an 40ar 39ar thermochronology of the ofoten troms region implications for terrane amalgamation and extensional collapse of the northern scandinavian caledonides fifteen 40ar 39ar cooling ages are reported for metamorphic hornblende and muscovite from far traveled terranes constituting the ofoten nappe stack of northern norway eight cooling ages on hornblende range from 425 to 394 ma and seven muscovite ages from the same or nearby outcrops as the hornblendes range from 400 to 373 ma these data are compared with 40ar 39ar ages from over a large part of the northern caledonides to evaluate regional mineral cooling patterns results indicate that 1 scandian silurian devonian metamorphism was predominant 2 most of the nappes investigated contain some vestige of pre scandian tectonism and or metamorphism 3 hornblende and muscovite cooling ages are progressively younger to the west and south which suggests a hinged to the east mineral cooling pattern and 4 a late out of sequence thrust is the only disruption of this cooling pattern synmetamorphic amalgamation of the nappes resulted from scandian a type subduction the hinged to the east mineral cooling pattern implies isostatic adjustment and exhumation of the footwall of a west dipping crustal scale extensional fault located somewhere west of the present norwegian coast during late synorogenic gravitational collapse the late out of sequence fault formed contemporaneously with uplift in the hinterland implying a kinematic and temporal connection with east directed contractional faulting in the foreland

the ochil fault and the kincardine basin key structures in the tectonic evolution of the midland valley of scotland the ochil fault one of the most prominent tectonic features in the midland valley of scotland juxtaposes lower devonian volcanic rocks against late westphalian strata implying a possible vertical displacement of up to 4 km the kincardine basin in its hanging wall although actively subsiding during the greater part of the silesian trends generally n s perpendicular to the ochil fault and its silesian sedimentary record shows little sign of tectonic control by that fault it is proposed that the ochil fault was initiated possibly as a sinistral strike slip feature in the devonian but acted as a sidewall fault during the early evolution of the kincardine basin attributed to extension on a hypothetical pre brigantian fault along the bo9ness line on the east side of the basin until late namurian times when active extension ceased both faults were probably buried during late namurian and westphalian times reactivation of the ochil fault during end carboniferous n s extension dated by quartz dolerite emplacement was responsible for probably at least 2 km displacement including the presently visible footwall uplift it is suggested that the hanging wall may have contained a permian basin now removed

implications for caledonian plate tectonic models of chemical data from volcanic rocks of the british old red sandstone volcanic rocks associated with the continental sediments known as the old red sandstone outcrop widely in northern britain and form a dominantly calc alkaline suite comparable to those developed on modern continental margins rocks rich in ni and cr are unusually abundant and are thought to have incompatible element concentrations little different from those of primary magmas such rocks show pronounced spatial chemical variation with concentrations of sr ba k light rare earth elements and p 2 o 5 and the ratio la y showing up to a six fold increase in a northwestward traverse across scotland in more evolved rocks a similar increase is shown by sr ba and la y but regional comparisons are made difficult by the varying effects of fractional crystallization the chemistry of all old red sandstone volcanic rocks n of the southern uplands fault is consistent with the former existence of a subduction zone that changed in strike from ene in ireland and southern scotland to n in the north sea this orientation in conjunction with almost e w plate motion may explain the great contrast in end silurian deformation styles between britain and scandinavia old red sandstone volcanic and plutonic rocks s of the southern uplands fault are thought to be younger and are perhaps unrelated to subduction activity

cyclostratigraphy and orbital tuning of the terrestrial upper santonian lower danian in songliao basin northeastern china abstract the songke 1 north sk 1n borehole recovered a continuous 1541 66 m late santonian early danian terrestrial succession in songliao basin sb northeastern china it provides a unique record for improving our understanding of continental paleoclimate and ecological system in cretaceous greenhouse world here we use thorium th logging data as a paleoenvironmental and paleoclimatic proxy to conduct a detailed cyclostratigraphic study on the sk 1n core power spectra evolutionary fast fourier transformation and wavelet analysis all reveal significant decameter to meter scale sedimentary cycles in the nenjiang k 2 n sifangtai k 2 s and mingshui k 2 m formations the ratios of cycle wavelengths in these stratigraphic units are 20 5 2 1 and are interpreted as milankovitch cycles of 405 kyr and 100 kyr eccentricity 38 4 kyr obliquity and 20 kyr precession cycles respectively an astronomical time scale ats is established by tuning filtered 405 kyr eccentricity cycles to a target curve of the astronomical solution la2010d based on the magnetostratigraphic time framework of the sk 1n borehole this ats provides precise numerical ages for stratigraphic boundaries biozones geological and geophysical events and serves as a basis for correlation of strata and events between marine and terrestrial systems the cretaceous paleogene k pg campanian maastrichtian santonian campanian boundaries are estimated at core depths of 318 m 752 8 m and 1751 1 m respectively a 3 8 myr long hiatus between the nenjiang k 2 n and sifangtai k 2 s formations occurs from 76 1 to 79 9 million years ago the ages and durations of magnetochrons c33r to c30n are precisely estimated and provide new constraints on the late cretaceous geomagnetic polarity time scale gpts and south atlantic sea floor spreading rates

dolomite cements in cenomanian continental sand deposits time evolution and significance zoovch ovoo u deposit east gobi basin mongolia abstract shallow buried unconsolidated sands generally provide very little information about diagenesis as most detrital minerals remain unchanged however in rare cases carbonate cemented nodules or sandstone layers may occur inside unconsolidated series these cements could help to reconstruct the chronology of events from early to late phase stages of diagenesis the late cretaceous sequence of the zoovch ovoo depocenter in east gobi basin is represented by 600 m of clastic deposits the 60 80 m of cenomanian unconsolidated sands and clays deposited in alluvial deltaic to lacustrine settings compose the upper part of the post riftmedium grained siliciclastic reservoir the sainshand formation which hosts uranium roll front systems dolomite cemented sandstone layers with 10 20 cm thickness occur among the unconsolidated rock facies calcite is absent from this formation but is present only in the overlying also outcropping bayanshiree formation samples from the dolomite cemented sandstone layers were investigated in detail to uncover their origin and diagenetic history four dolomite cement types were recognized that indicate recrystallization episodes and were classified based on the size and shape of the crystals namely i microcrystalline dolomite frequently associated with siderite ii euhedral dolomite also associated with siderite iii subhedral dolomite and iv finally anhedral dolomite their ree content varies significantly from dolomite i to iv in particular by a strong depletion in lree about 30 times the contrasted precipitation of calcite in bayanshiree and dolomite cements in sainshand formations could be attributed to different mg ca ratio of the circulation fluids in the two aquifers both carbonates display however rather homogenous oxygen and carbon isotopic compositions for 18o 10 1 v pdb and 13c 7 1 v pdb the 18o values are interpreted as inherited from typical meteoric waters quite close to present day waters the 13c values indicate a mixed source of both organic and mineral carbon all data taken into account a full paragenetic succession was constructed it includes the evolution of dolomite during burial diagenesis and the effects of the oxidizing roll front uranium rich waters in the system the latter induces partial dissolution followed by precipitation of a dolomite phase typical of roll front zones carbonate cements can be thus considered as the best and rather unique geochemical indicators for the recognition of a burial history framework to paleofluid circulations and fluid rock interactions in these intracontinental series of unconsolidated sands

ballast brook and beaufort formations late tertiary on northern banks island arctic canada abstract excellent exposures of late tertiary terrestrial sediments occur in the ballast brook region of northwestern banks island canadian arctic archipelago these sediments contain abundant concentrations of organic detritus as well as autochthonous peats which can be traced for some kilometres all of these deposits were previously assigned to the beaufort formation in this paper the deposits formerly grouped as the beaufort formation are subdivided into two formations the newly named ballast brook formation and the beaufort formation the ballast brook formation is characterized by alluvial sand silt clay and peat with compressed altered wood paleobotanical evidence indicates an early to mid miocene age with mid miocene being the most probable this formation is believed to overlie the eureka sound group and is in erosional contact with the overlying beaufort formation plant macrofossils from the ballast brook formation include a number of taxa now found in northern hardwood and southern boreal forests while the prominent peat which characterizes the formation contains a number of taxa that now grow or could be expected to grow in a cypress swamp type of environment for example the conifer glyptostrobus is well represented in the peat the beaufort formation at ballast brook consists of alternating sands and gravels and silt in the lower part it is characterized by an abundance of unaltered wood and other plant materials paleobotanical evidence indicates an early pliocene to early late pliocene age i e approx 5 3 ma like the ballast brook formation the beaufort formation contains an abundance of fossils of conifers but in contrast with the ballast brook formation nearly all of them belong to pinaceae a group well represented in the present boreal forest the beaufort formation also contains insect fossils which are very rare in the ballast brook formation together the insect and plant macrofossils suggest an environment similar to but richer in species some extinet others now found only in asia than present boreal forest and taiga the ballast brook formation flora resembles the flora from mary sachs gravel formerly beaufort formation on southwestern banks island and the flora from the west river beds on the northwest territories mainland it also is similar to a 40 ar 39 ar dated mid miocene flora from east central alaska and to the mamontova gora mid miocene flora from russia

permian magmatism and basin dynamics in the southern pyrenees a record of the transition from late variscan transtension to early alpine extension

stratigraphy fossils and age of sediments at the upper pit of the lost chicken gold mine new information on the late pliocene environment of east central alaska abstract the upper pit at the lost chicken placer gold mine in east central alaska contains fossils that provide information on the flora and insect fauna of interior alaska just before the onset of global cooling at 2 5 myr fossils come from sediments interbedded with the lost chicken tephra dated at 2 9 0 4 myr early late pliocene and portray the floodplain and valley of a small creek within a region dominated by a coniferous forest richer in genera and species than the present one climate was wetter and less continental and there was probably little or no permafrost at least one other pliocene tephra the fortymile tephra occurs at the site and is also associated with plant and insect fossils among these fossils are extinct plants and insects like those found at other tertiary sites in northern canada and alaska the lost chicken sequence is the same age as the beaufort formation on meighen island more than 1000 km to the north like lost chicken meighen island sediments contain fossils representing a diverse boreal environment this shows that the latitudinal climate gradient during early late pliocene time was shallower than at present and the boreal forest had a far greater latitudinal span than now

plate tectonics and the evolution of the british isles this paper is an essay on the rationalism and difficulties of the geological corollaries of plate tectonics with illustrations particularly from the geological history of the british isles there is special emphasis on the mechanics of continental lithosphere in extension when basins are formed and in convergence whereby continental lithosphere thinned in extension is shortened and restacked to form orogenic belts an upper lithosphere stress concentrating elastic lid suffers extremely complex inhomogeneous deformations above a simpler viscoelastic lower lithosphere whose deformation drives strain and displacement in the elastic lid the very nature of plate tectonics as relative motion among a multi plate mosaic of plates provides a rational semi quantitative framework for large scale geological complexity in space and time the caledonian and hercynian history of the british isles may be explained semi quantitatively in terms of plate boundary evolution but it is not possible to define unequivocal solutions the rationalism of plate tectonics is exhibited on a smaller more direct field scale by many of the complexities of ophiolite complexes such as ballantrae scotland that can be explained as the effects of the evolution of ridge ridge transforms and by diachronous deformation and sedimentation in subduction accretion prisms such as the southern uplands deformational and sedimentary patterns in nw europe from triassic times to the present day resulted from a complex interaction of extensional events related to diachronous atlantic opening and compressional events related to sequential alpine shortening phases those widespread events are typical of intracontinental plate boundary systems and create great difficulties for the geologist wishing to decipher relative plate motion from geological sequences because huge areas much larger than the british isles must be analysed and synthesized before much sense can be extracted further difficulties arise from the palinspastic and preservation problems of convergent boundaries orogenic shortening telescopes and partially subducts facies belts most orogenic belts were assembled as a collage of displaced and rotated terrain elements that were subsequently flattened elongated and straightened to an apparent but deceiving simplicity therefore while plate tectonics provides a rational geological framework against which for example british basin evolution can be tested and explained we cannot yet use the geological effects of plate boundary evolution to reconstruct relative plate motion quantitatively

carbon isotopes in continental weathering environments and variations in ancient atmospheric co2 pressure abstract abundance and carbon isotope data from an fe co3 oh component in apparent solid solution in oolitic goethites have been used to infer ancient atmospheric co2 pressures a test of the validity of these estimates might be comparisons of the carbon isotope compositions of fe co3 oh in oolitic goethites with time equivalent pedogenic calcites temporal trends of the oolitic goethite and pedogenic calcite 13c values are generally similar but time equivalent samples from each of these two groups are not common in the existing data to facilitate discussion of the concept comparisons were made of available goethite and calcite samples even though ages of the compared samples in each pair were not identical in four out of the five comparisons fe co3 oh abundance and 13c data were combined with pedogenic calcite 13c data to calculate physically reasonable soil co2 concentrations for the ancient calcitic soids this suggests that the compared oolitic goethite and pedogenic calcite systems were responding to the same global scale phenomenon i e atmospheric co2 atmospheric pco2 as determined from the goethites in these four well behaved cases ranged from values indistinguishable from modern within analytical uncertainty to values up to approximately 16 time modern modern atmospheric pco2 was taken to be 10 3 5 atm one interpretation of the fifth anomalous comparison is that atmospheric co2 levels increased from about 3 times modern to about 18 times modern from the triassic into the early jurassic this inferred value for the pco2 of the early jurassic atmosphere is not uniquely constrained by the existing data and needs to be substantiated however even considerably lower early jurassic atmospheric pco2 values of 6 to 9 times modern i e 1 3 to 1 2 of the estimated value of 18 times modern would still indicate significant differences between the global carbon cycles then and now these results highlight the need for more research on the behavior of the atmosphere during and after the triassic jurassic transition

paleosols associated with miocene basalts porcupine river northeastern alaska implications for regional paleoclimates abstract paleosols of middle miocene age consisting of wood peat organic matter rich mineral soil and weathered basalt are described from the upper ramparts of the porcupine river in northeastern alaska a highly acidic soil representing a floodplain wetland swamp forest environment underlies the basalts of the upper ramparts and is composed of 1 m of compressed peat and interbedded fluvial sediments wetland soils from between basalt flows were also observed in depressional sites on basalt surfaces palynological investigations indicate that these wetland peat profiles developed in association with temperate mixed hardwood conifer flora correlative to the early middle miocene seldovian floristic stage previously defined for southcentral alaska three well preserved types of basalt saprolites residual soils were identified in the study area depending on the drainage condition at the time of formation the greatest degree of basalt weathering occurred under apparent well drained conditions where a red clay rich soil with a solum depth greater than 1 m was observed between basalt flows the colour of this well drained paleosol and the presence of iron oxides including possible hematite is interpreted to reflect soil development under warm temperate climatic conditions

clumped isotope palaeothermometry and la icp ms u pb dating of lava pile hydrothermal calcite veins calcite veins are a common product of hydrothermal fluid circulation clumped isotope palaeothermometry is a promising technique for fingerprinting the temperature of hydrothermal fluids but clumped isotope systematics can be reset at temperatures of ca 100 c to model whether the reconstructed temperatures represent calcite precipitation or closed system resetting the precipitation age must be known la icp ms u pb dating of calcite is a recently developed approach to direct dating of calcite and can provide precipitation ages for modelling clumped isotope systematics in calcite veins in this study clumped isotope and la icp ms u pb calcite analyses were combined in basalt hosted calcite veins from three settings in scotland samples from all three localities yielded precipitation temperatures of ca 75 115 c from clumped isotope analysis but veins from only two of the sites were dateable yielding precipitation ages of 224 8 ma and 291 33 ma 2 modelling from the dated samples enabled confident interpretation that no closed system resetting had occurred in these samples however the lack of a precipitation age from the third location meant that a range of possible thermal histories had to be modelled meaning that confidence that resetting had not occurred was lower this highlights the importance of coupling clumped isotope thermometry and la icp ms u pb calcite dating in determining the temperature of hydrothermal fluids recorded in calcite veins this paired approach is shown to be robust in constraining the timing and precipitation temperature of calcite formation and thus for tracking hydrothermal processes

are spherulitic lacustrine carbonates an expression of large scale mineral carbonation a case study from the east kirkton limestone scotland lacustrine carbonate deposits with spherulitic facies are poorly understood but are key to understanding the economically important pre salt mesozoic strata of the south atlantic a major barrier to research into these unique and spectacular facies is the lack of good lacustrine spherulite dominated deposits which are known in outcrop stratigraphy and petrography suggest one of the best analogue systems is found in the carboniferous of scotland the east kirkton limestone here we propose a hydrogeochemical model that explains why the caco3 sio2 mg si al mineral suite associated with spherular radial calcite facies forms in alkaline lakes above basaltic bedrock demonstrating links between igneous bedrock chemistry lake and spring water chemistry and mineral precipitation this model has implications for studies of lacustrine sediments in rift basins of all ages using empirical and theoretical approaches we analyze the relationship between metal mobilization from sub surface volcaniclastic rocks and the potential for precipitation of carbonate minerals various mg bearing minerals and chalcedony in a lacustrine spherulitic carbonate setting this suite of minerals is most likely formed by in gassing of co2 to a carbon limited alkaline spring water consistent with the reaction of alkali igneous rocks in the subsurface with meteoric groundwater we suggest that an analogous system to that at east kirkton caused development of the pre salt spherulitic carbonate deposits

an 18 million year record of vegetation and climate change in northwestern canada and alaska tectonic and global climatic correlates abstract we reconstruct long term vegetation paleoclimatic trends spanning the last 18 million years in alaska yukon and far western northwest territories twenty one average percentage spectra for pollen and spores are assembled from eight surface subsurface sections the sections are dated independently or by correlation pollen and spore ratios indicate the direction of change in vegetation and climatic parameters growing season temperature test tree canopy density cest and paludification at study sites pest a global warm peak ca 15 ma is shown by the abundance of thermophilous taxa including fagus and quercus a temperature decline immediately following 15 ma parallels climatic reconstructions based on marine oxygen isotopes subsequent declines correlate to the messinian event and the onset of late pliocene pleistocene glaciation after 7 ma herbs and shrubs become more important elements of the palynological assemblages suggesting a more continental colder drier climate however a late pliocene warm interval is evident vegetation climatic changes during the early to late miocene show synchrony with and are most economically attributable to global events after 7 ma vegetation climate change is attributed primarily to latest miocene to pleistocene uplift of the alaska range and st elias mts the continuing influence of global climatic patterns is shown in the late pliocene warm interval despite uplift to the south the opening of the bering strait ca 3 ma may have moderated the climate in the study area

structural and tectonic setting of the permo triassic basins of northwest europe abstract the permo triassic basins of nw europe formed by i late orogenic spreading of the variscan mountain belt eventually leading to ocean floor formation in the mid atlantic ii continental rifting propagating south from the arctic and iii thermal subsidence following carboniferous volcanic activity in the north sea spreading values in the northernmost north sea west of shetland and west and southwest of britain are relatively high but the sediments are dominantly continental the permo triassic rifting affected lithosphere thickened during caledonian and variscan orogenesis however subsidence associated with the arctic rifting together with global sea level changes allowed marine incursions into the north sea producing the large zechstein salt basins interference of the different basin formation mechanisms led to a complex three dimensional fault pattern and multidirectional extension across britain and the north sea this fault pattern formed the basic framework for subsequent jurassic and cretaceous basin formation

selenium enrichment in carboniferous shales britain and ireland problem or opportunity for shale gas extraction research was partly supported by nerc grants ne l001764 1 and ne m010953 1 mrs a sandison provided skilled technical support barnett shale was kindly provided by hu qinhong the manuscript was improved by the helpful comments of a reviewer

asthenospheric and lower lithospheric mantle contributions to continental extensional magmatism an example from the british tertiary province abstract the compositions of palaeocene basic magmas in skye and mull british tertiary igneous province btip shed light on the general problem of the relative importance of lithospheric and asthenospheric mantle as sources of continental magmatism during extension after the effects of crustal contamination in some magmas have been detected and the samples showing it eliminated from consideration the remainder show a significant diversity of trace element compositions basic lavas from skye and mull which lack crustal contamination have contents of compatible and moderately compatible elements e g ni cr y yb and also of moderately incompatible elements e g ti p zr hf sr mree which are within the range shown by the tholeiitic and mildly alkalic ocean island basalts oib as from iceland in contrast their contents of strongly and very strongly incompatible elements e g k rb ba u th nb ta lree are within the range shown by normal mid ocean ridge basalts these btip magmas are interpreted as second stage melts from mantle which had already lost a very small melt fraction the latter is thought to be represented by the strongly alkalic permo carboniferous dyke swarms associated with rifting at that time in nw scotland residual uppermost asthenosphere from the late palaeozoic magma genesis event is postulated to have become attached to the thickening lithosphere beneath nw scotland and thus to have remained coupled to it throughout the mesozoic until reactivated by palaeocene stretching occasional hawaiites in the top third of the skye lava pile remnant and also basalt dykes of the swarm cutting the granites of the central complex the last significant magmatic event at this centre have the elemental characteristics of typical north atlantic oib notably la ta 10 12 these compositions are thought to demonstrate input from asthenospheric source basic magmas throughout the lithospheric source dominated skye and mull magmatism it is suggested that all the basic magmas in this province are ultimately derived from asthenospheric sources but that the larger magma batches became contaminated during uprise by melting and assimilating the most fusible parts of overlying lithospheric mantle followed by lower crust in many cases smaller magma batches traverse the overlying lithosphere with little or no contamination perhaps the difference between the two lies in their flow behaviour laminar or turbulent during uprise

late cretaceous climate changes recorded in eastern asian lacustrine deposits and north american epieric sea strata abstract cretaceous climate data of the long lived cretaceous songliao basin sb in eastern asia is correlated and compared with the western interior seaway wis on the northern american plate in order to understand better the dynamics of the earth s past greenhouse climates nearly continuous late cretaceous terrestrial deposition in the songliao basin is represented by two cores totaling 2431 m in length the turonian maastrichtian age of the section is based on integrated stratigraphy and is comparable in age with upper cretaceous strata in the wis being consistent with global trends the dynamic late cretaceous climates of both the sb and wis gradually cooled from the warmest albian cenomanian time to the end of the maastrichtian with several intervening warm periods as did the global climate however regional differences existed the songliao basin climate was humid to semi humid warm temperate subtropical and the western interior seaway was in the humid warm temperate zone and experienced only moderate climatic changes the shifts of oxygen isotope data in the songliao basin were frequent and abrupt whereas wis records more gradual change affected mainly by fresh water runoff mixing with southern tethyan and northern arctic waters sedimentary cycles of eccentricity obliquity and precession bands are recorded in both the sb and wis basins the sedimentary cycles in the wis and sb are interpreted to be related to variations of the wet dry runoff cycles which indicate that orbital forcing played an important role in global climate change in late cretaceous the most favorable condition for organic carbon burial in both the sb and wis basin was bottom water anoxia regardless of the cause of the anoxia but the organic carbon burial rate was usually much higher in the songliao lake than in the wi epeiric sea suggesting that giant lakes may serve as important sinks of atmospheric co 2 in both basins organic rich deposits formed during a rise in water level and incursion of saline waters the integration of paleoclimate data from cretaceous marine deposits and terrestrial sedimentary record will promote our understanding of the cretaceous greenhouse climate change and may provide insights for a future greenhouse world

geochemistry and sr nd pb hf isotopes of early cretaceous basalts from the great xinggan range ne china implications for their origin and mantle source characteristics abstract late mesozoic volcanism is widespread throughout northeastern china mainly clustering in the great xinggan range where the major period of volcanic eruption was during the early cretaceous the spatial distribution of volcanic rocks shows a nne extending pattern the lithology of mesozoic basaltic rocks in the great xinggan range ranges from trachytic basalts basalts to basaltic andesites on the basis of lithological associations and spatial relationships we divide the basalts into four groups i e tahe genhe zalute and xiwu the early cretaceous volcanism in the great xinggan range is characterized by significant large ion lithophile elements lile and light rare earth elements lree enrichment and high field strength elements hfse depletion with a slightly enriched to depleted nd hf and weakly enriched sr isotopic compositions initial 87sr 86sr 0 7046 0 7079 end t 3 6 to 6 9 and ehf t 8 9 to 4 6 the pb isotopic compositions are also variable with 206pb 204pb 207pb 204pb and 208pb 204pb values of 17 791 18 530 15 477 15 597 and 37 761 38 497 respectively the sr nd pb hf isotopic data indicate that the magmatic sources are heterogeneous showing an enriched to depleted signature of continental lithospheric mantle the magmatic sources of the genhe and zalute groups are characterized by mixing among pm em ii and dm whereas the tahe and xiwu groups derive from enriched lithospheric mantle that had experienced metasomatism by fluids or melts from subducted paleo asian and mongol okhotsk ocean slabs and possible influence of precambrian blocks the late mesozoic volcanic rocks in the great xinggan range resemble those of the cenozoic calc alkaline magmatism in the basin and range province of the united states we therefore suggest that the widespread mesozoic volcanic rocks in the great xinggan range were generated in an extensional tectonic setting

active versus passive continental rifting evidence from the west african rift system fitton j g 1983 active versus passive continental rifting evidence from the west african rift system in p morgan and b h baker processes of continental rifting tectonophysics 94 473 481 the west african rift system comprises the cretaceous benue trough and the tertiary to recent volcanic cameroon line the two features are remarkably similar in shape and size and may be superimposed perfectly by rotating one with respect to the other by 7 about a pole in sudan three stages in the geological history of the system are postulated 1 the benue trough was produced by lithosphere stretching as one arm of an rrr triple junction during the early stages of the opening of the south atlantic 2 at about 80 ma santonian a short lived period of clockwise rotation interrupted the otherwise anticlockwise rotation of africa and decoupled the lithosphere from the asthenosphere the hot zone in the asthenosphere beneath the benue trough thus became displaced relative to the lithosphere and moved to a new position beneath cameroon and the gulf of guinea 3 anticlockwise rotation and asthenosphere lithosphere coupling were restored allowing the hot zone to manifest itself as the cameroon line the cameroon line is possibly a unique example of what a rift system produced actively by a thermal anomaly in the asthenosphere would look like it is significant that despite a long history of volcanism and uplift the cameroon line has not developed a graben structure the implication is that rift systems with graben structures are produced passively by lithosphere stretching

identification of neogene woods from alaska yukon abstract woods collected from early middle miocene to late pliocene localities at high latitudes more than 60 n of alaska and canada were examined microscopically to determine taxonomic affinities all were conifers and most are pinaceae features useful in the identification of conifers are reviewed including characteristics of growth rings resin canals cross field pitting ray tracheids longitudinal and ray parenchyma helical thickenings and cell sizes some of the problems in feature recognition in fossil conifer woods due to compression and fungal and microbial degradation are discussed although relatively few wood samples were examined these samples provide information consistent with that derived from the pollen leaf and fruit and seed record obtained from the same deposits and provide additional documentation for a cooling of climate and changes in the flora and vegetation from the early middle miocene to the late pliocene in the early middle miocene samples from northeastern alaska there are woods of taxodiaceae and soft pines pinus spp with growth rings greater than 1 cm wide in the late pliocene there are woods of spruce picea and larch larix with growth rings less than 1 mm wide

systematic variation in chemistry and nd sr isotopes across a caledonian calc alkaline volcanic arc implications for source materials abstract sr and nd isotope compositions and major and trace element chemistry are reported for 42 primitive calc alkaline lavas from the siluro devonian scottish old red sandstone northwestward increases in concentrations of sr ba k p and lree associated with northwest subduction of iapetus ocean crust 1 are not accompanied by change in rb th or ti group elements these relationships show that the spatial variation cannot be simply the result of change in the degree of partial melting with depth initial 143 nd 144 nd expressed as e nd at 410 ma shows a wide range from 6 4 to 3 7 and in contrast to e sr decreases markedly to the northwest samples from the midland valley show a strong anticorrelation between e nd and e sr with the correlation band offset to more radiogenic compositions than that defined by modern oceanic volcanic rocks the mantle array such an offset is common in modern volcanic arc magmas but cannot be explained by addition to the overlying mantle of a single component enriched in radiogenic sr derived from subducted lithosphere southwest highland lavas lie in a completely separate field on an e sr e nd diagram most fall within the mantle array but samples with highest concentrations of sr etc are offset to less radiogenic compositions consideration of the chemical and isotopic relationships with respect to several models of crustal contamination shows that the additional lree in the northwest cannot be derived from a crustal source the data imply the existence beneath scotland of a large region of mantle with time integrated lree enrichment parts of which may have anomalous nd sr isotopic compositions less radiogenic than the mantle array midland valley lavas are probably derived from a long term lree depleted mantle source modified by interaction with subducted oceanic lithosphere the coexistence of two mantle sources with differing histories is best explained by vertical stratification with deeper more lree enriched layers accessible only to magmas formed at great depth in a subduction zone the spatial variation probably in part reflects this mantle layering and in part the operation of some mantle zone refining process that permits efficient concentration of incompatible elements from large regions of mantle

accretion of a rifted passive margin the late paleozoic rhenohercynian fold and thrust belt middle european variscides in the western rhenish massif the rhenohercynian fold and thrust belt of the middle european varsicides exposes a telescoped complete devonian to early carboniferous passive margin this permits the analysis of geometry and kinematic processes of passive margin accretion to an erogenic wedge during variscan collision 330 300 ma the sedimentary cover of the passive margin was shortened by some 50 or 180 km crustal scale balancing and restoration reveals a wide symmetric rift with a central graben a marginal plateau separated this failed lower devonian rift from an emsian middle devonian oceanic basin in the south remnants of which are preserved in the southernmost imbricates and the giessen harz nappes the seismically well imaged aachen midi detachment faille du midi acted as the basal decollement of this thin to thick skinned orogenic wedge it shows a ramp and flat geometry from the blind tip down to middle crustal levels owing to its position below the base of the basin fill the thick synrift sequence and structure controlled structural evolution during contraction by localizing thrust branch lines and by inversion of rift structures synthetic to the subduction direction with formation of basement footwall shortcuts moreover the three dimensional detachment geometry shows large scale oblique ramp flat features which control the architecture of the belt and the distribution of metamorphic grade rocks and fabrics from the detachment show that the latter was located at the transition into the ductile field at the fossil 300 400 c isotherm in the restored section the detachment trajectory displays a saucershaped geometry rising to the surface at the rear and at the front this suggests that the basal detachment propagated into the passive margin by ductile failure during lithospheric flexure under the load of an advancing upper plate the regional pattern of synkinematic metamorphic grade shows varying modes of margin accretion basal underplating into the orogenic wedge by the shelf slope and marginal plateau with formation of duplex stacks and elongate thrust sheets and frontal accretion of the remaining thicker failed rift in the north into the propagating wedge with formation of several imbricate fans cyclical changes in accretion history and or critical taper are suggested by spaced domains of out of sequence thickening these are also related to internal domainal kinematic partitioning of the wedge controlled by oblique collision

isotopic variations within a single oceanic island the terceira case since the early work of gast et al 1 it has been recognized that some isotopic variations exist on the scale of a single oceanic island2 3 although the cause of such isotopic heterogeneity remains a matter of debate for some authors such as grant4 the variations are related to local contamination in the island others for example chase5 consider isotopic variation within an oceanic island to reflect mantle heterogeneity so that it can be used to characterize the mantle and calculate the age of mantle differentiation mantle isochron this debate is extremely important in connection with the problem of the isotopic characteristics of the reservoir the product of which built the oceanic island and more generally for the structure of the mantle terceira is an island of the azores archipelago for which we have obtained several kinds of information including geological6 geochronological7 and geochemical8 9 data thus enabling us to study its isotopic composition in a well known context we report here a sr and pb isotopic analysis completed on the same samples as were analysed for the major and trace elements10 and k ar dating7 our isotopic results are correlated with the emplacement age of the rocks this observation is in agreement with a model of mixing between two different mantle components as has previously been proposed2 11 12 for other oceanic islands

the numerical age of the devonian carboniferous boundary the shrimp ion microprobe has been used to date zircons in a 1 cm thick bentonite located in the hasselbachtal auxiliary global stratotype section through the devonian carboniferous boundary in germany and a tuff located at a similar biostratigraphic level in australia multiple replicate analyses have yielded indistinguishable ages and indicate 353 2 4 0 ma 2 as the age of the boundary obtaining an age for the boundary in the german reference section depended on the ability of shrimp to date a small sample and to target small areas of structurally complex zircons future refinements of the age of this boundary may depend on re analysis of this uniquely placed bentonite and this highlights the value of defining biostratigraphic stratotypes in the vicinity of known dateable horizons

accretionary history and crustal evolution of the variscan belt in western europe abstract the variscan belt of western europe is part of a large intra paleozoic belt extending on both sides of the atlantic from the ouachitas in the us and the mauritanides in west africa to the bohemian massif in czechoslovakia and poland the belt was constructed between 500 and 250 ma as a result of convergence and collision between two main continents laurentia baltica and africa after the closure of various oceanic basins iapetus rheic and galicia massif central now recorded as discrete in part cryptic sutures which form the roots of large crystalline nappes in which are found dismembered remnants of oceanic crust and mantle the accretionary history of the variscan belt in western europe is related to the progressive closure of probably two oceanic basins the rheic in the north and another the galicia massif central in the south by respectively southward and northward intraoceanic subduction followed by obduction and intracontinental lithospheric subduction the result is a broad 700 800 km fan like divergent belt which must be considered as a classical obduction collision orogen with a long intracontinental history of about 100 150 ma its arcuate shape is probably due to the northwestward impingement of a promontory of the african continent into laurentia baltica

the relationship between calc alkaline volcanism and within plate continental rift volcanism evidence from scottish palaeozoic lavas lower carboniferous lavas from the midland valley and adjacent regions of scotland are mildly alkaline and intraplate in nature the sequence is dominated by basalt and hawaiite although mugearite benmoreite trachyte and rhyolite are also present basic volcanic rocks display the lil element and lree enrichment typical of intraplate alkali basalt terrains low initial87sr 86sr 0 7029 0 7046 high end 0 4 to 5 6 and moderately radiogenic206pb 204pb 17 77 18 89 ratios are also comparable with alkali basalts from other continental rifts and oceanic islands when the carboniferous lavas are compared with subduction related lavas of old red sandstone age erupted in and around the midland valley ca 50 ma earlier at 410 ma remarkable similarities are apparent significant overlap occurs in nd and pb isotopic compositions sr isotopic compositions are however more radiogenic in the older subduction related lavas this combined with high k and rb concentrations in ors lavas may be explained by the incorporation of a sediment component derived from the subducted slab which by lower carboniferous times had been lost from the mantle source region by convection a pronounced negative nb anomaly in the ors subduction related lavas may be explained by the retention of a nb bearing phase in the mantle during hydrous melting of the mantle wedge above the subduction zone allowing for the effects of the added component from the subducted slab there appears to be no necessity to invoke separate mantle source regions for the two suites of lavas both may have been derived from chemically similar portions of mantle if volcanic arc lavas are derived from the mantle wedge the implication is that such a source lies at relatively shallow depth within the upper mantle the same may therefore apply to the carboniferous continental rift basalts this evidence combined with the fact that there is no evident hot spot trail across the midland valley despite a long period of within plate volcanism and rapid plate movements during the carboniferous suggests that the alkali basalt magmatism is not the product of a deep seated mantle plume rather the volcanism appears to owe more to passive rifting and to diapiric upwelling from a source region within the uppermost mantle

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

non destructive geochemical and magnetic characterisation of group xviii dolerite stone axes and shaft hole implements from england thirty five polished stone axes and shaft hole implements which had been previously assigned by petrographic partially destructive study to group xviii assumed to be from the whin sill dolerite source in northern england were characterised non destructively using a combination of portable x ray fluorescence analysis pxrf and magnetic susceptibility measurements all the implements were compared with the whin sill and with other petrologically and or visually similar rock sources in the north of england and in scotland using a database of chemical elements constructed from the published literature and statistical atypicality testing twenty nine of the implements are good matches for the whin sill as expected but three do not match whin sill rocks and may therefore need to be re assessed as members of group xviii a further three implements have ambiguous characteristics perhaps as a result of surface weathering one axe an axe hammer and an adze that had not previously been assigned to implement groups were also analysed as a test of the robustness of the non destructive methods all three implements could be distinguished from group xviii on the basis of chemical and magnetic characteristics most of the distribution of group xviii implements is best explained by the opportunistic use of glacial erratics rather than trade from the primary source possible alternative sources for the non group xviii implements include the scottish old red sandstone age lavas which could also have been obtained as erratics the chemical and magnetic characteristics established in this paper provide a non destructive alternative to thin section study of potential group xviii artefacts

compositional variation and provenance of late cenozoic distal tephra beds fairbanks area alaska abstract thin fine grained discontinuous tephra beds from interior alaska can be divided into two compositional groups by their mineralogy and major and trace element glass geochemistry the source vents of these beds are unknown but are believed to be in the aleutian arc alaskan peninsula and wrangell volcanic field type i tephra has evolved trace element profiles while type ii is primitive type ii contains abundant hydrous minerals that are absent or rare in type i trace elements were used to compare the fairbanks tephra beds to volcanic rocks in the potential source areas there are very few published glass trace element analyses from these regions this necessitates comparing whole rock with glass analyses for this reason incompatible elements particularly rare earth elements are most useful whole rock analyses and petrography of lavas throughout the aleutian arc alaskan peninsula and the wrangell volcanic field are similar to type i tephra lavas and intrusive rocks similar to type ii tephra are rare and occur at one volcano in the alaskan peninsula and at three volcanoes in the wrangell volcanic field

inversion tectonics of the variscan foreland of the british isles late westphalian inversion structures on the variscan foreland display wide variations in orientation that are the product of the underlying basement grain the orientation of the major basement lineaments in relation to the direction of maximum shortening also determined the severity of deformation of the inverted basins ne sw trending faults were oriented roughly perpendicular to the nw se to nnw sse direction of maximum shortening determined from thrust transport directions in the variscan orogen to the south as a consequence ne sw trending basins in the variscan foreland have been strongly inverted the silesian post rift fill has commonly been expelled from the basins and the syn rift sediments have been deformed by chevron folds dublin and bowland basins in contrast the n s and nw se trending faults were oriented more obliquely to the direction of maximum shortening and as a consequence display a significant component of oblique slip this oblique slip component is manifested as en echelon periclines and flower structures in general the n s and nw se trending basins were less strongly inverted and the silesian post rift fill has been retained

palaeoclimate simulation of 21 ka for the tibetan plateau and eastern asia a modelling experiment with changes in vegetation types at the last glacial maximum 21 ka bp is performed by using an agcm coupled with a simplified simple biosphere model agcm ssib the results show that the decrease in temperature is large in tibet and eastern asia at 21 ka the amplitudes of the decrease vary with seasons and locations annual mean temperature decreases between 13 c and 2 c summer and annual precipitation in eastern china at 21 ka is only about 50 of that at present while little more or unchanged precipitation appears in northwest west and southwest of china the effective precipitation p e shows much drier conditions in eastern and southeastern china than today a comparison with geological evidences of lake status and pollen based vegetation shows that this simulation is in broad scale agreement with the geological records the changes by using palaeo vegetation data to prescribe land surface show improved signals in the 21 ka climate simulations in east asia this result encourages us to study the potential causes feedbacks and mechanisms of palaeoclimate changes using the agcm ssib modelling approach continuously

tectonic cycles in southern africa abstract the recurrence of major geological events within the 3600 ma stratigraphic record of southern africa suggests a periodicity of320 25ma for at least the last 3200 ma this periodicity is reflected in major episodes of continental volcanism granitoid plutonism orogeny reciprocity of terrestrial and marine dominated sequences platform carbonate sedimentation glaciation and first order changes in sea level these serve to define 11 completed megacycles each introduced by a major rifting event accompanied by listric faulting alluvial sedimentation in restricted fault bound troughs volcanism and a type granitoid plutonism prior to 3200 ma continental rift magmatism occurred subaqueously due to very high early archean sea levels resulting in pillow lavas and a lack of interbedded terrigenous siliciclastics the long term reciprocity of terrestrial and marine dominated sequences records eustatic first order changes in sea level with highstands characterized by generally humid warm continental climates low relief and tropical afforestation on the other hand lowstand climates were hot and arid with high relief and widespread desertification thick marine sequences accumulate in areally extensive epeirogenic basins without significant volcanism or faulting and commonly are divided into an early phase of open shelf sedimentation followed by deposition in a brackish marine foreland basin within openshelf environments an early phase of biochemical precipitation and or siliciclastic reworking along linear shorelines is separated from a later phase involving rapid deposition of immature siliciclastics along lobate shorelines evolution of the foreland basin is related to orogenic activity and the isolation of an epeiric sea which sometimes developed the characters of a barred basin marine dominated sequences display a deterministic stacking of lithofacies important glacial epochs commonly occur midway through first order regression sometimes with lesser events closely following peak transgression potentially they display 320 ma periodicity but with an unexplained mid proterozoic gap glaciation is related to the combined effect of climatic cooling associated with first order regression and depletion of atmospheric co2 by biological uptake associated with platform carbonate development terrestrial volcanism is believed to be the main contributor of atmospheric co2 climatic change is accompanied by cyclical patterns of cratonic weathering and pedogenesis

geochemistry of the tertiary volcanism of northern ireland the antrim plateau northern ireland forms the southwestern part of the british tertiary igneous province and is dominated by basaltic lavas previous work divided the province into three stratigraphic formations viz the lower middle and upper formations with the middle formation having a basaltic member known as the causeway member new chemical and sr nd isotopic data covering the spectrum of lava types are presented three distinct geochemical types are recognised 1 basalts of the lower formation and most of those from the upper formation are lree enriched but have characteristic convex up ree patterns with a maximum around nd 2 some of the upper formation basalts and the majority of the causeway member basalts are lree enriched with no convex shape in their ree pattern and 3 some of the causeway member basalts are lree depleted and similar to n morb isotopic compositions of sr and nd show considerable variation throughout the three formations with sr t 22 to 107 and nd t 11 to 8 5 the exceptionally wide ranges of isotopic compositions are believed to have been produced by assimilation of a crustal mainly dalradian derived component the ree patterns indicate that most of the basalts were derived from a lree depleted mantle and with the exception of the causeway member most have convex up ree patterns these are interpreted as being due to residual garnet in the mantle source which indicates melting at depths in excess of 80 km this suggests that at the start of tertiary volcanism the melt regime was controlled by a thick lithosphere which thinned with time such that the causeway tholeiites were produced at shallower levels the return to the convex up patterns of the upper formation means that simple models of lithospheric stretching and rifting are not able to explain the antrim situation

thermochronology of economic mineral deposits dating the stages of mineralization at panasqueira portugal by high precision 40 39 ar age spectrum techniques on muscovite 40 ar 39 ar age spectrum dates for 13 muscovites have been used to reconstruct the thermal history thermochronology of the panasqueira portugal tin tungsten deposit a deposit spatially associated with a belt of hercynian plutons muscovite samples with an age difference as small as 2 2 m y 0 7 of the age are statistically distinct statistics are even better for comparison of multiple samples from separate events that is a difference of 0 9 m y 0 3 can be resolved in this approximately 300 m y old deposit the major tin and tungsten ore forming stages which are the oxide silicate stage the main sulfide stage and greisenization occurred between 296 3 or 0 8 1 sigma and 291 6 or 0 8 m y 1 sigma the first substage of the oxide silicate stage was a short lived thermal pulse at 296 3 or 0 6 m y the fluids responsible may have emanated from the known granite cupola the main sulfide stage was active at 294 5 or 0 9 m y as a slightly longer lived pulse with oldest evidence for this stage 295 8 or 0 6 m y coming from areas farthest away from the known cupola and youngest evidence 293 5 or 0 8 m y closest to the cupola a second substage of the oxide silicate stage occurred as a short lived thermal pulse at 292 9 or 0 7 m y synchronous with greisenization of the cupola and alteration of the silica cap at 292 1 or 0 4 m y the duration of activity of the oxide silicate stage the main sulfide stage greisenization and alteration of the silica cap based on the ages of all 13 muscovites was greater than 4 2 or 0 5 m y 1 sigma minor argon loss from all dated muscovites occurred during later reheating probably during the longer lived pyrrhotite alteration stage a single center the known cupola had a prolonged role and was the source for main sulfide stage oxide silicate stage ii greisenization and alteration of the silica cap and possibly oxide silicate stage i and the pyrrhotite alteration stage however a separate source for these latter two stages cannot be ruled out this study is an example of a new and powerful application of 40 ar 39 ar age spectrum dating of muscovite because of the high precision demonstrated in this study it is now possible to establish time constraints necessary for solving some of the long standing problems in economic geology beyond this the unique geologic situation of panasqueira has allowed us to quantify the thermal characteristics of muscovite published fluid inclusion data have been used to estimate a muscovite argon closure temperature of approximately 325 degrees c during rapid cooling or short reheating and a temperature of approximately 270 degrees c during slow cooling or extended reheating argon loss patterns displayed by all dated muscovites resulted from reheating after original closure the mechanism for this argon loss appears to have been argon transport by volume diffusion thus 40 ar 39 ar age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age duration and number of episodes of mineralization

simulation of the last glacial maximum climate over east asia with a regional climate model nested in a general circulation model abstract the east asian climate at the last glacial maximum lgm 21 000 years b p has been simulated using a regional climate model regcm2 nested in an atmospheric general circulation model of the institute of atmospheric physics iap agcm boundary conditions for the lgm simulations are consistent with the paleoclimate modelling intercomparison project pmip the results show that the nested regional model reproduces well the colder lgm climates over east asia the simulated annual mean surface temperature is 2 c 4 c colder than the present over the east asian continent with the coldest anomaly of about 8 c in the vicinity of current coastal areas where land is exposed due to lowering sea level at the lgm the precipitation changes are complex with general features of drier conditions over eastern china and its neighborhood and wetter conditions over western china than the present compared with the driving iap agcm the regcm2 results display better agreement with geological reconstructions over east asia especially in the mideastern and southern china the simulated warming changes by the iap agcm disagree with cooling in paleodata whereas the regcm2 reproduces realistic cooler lgm climate thus the current work proves that the high resolution regcm2 can capture additional regional details in the lgm simulation produced by improved representation of topography and physics

cretaceous climate a comparison of atmospheric simulations with the geologic record abstract atmospheric simulations using realistic cretaceous geography 100 million years ago suggest that paleography is an important factor governing the nature of the circulation the simulated cretaceous atmospheric circulations are markedly different both from the present day atmospheric circulation and from the classical hypotheses of a weaker circulation and poleward displacement of circulation features e g the subtropical high therefore they pose specific questions which can be tested against the geologic record aspects of the cretaceous simulations are verified in comparisons with the geologic record the simulations serve to guide areas of future paleoclimatic research and to formulate better the nature of the problem of warm equable climates

geochronology of carboniferous permian magmatism in the midland valley of scotland implications for regional tectonomagmatic evolution and the numerical time scale four new u pb isotope dilution thermal ionization mass spectrometry dates from carboniferous igneous rocks of the midland valley of scotland are integrated with 16 recently published 40ar 39ar dates the numerical and stratigraphical ages of the dated samples are compatible to stage level allowing improved intrabasinal and regional correlations early carboniferous extension related volcanism in the midland valley was pulsed with a date of 343 4 1 0 ma from the garleton hills volcanic formation and dates of 334 7 1 7 and 335 2 0 8 ma from the clyde plateau volcanic formation the magmatic pulses are synchronous with synrift phases in the northumberland solway basin volcanism continued in mid to late carboniferous time contemporaneous with dextral strike slip tectonics in contrast to a post rift tectonic setting in northern england after late carboniferous basin inversion tholeiitic magmatism dated at 307 6 4 8 ma provides a maximum westphalian d age for post variscan magmatism and extension dextral transtension across scotland and northern england in the early permian as rift systems developed across nw europe alkaline extension related magmatism resumed in the midland valley from c 298 to 292 ma the improved geochronology provides important data for poorly constrained parts of the numerical carboniferous time scale such as stages within the visean and provides a well controlled tie point that supports a tournaisian visean boundary age of c 345 4 ma

linking changes in tectonic style with magmatism in northern europe during the late carboniferous to latest permian abstract early carboniferous to permian magmatism associated with rifting within the northern foreland of the variscan orogen was widespread across europe during the long period of magmatic activity the regional tectonic setting changed across the region from early carboniferous extension and basin formation to a rifting wrenching style of deformation in the late carboniferous stephanian to early permian wrenching and faulting were accompanied by widespread voluminous and episodic magmatic extrusion intrusion and underplating this was followed by thermal relaxation and the development of the northern and southern permian basins in later permian times thermal relaxation was punctuated by a permo triassic phase of extension and graben formation 40ar 39ar ar step heating dating for mineral separates and whole rock samples of magmatic rocks from southern scandinavia oslo graben and south sweden and rugen north germany provides further radiometric evidence for three of the proposed periods of magmatic activity in the region latest carboniferous to earliest permian ages c 300 310 ma were obtained for volcanic rocks in the oslo graben and dolerite sills and dykes in south sweden and north germany this phase can be time correlated with magmatic activity that occurred throughout europe during large scale dextral wrenching that followed the variscan orogeny a second phase of alkaline intrusions is confined to the oslo graben and related to caldera collapse around c 275 ma the third permo triassic phase c 250 ma is considered to be related to a new tectonic cycle involving extension that triggered minor melting of enriched fertile mantle

large dry humid fluctuations in asia during the late cretaceous due to orbital forcing a modeling study abstract cretaceous stratigraphy in the mid to low latitude asia indicates that the climate was overall dry with large variations in aridity in timescales of 1 100 ka different from the present day monsoonal humid climate to identify the possible mechanism for such variation we modeled the late cretaceous climate using a fully coupled atmosphere ocean general circulation model aogcm community earth system model version 1 2 cesm1 2 under different co2 concentrations and orbital configurations the simulation results show that the mid to low latitude asia was generally dry during that time consistent with reconstructions the arid area decreases and the semi arid area increases with the increase of co2 concentration but the change in total area is small even when co2 is increased by 8 folds in contrast the area of dryland can increase by 67 or 500 depending on how dryness is defined when the orbital configuration changes from one in which the northern hemispheric summer receives the most solar insolation to one in which it receives the least solar insolation therefore the mid to low latitude asia was likely going through dramatic dry humid cycles at orbital timescale during the late cretaceous similar to the saharan region during the late miocene pleistocene

isotope geochemistry and origin of calc alkaline lavas from a caledonian continental margin volcanic arc abstract analyses for major and trace elements including ree and sr nd and pb isotopes are reported from a suite of siluro devonian lavas from fife scotland the rocks form part of a major calc alkaline igneous province developed on the scottish continental margin above a wnw dipping subduction zone within the small area ca 15 km2 considered rock types range from primitive basalts and andesites high mg ni and cr to lavas more typical of modern calc alkaline suites with less than 30 ppm ni and cr there is a marked silica gap between these rocks 74 yet the latter can be generated by fractional crystallization from the more mafic lavas in contrast variation in incompatible element concentrations and ratios in the mafic lavas can not be generated by fractional crystallization processes increasing sio2 is accompanied by increasing rb k pb u and ba relative to sr and high field strength elements increasing lree enrichment and increasing sr calculated at 410 ma and by decreasing hree eu eu sm nd and nd 410 nd and sr are roughly anticorrelated and have more radiogenic compositions than the mantle array in common with data reported elsewhere from this part of the arc the correlation extrapolates up to cross the mantle array within the composition field of the contemporary morb source and extrapolates down towards the probable compositional range of lower palaeozoic greywackes which may form the uppermost 8 km of the crust or may be supplied to the source by subduction one sample however lies within the mantle array and closely resembles lavas from northwestern parts of the arc where a mantle source with mild time integrated rb sr and lree enrichment has been inferred the lavas have relatively high initial 207pb 204pb for their 206pb 204pb a feature which has been interpreted elsewhere as the result of incorporation of a sediment component into arc magmas the systematic changes with increasing sio2 in isotopic and chemical parameters can be explained by mixing of a greywacke derived component with depleted mantle the various possible mixing mechanisms are discussed and it is considered most likely that mixing occurred in the mantle source through greywacke subduction the bulk of the rb k ba and pb in the lavas is probably recycled from the crust whereas less than some 40 of the sr and nd is recycled the calc alkaline chemical trends are solely a function of mixing with the sediment component

u pb and hf isotopic study of zircons from migmatised amphibolites in the cathaysia block implications for the early paleozoic peak tectonothermal event in southeastern china abstract amphibolites occur in a number of localities in the cathaysia block some of them have been migmatised and their protoliths represent basaltic magmas erupted in various tectonic settings four migmatised amphibolites were collected from jiangxi and fujian provinces cathodo luminescence images of zircons extracted from the representative amphibolites show unzoned or sector zoned structure la icp ms analysis indicates that most zircons have high th u ratios and yield u pb zircon ages of 446 5 435 2 434 4 and 423 2 ma respectively lu hf isotopic analysis on these zircons gives hf model ages ranging from 900 to 1200 ma based on lithological observations and previously published geochronological data we interpret that these u pb ages record an important tectonothermal event that led to the migmatization this early paleozoic caledonian tectonothermal event in the southeastern china has a great tectonic implication for the evolutionary history of the cathaysia block

permo carboniferous magmatism and rifting in europe introduction an extensive rift system developed within the northern foreland of the variscan orogenic belt during late carboniferous early permian times post dating the devonian early carboniferous accretion of various neoproterozoic gondwana derived terranes on to the southern margin of laurussia laurentia baltica fig 1 rifting was associated with widespread magmatism and with a fundamental change at the westphalian stephanian boundary in the regional stress field affecting western and central europe ziegler 1990 ziegler cloetingh 2003 the change in regional stress patterns was coincident with the termination of orogenic activity in the variscan fold belt followed by major dextral translation between north africa and europe rifting propagated across a collage of basement terranes with different ages and thermal histories whilst most of the carboniferous permian rift basins of nw europe developed on relatively thin lithosphere the highly magmatic oslo graben in southern norway initiated within the thick stable and presumably strong cold lithosphere of the fennoscandian craton the rift basins in the north sea in contrast developed in younger caledonian age lithosphere which was both thinner and warmer than the lithosphere of the craton to the east

dating transitionally magnetized lavas of the late matuyama chron toward a new 40ar 39ar timescale of reversals and events the k ar based geomagnetic polarity timescale was constructed using data from lavas and tuffs that bracketed but rarely dated the transitions between polarity intervals subsequent 40ar 39ar dating indicated that the ages of some polarity transitions had been underestimated by about 6 although the accepted ages of the polarity chron boundaries have increased their precise temporal definition remained uncertain we have taken a different approach and used incremental heating techniques to obtain 18 new 40ar 39ar ages from basaltic lavas within flow sequences at punaruu valley tahiti and haleakala volcano hawaii these lavas record transitional paleomagnetic directions corresponding to four mid pleistocene polarity reversals or events three lavas from punaruu valley previously thought to record the cobb mountain normal polarity subchron cmns gave a mean age of 1 105 0 005 ma indicating that they were erupted about 76 kyr after the cmns this period of transitional field behavior is designated the punaruu event in addition seven new 40ar 39ar ages from the punaruu valley indicate that the jaramillo normal polarity subchron jns lasted about 67 kyr starting at 1 053 0 006 ma and ending 0 986 0 005 ma this agrees with astronomical estimates but conflicts with jns ages proposed by spell and mcdougall 1992 and izett and obradovich 1994 on the basis of 40ar 39ar dating of rhyolite domes in the valles caldera indistinguishable 40ar 39ar ages of seven lavas including one from punaruu valley and six from haleakala that record broadly similar intermediate paleodirections suggest that the kamikatsura event occurred at 0 886 0 003 ma moreover these data indicate that the kamikatsura event occurred 20 40 kyr after another geomagnetic event most probably taking place at 0 92 ma we designate this earlier field behavior the santa rosa event adopting its name from that of a transitionally magnetized rhyolite dome which happened to figure prominently in the original definition of the end of the jns in the 1968 study of doell et al 1968 the discovery of these new short lived polarity events during the matuyama reversed chron suggests that the 400 kyr period between 1 18 and 0 78 ma experienced no less than 7 and perhaps more than 11 attempts by the geodynamo to reverse this newly determined higher frequency of geomagnetic activity illustrates vividly the importance of obtaining precise age control directly from transitionally magnetized rocks

high elevation of jiaolai basin during the late cretaceous implication for the coastal mountains along the east asian margin abstract a large body of evidence suggests that there were extensive coastal mountains along the east asian margin during the late cretaceous however current knowledge of the paleo mountains the period range and elevation is limited therefore direct paleoaltimetry is needed to validate and evaluate the paleo mountains in east asia our study area is jiaolai basin which is located at the east asian continental margin we estimate the paleoelevation of jiaolai basin during the late cretaceous using carbonate clumped isotope paleothermometry after correcting for seasonal preference latitudinal difference and secular climate change we conclude that the paleoelevation of jiaolai basin was almost certainly 2 0 km at 80 ma combined with the evidence from stratigraphy paleogeography and paleoclimatology our results suggest that the existence of coastal mountains along east asia during the late cretaceous is likely and the model of okhotomorsk east asia collision is preferred

sensitivity of east asian monsoon climate to the uplift of the tibetan plateau abstract using the cola center for ocean land atmosphere studies general circulation model a series of numerical experiments were conducted to examine the impact of uplift of the tibetan plateau on the evolution of the monsoon climate in east asia an attempt was made to isolate the effect of the plateau uplift from the changes in other forcing mechanisms we examined the spatial and temporal variation patterns of a variety of climatic variables and indices including monsoon intensity sea level pressure surface and upper air winds temperature at different levels precipitation air humidity and soil moisture our results suggest that the evolution of the east asia monsoon may be more sensitive to the uplift of the tibetan plateau than that of the south asia monsoon moreover the effect of the plateau uplift on the east asia winter monsoon is more significant than that on the summer monsoon in the northern part of east asia north china the formation of the monsoon climate is marked mainly by the establishment of the northerly winds in winter or the winter monsoon system corresponding to the uplift of the plateau when the height reaches approximately 50 of its current elevation on the other hand the establishment of the monsoon climate in the southern part of east asia the yangtze river valley and the area south of it may be much earlier than that in the northern part

miocene and pliocene lacustrine and fluvial sequences upper ramparts and canyon village porcupine river east central alaska abstract cenozoic strata exposed along the porcupine river between the upper ramparts and canyon village alaska can be divided into five unconformity bounded units sequences which are lower and middle miocene unit a the white sandy fluvial sequence with peat beds middle miocene unit b the basalt sequence part b1 is basalt and part b2 is organic rich sedimentary beds upper miocene unit c mudrock dominated lake sequence late miocene or pliocene to pleistocene unit d terrace gravels detrital organic matter and associated sediments and holocene unit e mixed sand and gravel rich sediment and other sedimentary material including peat and eolian silt the sequence unit a of lower and middle miocene fluvial deposits formed in streams and on flood plains just before the inception of local volanism fossil pollen from unit a suggests conifer dominated regional forests and cool temperate climates peat beds and lake deposits from unit b contain pollen that indicates a warmer temperate climate coinciding with the middle miocene thermal maximum the lake deposits unit c downstream from the basalts accumulated in a small basin which resulted from a hydrologic system that was dammed in the late miocene but breached soon thereafter the lower part of the terrace gravels unit d expresses breaching of the dammed hydrologic system of unit c the porcupine river became a major tributary of the yukon river in late pleistocene time when laurentide ice blocked drainage from the yukon interior basins causing meltwater to spill over the low divide separating it from the porcupine river drainage initiating erosion and capture of the yukon interior basins

possible atmospheric co2 extremes of the middle cretaceous late albian turonian 1 atmospheric carbon dioxide co2 estimates for the middle cretaceous mk have a range of 4000 ppm which presents considerable uncertainty in understanding the possible causes of warmth for this interval this paper examines the problem of mk greenhouse forcing from an inverse perspective we estimate upper ocean water temperatures from oxygen isotope measurements of well preserved late albian turonian planktonic foraminifera and compare these against temperatures predicted by general circulation model gcm experiments with co2 concentrations of 500 7500 ppm at least 4500 ppm co2 is required to match maximum temperatures inferred from well preserved planktonic foraminifera approximately 900 ppm co2 produces a good match between the model and the minimum temperature estimates for the mk an ocean model forced by these two extremes in surface conditions brackets nearly all available bottom water temperature estimates for this interval the climate model results support nearly the entire range of mk co2 estimates from proxy data the ocean model suggests possible mk oceanographic changes from deep water formation in the high latitude region of one hemisphere to the other hemisphere in response to changes in atmospheric temperatures and hydrologic cycle strength we suggest that rather than contradicting one another the various proxy co2 techniques especially those with high temporal resolution may capture true variability in co2 concentrations and that mk co2 could have varied by several thousand ppm through this interval

upper palaeozoic basins of the british isles caledonide inheritance versus hercynian plate margin processes hypotheses to explain the origin and location of upper palaeozoic sedimentary basins are presented group a basins were those old red sandstone basins whose location and subsidence were controlled by caledonide features including active and remnant fore arc basins midland valley and major transcurrent movements orcadian basin newer granite plutonic magmas in the southern uplands subduction complex post dated subduction and resulted from post collision cratonization processes as yet little understood group b basins were those whose initial positions in space were controlled by palaeo plate factors in particular the location of granitoid plutons but whose subsidence was controlled by active hercynian neoplate processes some group a basins were regenerated by this process midland valley a new hypothesis is presented to account for the origin of a carboniferous rift to sag trend similar to that proven in modern continental margin basins such as the north sea the hypothesis is an adaptation of mckenzie9s lithospheric stretching model some of whose major features are well shown in the carboniferous history of the north and central british isles group b processes were controlled by ligurian bretonic plate consumption in the s brittany massif central vosges areas group c basins in the rheno hercynian zone also owe their location and origin to back arc rifting and continental crustal oceanization processes caused by liguro bretonic subduction

what triggers the transition of palaeoenvironmental patterns in china the tibetan plateau uplift or the paratethys sea retreat abstract geological research has illustrated the transition of palaeoenvironmental patterns by the earliest miocene from a planetary wind dominant type to a monsoon dominant type indicating that the east asian monsoon became markedly intensified and played a leading role in the east asian climate from a modeling point of view the pioneering research using the reduced number of scenarios had demonstrated that both the tibetan plateau uplift and the paratethys sea retreat were important for understanding the asian monsoon evolution however the sensitivity of the paratethys retreat to the east asian climate still needs further studies based on the more detailed scenarios thirty numerical experiments under the six paratethys sea and the five tibetan plateau conditions illustrate the shifts from zonal climate to the monsoon climate in east asia the results confirm again that both the paratethys retreat and the tibetan plateau uplift play important roles in the formation of the monsoon dominant environmental pattern and show that the paratethys retreat can strengthen the east asian monsoon and greatly increase humidity and aridity respectively in the monsoon areas and northwest china which is similar to the impact of the tibetan plateau uplift on the east asian climate furthermore the fact that the paratethys sea retreats to the turan plate is found to be the key criterion for the palaeoenvironmental patterns transition in china the shrinkage of paratethys sea leads to the reconstructions of the pressure system and the atmospheric circulations which result in the variations of precipitation and the transition of palaeoenvironmental patterns

modeling east asian climate and impacts of atmospheric co2 concentration during the late cretaceous 66ma abstract utilizing the community climate system model version 2 from the national center for atmospheric research ncar and the reconstructed paleogeographic data we simulate east asian climate in the late cretaceous 66 ma and investigate the impacts of atmospheric co 2 concentration on climate the simulations show that the large scale pressure systems and prevailing wind directions showed a remarkable seasonal variation over east asia at 66 ma which indicates a monsoon feature over east asia the east asian winter and summer monsoons showed a synchronous variation that is a strong weak winter monsoon accompanied a strong summer weak monsoon at 66 ma there was more precipitation over the eastern coasts of asia and less precipitation in the mid latitudes of the inland areas but there was no meiyu rainy belt in the subtropics of the east asian land like the present climate moreover the simulated cretaceous climate over east asia was warmer relative to the present day annual mean surface air temperature was higher over asia at that time and close to the estimation from the geological evidence in the late cretaceous when atmospheric co 2 concentration is reduced the east asia climate has a significant change with weaker winter and summer monsoons over east asia annual mean surface air temperature and annual total precipitation reduce in most of land and ocean negative difference of surface water budget appeared mainly in the eastern part of east asia indicating a drier soil surface while positive differences appeared in the mid latitudes of central western asia indicating a wetter soil surface

a model for atmospheric co 2 over phanerozoic time a new model has been constructed for calculating the level of atmospheric co sub 2 over phanerozoic time which is much simpler mathematically than the blag model but more complex geologically and biologically results suggest that there has been a notable pattern of varying atmospheric co sub 2 level over the past 570 my with high levels during the mesozoic and early paleozoic and low levels during the permo carboniferous and late cenozoic sensitivity analysis shows that within reasonable limits of the principal governing parameters this qualitative trend of varying co sub 2 is relatively insensitive to the actual values chosen for these parameters causes of the co sub 2 variation are multiple and no single geological or biological process can be called upon to explain all co sub 2 variation for all time the calculated trend of co sub 2 over time agrees well with independent estimations of paleoclimates thus the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study

palynology paleoclimatology and correlation of middle miocene beds from porcupine river locality 90 1 alaska abstract beds in the upper ramparts canyon of the porcupine river alaska 67 20 n 141 20 w yielded a flora rich in pollen of hardwood genera now found in the temperate climates of north america and asia the beds are overlain or enclosed by two basalt flows which were dated to 15 2 0 1 ma by the 40 ar 39 ar method fixing the period of the greatest abundance of warm loving genera to the early part of the middle miocene the assemblage is the most northern middle miocene flora known in alaska organic bed 1 underlies the basalt and is older than 15 2 ma but is of early to middle miocene age the pollen assemblage from organic bed 1 is dominated by conifer pollen from the pine and redwood cypress yew families with rare occurrences of temperate hardwoods organic bed 2 is a forest floor containing redwood trees in life position engulfed by the lowest basalt flow a pine log has growth rings up to 1 cm thick organic beds 3 and 4 comprise lacustrine sediment and peat between the two basalt flows their palynoflora contain conifers and hardwood genera of which about 40 have modern temperate climatic affinities hickory katsura walnut sweet gum wingnut basswood and elm pollen are consistently present and beech and oak alone make up about 20 of the pollen assemblage a warm high latitude climate is indicated for all of the organic beds but organic bed 3 was deposited under a time of peak warmth climate data derived by comparison with modern east asian vegetation suggest that at the time of deposition of organic bed 3 the mean annual temperature mat was ca 9 c the warm month mean temperature wmmt was 20 c and the cold month mean temperature cmmt was ca 2 c in contrast the modern mat for the region is 8 6 c wmmt is 12 6 c and cmmt is 28 c organic beds 3 and 4 correlate to rocks of the middle miocene late seldovian stage of cook inlet and also probably correlate to and more precisely date the lower third of the suntrana formation in the alaska range beds at unalaklect part of the upper mackenzie bay sequence in the beaufort mackenzie basin and the mary sachs gravel of banks island this suggests that forests with significant percentages of temperate deciduous angiosperms existed between latitudes 60 and 72 n during the early middle miocene

40ar 39ar geochronology of carboniferous permian volcanism in the midland valley scotland twenty one new 40 ar 39 ar step heating experiments on mineral separates from intrusive and extrusive carboniferous and permian igneous rocks in the midland valley of scotland yielded 17 concordant experiments with a relative age precision better than 1 2 these ages resolve inconsistencies between existing k ar dates on the same samples and their stratigraphical constraints correlated to recently published timescales the precise 40 ar 39 ar dates are stratigraphically constrained to stage level and can contribute to carboniferous timescale tie points at the tournaisian visean boundary within the visean and at the carboniferous permian boundary situated in the extending variscan foreland two distinct phases of extension related transitional alkaline volcanism have been resolved in the dinantian the garleton hills volcanic formation in the eastern midland valley near the tournaisian visean boundary 342 1 1 3 and 342 4 1 1 ma and the clyde plateau volcanic formation in the western midland valley during the mid visean 335 2 329 2 1 4 ma alkaline basic sills near edinburgh previously thought to be namurian appear to be coeval with the clyde plateau volcanic formation at 331 8 1 3 329 3 1 5 ma the new ages allow correlation between these short lived dinantian magmatic pulses and extensional and magmatic phases in the northumberland solway and tweed basins to the south after late westphalian end variscan compression and a regionally important tholeiitic intrusive phase at c 301 295 ma alkaline magmatism related to post variscan extension occurred in the central and western midland valley during the latest carboniferous or permian from 298 3 1 3 to 292 1 1 1 ma this correlates well with post varsican extension and magmatism observed across the nw european foreland from 300 to 280 ma

recognition of milankovitch cycles in xrf core scanning records of the late cretaceous nenjiang formation from the songliao basin northeastern china and their paleoclimate implications abstract cretaceous terrestrial sedimentary records are crucial for our understanding of geological systems responses to past climate change under greenhouse condition numerous publications have documented that milankovitch cycles were a dominant climate driver over multi millennial timescales however most of these orbital signals were derived from marine records obtained during the cenozoic geological period whereas knowledge of milankovitch cycles preserved in lacustrine sediments prior to the cenozoic is limited due to the lack of a precise chronological framework poor preservation rate of terrestrial sediments limited records and fewer experts in this research area this paper reports high resolution x ray fluorescence xrf elemental records of k ti rb sr zr zr rb rb sr and k ti from member 1 k2n1 and member 2 k2n2 of the nenjiang formation which were obtained from a near continuous sk 2 east sk 2e borehole drilled in the songliao basin sb of northeastern ne china variations of the elemental records reveal a humid arid humid semiarid climatic evolution throughout the deposition of k2n1 and a humid arid humid arid climatic variation throughout the deposition of k2n2 in this context k2n1 experienced a relatively longer humid period and more pronounced climatic fluctuation than k2n2 a method of average spectral misfit asm was adopted to successfully identify two optimal sedimentation rates of 6 577 and 8 369 cm ka for k2n1 and k2n2 respectively based on these two sedimentation rates nearly all significant milankovitch cycles preserved in the rb sr record were recognized it is suggested that westerly wind was the main climatic driving factor of climate evolution in the sb under the forcing of milankovitch cycles the collectively regulation of obliquity and precession increased the seasonal contrasts during humid periods in the nenjiang formation and thereby amplified the paleomonsoon effect thus bringing more moisture towards the sb and lead to enhanced rainfall

deep sea paleotemperature record of extreme warmth during the cretaceous oxygen isotope analyses of well preserved foraminifera from blake nose 30 n paleolatitude north atlantic and globally distributed deep sea sites provide a long term paleotemperature record for the late albian maastrichtian interval that is difficult to reconcile with the existence of significant cretaceous ice sheets given reasonable assumptions about the isotopic composition of cretaceous seawater our results suggest that middle bathyal water temperatures at blake nose increased from 12 c in the late albian through middle cenomanian to a maximum of 20 c during the latest cenomanian and earliest turonian bottom waters were again 12 c during the middle campanian and cooled to a minimum of 9 c during the maastrichtian correlative middle bathyal foraminifera from other ocean basins yield paleotemperature estimates that are very similar to those from blake nose comparison of global bottom water temperatures and latitudinal thermal gradients suggests that global climate changed from a warm greenhouse state during the late albian through late cenomanian to a hot greenhouse phase during the latest cenomanian through early campanian then to cool greenhouse conditions during the mid campanian through maastrichtian

late mesozoic calc alkaline volcanism of post orogenic extension in the northern da hinggan mountains northeastern china abstract late mesozoic calc alkaline volcanism in the northern da hinggan mountains ndhm ne china exhibits geochemical and sr nd isotopic characteristics similar to those of cenozoic calc alkaline volcanism in the basin and range province usa whole rock k ar dating results show that these volcanic sequences were erupted during 138 116 ma composed of basaltic andesites trachyandesites group 1 hornblende andesites trachytes group 2 and rhyolite lavas group 3 they are characterized by low mgo contents 4 20 lile lree enrichment and significant nb ta depletion as well as a little depleted to slightly enriched nd and weakly enriched sr isotopic ratios group 1 initial 87sr 86sr 0 70502 0 70572 nd t 0 78 to 0 91 group 2 initial 87sr 86sr 0 70497 0 70518 nd t 0 86 to 1 26 group 3 initial 87sr 86sr 0 70510 0 70635 nd t 0 41 to 0 25 the systematic variations in major and trace elements homogeneous sr nd isotope data and temporal consistency among three volcanic groups indicate that they were derived from a similar mantle source metasomatized by fluids related to the closure of the paleo asian and or mongolia okhotsk oceans and were produced through different degrees of fractional crystallization of the primary melts group 1 basaltic rocks were formed through removal of olivine and pyroxene of the primary melts while group 2 trachytes which contain the lowest lree contents e g la 24 28 ppm and relatively less enriched sr and higher nd isotope ratios were generated after removal of a few percent of lree rich minerals such as hornblende clinopyroxene and apatite of melts like group 1 group 3 rhyolite lavas exhibiting the highest abundances of strongly incompatible elements such as rb and k moderate lree contents e g la 28 53 ppm as well as apparently negative eu and sr anomalies represent the final crystallized products following a plagioclase predominant fractionation of melts like group 2 the low mgo contents and evolved affinities of the volcanic rocks imply that beneath the ndhm there existed many crustal magma reservoirs throughout the eruption episodes in which mantle derived primary melts had experienced intense differentiation these facts in combination with the contemporaneous basin and range tectonic regime suggest that the extensive calc alkaline volcanism in the ndhm was attributed to post orogenic diffuse extension rather than either an upwelling mantle plume or mesozoic oceanic plate subduction

pliocene terrace gravels of the ancestral yukon river near circle alaska palynology paleobotany paleoenvironmental reconstruction and regional correlation abstract gravels deposited by the ancestral yukon river are preserved in terrace remnants on the margins of the yukon river valley near the village of circle in east central alaska plant fossils recovered from sandy silt lenses within these gravels include cones and needles of picea and larix and a variety of seeds seed types include several taxa which no longer grow in alaska such as epipremnum prunus and weigela pollen types recovered from these deposits represent tree and shrub taxa that grow in interior alaska today such as picea larix betula and alnus as well as several taxa that no longer grow in interior alaska today such as pinus tsuga abies and corylus pollen of herb taxa identified include gramineae cyperaceae caryophyllaceae compositae polemonium and epilobium the fossil flora from the gravels near circle are similar and probably age equivalent to the flora recovered from the nenana gravel in the alaska range 250 km to the south palynological and tectonic evidence summarized in this paper now suggests that the nenana gravel was deposited during the early and middle pliocene the presence of plant fossils of tsuga abies pinus weigela and prunus suggests that the mean annual temperature mat of eastern interior alaska during the early and middle pliocene was perhaps 7 9 c warmer and less continental than today s mat of 6 4 c

vegetation and soil feedbacks at the last glacial maximum abstract vegetation feedback at the last glacial maximum lgm about 21 000 calendar years ago remains an unresolved question a global atmospheric general circulation model agcm is asynchronously coupled with an equilibrium terrestrial biosphere model in the present study the coupled model is then used to investigate the influences of vegetation and soil feedbacks on the lgm climate it is found that the simulated geographical distribution of vegetation at the lgm differs from the present pattern dramatically and glacial vegetation cover tends to be reduced on average vegetation feedback alone leads to an annual surface temperature decrease of 0 31 c over the lgm ice free continental areas additional soil feedback reinforced vegetation induced cooling over high latitude eurasia and from the eastern middle east eastward to the indian peninsula significantly in the tropics a terrestrial annual surface cooling of 0 45 c is produced by vegetation and soil feedbacks it is shown that vegetation and soil feedbacks partly reduce data model discrepancy as produced by the agcm alone in some regions such as central africa the indian peninsula south china and north australia

deccan volcanism caused coupled pco2 and terrestrial temperature rises and pre impact extinctions in northern china evaluating the terrestrial climate record provides a critical test of the roles of chicxulub impact and deccan traps volcanism during the cretaceous paleogene k pg mass extinction most evidence came from marine records but our new clumped isotopes data from paleosol carbonates in the songliao basin provide a terrestrial climate history from northern china this reveals there was a pre impact warming caused by the onset of deccan traps volcanism whereas the following short term cooling then another warming episode were likely caused by chicxulub impact and post boundary volcanism our study suggests that the pco levels were probably the main control on the latest cretaceous cooling and the climatic fluctuations across the k pg boundary interval in northern china in the songliao basin the pre impact deccan traps volcanism links to losses of half of the lacustrine algae species charophytes and almost all of the lacustrine ostracodes this suggests that the deccan traps volcanism had already destabilized the ecosystem and caused extinctions prior to the chicxulub impact

etruria formation westphalian c palaeoenvironments and volcanicity on the southern margins of the pennine basin south staffordshire england the westphalian c etruria formation of tansey green south staffordshire comprises three facies associations deposited during a period of extensional faulting subsequent to upper delta plain deposition during westphalian a and b times the lower etruria formation was deposited upon a poorly drained alluvial plain fed by low sinuousity east and northeast flowing streams which were periodically inactive whilst channel geometry remained unchanged continued sedimentation resulted in relative lowering of the water table and development of a second facies association characterized by well drained alluvial plain conditions upon which conifers thrived these alluvial associations include occasional well developed palaeosol horizons indicative of variable drainage conditions continued extensional faulting culminated in alkaline basaltic and phreatomagmatic volcanism and deposition of the third facies association which comprises volcaniclastic and possible epiclastic rocks rapid deposition of the third association resulted in the excellent preservation of a westphalian c conifer flora although extensional tectonism provided the dominant control on sedimentation this is believed to be only of localized importance during a period of variscan compression and associated uplift which characterizes much of the southern margin of the pennine basin

mid latitude terrestrial climate of east asia linked to global climate in the late cretaceous reply the late cretaceous late campanian to maastrichtian was characterized by a variable greenhouse climate with evidence for cooling and or glaciation and warming events most of these climatic signals are derived from marine records and knowledge of the terrestrial climate especially in the mid latitudes is limited due to fragmentary geological records on continents here we report mid latitude terrestrial stable oxygen and carbon isotope data from pedogenic carbonates in the nearly continuous late cretaceous age sk 1 core drilled in the songliao basin northeastern china our data indicate a punctuated mid latitude terrestrial climate in the late cretaceous we interpret the negative excursion of pedogenic carbonate 18o in the early maastrichtian to be the result of decreasing temperature and or strengthened westerlies during global cooling and possible glaciation providing valuable mid latitude terrestrial evidence for this event the negative 13c isotopic excursion ca 66 ma is modeled as higher primary productivity caused by increasing temperature and precipitation in response to a warming climate in the latest cretaceous our continuous stable isotopic records in the songliao basin are in accordance with previously published global late cretaceous records of climate variability from marine and terrestrial regions and demonstrate the sensitivity of mid latitude terrestrial climate in a greenhouse world

zircon u pb age for the orkney lamprophyre dyke swarm scotland and relations to permo carboniferous magmatism in northwestern europe abstract magmatic zircon in the syenite bostonite part of a composite ne sw trending cogenetic bostonite camptonite dyke in orkney scotland yields a laser ablation inductively coupled plasma mass spectrometry age of 313 4 ma and e hf 313 ma values of 6 to 11 this suggests that the ne sw east west and nw se trending scottish lamprophyre dyke swarms were emplaced during one late carboniferous magmatic event contrasting with published k ar dates ranging between c 325 and 250 ma this magmatism is interpreted as a response to late variscan regional extension or an early response to the skagerrak mantle plume lamprophyre magmatism was initiated some 10 ma earlier in scotland than in the oslo rift supplementary material thin section images of the investigated rocks geochemical data and an ree plot u pb and hf isotopic data and a hf v time diagram are available at www geolsoc org uk sup18501

late cretaceous stratigraphy songliao basin ne china sk1 cores abstract the songliao basin is the largest cretaceous oil and gas producing lacustrine basin in china with its greatest aerial extent in the middle cretaceous a coring program sk1 has to date yielded 2485 89 m of continuous core 96 46 recovery and provides significant material for cretaceous research the sequence of the core consists mainly of lacustrine sandstone dark grey mudstone shale and oil shale the upper cretaceous stratigraphic section has been subdivided into the quantou qingshankou yaojia nenjiang sifangtai and mingshui formations in ascending order late cretaceous microfossils are diverse and abundant a detailed biostratigraphic study has subdivided the sequence into high precision biozones 21 ostracode assemblages 10 phytoplankton assemblages 7 palynological zones and 4 charophyta assemblages respectively in addition marine foraminifera were first discovered from the basin three 206pb 238u ages and one 40ar 39ar age were analysed ten local magnetozones have been recognised in the sk1 north and two magnetozones have been indicated in the sk1 south based on biostratigraphy high resolution magnetostratigraphy and sims u pb zircon analyses the sk1 stratigraphy is correlated with upper cretaceous stages in the international geologic time scale the upper part of the quantou formation is the lower turonian the qingshankou formation is the upper turonian lower coniacian the yaojia formation is from the upper coniacian to middle santonian the nenjiang formation is the upper santonian to middle campanian the sifangtai formation is limited to the upper campanian and the mingshui formation is the uppermost campanian to maastrichtian it is likely that the upper part of the mingshui formation belongs to the paleocene and the k pg boundary is within the member 2 of the mingshui formation around the depth of 328 m by new micropalaeontologic and magnetostratigraphic data

enhanced continental weathering and large igneous province induced climate warming at the permo carboniferous transition abstract tracking climate change and its relationships with chemical weathering and massive volcanic activity in deep time greatly improves our understanding of the earth s climate system the permo carboniferous period is a critical time interval with million year scale glacial deglacial cycles and massive basaltic volcanism such as the skagerrak centered also named skagerrak or jutland large igneous province to explore the volcanism climate interactions in this period we obtained high precision ca tims u pb zircon ages for three tuffaceous layers from a cored upper pennsylvanian lower permian marginal marine succession in southern north china these ages calibrate the permo carboniferous biostratigraphy between 301 296 ma in north china from this dated core succession mudrock samples and their calculated weathering index values were screened to constrain the weathering trends for the source landscapes and demonstrate a rapid increase with a subsequent decrease in source chemical weathering intensity during the period of 299 to 296 5 ma these trends coincide with the southern gondwana glacial records low latitude temperature changes relative sea level variations and shifts in atmospheric pco2 that together document an earliest permian climate warming cooling perturbation with a temperature maximum at 298 ma this climate warming in the permo carboniferous icehouse correlates with the emplacement of the skagerrak centered large igneous province which likely released voluminous co2 that led to climate warming during the permo carboniferous transition the immediately following cooling could possibly result from the rapid post eruptional weathering of the massive basaltic rocks of this province in tropical latitudes which would have sequestered atmospheric co2 and promoted return to cooler icehouse conditions this study supports the assertation that massive basaltic volcanism could first cause rapid climate warming and then may have an overall net cooling effect as previously suggested for the deccan traps and the central atlantic magmatic province

late carboniferous tectonic subsidence in south wales implications for variscan basin evolution and tectonic history in sw britain detailed stratigraphic data have been used to backstrip seven sections from the carboniferous south wales coal basin resulting tectonic subsidence curves for the interval 319 305 ma namurian westphalian d are convex up indicating increasing subsidence rate with time with rates between 130 and 250 m ma 1 suggesting a foreland basin setting forward modelling of subsidence due to flexural loading in front of a propagating orogenic wedge shows that an orogenic load migrating in a north northeasterly direction across sw england between 319 and 305 ma could have generated the backstripped subsidence patterns sensitivity tests show that while many of the forward model parameters are poorly constrained and the model results non unique backstripped subsidence patterns allow reasonable constraint on the different model cases so that model predictions can be treated as one possibility in a limited range the predicted load evolution is consistent with current knowledge of tectonic and stratigraphic features of sw england these results suggest that subsidence in other late carboniferous uk basins may also have been influenced by flexure due to a propagating orogenic load

structural synthesis of s staffordshire uk implications for the variscan evolution of the pennine basin the presence of strata of westphalian a to possibly stephanian age in south staffordshire located at the southern margin of the pennine basin provides a rare control on the timing of late carboniferous deformation in central england during westphalian a c times sedimentation in south staffordshire was controlled by thermal subsidence with a superimposed influence of synsedimentary normal and reverse faulting alkaline basic igneous activity occurred during westphalian c times synchronous with uplift of the southern margin of the pennine basin uplift culminated during westphalian c d times in a phase of variscan inversion along basement lineaments and the development of a regional unconformity renewed subsidence and deposition of a relatively thick sedimentary sequence of westphalian d to possibly stephanian age was followed by a final phase of variscan deformation comprising possibly two pulses of uplift tilting and erosion observations presented for south staffordshire in conjunction with studies from other parts of the pennine basin indicate a complex interrelationship between rifting thermal subsidence and variscan basin inversion pulses of n s extension and e w to nw se compression are interpreted as the product of regional strike slip deformation superimposed upon a regime of thermal subsidence alkaline igneous activity is considered to be the product of mantle partial melting in response to limited decompression due to transtensional displacements on crustal thickness faults

lead isotope evidence for the nature of the mantle beneath caledonian scotland abstract recent nd sr pb isotope studies of caledonian granitoids 1 4 have reopened the question of the existence of an unusual or enriched mantle source beneath caledonian scotland this was postulated 5 following a nd sr isotope geochemical study of lavas associated with the scottish old red sandstone pb isotope data for the same lavas reported here restrict any major crustal involvement in southwest highland primitive lavas to ca 1750 ma old rb depleted granulites the lack of such crustal material within scotland together with pb sr isotopic relationships strongly suggests that a large volume mantle source with low rb sr and sm nd has been present at depth under western scotland since the early proterozoic it is unlikely that this is the same enriched mantle source observed from xenoliths in younger magmas 25 and is probably located deep in the lithosphere or within the asthenosphere this source has contributed extensively to the incompatible element budget of caledonian granitoids implying that the caledonian orogeny did result in significant growth of the british crust

age constraints on neogene sedimentary beds upper ramparts half way pillar and canyon village sites porcupine river east central alaska abstract 40 ar 39 ar ages of volcanic rocks are used to provide numerical constraints on the age of middle and upper miocene sedimentary strata collected along the porcupine river intercalated sedimentary rocks north of latitude 67 10 n in the porcupine terrane of east central alaska contain a rich record of plant fossils the fossils are valuable indicators of this interior region s paleoclimate during the time of their deposition integration of the 40 ar 39 ar results with paleomagnetic and sedimentological data allows for refinements in estimating the timing of deposition and duration of selected sedimentary intervals 40 ar 39 ar plateau age spectra from whole rock basalt samples collected along the upper ramparts and near half way pillar on the porcupine river range from 15 7 0 1 ma at site 90 6 to 14 4 0 1 ma at site 90 2 with exception of the youngest basalt flow at site 90 2 all of the samples are of reversed magnetic polarity and all 40 ar 39 ar age spectrum results are consistent with the deposition of the entire stratigraphic section during a single interval of reversed magnetic polarity the youngest flow at site 90 2 was emplaced during an interval of normal polarity with age paleomagnetic and sedimentological data the ages of the middle miocene sedimentary rocks between the basalt flows at sites 90 1 and 90 2 can be assigned to an interval within the limits of analytical precision of 15 2 0 1 ma thus the sediments were deposited during the peak of the middle miocene thermal maximum sediments in the upper parts of sites 90 1 and 90 2 were probably deposited during cooling from the middle miocene thermal maximum 40 ar 39 ar results of plagioclase and biotite from a single tephra collected at sites 90 7 and 90 8 along the canyon village section of the porcupine river indicate an age of 6 57 0 02 ma for its time of eruption and deposition these results together with sedimentological and paleomagnetic data suggest that all of the upper miocene lacustrine sedimentary rocks at these sites were deposited during a single interval of reversed magnetic polarity and may represent a duration of only about 40 000 years the age of this tephra corresponds with a late late miocene warm climatic interval the results from the upper ramparts and half way pillar sites are used to estimate a minimum interval of continental flood basalt activity of 1 1 1 5 million years and to set limits for the timing and duration of tertiary extensional tectonic activity in the porcupine terrane our data indicate that the oroclinal flexure that formed before the deposition of the basalts at the eastern end of the brooks range was created prior to 15 7 0 1 ma

onset of southwesterly wind over eastern china and associated atmospheric circulation and rainfall using the 5 day averaged data from the national center for environmental prediction national center for atmospheric research ncep ncar reanalysis and precipitation from rain gauge stations in china for the period 1981 2000 we investigated seasonal variations and associated atmospheric circulation and precipitation of the southwesterly wind over eastern china the southwesterly wind over eastern china begins earliest over southeastern china and strengthens gradually from spring to the early summer as it extends northward the strengthening of the spring southwesterly wind the tropospheric upward motion and the convergence of low level water vapor over southeastern china results in the beginning of the local rainy season the beginning of the mei yu plum rainfall is connected with the northward march of the southwesterly wind the southwesterly wind reaches the valley of the yangtze river in the early summer and northern china in the middle summer this signifies an onset of the large scale southwesterly wind over eastern china accordingly the rain belt over southeastern china moves to the valley of the yangtze river in the early summer and to northern china in the middle summer moreover the southerly wind extends southward to the south china sea from the spring to summer though it does not stretch from the south china sea to southeastern china at those times the strengthening of the southerly wind over southeastern china is associated with a weakening strengthening of the eastward westward subtropical tropospheric temperature gradient between southwestern china and the western north pacific the developments of a low pressure system over southwestern china and the subtropical high pressure system over the western north pacific may contribute to the strengthening of the southwesterly wind a northward advance of the high pressure system favors the southwesterly wind stretching from southeastern china to northern china the onset of the indian summer monsoon also strengthens the summer southwesterly wind over eastern china

did the variscides collapse or were they torn apart a quantitative evaluation of the driving forces for postconvergent extension in central europe extension following immediately after the end of convergence caused rapid destruction of the european variscan orogen and resulted in the formation of numerous sedimentary basins and widespread magmatism possible driving forces for this phase of extension i e gravitational collapse of the thickened crust or reorientation of the far field stress regime are assessed quantitatively using a two dimensional thermomechanical finite element modeling approach the initial model setup approximates the geometry and physical properties of a lithosphere scale half profile through the variscan orogen and its foreland various numerical simulations and parameter studies suggest that the gravitational instability of the variscan orogen alone was not sufficient to explain the observed amount and timing of crustal extension tensile plate boundary stresses of the order of 10 mpa superposed on the gravitational forces are required to overcome the finite strength of the crust and restore a uniform crustal thickness in the variscan realm modeling results are constrained by comparison with existing data sets from the central european variscides for example crustal structure seismic reflectivity as well as temporal and spatial distribution of magmatic activity

diachronous variscan late orogenic collapse as a response to multiple detachments a view from the internides in france to the foreland in the irish sea