarine canyons gullies channels of turbidite systems and a mid ocean channel have been characterized in the ebro and the gulf of lion distal margins in the catalan sea together with three main types of depositional bodies pyrenean canyon deep sedimentary body pcdsb apron deposits and channel levee complexes related to the development of these sea valleys erosion and deposition mainly during the quaternary have formed the majority of these sea valleys although some structurally controlled sea valleys also exist as an example a messinian entrenchment has been confirmed in the petit rhone canyon the evolution of the drainage patterns is established from the detailed analysis of the sedimentary structure this analysis revea s the presence of buried sedimentary bodies and older drainage systems differing from those observed in the bathymetric charts specific factors determine the evolutionary differences between both margins including the absence or presence of underlying evaporitic messinian layers and the regional geodynamic evolution during and after the alpine orogeny we propose a dual evolutionary model from the end of the miocene to the quaternary

the xiong er volcanic belt at the southern margin of the north china craton petrographic and geochemical evidence for its outboard position in the paleo mesoproterozoic columbia supercontinent abstract the xiong er volcanic belt covering an area of more than 60 000 km 2 along the southern margin of the north china craton has long been considered an intra continental rift zone and recently interpreted as part of a large igneous province formed by a mantle plume that led to the breakup of the paleo mesoproterozoic supercontinent columbia however such interpretations cannot be accommodated by lithology mineralogy geochemistry and geochronology of the volcanic rocks in the belt lithologically the xiong er volcanic belt is dominated by basaltic andesite and andesite with minor dacite and rhyolite different from rock associations related to continental rifts or mantle plumes which are generally bimodal and dominated by mafic components however they are remarkably similar to those rock associations in modern continental margin arcs in some of the basaltic andesites and andesites amphibole is a common phenocryst phase suggesting the involvement of h 2 o rich fluids in the petrogenesis of the xiong er volcanic rocks geochemically the xiong er volcanic rocks fall in the calc alkaline series and in most tectono magmatic discrimination diagrams the majority of the xiong er volcanic rocks show affinities to magmatic arcs in the primitive mantle normalized trace element diagrams the xiong er volcanic rocks show enrichments in the lile and lree and negative nb ta ti anomalies similar to arc related volcanic rocks produced by the hydrous melting of metasomatized mantle wedge nd isotope compositions of the xiong er volcanic rocks suggest that 5 15 older crust has been transferred into the upper lithospheric mantle by subduction related recycling during archean to paleoproterozoic time available shrimp and la icp ms u pb zircon age data indicate that the xiong er volcanic rocks erupted intermittently over a protracted interval from 1 78 ga through 1 76 1 75 ga and 1 65 ga to 1 45 ga though the major phase of the volcanism occurred at 1 78 1 75 ga such multiple and intermittent volcanism is inconsistent with a mantle plume driven rifting event but is not uncommon in ancient and existing continental margin arcs taken together the xiong er volcanic belt was most likely a paleo mesoproterozoic continental magmatic arc that formed at the southern margin of the north china craton similar paleo mesoproterozoic continental magmatic arcs were also present at the southern and southeastern margins of laurentia the southern margin of baltica the northwestern margin of amonzonia and the southern and eastern margins of the north australia craton which are considered to represent subduction related episodic outbuilding on the continental margins of the paleo mesoproterozoic supercontinent columbia therefore in any configuration of the supercontinent columbia the southern margin of the north china craton could not have been connected to any other continental block as proposed in a recent configuration but must have faced an open ocean whose lithosphere was subducted beneath the southern margin of the north china craton

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

contrasted tectonic styles for the paleoproterozoic evolution of the north china craton evidence for a 2 1 ga thermal and tectonic event in the fuping massif structural analysis along with 40ar 39ar and u pb datings in the fuping massif provide new insight into the evolution of the eastern part of the trans north china belt north china craton from 2 7 ga to 1 8 ga d1 is responsible for the development of a dome and basin structure coeval with crustal melting giving rise to migmatite and nanying gneissic granites at 2 1 ga this dome and basin architecture resulted from the interference between a n s compression of a weak ductile crust and gravity driven vertical flow in a high thermal regime the next events involved flat lying ductile thrusting d2 and normal faulting d3 dated at around 1880 ma and 1830 ma respectively the d2 and d3 events belong to the trans north china orogeny that results in the final amalgamation of the north china craton the d1 deformation is considered as evidence for an earlier orogen developed around 2 1 ga prior to the trans north china orogeny the change in the deformation style between the 2 1 ga and 1 8 ga could be viewed as a consequence of the cooling of the continental crust in the north china craton

the wutaishan orogenic belt within the shanxi province northern china a record of late archaean collision tectonics abstract the archaean crust of northeastern shanxi province northern china is dominated by three distinct terranes the high grade gneiss terranes hengshan in the north and fuping in the southeast and the intervening low grade terrane of the wutaishan belt the 2 5 ga beitai arc complex which constitutes the major part of the wutaishan belt is interpreted as a pre collision magmatic arc there was a marginal sea basin between the beitai arc and the fuping terrane at the fore arc collision stage the passive margin deposits which occurred along the western margin of the fuping terrane became a foreland fold thrust belt after the closure of the marginal sea basin the remnants of sea floor occur as a melange zone along the suture zone between the beitai arc and fuping terrane nearly at the same time at 2 5 ga the back arc oceanic lithosphere started to subduct beneath the hengshan terrane then the hengshan terrane came into collision with the arc and the fuping terrane some dismembered sea floor rocks are preserved as a back arc melange zone between the hengshan terrane and the beitai arc the term wutaishan orogeny should be reserved for the processes which lasted from 2600 to 2450 ma

a late archean tectonic melange in the central orogenic belt north china craton abstract laterally extensive belts of melange characterize phanerozoic convergent plate margins but are rare in archean terranes we document a late archean melange in the zanhuang massif of the north china craton ncc the zanhuang melange separates a passive margin to foreland basin sequence developed on the western edge of the eastern block of the ncc from an arc terrane consisting of trondhjemitic tonalitic and granodioritic ttg gneisses in the central orogenic belt cob of the ncc the melange belt contains a structurally complex tectonic mixture of metapelites metapsammites marbles and quartzites mixed with exotic tectonic blocks of ultramafic and metagabbroic rocks metabasalts that locally include relict pillow structures and ttg gneisses all units in the melange have been intruded by mafic dikes that were subsequently deformed and are now preserved as garnet amphibolite boudins we interpret the melange to mark the suture zone between the eastern block and the arc terrane in the cob field relationships and geochemistry suggest that the exotic ultramafic metagabbroic metabasaltic blocks are possible slivers of an intra oceanic arc or fore arc ophiolite incorporated into the melange during the arc continent collision process a circa 2 5 ga granitic pluton intrudes the melange and undeformed circa 2 5 ga pegmatites cut the melange tectonic models for the evolution of the cob are varied but include models that favor collision at 2 5 ga 2 1 ga and 1 8 ga this work shows clearly from field structural relationships and geochronology that the first collision must have occurred prior to 2 5 ga consistent with late archean suturing of the western margin of the eastern block with an arc terrane fuping terrane during an arc continent collision the presence of an archean melange with exotic blocks in a suture zone between an archean arc and continental margin is clear evidence for the operation of plate tectonics at circa 2 5 ga

neoarchean paleoproterozoic terrane assembly and wilson cycle in the north china craton an overview from the central segment of the trans north china orogen abstract the north china craton ncc is one of the important precambrian nuclei of the globe as well as an integral component of the paleoproterozoic supercontinent columba the ncc is considered in popular models as an assembly of two major crustal blocks the eastern and western blocks which were sutured along the trans north china orogen tnco which represents a major paleoproterozoic collisional orogen the central segment of the tnco preserves important keys to unravel the tectonic history of amalgamation and cratonization of the ncc here we present an overview on the lithology geochemistry geochronology lu hf isotopes and metamorphic history of the neoarchean to paleoproterozoic rocks in the major basement terranes from the central segment of the tnco the available data allow us to re construct the major precambrian events from the heart of the ncc as follows 1 2 58 2 48 ga amalgamation of three microblocks ordos qianhuai and xuchang along the wutai granite greenstone belt and its branch at the zanhuang area together with the convergence of major microblocks along other 2 5 ga granite greenstone belts leading to the initial cratonization of the ncc 2 2 50 2 45 ga post collisional extension as represented by undeformed mafic dykes and granitoid dykes or plutons resulting in the opening of an oceanic basin along the hengshan and huai an xuanhua complexes 3 2 45 2 12 ga subduction in the hengshan huai an xuanhua and luliang complexes and simultaneous rifting in the fuping wutai and zanhuang complexes 4 2 12 1 98 ga opening of oceanic basins in the wutai and fuping areas followed by double subduction of the oceanic lithosphere and arc magmatism in the fuping wutai and luliang complexes with coeval rifting in the northern part as represented by the hengshan and huai an xuanhua complexes and the southern side as represented by the zanhuang complex 5 1 96 1 80 ga the assembly of the separated terranes or complexes driven by the amalgamation of the western and eastern blocks the collisional event may have occurred at 1 96 1 90 ga and the 1 88 1 80 ga metamorphic ages might represent the retrograde cooling during exhumation 6 termination of the collisional event represented by post collisional intrusions of granitoids charnockites and pegmatites until ca 1 74 ga thus the central segment of the tnco records a prolonged wilson cycle following the initial cratonization of the ncc during neoarchean and involved multiple rift subduction and collisional processes in the paleoproterozoic resulting in the unified ncc and its incorporation into the supercontinent columbia

shrimp data on zircons from the wanzi series constraints on the rock formation time and implications of migmatization at 2 1 2 0 ga in the fuping complex north china craton in most of the rocks of the fuping complex in the trans north china orogen a large quantity of leucocratic veins dykes and granitic intrusions are present as migmatites the incongruent partial melting of biotite to hornblende suggests the water fluxed anatexis of the migmatization of which the melt is manifested by the euhedral crystallization of some quartzofeldspathic minerals and presence of albite rim on earlier plagioclase or k feldspar importantly some melt may be segregated in the sillimanite gneisses or extracted and injected as faint dispersed melt into the competent metasedimentary quartzite of the wanzi series rocks the quartzite has plenty of zircon ages cluster at c 2 5 ga and some at c 2 1 2 0 ga the former may be detrital zircon age while the latter represents the age of migmatization or crystallization of the injected melt not detrital zircon ages as conventionally believed the data have constrained that the sedimentation time of the protolith of the quartzite of the wanzi series was between c 2 5 ga and c 2 1 2 0 ga not younger than c 2 1 2 0 ga as once proposed therefore it must be cautious in applying detrital zircon ages in constraining the time of sedimentation if the rocks have undergone middle high grade metamorphism especially when migmatization was involved in the metamorphism process

did the ebro basin connect to the mediterranean before the messinian salinity crisis the connection of the ebro basin via the ebro river to the mediterranean sea is supposed to have played a major role in the rejuvenation of relief of northern spain and especially of the south pyrenees from the neogene by lowering the initial base level of the ebro internal drainage area down to sea level however the timing and causes of this connection are still debated a fundamental issue is whether the ebro basin became connected to the mediterranean before or after the messinian salinity crisis morphological analysis and numerical modeling of landscape evolution show that this connection did not exist before the messinian salinity crisis but is effective from the pliocene because of progressive regressive erosion

late quaternary depositional architecture of po and tevere river deltas italy and worldwide comparison with coeval deltaic successions abstract po and tevere rivers form two of the most important deltas of the whole mediterranean area detailed investigations have been carried out in the last decade beneath the present delta plains of these two river systems using borehole data correlation with the aid of radiocarbon dates and other dating methods pollens archaeology a detailed sequence stratigraphic framework has been constructed in both areas especially for the last glacial interglacial cycle regional subsidence combined with short term sea level fluctuations of relatively high amplitude played a fundamental role in creating subtracting accommodation during the long phase of falling sea level which followed the tyrrhenian substage 5e transgressive event a discontinuous record of this phase is present in the subsurface of the po plain whereas poor or no preservation has been detected in the tevere area progradational lowstand wedges accumulated during the last glacial maximum mostly in the central part of the basins far from the present deltas and are lacking in the study areas where a hiatal surface is invariably recorded below the transgressive deposits glacioeustasy exerted a major control on sedimentation in both areas during the latest pleistocene holocene sea level rise infilling of fluvial valleys and rapid landward migration of barrier lagoon systems in the context of wave dominated estuaries characterized the transgressive phase in both po and tevere systems in place drowning and transgressive submergence mechanisms of barrier migration were effective predominantly between 13 5 and 9 ka bp in contrast shoreface retreat was dominant in the late transgressive phase the maximum flooding surface mfs can be traced physically from continental to marine deposits and has similar characteristics in the po and tevere river systems being marked by peat layers or lagoonal deposits at landward locations and by distinctive lithological characteristics and micro and macrofossils assemblages basinwards above the mfs the early highstand systems tract records initially the filling of the lagoons followed by the rapid progradation of wave dominate delta systems and flanking strandplains autocyclic processes such as distributary channel avulsion delta lobe abandonment and local subsidence due to sediment compaction were the fundamental controlling factors on sedimentation during deposition of the hst the stratigraphic architecture of the post glacial po and tevere delta complexes closely resembles the basic facies successions documented from coeval deposits of wave dominated and wave influenced clastic coasts both locally within the mediterranean area and in other parts of the world our study emphasizes however some additional features and major differences with previously published depositional models including i the development of backstepping wave dominated estuaries during transgression ii consistent changes through time in the mechanism of barrier migration iii a later construction of the delta systems with respect to what traditionally considered

geochronology and petrogenesis of neoarchean potassic meta granites from huai an complex implications for the evolution of the north china craton abstract neoarchean potassic meta granites occurring in the huai an complex within the north central part of the north china craton ncc comprise leucocratic syenogranites biotite monzogranites and garnet bearing syenogranites high pressure garnet granulites occur as lenses sheets or dismembered dikes with the granitoids here we present shrimp zircon u pb data from the leucocratic syenogranites which show an age of 2493 6 ma mswd 1 and la icp ms u pb data from the biotite monzogranites and garnet syenogranites revealing their formation ages of 2437 10 ma mswd 2 0 and 1977 2003 ma respectively we also report metamorphic ages of ca 1800 ma from zircons in the garnet syenogranites geochemical studies show low mgo 0 5 0 06 wt cr 6 19 0 53 ppm and ni 27 66 2 01 ppm with varying sio2 62 3 to 76 8 wt contents indicating their derivation from a crustal source the leucosyenogranites exhibit elevated positive eu anomalies with decreasing sr th u and bulk ree concentrations and th u ratio whereas rb and ba values increase with decreasing th u ratio indicating fluid melt interaction the leucosyenogranites have high sr and ba contents and sr y and la yb n ratios and low y and hrees with zircon ehf t values ranging from 1 7 to 5 8 and hf model ages of 2 60 2 73 ga reflecting their derivation by partial melting of overthickened juvenile lower crust of eclogitic composition or an eclogitic mineral assemblage in the residue geochemical compositions of the biotite monzogranites with positive end t values 2 3 to 2 5 and model ages

lower pleistocene to present structural deformation and sequence stratigraphy of the continental shelf offshore eel river basin northern california seismic stratigraphic sequences and deformational features are mapped beneath the continental shelf of the offshore eel river basin of northern california using a closely spaced high resolution multichannel seismic grid geometries of sequences and morphologies of bounding unconformities reflect competing tectonic and glacioeustatic influences producing shifting sedimentation patterns in the offshore basin during the last v1 myr estimated timing of unconformity formation correlates generally with a deep ocean global n 18 o curve both before and after a v500kyr transition from 41 kyr to 100 kyr dominated cycles we suggest that glacioeustatic fluctuations are the dominant control on unconformity formation basinwide however regional tectonic influences on sequence development are also observed folding associated with gorda north america plate convergence ended progressively from south to north between v1 0 ma and v500 ka in response to northward migration of the mendocino triple junction mtj since v500 ka continued encroachment of the mtj produces rotation of preexisting structures uplift of the table bluff anticline tba related periods of channel incision south of the tba and generally reduced sediment preservation across the shelf mtj related uplift may also have induced formation of eel canyon over the past v1 0 myr a dominant northern sediment source becomes progressively less important a southern source probably the paleo eel river has become dominant since v750 ka seismic unconformities fall into two categories 1 irregular surfaces of limited mappable extent interpreted as incision exposure surfaces forming during relative sea level lowstands and 2 smooth laterally extensive regional unconformities interpreted as ravinement surfaces that erode lowstand surfaces in all but deeply incised areas during sea level transgressions a sequence stratigraphic model for sediment deposition and preservation on the eel river shelf predicts that preserved sediment on the eel margin is dominated by fluvially derived highstand silts and muds deposited by longshore directed currents and waves lowstand sediments are preserved only in fluvial channels infilled during late lowstand early transgression preserved transgressive sediments are likely limited to a thin veneer of well sorted coarse sediment or shell debris deposited above the transgressive ravinement future deep coring will be required to confirm these predictions 2002 elsevier science b v all rights reserved

microblock amalgamation in the north china craton evidence from neoarchaean magmatic suite in the western margin of the jiaoliao block abstract the archaean earth is considered to have been characterized by microcontinents that formed dominantly through the accretion of oceanic arcs and plateaus the north china craton ncc provides a typical case where at least seven ancient microcontinental nuclei with distinct lithological features and independent tectonic histories were amalgamated into the cratonic framework at the end of the archaean here we investigate a suite of magmatic rocks developed at the periphery of one of these microblocks the jiaoliao block that forms part of the composite eastern block of the ncc we present petrological geochemical and zircon u pb geochronological data from the taipingzhai charnockite suite and associated amphibolites metagabbros and orthogneisses from the qianxi complex geochemically the rocks show a wide range of sio 2 charnockite suite 52 57 75 50 wt metagabbro 43 71 wt amphibolite 50 24 wt garnet bearing biotite 63 73 wt and mgo charnockite suite 0 89 5 01 wt metagabbro 3 99 wt amphibolite 6 23 wt garnet bearing biotite 2 08 wt the composition of the felsic units straddle from diorite through syeno diorite to granite with both alkalic and subalkalic affinity with dominantly magnesian composition and arc related features their immobile trace element relationships suggest calc alkaline affinity they show positive pb ba la nd and gd and negative nb ta sr th and ti anomalies with slightly negative anomalies of ce and y attesting to arc related features in tectonic classification diagrams the rocks plot in the vag syn colg field or the vag area suggesting subduction related origin the dominant population of zircons in all these rocks displays magmatic crystallization features including high th u values with core rims textures indicating subsequent thermal events the zircon u pb data yield upper intercept ages of 2587 10 ma to 2543 17 ma and 207 pb 206 pb mean ages of 2578 7 3 ma to 2536 8 ma for the charnockite suite marking the timing of emplacement of the arc magmas the overgrowth rims as well as discrete neoformed grains are interpreted as dating subsequent metamorphism and yield 207 pb 206 pb ages between 2533 ma to 2490 ma zircons in the metagabbro preserve upper intercept ages of 2556 20 ma representing the crystallization age of this rock the younger ages of 2449 58 ma upper intercept age and 1845 25 ma 207 pb 206 pb spot age are interpreted to represent subsequent multiple thermal events in this area zircons in the amphibolite preserve the 207 pb 206 pb mean age of 2539 9 ma representing the crystallization age of this rock the garnet bearing biotite gneiss shows an upper intercept age of 2562 10 ma mswd 0 66 n 36 and the 207 pb 206 pb mean age of 2561 9 ma mswd 0 63 n 33 which is taken to represent the crystallization age of this rock some inherited zircons are also identified with 207 pb 206 pb ages of 2664 26 ma and 2628 26 ma zircon lu hf data show dominantly positive ehf t values and combined with crustal residence ages the results suggest mesoarchean to neoarchean juvenile crust formation in the ncc we interpret the data presented here to represent a phase of major late neoarchaean arc magmatism along the western margin of the jiaoliao block related to the birth of microcontinental nuclei within the ncc our data suggest that the western and eastern blocks might not have existed as discrete crustal blocks and that the construction of the ncc is a result of the assembly of several microblocks or terranes at the end of archaean similar archean cratonic nuclei in other regions of the world might have formed part of a primitive supercontinent in the early earth

geochronology mantle source composition and geodynamic constraints on the origin of neoarchean mafic dikes in the zanhuang complex central orogenic belt north china craton abstract mafic granulitic and amphibolitic boudins dispersed in archean felsic gneisses are widely distributed in the central orogenic belt cob and the eastern block of the north china craton ncc and are considered to constitute deformed mafic dike swarms previous studies have demonstrated that the mafic dikes in the zanhuang complex of the ncc intruded the fabrics of an archean melange belt and were boudinaged during younger deformation igneous zircons from an undeformed mafic dike yield a 207 pb 206 pb age of 2535 30 ma which is interpreted as the crystallization age in addition pegmatites cutting across the mafic dikes in the field also yield an igneous zircon 207 pb 206 pb age of 2504 16 ma providing strong evidence that the mafic dikes in the ncc intruded during the neoarchean metamorphic zircons from one deformed mafic dike sample yield a metamorphic 207 pb 206 pb age of 2090 83 ma and another four samples from deformed mafic dikes have a consistent metamorphic zircon age of ca 1850 ma indicating that the mafic dikes underwent at least two generations of paleoproterozoic metamorphism of ca 2 1 ga and ca 1 85 ga previously reported trace element systematics of the mafic dikes are consistent with an arc related lithospheric mantle source region rather than an ocean island basalt oib like source region the new whole rock nd isotopic composition nd t 0 71 to 3 70 is relatively more evolved compared to that of the depleted mantle at 2 5 ga indicating an enriched lithospheric mantle source accordingly the mafic dikes are proposed to have been formed in a subduction related environment and their enriched mantle source was metasomatized by the melts and fluids derived from the subducted slab based on previous studies of the ncc and new geochronological and isotopic data in this contribution a new comprehensive tectonic model is proposed for the evolution of the ncc between 2 7 ga and 1 85 ga 1 from 2 7 to 2 5 ga an oceanic arc terrane belt developed in what is now the cob of the ncc while a passive margin sequence was deposited on the western edge of the eastern block on the margin of the intervening ocean 2 the oceanic arc terrane collided with the passive margin sequence at 2 5 ga above a west dipping subduction zone 3 the subduction polarity was reversed at ca 2 5 ga and a new east dipping subduction zone gave rise to the intrusion of the 2 5 ga mafic dikes of the ncc 4 the final collision between the western block and the eastern block occurred at ca 2 1 ga 5 the whole ncc then collided with the columbia supercontinent along the north margin of the craton at 1 9 1 8 ga

granitoid evolution in the late archean wutai complex north china craton abstract two temporally discrete episodes of granite magmatism have been identified in the wutai complex of the north china craton based on shrimp u pb zircon dating of all major granitoid bodies in the area the older period is latest archean and ranges in age from 2560 to 2515 ma whereas the younger episode is paleoproterozoic with magmatism at 2170 and 2120 ma archean magmatism can be further separated into two pulses based on geochemistry and the association of the younger plutons with extensive coeval volcanic activity in the wutai complex the early phase of archean activity is represented by the lanzhishan ekou and portions of the chechang betai granites with ages ranging from 2560 to 2540 ma the lanzhishan granite is the only one at wutaishan that contains inherited zircon with a number of cores and individual grains giving ages in excess of 2700 ma these are relatively evolved granitoids interpreted to be derived from older basement of the eastern block of the north china craton the shifo guangmingshi the main grey phase of the wangjiahui granite and the major components of the chechang betai granite have ages of 2540 2515 ma and are coeval with felsic volcanism in the wutai complex which is a consequence of subduction and related arc magmatism the dawaliang granite and pink phase of the wangjiahui granite are considerably younger with paleoproterozoic ages of 2170 and 2120 ma respectively these are also evolved granitoids most likely derived by partial melting of the older basement although we have found no evidence of inheritance the petrogenesis of the granitoids reflects the precambrian amalgamation history of the north china craton indicating derivation along the western edge of the eastern block during development and amalgamation of the wutai arc and prior to collision with the western block of the craton 1 8 ga ago

petrogenesis of the 2090 ma zanhuang ring and sill complexes in north china a bimodal magmatism related to intra continental process abstract it is widely debated as to whether the 2100 ma bimodal magmatic events in the eastern north china craton represent intra continental rifting or marginal processes the genetic relationship between the two components of bimodal suites is the key solution to this issue and this is investigated on a group of newly identified ring complexes as well as the apparently associated sills in zanhuang southern taihang mts these ring complexes comprise varied components pyroxenite gabbro anorthosite k rich a type granite and minor na rich a type granite u pb analyses on baddeleyite and zircon grains liberated from a gabbro sample both yield a 2090 ma age which represents crystallization timing and is contemporaneous with a type granites of the ring complexes as well as the sills in the gantaohe group the mafic rocks of the ring complexes and sills show similar chemical features they were characterized by enriched light rare earth elements compared to middle and heavy ones la ybn 1 4 2 8 enriched large lithosphile elements but depleted high field strength elements and enriched sr nd isotopes endt t 2090 ma 1 9 0 6 nd tdm 2 7 ga they were most likely originated from the same magma source resided in the sub continental lithospheric mantle which formed in the late archean the compositional variation of the mafic sills may be resulted from the fractionation of olivine and plagioclase the k rich a type granite as well as the dacitic sills could be originated from this same source with firstly olivine plagioclase dominated fractionation in the lower magma chamber to more felsic compositions and then with significant removal of clinopyroxene plagioclase in the upper magma chamber which at the same time produced pyroxenite gabbro and minor anorthosite cumulates in the ring complexes na rich a type granite was likely formed locally under relatively high water fugacity with fractionation of k feldspar plagioclase clinopyroxene from a parental magma similar to the k rich a type granite this bimodal zanhuang ring and sill complexes and other comparable bimodal suites widely distributed in the eastern north china craton were likely intra continental representing a craton scale extension at 2100 ma

deformation history of the hengshan complex implications for the tectonic evolution of the trans north china orogen structural analysis indicates that the hengshan complex underwent five distinct episodes of deformation d1 d5 the d1 episode formed small isoclinal folds f1 penetrative axial planar foliations s1 and mineral stretching lineations l1 d1 fabrics were reworked by following d2 deformation associated with d2 was the development of nw verging asymmetric folds and accompanying thrust faults both d1 and d2 resulted from crustal thickening and coherent with prograde and peak metamorphism d2 deformation was followed by transpressional dextral shearing d3 including top to nw oblique slip shearing and nne ssw dextral strike slip shearing ongoing collision led to development of the zhujiafang ductile shear zone d4 a near e w trending high strain belt across the hengshan complex d5 deformation is characterized by f5 open folds and associated normal faults probably related to exhumation of the complex structural patterns of the hengshan complex can place important insights into a recently proposed tectonic model suggesting that an ocean between the eastern and western blocks underwent eastward directed subduction beneath the western margin of the eastern block and closure of this ocean finally led to collision between the two blocks to form the coherent north china craton

shrimp zircon u pb dating and hf isotope analyses of the muniushan monzogranite guocheng jiaobei terrane china implications for the tectonic evolution of the jiao liao ji belt north china craton abstract the paleoproterozoic granitoid rocks in the jiaobei terrane which lies in the southern part of the jiao liao ji belt jljb in china provide valuable information on the tectonic and evolutionary history of the north china craton ncc shrimp u pb dating of zircons from the muniushan monzogranite in the guocheng gold deposit area as well as in situ hf isotope analyses of the zircons were used to constrain the ages of emplacement and metamorphism and to understand the petrogenesis of the granite the geochronological data show emplacement ages of ca 2 1 ga and metamorphic ages of ca 1 85 ga the magmatic cores of the zircons have ehf t values of 0 51 to 4 00 average 1 98 and depleted mantle two stage model ages tdm2 of 2444 2703 ma average 2563 ma the rocks show the same trends of crustal evolution as ca 2 5 ga tonalite trondhjemite granodiorite ttg rocks in the jiaobei terrane indicating that they were formed by the remelting of those ttg rocks the muniushan monzogranite is part of a linear belt of ca 2 2 2 0 ga paleoproterozoic granitoids within the jljb the granitoids are a types and are accompanied by coeval mafic intrusions and bimodal volcanic rocks thus indicating widespread extension along the jljb in the period 2 2 2 0 ga the ca 1 85 ga metamorphism was related to the collision of the longgang and nangrim blocks the paleoproterozoic evolution of the ncc constrains the crustal architecture and the source of mesozoic granitoids in the jiaobei sulu region inherited zircons of paleoproterozoic age are widespread in the mesozoic granitoids in addition paleoproterozoic ages have been reported from lower crustal granulite xenoliths in the sulu orogen and the southeastern margin of the ncc mirrors the evolution of the jljb it is probable therefore that ncc lower crust underlies the sulu orogen and that the ncc was the main source for the mesozoic granitoids in the jiaobei sulu region this view is consistent with the appearance of inherited zircons of archean and paleoproterozoic age on both sides of the orogen normal 18o values of magmatic zircons and paleoproterozoic to archean two stage hf model ages for the granitoids

casablanca field offshore spain a paleogeomorphic trap the casablanca field which is the largest of four producing fields in the spanish mediterranean is located about 30 mi 48 km south of tarragona using the halbouty classification in aapg memoir 16 it is a paleogeomorphic trap the field is producing about 18 000 b d of oil from two wells in an early production phase the crude has a density of 33 7 api sulfur content of 0 2 and a gas oil ratio gor of 155 cu ft bbl full daily field production of about 35 000 to 40 000 b d of oil will start in 1982 after a platform is installed the reservoir is a weathered and fractured upper jurassic carbonate rock the primary matrix porosity averages about 3 however weathering during the early tertiary has enlarged fractures and previously existing porous zones to a depth of 300 to 500 ft 91 to 152 m below the top of the carbonate rocks this secondary porosity in combination with an extensive fracture network has converted the otherwise dense carbonate into a commercially exploitable reservoir a contour map on the top of the eroded mesozoic carbonate reservoir defines a closure 6 8 by 1 5 mi 11 by 2 5 km the field is elongate parallel with miocene faults with an overall configuration of a rounded limestone ridge the ridge is covered by middle miocene organic rich marls which were the source of the oil these and younger shales are a cap for the accumulation the use of the paleogeomorphic model aids the interpreter in mapping data in the casablanca area which otherwise would seem uninterpretable or at least difficult to interpret the model may be of use in other carbonate areas

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