tectonothermal evolution of the mayuan assemblage in the cathaysia block implications for neoproterozoic collision related assembly of the south china craton the mayuan assemblage in the cathaysia block southeast china consists of felsic paragneiss pelitic schist greenschist amphibolite marble calcsilicate and quartzite that underwent three episodes of deformation d1 d3 and four episodes of metamorphism m1 m4 in the early neoproterozoic the m1 assemblage consists of mineral inclusions defining an early foliation s1 within porphyroblasts represented by chlorite muscovite biotite plagioclase quartz in pelitic schist and actinolite chlorite epidote albite quartz enclosed in amphibolite m2 coincides with the development of the regional schistosity s2 and represents the formation of the porphyroblasts and growth of matrix minerals resulting in development of prograde metamorphic zones chlorite biotite garnet staurolite and kyanite zones m3 is simultaneous with the third phase of deformation d3 and produced sillimanite bearing mineral assemblages in pelitic schist and hornblende bearing assemblages in amphibo lite the last metamorphic episode m4 gave rise to the retrogressive assemblage chlorite muscovite in pelitic rock and actinolite chlorite epidote in amphibolite the sequence of mineral assemblages and history of metamorphic reactions built from the petrogenetic grid of pelites suggest a near isothermal decompression clockwise p t path for the mayuan pelitic schists using the tweequ software program the garnet biotite thermometer and garnet muscovite biotite plagioclase barometer yield p t conditions for m1 of 5 5 to 6 0 kb and 450 to 500 c and conditions for the garnet staurolite and kyanite zones of m2 of 6 0 to 7 0 kb and 550 to 600 c 6 0 to 7 5 kb and 600 c and 11 0 to 11 5 kb and 600 c the p t conditions of m3 were estimated at 570 to 625 c and 4 0 to 4 5 kb using the muscovite biotite thermometer and hornblende plagioclase geothermo barometer the garnet chlorite thermometer yields temperatures of 300 to 400 c for m4 but the pressures of m4 cannot be quantitatively estimated because of the lack of a suitable geobarometer these p t estimates also define an near isothermal decompression clockwise p t path which is involved in initial crustal thickening followed by rapid exhumation and final cooling and is related to amalgamation of the cathaysia and yangtze blocks to form the south china craton

the interactive multisensor snow and ice mapping system the interactive multisensor snow and ice mapping system ims was developed to give snow and ice analysts the tools on one platform to inspect visually the imagery and mapped data from various sensor sources to determine the presence of snow and ice and to depict snow and ice covered areas on a map on a daily basis in one hour or less snow and ice analysts in the national environmental satellite data and information service have been creating weekly maps showing the extent of snow cover for the northern hemisphere since 1966 using visible imagery from polar orbiting and geostationary satellites and surface observations as data sources the current process is mostly manual and time consuming taking up to 10 hours to produce a map during the snow season where cloud cover precludes an unobstructed view of an area during the entire week the analysis from the previous week is carried forward each week the analyst draws a new map by hand then digitizes the extent of snow and ice cover using an 89 89 line grid overlaid on a stereographic map of the northern hemisphere the hand drawn map is photocopied and distributed and the digitized map is saved to a file for use in national weather service numerical models and for archival storage ims was designed and built to replace and improve this process by producing a more accurate and timely product

where was south china in the rodinia supercontinent evidence from u pb geochronology and hf isotopes of detrital zircons abstract u pb geochronology and lu hf isotopic studies on detrital zircons from late neoproterozoic sediments of the cathaysia block south china show abundant grenville age 1 0 ga and neoarchaean populations and minor eoarchaean 3 8 ga paleo to mesoarchaean 3 3 3 0 ga mesoproterozoic 1 7 1 4 ga and pan african 0 70 0 54 ga populations this is the first report of 3 8 ga material in the crust of the cathaysia block the presence of euhedral 1 0 ga zircons indicates that a grenville orogenic belt was within or very close to the southern cathaysia block however the provenance containing the 3 8 ga 3 3 3 0 ga 2 5 ga 1 0 ga and 0 70 0 54 ga zircon populations cannot be found in the south china block the combination of zircon age distributions and the rounded strongly abraded shapes of the archean zircons suggesting long transport is consistent with derivation from other continental terranes previously linked with the southern part of the south china block comparison with the tectono magmatic history and compositions of rocks in western laurentia eastern australia and eastern india east antarctica western australia we suggest that these late neoproterozoic sediments may have originated mainly from eastern india east antarctica this indicates that the south china block was linked with the eastern india east antarctica continents in the late neoproterozoic rather than being located between the western laurentia and eastern australia continental blocks u pb and hf isotope studies on detrital zircons provide an important independent constraint on the palaeogeography of the south china block in the context of the breakup of rodinia and the subsequent assembly of gondwana in late neoproterozoic time and insights into the relationship between the cathaysia and yangtze blocks

850 790 ma bimodal volcanic and intrusive rocks in northern zhejiang south china a major episode of continental rift magmatism during the breakup of rodinia abstract shrimp u pb zircon ages and geochemical and nd isotopic data are reported for mid neoproterozoic igneous rocks in northern zhejiang province south china the shenwu dolerite dykes the daolinshan granite diabase complex and the shangshu bimodal basalt rhyolite volcanic rocks were dated at 849 7 ma 794 9 ma and 792 5 ma respectively all the studied mafic rocks are tholeiitic in compositions and exhibit overall moderate enrichments in most incompatible trace elements resembling intraplate basaltic rocks in continental rifts the 850 ma shenwu dolerites are the earliest anorogenic basaltic rocks identified so far after the ca 1 1 0 9 ga sibao orogeny but seem to predate the neoproterozoic rifting our results are clearly at variance with the alternative tectonic model that an active continental margin existed along the southern margin of the yangtze block until ca 800 ma the intensive 790 ma bimodal volcanic and plutonic rocks part of a major phase of mid neoproterozoic rifting are concurrent with the widespread mid neoproterozoic intraplate magmatism throughout south china they are most likely related to the proposed mantle superplume that led to the breakup of the supercontinent rodinia

ordovician appinites in the wugongshan domain of the cathaysia block south china geochronological and geochemical evidence for intrusion into a local extensional zone within an intracontinental regime abstract palaeozoic mafic igneous rocks are potentially significant in constraining the tectonic nature and evolution of the kwangsian orogeny in the eastern south china block yet they have received little attention because of their limited outcrop geochemistry and geochronology was carried out on newly identified ordovician ultramafic mafic appinites in the wugongshan domain of the cathaysia block seven appinite samples yielded 206pb 238u crystallisation ages ranging from 452 4 ma to 473 3 ma abundant 480 500 ma zircon xenocrysts and or inherited zircons were found in the appinites possibly indicating an earlier magmatism episode in the early palaeozoic period the wugongshan appinites are ultramafic to mafic in composition and the ultramafic rocks display features of cumulates high concentrations of mgo fe2o3t cr ni and low concentrations of total alkali and total rare earth elements ree the appinite geochemistry displays relatively flat chondrite normalised ree patterns with slight enrichment in light ree and weak negative eu anomalies enrichment in large ion lithophile elements such as rb k and weak depletion in nb ta in primitive mantle normalised trace element patterns we suggest that the wugongshan appinites likely originated from an ancient metasomatised mantle and that crustal assimilation fractional crystallisation afc magma mingling and hydration were involved in the petrogenetic process based on the combination of geochemistry crust like bulk sr nd and zircon hf isotopic compositions end t 8 2 to 3 2 initial 87sr 86sr ratios of 0 7067 0 7144 zircon ehf t values peaking at 9 to 3 and regional geological data further considering the alignment and chronology of the appinites we suggest that the appinitic magmas probably were emplaced along the jiangshan shaoxing fault in a local extensional zone in an intracontinental regime in the early palaeozoic

contrasting zircon hf and o isotopes in the two episodes of neoproterozoic granitoids in south china implications for growth and reworking of continental crust abstract the genetic links among rift magmatism crustal growth and water rock interaction are an important issue about mass and heat transfer between mantle and crust during supercontinent breakup a combined study of hf and o isotopes in zircons from neoproterozoic granitoids in south china provides evidence for growth and reworking of juvenile and ancient crusts with different styles of water rock interactions along rift tectonic zones two generations of the granitoids show contrasting features in both zircon hf and o isotope compositions indicating their distinct petrogenesis the 825 ma granitoids exhibit negative ehf t values of 3 4 0 8 to 1 6 0 8 with old model hf ages of 1 81 0 07 to 1 92 0 10 ga and high 18o values of 8 7 to 10 4 these indicate that the source material of granitoid magmas was derived from melting of paleoproterozoic basement that has the hf isotope signature similar to the enriched mantle but experienced chemical weathering process before anatexis reworking of ancient crust is demonstrated to occur at 825 ma in the orogenic collapse zone with overprinting of subsolidus hydrothermal alteration during magma emplacement in contrast the 760 750 ma bimodal intrusives are characterized by positive ehf t values of 3 5 0 8 to 9 9 0 8 with young model hf ages of 0 94 0 06 to 1 18 0 06 ga and both low and high 18o values of 4 2 to 6 2 relative to 5 3 0 3 for the normal mantle zircon prompt reworking of juvenile crust is suggested to occur at 750 ma in the rifted tectonic zone with occurrence of supersolidus hydrothermal alteration and local low 18o magmatism during supercontinent breakup contributions of the depleted mantle to their magma sources are contrasting in the two episodes of magmatism in association with breakup of the supercontinent rodinia while the change in melt source from the crust to the mantle keeps pace with the advance from continental rifting to supercontinent breakup significant transport of both heat and material from the depleted mantle to the continental crust only occurred along the active rifting zone in either case the growth and reworking of continental crust are episodically associated with rift magmatism

a look at the date of snowmelt and correlations with the arctic oscillation spring snow cover across arctic lands has on average retreated 5 days earlier since the late 1980s compared to the previous 20 years however it appears that since about the late 1980s the date the snowline first retreats north during the spring has changed only slightly in the last 20 years snow has not been disappearing significantly earlier snowmelt changes observed since the late 1980s have been step like unlike the more continuous downward trend seen in arctic sea ice extent at 70 n several longitudinal segments of 10 show significant negative trends while only two longitudinal segments at 60 n show significant trends one positive and one negative these variations appear to be related to variations in the arctic oscillation ao when the springtime ao is strongly positive snow melts earlier when it is strongly negative snow disappears later in the spring the winter ao is less straightforward at higher latitudes 70 n a positive ao during the winter months is correlated with later snowmelt but at lower latitudes 50 n and 60 n a positive wintertime ao is correlated with earlier snowmelt if the ao during the winter months is negative the reverse is true similar stepwise changes since the late 1980s have been noted in sea surface temperatures and in phytoplankton abundance as well as in snow cover

magmatism along the southeast margin of the yangtze block precambrian collision of the yangtze and cathysia blocks of china the time and the environment of formation of igneous rocks along the southern margin of the yangtze continental block in southern anhui province and northeastern jiangxi province china are discussed sm nd dating for samples from two ophiolite suites give ages of about 1 ga late proterozoic granodiorites in the study area have ages of about 0 9 ga and have normal intrusive relations against banxi group metamorphic country rocks trace element abundances and initial nd isotope ratios for ophiolite and proterozoic granodiorites are consistent with formation in an island arc environment in contrast sr and nd isotopes for mesozoic granitoids of the region suggest that they are products of remelting of crustal sources similar to the basement of the yangtze block these relations do not support a recently proposed mesozoic overthrust tectonic model for southeast china but rather favor a late precambrian collision history for the yangtze and cathysia blocks

measuring snow and glacier ice properties from satellite satellite remote sensing is a convenient tool for studying snow and glacier ice allowing us to conduct research over large and otherwise inaccessible areas this paper reviews various methods for measuring snow and glacier ice properties with satellite remote sensing these methods have been improving with the use of new satellite sensors like the synthetic aperture radar sar during the last decade leading to the development of new and powerful methods such as sar interferometry for glacier velocity digital elevation model generation of ice sheets or snow cover mapping some methods still try to overcome the limitations of present sensors but future satellites will have much increased capability for example the ability to measure the whole optical spectrum or sar sensors with multiple polarization or frequencies among the methods presented are the satellite derived determination of surface albedo snow extent snow volume snow grain size surface temperature glacier facies glacier velocities glacier extent and ice sheet topography in this review emphasis is put on the principles and theory of each satellite remote sensing method an extensive list of references with an emphasis on studies from the 1990s allows the reader to delve into specific topics

melting of enriched archean subcontinental lithospheric mantle evidence from the ca 1760ma volcanic rocks of the xiong er group southern margin of the north china craton abstract the xiong er group is an important geologic unit in the southern margin of the north china craton it is dominated by the volcanic rocks dated at 1763 15 ma that have sio2 contents ranging from 52 10 wt to 73 51 wt these volcanic rocks are sub alkaline and can be classified into three subgroups basaltic andesites andesites and rhyolites they unexceptionally show enrichment of light rare earth elements lree and share similar trace element patterns depletions in nb ta sr p and ti relative to the adjacent elements are evident for all the samples the volcanic rocks are evolved with low mgo contents 0 29 5 88 wt and accordingly low mg values of 11 53 the nd isotopes are enriched and show a weak variation with nd t 7 12 to 9 63 zircon hf isotopes are also enriched with hf t 12 02 0 45 the volcanic rocks of the xiong er group are interpreted to represent fractional crystallization of a common mantle source the volcanic rocks might have been generated by high degree partial melting of a lithospheric mantle that was originally modified by the oceanic subduction in the late archean this brings a correlation with the subduction modified lithospheric mantle in an extensional setting during breakup of the columbia supercontinent in the late paleoproterozoic rather than in an arc setting the elevated sio2 contents and evolved radiogenic isotope features indicate the possible incorporation into their source of lower crustal materials that have similar nd isotopic characteristics to the subcontinental lithospheric mantle the existence of extensive xiong er volcanic rocks 60 000 km2 indicates an early large scale subduction related metasomatism in the area and probably suggest a flat subduction model for the plate margin magmatism in the late archean

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

petrogenesis and tectonic implications of neoproterozoic highly fractionated a type granites from mianning south china abstract the origin of neoproterozoic intrusions ca 860 750 ma along the western part of the yangtze craton has been the subject of debate in recent years with two competing models proposed the plume model argues for an extensional setting and emphasizes the role of a superplume in the rodinia breakup whereas the arc model argues for the presence of a subduction zone in the yangtze craton as a contribution to this animated dispute geochronologic and geochemical analyses have been carried out on the mianning granite which is the largest pluton 700 km2 in the northern kangdian rift of the western yangtze craton it is shown that the mianning granites were emplaced at ca 780 ma and display highly fractionated feature i e sio2 75 wt eu eu 0 03 0 50 enrichment of k rb th u zr hf y and rees depletion of nb ta ba sr p eu and ti they are metaluminous to strongly peraluminous a cnk 0 93 1 55 and contain abundant perthite and minor alkali riebeckite and sphene sharing the petrological and geochemical characters of a2 type granites positive nd t 2 97 5 24 and zircon hf t 9 2 12 1 values are consistent with a derivation by partial melting of a relatively young crust formed about 1000 900 ma given the general absence of a type granites in arc settings the mianning a type granites are suggestive of an anorogenic crustal extensional environment for the western yangtze craton during the neoproterozoic the data presented in this study are therefore consistent with an intracontinental rift model but are not sufficient to identify plume involvement in the neoproterozoic magmatism

a model for continental crust genesis by arc accretion rare earth element evidence from the irish caledonides abstract the formation of continental crust is a complex problem with a paradox at its center continental material is believed to form by arc magmatism a model that does not reconcile the bulk mafic and light rare earth element lree depleted composition of intra oceanic arcs with the andesitic lree enriched composition of continents we present evidence supporting an arc origin for continental crust by demonstrating significant changes in magmatic chemistry during arc continent collision we use as an example the connemara region of the western irish caledonides where metamorphism and orogenesis of dalradian sedimentary sequences record the collision of the oceanic lough nafooey arc with the passive margin of laurentia at 475 ma arenig this arc was mafic and lree depleted during its oceanic activity during collision rhyolites more lree enriched than the surrounding continental crust were erupted while the mid crust was intruded by similarly lree enriched gabbro and diorite crystal fractionation caused lree enrichment to exceed that expected by assimilation of continental crust alone we propose that subsequent loss of the corresponding lower crustal cumulates into the mantle removed this lree depleted material from the net crust added to the continent the combined processes of crystal fractionation and lower crustal loss during arc continent collision drive the average bulk arc composition toward that of average continental crust

reconstruction of landsat time series in the presence of irregular and sparse observations development and assessment in north eastern alberta canada abstract time series analysis of landsat is limited by sparse and irregular sampling of clear sky observations due to acquisition limitations clouds shadows atmosphere and sensor artifacts many remote sensing applications utilizing coarse spatial resolution time series methods are not suitable for landsat due to observation sparsity in this research we develop an imputation based approach to constrain the harmonic modeling method of zhu et al 2012 zhu et al 2015 and zhu and woodcock 2014b to reconstruct landsat time series at a regular temporal interval the approach was assessed for a boreal forest region in central canada for different sparsity conditions the imputed landsat estimates for a specific pixel were predicted from climate or avhrr data these estimates were given a small weight relative to available landsat observations in fitting the final harmonic model essentially constraining it to a more plausible range in addition we implemented the model in a piecewise manner to handle non linear temporal drift related to factors such as climate change drought or the allometric nature of vegetation regrowth results show that the inclusion of imputed estimates improved model predictions in the presence of observation sparsity where there were less than 3 observations within 20 days the imputation approach performed better with a reduction in average reflectance error of 0 001 to 2 5 error assessment with hold out observations comparison to modis time series and example predicted images are presented

alternating braidplain and lacustrine deposition in a strike slip setting the pennsylvanian boss point formation of the cumberland basin maritime canada abstract the boss point formation was deposited in the cumberland basin of southeastern new brunswick and northern nova scotia during the early pennsylvanian the basin is bounded to the northwest and south by strike slip faults active during the pennsylvanian the boss point comprises two main fades associations sandy braidplain bfa and muddy lacustrine lfa the abrupt alternation of which allows 16 depositional megacycles to be defined the lfa forms units 50 m thick that rest sharply but nonerosively on braidplain sandstone in some instances the contact can be traced for over 12 km perpendicular to paleoflow commonly dunes and ripples are preserved in relief beneath lacustrine mudstone implying rapid but very low energy flooding of t e braidplain the bfa comprises multistory channel sandbodies 90 m thick separated from the underlying lfa by sixth order surfaces with up to 15 m of erosional relief the erosion surfaces are commonly overlain by spectacular mudstone breccias and boulders that reflect deep erosion and rotational slumping into channels cut into and sometimes right through lacustrine deposits bfa packages are internally partitioned by fifth order erosion surfaces into individual channel fill units commonly about 5 m thick the bfa is dominated by trough cross bedded fine to lower medium sandstone conglomerate pebbly sandstone and ripple laminated and planar laminated sandstone are minor components rare mud filled abandoned channels suggest a mean width and de th of 160 m and 4 8 m respectively the dominance of trough cross bedding suggests relatively deep channels whose banks may have been maintained by a dense vegetation cover repeated channel avulsion and flood related erosion resulted in a rock record dominated by deep channel and flood stage deposits bartop facies were rarely preserved channel dimensions lateral consistency of facies paucity of muddy channel plugs and regionally consistent paleoflow suggest deposition on a braidplain the distribution of conglomerates indicates a local gravel source area in the caledonia highlands to the northwest but much of the sand is likely to have been sourced far to the southwest the boss point falls into two sharply disjunct paleoflow domains one directed to the north and northeast and the other to the east and southeast separated by the harvey hopewell fault zone the absence of an adequate watershed between the two domains strongly suggests tectonic juxtaposition involving several tens of kilometers of sinistral offset

subduction related origin of the 750 ma xuelongbao adakitic complex sichuan province china implications for the tectonic setting of the giant neoproterozoic magmatic event in south china abstract the xuelongbao plutonic complex in the eastern margin of the tibetan plateau is dated at 748 7 ma using the shrimp zircon u pb method and represents part of the neoproterozoic igneous assemblage of south china rocks in the complex include tonalite and granodiorite and have sio2 ranging from 62 0 to 74 8 wt and al2o3 from 14 3 to 20 9 wt their na2o contents range from 4 2 to 6 7 wt and k2o from 0 47 to 1 96 wt indicating that they belong to the na series these rocks show chondrite normalized ree patterns depleted in hree and variably enriched in lree they have positive sr and negative nb and ti anomalies in the primitive mantle normalized trace elemental spider diagram their sr contents range from 320 to 780 ppm and y contents are lower than 10 ppm resulting in high sr y ratios 52 320 characteristic of typical adakites their end t and initial sr isotopic compositions range from 0 36 to 2 88 and from 0 7033 to 0 7054 respectively the geochemical features of the xuelongbao plutonic complex are consistent with an origin from adakitic magmas that were likely derived from partial melting of a subducted oceanic slab together with arc signatures of other granites and mafic intrusions in the region the 750 ma xuelongbao adakitic complex provides evidence for a major subduction related neoproterozoic magmatic event of south china

slab breakoff a model of lithosphere detachment and its test in the magmatism and deformation of collisional orogens we present a model proposing that oceanic lithosphere detaches from continental lithosphere during continental collision slab breakoff allowing an explanation of syn to post collisional magmatism and metamorphism continental collisions are preceded by subduction of dense oceanic lithosphere and followed by attempted subduction of buoyant continental lithosphere this situation of opposing buoyancy forces leads to extensional deformation in the subducted slab a narrow rifting mode of deformation will result if there is strain localization slab breakoff results we have assessed the plausiblity of this process by quantitatively evaluating an upper bound for the strength of the lithosphere and have compared it with the change in buoyancy force during continental sbduction whether breakoff will occur and the depth at which it will occur is a strong function of temperature and hence the subduction velocity for a subduction velocity of 1 cm yr breakoff could occur at depths of between 50 and 120 km while at higher velocities it is still likely to occur but at deeper depths as a result of the rifting during breakoff the asthenosphere upwells into the narrow rift and following breakoff it impinges on the mechanical lithosphere of the overriding plate the resulting conducted thermal perturbation leads to melting of the metasomatised overriding mantle lithosphere producing basaltic magmatism that leads to granitic magmatism in the crust dry asthenospheric mantle will melt only if breakoff occurs at a depth shallower than ca 50 km breakoff removes the force at the downdip side of the continental crust while the enhanced heating leads to a reduction of the strength of the underlying crust both effects facilitate the freeing of buoyant crustal sheets which can then rise towards the surface leading to the rapid exhumation of eclogite facies continental crust the cessation of subduction and replacement of the cold oceanic lithosphere by asthenosphere leads to rapid uplift of the orogen we have tested the variety of predicted expressions of slab breakoff in the geological record of the alps the aegean islands and the dabie shan a comparison of the various belts highlights 1 that the magmatism and metamorphism are found near the suture and the centre of the orogen demonstrating the general steepening of suture during collision 2 that a vague inverse correlation exists between maximum depth of metamorphism and volume of syn orogenic magmatism and 3 that the melts can be emplaced in both compressive and extensional environments we suggest that slab breakoff is an important step in the evolution of many orogenic belts and it allows an explanation for the combined presence in collisional orogens of magmatism with a mantle parentage and ultra high pressure metamorphics

kinematics and geochronology of the proterozoic dongxiang shexian ductile shear zone with hp metamorphism and ophiolitic melange jiangnan region south china abstract a kinematic and geochronological analysis of the 10 20 km wide northeast trending dongxiang shexian ductile shear zone that trends along a length of 250 km in the eastern part of the jiangnan belt indicates a sinistral strike slip ductile shear that was formed during the neo proterozoic the zone experienced polyphase deformation related to tectonic collision between the huaiyu and the jiuling terranes geochronological data and kinematic analysis of macroscopic structures microscopic shear indicators and quartz c axes fabrics shows that a ductile southeastward thrusting occurred at about 950 900 ma followed by a sinistral strike slip shearing along a northeast trend at about 770 ma coarse clastic sedimentary rocks of sinian age were deposited unconformably on the entire jiangnan belt including the huaiyu and the jiuling terranes this paper emphasizes that the jiangnan belt in the se margin of yangzi plate is a neo proterozoic orogenic belt with hp metamorphism and ophiolitic melange not a late paleozoic mesozoic collisional orogen

detrital zircon u pb hf isotopes and whole rock geochemistry of neoproterozoic cambrian successions in the cathaysia block of south china implications on paleogeographic reconstruction in supercontinent abstract paleogeographic reconstruction of the cathaysia block of south china and its link with orogeny associated with rodinia and gondwana remain enigmatic leading to controversial models proposed for supercontinental configuration this study presents detailed provenance analysis of late neoproterozoic to early paleozoic sedimentary successions from the cathaysia block to trace the sedimentary provenance that was essentially linked to previously adjacent continents blocks zircon u pb dating combined with published paleontological evidence suggests an ediacaran depositional age range 633 542 ma for the lechangxia group while deposition of the bacun group most likely commenced during early cambrian the older strata were sourced mainly from recycling of quartz rich sedimentary rocks while the younger one received sediments dominantly from felsic igneous rocks high sio2 contents 54 6 79 3 wt and k2o na2o ratios 0 69 35 7 detrital zircon age distribution and abundant monocrystalline quartz indicate a passive setting for ediacaran and early cambrian successions in great contrast the middle cambrian strata was likely deposited in collisional setting considering relatively lower sio2 contents 67 9 74 5 wt and k2o na2o ratios 0 97 1 63 plus absence of old zircons this tectonic transition is consistent with the change from quartz arenite to arkose that could be related to a disconformity between early and middle cambrian strata dominant late mesoproterozoic detritus 1250 1050 ma in the lechangxia group was possibly sourced from older grenville orogens 1300 1050 ma in western australia and east antarctica because rocks of these ages are rare in the cathaysia block similarly abundant early neoproterozoic clastic 1000 950 ma in the late ediacaran and early cambrian successions imply an increasing input from younger grenville orogens 990 950 ma in east antarctica and eastern india thus the cathaysia block was a part of the east gondwana assembly and was linked to eastern india east antarctica and western australia during ediacaran and cambrian the source change was coeval with the pinjarra orogeny 550 520 ma and the early stage of the kuunga orogeny 570 550 ma in middle cambrian strata the middle neoproterozoic sediments 850 700 ma were mainly derived from intrinsic sources likely to be the wuyishan terrane this provenance variation can be linked to the middle cambrian uplift of the cathaysia block in synchronous with the later phase of the kuunga orogeny 530 480 ma

post orogenic extension in the eastern part of the jiangnan orogen evidence from ca 800 760ma volcanic rocks we present a systematic geochronological and geochemical study on ca 800 760 ma volcanic rocks in the eastern part of the jiangnan orogen the xucun composite dykes are dated at ca 805 ma the mafic components have oib like trace element patterns and positive anomalies in zr and hf the least contaminated sample has relatively depleted nd isotopic features suggesting the xucun mafic dykes may have been generated from the partial melting of oib like asthenosphere with later crustal contamination the xucun felsic dykes have decoupled nd hf isotopes and the hf isotope compositions of zircons indicate that the dykes may be derived from the partial melting of the early neoproterozoic juvenile crustal materials with minor incorporation of paleoproterozoic crustal components the ca 800 790 ma shangshu volcanics include two compositional series calc alkaline and tholeiitic the shangshu calc alkaline volcanics in the minjiawu area have low abundances of lile hfse and high na2o contents and sr y ratios similar to adakitic rocks the evident arc like geochemical features and radiogenic nd isotopes nd t values of 3 7 to 4 8 suggest that these rocks may have been generated from the partial melting of juvenile lithospheric mantle metasomatized by na rich melts released from the subducted slab the tholeiitic mafic rocks from the shangshu bimodal volcanics represent two different magma sources the partial melting of metasomatized lithospheric mantle led to the formation of arc like basalts with low tio2 contents negative anomalies in zr and hf and high values of mg and nd t 6 2 whereas the partial melting of asthenospheric mantle generated volcanic rocks with high tio2 contents and low positive nd t 1 4 to 2 7 without negative anomalies of nb ta zr and hf the shangshu felsic rocks were formed by the reworking of early neoproterozoic juvenile arc crustal materials the ca 760 ma mafic rocks from the puling bimodal volcanics generally have low tio2 contents 0 9 wt nearly flat ree distributions and arc like trace element patterns they may have been generated from the high degree partial melting of metasomatized lithospheric mantle one sample has a high tio2 content 2 41 wt and high nd t 6 2 with overall oib like trace element patterns implying the local partial melting of asthenospheric mantle the occurrence of significant volumes of bimodal volcanics in the eastern part of the jiangnan orogen suggests an extensional setting in the period ca 800 760 ma the evident partial melting of newly metasomatized lithospheric mantle and subordinate partial melting of asthenosphere suggest that post orogenic extension shortly after the neoproterozoic orogenesis may be a better explanation for the genesis of the mid neoproterozoic magmatic rocks in the eastern part of the jiangnan orogen post orogenic extension may be diachronous along the whole orogenic belt and probably has no direct relationship with the rodinia rifting event a more detailed model is presented to illustrate the evolution of the eastern part of the jiangnan orogen

assessment of the relative accuracy of hemispheric scale snow cover maps there are several hemispheric scale satellite derived snow cover maps available but none has been fully validated for the period october 23 december 25 2000 we compare snow maps of north america derived from the moderate resolution imaging spectroradiometer modis and the national oceanic and atmospheric administration noaa national operational hydrologic remote sensing center nohrsc which both rely on satellite data from the visible and near infrared parts of the spectrum we also compare modis and defense meteorological satellite program dmsp special sensor microwave imager ssm i passive microwave snow maps the maps derived from visible and near infrared data are more accurate for mapping snow cover than are the passive microwave derived maps however discrepancies exist as to the location and extent of the snow cover among those maps the large approx 30 km footprint of the ssm i data and the difficulty in distinguishing wet and shallow snow from wet or snow free ground reveal differences up to 5 32 million sq km in the amount of snow mapped using modis versus ssm i data algorithms that utilize both visible and passive microwave data which would take advantage of the all weather mapping ability of the passive microwave data will be refined following the launch of the advanced microwave scanning radiometer amsr in the fall of 2001

precambrian geology of china preface abstract the north china south china and tarim cratons compose the tectonic framework of china in the last decade extensive structural metamorphic geochemical geochronological and geophysical investigations have been carried out on these cratonic blocks producing an abundant amount of new data and competing interpretations which have resulted in refinement of and in some cases significant reinterpretations of the precambrian crustal formation and evolution of china this forms a justification for organizing this special issue in which we invited representative experts working in the north china south china and tarim cratons to present overviews or detailed studies on the formation and tectonic evolution of major precambrian blocks in china twenty four contributions collected in this special issue provide current knowledge of the components and tectonic evolution of major precambrian blocks in china and discuss some key issues based on new data and interpretations which will provide important insights into understanding the precambrian geology of china

components and episodic growth of precambrian crust in the cathaysia block south china evidence from u pb ages and hf isotopes of zircons in neoproterozoic sediments abstract detailed lam icpms u pb dating and lam mc icpms lu hf isotope analysis were carried out on zircons from nine samples of basement metamorphic rocks in the southern cathaysia block south china the chemical compositions of these metamorphic rocks and zircon morphology indicate that their protoliths were sedimentary zircon u pb dating results show they mainly formed during the late neoproterozoic the precambrian crust of the cathaysia block can be divided into two distinct tectonic domains the wuyishan terrane to the northeast and the nanling yunkai terrane to the southwest the nearly e w boundary between these two terranes is also supported by geophysical petrological and geochemical evidence and the basement rocks of the two terranes are comprised of different components the wuyishan terrane is characterized by dominant paleoproterozoic 1 86 ga and lesser neoarchean magmatism and the southern central part of the terrane suffered strong neoproterozoic and early paleozoic tectonothermal reworking the zircon data suggest that there were five important episodes of juvenile crust generation 3 6 ga 2 8 ga 2 6 2 4 ga 1 85 ga and 0 8 0 7 ga in the wuyishan terrane strong paleoproterozoic 1 85 ga magmatism in northern wuyishan and neoproterozoic 0 8 0 7 ga magmatism in central and southern wuyishan both principally involved the remelting of old crust with minor input of juvenile material in contrast the nanling yunkai terrane contains abundant neoarchean and grenvillian zircons some evidence of mesoproterozoic activity and rare paleo to meso archean and neoproterozoic zircons u pb ages and hf isotopic compositions of the detrital zircons from the late neoproterozoic to early paleozoic meta sedimentary rocks in the nanling yunkai area suggest that the growth of juvenile crust mainly occurred at 3 6 ga 3 3 ga 2 5 2 6 ga 1 6 ga 1 0 ga and 0 8 0 7 ga neoarchaean 2 6 2 5 ga grenvillian 1 0 ga and neoproterozoic 0 8 0 7 ga magmatism mainly involved the recycling of old crust minor remnants of 4 1 ga crust may remain in the terrane this crustal history is distinct from that of the wuyishan terrane and analogous to those recorded for the eastern india east antarctic domain of northern gondwanaland suggesting that they probably were once linked

a spatio temporal analysis of trends in northern hemisphere snow dominated area and duration 1971 2014 seasonal snow cover modulates water and energy budgets across large areas of the northern hemisphere previous research based on satellite imagery interpreted and curated by the rutgers university snow laboratory has identified significant negative and positive trends in annual snow covered duration and area at hemispheric and continental scales between 1971 and 2014 this study uses the same dataset to generate more detailed descriptions of spatial variations in these trends maps intraannual variations in sign statistical significance and strength and quantifies associations with latitude and elevation it also considers the limitations and uncertainties associated with a binary classification of this type and the implications for trend magnitudes of adopting alternatives to the conventional assumption of 100 0 actual fractional snow covered area in snow covered snow free spatial units at different stages of the snow season this prompts adoption of alternative terminology referring to snow dominated area and duration in response to questions about the dataset s veracity raised by some prior studies it discusses climatological factors of potential relevance in explaining spatio temporal trend patterns and considers how biases might possibly have been introduced as a result of extraneous influences

reappraisal of the ages of neoproterozoic strata in south china no connection with the grenvillian orogeny the jiangnan fold belt separates the yangtze and cathaysia blocks in south china and has long been considered grenvillian in age in order to place south china in central rodinia it consists of deformed early neoproterozoic strata that are unconformably overlain by undeformed late neoproterozoic strata and intruded by undeformed and unmetamorphosed granitic plutons zircons from the early neoproterozoic strata yield u pb ages as young as 830 ma and one granitic pluton has a zircon u pb age of ca 827 ma the 830 ma mafic rocks along the southeastern margin of the yangtze block have arc affinity geochemical characters whereas mafic rocks younger than 830 ma have typical ocean island basalt oib like compositions thus we suggest that the early neoproterozoic strata were deposited on an active continental margin prior to amalgamation of the yangtze and cathaysia blocks at ca 830 ma the overlying late neoproterozoic strata were deposited in the intracontinental rifted nanhua basin at 820 730 ma and probably reflect backarc spreading above the long lived 950 735 ma oceanic subduction zone along the northern and western margin of the yangtze block this model is consistent with the secular tectonic evolution of south china during the neoproterozoic the jiangnan fold belt is therefore not a grenvillian feature as previously suggested and there is no evidence to place south china in central rodinia instead we believe that south china was located in a marginal position relative to this supercontinent

calc alkaline and tholeiitic dyke swarms of tandilia rio de la plata craton argentina u pb sm nd and rb sr 40ar 39ar data provide new clues for intraplate rifting shortly after the trans amazonian orogeny abstract the tandilia system argentina southernmost part of rio de la plata craton rlpc is intruded by two paleoproterozoic unmetamorphosed dyke swarms which are i intermediate i and acid a and ii basic b1 and b2 in composition the latter dykes have tholeiitic characteristics while for both i and a dykes major minor and trace elements including ree e g the higher values of sio2 k2o and ba compared to tholeiitic dykes are characteristic of calc alkaline suites the calc alkaline dykes i and a yielded 40ar 39ar step heating plateau ages of emplacement of 2020 24 and 2007 24 ma these ages are within error in agreement with a rb sr errorchron of 1956 110 ma 1 initial 87sr 86sr 0 7038 0 0025 mswd 19 an upper intercept u pb age on two baddeleyites from a tholeiitic b1 dyke places the intrusion at 1588 11 ma the tholeiitic dykes b1 and b2 have k ar whole rock ages from 803 14 to 1193 18 ma and a 40ar 39ar plateau age of 811 36 ma 2 on plagioclase these discordant apparent ages suggest variable ar loss of the mineral systems calc alkaline dykes mainly trend e w and were emplaced during the transtensional stage of the trans amazonian orogeny during which the plutonic rocks of the tandilia system were formed such a scenario has similarities with the eburnean evolution of the richtersveld plutonic arc complex of the southern african subcontinent namaqualand that faces the rlpc in the west gondwana reconstruction the significantly younger tholeiitic dykes of tandilia 1 59 ga trend mainly nw se their presence constrains the time of crustal extension at the paleo mesoproterozoic boundary during which basin formation tectonics and anorogenic magmatism took place worldwide within a stabilized paleoproterozoic lithosphere such an intraplate regime for the emplacement the youngest dykes of tandilia is consistent with transcontinental scale diachronous extensional episodes within the south american continent which initiated shortly after the trans amazonian orogeny as illustrated by the 1 73 ga florida tholeiitic dyke swarm and coeval anorogenic granitoids scattered across the rlpc uruguay and tandilia paleoproterozoic geologic features of the rlpc namely the occurrence of plutonic arc rocks 2 14 2 07 ga succeeded by emplacement of anorogenic granitoids and mafic dykes 1 73 1 59 ga allow direct correlation with the postulated gondwana counterpart mirrored by broadly contemporary plutonic rocks of the richtersveld and bushmanland subprovinces of namaqualand the broad picture reinforces the idea that the trans amazonian eburnean orogenies played an important role for juvenile crustal accretion within the southern south america and its southern africa counterpart which was followed by a tendency to dispersion of the stabilized continental fragments during the mesoproterozoic preceding the assembly of the rodinia supercontinent

alkali calcic and alkaline post orogenic po granite magmatism petrologic constraints and geodynamic settings abstract the end of an orogenic wilson cycle corresponds to amalgamation of terranes into a pangaea and is marked by widespread magmatism dominated by granitoids the post collision event starts with magmatic processes still influenced by subducted crustal materials the dominantly calc alkaline suites show a shift from normal to high k to very high k associations source regions are composed of depleted and later enriched orogenic subcontinental lithospheric mantle affected by dehydration melting and generating more and more k and lile rich magmas in the vicinity of intra crustal magma chambers anatexis by incongruent melting of hydrous minerals may generate peraluminous granitoids bearing mafic enclaves the post collision event ends with emplacement of bimodal post orogenic po suites along transcurrent fault zones two suites are defined i the alkali calcic monzonite monzogranite syenogranite alkali feldspar granite association characterised by biotite plagioclase fractionation and moderate lile hfse enrichments and ii the alkaline monzonite syenite alkali feldspar granite association characterised by amphibole alkali feldspar fractionation and displaying two evolutionary trends one peralkaline with sodic mafic mineralogy and higher enrichments in hfse than in lile and the other aluminous biotite bearing marked by hfse depletion relative to lile due to accessory mineral precipitation alkali calcic and alkaline suites differ essentially in the amounts of water present within intra crustal magma chambers promoting crystallisation of various mineral assemblages the ultimate enriched and not depleted mantle source is identical for the two po suites the more primitive lile and hfse rich source rapidly replaces the older orogenic mantle source during lithosphere delamination and becomes progressively the thermal boundary layer of the new lithosphere present rock compositions are a mixture of major mantle contribution and various crustal components carried by f rich aqueous fluids circulating within convective cells created around magma chambers in favourable areas po suites pre date a new orogenic wilson cycle

understanding dual geochemical characters in a geological context for the gaojiacun intrusion response to munteanu and yao s discussion precambrian res 154 2007 164 167

the isotopic composition of yb and the precise and accurate determination of lu concentrations and lu hf ratios by isotope dilution using mc icpms 1 we report yb isotopic data for the purpose of accurately correcting measurements of lu and lu hf ratios during multicollector inductively coupled plasma mass spectrometer mc icpms analysis the yb isotopic ratios agree with recent results of chu et al 2002 and amelin and davis 2004 when corrected for mass fractionation to the same reference values protocols for lu measurement involving simultaneous subtraction of yb interference and application of a fractionation correction based on yb are described it is shown that lu concentrations and lu hf ratios determined by mc icpms using this methodology are more precise and potentially more accurate than results based on analysis of lu by thermal ionization mass spectrometry tims a number of mc icpms lu hf isotopic analyses of standard rocks and other geological samples previously analyzed by tims are presented these document reproducibility of lu hf within 0 2 where most discrepancies can be assigned to the unknown lu mass fractionation during tims analysis

complex growth and reworking processes in the yangtze cratonic nucleus abstract the kongling complex kc including the northern nkc and southern parts skc represents a rare relic of archean crust in the yangtze craton and an ideal target to investigate the precambrian evolution of the continental crust in the skc history of archean paleoproterozoic growth and reworking has not yet been clearly understood new geochemical and geochronological data on the basement rocks i e gneiss migmatite amphibolites and their overlying metasediments in the skc combined with published results from the nkc allow a further subdivision into western middle and eastern zones which has proven useful in understanding the precambrian history of the yangtze cratonic nucleus u pb dating and lu hf isotopes of zircons in biotite gneisses with or without amplibole and amphibolites suggest that the skc experienced a crustal re melting reworking event at 2 9 ga an accretion reworking event at 2 7 ga and later reworking at 1 73 ga and 0 8 ga these records are partly consistent with what is known about the nkc the main differences between them are that rocks with ages 3 0 ga and 2 1 2 0 ga are only found in the nkc but not in the skc hence the skc is not a copy of the nkc according to the consistent rock assemblages and ages the skc may have affinity to the western zone of the nkc that affinity is also supported by geophysical results that suggest the presence of a fossil huangling magma chamber beneath the skc and the western nkc at 10 20 km depth mei et al 2013 therefore our data provide a new understanding of the kongling complex the skc stayed together with the western part of the nkc from mesoarchean to neoproterozoic 2 9 0 8 ga time and they were separated by the intrusion of the huangling magmas at 0 8 ga

large igneous provinces lips definition recommended terminology and a hierarchical classification abstract this article is an appeal for the adoption of a correct and appropriate terminology with respect to the so called large igneous provinces lips the term lip has been widely applied to large basaltic provinces such as the deccan traps and the term silicic large igneous province slip to volcanic provinces of dominantly felsic composition such as the whitsunday province however neither term lip slip has been applied to the large granitic batholiths of the world e g andes to which both terms are perfectly applicable lip has also not been applied to broad areas of contemporaneous basalt magmatism e g indochina mongolia and sizeable layered mafic intrusions e g bushveld which in many significant respects may also be considered to represent large igneous provinces here i suggest that the term lip is used in its broadest sense and that it should designate igneous provinces with outcrop areas 50 000 km 2 i propose a simple hierarchical classification of lips that is independent of composition tectonic setting or emplacement mechanism i suggest that provinces such as the deccan and whitsunday provinces should be called large volcanic provinces lvps whereas large intrusive provinces mafic ultramafic intrusions dyke sill swarms granitic batholiths should be called large plutonic provinces lpps lvps and lpps thus together cover all lips which can be felsic mafic or ultramafic of sub alkalic or alkalic affinity and emplaced in continental or oceanic settings lvps are subdivided here into four groups i the dominantly wholly mafic large basaltic provinces lbps e g deccan ontong java ii the dominantly felsic large rhyolitic provinces lrps e g whitsunday sierra madre occidental iii the dominantly andesitic large andesitic provinces laps e g andes indonesia cascades and iv the bimodal large basaltic rhyolitic provinces lbrps e g snake river high lava plains the intrusive equivalents of lrps are the large granitic provinces lgps e g the andean batholiths although an equivalent term for intrusive equivalents of lbps is not necessary or warranted the accuracy and usefulness of the terms flood basalt plateau basalt and trap are also examined the largest lbp lvp and lip is of course the bulk of the ocean floor it is contended that the proposed lip nomenclature and classification will lead to more accurate and precise terminology and hence better understanding of the wide variety of large igneous provinces