u pb dating of monazite and its application to geological problems monazite is an underutilized mineral in u pb geochronological studies of crustal rocks it occurs as an accessory mineral in a wide variety of rocks including granite pegmatite felsic volcanic a

tectonic evolution of a composite collision orogen an overview on the qinling tongbai hong an dabie sulu orogenic belt in central china abstract the formation of collisional orogens is a prominent feature in convergent plate margins it is generally a complex process involving multistage tectonism of compression and extension due to continental subduction and collision the paleozoic convergence between the south china block scb and the north china block ncb is associated with a series of tectonic processes such as oceanic subduction terrane accretion and continental collision resulting in the qinling tongbai hong an dabie sulu orogenic belt while the arc continent collision orogeny is significant during the paleozoic in the qinling tongbai hong an orogens of central china the continent continent collision orogeny is prominent during the early mesozoic in the dabie sulu orogens of east central china this article presents an overview of regional geology geochronology and geochemistry for the composite orogenic belt the qinling tongbai hong an orogens exhibit the early paleozoic hp uhp metamorphism the carboniferous hp metamorphism and the paleozoic arc type magmatism but the three tectonothermal events are absent in the dabie sulu orogens the triassic uhp metamorphism is prominent in the dabie sulu orogens but it is absent in the qinling tongbai orogens the hong an orogen records both the hp and uhp metamorphism of triassic age and collided continental margins contain both the juvenile and ancient crustal rocks so do in the qinling and tongbai orogens in contrast only ancient crustal rocks were involved in the uhp metamorphism in the dabie sulu orogenic belt without involvement of the juvenile arc crust on the other hand the deformed and low grade metamorphosed accretionary wedge was developed on the passive continental margin during subduction in the late permian to early triassic along the northern margin of the dabie sulu orogenic belt and it was developed on the passive oceanic margin during subduction in the early paleozoic along the northern margin of the qinling orogen three episodes of arc continent collision are suggested to occur during the paleozoic continental convergence between the scb and ncb the first episode of arc continent collision is caused by northward subduction of the north qinling unit beneath the erlangping unit resulting in uhp metamorphism at ca 480 490 ma and the accretion of the north qinling unit to the ncb the second episode of arc continent collision is caused by northward subduction of the prototethyan oceanic crust beneath an andes type continental arc leading to granulite facies metamorphism at ca 420 430 ma and the accretion of the shangdan arc terrane to the ncb and reworking of the north qinling erlangping and kuanping units the third episode of arc continent collision is caused by northward subduction of the paleotethyan oceanic crust resulting in the hp eclogite facies metamorphism at ca 310 ma in the hong an orogen and low p metamorphism in the qinling tongbai orogens as well as crustal accretion to the ncb the closure of backarc basins is also associated with the arc continent collision processes with the possible cause for granulite facies metamorphism the massive continental subduction of the scb beneath the ncb took place in the triassic with the final continent continent collision and uhp metamorphism at ca 225 240 ma therefore the qinling tongbai hong an dabie sulu orogenic belt records the development of plate tectonics from oceanic subduction and arc type magmatism to arc continent and continent continent collision

electron microprobe and la icp ms study of monazite hydrothermal alteration implications for u th pb geochronology and nuclear ceramics this paper presents new data that quantify the response of magmatic monazite to three main types of hydrothermal alteration namely sericitization chloritization and greisenization the samples were taken from three paleozoic granites the st nectaire granite massif central france the carnmenellis granite cornwall england and the skiddaw granite lake district england fluid inclusion thermometry and hydrothermal parageneses indicate that alteration took place at temperatures ranging from 260 to 340 c and salinities from 3 to 18 wt nacl equivalent possible monazite alteration mechanisms found in the course of this study using backscattered scanning electron microscopy bse sem electron microprobe laser raman spectroscopy and laser ablation inductively coupled plasma mass spectrometry la icp ms include cationic substitutions monoclinic to hexagonal structure transition accompanied by chemical exchanges selective th removal dissolution reprecipitation and dissolution with replacement by a different mineral these results show that despite the compositional and crystallographic simplicity of monazite it exhibits varied chemical responses to different mineral fluid interactions elemental and isotopic measurements by la icp ms for the unaltered monazites yield statistically significant 232th 208pb and 238u 206pb magmatic crystallization ages in some cases it was possible to give a reasonable estimate of the age of mineral fluid interaction using the altered parts of the monazites or newly precipitated crystals for other minerals 232th 208pb and 238u 206pb systematics were strongly disturbed by variable inputs and or depletions of u th and pb the data suggest that monazite like nuclear waste forms would be good hosts for tetravalent actinides but may release the lanthanides and actinides with lower and higher valencies especially if the fluids are oxidizing or tend to dissolve monazite

diamictic sediments within high arctic lake sediment cores evidence for lake ice rafting along the lateral glacial margin sediment cores from six small lake basins in the canadian high arctic reveal a gravel rich 30 by weight to gravel poor 2 diamict facies underlying massive post glacial clayey silt ten other lakes contain a second diamict facies within what are interpreted to be glaciolacustrine sedimentary assemblages the sedimentology clast fabrics and fossil remains diatoms ostracodes and chironomid head capsules within both diamict facies suggest that these deposits are not tills clast fabrics yielded low s1 0 41 0 57 and high s3 0 09 0 22 eigenvalues placing them within the range of ice rafted diamictons and glacigenic sediment flows the high percentage of clast dip angles 45 15 61 random clast azimuth and lower diamict contacts conformable to underlying current bedded sediment favours an origin as a rain out or settling deposit samples of the matrix and scrapings of clasts from the diamicts revealed a diatom assemblage dominated by littoral and planktonic forms such as are found in the littoral regions of the lakes today this contrasts sharply with the assemblages within the overlying clayey silt in which benthic forms predominate clasts are thus interpreted to have been rafted from the littoral areas of the lake the process proposed to explain this is rafting by the lake ice cover in a glacial marginal environment early season meltwater impounded along the lateral margin of retreating cold based glaciers would buoyantly lift the lake ice cover and any adfrozen lake sediment higher lake levels and increased areal extent of seasonal freeze on between the lake ice cover and the lake bed would allow the redeposition of littoral sediments to the benthic regions through greater lateral shifting of the ice cover as it broke up incision by meltwater streams into the lateral glacial margins would later isolate the lake allowing seasonal warming of lake water enough to support the growth and maturation of the ostracode and chironomid species found as fossils within the diamicts

holocene vegetational history of the kootenai river valley montana abstract pollen records in the kootenai and fisher river drainages in western montana reveal a fivezone sequence of holocene vegetation change deposition of glacier peak ash layer g ca 10 540 660 yr b p in the lowermost sediments clay intermixed with pebbles at tepee lake gives a minimum date for the initiation of sedimentation initial vegetation on the newly deglaciated terrain was dominated by pinus probably white bark pine with small amounts of gramineae picea and abies reflecting a relatively cool moist macroclimate two vegetation units appear to contribute to pollen zone ii ca 11 000 7100 yr b p arboreal communities with pines along with pseudotsuga or larix or both and treeless vegetation dominated by artemisia pollen zone ii represents an overall warmer macroclimate than occurred upon ice withdrawal after ca 7100 yr b p pollen zone iii diploxylon pines became a major pollen contributor near both tepee lake and mckillop creek pond indicating an expansion of xerophytic forest p contorta and p ponderosa along with an increase in the prominence of pseudotsuga menziesii or larix occidentalis or both artemisia briefly expanded coverage near tepee lake concomitant with the mazama ashfall ca 6700 yr b p a short term climatic trend with more available water began after ca 4000 yr b p as abies probably a grandis along with picea engelmannii became a more regular component of the forest surrounding both sites emergence of the modern macroclimate is indicated primarily with the first regular appearance of tsuga heterophylla in the pollen record by ca 2700 yr b p synchronous with the development of western hemlock forest within the same latitudes in northern idaho and northeastern washington

resetting monazite ages during fluid related alteration abstract fluid related coupled dissolution reprecipitation processes can modify the composition of monazite and other orthophosphate minerals at temperatures well below diffusional closure temperatures it is critical to evaluate the effects of alteration processes on th u pb dates especially because incomplete removal of pb during alteration could lead to spurious dates either older or younger than the actual age of the monazite formation experimental alteration of monazite at 450 mpa and 450 c has resulted in the production of altered domains in the vicinity of the grain rim as well as in the vicinity of inclusions and microfractures without any obvious structural control within grains the composition of the altered domains is relatively constant from domain to domain and from grain to grain thorium was reduced from ca 7 wt tho 2 to ca 2 wt uranium and pb were almost entirely removed from the altered domains while unaltered areas of the monazite grains as well as the original monazite grains before the experiment yield very consistent dates of ca 350 ma dates from the altered domains are consistently near zero the implication is that fluid aided alteration of monazite for the conditions of this experiment has resulted in a near complete resetting of the monazite age at temperatures well below the closure temperature because alteration textures in monazite are relatively common in nature careful analysis of such textures offers a means of recognizing and potentially dating fluid rock interactions

postglacial vegetation history of the mackenzie river basin abstract three radiocarbon dated cores from small lakes provide pollen records of postglacial vegetation change in the central mackenzie river basin these data are combined with previously published records to reconstruct vegetation development from central alberta to the mackenzie delta the paleoecological data demonstrate that a continuous corridor of herb and shrub dominated vegetation extended between beringia and the great plains of north america from deglaciaiton until about 10 000 yr b p the initial vegetation was replaced by spruce forests between 10 000 and 8500 yr b p significant vegetation change continued until approximately 500 yr b p when the muskeg dominated landscape typical of the present subarctic was established the initial herb and shrub vegetation was likely a reprise of conditions which existed during earlier pleistocene deglaciations these conditions may have provided a favorable environment for animals adapted to nonforested vegetation and promoted migration southward from beringia and northward from the great plains during the last deglaciation and earlier pleistocene deglaciations the sequence of postglacial vegetation change in the mackenzie basin likely reflects a combination of climatic change edaphic change and plant migration patterns and interactions

geochemistry of ttg and ttg like gneisses from lushan taihua complex in the southern north china craton implications for late archean crustal accretion the late archean taihua complex mainly composed of amphibolite and ttg and ttg like gneisses is volumetrically most important metamorphic rock suites scattered along the southern margin of the north china craton ncc zircon shrimp u pb dating shows two episodes 2765 13 and 2723 9 ma of archean magmatism in the lushan area with distinct geochemical features the early 2765 13 ma suite ttg like gneisses has low sio2 52 5 66 1 wt high mg 0 47 0 68 low hree ybn 3 0 5 4 and y 8 07 13 9 ppm with low to moderate la yb n 6 7 37 1 and sr y 25 9 119 3 the younger 2723 9 ma suite ttg gneisses has high sio2 63 5 74 3 wt low mg 0 13 0 52 very low ree ybn 1 1 20 2 43 both suites show pronounced negative nb ta and ti anomalies on the primitive mantle normalized spidergram the ttg like gneiss suite has similar bulk rock nd and zircon hf model ages 3 0 ga with end t 0 0 26 1 46 and is interpreted as resulting from melt of mantle interactions with the melts derived from partial melting of subducted ocean crust with a residual assemblage of garnet clinopyroxene rutile amphibole which favors subducted slab model for the late archean ttg the ttg gneiss suite has abundant relic zircons 2 95 2 80 ga with end t 0 1 31 to 0 23 which is best interpreted as derived from partial melting of thickened lower continental crust with a garnet amphibolite residue garnet amphibole rutile significant high pressure fractional crystallization garnet amphibole and accumulation plagioclase are also required in the petrogenesis the lushan amphibolite with nearly flat primitive mantle normalized trace element pattern is interpreted to represent early ocean crust metamorphism these observations suggest a possible model of late archean crustal accretion from ocean crust to continental terrain in the southern north china craton

an 18 000 year palynological record from the southern alberta segment of the classical wisconsinan ice free corridor radiocarbon dates of 18 300 380 years bp gsc 2668 and 18 400 1090 years bp gsc 2670 on moss fragments from the clay near the base of a core from chalmers bog alberta indicate that the classical wisconsinan ice free corridor was in existence in the foothills of southern alberta by this time palynological studies show sparse herbaceous tundra like vegetation probably prevailed at this time in the area surrounding the small lake formed in the abandoned glacial spillway later shrubs became more prominent to form a shrub tundra environment sometime before 8220 years bp gsc 2851 trees began to invade the area and the pinus contorta dominated coniferous forest extant in the area today began to form bog and fen vegetation invaded the shallow lake basin about this time as well to form the bog that occupies the basin to the present day

multiple episodes of tectono thermal disturbances in the huayangchuan u nb pb polymetallic deposit in the xiaoqinling region central china and their significances on metallogeny abstract the huayangchuan u nb pb polymetallic deposit is hosted in a suite of neoarchean to paleoproterozoic gneisses in the xiaoqinling region central china the deposit is composed mainly of discrete small scale carbonatite veins emplaced largely along shallow lying brittle fractures various regimes of deformation from ductile flow to brittle fracturing are documented in the deposit and its adjacent areas these include an earliest phase of contracting deformation d1 manifested as well developed boudinages abundant relict rootless folds and penetrative compositional bands i e gneissosity generally trending e w a subsequent phase of disperse dextral ductile shear d2 along the e w trending gneissosity and a following phase of general ne sw compression d3 resulting in local contraction deformation bands and abundant sinistral ductile shear along the e w trending gneissosity all of which are affected by an overwhelming nne ssw compression d4 with hemi ductile to brittle deformation behaviors the deformation after d4 is generally brittle and may arise from an earlier regime of dominant compression nw se d5 and a later regime of extensive extension d6 multiple thermal events are superimposed on gneisses as revealed by 40ar 39ar dating on biotite collected from various lithologies in the deposit and its adjacent areas which yields ages ranging from late triassic 238 203 ma through earliest cretaceous 139 134 ma and middle cretaceous 117 92 ma to latest cretaceous 72 ma and even early cenozoic 53 ma this sequence of thermal disturbances unlikely predates the d4 deformation given that it is the last ductile deformation experienced by the precambrian rocks ore bearing carbonatite veins have their shallowly lying attitudes consilient with the d4 and d5 deformation and ages compatible with the first two thermal overprints accordingly a two stage mineralization model is proposed for the huayangchuan polymetallic deposit with an early phase of ore veining in the late triassic to latest jurassic during the nearly n s collision between the south and north china blocks and a late phase of ore veining or more possibly reworking in the early cretaceous related to the yanshanian orogeny due to a generally nw directed subduction of the paleo pacific oceanic plate beneath the eastern asia continent

neoproterozoic tectonic evolution of south qinling china evidence from zircon ages and geochemistry of the yaolinghe volcanic rocks abstract the south qinling terrain is located at the northern margin of the yangtze block neoproterozoic volcanic sedimentary sequences of the yaolinghe group play the most significant role in studying the tectono magmatic evolution of the south qinling based on temporal and spatial geochemical variations the yaolinghe group can be divided into three volcanic cycles basaltic lavas of cycle 1 crystallized at 847 8 ma and exhibit typical island arc basalt characteristics with enrichment of liles th u and lrees depletion of hfses nb ta zr hf ti and homogeneous initial 143nd 144nd ratios ranging from 0 51162 to 0 51172 corresponding to initial nd values of 1 6 to 3 5 these features suggest that they were derived from a depleted mantle source during a subduction period volcanic rocks of cycle 2 show a complete lithological evolution from basalt through andesite to rhyolite without a significant gap of sio2 content they formed between 731 11 ma and 768 7 ma and display trace element signatures similar to arc volcanics with positive lile and negative hfse anomalies these basalts have lower initial 87sr 86sr ratios from 0 7030 to 0 7052 and higher initial 143nd 144nd ratios from 0 51172 to 0 51194 with positive initial nd values ranging from 0 9 to 5 3 whereas intercalated felsic rocks show lower initial 143nd 144nd ratios from 0 51150 to 0 51177 with initial nd values varying from 4 5 to 1 9 suggestive of metasomatic alteration of lithospheric mantle by slab derived fluids melts cycle 3 lavas show undepleted hfses nb ta zr hf and slightly enriched liles th u and ti concentrations they were generated in a rift related setting between 680 ma and 650 ma geochronological and geochemical evidence from lavas of the yaolinghe group suggest that the panxi hannan arc system extended to northern south qinling and the magmatism in the northern margin of the yangtze block evolved from arc to rift magmatism during the neoproterozoic

the north sea pole tide described through a tide surge numerical model monthly mean sea level values from tide gauges at the coasts of the north sea are compared with the monthly means from an operational tide surge numerical model for the time period 1955 1984 the model describes most of the variability at all frequencies except the annual most of the energy around the pole tide frequency is also reproduced by the model and since its tidal forcing does not include the equilibrium pole tide frequencies it is concluded that the deviations from the equilibrium pole tide are of meteorological origin the east west wind stress component is found to be energetic at this frequency thus providing the meteorological forcing the annual cycle due to steric effects is also estimated the meteorological correction modifies the determined sea level secular trends by up to 0 8mm yr for this 30 year period for stations in the eastern north sea

new aspects of the equilibrium pole tide summary we have developed a new spherical harmonic algorithm for the calculation of the loading and self gravitating equilibrium pole tide based on a suggestion of dahlen this approach minimizes the distortions in tide height caused by an incomplete representation of the ocean function with slight modification our approach easily could be used to compute self gravitating and loading luni solar tides as well using our algorithm we have compared the static pole tide with tide observations at a variety of locations around the world we find statistically significant evidence for pole tide enhancements in mid ocean as well as the shallow seas we have also re investigated the effect of the static tide on the chandler wobble period the difference between the wobble period of an oceanless elastic earth with a fluid core smith dahlen and the period of an earth minus static oceans yields a 7 4 day discrepancy we conclude from tide observations that much of the discrepancy can probably be accounted for by non equilibrium pole tide behaviour in the deep oceans

timing of collision of the north and south china blocks controversy and reconciliation the qinling orogen was formed by the joining of the north and south china blocks but the timing of their integration has been debated for more than a decade the controversies obviously stem from different approaches to reconstruction of the integration history two contrasting lines of evidence yield two different ages for collision of the north and south china blocks middle paleozoic and late triassic the shangdan suture within the qinling was regarded in previous studies as the trace along which the north and south china blocks collided our studies however demonstrate that there are two sutures within the qinling the well documented shangdan suture and the newly discovered mianlue suture we show in this paper that the late proterozoic to early mesozoic evolution of the qinling involved interactions between the north china block the north and south qinling orogens and the south china block the middle paleozoic collision along the shangdan suture as constrained by some evidence accreted only the south qinling orogen to the southern part i e the north qinling of the north china block contemporaneous rifting of the south china block and subsequent drifting separated the south qinling from the south china block during the middle to late paleozoic the separation of the south from the north china blocks is supported by other evidence in particular geomagnetic data evidently it was the late triassic collision of the south china block with the south qinling orogen along the mianlue suture that led to final integration of the north and south china blocks

a reconstruction of holocene geomorphology and climate western cypress hills alberta and saskatchewan received january 28 1990 revision accepted july 18 1990 the cypress hills of southwestern saskatchewan and southeastern alberta are a key area for quaternary research because the permanent lakes and coniferous forest are sources of proxy paleoenvironmental data generally not available on the surrounding northern great plains in this paper the holocene paleoclimate of the western cypress hills is reconstructed from the pollen and organic matter contents of a 9 6 m sediment core from harris lake saskatchewan this climatic history is considerably longer than others from the semiarid interior plains of canada chronological control consists of a basal conventional radiocarbon date of 9120

postglacial palaeoecology of the subalpine forest grassland ecotone of southwestern alberta new insights on vegetation and climate change in the canadian rocky mountains and adjacent foothills postglacial vegetation change at the subalpine forest grassland ecotone in the foothills of southwestern alberta is reconstructed from fossil pollen plant macrofossils and fossil charcoal the fossils were obtained from the sediments of a small lake chronological control for the record is provided by tephra analysis and the 14c dating of terrestrial plant macrofossils the fossil record is compared with the results from similar studies at sites in the rocky mountains and foothills of alberta and british columbia the comparison of vegetation change at the upper and lower elevational limits of the subalpine forest provides a record of changes in temperature and aridity over the holocene at 10 000 yr b p the study site supported a shrub and herb dominated vegetation picea pinus abies forests were present at mid to high elevations in the mountains and in the northern foothills by this time the climate in the southern foothills was likely arid but not severely cold a relatively open picea and pinus forest was established in the study area between 9400 yr b p and 8000 yr b p fire activity in the region was at a postglacial maximum during this period the transition to forest suggests moister conditions by 8000 yr b p the importance of members of the chenopodiaceae amaranthaceae and typha latifolia increased suggesting an onset of arid conditions characterised by low and fluctuating water levels in lakes between 8000 yr b p and 5000 yr b p the picea and pinus contorta forest at the study site was largely replaced by grassland and pinus flexilis at high elevation sites treeline was located above its modern position during this period little vegetation change is recorded at sites in the northern foothills and at mid elevations at this time the vegetation change in the southern foothills and at high elevations suggests both an elevational and latitudinal displacement of vegetation zones during the mid holocene warm and arid conditions were prevalent in southwestern alberta picea glauca pinus contorta populus tremuloides forest has occupied the site since 5000 yr b p when cooler and moister conditions were established

partial resetting of the u th pb systems in experimentally altered monazite nanoscale evidence of incomplete replacement alteration experiments on natural monazite crystals manangotry standard madagascar under alkali conditions at 300 400 500 and 600 c and 200 mpa were conducted to clarify mechanisms behind incomplete resetting of u th pb geochronological systems in monazite replaced by dissolution and precipitation processes above 400 c experimental products show typical replacement textures a compositionally distinct monazite rim referred as altered rim surrounds the primary monazite mnz1 isotopic and electron microprobe u th pb in situ dating of the altered rim yields intermediate ages between pristine monazite 555 ma and complete experimental resetting 0 ma lead is systematically detected in altered rims with concentration decreasing from 400 c to 600 c the origin of incomplete resetting is elucidated with transmission electron microscope images that reveal an incomplete replacement of mnz1 by a secondary monazite mnz2 within the altered rim with increasing temperature the size and volume of the mnz2 within the altered rim become more important because no structural pb or pb nanoinclusions were observed pb in the altered rim is attributed to the mnz1 component partial resetting of u th pb systems depends on the nanomixture of different mnz1 proportions in the analyzed volume and explains the higher rejuvenation at 600 c than at lower temperatures although microanalytical techniques have the spatial resolution to date micrometer sized rims they are unable to resolve a nanoscale mixture of pristine and secondary monazite that could occur in altered rims formed by fluid driven replacement especially at low temperatures porosity and or inclusions and complex age scattering in zoned monazite are significant markers that can indicate a possible nano sized partial replacement

late wisconsinan and holocene history of southwestern saskatchewan the late wisconsinan laurentide ice sheet reached the limit of glaciation along the north facing slope of the unglaciated part of the cypress hills nunatak but elsewhere around the cypress hills and wood mountain uplands of southwestern saskatchewan it did not reach the limit of glaciation an interval of deglaciation was followed by a readvance of the ice sheet about 15 ka to a position near the late wisconsinan limit and was marked by strong flow of keewatin ice from the north and weaker flow of hudson ice from the northeast final deglaciation resulted in the formation of glacial lakes around the cypress hills nunatak a network of ice marginal and subglacial trenches presently occupied by the frenchman valley and its tributaries was formed when these lakes drained along over and under ice towards the western part of the wood mountain upland to the east the main trench joined an ancestral part of frenchman valley along the ice free southern slopes of wood mountain upland meltwater from the ic

early mesozoic mo mineralization in the qinling orogen an overview abstract as one of the most important mo provinces in the world the qinling orogen is host to mainly late mesozoic late jurassic early cretaceous porphyry mo systems recently additional early mesozoic mainly triassic plus minor early jurassic mo deposits have been identified which occur as fault controlled quartz veins or as carbonatite veins and as such they are fundamentally different from the commonly observed porphyry systems furthermore early mesozoic porphyry systems are also present but they are different from those of late mesozoic age thus early mesozoic mo systems not only offer a new and comprehensive view of the mo metallogenesis but also provide unique insight into the tectonic evolution of the qinling orogen taking into consideration the role of mineral deposits as ideal probes of the geodynamic evolution the known early mesozoic mo deposits in qinling can be classified into three types based on their geological and geochemical features porphyry carbonatite and orogenic systems porphyry mo systems including porphyry porphyry skarn and intrusion related veins are spatially and genetically associated with granitic porphyries they display typical porphyry type alterations and are formed by magmatic water carbonatites are considered as mantle derived igneous rocks and mo mineralization is associated with magmatic fluids orogenic mo systems occur as fault controlled quartz lodes and the ore forming fluids are medium high temperature co2 rich metamorphic fluids spatially early mesozoic porphyry mo systems are concentrated in the western and middle part of the qinling orogen whereas carbonatite veins and orogenic mo systems are located in the northeastern part temporally orogenic mo deposits were the earliest mainly between 220 and 250 ma followed by carbonatite veins mainly between 205 and 225 ma and porphyry mo systems mainly between 190 and 205 ma with some exceptions there is generally a trend of decreasing deposit ages toward the western part of the orogen detailed comparison reveals that the early mesozoic porphyry mo systems in the qinling orogen are different from the late mesozoic ones in terms of their economic importance spatial distribution ore causative intrusions hydrothermal alteration and the ore forming fluids to explain the above geological and geochemical features the triassic qinling is considered as an active continental margin caused by the northward subduction of the mian lue oceanic plate a transition from continental arc to back arc basin is suggested for the formation of triassic orogenic and carbonatite vein mo deposits whereas continental arc is host to the early mesozoic porphyry mo systems

geological characteristics and molybdenite re os isotopic dating of huangshuian carbonatite vein type mo pb deposit in songxian county henan province the huangshuian large sized deposit in songxian country of henan province is one of the typical mo pb carbonatite vein type deposits in the east qinling molybdenum belt the ore bodies that occur in the quartz calcite carbonatite dykes hosted in the metamorphic rocks of the taihua group are veinlike stratoid or lenticular in form molybdenite as the main metallic mineral in the deposit assumes laminated disseminated and crumb mineralization types in the quartz calcite carbonatite dykes the particular mineral association of galena molybdenum quartz calcite was formed in the main metallogenic phase the main alterationsof the wall rock include silicification k feldspathization pyritization fluoritization and anhydritization eight molybdenite bearing samples were selected for precise re os dating which yielded model ages ranging from 210 9 3 8 ma to 207 9 3 0 ma and an isochron age of 208 4 3 6 ma the deposit was formed in the late triassic th re content of molybdenite is 60 12 137 79 10 6 indicating that they were mainly derived from mantl sources the deposit was formed in the extensional period of the post collision orogenic process between north china and yangtze cratons at the extensional stage the carbonate melt solution that originated from the enriched mantle carried ore forming metals such as molybdenum and lead upward along fractures and eventually precipitated in the suitable place to form ore deposit

two episodes of ree mineralization in the qinling orogenic belt central china in situ u th pb dating of bastnasite and monazite recent exploration revealed a number of rare earth element ree deposits that are distributed along the qinling orogenic belt central china these deposits have an estimated total reserve of about 2 mt ree2o3 thus making this belt a world class ree metallogenic province understanding the metallogenesis of the belt requires direct dating of ree minerals in this study la icp ms u th pb dating on bastnasite and monazite from the huangshuian taipingzhen and miaoya deposits in different units of the belt was used to precisely determine the timing of the ree mineralization the huangshuian deposit in the north is a carbonatite related mo ree deposit in which the ree minerals are closely associated with molybdenite after correction for common pb and excessed 206pb decayed from 230th a weighted average 206pb 238u age of 207 4 ma n 17 mswd 1 9 is obtained for bastnasite grains from this deposit such an age is slightly younger than that of the final collision peak at 230 220 ma of the qinling orogenic belt thus indicating that the mo ree mineralization is likely related to a post collisional extension setting the taipingzhen ree deposit in the middle contains sheet like ore bodies composed of veins where bastnasite the dominant ree mineral is closely associated with quartz fluorite and barite in situ bastnasite u th pb dating shows that the ree mineralization in this deposit has formed at 421 7 ma n 17 mswd 1 5 synchronous with extension related magmatism in the region the miaoya deposit in the south is the largest one in the belt and it is essentially a ree mineralized syenite carbonatite complex in this deposit the monazite grains are closely associated with major minerals of the syenites or carbonatites e g k feldspar or calcite but commonly exhibit complex internal textures different domains of monazite yield two groups of u pb ages at 414 11 ma n 5 mswd 0 91 and 231 2 ma n 21 mswd 3 1 whereas the bastnasite has an age of 206 4 ma n 14 mswd 1 5 the early age of 414 ma is obtained from homogenous monazite grains and in good agreement with zircon u pb ages of the miaoya syenite carbonatite complex and thus is considered to represent the timing of the major ree mineralization in the deposit the younger ages of 231 206 ma are obtained from monazite grains with complex internal textures and bastnasite in late veinlets thus recording secondary consecutive ree remobilization events likely related to the compression process during formation of the qinling orogenic belt our new u th pb ages in combination with previously geochronological data demonstrate that there are two episodes of ree mineralization at 440 410 ma and 220 200 ma in the qinling orogenic belt

quaternary stratigraphy of the prophet river northeastern british columbiathis article is one of a selection of papers published in this special issue on the theme geology of northeastern british columbia and northwestern alberta diamonds shallow gas gravel and glaciers exposures in the prophet river valley in northeast british columbia provide a unique glimpse into the quaternary history of the northwest canadian boreal plains the region shows evidence of late wisconsinan laurentide glaciation in the form of widespread till containing abundant erratic clasts derived from the canadian shield vertical sections along the prophet river expose non glacial and advance glacial sediments below this till pre late wisconsinan non glacial or interglacial floodplain sediments are interbedded with fluvial gravels at many sites macrofossils within horizontally laminated organic rich black clay and silt indicate deposition on the floodplain of the paleo prophet river within an oxbow lake the climate during deposition is interpreted to be similar to present supporting a dominantly spruce forest wood obtained from eight sites provided non finite radiocarbon ages and one sample provided an age of 49 300 2000 bp which is also considered non finite glaciolacustrine clays and s

correlation between some major geological events and resonances between the free core nutation and luni solar tidal waves summary we suggest that some major geological events observed during the history of the earth such as the worldwide continental crust forming episodes could result from very large oscillations of the fluid core induced by the luni solar tidal forces as a consequence of the secular deceleration of the time dependent axial rotation of the earth the rotational free core nutation of the fluid core and some solar tidal waves were in resonance around 3 0 gyr 1 8 gyr and 300 myr ago the associated viscomagnetic frictional power may be converted into heat and may on the one hand create instability of the d thermal layer leading to the generation of a deep mantle plume and on the other hand increase the temperature at the top and bottom of the fluid core perturbing the core dynamo processes

late quaternary landscape history and archaeology in the ice free corridor some recent results from alberta abstract multidisciplinary research programs conducted within the alberta portion of the ice free corridor since 1986 as part of the archaeological survey s first albertans project have used studies of palaeogeography and palaeoenvironments to formulate archaeological search strategies this approach has resulted in the discovery of two new important sites saskatoon mountain ghqt 4 and the james pass meadow complex ekpu 3 to 9 that are yielding information on terminal late wisconsinan early holocene human occupation of the corridor both sites are dated by ams or conventional radiocarbon dates to the millennium 10 000 9 000 bp in the fifteen years since the 1978 amqua conference on the corridor other researchers have identified four additional significant paleo indian sites in this region so far none confirm human occupation of the ice free corridor region before about 11 000 bp

paraglacial origin for terraced river sediments in bow valley alberta fluvial terraces flank the course of the bow river for 100 km from the eastern margin of the rocky mountain front ranges to calgary and beyond the terraces are cut predominantly in gravel fill which ranges in thickness from approximately 10 m in the calgary area to 30 m near the mountain front sedimentary structures in the gravels indicate a braided stream sedimentary environment in contrast to the present quasi stable sinuous single channel form of the bow river radiocarbon dates on ungulate remains from the gravels indicate the main period of fill occurred ca 11 500 10 000 rcybp radiocarbon years before present previous workers have postulated that the gravels originated directly as outwash from a glacial advance to or beyond the mountain front this explanation has been refuted by recent stratigraphic and palynological investigations a complex nonglaciofluvial origin is proposed for these terraces and the sediments that form them the last glacial advance to reach the mountain front was well

collision leading to multiple stage large scale extrusion in the qinling orogen insights from the mianlue suture abstract the geologic framework of the phanerozoic qinling dabie orogen was built up through two major suturing events of three blocks from north to south these include the north china craton including the north qinling block the qinling dabie microblock and the south china craton including the bikou block separated by the shangdan and mianlue sutures the mianlue suture zone contains evidence for mesozoic extrusion tectonics in the form of major strike slip border faults surrounding basement blocks a late paleozoic ophiolite and a ca 240 200 ma thrust belt that reformed by 200 150 ma thrusts during a type intracontinental subduction the regional map pattern shows that the blocks are surrounded by complexly deformed devonian to early triassic metasandstones and metapelites forming a regional scale block in matrix melange fabric five distinct tectonic units have been recognized in the belt 1 basement blocks including two types of precambrian basement crystalline and transitional 2 continental margin slices including early paleozoic strata and late paleozoic fluviodeltaic sedimentary rocks proximal and distal fan clastics reflecting the development of a north facing rift margin on the edge of the south china plate 3 out of sequence oceanic crustal slices including strongly deformed postrift deep water sedimentary rocks sheeted dikes basalts and mafic ultramafic cumulates of a late paleozoic ophiolite suite developing independent of the rift margin in a separate basin 4 out of sequence island arc slices 5 accretionary wedge slices all the tectonic units were deformed during three geometrically distinct deformation episodes d 1 d 2 and d 3 during 240 200 ma units 2 4 involved southward thrusting and vertical then southward extrusion of about 20 km of horizontal displacement above the autochthonous basement during the d 1 episode thrust slices 20 km south of the mianlue suture are related to this vertical extrusion due to the same rock assemblages ages and kinematics the d 2 and d 3 episodes folded all the units in a thick skinned style about east west d 2 and west northwest d 3 axes in the mianlue suture zone an early foreland propagating sequence of accretion of late paleozoic rocks deposited above the yangtze craton is not involved in d 1 deformation but is temporally equivalent to the d 2 and d 3 deformation in the mianlue suture two stages of strike slip faulting mainly occurred at the end of d 2 and d 3 respectively during d 2 deformation the bikou block was obliquely indented to the ese into the mianlue suture rather than being thrust over the mianlue suture from the north as a part of the qinling dabie microblock during d 3 deformation however the bikou block was bounded by the south boundary fault of the mianlue suture and the yangpingguan fault on the south these faults are coeval strike slip faults but of opposite senses and accommodated minor southwestward extrusion of the bikou block into songpan ganze orogen the other basement blocks north of the mianlue suture were extruded eastward by about 20 km of lateral displacement based on the offset of the wudang dome during the d 3 episode due to the northeastward indentation of the hannan complex of the south china craton post d 3 emplacement of granite cutting across the strike slip faults such as the mianlue suture provides a minimum age of 200 ma for d 3 deformation therefore based on insights from the evolution of the mianlue suture the d 2 and d 3 episodes in the mianlue suture and its neighbors are not responsible for and associated with the two stage extrusion of the dabie uhp hp terranes from the foping dome to the present erosional surface more than 350 km

mineralogical and geochemical constraints on mobilization and mineralization of rare earth elements in the lala fe cu mo ree deposit sw china the lala fe cu mo ree deposit in the northern kangdian iocg metallogenic province sw china has a paragenetic sequence that includes pre ore na alteration stage i fe p mineralization stage ii and sulfide mineralization stage iii rare earth element ree minerals which are chiefly monazite parasite and bastnasite with minor xenotime are associated with sulfide mineralization these ree minerals together with biotite muscovite and calcite are accompanied with k ca carbonate alteration of stage iii where magnetite and apatite of stage ii are overprinted by minerals of stage iii the apatite grains are commonly embayed or eroded and contain abundant rounded to subrounded and needle like inclusions of monazite and minor bastnasite calcite and sulfide minerals these monazite bearing apatite grains are texturally similar to metasomatized apatite in the laboratory and can be attributed to the formation from stage ii apatite via a dissolution precipitation process during fluid infiltration the monazite bearing apatite has ree contents and la sm ratios much lower than the original stage ii apatite suggesting that rees were leached and mobilized from this stage ii apatite and that these processes were responsible for the formation of monazite inclusions within the apatite hosts the monazite inclusions have compositions similar to those of stage iii monazite suggesting that rees in stage ii apatite were mobilized by stage iii fluids consistent with occurrences of sulfide and calcite inclusions within the apatite mass balance analysis using bulk compositional data for host rocks that underwent k ca carbonate alteration indicates that rees of the hosting rocks were also mobilized and that up to 70 percent of the light rees were leached out during alteration therefore ree mobilization recorded in apatite grains and country rocks support a model in which the country rocks were important sources for rees in the lala deposit compositions of amphibole and biotite together with previously acquired fluid inclusion data demonstrate that stage iii fluids are dominated by na and cl but had higher k co2 or hco3 and co32 and hf hcl fugacity and lower salinity nacl than stage ii fluids elevated k and co2 in stage iii fluids or associated k carbonate alteration is proposed to be important for extensive ree mobilization on country rocks the rees leached from country rocks are inferred to have been transported as chloride complexes prior to being deposited as ree minerals deposition of ree minerals from stage iii fluids was likely triggered by mixing with external relatively low temperature f rich and high ph fluids and or by local interaction with carbonate host rocks we suggest that the common association of rees with cu ores in many iocg deposits is related to the unique nature of the cu mineralizing fluids

high resolution 5 μm u th pb isotope dating of monazite with excimer laser ablation ela icpms abstract monazite lree po 4 a common accessory mineral in magmatic and metamorphic rocks is complementary to zircon in u th pb geochronology because the mineral can record successive growth phases it is useful for unravelling complex geological histories a high spatial resolution is required to identify contrasted age domains that may occur at the crystal scale bulk mineral techniques such as id tims applied to single monazite grains recording multiple overgrowths or isotope resetting can result in partly scattered discordant analytical points that produce inaccurate intercept ages laser ablation la icpms has been demonstrated to be a useful technique for u th pb dating of zircons and this study tests its analytical capabilities for dating monazite a sector field high resolution icpms coupled with a 193 nm arf excimer laser ablation microprobe is capable of achieving a high spatial resolution and producing stable and reliable isotope measurements the u th pb systematic was applied to monazite grains from several samples a lower palaeozoic lens from high grade terrains in southern madagascar neogene hydrothermal crystals from the western alps a palaeoproterozoic very high temperature granulite from central madagascar and a variscan leucogranite from spain directly on a polished thin section the major aim was to compare and or reproduce tims and emp ages of monazite from a variety of settings and ages the three independent 206 pb 238 u 207 pb 235 u and 208 pb 232 th ratios and ages were calculated isotope fractionation effects mass bias laser induced fractionation were corrected using a chemically homogeneous and u pb concordant monazite as external standard this study demonstrates that excimer laser ablation ela icpms allows u th pb dating of monazite with a high level of repeatability accuracy and precision as well as rapidity of analysis a spatial resolution almost comparable to that of emp in terms of crater width 5 m produced precise 208 pb 232 th 206 pb 238 u and 207 pb 235 u ratios for dating palaeozoic to precambrian monazites the advantages of ela icpms isotope dating are precision accuracy and the ability to detect discordance in the case of late miocene hydrothermal monazites from the alps a larger spot size of 25 m diameter is required and precise and accurate ages were obtained only for 208 pb 232 th systematics results from the variscan granite show that in situ u th pb dating of monazites with ela icpms is possible using a 5 m spot directly on thin sections so that age data can be placed in a textural context

evidence of cordilleran late wisconsinan glaciers in the ice free corridor abstract glaciers flowing down the athabasca river valley during the last glacial period were fed both by local montane glaciers and by cordilleran ice moving easterly across the continental divide from british columbia resulting in a major eastward surge into the ice free corridor the timing of this event has been disputed for many years and has important implications for the study of paleoenvironmental conditions and the north south migration of biota in the corridor chronologic and lithostratigraphic data from the jasper region suggest that this event took place in the late wisconsinan subtill radiocarbon dates on wood in the athabasca river valley indicate that non glacial alluvial sediments began accumulating there sometime before 48 ka a finite date of 29 100 560 bp gsc 3792 on wood under till near jasper provides a maximum age for the onset of the last glaciation in the region although ice from west of the rocky mountain trench probably did not cross the continental divide until after 21 5 ka the occurrence of supraglacial metamorphic erratics as well as the distribution and nature of mapped glacial deposits and the trend of subglacial paleoflow indicators in the region east of the rockies suggests that late wisconsinan glaciers flowing from the mountains coalesced with laurentide glaciers and were deflected southeasterly along the mountain front an even more extensive glacial event may have effected the region in pre late wisconsinan times the model of late wisconsinan glaciation presented here is in agreement with all known radiocarbon data from the area and is especially attractive when supratill dates on non woody lacustrine organics are viewed in light of possible contamination by old carbon

tectonics of the qinling central china tectonostratigraphy geochronology and deformation history abstract the qinling orogen preserves a record of late mid proterozoic to cenozoic tectonism in central china high pressure metamorphism and ophiolite emplacement songshugou ophiolite assembled the yangtze craton including the lower qinling unit into rodinia during the 1 0 ga grenvillian orogeny the lower qinling unit then rifted from the yangtze craton at 0 7 ga subsequent intra oceanic arc formation at 470 490 ma was followed by accretion of the lower qinling unit first to the intra oceanic arc and then to the sino korea craton subduction then imprinted a 400 ma andean type magmatic arc onto all units north of the northern liuling unit oblique subduction created silurian devonian wnw trending sinistral transpressive wrench zones e g lo nan shang dan and late permian early triassic subduction reactivated them in dextral transpression lo nan shang xiang shang dan and subducted the northern edge of the yangtze craton exhumation of the cratonal edge formed the wudang metamorphic core complex during dominantly pure shear crustal extension at 230 235 ma post collisional south directed shortening continued through the early jurassic cretaceous reactivation of the qinling orogen started with nw se sinistral transtension coeval with large scale early cretaceous crustal extension and sinistral transtension in the northern dabie shan it presumably resulted from the combined effects of the siberia mongolia sino korean and lhasa west burma qiangtang indochina collisions and pacific subduction regional dextral wrenching was active within a ne sw extensional regime between 60 and 100 ma an early cretaceous andean type continental magmatic arc with widespread early cretaceous magmatism and back arc extension was overprinted by shortening related to the collision of yangtze indochina block with the west philippines block strike slip and normal faults associated with eocene half graben basins record paleogene nne ssw contraction and wnw ese extension the neogene is characterized by normal faults and nne trending sub horizontal extension pleistocene quaternary nw se extension and ne sw contraction comprises sinistral strike slip faults and is part of the nw se extension imposed across eastern asia by the india asia collision

the period and q of the chandler wobble summary we have extended our calculation of the theoretical period of the chandler wobble to account for the non hydrostatic portion of the earth s equatorial bulge and the effect of the fluid core upon the lengthening of the period due to the pole tide we find the theoretical period of a realistic perfectly elastic earth with an equilibrium pole tide to be 426 7 sidereal days which is 8 5 day shorter than the observed period of 435 2 day using rayleigh s principle for a rotating earth we exploit this discrepancy together with the observed chandler q to place constraints on the frequency dependence of mantle anelasticity if q in the mantle varies with frequency u as u between 30 s and 14 months and if q in the lower mantle is of order 225 at 30 s we find that 0 04 5 a 5 0 1 1 if instead q in the lower mantle is of order 350 near 200 s we find that 0 11 5 a 0 19 in all cases these limits arise from exceeding the 68 per cent confidence limits of 2 6 day in the observed period since slight departures from an equilibrium pole tide affect the q much more strongly than the period we believe these limits to be robust

hydrothermal alteration of magmatic zircon related to nacl rich brines diffusion reaction and dissolution reprecipitation processes magmatic zircon from altered gabbros adjacent to the 1 07 ga lala fe cu deposit sw china was modified by nacl rich brines related to the fe cu mineralization the modified zircon grains are composed mostly of both inclusion free and porous domains and some grains also have overgrowth rims the inclusion free domains commonly overgrown by the porous domains are roughly homogeneous under bse imaging but display oscillatory or sector zoning under cl imaging in contrast the porous domains are distinctly mosaic like under cl imaging and contain abundant pores and mineral inclusions such as thorite xenotime ree rich phases actinolite albite biotite and calcite the inclusion free domains have concentrations of non formula elements for example al ca and fe much higher than the magmatic zircon and are thus interpreted to be products of interaction between magmatic zircon possibly metamictized and the fluids via a diffusion reaction process however these resultant domains have retained the th and u contents ree patterns u pb ages and hf isotopes of the precursor magmatic zircon on the other hand the porous domains have stoichiometric end member compositions that is lowered th u ree y and p and given that they are porous and inclusion rich we proposed that they have formed from the precursor element rich inclusion free domains or magmatic zircon via a fluid induced dissolution reprecipitation process it is notable that the porous domains retained the 177hf 176hf ratios of the precursors but possess modified and meaningless u pb ages instead a meaningful u pb age 1006 62 ma similar to the timing of the lala deposit is well recorded by the overgrowth rims with distinctly high lrees la 50 700 ppm and elevated hf isotopic ratios our new results reveal that in the presence of the nacl rich brines the nature of the precursor magmatic zircon that is high element budgets and or metamictization plays a key role on hydrothermal alteration of zircon

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

geologic framework and tectonic evolution of the qinling orogen central china abstract the geologic framework of the qinling orogen was built up through interplay of three blocks the north china block including the north qinling the south qinling and the south china block separated by the shangdan and mianlue sutures the shangdan suture resulted from middle paleozoic collision of the north china block and the south qinling the mianlue suture resulted from late triassic collision of the south qinling and the south china block present upper crust of the qinling is structured dominantly by thrust fold systems the north qinling displays thick skinned deformation with crystalline basement involved whilst the south qinling is characterized by thin skinned thrusts and folds detached above the lower sinian two types of precambrian basement crystalline and transitional are defined according to lithology and metamorphic grade and different in age stratigraphic and sedimentary architecture is characterized by distinct zonation the qinling orogen experienced a prolonged continental divergence and convergence between blocks during the period from late neoproterozoic to early paleozoic times the south qinling was the northern margin of the south china block and the north qinling was the southern margin of the north china block separated by a proto tethyan qinling ocean the north qinling evolved into an active margin when the proto tethyan qinling ocean subducted northward during ordovician time collision of the south and north qinling took place in middle paleozoic along the shangdan suture synchronous with the collision rifting occurred at the southern rim of the south qinling and was followed by the opening of the paleo tethyan qinling ocean during the late paleozoic resulting in the splitting of the south china block from the south qinling collision of the south qinling and the south china block came about in the late triassic along the mianlue suture the late triassic collisional orogeny caused extensive fold and thrust deformation and granitoid intrusions throughout the qinling and led to final amalgamation of the north and south china blocks

the self consistent dynamic pole tide in non global oceans summary fluid dynamic theories of the pole tide are in conflict with pole tide observations the former predict that the oceanic response to the chandler wobble should be nearly static while the latter reveal the tide to possess significant non equilibrium characteristics resolution of the conflict would determine whether mantle anelasticity or non equilibrium oceans is responsible for a measurable contribution to the chandler period it is possible that resolution might be achieved through a more exact mathematical investigation of pole tide fluid dynamics than theories have carried out to date the theories have also neglected to consider a unique property of the pole tide its ability to lengthen the period of its own forcing function this property implies that the pole tide characteristics and effects on wobble cannot be correctly determined unless the tide and wobble equations are jointly solved this work constitutes a first attempt to determine accurately and self consistently the nature of the pole tide and its effects on the chandler wobble the laplace tidal equations modified by the addition of bottom friction but with no simplifying approximations are employed together with the liouville equations to elucidate pole tide characteristics this work is a first attempt because the earth model chosen is a crude one consisting of global oceans of uniform depth overlying a rigid mantle with a fluid core results for this model suggest that departures of the pole tide from equilibrium may indeed be minimal the relevance of these results to the actual pole tide however must await the application of our self consistent and more exact dynamical theory to the situation of realistic oceans

age and tectonic setting of late archean greenstone gneiss terrain in henan province china as revealed by single grain zircon dating the authors report precise u pb zircon ages for single grains of a metarhyodacite from the late archean dengfeng greenstone belt in henan province china near the southern margin of the north china craton most grains belong to an igneous population whose u pb isotopic systematics define a straight line intersecting concordia at 2512 12 ma and this is interpreted as the time of crystallization of the original greenstone volcanics several grains are distinctly older between 2576 9 and 2945 44 ma and the authors interpret the older grains as xenocrysts of pre greenstone continental crust that provide evidence for crustal derivation or crustal contamination of the original rhyodacitic lava the xenocrysts suggest evolution of the dengfeng greenstone belt in a continental environment that may be represented by the taihua high grade gneisses bordering the dengfeng greenstones and for which the authors obtained ages of 2806 7 and 2841 6 ma the data add evidence to the now widely held concept that most archean greenstones developed on or near older continental crust and were therefore prone to crustal contamination in such cases conventional zircon dating may not always record the precise age of rock formation

fluid mediated partial alteration in monazite the role of coupled dissolution reprecipitation in element redistribution and mass transfer monazite ce lree th u ca p si o4 with complex zoning in th and other elements is commonly observed in metamorphic and igneous rocks the hypothesis that this alteration is a product of fluid mediated element mass transfer has been tested in the piston cylinder press caf2 assembly cylindrical graphite oven at 1 000 mpa and 900 c and in cold seal autoclaves on a hydrothermal line at 500 mpa and 600 c experiments included a relatively homogeneous monazite ce 7 8 wt tho2 from a heavy mineral sand plus a series of alkali bearing fluids including 2n naoh 2n koh and na2si2o5 h2o experiments were conducted using bse imaging emp analysis and both tem and hrtem a subset of monazite grains from each experiment show evidence of partial alteration in the form of areas enriched in th si with sharp curvilinear compositional boundaries extending from the grain rim into the monazite interior these thsio4 enriched textures are similar to those commonly seen in natural examples of metasomatised monazite in both magmatic and metamorphic rocks in the na2si2o5 h2o experiments scarce inclusions of britholite formed in the altered monazite the altered monazite is also characterised by strong depletion in pb ca and y thorium and si mobility coupled with the formation of britholite inclusions during partial alteration in the monazite grain is considered to be the product of fluid aided coupled dissolution reprecipitation as opposed to solid state diffusion since other fluids including nacl and kcl brines do not result in the formation of these textures the experimental replication of thsio4 enriched areas in the monazite strongly suggests that similar textures in monazite observed in nature are fluid induced specifically by alkali bearing fluids if true complex metasomatically induced textures in monazite could yield information concerning the nature of the fluid responsible for their formation as well as allow for the dating of the metasomatic event presuming that all the original radiogenic pb has been removed

the rotation of the ocean solid earth system it is shown that the long period highly elliptical markowitz wobble can be viewed as a natural wobble of the coupled mantle ocean system from a rotational point of view oceanic wobble is possible even if the oceans respond in an equilibrium manner to wobble because the oceans are nonglobal and a thin layer either of the latter conditions or an oceanic response which is nonequilibrium can maintain the separation of rotation and figure axes constituting wobble characteristics of the uncoupled bodies are first determined the inertia tensor of the oceans yields an oceanic body whose free wobble is retrograde and short period under the assumption of an equilibrium fluid response it also yields an oceanless earth whose precessional constant more nearly equals the hydrostatic rather than the observed whole earth value the equations governing wobbles of a coupled two body system rigid or deformable are developed and referred to the same wobbling coordinate system solutions are found for various general types of coupling for a deformable system the retrograde character of the free oceanic wobble leads to coupled motions which are at best undamped and at worst unstably damped those types of coupling which avoid unstable rotational behavior and also generate one wobble mode with the characteristics of the chandler wobble predict a second wobble mode with the period and retrograde or marginally prograde sense of the markowitz wobble since those couples are nondissipative attenuation of the wobbles is presumably achieved by a combination of shallow sea interactions and internal friction within mantle and oceans some of the amplitude characteristics predicted for the wobble modes fail to match observations adequately resolution of these disparities within the coupled system framework may enhance our understanding of wobble excitation and the open ocean pole tide

mesozoic molybdenum deposits in the east qinling dabie orogenic belt characteristics and tectonic settings abstract the east qinling dabie orogenic belt accommodates the largest mo ore district in the world it contains 8 43 mt of proven mo metal reserves which accounts for 66 of the total proven chinese mo reserves the mo ore district includes 24 deposits and 12 occurrences with four major types of mo mineral systems i e porphyry porphyry skarn skarn and hydrothermal veins the latter can be further subdivided into quartz vein and carbonatite vein types although mo mineralization in the belt began in the paleoproterozoic 1680 24 to 2044 14 ma all economically significant deposits were formed during the mesozoic re os dating of molybdenite has shown that there are three episodes of mo mineralization i e late triassic 233 221 ma late jurassic to early cretaceous 148 138 ma and early to middle cretaceous 131 112 ma late triassic mo deposits developed as molybdenite quartz veins and carbonatite vein types stable isotope systematics c o s and high contents of re and sr indicate that the carbonatite mo veins are mantle derived porphyry and porphyry skarn mo mineral deposits were formed in the late jurassic to early cretaceous and early to middle cretaceous the late jurassic to early cretaceous granite porphyries that are associated with the mo deposits usually occupy less than 1 5 km2 at the surface and are situated in the east qinling area far west of china s continental margin on the other hand the early to middle cretaceous batholiths and granite porphyries with associated mo deposits are located in the dabieshan area and eastern part of the east qinling area the late jurassic to early creataceous granitoids and related mo deposits possibly formed in a back arc extensional setting of the eurasian continental margin which was probably triggered by the oblique subduction of the izanagi plate the early to middle cretaceous batholiths and granite porphyries are linked to the tectonic regime of lithospheric thinning asthenospheric upwelling and partial melting of the crust induced by a change in izanagi plate motion parallel to the continent margin in the east qinling dabie belt there are vein type pb zn ag deposits surrounding porphyry and or porphyry skarn mo w deposits forming well defined ore clusters the same spatial arrangement i e porphyry mo stockworks and outlying pb zn ag ore veins is also observed at the deposit scale thus mo porphyry stockworks and distal polymetallic veins belong to the same ore system and may reflect an outward temperature decrease from the highly fractionated granite plutons both porphyry stockworks and polymetallic veins can be used as vectors for further prospecting

petrogenesis and tectonic implications of the early paleozoic intermediate and mafic intrusions in the south qinling belt central china constraints from geochemistry zircon u pb geochronology and hf isotopes abstract the characteristics and tectonic implications of the early paleozoic alkaline magmatic belt in the south qinling belt which was originally part of the northern yangtze block prior the devonian have remained elusive whether this magmatic belt is related to rifting of the passive continental margin to back arc extension in the active continental margin or to mantle plume activity is debated understanding the origin and geodynamic significance of this magmatic belt can provide new constraints on the early paleozoic tectonic evolution of the northern yangtze block here we present zircon u pb data from a suite of nepheline syenite quartz syenite diabase and gabbro from the northern margin of the yangtze block which show an age range of ca 435 440 ma the ehf t values of the intermediate rocks up to 16 59 suggest magma generation from depleted mantle sources and new crustal growth geochemically the syenites showing high total alkali contents and are enriched in lree lile rb ba and k and hfse th u nb ta zr and hf with depletion in sr p and ti the intermediate and mafic magmatic rocks were generated through magmas sourced from the subcontinental lithospheric mantle metasomatized by asthenospheric mantle and underwent fractional crystallization without significant crustal contamination the magmatic suite represents a significant phase of crustal extension in the northern margin of the yangtze block

late quaternary vegetation history of wilcox pass jasper national park alberta five pollen zones are recognized in a radiocarbon and tephra dated core from an alpine site at an elevation of ca 2355 masl in wilcox pass jasper national park and record late quaternary vegetation history the two lower zones underlie material dated at 9600 305 yr b p gx 8785 and record early postglacial vegetation the basal zone wp1 containing an artemisia dominated assemblage represents tundra vegetation after deglaciation in zone wp2 arboreal pollen mainly diploxylon pine becomes dominant and represents a lodgepole pine forest the pollen assemblage of zone wp3 which initially contains large amounts of haploxylon pine as well as picea and abies pollen shows a transition from a forest with large amounts of whitebarkpine to vegetation resembling present day subalpine forest during this phase temperatures were probably warmer than present zone wp4 beginning after the influx of mazama tephra 6800 yr b p to the site records an expansion of the subalpine forest to higher elevations with a warmer climate in zone wp5 beginning about 2800 yr b p values of the main arboreal components fluctuate indicating cooler temperatures and less favourable environmental conditions probably associated with neoglacial ice advances the environmental trends observed from this record accord with those from other vegetation records in the canadian rockies

stratigraphy and correlation of the glacial deposits on the montana plains till units representing at least three pre illinoian continental glaciations at least one illinoian glaciation and a late wisconsin glaciation have been identified on the montana plains early wisconsin or middle wisconsin till units have not been identified the southernmost limit of late wisconsin glaciation is in montana more than 170 km south of the lethbridge moraine in alberta canada figs 1 and 2 an interpretation that the lethbridge moraine is the limit of late wisconsin glaciation stalker 1977 1980 1983b stalker and harrison 1977 rutter 1980 1981 jackson 1983 is incompatible with stratigraphic and morphologic evidence from montana

peatland development in relation to holocene climatic change in manitoba and saskatchewan canada two peat cores from the southern boreal forest in south central manitoba and central saskatchewan canada were analyzed for microfossils macrofossils and physicochemical properties regional vegetation and local peatland development at these sites show the influence of warm and dry climatic conditions during the middle holocene pollen assemblages at the base of the manitoba site indicate the presence of grassland parkland vegetation in the area prior to 4230 bp at the saskatchewan site boreal forest was present throughout the development of the peatland from before 5020 bp to present both the manitoba and saskatchewan records suggest a more open deciduous character of the regional vegetation cover during the middle holocene in the southernmost part of the expanding boreal forest in comparison with the modern southern mixed wood boreal forest the presence of a typha latifolia domimted marsh phase in the initial stages of development of both peatlands is indicative of marked water level fluctuati

zircon trace element and isotopic sr nd hf pb effects of assimilation fractional crystallization of pegmatite magma a case study of the guangshigou biotite pegmatites from the north qinling orogen central china abstract evidence for open system magmatic processes related to wallrock assimilation accompanied by fractional crystallization afc is present in the guangshigou biotite pegmatites north qinling orogen the biotite pegmatite gneiss contacts generally coincide with the greatest enrichment of u and th zircon u pb dating constrains the crystallization ages of the biotite pegmatite rim zone 415 2 6 ma internal zone 413 5 2 5 ma in line with a pyrite pb pb isochron age 413 22 ma metamict areas in zircon show generally elevated concentrations of trace elements and expulsion of radioactive pb internal zone samples representing uncontaminated magma have negative to positive zircon 413 ma ehf t 1 53 3 24 low end t values 2 4 and old hf and nd model ages tdm2 1 5 1 19 ga t2dm 1 35 ga respectively indicating a dominantly recycled mesoproterozoic lower crustal material with involvement of some juvenile materials in the source region the magmatic oxygen fugacity fo2 and crystallization temperatures ranges from 24 81 to 13 34 of log fo2 and 570 c to 793 c respectively compared to the internal zone pegmatite rim samples display a variable and lower end t values 3 9 to 2 8 and t2dm 1 47 1 37 ga but similar hf isotopic compositions favouring a three component isotopic mixing model recycled mesoproterozoic lower crust materials juvenile materials and host gneiss pronounced variations of ti y u th hf and ree concentrations in zircon from grain to grain in individual samples and from area to area within individual grains suggest a fluctuating crystallization environment in hybridized magma from which the rim hosted zircons crystallized variable and high radiogenic pb ratios of pyrites forming in the hybridized magma were inherited from the matrix zircons from both zones exhibit similar hf isotope patterns indicating the rim hosted zircons crystallized during the early stage of hybridization of magma however the heterogeneous nd isotopic composition in individual pegmatites imply an incorporation of wallrock derived melt with less radiogenic nd

early paleozoic tectonic evolution of the north qinling orogenic belt in central china insights on continental deep subduction and multiphase exhumation abstract the north qinling orogenic belt is an important component of qinling composite orogen in central china high pressure and ultra high pressure hp uhp rocks occur as lenses or layers surrounded by gneissic rocks in the northern central and southern qinling complex of the north qinling belt considered to have formed through deep continental subduction the magmatic protoliths of the hp uhp metamorphic rocks show formation ages ca 800 ma geochemical characteristics and pb nd isotopic compositions similar to those of the neoproterozoic igneous rocks of the south qinling belt continental materials of the south qinling belt were dragged down to mantle depths by the shangdan oceanic crust subducted and subjected to hp uhp metamorphism at ca 500 ma the erlangping and kuanping backarc basin formed in response to subduction of the shangdan ocean and might have developed into a limited small ocean basin at ca 500 ma the hp uhp rocks yielded retrograde metamorphic ages of ca 470 450 ma and ca 420 400 ma these ages are identical to the age of magmatic events in the north qinling hp uhp belt at 500 ma 450 ma and 420 ma related to deep subduction collision slab breakoff and crustal thinning during post collisional extension the dominant ca 500 400 ma ages of detrital zircons from the liuling group of the south qinling belt match well with those from the three stages of magmatic rocks and hp uhp rocks in the qinling complex this correlation suggests that the magmatic rocks and hp uhp metamorphic rocks in the north qinling belt initially exhumed to the surface eroded and were then deposited in the liuling basin in a post orogenic extensional setting during middle to late devonian new evidence suggests that the qinling complex is a tectonic complex rather than a uniform stratigraphic unit or a microcontinent as previously believed and is mainly composed of the exhumed hp uhp metamorphic rocks deep subduction exhumation related magmatic rocks and the early neoproterozoic granites together with the host rocks from the over riding plate at an active continental margin the early paleozoic tectonic history of the nqb includes oceanic slab subduction and formation of arc backarc spreading continental deep subduction arc continent collision break off and multi stage exhumation of the deep subducted slab as well as extension and thinning and associated erosion and deposition

a continuous record of holocene pollen from harris lake southwestern saskatchewan canada abstract holocene vegetation change in the west block of the cypress hills on the northern great plains is interpreted from a continuous 9120 year pollen record this is one of the few continuous pollen records available from the northern great plains which extends to the early holocene the west block rises to a maximum elevation of 1465 m and is a mosaic of grassland populus forest coniferous forests and wetland vegetation because of the ecotones present climatic changes produced vegetation changes discernible from the pollen record the record indicates that a populus forest grassland complex was established by 9000 yr bp very little coniferous forest was present at that time the predominance of grassland and saline tolerant vegetation between 7700 and 5000 yr b p defines the altithermal for this region climatic deterioration followed as indicated by increases in relative amounts of conifer and aquatic taxa pollen the pinus contorta and picea glauca forests characteristics of the cypress hills today only have been prevalent since about 4600 yr b p both species were present in very low numbers throughout the altithermal by 3230 yr b p the modern vegetation was established with little change since then

late quaternary environmental change in the lake o hara region yoho national park british columbia abstract palaeoenvironmental reconstructions for the upper cataract brook valley are derived from radiocarbon and tephra dated cores recovered from subalpine lake o hara and alpine opabin lake located near the continental divide in the central canadian rocky mountains late quaternary vegetational and climatic changes are based on pollen and macrofossil data and are supplemented by preliminary diatom data the postglacial colonizing vegetation prior to ca 10 100 yr b p at lake o hara and before ca 8530 yr b p at opabin lake was a shrub herb community dominated by artemisia gramineae and alnus pioneering forests at both sites were composed of pinus cf albicaulis flexilis and abies with lesser abundances of picea and pinus cf contorta timberline remained above the elevation of opabin lake at least 90 m above modern timberline elevation during the period ca 8500 yr b p to ca 3000 yr b p in response to warmer climatic conditions associated with restricted glacial activity forest compositions resembling the modern subalpine picea abies forest had developed by the end of this period the period ca 3000 yr b p to present was marked by deteriorating climatic conditions associated with renewed glacial activity in the opabin cirque and declining timberlines to below the elevation of opabin lake glacigenic sediments in the opabin record from the post bridge river ca 2350 yr b p interval are associated with reduced diatom production and a change in dominant diatom taxa to those characteristic of turbid water conditions and unstable catchment areas

early paleozoic high mg granodiorite from the erlangping unit north qinling orogen central china partial melting of metasomatic mantle during the initial back arc opening abstract this study discussed the petrological classification petrogenesis and tectonic significance of early paleozoic high mg granodiorite from the erlangping unit in the north qinling orogen to achieve this target we conducted integrated investigation of in situ zircon u pb dating whole rock geochemical as well as sr nd hf o isotopic compositions for the kanfenggou pluton from the erlangping unit la icp ms zircon dating for the kanfenggou samples yields u pb ages of 442 9 6 2 and 438 0 6 7 ma suggesting that the pluton was emplaced at ca 440 ma whole rock geochemical compositions of the samples display intermediate sio 2 60 48 64 67 wt and k 2 o 1 21 to 2 10 wt but high al 2 o 3 15 44 to 16 51 wt and na 2 o 4 01 to 4 81 wt contents the granodiorite samples are characterized by elevated mgo ranging from 2 30 to 3 44 wt and mg values of 53 35to 56 66 implying they are high mg granodiorites they are characterized by very high ba 524 1132 ppm and sr 684 980 ppm contents but depleted in hree and high la yb n ratios of 6 34 to 16 5 and slightly negative to weak positive eu anomalies eu eu 0 68 1 09 these evidence that the kanfenggou pluton belongs to the sanukitoid series the high mg granodiorite samples exhibit a mantle signature with high mg values 53 35 56 66 cr 45 8 to 93 3 ppm and ni 28 2 to 48 2 ppm contents but enriched in lile pointing to an enriched mantle source the samples show relatively depleted radiogenic isotopic compositions with initial 87 sr 86 sr ratios varying from 0 7044 to 0 7047 e nd t values from 0 31 to 4 21 and zircon e hf t values from 7 3 to 8 3 the zircons have a mean 18 o value of 5 20 0 17 based on the trace element geochemical features the metasomatic agent was suggested to be the fluids generated from dehydration of subducted slab therefore we suggest two stage processes for the formation of the erlangping high mg granodiorites 1 interaction between slab fluids and mantle peridotite 2 partial melting of metasomatized mantle peridotite caused by the asthenosphere mantle upwelling and the initial back arc opening resulted from the oceanic slab rollback

fluid induced nucleation of y ree phosphate minerals within apatite nature and experiment part i chlorapatite this study investigates chlorapatite ideally ca10 po4 6cl2 from two spatially separated locations in the odegardens verk apatite mine bamble sector se norway which was partially metasomatized under amphibolite facies conditions relative to the original chlorapatite metasomatized areas in sample dl136 are enriched in oh and f depleted in na si and y ree and contain numerous inclusions 1 15 m of monazite and xenotime in contrast metasomatized areas in sample tn174 are enriched in f and si depleted in na show y ree abundances similar to the original chlorapatite and host only a few monazite and xenotime grains in order to define the role of fluids in the formation of y ree phosphate minerals associated with apatite a series of experiments covering wide ranges of temperature 900 300 c and pressure 1000 500 mpa for a series of fluid compositions pure h2o a 50 50 molar mix of h2o and caf2 and co2 with 1 2 wt h2o were conducted on unaltered chlorapatite from the odegardens verk in the h2o experiments features due to metasomatic alteration depletion in na si and y ree as well as numerous monazite and xenotime inclusions as observed in the natural sample dl136 were fully reproduced monazite and xenotime grains were also observed growing on the surface of the apatite in dissolution embayments in metasomatized areas in the 50 50 caf2 h2o experiments metasomatized regions are strongly enriched in f and si depleted in na show unchanged y ree abundances and contain only a very few small monazite and xenotime grains similar to what was observed in sample tn174 natural and experimental observation imply the presence of two coupled substitutions na y ree 3 2 ca2 and si4 y ree 3 p5 ca2 in the case of dl136 and h2o fluid experiments na and si4 went into solution whereas the released y ree contributed to the growth of monazite and xenotime within the metasomatized apatite structure for sample tn174 and the 50 50 caf2 h2o fluid experiments na in apatite became depleted but si was enriched thereby stabilizing the y ree in the now recrystallized fluor hydroxylapatite structure which retarded the growth of monazite or xenotime inclusions the basic conclusion of this study is that nucleation of monazite and xenotime in the metasomatized chlorapatite is principally a function of the composition of the infiltrating fluid and to a much lesser extent temperature and pressure

further evidence for 1 85 ga metamorphism in the central zone of the north china craton shrimp u pb dating of zircon from metamorphic rocks in the lushan area henan province abstract this paper reports shrimp zircon u pb dating of precambrian supracrustal and granitic rocks from the lushan area henan province in the southern portion of the central zone also referred to as the trans north china orogen of the north china craton a graphite garnet sillimanite gneiss sample tw0006 1 of the shangtaihua group gives a range of inherited zircon ages from 2 73 to 2 26 ga and a metamorphic zircon age of 1 84 0 07 ga a garnet bearing gneissic granitoid sample twj358 1 which is considered to intrude the shangtaihua group gives a magmatic zircon age of 2 14 0 02 ga and a metamorphic zircon age of 1 87 ga the metamorphic zircon ages of 1 87 1 84 ga obtained in this study indicate that an important tectonothermal event occurred at the end of the paleoproterozoic in the lushan area this supports the southern continuation of a central zone in the north china craton that workers have recently considered to result from continent continent collision it is also evident that the shangtaihua group was formed during the paleoproterozoic between 2 26 and 2 14 ga and not during the archean as previously considered

timing and genesis of the adakitic and shoshonitic intrusions in the laoniushan complex southern margin of the north china craton implications for post collisional magmatism associated with the qinling orogen abstract the nww striking qinling orogen formed in the triassic by collision between the north china and yangtze cratons triassic granitoid intrusions mostly middle to high k calc alkaline are widespread in this orogen but contemporaneous intrusions are rare in the southern margin of the north china craton an area commonly considered as the hinterland belt of the orogen in this paper we report zircon u pb ages elemental geochemistry and sr nd hf isotope data for the laoniushan granitoid complex that was emplaced in the southern margin of the north china craton zircon u pb dating shows that the complex was emplaced in the late triassic 228 1 to 215 4 ma indicating that it is part of the post collisional magmatism in the qinling orogen the complex consists of from early to late biotite monzogranite quartz diorite quartz monzonite and hornblende monzonite which span a wide compositional range e g sio2 55 9 70 6 wt k2o na2o 6 6 10 2 wt and mg of 24 to 54 the biotite monzogranite has high al2o3 15 5 17 4 wt sr 396 1398 ppm and ba 1284 3993 ppm contents and relatively high la yb mostly 14 30 and sr y mostly 40 97 ratios but low yb mostly 1 3 1 6 ppm and y mostly14 19 ppm contents features typical of adakitic rocks the quartz monzonite hornblende monzonite and quartz diorite have a shoshonitic affinity with k2o up to 5 58 wt and k2o na2o ratios averaging 1 4 the rocks are characterized by strong lree hree fractionation in chondrite normalized ree pattern without obvious eu anomalies and show enrichment in large ion lithophile elements but depletion in high field strength elements nb ta ti the biotite monzogranite 228 ma has initial 87sr 86sr ratios of 0 7061 to 0 7067 end t values of 9 2 to 12 6 and ehf t values of 9 0 to 15 1 whereas the shoshonitic granitoids mainly 217 215 ma have similar initial 87sr 86sr ratios 0 7065 to 0 7075 but more radiogenic end t 12 4 to 17 0 and ehf t 14 1 to 17 0 the sr nd hf isotope data indicate that the rocks were likely generated by partial melting of an ancient lower continental crust with heterogeneous compositions as partly confirmed by the widespread presence of early paleoproterozoic inherited zircons mafic microgranular enclaves mmes characterized by fine grained igneous textures and an abundance of acicular apatites are common in the laoniushan complex compared with the host rocks they have lower sio2 48 6 53 7 wt and higher mg 51 56 cr 122 393 ppm and ni 24 79 ppm but equivalent sr nd isotope compositions indicating that the mmes likely originated from an ancient enriched lithospheric mantle the abundance of mmes in the granitoid intrusions suggest that magma mixing plays an important role in the generation of the laoniushan complex collectively it is suggested that the laoniushan complex was a product of post collisional magmatism related to lithospheric extension following slab break off formation of the adakitic and shoshonitic intrusions in the laoniushan complex indicates that the qinling orogen had evolved into a post collisional setting by about 230 210 ma