nd isotopic and geochemical constraints on the provenance and tectonic setting of the low grade meta sedimentary rocks from the trans north china orogen north china craton abstract in the trans north china orogen tnco of the north china craton low grade supracrustal successions extensively occur in the wutai luliang zanhuang zhongtiao and dengfeng complexes from north to south meta sedimentary samples from the wutai and zhongtiao complexes were collected for geochemical and nd isotopic studies and several samples from the zanhuang and dengfeng complexes were also analyzed for nd isotopic studies for comparative purpose most of the meta siltstones and meta sandstones from the wutai and zhongtiao complexes are characterized by depletions in mobile elements like cao sr and na2o high chemical index of weathering ciw values and strong positive correlation between al2o3 and tio2 indicating intense weathering conditions significant post depositional k metasomatism is indicated in the a cn k diagrams for most of the analyzed samples and the relatively high pre metasomatized chemical index of alteration cia values 43 87 also imply a high degree of source weathering depleted transitional trace elements ni cr co and sc fractionated light rare earth elements patterns mild negative eu anomalies in the majority of these meta sedimentary samples point toward felsic source rocks including the 2 5 ga granitics ttg gneisses and the paleoproterozoic granitics in the tnco minor contribution from mafic rocks is evidenced from relative high contents of mgo fe 2 o 3 t sc and lower la ybn ratios in some older sequence set samples from the zhongtiao complex our geochemical and nd isotopic data combined with previous studies in the lithostratigraphic sequence provenance and depositional age suggest that the older and younger sequence sets of the low grade supracrustal successions in the tnco were deposited in the different depositional environments the older sequence set was deposited in a back arc basin between the andean type continental margin arc and the eastern block after 2 1 ga whereas the younger sequence set formed in a foreland basin between 1 88 and 1 80 ga which is consistent with the model that the collision between the eastern and western blocks to form the trans north china orogen occurred at 1 85 ga

element geochemistry and neodymium isotope systematics of the neoarchean banded iron formations in the qingyuan greenstone belt north china craton abstract pure marine chemical sediments such as banded iron formations bif are excellent archives of ancient seawater and may also provide constraints on the coeval hydrosphere atmosphere system however on the bases of interpreted depositional settings it has long been argued that algoma type bif merely recorded the intrabasinal volcanic or hydrothermal conditions here we couple systematic major and trace elements data with samarium sm neodymium nd isotopic analyses of 2 56 ga old algoma type bifs and associated schists from different stratigraphic horizons of the qingyuan greenstone belt qgb in the north china craton ncc to characterize the source and depositional environment over a short period 30 ma meanwhile we also compare our results with data for other archean to paleoproterozoic superior and algoma type bifs especially those near contemporaneous counterparts in the ncc to further evaluate the reliability of qgb bifs as proxies for the neoarchean seawater low al2o3

alteration mineralogy and stable isotope geochemistry of paleoproterozoic basement hosted unconformity type uranium deposits in the athabasca basin canada unconformity type uranium deposits are characterized by mineralization developed along the contact between younger sandstone cover and underlying crystalline basement rocks mineralization may extend up to 400 m into the underlying basement rocks whereas sandstone hosted unconformity type deposits have been well studied deposits hosted primarily in the basement have not this study examines the deposits at rabbit lake dawn lake and mcarthur river in the athabasca basin of canada which are hosted by the metamorphic archean and early paleoproterozoic rocks forming the basement to younger late paleoproterozoic sandstones alteration is similar in the three deposits and is characterized by three distinct paragenetic stages 1 preore alteration involving illitization of plagioclase and amphibole followed by chloritization of biotite and illite which formed at ca 230 c 2 ore stage alteration characterized by uraninite and coarse grained illite which formed at ca 240 c 3 postore alteration comprising spherulitic dravite vein chlorite quartz calcite and fe cu co and pb sulfides which formed at ca 135 c fluid circulation associated with emplacement of later mackenzie dikes initiated partial recrystallization of uraninite a later stage of alteration includes kaolinite and iron hydroxide precipitation formed at much lower temperatures of ca 50 c stable isotope compositions of the alteration minerals in conjunction with their paragenesis indicate that oxidized basinal fluids d 43 to 21 18o 3 8 were derived primarily from evolved seawater and leached uranium from the overlying sandstones of the athabasca formation and transported it into the basement via infiltration along fracture zones associated with reverse faults graphitic units in the basement and preore alteration served as both physical fractured zones and chemical reductants traps for the uranium mineralization the basinal fluids were responsible for the preore illite chlorite synore uraninite illite and the early postore alteration events this differs from many other sandstone hosted deposits where both oxidized basinal and reduced basement derived fluids were responsible for uranium precipitation

rare earth element and mineralogic changes in holocene soil and stream sediment a case study in the wet mountains colorado u s a size fractions of soil and stream sediment developed on plutonic metamorphic or mixed plutonic metamorphic sources in the wet mountains colorado have been analyzed for ree rare earth elements and mineralogy the clay sized fractions 0 5 m and 0 5 2 m or 2 m have ree contents that are similar to more enriched than the source eu sm ratios that are similar to the source and la lu ratios that are higher than their corresponding source the 0 5 m fractions have lower ree contents than the corresponding 0 5 2 m fraction in every stream sediment for example unweathered san isabel batholith near the sampled stream sediment contains ree 511 712 ppm and eusmratio 0 17 0 19 and lalu cn 9 8 10 3 the corresponding 0 5 and 0 5 2 m fractions of sediment formed from san isabel batholith are enriched in the ree ree 1135 and 2225 ppm respec are slightly lower in eu sm ratios 0 16 and 0 14 respec and are higher in la lu ratios 12 2 and 16 3 respec than the unweathered rocks the silts have lree light ree contents and eu sm ratios very similar to the source due to similar mineralogy but silts have hree heavy ree contents higher than the source due to high zircon for example silt sized fractions in stream sediment draining the san isabel batholith contain ree 808 ppm eusmratio 0 18 and lalu cn 7 4 in contrast the sands contain lower ree contents similar to higher eu sm ratios and lower la lu ratios than the corresponding source due to depletion in heavy minerals concentrated in the ree and containing lower eu sm ratios relative to quartz and feldspar depleted in the ree and containing higher eu sm ratios for example the sand fraction from stream sediment from the san isabel batholith has ree 206 ppm eusmratio 0 17 and lalu cn 5 6 small variations of accessory minerals concentrated in the ree like allanite or sphene may cause drastic variation in ree content in the sand fraction clays and silts derived only from the plutonic rocks have higher ree and similar to lower eu sm ratios than corresponding fractions derived only from migmatites e g ree of silt fractions from migmatites 224 ppm and from plutons 375 808 ppm eu sm ratios from migmatites 0 17 and from plutons 0 11 0 18 the ree content and the eu sm ratio of clays and silts derived from migmatites are much more similar to the average of mcps mid continent platform sediment than corresponding fractions derived from the plutons mcps has ree 192 ppm eusm 0 19 lalu 8 0 the eusm ratio of sands derived from plutons and migmatite are lower to mostly higher than the mcps the ree content of sands from plutons are not necessarily higher than the mcps due to variation in heavy minerals like allanite or sphene concentrated in the ree sediments derived from mixed sources have ree contents in fine fractions that may not necessarily reflect the ree content of the nearest source for example 0 5 2 m and silt fractions developed on the san isabel batholith with a migmatite upstream have the high ree content of the batholith ree in 0 5 2 m fraction 1100 ppm silt 573 ppm while the corresponding 0 5 m fraction has the very low ree content of the migmatites ree 110 ppm these results suggest fine grained material near the source may sample a much larger area than coarser material near the source thus analysis of fine grained sediment associated with coarse grained material near the source may give a much different impression of the source than would determination of the source using classic petrographic examination of the sand or gravels

tectonic affinity of nisutlin and anvil assemblage strata from the teslin tectonic zone northern canadian cordillera constraints from neodymium isotope and geochemical evidence we present geochemical and isotopic data for nisutlin assemblage metasedimentary rocks and anvil assemblage greenstones from the teslin tectonic zone of the northern canadian cordillera this study aims to establish the tectonic setting of formation for the sedimentary and basaltic protoliths of these highly deformed and metamorphosed rocks and thereby place constraints on the origin of these enigmatic rocks for which differing tectonic models have been proposed for the nisutlin assemblage metasedimentary rocks the geochemical and isotopic data show that two widely different source regions contributed detritus to the original sediments one source region was felsic upper crustal material with nd isotopic compositions compatible with ultimate derivation from the north american continent depleted mantle model age tdm 2 5 2 8 ga the second source region is deduced to be chemically primitive crust basaltic andesitic with a short crustal residence history 0 9 ga for the anvil assemblage greenstones immobile trace element abundances are dissimilar to within plate oceanic arc and normal mid ocean ridge basalts and similar to calc alkaline basalts in active continental margin settings we interpret the paleosetting for the nisutlin assemblage to be at the outermost margin of the ancestral north american continent in an area which received detrital input from the distal north american craton in the early paleozoic however this area also received detritus from a chemically and isotopically juvenile magmatic arc source a source type not known from paleozoic metasedimentary rocks from the miogeoclinal sequence on the basis of similar nd isotopic relationships recorded elsewhere in deformed paleozoic rocks of the orogen we infer that these geochemical signals reflect tectonic processes of regional extent the trace element geochemistry of the anvil assemblage greenstones does not support a correclation with known paleozoic greenstones of the slide mountain terrane which some tectonic models have advocated

the wathaman batholith an early proterozoic continental arc in the trans hudson orogenic belt canada the wathaman batholith a major element of the trans hudson orogenic belt in northern saskatchewan and manitoba has an exposed strike length of 900 km this immense body separates dominantly archean rae hearne provinces to the northwest from early proterozoic arc related terranes of the orogen to the southeast major and trace element data for 42 samples from the saskatchewan part of the batholith are similar to those of phanerozoic arc batboliths for example sierra nevada and andean batholiths data plotted on trace element discrimination diagrams show that the batholith has continental arc affinities u pb zircon geochronology of five main phase granite samples suggests that most of the batholith formed between 1865 and 1850 ma and is coeval with smaller plutons of the la rouge arc the main deformation of the batholith is limited by the 1830 ma age of a late granite sheet that crosscuts folds and foliation of main phase granites the 15 to 25 m y crystallization span of the batholith is similar to the histories of many more recent continental magmatic arcs

crustal history of the rae and hearne provinces southwestern canadian shield saskatchewan constraints from geochronologic and isotopic data abstract the cree lake zone hearne province and western granulite domain rae province in northern saskatchewan are contrasting parts of the variably reworked upper plate western hinterland of the paleoproterozoic trans hudson orogen their junction is defined by the virgin river shear zone a part of the more extensive snowbird tectonic zone subsurface extension of the 2 0 ga thelon orogen lies west of the western granulite domain we present u pb zircon ages sm nd and rb sr isotopic data from the cree lake zone and western granulite domain and from the junction granite which intrudes the virgin river shear zone data from the western granulite domain indicate that prevalent granulite facies metamorphism occurred between 2 3 and 2 0 ga but is imposed on archean protoliths 2 8 3 0 ga old low amphibolite facies retrogression which increases toward the virgin river shear zone probably postdates 2 1 ga data from the cree lake zone also yield archean protolith ages as old as 3 0 ga and some rocks yield interpreted high grade metamorphic overprint ages of 2 3 2 0 ga however two samples yield data indicating hudsonian high grade metamorphic overprint 1 87 to 1 81 ga the junction granite has a u pb zircon age of 1 82 0 30 ga but relict zircons and sm nd data show that it was derived by melting of archean crust high grade mid crustal thermal resetting in the western granulite domain may be coeval with the 1 9 2 0 ga thelon orogen although the data do not preclude an earlier event or events similar 2 3 2 1 ga reworking extends into the cree lake zone but high grade hudsonian 1 87 1 84 ga reworking is also evident in parts of this zone well to the west of the wollaston domain and may extend entirely across the zone to the virgin river shear zone relative importance of the thelon and hudsonian overprints in cree lake zone is unknown data from the junction granite and western granulite domain suggest that all recorded high strain events in the virgin river shear zone postdate 2 3 ga and are thus unrelated to deep crustal archean granulite facies mylonites in the tantato black lake segment of the snowbird tectonic zone north of the athabasca basin

sedimentary rocks and crustal evolution tectonic setting and secular trends a significant change in the composition of turbidites deposited at active tectonic settings is seen at the archean post archean transition in comparison to post archean active margin turbidites archean greenstone turbidites exhibit more uniform th sc ratios but with a similar average greater hree depletion gd n yb n 2 less eu depletion eu eu mostly 0 85 and an absence of low th u ratios th u 3 these data indicate that differing mantle sources and or conditions of mantle melting existed during the archean and that intracrustally differentiated rocks older cratons or young differentiated arcs were relatively unimportant as provenance components for archean turbidites in contrast some sedimentary rocks preserved in archean platformal sequences of high grade terranes display significant negative eu anomalies similar to the majority of post archean shales indicating that the general process of cratonization including intracrustal differentiation has taken place since at least 3

late quaternary paleoseismology and faulting behavior of the yilan yitong fault zone and implications for seismic hazards of the tanlu fault zone eastern china abstract along the north branch of the tanlu fault zone tlfz the yilan yitong fault zone yyfz displaces quaternary geomorphic features forming a 70 km long fresh surface rupture in this study we investigated offset landforms and paleoearthquake history by excavating four trenches along the yyfz within the fangzheng graben combined with quaternary dating of landforms and trench horizons four paleoearthquakes are identified with their timings constrained at 1730 40 a bp to 770 30 a bp 28 5 1 2 ka bp to 21 7 0 9 ka bp 59 4 2 4 ka bp to 33 1 1 1 ka bp and before 59 4 2 4 ka bp respectively seismic recurrence behavior of the yyfz follows a quasi periodic pattern with a very long interval of 10 20 ka geological and geomorphic features show that the yyfz is dominated by right lateral strike slip movement with a low dextral slip rate of 0 2 0 3 mm a in late quaternary in accord with present day geodetic observations as with the yyfz paleoearthquakes along the tlfz commonly share a recurrence interval of 10 20 ka we suggest that active segments of the tlfz that have been dormant for thousands of years may pose significant earthquake hazards in the future moreover strain transfer from the bounding faults to those more central in the graben may be significant on the tlfz and should be given consideration when assessing regional seismic hazards insight into past earthquakes and faulting behavior in a low strain environment is crucial for earthquake hazard analysis and often requires multidisciplinary approaches

the sask craton and hearne province margin seismic reflection studies in the western trans hudson orogen a three dimensional model of the regional crustal architecture of the western trans hudson orogen based on the interpretation of 590 km of deep sounding seismic reflection data and a comparable length of existing seismic reflection information is presented the seismic images identify the regional geometry of the basal detachment zone pelican thrust that separates juvenile allochthonous terranes from the underlying archean microcontinent sask craton the sask craton is inferred to have a minimum spatial extent of over 100 000 km2 with an associated crustal root that extends for 200 km along strike during terminal collision complete convergence of the rae hearne and superior continental blocks was precluded by the presence of the sask craton resulting in the preservation of anomalous amounts of oceanic and associated sedimentary juvenile material along regional tectonic strike consistency of crustal structure across the rae hearne margin reindeer zone boundary is established several phases of

continental arc magmatism along the southeast hearne craton margin in saskatchewan canada comparison of the 1 92 1 91ga porter bay complex and the 1 86 1 85ga wathaman batholith abstract detailed mapping coupled with geochronological and geochemical investigations has revealed the presence of a 1917 1913 ma gabbro monzodiorite monzonite suite along the southeast margin of the hearne craton in northern saskatchewan canada the predominantly plutonic suite is also characterised by 1915 ma old trachyandesitic subvolcanic and volcaniclastic inclusions the rocks are hornblende epidote titanite augite bearing and collectively termed the porter bay complex the plutonic rocks cut the 2569 ma lueaza river granitoid suite a component of the hearne craton and are themselves intruded by 1859 ma pegmatitic diorite 1856 ma layered gabbro anorthosite and 1853 ma quartz diorite belonging to the wathaman batholith one of the world s largest paleoproterozoic andean type continental arcs wholerock major element geochemistry characterises the porter bay complex as calc alkalic to alkali calcic metaluminous and variable from ferroan to magnesian trace element concentrations are characterised by negative high field strength element anomalies suggesting emplacement along a destructive plate margin the geochemical signatures of the wathaman batholith and the porter bay complex are largely identical the geographic location map relationships and geochronological geochemical and petrographic constraints are consistent with the porter bay complex having formed in a subduction related continental arc setting the southeastern margin of the hearne craton was therefore a long lived active continental margin with two separate periods of continental arc magmatism between 1 92 1 91 ga and 1 86 1 85 ga

granulite fades nd isotopic homogenization in the lewisian complex of northwest scotland a published sm nd whole rock isochron of 2 920 50 myr obtained from a wide range of lithologies in the lewisian complex of north west scotland was interpreted1 as the time of protolith formation this date is 260 myr older than estimates for the timing of high grade metamorphism in the complex at 2 660 myr2 3 and this period is considered to represent the duration of the lewisian crustal accretion differentiation superevent cads 4 here we give new sm nd data obtained specifically from granulite facies tonalitic gneisses that yield a date of 2 600 155 myr although depleted mantle model ages tdm suggest 200 myr of premetamorphic crustal residence the regression date and its associated initial nd isotopic parameters demonstrate nd isotopic homogenization during the high grade event as well as the probability of general rare earth element ree mobility models for selective element depletion in the complex have previously assumed ree immobility since 2 920 myr but the data presented here suggest that a reappraisal of the depletion mechanism is required

geochemical and nd isotopic constraints for the origin of late archean turbidites from the yellowknife area northwest territories canada abstract a detailed geochemical and isotopic study of late archean turbidites and volcanic rocks from the yellowknife area slave province was undertaken to constrain the nature of exposed crust at the time of 2 6 to 2 7 ga crustal consolidation the nd t values of the volcanic rocks range from 1 7 to 4 4 this variation can be produced by assimilation of pre 2 8 ga basement by a depleted mantle derived magma possibly followed by fractional crystallization the turbidites are typically metamorphosed to greenschist to amphibolite facies and where metamorphosed to greenschist facies different units of bouma sequence can be observed the different units of bouma sequence were sampled and analyzed separately to evaluate the possible differences in geochemical and isotopic signatures the geochemical data presented here is in accord with the previously proposed model that argues for a mixture of 20 mafic intermediate volcanic rocks 55 felsic volcanic rocks and 25 granitic rocks as a source of these turbidites however our revised calculation with the new data presented here argues for 1 to 2 input from an ultramafic source as well as somewhat higher input from mafic intermediate volcanic sources in the upper shale units compared to the lower sand units the nd t values of the turbidites generally are lower in the upper shale units compared to the lower sand units detailed inspection of trace element data suggest that this is not an artifact of rare earth element rich heavy minerals concentrating in the lower sand units of the turbidites but rather is a result of unmixing of detritus with different nd t values during sediment transportation and deposition the upper shale units of the turbidites are isotopically compatible with a derivation mainly from crustally contaminated volcanic rocks similar to those exposed in the yellowknife area the lower sand units contain a higher proportion of westerly derived plutonic rock detritus characterized by higher nd t suggesting that there are area s west of yellowknife not underlain by older 2 8 4 0 ga basement the trace element characteristics of these turbidites i e cr ni la th sc eu eu and gd n yb n are distinct from those of typical post archean turbidites this observation is consistent with the models that predict that the chemical composition of the upper continental crust was slightly different in the archean compared to post archean time

mesoproterozoic neoproterozoic transition geochemistry provenance and tectonic setting of clastic sedimentary rocks on the se margin of the yangtze block south china abstract the se margin of the yangtze block south china is composed of the mesoproterozoic lengjiaxi group and the neoproterozoic banxi group with sinian and post sinian cover a geochemical study was undertaken on the mesoproterozoic neoproterozoic clastic sediments in order to delineate the characteristics of the sediment source and to constrain the tectonic development and crustal evolution of south china our results show that the mesoproterozoic clastic sediments have a dominant component derived from a metavolcanic plutonic terrane with a large of mafic component there is a minor contribution of mafic rocks and older upper crustal rocks to the provenance strong chemical weathering in the source area occurred before transport and deposition the provenance for the neoproterozoic clastic sediments was most likely old upper continental crust composed of tonalite granodiorite dominated tonalite granodiorite granite source rocks which had undergone strong weathering and or recycling a minor component of older k rich granitic plutonic rocks and younger volcanogenic bimodal rocks is also indicated based on the regional geology the geochemical data and the inferred provenance the mesoproterozoic group is interpreted as a successive sedimentary sequence deposited in an extensional rifting back arc basin adjacent to a 1 80 ga continental margin arc terrane the progressive extension rifting of the back arc basin was followed by increasing subsidence and regional uplift during continental marginal arc continent the cathaysian block collision at 1 0 ga caused the deposition of the neoproterozoic group into back arc to retro arc foreland basin therefore the depositional setting of the proterozoic clastic sediments and associated volcanic rocks within the back arc basin reflected basin development from an active continental margin back arc basin with extension or rifting of the back arc basin to a passive continental margin

nd isotopic evolution of the taltson magmatic zone northwest territories canada insights into early proterozoic accretion along the western margin of the churchill province the taltson magmatic zone is a north trending belt of early proterozoic granitoids exposed over an area exceeding 18 000 km 2 in the northwest territories of canada three petrologically and geochronologically discrete intrusive suites comprise the taltson zone these are the 1986 ma deskenatlata suite the 1955 to 1925 ma slave suite and the 1935 ma konth suite the deskenatlata suite is composed of biotite hornblende diorite to granite and displays a more mafic geochemical character relative to the other two intrusive suites initial epsilon nd values for the deskenatlata suite range from 2 7 to 3 6 the slave and konth suites are compositionally heterogeneous to homogeneous leucocratic granitoids that contain numerous xenoliths of dominantly pelitic high grade paragneiss and display a peraluminous granite mineralogy and geochemistry initial epsilon nd values for the konth suite cluster within 4 7 and 5 5 and are completely overlapped by the 4 1 to 6 0 range of the pelitic xe

a cordilleran type batholitic belt in the churchill province in northern saskatchewan abstract the rottenstone and western la ronge domains of the south central churchill province in saskatchewan consist mostly of hudsonian batholithic complexes spatially and structurally related to an aphebian hudsonian volcanic arc the batholithic belt is of comparable dimensions and compositional variation to cordilleran type phanerozoic batholiths and appears to be emplaced in close proximity to a prior late archean early aphebian continental crustal margin a quartz diorite line separating dominant quartz diorite tonalite granodiorite plutonic rocks from dominant granodiorite quartz monzonite granite intrusives can be defined these general characteristics as well as more detailed features of aphebian deposition and hudsonian thermotectonism within and on either side of the rottenstone domain suggest a continental margin rather than an intracontinental location for evolution of the hudsonian orogenic belt of the south central churchill province and provide some insights into the possible development of this part of the canadian shield as part of a hudsonian wilson cycle

geochemical and nd isotopic compositions of the metasedimentary rocks in the la ronge domain trans hudson orogen canada implications for evolution of the domain abstract metasedimentary rocks of greenschist to amphibolite facies occur in various belts in the paleoproterozoic la ronge domain of the trans hudson orogen metasedimentary rocks in the central metavolcanic greenstone belt are low to intermediate in sio2 contents have nd values of 2 3 to 4 5 with two rare earth element ree patterns of la yb n 8 5 respectively the predominant component meta arkoses of the overlying mclennan lake belt have distinctly high k2o and sio2 contents high la yb n ratios 11 46 large negative eu anomalies eu eu 0 1 0 58 and uniformly low nd values 0 8 to 0 2 the maclean lake belt is comprised of a variety of metasedimentary gneisses the volumetrically minor amphibole and diopside rich gneisses have high ferromagnesian element sc and co concentrations high nd values of 4 1 to 5 7 and flat ree patterns with no eu anomalies the predominant lithological unit in the maclean lake belt the psammitic gneisses is geochemically more variable the mafic psammitic gneiss samples in the maclean lake belt and the metasedimentary rocks in the central metavolcanic belt are similar in trace and major element geochemistry and nd isotope composition whereas those more felsic psammitic gneisses are similar to the mclennan lake meta arkoses geochemical data combined with lithological and geochronological evidence indicate that sediments in the central metavolcanic belt were derived mainly from contiguous volcanic debris with minor addition of felsic components from exotic sources in contrast the mclennan lake meta arkoses were derived from a distinct felsic source whereas the psammitic gneisses in the maclean lake belt are mixtures of volcanic materials in the central metavolcanic belt and meta arkoses like felsic components nd isotopic data and ages of detrital zircon suggest that proterozoic juvenile materials were dominant sources for metasedimentary rocks in the la ronge domain comparison of geochemical signatures of the metasedimentary rocks with those of the felsic plutonic rocks in the central metavolcanic belt suggests that the felsic materials in the mclennan lake and maclean lake belts could not have been derived predominantly from the plutonic rocks implying more distal sources topographic changes during collision may have resulted in a shift from mixing of both local and distal sources for the rocks in the maclean lake belt to the dominance of a more distal source for the mclennan lake meta arkoses

the control of depositional depth tectonic uplift and volcanism on sedimentation processes in the back arc basins of the western pacific ocean nine sediment types are recognized in cores recovered by the deep sea drilling project from back arc basins in the western pacific these include submarine fan turbidites debris flows silty basinal turbidites biogenic pelagic carbonate sediments resedimented carbonates biogenic pelagic silica sediments pyro clastics hemipelagic clays and pelagic clays most of these sediments were deposited independent of basinal rifting spreading processes the transition from biogenic pelagic carbonate sediments into overlying pelagic clays is the only sedimentary sequence dependent on basinal tectonic processes through post rifting subsidence associated with heat loss hemipelagic clays and silty turbidites are controlled by sediment yield from continental sources and by climatic change whereas deposition of biogenic pelagic sediments depend on ocean circulation and on latitudinally defined productivity zones coarse pyroclastics are the product of local volcanic periodicity whereas ash deposition is contr

continental tholeiitic mafic rocks of the paleoproterozoic hurwitz group central hearne sub domain nunavut insight into the evolution of the hearne sub continental lithosphere the paleoproterozoic hurwitz group of the western churchill province is an erosional remnant of an areally extensive predominantly shallow water intracratonic basin comprised of four major sequences sequence 2 forming the central part of the stratigraphy contains the ameto formation a sequence of pillowed and massive basaltic rocks and associated gabbro sills termed the happotiyik member that are interlayered with subordinate deep water mudstones siltstones and diamictites whole rock geochemical data for the mafic rocks reveals a suite of homogeneous tholeiitic basalts with affinities to both continental and volcanic arc tholeiites compatible trace elements and large ion lithophile elements exhibit scattered behavior whereas all high field strength elements show a systematic increase with zr the rocks are large ion lithophile and light rare earth element enriched and have parallel primitive mantle normalized extended trace element patterns with prominent negative nb ta and ti anomalies end

behavior of isotopic systematics during deformation and metamorphism a hf nd and sr isotopic study of mylonitized granite a combined compositional and hf nd and sr isotopic study was performed on a suite of samples of progressively deformed granite from a mylonite zone in the harquahala mountains western arizona to evaluate the effects of deformation and metamorphism on the isotopic systematics of typical continental crustal rocks the 1 4 ga harquahala granite was deformed during mesozoic thrusting along the harquahala thrust granite in the resulting 60 m wide shear zone ranges from protomylonite to ultramylonite in most of these mylonites the protolith is not megascopically recognizable and can be discerned only by the progressive transition to undeformed granite isotopic analyses of hf nd and sr from the shear zone document the immobility of the hf and nd isotopic systems relative to that of the sr isotopic system during deformation the rb sr isotopic data show considerable scatter on an isochron plot exhibiting both gains and losses of rb and sr from the whole rock systems in contrast the sm nd and lu hf isotopic systematics are mostly well behaved on isochron diagrams plotting mostly in tight clusters or along 1 4 ga isochrons these results show that while the sr isotopic system in crustal rocks is quite susceptible to later tectonic disturbance both hf and nd isotopic systems can provide reliable model age information in continental crustal terranes even when the rocks have been subjected to low to medium grades of deformation and metamorphism

geochemistry zircon u pb dating and tectonic implications of the palaeoproterozoic ji an and laoling groups northeastern jiao liao ji belt north china craton abstract the jiao liao ji belt is located between the longgang and langrim blocks in the eastern block of the north china craton ncc the belt comprises palaeoproterozoic volcanic sedimentary successions that are divided into the ji an south liaohe and jingshan groups in the south and the laoling north liaohe and fenzishan groups in the north the tectonic setting and depositional environments of the liao ji area are debated this paper presents geochemical and detrital zircon u pb data for the boron bearing graphite bearing aluminum rich ji an group and the clastic sediments and carbonates of the laoling group in southern jilin province in order to constrain their depositional ages provenance and tectonic setting zircon geochronology for both the ji an and laoling groups yields age peaks of 2 57 2 41 2 23 2 09 and 2 04 2 02 ga indicating that the sediments were derived from the longgang and or liaonan block s the 2 2 2 1 ga liaoji granitoids and 2 0 ga igneous rocks respectively on the basis of the youngest detrital zircons and the oldest metamorphic zircon peaks depositional ages can be constrained to the period of 2 13 1 94 2 10 1 94 and 1 95 1 90 ga for the mayihe huangchagou and dadongcha formations of the ji an group and 2 18 1 90 2 08 1 91 1 99 1 90 1 96 1 90 and 1 94 1 90 ga for the dataishan zhenzhumen huashan linjiang and dalizi formations of the laoling group respectively the zircon age spectra of each formation indicate that deposition of the ji an and laoling groups was related to the opening and closing of a back arc during the period 2 2 1 9 ga the dataishan formation laoling group was deposited in the rift environment during opening of the back arc during the early stage the mayihe and huangchagou formations ji an group were deposited on the side of the magmatic arc and the zhenzhumen formation laoling group was deposited on the passive margin side during the late stage both ji an and laoling groups were deposited in a pre orogenic setting including the dadongcha huashan linjiang and dalizi formations detrital zircon age spectra of the ji an group are similar to those of the south liaohe group with the exception of the gaojiayu formation indicating that the two groups had a similar provenance

u pb zircon ages from the lynn lake and rusty lake metavolcanic belts manitoba two ages of proterozoic magmatism two ages of magmatism have been determined from zircon in felsic flows and plutons in the churchill province of manitoba a rhyolite flow from the lynn lake metavolcanic belt has a u pb age of and a rhyolite flow from the adjacent rusty lake metavolcanic belt has an age of tonalite and quartz diorite from two composite plutons emplaced into the volcanic rocks at lynn lake have ages of and indistinguishable from the age of the rusty lake belt rhyolite the arcuate domain of metavolcanic rocks that includes the rusty lake belt in the southeast the lynn lake belt in the north and the la ronge belt saskatchewan in the southwest has previously been considered a single structural sub province with similar ages throughout our results and published u pb ages from saskatchewan indicate that an older magmatism is represented by volcanic rocks in the lynn lake belt a younger magmatism by volcanic rocks in the rusty lake and la ronge belts and plutons in the lynn lake belt at lynn lake the older magmati

mineral reactions and element migration during metamorphism of calcareous sediments from the vassalboro formation south central maine k na and co 2 were progressively lost during the metamorphic event no mass transfer of fe mg ti si or ca sodium was probably lost through a mineral fluid hydrolysis reaction that destroyed the albite component of plagioclase and produced quartz anorthite and a soluble na bearing fluid species potassium was probably lost independently through a mineral fluid hydrolysis reaction that destroyed biotite and formed calcic amphibole sphene anorthite and a soluble k bearing fluid species h 2 o was also progressively lost observed amount of mass transport of k and na requires 1 10 rock volumes of fluid interacting with the carbonate rocks regional metamorphism considered as possible large scale acid metasomatism modified journal abstract

contrasting patterns of alteration at the wheeler river area athabasca basin saskatchewan canada insights into the apparently uranium barren zone k alteration system previous studies on athabasca basin unconformity related uranium deposits have focused on major deposits and have not investigated sites with barren alteration systems that could clarify some of the critical factors controlling mineralization processes a paragenetic study of the wheeler river area reveals the presence of minerals that formed during the diagenetic the main hydrothermal which is subdivided into early mid and late hydrothermal substages and the late alteration stages the diagenetic stage consists of early quartz overgrowths siderite rutile hematite and abundant dickite in the pore spaces of the manitou falls formation the early hydrothermal alteration substage is characterized by pervasive 1mc muscovite alteration and minor goyazite clusters which formed from oxidizing basinal fluids at temperatures around 240 c prior to 1550 ma based on ar ar dates the mid hydrothermal alteration substage comprises dravite and sudoite in the basal 200 m of the manitou falls formation which are interpreted to have formed at temperatures around 175 c from fluids chemically distinct but isotopically similar to the basinal fluids involved during the early hydrothermal alteration substage the late hydrothermal substage was observed only at zone k of the wheeler river area and is characterized by the precipitation of clinochlore copper sulfides and florencite from reducing basement fluids emerging into the manitou falls formation at temperatures around 230 c creating a 250 m high by 250 m wide reducing halo oxidized uranium bearing basinal fluids interacted with the manitou falls formation during the early hydrothermal substage prior to the arrival of the reducing fluids during the mid and late hydrothermal substages and this precluded uranium precipitation the post hydrothermal alteration stage is characterized by formation of kaolinite after late hydrothermal clinochlore near fractures by meteoric waters a minimal amount of leachable radiogenic pb with a pb pb model age of 1907 ma that is older age than both the athabasca basin and the main mineralization event of 1590 ma was encountered at zone k indicating low probability of this area to host uranium mineralization however areas of possible unconformity related uranium deposits were identified outside zone k wherein significant amounts leachable radiogenic pb were observed

proterozoic collisional tectonism in the trans hudson orogen saskatchewan isotopic and structural data from the juvenile reindeer zone of the trans hudson orogen northern saskatchewan indicate a pre 1 85 ga thermotectonic event possibly reflecting arc continent collision followed by a more extensive nappe forming ca 1 83 1 80 ga thermotectonism during terminal continent continent collision preliminary data from the adjacent ensialic cree lake zone suggest high grade reworking of archean crust by the pre 1 85 ga event in the rae province to the west high grade metamorphism and reworking of archean crust occurred about 2 0 ga and may be related to the formation of the coeval taltson magmatic zone

tectonic setting of western pacific marginal basins abstract global kinematics as well as magnetic anomalies of marginal basins with continental geology and paleomagnetic data as additional constraints are used to present a set of reconstructions of the western pacific marginal basins between 56 ma and the present at key periods 56 43 32 20 12 and 3 ma our model accounts for the rapid motion of exotic terranes along the whole of the western pacific convergent zone marginal basins appear to open in a great variety of tectonic settings the two extreme examples being the mariana trough where trench suction may be the predominant driving force and the south china sea where intracontinental deformation appears to be the major mechanism the study of marginal basins is a 3 d problem which must take into account the whole tectonic context subduction related tectonics in cross section and upper plate deformation in map view and not only a 2 d problem the classical trench arc back arc problem

andean tectonics related to geometry of subducted nazca plate seismological and geological data show that tectonic segmentation of the andes coincides with segmentation of the subducted nazca plate which has nearly horizontal segments and 30 east dipping segments andean tectonics above a flat subducting segment between 28 s to 33 s are characterized by from west to east 1 a steady topographic rise from the coast to the crest of the andes 2 no significant quaternary and possibly neogene magmatism 3 a narrow belt of eastward migrating apparently thin skinned neogene to quaternary shortening of the andes and 4 plio pleistocene uplift of the crystalline basement on reverse faults in the pampeanas ranges from about 15 to 24 s over a 30 dipping subducted plate a west to east andes cross section includes 1 a longitudinal valley east of coastal mountains 2 an active neogene and holocene andesitic volcanic axis 3 the altiplano puna high plateau 4 a high neogene but inactive thrust belt eastern cordillera and 5 an active eastward migrating subandean thin skinned thrust belt tectonics above a steeply subducting segment south of 33 s are similar west of the volcanic axis but quite different to the east early cenozoic tectonics of western north america were quite similar to the neogene andes however duration of segmentation was longer and the width of deformation was greater in the western united states patterns of crustal seismicity are systematically related to plio quaternary structural provinces implying that current deformational processes have persisted since at least the pliocene horizontal compression parallel to the plate convergence direction is indicated to a distance of 800 km from the trench above flat subducting segments crustal seismicity occurs over a broad region whereas over steep segments it is confined to the narrow thrust belt strain patterns in the forearc region are complex and perhaps extensional and a broad region of the altiplano puna and eastern cordillera appears to be aseismic

are turtleback fault surfaces common structural elements of highly extended terranes abstract the death valley region of the u s a contains three topographic surfaces resembling the carapace of a turtle these three surfaces are well exposed along the black mountain front and are named the badwater copper canyon and mormon point turtlebacks it is widely accepted that the turtlebacks are also detachment surfaces that separate brittlely deformed cenozoic volcanic and sedimentary rocks of the hanging wall from the strongly mylonitic ductilely deformed pre cenozoic rocks of the footwall we have found a turtleback like detachment surface along the southern margin of the alasehir gediz graben in western anatolia turkey this surface qualifies as a turtleback fault surface because it a is overall convex upward and b separates brittlely deformed hanging wall cenozoic sedimentary rocks from the ductilely to brittlely deformed strongly mylonitic pre cenozoic footwall rocks the surface named here horzum turtleback contains striations that overprint mylonitic stretching lineations indicating top to the ne sense of shear this suggests that the northeasterly directed cenozoic extension in the region resulted in a ductile deformation at depth and as the crust isostatically adjusted to the removal of the rocks in the hanging wall of the detachment fault the ductilely deformed mylonitic rocks of the footwall were brought to shallower depths where they were brittlely deformed the turtleback surfaces have been considered unique to the death valley region although detachment surfaces rollover folds and other extensional structures have been well observed in other extended terranes of the world the presence of a turtleback fault surface in western anatolia turkey suggests that the turtleback faults may be common structural features of highly extended terranes

rare earth element geochemistry of australian paleozoic graywackes and mudrocks provenance and tectonic control abstract in the paleozoic graywackes of eastern australia there is an increase in the total abundance of rare earth elements ree a light to heavy ree ratio and a decrease in the chondrite normalized eu anomaly with the increase in sio2 al2o3 and k2o na2o ratios this is due to the change in the dominant source rocks from andesite to dacite to granite gneiss and sedimentary rocks similarly an increase in total ree and a decrease in eu anomaly is also seen in the associated mudrocks with the increase in total clay content this correlation in paleozoic sedimentary rocks suggests that the ree characteristics of terrigenous sedimentary rocks reflect the depositional tectonic setting of the basin the oceanic island arc type graywackes are characterised by their lower total ree abundance only slight enrichment of lree over hree and the absence of a negative eu anomaly on chondrite normalised plots the continental island arc type graywackes are discriminated by their higher ree abundance and la yb ratio the presence of a small negative eu anomaly on the chondrite normalised plots and the significant enrichment of eu compared to paas post archean average australian shale the sedimentary rocks deposited on andean type active continental margins passive margins platform and cratonic basins are all characterised by the high enrichment of lree over hree and the presence of a pronounced negative eu anomaly on chondrite normalised plots and can not be discriminated from each other by ree patterns alone

u pb geochronology in the trans hudson orogen northern saskatchewan canada we have obtained u pb ages on zircons from volcanic and plutonic units in several lithotectonic domains of the southern trans hudson orogen in northern saskatchewan these data constrain the timing of early proterozoic orogenic events in the region and enhance our understanding of both the relationships among local domains and the relationship of the trans hudson orogen to other early proterozoic orogens in north america with one exception all units studied so far yield zircon ages of 1890 1835 ma most of which are systematically earlier than previously reported rb sr isochron ages on the same or similar units suggesting open system behavior in the rb sr systems five metarhyolites from volcanic sequences in the la ronge domain glennie domain and hanson lake block give ages ranging from 1888 to 1876 ma most of the plutons we dated ranging from gneissic syntectonic tonalites and granodiorites to less deformed late intrusions such as the wathaman batholith and other smaller bodies yield ages of 18

nd isotope and geochemical constraints on the depositional setting of paleoproterozoic metasedimentary rocks along the margin of the archean hearne craton saskatchewan canada abstract the cree lake zone in the southwestern part of the hearne craton reworked during the paleoproterozoic trans hudson orogeny includes the wollaston group a sequence of paleoproterozoic metasedimentary rocks as these rocks have been multiply deformed and metamorphosed to high grade a geochemical and isotopic study was initiated to see through the overprinting events to better constrain the provenance and evolution of the wollaston group the wollaston group consists of thick sedimentary successions representing different depositional and tectonic environments that can be subdivided into two subgroups the lower subgroup is represented by deep water turbidite to shallow water marine deposits the upper subgroup separated from the lower one by a regional unconformity comprises molasse type assemblages ranging from talus to shallow marine lacustrine with subordinate volcanogenic rocks major and trace element data obtained from 31 psammopelitic rocks indicate that the clastic material was derived from sources consisting of both felsic and mafic material although felsic sources are more important in the samples from the lower subgroup sedimentary tectonic discrimination diagrams demonstrate that most of the wollaston group was deposited on an active continental margin rather than a passive margin the e nd values for the wollaston group psammopelites calculated at 1 92 ga the approximate age of the boundary between the lower and upper subgroups vary from 3 4 to 6 8 which yields an approximate 70 30 mixture between juvenile paleoproterozoic detritus and archean detritus from the hearne craton a secondary source of detritus may be 1 95 2 0 ga rocks of the taltson orogen which is exposed to the west of the archean rae hearne craton the wollaston group records the complete evolution of the western margin of the trans hudson orogen during the paleoproterozoic the rifting of an archean continent at ca 2 1 ga led to the deposition of the passive margin siliciclastic sediments comprising the lowermost but poorly preserved part of wollaston group the formation of a continental arc rottenstone along the hearne margin at ca 1 92 ga resulted in a change in tectonic environment from a passive margin to a back arc basin and detritus in most of the lower subgroup was then derived from both basement and newly formed magmatic arc collision with the juvenile la ronge arc led to uplift along the hearne margin which transformed the back arc basin into a retroarc foreland basin at ca 1 88 ga sedimentary starvation and shallowing of the basin led to widespread accumulation of carbonate and evaporite deposits in the west whereas rapidly uplifted orogenic belts in the east provided sources of coarse grained clastic detritus forming the wollaston upper subgroup closure and inversion of the sedimentary basin occurred by ca 1 86 ga coincident with the emplacement of mafic to felsic intrusive rocks in the cree lake zone and the emplacement of the voluminous ca 1860 ma andean type wathaman batholith into the continental margin closure was manifested by the onset of foreland directed thrusting of the wollaston group