u pb zircon and geochemical constraints on the age origin and evolution of paleozoic arc magmas in the oyu tolgoi porphyry cu au district southern mongolia abstract uranium pb zircon ages are linked with geochemical data for porphyry intrusions associated with giant porphyry cu au systems at oyu tolgoi to place those rocks within the petrochemical framework of devonian and carboniferous rocks of southern mongolia in this part of the gurvansayhan terrane within the central asian orogenic belt the transition from devonian tholeiitic marine rocks to unconformably overlying carboniferous calc alkaline subaerial to shallow marine volcanic rocks reflects volcanic arc thickening and maturation radiogenic nd and pb isotopic compositions e nd t range from 3 1 to 7 5 and 206 pb 204 pb values for feldspars range from 17 97 to 18 72 as well as low high field strength element hfse contents of most rocks mafic rocks typically have 2 are consistent with magma derivation from depleted mantle in an intra oceanic volcanic arc the late devonian and carboniferous felsic rocks are dominantly medium to high k calc alkaline and characterized by a decrease in sr y ratios through time with the carboniferous rocks being more felsic than those of devonian age porphyry cu au related intrusions were emplaced in the late devonian during the transition from tholeiitic to calc alkaline arc magmatism uranium pb zircon geochronology indicates that the late devonian pre to syn mineral quartz monzodiorite intrusions associated with the porphyry cu au deposits are 372 ma whereas granodiorite intrusions that post date major shortening and are associated with less well developed porphyry cu au mineralization are 366 ma trace element geochemistry of zircons in the late devonian intrusions associated with the porphyry cu au systems contain distinct th u and yb gd ratios as well as hf and y concentrations that reflect mixing of magma of distinct compositions these characteristics are missing in the unmineralized carboniferous intrusions high sr y and evidence for magma mixing in syn to late mineral intrusions distinguish the late devonian rocks associated with giant cu au deposits from younger magmatic suites in the district

re os ages for the erdenet and tsagaan suvarga porphyry cu mo deposits mongolia and tectonic implications the erdenet and tsagaan suvarga deposits are the two largest known porphyry cu mo deposits in mongolia replicate re os analyses of molybdenite from these deposits yield ages of 240 7 0 8 and 240 4 0 8 ma for erdenet and 370 1 1 2 and 370 6 1 2 ma for tsagaan suvarga 2 errors the re os age of erdenet is significantly older and that of tsagaan suvarga is slightly older than published 40ar 39ar ages for sericite associated with mineralization in these deposits 207 4 5 0 and 364 9 7 0 ma respectively these re os results suggest that in the hydrothermal environment 40ar 39ar ages may be partly to significantly reset whereas re os ages record and maintain the age of primary mineralization events these re os ages indicate that porphyry mineralization at erdenet and tsagaan suvarga are related to porphyritic intrusions representing the youngest event during regional magmatism in northern and southern mongolia respectively the re os age of erdenet marks the final stage of arc magmatism in northern mongolia followed by late permian collision between the mongolian north china and siberian blocks the re os age of tsagaan suvarga indicates that devonian arc magmatism in southern mongolia was active at the present latitude of 44 n at least until 370 ma

great jurassic thrust sheets in beishan north mountains gobi areas of china and southern mongolia abstract jurassic thrust sheets with minimum displacements of 120 180 km have been discovered within the hercynian indosinian orogenic belt of the beishan of china and south gobi area the thrusts strike e w extend over 1200 km in length and carried meso proterozoic massive dolomitic limestones over strata ranging from neoproterozoic cryogenian and terminal proterozoic to lower middle jurassic slip linear plots based on kinematic indicators such as slickenlines and groove lineations fiber lineations and drag folds adjacent to the fault surface vergence of folds and imbricated thrusts in the upper plate indicate northward movement in the beishan area to the west and southward movement in the south gobi area to the east the two major thrust faults the beishan thrust and south gobi thrust are presumably separated by a major tear fault the ruo shui fault the major thrust faults were later deformed into a series of e w antiforms and synforms and the sheets are separated due to erosion into a number of klippen mainly located on synforms of the major faults the yagan metamorphic core complex which is a result of an extensional event that postdates the thrust event yields an 40 ar 39 ar plateau age of 155 1 10 ma and rb sr isochron age of 153 6 2 ma the thrust sheets formed during the late middle jurassic long after the closure of any oceans in the study area previously reported for this region and are ascribed to a phase of intracontinental deformation the closing of the jurassic tethys or retroarc deformation behind an active continental margin at the southern edge of asia prior to the tethyan collision or and the closing of mongolo okhotsk oceans might be responsible for this event

deposition and fate of organic carbon in floodplains along a tropical semiarid lowland river tana river kenya inland waters organic carbon oc burial by sedimentation has recently been shown to be an important component in river catchment carbon c budgets however data on oc burial by sedimentation are hitherto largely limited to temperate zones we investigated the deposition and fate of sediment associated oc in the floodplains of the tropical lowland tana river kenya between two main gaging stations garissa and garsen freshly deposited surface sediments and sediment cores were sampled and analyzed for oc total nitrogen content stable isotope signatures 13c of oc and grain size distribution in addition we incubated sediment cores to quantify co2 production as a proxy for oc mineralization while the floodplain receives sediment with a relatively low oc content 1 56 0 42 sediments are enriched with oc inputs from floodplain vegetation to levels above 3 sediment cores show a sharp decrease of oc with depth from 3 to 12 oc in the sub surface to less than 1 oc below approximately 60 cm depth relatively elevated oc mineralization rates 0 14 0 07 mol co2 kgc 1 d 1 were recorded we used these data to make a first assessment of the c burial efficiency of the tana river floodplain in contrast to what is observed in temperate environments over 50 of c present in the top layers is lost in less than a century while significant amounts of oc are buried in the tana river floodplain the high rates of postdepositional loss limit the development of a long term c sink within this tropical floodplain

trends and controls of holocene floodplain sedimentation in the rhine catchment article i nfo holocene floodplain sedimentation in the rhine catchment is controlled by human and climate impacts intricate river behaviour modifies the fluvial response to the external impacts making cause effect analysis difficult especially on large spatial scales to better understand the relative importance and interdependencies of external and internal controls temporally resolved floodplain sedimentation rates are established using three different methods i floodplain storage studies on the trunk stream ii depth age analysis of overbank deposits from different parts of the catchment and iii cumulative frequency distributions of 14 c ages from floodplain deposits from various parts of the catchment the applied methodology strongly differs with the available temporal resolution and the size of the corresponding catchment all three methods show a strong increase in sedimentation rate for more recent periods that can be linked to increasing human impact evidences for climate impacts and intricate river behaviour are less clear and hindered by insufficient temporal resolution of the currently available data

compositional trends in arc related deep marine sand and sandstone a reassessment of magmatic arc provenance detrital modes for 524 deep marine sand and sandstone samples recovered on circum pacific caribbean and mediterranean legs of the deep sea drilling project and the ocean drilling program form the basis for an actualistic model for arc related provenance this model refines the dickinson and suczek 1979 and dickinson and others 1983 models and can be used to interpret the provenance tectonic history of ancient arc related sedimentary sequences four provenance groups are defined using qfl qmkp lmlvls and lvflvmilvl ternary plots of site means 1 intraoceanic arc and remnant arc 2 continental arc 3 triple junction and 4 strike slip continental arc intraoceanic and remnant arc sands are poor in quartz mean qfl q 75 they are predominantly composed of plagioclase feldspar and volcanic lithic fragments continental arc sand can be more quartzofeldspathic than the intraoceanic and remnant arc sand mean qfl q values as much as 10 mean qfl f values as much as 65 and mean qmkp qm as much as 20 and has more variable lithic populations with minor metamorphic and sedimentary components the triple junction and strike slip continental groups compositionally overlap both are more quartzofeldspathic than the other groups and show highly variable lithic proportions but the strike slip continental group is more quartzose modal compositions of the triple junction group roughly correlate with the qfl transitional arc field of dickinson and others 1983 whereas the strike slip continental group approximately correlates with their dissected arc field

quantifying historical gully erosion in northern bavaria the wolfsgraben is one of many ravines that cut into the silty sandy material of the triassic benchlands of northern bavaria germany within the research area a gully several meters in depth has carved in to a bluff 500 m west of the upper main valley an analysis of 17 exposures and 30 drillings was conducted within the gully and its colluvial fan in order to reconstruct the soil formation extreme rainfall events and land use changes throughout history detailed field studies chemical soil analysis dating methods of charcoal and pottery as well as written documents were combined to produce a high resolution stratigraphy nine main phases of landscape evolution caused by extreme rainfall runoff and soil erosion in agriculturally used areas have been identified since the medieval period the highest amount of soil loss occurred during 14th 18th and 19th centuries a result of intensive land use climate changes affected the intensity of rainfall and the magnitude of soil loss during these periods d 2003 elsevier science b v all rights reserved

transport of terrestrial organic carbon to the oceans by rivers re estimating flux and burial rates this study re estimates one important component in the global carbon cycle the modern global fluviatile organic carbon discharge and burial rates according to these results approximately 430 1012 g of terrestrial organic carbon are transported to the ocean in modern times this amount is higher than the latest estimates but takes into account new data from oceania not previously considered in global flux studies however only the minor amount of 10 or approximately 43 1012 gc year 1 is most likely buried in marine sediments this amount is similar to the burial of marine organic carbon in the coastal ocean 55 1012 gc year 1 adding both estimates gives approximately 100 1012 gc year 1 which is the value calculated by berner 1982 for terrestrial deltaic shelf sediments however the results in this study suggest that on a global scale the organic carbon content in coastal ocean sediments is not solely of terrestrial origin but a mixture of nearly equal amounts of marine and terrestrial organic carbon the major part of the terrestrial organic carbon that enters the ocean by rivers approximately 400 1012 gc year 1 seems to be either a remineralised in the ocean whereas the mechanism by which the terrestrial organic carbon is oxidised in the ocean are unknown or b is dispersed throughout the oceans and accumulates in pelagic sediments

palaeozoic accretionary and convergent tectonics of the southern altaids implications for the growth of central asia the southern altaids present a unidirectional section from mongolia to china through an accretionary orogen that youngs progressively from neoproterozoic in the north to permian in the south the orogen formed by forearc accretion of island arcs accretionary wedges ophiolites and precambrian microcontinents this regularity was upset by early growth within the ocean of arcs that later collided at the accreting continental margin by imbrication of old ophiolites with young arcs and by himalayan style thrust nappe tectonics when an arc collided into a microcontinent lateral growth of the southern altaids represents a massive addition of juvenile material to the palaeozoic crust

left lateral sense offset of upper proterozoic to paleozoic features across the gobi onon tost and zuunbayan faults in southern mongolia and implications for other central asian faults abstract we present a preliminary study of upper proterozoic to paleozoic features adjacent to and offset across three faults in southern mongolia restoration of four offset stratigraphic units adjacent to the gobi onon fault indicates a left lateral sense offset of 70 95 km the tost fault has a left lateral sense offset of 95 125 km defined by three offset features the zuunbayan fault has seven offset features that display left lateral sense offsets of 185 235 km deformation on these faults apparently occurred during the mesozoic prior to the late cretaceous based upon the age of offset features the age of overlap sequences and inferred timing relationships with regional contractional structures although cenozoic overprinting and reactivation has occurred along parts of these faults thus complicating their restorations we present a testable hypothesis which predicts possible connections between these faults and faults within china

zircon ages and geochemical compositions of the manlay ophiolite and coeval island arc implications for the tectonic evolution of south mongolia abstract numerous small dismembered ophiolite fragments occur in south mongolia but they are very poorly studied the lack of age data and geochemical analysis hampers our understanding of the paleozoic tectonic evolution of the region we conducted detailed studies on the manlay ophiolitic complex and huree volcanic rocks south of the main mongolian lineament mml to provide some constraints on these rocks the manlay ophiolite consists of dunite harzburgite pyroxenite gabbro plagiogranite basalt and chert locally with chromite mineralization in dunite the gabbro and plagiogranite yielded shrimp zircon weighted mean 206 pb 238 u ages of 509 5 ma and 482 4 ma respectively the basalt and dolerite samples of this complex show enrichment in lree and lile and negative nb ta and ti anomalies and the chrome spinel from the chromitite lens in the dunite is characterized by high cr and low tio 2 contents these features suggest a supra subduction zone ssz origin for the ophiolitic complex the huree volcanic rocks ranging from basalt to dacite display enrichment in lree and lile weak eu anomalies and distinctly negative nb ta and ti anomalies consistent with those of typical magmas in a subduction environment an andesite sample from this arc yielded a shrimp 206 pb 238 u zircon age of 487 5 ma which is the oldest reliable age for an island arc in south mongolia recognition of an early paleozoic ophiolitic complex and a coeval island arc indicates that south mongolia underwent a period of active volcanism during late cambrian to ordovician additionally the tuff overlying the ophiolitic complex and a granite intruding the ophiolite have shrimp zircon u pb ages of 391 5 ma and 304 4 ma respectively combining the available data we propose that the early paleozoic subduction accretionary complexes likely constitute the basement of the late paleozoic arc formations and correlate with the lake zone in western mongolia

granites of the southern mongolia carboniferous arc new geochronological and geochemical constraints the crust in southern mongolia is part of the central asian orogenic belt a vast accretionary orogen that records the opening and closure of the palaeo asian ocean in the late proterozoic to palaeozoic the crustal evolution of the region is revealed in basement inliers that also contain intrusion related porphyry ore bodies that are important mineral exploration targets the saykhandulaan inlier in southeast mongolia is a devonian carboniferous segment of island arc crust which is dominantly composed of extrusive and sedimentary lithologies but which also contains the oyut ulaan i type quartz monzonite intrusion a u pb zircon age for the oyut ulaan monzonite indicates emplacement at 330 0 0 5 ma to the east of the saykhandulaan inlier intrusive complexes dominate the neighbouring mandakh inlier new ages are presented for four of these plutons the bronze fox granodiorite 333 6 0 6 ma the narin hudag monzonite 333 2 0 6 ma the shuteen quartz monzonite 325 5 1 0 ma and the north mandakh granite 292 3 0 5 the intrusive bodies of the saykhandulaan and mandakh inliers have two distinct geochronological and geochemical associations 1 mid carboniferous i type monzonites that constitute the most easterly intrusive expression of the southern mongolia carboniferous arc and 2 early permian a type and peralkaline granites that represent a post orogenic phase of voluminous granite emplacement both groups are significantly younger than the nearby oyu tolgoi and tsagaan suvarga cu porphyry ore bodies which have previously been dated as early and late devonian respectively the new data presented here provide constraints on the timing of the transition from island arc magmatism to post collisional extension related magmatism in the region and possible controls on fertile and infertile granitoid intrusions with respect to cu au mineralisation

tertiary strike slip faulting in southeastern mongolia and implications for asian tectonics abstract geologic maps have long portrayed the late cretaceous recent geologic history of southeastern mongolia as tectonically quiescent we present new data based on outcrop observations that indicate the northeast trending east gobi fault zone egfz was reactivated in the cenozoic as a sinistral strike slip fault system inversions of cenozoic fault slip data imply that faulting was associated with north northwest subhorizontal shortening and east northeast subhorizontal extension we propose that faulting is tertiary in age based on published interpretations of seismic reflection data which reveal that the mid cretaceous 100 95 ma unconformity is deformed by strike slip faults and based on field observation of strike slip faults and fracture sets that cut upper cretaceous and cenozoic strata but lack evidence for neotectonic activity published seismicity maps also appear to argue against significant quaternary faulting within the egfz these new data may lend credence to published models proposing a middle miocene or older kinematic linkage between the egfz and the altyn tagh fault in china the recognition that the egfz has a history of left lateral displacement in both the early mesozoic and cenozoic means that currently available estimates of offset based on displaced paleozoic rocks constrain total offset only this reactivation history supports the notion that inherited lithospheric structures are important in controlling the location and thus modes of intracontinental deformation in asia as a function of collisional far field effects and evolving boundary conditions of the pacific margin

a carbon storage perspective on alluvial sediment storage in the rhine catchment abstract floodplains are important sinks in terms of the sediment and carbon flux in fluvial systems despite the large amount of detailed geomorphological studies which include measurements on total organic carbon little is known of the coupling of long term carbon and sediment flux and on the amount of carbon storage in floodplains therefore the influence of the sedimentary facies in fluvial systems was investigated based on a statistical analysis of 1948 organic carbon measurements in different parts of the rhine catchment the analysis allows to develop a conceptual carbon budget model of fluvial systems which was coupled with a holocene alluvial sediment budget to estimate the holocene sequestration rates of carbon storage in floodplains averaged over the rhine catchment the sedimentary carbon sequestration ranges between 3 4 to 25 4 g m 2 yr 1 with more reasonable values between 5 3 to 17 7 g m 2 yr 1 compared to the recent particulate carbon export these values are in the same order of magnitude but somewhat smaller indicating that approximately the same amount of the exported carbon may be stored in floodplains however compared to sedimentary carbon sequestration rates obtained elsewhere the presented values are at the lower limit corresponding to the lower mean holocene soil erosion and floodplain accumulation rates

holocene floodplain sediment storage and hillslope erosion within the rhine catchment the response of fluvial systems to land use and climate change varies depending on catchment size while forcing response mechanisms of small catchments are reasonably well understood the response of larger drainage basins is less clear in particular the impact of land use and climate change on the rhine system is poorly understood because of the catchment size 185 000 km 2 and the long history of human cultivation which started approximately 7500 years ago a sediment budget is calculated to specify the amount of alluvial sediment that was deposited during the holocene and to estimate long term soil erosion rates the results suggest that 599 14 10 9 t of holocene alluvial sediment is stored in the non alpine part of the rhine catchment south and central germany eastern france the netherlands about 50 of holocene alluvial sediment is deposited along the trunk valley and the delta upper rhine lower rhine coastal plain while the rest is stored along the tributary valleys the floodplain sediment storage corresponds to a mean erosion rate of 0 559 0 16 t ha per yr 38 59 10 7 mm kyr across the rhine catchment outside the alps this holocene averaged estimate amounts for sediments that were delivered to the channel network and is at the lower limit of erosion rates from other studies of different methodology

crustal evolution of the saykhandulaan inlier mongolia implications for palaeozoic arc magmatism polyphase deformation and terrane accretion in the southeast gobi mineral belt abstract the saykhandulaan inlier in south east mongolia lies within the central asian orogenic belt caob and records a complex history of palaeozoic tectonism and magmatism associated with terrane accretion on the northern margin of the palaeo asian ocean the inlier spans the boundary between the gobi altai back arc basin terrane in the north and the mandalovoo and gurvansayhan island arc terranes in the south which are notable for their many mineralised intrusions including the oyu tolgoi gold rich copper porphyry deposit results from cross strike transects within the saykhandulaan inlier reveal that it can be subdivided into five parallel east west striking litho tectonic domains 1 the northern slate belt comprising devonian greenschist grade pelites and psammites with deep marine to coastal siliciclastic protoliths 2 the saykhandulaan valley lineament zone svlz a tectonised zone of faulted and lithologically altered volcanic rocks 3 the high strain belt consisting of tightly folded and flattened metamorphosed clastic sedimentary rocks 4 the molasse succession consisting of relatively undeformed coarse conglomerates and sandstones and 5 the oyut ulaan volcanic group a nearly 5 km thick folded carboniferous volcanic succession that hosts the mid carboniferous oyut ulaan mineralised granite the northern slate belt metasedimentary rocks record a northerly cratonic provenance whereas all rocks to the south of the svlz have arc affinities the svlz is thus interpreted to be the boundary between the gobi altai and mandalovoo terranes two major deformation events are documented 1 back arc basin closure and inversion involving regional scale folding and greenschist grade metamorphism in the northern slate and high strain belts 2 contraction associated with mandalovoo terrane accretion and final closure of the palaeo asian ocean to the south following terrane accretion and cessation of subduction crustal extension and strike slip faulting further modified the crustal architecture of the inlier the results presented here provide a useful framework for understanding the crustal evolution of adjacent regions within the southeast gobi mineral belt

radiocarbon anomalies suggest late onset of agricultural intensification in the catchment of the southern part of the yangtze delta china abstract previously underused information from radiocarbon dates in well characterised sedimentary sequences in the southern yangtze delta china is here utilised in reconstruction of patterns of ancient erosion the southern yangtze delta was an important focus of food production in the early neolithic anomalous radiocarbon dates in holocene sediments from the southern part of the delta are unevenly distributed through time two clusters of dates in sediments ca 9000 7000 cal bp and ca 3000 1000 cal bp most likely indicate two periods of intensive erosion and redeposition of organic materials the older of the two clusters may have been associated with a marked episode of marine transgression whereas the younger cluster could reflect increasing levels of human disruption of soils and sediments in the catchment a relatively late increase in anthropogenic soil erosion supports recent archaeological evidence that following its early neolithic origins agricultural expansion and intensification occurred later on the southern yangtze delta than previously thought

petrogenesis and tectonic implications of late carboniferous continental arc high k granites in the dongwuqi area central inner mongolia north china abstract central inner mongolia is located in the southeastern segment of the central asian orogenic belt caob and controversy has long surrounded its late paleozoic tectonic evolution here we present an integrated study of zircon u pb ages whole rock major and trace elements and zircon hf isotopes for five less studied alkali feldspar granitic plutons in the dongwuqi area to the north of the erenhot hegenshan heihe suture zone zircon u pb dating by laser ablation inductively coupled plasma mass spectrometry la icp ms indicates that these granitic plutons were emplaced in the late carboniferous 315 300 ma the late carboniferous alkali feldspar granites belong to high k calc alkaline series and are evolved i type granites they are high in sio2 73 22 77 36 and low in mgo 0 07 0 49 with enrichments in light rare earth elements lrees zr hf rb th and u and depletions in ba nb ta sr and eu the dongwuqi granitic rocks are characterized by high positive zircon ehf t values 7 6 to 15 1 and relatively young two stage hf model tdm2 ages 364 835 ma these geochemical data together the common miarolitic texture indicate that they were derived from partial melting of juvenile arc related mafic to intermediate rocks in the lower crust and eventually emplaced in low pressure conditions or at shallow crustal levels with involvement of extensive fractional crystallization during magma evolution our new results along with the published regional data delineate a ne trending carboniferous continental arc belt more than 1700 km in the northern accretionary zone of the erenhot hegenshan heihe suture accordingly we invoke that the dongwuqi late carboniferous high k granites were emplaced in an active continental margin setting which was probably related to the northwestward subduction of the hegenshan oceanic plate beneath the xing an uliastai nuhetdavaa block

carbon burial in soil sediments from holocene agricultural erosion central europe 1 natural and human induced erosion supplies high amounts of soil organic carbon oc to terrestrial drainage networks yet oc fluxes in rivers were considered in global budgets only recently modern estimates of annual carbon burial in inland river sediments of 0 6 gt c or 22 of c transferred from terrestrial ecosystems to river channels consider only lakes and reservoirs and disregard any long term carbon burial in hillslope or floodplain sediments here we present the first assessment of sediment bound oc storage in central europe from a synthesis of 1500 holocene hillslope and floodplain sedimentary archives we show that sediment storage increases with drainage basin size due to more extensive floodplains in larger river basins however hillslopes retain hitherto unrecognized high amounts of eroded soils at the scale of large river basins such that average agricultural erosion rates during the holocene would have been at least twice as high as reported previously this anthropogenic hillslope sediment storage exceeds floodplain storage in drainage basins 105 km2 challenging the notion that floodplains are the dominant sedimentary sinks in terms of carbon burial oc concentrations in floodplains exceed those on hillslopes and net oc accumulation rates in floodplains 0 7 0 2 g c m 2a 1 surpass those on hillslopes 0 4 0 1 g c m 2a 1 over the last 7500 years we conclude that carbon burial in floodplains and on hillslopes in central europe exceeds terrestrial carbon storage in lakes and reservoirs by at least 2 orders of magnitude and should thus be considered in continental carbon budgets

geochemical evidence of the chinese loess provenance during the late pleistocene abstract the provenance of chinese loess plateau sediments is an often posed question that has not been satisfactorily resolved elemental geochemistry characteristics of the deposition may provide important evidence in this regard to this end geochemical analyses were undertaken on densely sampled strata from four loess sections one of which is located in northwestern china at the desert margin and the other three on the loess plateau as well as sediments from the badain jaran desert it was found that loess deposition on the chinese loess plateau and the northern foot of the qilian mountains had strong geochemical similarity during the last glacial cycle but had remarkable differences with the badain jaran desert samples it is inferred that the desert was not the most important direct provider of dust material to the loess plateau rather one of the main source areas appears to have been the vast silt rich piedmont alluvial fan distributed at the northern foot of the qilian mountains

late triassic sinistral shear in the east gobi fault zone mongolia abstract tectonic studies of the east gobi fault zone in southeastern mongolia reveal multiple distinct intracontinental deformation events postdating late paleozoic arc accretion and continental amalgamation metamorphic tectonites of the tsagan subarga and tavan har blocks previously mapped as precambrian basement comprise a sinistral shear zone dominated by steeply dipping northeast striking foliations field observations and petrographic analyses indicate that the protoliths of the metamorphic tectonites are paleozoic arc volcanic and sedimentary sequences 40ar 39ar step heating analyses of minerals from pre syn and late to post kinematic lithologies bracket the timing of ductile sinistral shear as late triassic the main phase of distributed deformation associated with cooling through amphibolite upper greenschist facies conditions occurred ca 225 ma and shear zone activity waned ca 210 ma cooling rates inferred from the 40ar 39ar data are on the order of 40 20 c myr 1 apparent differences for the two basement blocks may reflect subsequent differential uplift during late jurassic cretaceous rifting relatively rapid late triassic cooling suggests a transtensional component to the deformation and is coincident with core complex formation in northern china late triassic intraplate deformation in southeastern mongolia is likely the result of far field forces associated with collision between mongolian arcs and the siberian craton i e closure of the mongol okhotsk ocean and or collisions associated with closure of the paleotethys the ductile shear zone has been documented over 250 km along strike and has been modified by subsequent brittle deformation events in the mesozoic and cenozoic

late paleozoic magmatic record of middle gobi area south mongolia and its implications for tectonic evolution evidences from zircon u pb dating and geochemistry abstract late paleozoic subduction accretion complexes occur widely in middle gobi area and provide a good opportunity for unraveling the paleozoic tectonic evolution of south mongolia the magmatic rocks in the tsavchir hudug district mainly consist of rhyolites and volcaniclastic rocks the rhyolites show enrichment in lree and lile and negative nb ta and ti anomalies indicating genesis in the subduction zone a rhyolite sample from the tsavchir hudug region yielded a shrimp 206pb 238u zircon age of 315 4 ma mswd 0 79 n 15 the andesite overlying the namdain hundy early paleozoic ophiolite shows adakite geochemical features and the two andesite samples yielded shrimp 206pb 238u zircon ages of 325 3 ma mswd 1 6 n 14 and 319 4 ma mswd 0 56 n 13 respectively suggesting that the carboniferous island arc formed on the basis of early paleozoic accretionary complex the granodiorite sample that intrudes the early paleozoic accretion complex with adakite geochemical features yielded a shrimp 206pb 238u zircon age of 333 4 ma mswd 1 6 n 16 representing the late paleozoic island arc intrusive the shrimp u pb analyses for the tuff sandstones that occur associated with early paleozic oceanic inliers in middle gobi area suggest detrital zircons mainly stem from the devonian carboniferous arc the age data obtained from the ophiolite 528 509 ma and tuff sandstone indicate the accretion in middle gobi area lasted from early paleozoic to late paleozoic for at least ca 200 ma suggesting the ocean of the accretionary complex was the major paleo asain ocean basin the subduction related magmatic belt in middle gobi area includes both early paleozoic and late paleozoic island arc activities which is consistent with the accretion duration time obtained from accretionary complex and also attests the argument of major paleo asain ocean basin

regional mineral mapping of island arc terranes in southeastern mongolia using multi spectral remote sensing data abstract over the last few decades many porphyry cu deposits have been discovered in southeastern se mongolia in particular the gurvansayhan and mandalovoo island arc terranes have high potential for ore deposits regional mineral mapping of these terranes using data from the landsat enhanced thematic mapper plus etm and the advanced spaceborne thermal emission and reflection radiometer aster have provided new geological information on the metallogenic province revealing potential mineral deposits for future explorations iron oxides hydroxides with high etm band 1 3 ratio values occur extensively in quaternary deposits located at the boundary between the gurvansayhan and mandalovoo island arcs terranes and basins the high average band ratios 1 35 registered for the porphyry cu and au deposits and their occurrences are associated with iron oxidation which originates from the erosion and weathering of ore zones regional mapping of the island arc terranes using the aster shortwave infrared swir logical operators showed circular or semicircular alteration patterns which usually cluster along faults the mineral assemblages mapped by the aster swir analysis in five major porphyry cu districts can be divided into two types the first type includes argillic phyllic and propylitic mineral assemblages as exemplified by the shuteen ikh shankhai and oyu tolgoi deposits the second type of assemblage includes phyllic and propylitic mineral assemblages as exemplified by the kharmagtai and tsagaan suvarga deposits within the deposits of the first type quartz was also mapped using the aster thermal infrared tir mineral index the difference between the two types may be related to the presence of a lithocap the results of a field survey including spectral reflectance measurements in the ikh shankhai porphyry cu district showed a good correlation with the image analysis results

plate interior polyphase fault systems and sedimentary basin evolution a case study of the east gobi basin and east gobi fault zone southeastern mongolia abstract structural interpretation of 2 d seismic reflection data and subsurface outcrop correlations reveal six distinct phases of deformation recorded in the paleozoic basement rocks and mesozoic cenozoic basin fill of the east gobi basin egb southeastern mongolia these phases include arc accretion and arc continent collision in late paleozoic time late triassic sinistral shear zone development early jurassic fold and thrust belt style shortening middle jurassic lower cretaceous extension and rift basin development middle cretaceous shortening with basin inversion and regional unconformity development and late cretaceous oligocene thermal subsidence with renewed paleogene left lateral strike slip faulting across the fault zone the five post amalgamation deformation phases are localized along the east gobi fault zone suggesting that preexisting structures and boundary conditions exert fundamental controls on the long term evolution of intracontinental basins such as the egb subsurface geophysical data and outcrop correlations demonstrate that the main subbasins of the egb contain major differences in basement metamorphic and structural fabrics basin fill patterns and distinct mesozoic cenozoic fault generations potential causes related to far field boundary conditions and other driving factors are suggested for each of the major deformation phases

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

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

geochronology petrogenesis and tectonic implication of late paleozoic volcanic rocks from the dashizhai formation in inner mongolia ne china abstract in this paper we present geochemical zircon u pb and hf isotopic data on the late paleozoic volcanic rocks of the dashizhai formation which are exposed along the northwestern margin of the songnen terrane in eastern inner mongolia our aim is to constrain the petrogenesis and tectonic setting of the volcanic rocks and to unravel the late paleozoic tectonic evolution of the northwestern part of the songnen terrane along the eastern segment of the central asian orogenic belt lithologically the dashizhai formation is composed mainly of rhyolitic tuff rhyolite dacite andesite basaltic andesite and basalt with minor basaltic trachyandesite the zircons separated from these rocks are euhedral subhedral have high th u ratios 0 2 1 6 and display broad oscillatory growth zoning indicating a magmatic origin the results of zircon u pb dating indicate the volcanic rocks formed during the early permian 295 283 ma geochemically these volcanic rocks belong to the mid k to high k calc alkaline series and are characterized by an enrichment in large ion lithophile elements liles and a depletion in high field strength elements hfses such as nb ta and ti similar to igneous rocks that form in active continental margin settings most magmatic zircons of the rhyolites show positive e hf t values 3 65 to 13 0 and two stage model ages t dm2 of 1396 551 ma these geochemical characteristics indicate that the acidic volcanic rocks of the dashizhai formation were most likely derived from the partial melting of dominantly juvenile crustal components with a possible addition of old materials in contrast the basic to intermediate volcanic rocks were derived from the partial melting of a depleted lithospheric mantle that had been metasomatized by fluids derived from a subducted slab these data together with regional geological investigations suggest that the generation of the early permian volcanic rocks of the dashizhai formation was related to the southward subduction of the paleo asian oceanic plate beneath the songnen terrane this also implies that the terminal collision between the songnen and xing an terranes did not occur before the early permian

early paleozoic oceanic inliers and reconstruction of accretionary tectonics in the middle gobi region mongolia evidence from shrimp zircon u pb dating and geochemistry abstract the ophiolites that occur as inliers among the late paleozoic formations in the middle gobi area are crucial for understanding the tectonic evolution of south mongolia in this paper we conducted detailed studies on the namdain hundy ophiolite to provide some constraints on the early paleozoic evolution of the middle gobi region in mongolia the ophiolite mainly consists of ultramafic rocks carbonatation plagiogranite metagabbro basalt and chert the metagabbro and plagiogranite from namdain hundy ophiolite yielded shrimp zircon u pb ages of 528 7 ma and 519 5 ma respectively though most of the volcanic rocks of this ophiolite show supra subduction zone ssz affinity samples with oib and n morb geochemical features were also identified indicating genesis in a forearc setting the granodiorite intruding into the namdain hundy ophiolite yielded a shrimp zircon u pb age of 491 3 ma which constrained the upper age limit of ophiolite emplacement this granodiorite shows adakitic geochemical affinity attesting to the existence of cambrian paleo subduction in south mongolia based on the available data so far we suggest the middle gobi area comprises of the manlay accretion complex the island arc and the biluutiin ovoo back arc basin the spatial configuration of these three tectonic belts suggests that the polarity of the paleo ocean subduction was from south to north in the early paleozoic forming a trench arc basin system south of the central mongolia microcontinent

the oyut ulaan volcanic group stratigraphy magmatic evolution and timing of carboniferous arc development in se mongolia abstract the palaeozoic mesozoic tectonic evolution of central asia including the vast terrane collage that makes up mongolia has been a topic of considerable debate the oyut ulaan volcanic group is a sequence of volcanic and sedimentary rocks in se mongolia that forms the southern part of the devonian permian saykhandulaan inlier fieldwork traverses and mapping have established four distinct formations in the oyut ulaan volcanic group that record the nature of arc activity in part of the central asian orogenic belt during the carboniferous physical volcanological and sedimentological characteristics of the four formations suggest three clear eruptive styles 1 periodic andesite volcanism in an actively eroding arc setting that also contained large rivers and swamps 2 highly effusive plateau andesite volcanism 3 explosive rhyolitic effusion geochemical analyses of volcanic lithologies suggest that the group represents subduction related mature continental arc volcanism geochemical results document an evolving magma system to which surface processes of the volcano sedimentary model may be linked magma pulses and replenishments are identified from variations in chemostratigraphy newly obtained zircon ages from the volcanic succession fix its emplacement eruption at 323 0 0 7 ma mid carboniferous or late mississippian a granite cobble from the lower part of the oyut ulaan volcanic group gives a u pb zircon age of 338 9 0 4 ma indicating that arc plutons were emplaced 10 ma prior to the oyut ulaan volcanism and were eroded soon after our work provides timing constraints for final accretion and continental assembly in se mongolia and also sheds light on the petrological development of a magmatic arc system within an evolving accretionary orogen

oyu tolgoi mongolia siluro devonian porphyry cu au mo and high sulfidation cu mineralization with a cretaceous chalcocite blanket the oyu tolgoi porphyry cu au mo deposit is located in the gobi desert of southern mongolia the deposit consists of three main mineralized zones north central and south oyu interpreted to constitute at least two separate porphyry copper centers oyu tolgoi is associated with a series of small structurally controlled stocks and dikes of monzonitic and dioritic composition which intrude a sequence of siluro devonian volcanic and sedimentary rocks country rocks consist of pillow basalt and basaltic andesite interbedded with fine grained clastic sedimentary horizons the sequence is interpreted to have formed in a subaqueous island arc volcanic environment which formed part of the extensive paleozoic tuva mongol arc these island arc rocks are covered by carboniferous terrigenous sequences and are intruded by carboniferous syenite and granite and permian alkaline granite much of the area is covered by poorly consolidated cretaceous sedimentary sequences central oyu consists of a multiple phase hydrothermal breccia crosscutting an altered fine grained feldspar porphyry containing porphyry type alteration and mineralization the breccia underwent texture destructive advanced argillic alteration characterized by several associations of quartz alunite dickite pyrophyllite sericite and zunyite plus lesser svanbergite and fluorite these associations overprint earlier formed k silicate and quartz sericite illite assemblages copper mineralization at central oyu is present in a supergene chalcocite blanket that formed at the expense of a pyrite rich hypogene chalcocite covellite tennantite arsenosul vanite sulvanite chalcopyrite bornite sulfide suite that accompanied the advanced argillic alteration event at south oyu a feldspar hornblende porphyry of monzonitic composition intrudes a sequence of fine grained andesite and basaltic andesite hypogene copper gold mineralization occurs as early magnetite rich pyrite poor quartz chalcopyrite bornite stockworks and sheeted veinlets hydrothermal alteration is composed of biotite and k feldspar with apatite and minor albite magnetite averages 7 to 10 vol percent and copper and gold grades vary sympathetically these early assemblages are overprinted by a sericite chlorite event with ore grade copper and erratic gold and molybdenum values and also by structurally controlled pyrite rich advanced argillic alteration k ar ages show that the hypogene copper gold mineralization at south oyu is latest silurian earliest devonian 411 3 ma and that the entire district was intruded by postmineralization syenite during the carboniferous 307 4 ma the supergene chalcocite blanket at central oyu formed in the early cretaceous earliest late cretaceous based on ages for supergene alunite of 117 1 and 93 1 ma which makes central oyu one of the oldest preserved chalcocite blankets in the world chalcocite blanket preservation was favored by climatic desiccation into the late cretaceous and the tertiary it is inferred that significant regional uplift took place at the silurian devonian boundary this synmineral ization uplift and erosion may have been in part responsible for the telescoping of the hydrothermal systems at oyu tolgoi including the superposition of epithermal style associations over higher temperature deeper seated assemblages typical of the porphyry environment