origin and tectonometamorphic history of the repulse bay block melville peninsula nunavut exotic terrane or deeper level of the rae craton the rae craton on melville peninsula nunavut comprises several lithotectonic domains including a structurally and lithologically distinct yet poorly known crustal terrane the repulse bay block rbb this study presents new lithological and petrographic observations combined with u pb zircon data to better understand the archean and paleoproterozoic crustal evolution of the rbb the new data demonstrate that the central eastern rbb consists of the following i upper amphibolite to granulite facies ca 2 73 2 71 ga intermediate granitoid gneisses and gabbroic sheets ii ca 2 69 ga two pyroxene charnockite to enderbite intrusions and iii thin slivers of both archean and paleoproterozoic supracrustal rocks inherited zircon also attests to the presence of a mesoarchean to paleoarchean substrate a semi pelitic gneiss from one of the paleoproterozoic supracrustal panels was deposited sometime after ca 1 89 ga and shows a similar detrital zircon age profile to a 1 92 ga semi pelitic gneiss fr

impact of halite dissolution subsidence on quaternary fluvial terrace development case study of the huerva river ebro basin ne spain abstract this paper analyses the control of evaporite dissolution subsidence on the evolution of the lower 30 km long reach of the huerva river up to its confluence with the ebro river in the study area the huerva river flows across different interfingered lithofacies of the subhorizontally lying ebro basin fill 1 shales and sandstones upstream of cadrete 2 evaporites dominated by gypsum between cadrete and cuarte 3 gypsum with glauberite and halite units in the subsurface downstream of cuarte the halite shows a marked downvalley increase in thickness twelve terrace levels and seven pediment levels correlative to some of the terraces have been mapped in the studied area upstream of cadrete the terrace deposits with a relatively constant thickness less than 4 m and overlying unsoluble bedrock remain undeformed between cadrete and cuarte the deposits of some terraces show local thickening 60 m thick terrace alluvium that fills a 5 km long trough generated by synsedimentary subsidence phenomena caused primarily by the interstratal dissolution of halite the older terraces t1 to t4 show slight thickening 18 m and locally truncate paleocollapse structures ascribed to the interstratal karstification of halite beds the intermediate terraces t5 to t7 correspond to degradation surfaces that grade downstream of cuarte into aggradation flights underlain by the abruptly thickened deposits that fill this 5 km long dissolution trough subsidence migrated episodically downstream during the generation of these terraces and the subsidence aggradation rate was probably large enough to induce a base level drop and knickpoint migration upstream generating strath terraces with convergent longitudinal profiles the sedimentological changes that show the thickened terrace deposits in the subsidence area high proportion of overbank fines 60 including palustrine facies gravel channels with lower width depth ratio multiple fining upward cycles decrease in the calibre of the channel gravels indicate a change in the channel pattern from braided to meandering due to the lowering of the valley slope in the reach affected by subsidence some of the anomalous features of the lower terraces t8 to t12 attributable to dissolution subsidence include 1 steepening of the t8 terrace profile 2 change of the t10 terrace from degradational to aggradational downstream cuarte and 3 thickening recorded beneath the t11 terrace surface

collisional snowbird tectonic zone resurrected growth of laurentia during the 1 9 ga accretionary phase of the hudsonian orogeny the 2800 km long snowbird tectonic zone is one of the most controversial tectonic features of the canadian shield metamorphic and in situ geochronologic data reported here reveal that a 1 9 ga medium to high pressure belt extends along most of this tectonic zone in contrast to recent interpretations a collisional origin is indicated by the length of this metamorphic belt tectonic thickening documented in parts of it geological contrasts across it and subduction type microdiamonds within it this collisional event marks a pre 1 865 ga phase of the hudsonian orogeny involving microcontinent accretion that was fundamental to the growth of laurentia

age constraints on the paleoproterozoic tectonometamorphic history of the committee bay region western churchill province canada evidence from zircon and in situ monazite shrimp geochronology in situ u pb sensitive high resolution ion microprobe shrimp analyses of monazite from upper amphibolite facies paragneiss of the committee bay supracrustal belt central rae domain canada reveal three age populations ca 2350 1850 and 1780 ma the ca 1850 ma age also corresponds to growth of low th u zircon as indicated by u pb shrimp analyses of zircon separates from melanosome and leucosome the contextual advantage of the in situ monazite analysis allows evaluation of the geochronological data in terms of the regional structural and metamorphic evolution the region is dominated by a northeast striking s2 s1 fabric axial planar to tight northwest vergent f2 folds early garnet is enveloped by this biotite sillimanite cordierite s2 fabric garneti hosts ca 1850 ma monazite inclusions with ca 2350 ma cores placing a maximum age on garneti growth and s2 development d2 metamorphic conditions progressed through 3 5 kbar 1 kbar 100 mpa and 600 c to near peak conditions of 5 kbar and 675 c a minimum age for s2 is provided by unstrained ca 1820 ma monzogranite that locally and regionally truncates s2 dominantly ca 1780 ma matrix monazite is interpreted to date post s2 garnetii and cordierite which record 5 kbar and 675 c these data indicate that the committee bay region experienced penetrative d2 tectonometamorphism at ca 1850 1820 ma with a subsequent static overprint the absence of a ca 1 85 ga plutonic suite in the region suggests that low pressure metamorphism was a response to thick skinned crustal thickening initiated at ca 1870 ma the new data highlight the importance of paleoproterozoic reworking of the central rae domain in the hinterland of the trans hudson orogen

the structural and diagenetic evolution of injected sandstones examples from the kimmeridgian of ne scotland injected sandstones occurring in the kimmeridgian of ne scotland along the bounding great glen and helmsdale faults formed when basinal fluids moved upward along the fault zones fluidizing oxfordian sands encountered at shallow depth and injecting them into overlying kimmeridgian strata the orientation of dykes in addition to coeval faults and fractures was controlled by a stress state related to dextral strike slip along the bounding fault zones diagenetic studies of cements allow the reconstruction of the fluid flow history the origin of deformation bands in sandstone dykes and sills was related to the contraction of the host rocks against dyke and sill walls following the initial stage of fluidized flow and these deformation bands are the earliest diagenetic imprint early non ferroan calcite precipitated in injection structures at temperatures between 70 and 100 c indicating that it precipitated from relatively hot basinal fluids that drove injection coeval calcite filled fractures show similar temperatures suggesting that relatively hot fluids were responsible for calcite precipitation in any permeable pathway created by dextral simple shear along the faults during progressive burial percolating sea water was responsible for completely cementing the still relatively porous injected sandstones with a second generation of ferroan calcite which contains fluid inclusions with homogenization temperatures below 50 c during this phase depositional host sandstones were also cemented

stream profile adjustment to crustal warping nonlinear results from a simple model three numerical experiments have been performed modeling response of a greatly simplified stream system to initiation of crustal tilting and domal uplift model results show signs of nonlinear behavior in varying degrees these signs include river profile adjustments that have forms quite different from the geometries of crustal movements cases of channel erosion following deposition at the same location and spatial transition points between opposing adjustments i e erosion and deposition that fail to coincide with boundaries or axes of crustal movement particular nonlinear effects wax or wane as the system adjusts to a new dynamic equilibrium with the continuing crustal movement the modeled features of stream adjustment are not in so extreme a class as the commonly discussed complex response of fluvial systems but they do serve to suggest some caution in studies that employ stream profile information as an indicator of crustal movement

stabilization and reactivation of cratonic lithosphere from the lower crustal record in the western canadian shield new u pb geochronology for an extensive exposure of high pressure granulites in the east lake athabasca region of the western canadian shield is consistent with a history characterized by 2 55 ga stabilization of cratonic lithosphere 650 million years of lower crustal residence and cratonic stability and 1 9 ga reactivation of the craton during lithospheric attenuation and asthenospheric upwelling high precision single grain and fragment zircon data define distinctive discordia arrays between 2 55 and 1 9 ga u pb ion microprobe spot analyses yield a similar range of u pb dates with no obvious correlation between date and cathodoluminescence zonation we attribute the complex u pb zircon systematics to growth of the primary populations during a 2 55 ga high pressure granulite facies event 1 3 gpa 850 c recorded by the dominant mineral assemblage of the mafic granulite gneisses with subsequent zircon recrystallization and minor secondary zircon growth during a second high pressure granulite facies event 1 0 gpa 800 c at 1 9 ga the occurrence of two discrete granulite facies metamorphic events in the lower crust separated by an interval of 650 million years that included isobaric cooling for at least some of this time suggests that the rocks resided at lower crustal depths until 1 9 ga we infer that this phase of lower crustal residence and little tectonic activity is coincident with an extended period of cratonic stability detailed structural and thermochronological datasets indicate that multistage unroofing of the lower crustal rocks occurred in the following 200 million years extended lower crustal residence would logically be the history inferred for lower crust in most cratonic regions but the unusual aspect of the history in the east lake athabasca region is the subsequent lithospheric reactivation that initiated transport of the lower crust to the surface we suggest that a weakened strength profile related to the 1 9 ga heating left the lithosphere susceptible to far field tectonic stresses from bounding orogens that drove the lower crustal exhumation an ultimate return to cratonic stability is responsible for the preservation of this extensive lower crustal exposure since 1 7 ga

geology and geochemistry of bitumen vein deposits at ghost city junggar basin northwest china veins of solid bitumen occur in cretaceous sandstones at the northwest margin of the junggar basin china the bitumen has a low aromaticity and a composition comparable to gilsonite the bitumen contains abundant steranes and terpanes and s carotane although most n and i alkanes have been removed which is characteristic of the local crude oil the sterane and triterpane maturity parameters show that the bitumen local crude oil and source rocks are all mature bitumen wallrock relationships suggest that the host sandstone was not completely consolidated at the time of emplacement of the bitumen veins although bitumen emplacement was a relatively late diagenetic event the burial history for the northwest junggar basin shows that hydrocarbon generation from the assumed upper permian source rocks commenced in late triassic early jurassic times and suggests that rapid hydrocarbon generation may have resulted in overpressure contributing to the bitumen emplacement

timescales and significance of high pressure high temperature metamorphism and mafic dike anatexis snowbird tectonic zone canada new geochronological isotopic and geochemical data for a spectacular swarm of deep crustal migmatitic mafic dikes offer important insight into processes operative during 1 9 ga high pressure high temperature metamorphism along the snowbird tectonic zone in northern saskatchewan high precision u pb zircon dates reveal anatexis of chipman mafic dikes at 1 896 2 0 3 ma during syntectonic and synmetamorphic intrusion at conditions of 1 0 1 2 gpa 750 c u pb zircon dates of 1 894 1 891 ma for cross cutting pegmatites place a lower bound on major metamorphism and deformation at the currently exposed crustal levels the persistence of elevated temperatures for 14 m y following peak conditions is implied by younger u pb titanite dates and by sm nd whole rock isotopic data that suggest the derivation of the pegmatites by melting of a mafic source limited melting of the host felsic gneiss at 1 9 ga despite high temperature is consistent with evidence for their previous dehydration by granulite facies metamorphism in the archean spatial heterogeneity in patterns of mafic dike and tonalitic gneiss anatexis can be attributed to lateral peak temperature and compositional variability we correlate 1 896 ma chipman mafic dike emplacement and metamorphism with substantial 1 9 ga mafic magmatism over a minimum along strike extent of 1 200 km of the snowbird tectonic zone this suggests a significant continent wide period of asthenospheric upwelling that induced incipient continental rifting extension was subsequently terminated by hinterland contraction associated with trans hudson accretion and orogenesis little activity in the lower crust for ca 650 m y prior to proterozoic metamorphism and mafic magmatism implies an extended interval of cratonic stability that was disrupted at 1 9 ga this episode of destabilization contrasts with the record of long term stability in most preserved cratons and is important for understanding the lithospheric characteristics and tectonic circumstances that control the destruction or survival of continents

mathematical modeling of graded river profiles numerical modeling of the longitudinal profiles of rivers at grade is accomplished using the basic equations of open channel flow sediment transport equations and empirical relations for downstream variation in flow discharge sediment discharge sediment caliber and channel width only in some cases are the computed stream profiles fit exactly by any one of the commonly supported mathematical function analogs to graded profile form exponential logarithmic or power function but in most cases any of these functions can provide a fit with a degree of error smaller than would be noted in treating field data profiles dominated by spatial change in fluid and sediment discharge are distinctly power functions while profiles dominated by sediment size reduction are not necessarily exponential in form other important controls on profile shape are the degree of downstream width change in response to increasing discharge and the general range of sediment size a dynamic model of a river s approach to grade

incision of alluvial channels in response to a continuous base level fall field characterization modeling and validation along the dead sea abstract the dramatic lake level drop of the dead sea during the twentieth century 30 m provides a field scale experiment in transport limited incision of gravel bed channels in response to quasi continuous base level fall at approximately constant rate we apply a one dimensional numerical incision model based on a linear diffusion equation to seven ephemeral channels draining into the dead sea the model inputs include the measured twentieth century lake level curve annual shoreline location i e annual channel lengthening following the lake level drop reconstructed longitudinal profiles of each of the channels based on mapped and surveyed terraces and the current profiles of the active channels the model parameters included the diffusion coefficient and the upstream derived sediment flux both were first calibrated using a set of longitudinal profiles of known ages and then validated using additional sets of longitudinal profiles the maximum at station total incision observed at each of the studied channels was significantly less then the total lake level drop and varied in response to both drainage area and lake bathymetry the model applied predicted degradation rates and the pattern of degradation with high accuracy this suggests that sediment flux in the modeled channels is indeed linearly dependent on slope further support for this linear dependency is provided by a linear correlation between the diffusion coefficient and the mean annual rain volume over each basin a proxy for discharge the model presented could be a valuable tool for planning in rapid base level fall environments where incision may risk infrastructure

active tectonics of ne gujarat india by morphometric and morphostructural studies of vatrak river basin abstract landscape owes its shape to the combination of tectonic and climatic forces differential displacement of land by tectonic processes changes the elevation of earth s surface locally and in turn affects the rate of geomorphic processes which are altitude dependent the tectonic and geomorphic processes are very tightly coupled and their results are intertwined to extract the tectonic signal the numerical modelling of the landscape of the vatrak river basin part of which falls in the northern part of the gujarat alluvial plains of western india has been undertaken applying morphometric and morphostructural approach the study helped in understanding the role of tectonic elements in the evolution of the basin demarcation of geomorphic indicators of active tectonics which include the analyses of asymmetry factor valley floor ratio gradient basin elongation ratio long profile and related parameters pseudo hypsometric integral drainage basin asymmetry drainage pattern analysis and azimuthal distribution of stream channels have been performed for each drainage network and associated basin the morphological field evidence of tectonics combined with the results of morphometric analysis has been used to obtain information about the orientation of tectonic elements and the possible reconstruction of their activity in recent times the analyses indicate eastward tilting of the drainage systems strong asymmetry in some reaches pronounced elongation of certain tributaries long profiles indicating base level lowering poor organisation of the hydrographic network and close alignment between lower order streams and active faults all these analyses point towards the active tectonism in the area data obtained through the statistical analysis of preferred stream orientations confirm that the old tectonic directions markedly influenced the drainage network development of the older order streams whereas streams of lower order which preferentially follow the n s and ne sw directions suggest that these tectonic trends were active until very recent times

mixed marine and lacustrine input to an oil cemented sandstone breccia from brora scotland abstract a rounded cobble collected from a beach near brora scotland contains angular brecciated sandstone clasts cemented together by crude oil no oil occurs within the tight dolomite cemented clasts except along fractures provenance of the cobble is uncertain however the lithology and shape of the clasts suggests that they are fault gouge breccia composed of old red sandstone from the nearby helmsdale fault oil emplacement presumably along the fault cemented the breccia prior to transport and weathering of the cobble independent source and biodegradation parameters support mixing of two charges of oil like oil from the nearby beatrice field the oil cement contains 24 n propylcholestanes and carotane that indicate marine and lacustrine source rocks respectively the oil cement also contains pristane phytane residual n alkanes and a complete series of 25 norhopanes which indicate mild and heavy biodegradation respectively the first charge consisted of lacustrine devonian oil that was heavily biodegraded at shallow depth the origin of the second charge is unclear unlike beatrice oil the oil cement contains oleanane and shows a higher 24 24 27 nordiacholestane ratio suggesting input from a cretaceous or younger paralic marine shale source rock although cretaceous and paleocene source rocks are inferred to exist in various depocenters in the northeast atlantic margin subcrops of these rocks offshore brora are thermally immature alternately the second charge could originate from an effective middle jurassic source rock that contains oleanane this hypothesis is supported by mass spectrometric confirmation of oleanane in an extract from the marine equivalent of the middle jurassic brora coal in the nearby ukcs 11 30 2 well oleanane in crude oil is not positive proof of a cretaceous or younger source rock for the oil

geochronological constraints on the legs lake shear zone with implications for regional exhumation of lower continental crust western churchill province canadian shield the legs lake shear zone marks the southeastern boundary of an extensive region 20 000 km2 of high pressure 0 8 1 5 gpa granulite facies rocks in the western churchill province canada the shear zone is one of the largest exhumation related structures in the canadian shield and coincides with the central segment of the 2 800 km long snowbird tectonic zone the movement history of this shear zone is critical for the development of models for the exhumation history of the high pressure region we used electron microprobe u th pb dating of monazite with supplemental id tims u pb geochronology to place constraints on the timing of shear zone activity combining these and other data we suggest that regional exhumation occurred during at least three distinct phases over an 150 million year period the first phase involved high temperature decompression from 1 0 to 0 8 0 7 gpa shortly following 1 9 ga peak metamorphism possibly under an extensional regime the second phase involved rock uplift and decompression of the hanging wall to 0 5 0 4 gpa during east vergent thrusting across the legs lake shear zone at ca 1 85 ga this phase was likely driven by early collision related convergence in the trans hudson orogen the final phase of regional exhumation involving the removal of 15 20 km of overburden from both footwall and hanging wall likely occurred after 1 78 ga and may have been related to regional extensional faulting

subsurface biodegradation of crude oil in a fractured basement reservoir shropshire uk subsurface biodegradation of crude oil in current oil reservoirs is well established but there are few examples of ancient subsurface degradation biomarker compositions of viscous and solid oil residues bitumen in fractured precambrian and other basement rocks below the carboniferous cover in shropshire uk show that they are variably biodegraded high levels of 25 norhopanes imply that degradation occurred in the subsurface lower levels of 25 norhopanes occur in active seepages liquid oil trapped in fluid inclusions in mineral veins in the fractured basement confirms that the oil was emplaced fresh before subsurface degradation a triassic age for the veins implies a 200 myr history of hydrocarbon migration in the basement rocks the data record microbial biodegradation of hydrocarbons in a fractured basement reservoir and add to evidence in modern basement aquifers for microbial activity in deep fracture systems buried basement highs may be especially favourable to colonization through channelling fluid flow to shallow depths and relatively low temperatures and are therefore an important habitat within the deep biosphere

geochronological constraints on metamorphism magmatism and exhumation of deep crustal rocks of the kramanituar complex with implications for the paleoproterozoic evolution of the archean western churchill province canada u pb and sm nd geochronology establishes an important paleoproterozoic 1 9 ga history for the kramanituar complex located in the interior of the archean western churchill province and provides further insight into the snowbird tectonic zone a crustal scale 2000 km feature whose role during precambrian time remains controversial the kramanituar complex is a window of deep crustal rocks dominated by a granulite facies metagabbroic suite of 1902 ma age with minor supracrustal rocks and charnockite these yield peak equilibrium conditions of 12 15 kbar and 850 900 c which are bracketed between 1910 ma the age of prograde metamorphic monazite in sillimanite and kyanite bearing paragneiss and 1901 ma the cooling ages of titanite and rutile in gabbroic and paragneissic rocks although mineral assemblages reflecting peak metamorphic conditions are widespread some rocks record near isothermal decompression to 8 kbar and 800 c the timing of uplift and exhumation is tightly bracketed between magmatic crystallization of gabbroic anorthosite under granulite facies conditions at 1902 ma and widespread rutile cooling ages of 1901 ma time averaged cooling rates of 100 c ma are estimated for gabbroic anorthosite and leucogranite rocks surrounding the kramanituar complex are mainly amphibolite facies archean plutonic and supracrustal rocks those to the north were at deep crustal conditions coeval with the complex whereas those to the south appear to preserve a record of older mainly neoarchean tectonometamorphic assemblages and fabrics the southern boundary of the complex is inferred to be a normal fault that accommodated tectonic unroofing of the kramanituar complex at 1 9 ga this geochronological data set highlights the protracted history of a segment of the geophysically defined snowbird tectonic zone a structure along which latest significant magmatism and tectonometamorphism has been interpreted as either 2600 or 1800 ma penetrative 1900 ma activity in the east trending chesterfield segment as documented at the kramanituar complex suggests that the complex may have represented a favorably oriented segment of a crustal scale archean fault that was reactivated during paleoproterozoic time possibly in response to collision between the slave and churchill cratons thelon orogen at 1 97 1 9 ga

thermobarometry and geochronology of the uvauk complex a polymetamorphic neoarchean and paleoproterozoic segment of the snowbird tectonic zone nunavut canada the uvauk complex is an ultramylonite bounded granulite facies suite of anorthosite gabbro that forms part of the chesterfield inlet segment of the snowbird tectonic zone following initial anorthosite gabbro magmatism at ca 2 71 ga and a cryptic 2 62 2 60 ga event marked by zircon and monazite growth the uvauk complex experienced two high grade tectonometamorphic events at 2 56 2 50 and 1 91 1 90 ga similar to the 2 56 2 50 ga development of other shear zones in the region the upper amphibolite facies to granulite facies moderately high pressure 8 4 11 0 kbar and 705 760 c 1 kbar 100 mpa m1 event is interpreted to have involved the structural emplacement of ca 2 71 ga uvauk complex rocks on ca 2 68 ga tonalitic rocks to the south granulite facies high pressure 11 2 14 7 kbar and 695 865 c m2 metamorphism gabbroic magmatism and mylonite development within the complex at ca 1 9 ga culminated with 3 5 kbar decompression at high temperature clockwise pressure temperature time p t t

numerical study of degradation of fluvial hanging valleys due to climate change 1 hanging fluvial valleys form at mouths of tributaries that are unable to incise as quickly as the trunk stream although hanging valleys at tributary mouths are uncommon in very rapidly eroding ranges such as the himalaya they can attain heights of 1 km and display mean channel slopes exceeding 30 given a hypothesis based on bed load saltation erosion for how such features form this study addresses the question of why hanging valleys are not more common and what limits their growth we implement a numerical model of bed load saltation erosion for a tributary junction experiencing base level fall to explore conditions that may lead hanging valleys to form or subsequently degrade owing to climate variability we find that increased frequency of bed load mobilization and enhanced bed load supply can drive the degradation of hanging fluvial valleys moreover when trunk aggradation overtops the hanging valley the knickpoint tends to be removed during subsequent degradation of the alluvial surface channel narrowing increased bed load size or bed load supply each can inhibit the formation of hanging fluvial valleys under steady hydrological and sedimentologic conditions bed load saltation models predict hanging valleys could be quite common where main stem erosion is rapid the frequency and magnitude of changes in climatically modulated sediment loads in natural systems however typically overwhelm factors that promote hanging valley formation without such bed load variability because rates of channel aggradation commonly outpace rates of hanging valley formation we propose that hanging valleys tend to be preserved only in regimes where trunk stream erosion exceeds several millimeters per year

development of offset channels across the san andreas fault the san andreas fault offsets some small gullies incising the relatively flat surfaces in the carrizo plain california among these gullies those with larger drainage basins have larger offsets probably because gullies that have larger floods can keep the channels entrenched and subjected to the fault displacement longer on the other hand older offset channels in the area which have much larger offsets indicate that the gradual shift to straighter courses seems probable only for offset channels able to keep and accumulate the offset for a long time the strike slip fault displacement offsets a channel as much as the channel can follow with some modification by fluvial processes until overbank floods at the upper bend induce channel avulsion to a straighter course or until the channel is captured by the beheaded and abandoned downstream reach of the adjacent channel moved with the fault displacement the offset channel promotes aggradation upstream from the upper bend and this makes the channel increasingly susceptible to overbank floods the older offset channels are confined in valleys and this condition is apparently preventive of channel avulsion or capture the strike slip fault displacement also deforms longitudinal profiles of channels assuming that the elimination of discontinuities in the longitudinal profile is the main response of fluvial processes to the deformation by fault displacement nearly continuous longitudinal profiles of some old offset channels seem to indicate the full adjustment the condition in which no more changes will occur as a response to fault displacement until the next fault slip deforms them the irregularities in longitudinal profiles of other offset channels indicate that the channel adjustment by fluvial processes may be occurring but not enough to eliminate the irregularities an offset river can attain a continuous longitudinal profile if it has enough time to adjust its longitudinal profile after the fault displacement otherwise the discontinuity reflecting a various degree of adjustment would remain in the longitudinal profile until channel avulsion or capture occurs the degree of adjustment and the probability of channel avulsion or capture depend highly on the fluvial ability and condition of each river as well as the time after the deformation

shale tectonics and deformation associated with active diapirism the jerudong anticline brunei darussalam the jerudong anticline provides an outcrop example of multiple phases of diapir growth and interaction with the country rock the n s trending anticline overlies a high angled basement fault zone that was episodically active moving predominantly sinistrally in response to transpressive stresses the earliest stage of deformation in the study area was mid miocene e w to ne sw trending growth faulting and shale diapir growth early normal faults exerted an important influence on the large and small scale bedding geometries and facies changes of syn tectonic shallow marine shoreface and tidal strata in particular there are laterally rapid facies changes and differential rotation of strata across growth faults diapir activity is indicated by the presence of shale dykes which commonly intrude normal fault planes and concordant shale intrusions shale intrusions associated minor thrust faults and normal faults were rotated during a late miocene early pliocene phase of folding related to transpression few shale dykes were intruded during this phase probably because the horizontal principal stresses were relatively large compared with the pore fluid pressure at the end of the transpressive phase shale dykes were intruded into steeply dipping beds as a result of stress relaxation continued uplift and erosion elevated overpressured horizons to a point where hydraulic fracturing reached the surface and holocene age mud volcanoes were developed

unraveling the western churchill province paleoproterozoic gold metallotect constraints from re os arsenopyrite and u pb xenotime geochronology and la icp ms arsenopyrite trace element chemistry at the bif hosted meliadine gold district nunavut canada the gold endowment of the western churchill province is conventionally attributed to reworking and attendant metamorphism during the trans hudson orogeny 1 9 1 8 ga the meliadine gold district is regarded as a type example of this inferred paleoproterozoic gold metallotect and also represents one of canada s largest emerging orogenic greenstone and banded iron formation bif hosted gold districts 2 8 moz contained au in reserves and total resource of 5 8 moz au the largest gold deposits are cospatial with the pyke fault and associated quartz ankerite veining which cuts neoarchean ca 2 66 ga plutonic and supracrustal rocks comprising the rankin inlet greenstone belt meliadine gold occurs as inclusions within idioblastic arsenopyrite crystals at sulfide crystal boundaries and or as sulfide fracture fills in hydrothermally altered sulfidized and veined bif clusters of gold bi mo telluride chalcopyrite and galena inclusions characterize high grade ore zones and are spatially associated with sieve textured arsenopyrite domains these microtextural relationships suggest that incipient sulfide recrystallization liberated gold which along with other precious and base metals was redistributed during late fluid assisted and deformation metamorphic driven remobilization late precious and base metal enrichment is also demonstrated by in situ laser ablation inductively coupled plasma mass spectrometry la icp ms arsenopyrite mapping hydrothermal xenotime crystals occur with gold in low strain microtextural sites and yield u pb ages at ca 1 86 ga suggesting that remobilization was concomitant with trans hudson orogenesis new re os arsenopyrite model ages range from 2 3 to 1 8 ga and document a hitherto unrecognized pre 1 86 ga hydrothermal activity the range of re os model ages tends to support partial open system behavior and or mixing of disparate arsenopyrite generations that are evident from microtextural observations and in situ la icp ms element mapping replicate analyses of the two most rhenium rich arsenopyrite samples yield reproducible re os model ages at ca 2 27 and 1 90 ga these rhenium rich samples are also gold poor and likely yield ages that predate gold remobilization and subsequent enrichment along arsenopyrite crystal boundaries and fractures we suggest that pre 1 86 ga hydrothermal activity was likely critical to the gold endowment of the district but is obscured by reworking during the later stages of the trans hudson orogeny at 1 86 ga if correct these new ages imply that the paleoproterozoic gold metallotect which is recorded across the western churchill province in fact comprises multiple temporally distinct gold events differentiating between disparate paleoproterozoic gold events represents a critical step for effective mineral exploration in the western churchill province and at other reworked archean terranes

25 norhopanes formation during biodegradation of petroleum in the subsurface abstract quantitative data from petroleum systems in china liaohe basin and canada athabasca tar sands support the theory that 25 norhopanes are produced during biodegradation of petroleum in the subsurface within a single oil column both case histories showed increasing severity of degradation indicated by destruction of hopanes and production of 25 norhopanes downward to the oil water contact in the athabasca samples between the peters k e moldowan j m 1993 the biomarker guide interpreting molecular fossils in petroleum and ancient sediments prentice hall englewood cliffs new jersey p 363 scale of biodegradation levels 5 9 concentrations of c 28 20s triaromatic steroids and other biodegradation resistant compounds increased by 35 reflecting a concentration effect as a consequence of removal of more degradable compounds over the same interval the concentrations of c 28 17 25 norhopane and c 29 17 25 norhopane increased by an order of magnitude thus requiring that the balance be met by their net production during degradation a detailed molecular investigation of the athabasca bitumen revealed that c 30 17 hopane degrades faster than c 29 17 hopane whilst the rate of formation of both c 29 17 25 norhopane and c 28 17 25 norhopane are similar complicating a straightforward interpretation of demethylation of hopanes to form 25 norhopanes hopane degradation in the athabasca tar sand may also occur without the production of 25 norhopanes the results show that even within a single petroleum accumulation a number of mechanisms control changes in the abundance and composition of hopanes and 25 norhopanes

contractional uplift of deep crustal rocks along the legs lake shear zone western churchill province canadian shield the legs lake shear zone juxtaposes high pressure 1 0 gpa granulite and eclogite facies rocks with low pressure 0 5 gpa amphibolite to granulite facies rocks and thus may represent an important crustal scale exhumation related structure in the western canadian shield field mapping and structural and petrologic analysis document the deformation and metamorphic history of rocks within and adjacent to the shear zone at least two important phases of deformation are recorded 1 early oblique thrusting d2 that placed high grade rocks over lower grade rocks and 2 more discrete and lower grade brittle ductile normal faulting d3 that may represent the later part of the exhumation history the northwest dipping shear zone consists of 5 8 km of mylonite in map view which bounds the southeast margin of the east athabasca mylonite triangle high pressure granulite facies metamorphism 750 850 c 1 0 1 2 gpa occurred in the east athabasca mylonite triangle at ca 1900 ma prior to d2 juxtaposit

reconstruction of a large deep crustal terrane implications for the snowbird tectonic zone and early growth of laurentia the 2800 km long snowbird tectonic zone is a well recognized but still enigmatic feature in the western canadian shield it has been interpreted as a paleoproterozoic continental suture or an archean strike slip fault system but here we suggest that the distinctive geometry of the central snowbird tectonic zone is primarily due to the interaction of crosscutting paleoproterozoic intracontinental thrust and strike slip shear zones having a length of hundreds of kilometers first a major zone of thrust sense shearing coeval with early continent continent collision between the superior and western churchill provinces accommodated uplift of a large exposure of granulite facies lower continental crust younger strike slip shear zones perhaps analogous to asian fault systems behind the himalayan orogen offset the thrust zone thus the current geometry and distribution of deep crustal rocks in this region represent a relatively late stage in the tectonic evolution of the western churchill province rather than an accretionary one earlier structures oriented at a high angle to the snowbird tectonic zone may record the fundamental accretionary history in this part of laurentia

lacustrine organic facies a biomarker study using multivariate statistical analysis abstract four distinct depositional settings in the devonian orcadian basin of scotland have been characterised by their minerology and organic geochemistry with the help of multivariate statistical analysis the data visualise the organic matter source input the depositional environment and the level of thermal maturity principal component analysis proved invaluable for extracting information from a data set composed of a large number of parameters the thermal maturity of the majority of the samples lies within a restricted range in the oil window and biomarker composition reflects predominantly organic input and depositional environment basin margin deposits are clearly differentiated from deeper water central lake deposits salinity and anoxicity variations are seen within the latter type of deposits

new structural and re os geochronological evidence constraining the age of faulting and associated mineralization in the devonian orcadian basin scotland the devonian orcadian basin in northern scotland belongs to a regionally linked system of post caledonian continental basins extending northwards to western norway and eastern greenland extensional fault systems that cut the orcadian basin sequences are commonly assumed to be devonian with some limited inversion and reactivation proposed during the carboniferous and later times we present a detailed structural study of the regionally recognized fault systems exposed in the dounreay area of caithness which host significant amounts of authigenic mineralization carbonate base metal sulphides bitumen structural and microstructural analyses combined with re os geochronology have been used to date syndeformational fault infills pyrite suggesting that faulting brecciation and fluid flow events are likely to have occurred during the permian 267 5 3 4 3 5 ma stress inversion of fault slickenline data associated with mineralization suggest nw se regional rifting an episode also recognized farther west in sutherland thus a dominant set of permian age brittle faults is now recognized along the entire north coast of scotland forming part of the regional scale north coast transfer zone located on the southern margin of the offshore west orkney basin supplementary material onshore and offshore fault and fracture lineament data are available at https doi org 10 6084 m9 figshare c 2182433

emplacement of bitumen asphaltite veins in the neuquen basin argentina veins of solid bitumen asphaltite have been commercially exploited in the neuquen basin argentina for over 100 yr veins are up to 5 m wide and several kilometers in length over a region of 15 000 km2 these veins were emplaced in fractures both parallel and at high angles to bedding in close proximity to their source rocks in the vaca muerta and agrio formations late jurassic early cretaceous two or more phases of bitumen emplacement can be recognized in several localities structures bearing viscous oil are younger than structures having solid bitumen bitumen emplacement was vigorous and caused brecciation and spalling of the host rocks the bitumen was also viscous and supports rock debris ranging in size from sand grains up to meter scale slabs brecciation bedding parallel injection and wall rock impregnation suggest high fluid pressures during emplacement high fluid pressure may have been engendered by substantial hydrocarbon generation from rich source rocks in a low permeability sequence and probably caused the fractures into which the bitumen migrated the bedding parallel veins facilitated decollement during thrusting that took place during and after bitumen emplacement the timing of emplacement relative to thrusting and oil migration constrains bitumen emplacement to the eocene oligocene

sedimentological and geochemical basin analysis of the paleoproterozoic penrhyn and piling groups of arctic canada abstract paleoproterozoic metasedimentary successions on the western churchill province record a history of regional tectonic events spanning the breakup and amalgamation of supercontinents metasedimentary successions in the northeastern part of the trans hudson orogeny including the penrhyn and piling groups of melville peninsula and baffin island respectively have been understudied with respect to their basin evolution records we present new sedimentological geochemical and geochronological data for the penrhyn and piling groups that record deposition on the rae craton new detrital zircon u pb age data indicate that deposition of the penrhyn group started after 1897 ma and post dates deposition of most of the piling group the new maximum age constraints and stratigraphy of the penrhyn group do not support previous lithostratigraphic correlation with the piling group deposition of the lower piling group likely occurred in an epicontinental basin setting the occurrence of detritus from the meta incognita microcontinent in the upper piling group bravo lake and longstaff bluff formations is interpreted to signal the onset of foreland basin deposition the details of sedimentation in the piling foreland basin provide an additional constraint to discerning the polarity of subduction between the rae craton and meta incognita microcontinent that closed the piling basin we conclude that the piling foreland system shows characteristics of a pro foreland basin implying that the rae craton was the lower plate in the collision with the meta incognita microcontinent finally with new stratigraphic and detrital zircon geochronological data for the penrhyn and piling groups we provide a comparison with other sedimentary successions on the rae craton whose histories were influenced by similar regional tectonic events

quaternary rate of folding of the ventura avenue anticline western transverse ranges southern california upper quaternary terraces of the ventura river california are uplifted tilted and folded over the ventura avenue anticline rates of uplift and tilting have decreased since inception of the structure over the past 200 ka assuming that the chronology based on amino acid racemization 14c dates and soils correlation is approximately correct then the minimum possible average rate of uplift in the axial region of the fold has decreased from 14 mm yr to 2 mm yr during the past 200 ka interval rates of uplift for the periods 200 ka to 80 or 105 ka 80 or 105 ka to 30 ka and 30 ka to present are respectively about 20 mm yr 9 mm yr and 5 mm yr the rate of tilting shows a similar trend decreasing from 5 8 urad yr 2 5 urad yr and 1 2 urad yr for the same time intervals respectively based on the mechanics of flexural slip folds in stratified sedimentary rocks these data suggest that the rootless ventura avenue anticline is a fold that has been shortening at a relatively constant rate of about 9 mm yr since its inception

mechanisms and controls on the formation of sand intrusions sandstone intrusions are found in all sedimentary environments but have been reported most commonly from deep water settings they also appear to be more frequently developed in tectonically active settings where applied tectonic stresses facilitate development of high fluid pressures within the sediments a variety of mechanisms have been cited as triggers for clastic intrusions these include seismicity induced liquefaction application of tectonic stresses excess pore fluid pressures generated by deposition related processes and the influx of an overpressured fluid from deeper within the basin into a shallow sand body the formation of sandstone dykes and sills is investigated here by considering them as natural hydraulic fractures when the seal on an unconsolidated overpressured sand body fails the resulting steep hydraulic gradient may cause the sand to fluidize the fluidized slurry can then inject along pre existing or new fractures to form clastic intrusions the scale and the geometry of an intrusive complex is governed by the stress state depth and pre existing joints or faults within the sedimentary succession as well as the nature of the host sediments for the simplest tectonic setting where the maximum stress in a basin is vertical gravitational loading small irregular intrusions commonly result in the formation of sills at shallow depths within a few metres of the surface whereas at greater depth dykes and sills forming clastic intrusion networks are more typical a simple relationship is derived to calculate the maximum burial depth at which a dyke sill complex forms as a function of the source bed to sill height the bulk density of the surrounding sediments and the ratio of the vertical to horizontal effective stresses k 0 when applied to three examples of large scale dyke sill complexes developed within paleocene and eocene deep water reservoir sand bodies of the north sea maximum burial depths in a range of 375 to c 500 m 450 700 m and 550 850 m are estimated for intrusion of each of the three complexes

the recognition of multiple hydrocarbon generation episodes an example from devonian lacustrine sedimentary rocks in the inner moray firth scotland burmah well 12 27 1 drilled on a structural high in the inner moray firth penetrated over 3000 ft 914 m of lower devonian organic rich sedimentary rocks these have been analysed for source rock potential and contain a substantial proportion of oil prone thermally mature kerogen a decompacted vitrinite reflectivity profile shows that the lower part of the devonian section has a steeper thermal maturity gradient which is interpreted as indicating a high devonian geothermal gradient associated with basin extension solid bitumen reflectivities and organic petrography show that the most recent hydrocarbon generation occurred in the upper part of the devonian interval during maximum tertiary burial vitrinite reflectivity data from the jurassic rocks in the beatrice field and onshore east sutherland enable the position of the oil generation window to be predicted in relation to the depth of the top of the devonian sequence the main controls on devonian source rock potential in the inner moray firth are not the depth of mesozoic and tertiary burial but the distribution of source rocks their degree of permian truncation and the pre permian thermal maturity level

origin of beatrice oil by co sourcing from devonian and middle jurassic source rocks inner moray firth united kingdom commercial hydrocarbons in the moray firth area of the north sea occur in reservoirs ranging in age from devonian to tertiary with the bulk of the reserves located in upper jurassic and lower cretaceous clastic rocks most hydrocarbon discoveries in this area have been made in the outer moray firth primarily in the witch ground graben a single oil field beatrice has been developed in the inner moray firth area the unusual location and chemical composition of beatrice compared to piper and other north sea oils generated from the kimmeridge clay have contributed to the longstanding controversy on its origin oil source potential in the inner moray firth has been recognized in lacustrine devonian dolomitic siltstones middle jurassic paralic coals upper jurassic marine shales and other rocks however prior to this study only the upper jurassic kimmeridge clay was recognized as a significant effective source rock in the main graben area of the north sea biomarker and stable carbon isotope analyses conclusively show that beatrice oil could not have been generated from the classic kimmeridge clay source rock but is a mixture of products derived from effective devonian and middle jurassic source rocks this work demonstrates the power of a multiparameter geochemical approach in solving this difficult oil to source rock correlation problem use of this approach can lead to the recognition of new exploration plays in previously well explored basins

origin of organic matter from tectonic zones in the western tatra mountains crystalline basement poland an example of bitumen source rock correlation abstract solid bitumens of unknown origin found in brittle tectonic shear zones cutting the crystalline basement of the western tatra mts show uniform geochemical characteristics that suggest a uniform source for the original hydrocarbons on the basis of gc ms data a similarity between these solid bitumens and organic matter dispersed in the mesozoic source rocks of podhale trough and sedimentary cover of the northern tatra mts is observed the organic matter in the mesozoic source rocks shows a higher maturation level than that in the solid bitumens the molecular composition of the organic matter in both the solid bitumens and the basement rocks is significantly different from that in the paleogene sedimentary rocks infilling the podhale trough these immature to early mature paleogene sedimentary rocks contain organic compounds typical of terrestrial plants both conifers simonellite and retene and angiosperms lupane oleanane and taraxastene which are absent in the solid bitumens and in the mesozoic source rocks water co2 fluid inclusions in quartz sealing the shear zones have marine like salinity a dominance of cacl2 and mg2 depletion suggesting genetic affinity to dolomitised carbonate rocks such as potential middle triassic source rocks the low maturity of the solid bitumen in the shear zones relative to its mesozoic source can be explained by continued maturation of the mesozoic source rocks after expulsion and migration into the shear zones the results of hydrocarbon generation modeling indicate that oil expulsion from the mesozoic source rocks its migration through the shear zones and the subsequent maturation of the mesozoic source rocks all occurred within a short oligocene time interval

tectonic uplift of the northern qinling mountains central china during the late cenozoic evidence from dem based geomorphological analysis abstract the qinling mountains which stretch from east to west in central china represent an important geological and geographical boundary between north china and south china because of the northeastward growth of the tibetan plateau since the late cenozoic the northern qinling mountains have been strongly reactivated and uplifted to investigate the landscape response to the tectonic uplift the geomorphic indices of the northern qinling mountains including the hypsometry mathematical function of the longitudinal profile channel longitudinal profile and steepness index were analyzed the topographic analysis reveals that the landscape evolution of the heihe river basin is in a transient state the upstream of the heihe river basin has undergone a long period of erosion and represents relict landscape in contrast the downstream represents adjusting landscape which formed by river incision in response to the rapid uplift of the northern qinling mountains this is a result of the extension of the weihe graben which has formed due to the northeastward growth of the tibetan plateau during the late cenozoic the spatial distribution of the geomorphic indices reveals that the ne striking taibai fault has experienced strong tectonic activity since the late cenozoic and is a secondary fault that accelerated the uplift rate of the northern qinling mountains the tectonic stress due to the northeastward growth of the tibetan plateau has been transmitted to the northern qinling mountains along the taibai fault therefore we proposed that the uplift of the northern qinling mountains is due to the combined effects of the weihe graben extension and taibai fault activity forming the highest peak taibai mountain of the northern qinling mountains near the intersection of the qinling piedmont fault and taibai fault

river history and tectonics the analysis of crustal deformation by tectonic processes has gained much from the clues offered by drainage geometry and river behaviour while the interpretation of channel patterns and sequences benefits from information on earth movements before or during their development the interplay between the two strands operates at many scales themes which have already benefited from it include the possible role of mantle plumes in the breakup of gondwana the cenozoic development of drainage systems in africa and australia himalayan uplift in response to erosion alternating episodes of uplift and subsidence in the mississippi delta buckling of the indian lithospheric plate and changes in stream pattern and sinuosity along individual alluvial channels subject to localized deformation developments in remote sensing isotopic dating and numerical modelling are starting to yield quantitative analyses of such effects to the benefit of geodymamics as well as fluvial hydrology

knickpoint series of gullies along the luoyunshan piedmont and its relation with fault activity since late pleistocene abstract the authors surveyed the longitudinal profiles of 28 gullies across the luoyunshan piedmont fault lpf by differential gps and dating of sediments well preserved in the typical terraces and obtained 6 level knickpoint series of the gullies along the luoyunshan piedmont the authors compared it with previous studies on the paleo earthquakes of the lpf revealed by trenches and found that the paleo earthquake events from knickpoint and trench studies are in good agreement in terms of the time of occurrence and vertical displacement of the fault it shows studying the paleo earthquake events of the fault by knickpoint series is feasible at last the authors established a more complete paleo earthquake sequence of the lpf supported by geomorphologic and sedimentary evidence i e six paleo earthquake events happened on the lpf from about 28 000 years ago the lpf has the characteristic of quasi periodic recurrence and the average recurrence interval is 4585 years the vertical displacement of the paleo earthquake events is 2 4 3 0 m according to the empirical equations between co seismic displacement and earthquake magnitude the magnitude of these events is ms 7 0 7 5 this study aims to complement and improve the traditional trenching method provide theoretical and methodological support for the research of active tectonics and contribute important information for the seismic hazard assessment of the densely populated linfen area

constraining causes of fish mass mortality using ultra high resolution biomarker measurement lamina by lamina measurement of biomarkers at a sub millimetre resolution within the achanarras limestone member has helped to resolve the changing environmental conditions associated with a fish mass mortality horizon an anomalous proportion of c30 sterane 24 n propylcholestane marks the beginning of the horizon and likely corresponds to an influx of marine water this appears to have been short lived and was likely analogous to a modern day storm tide the subsequent laminae record an increased incidence of water column stratification and hypoxic bottom waters in the form of an elevated gammacerane index the mass mortality horizon studied was from an upper interval of the achanarras limestone member with a fossil fish assemblage comprising mostly dipterus an early dipnoan lungfish however lower intervals of the achanarras limestone member have greater assemblage diversity including species associated with marine conditions such as coccosteus and evidence higher proportions of c30 sterane indicating better connection to the marine environment therefore it appears that ingressing seawater in and of itself was not responsible for creating a stressed environment rather disconnection of the lake from marine waters stranded fish in a lake that when perturbed by storm tides killed en masse by exposing fish to hypoxic conditions in a similar way to modern water bodies affected by storm tides generated during hurricanes

morphology and long term landscape evolution of the south african plateau in south namibia the south namibian plateau which belongs to the south african plateau is situated between 25 29 s and 15 20 e this study examines the relationships between this portion of the plateau and the development of planation surfaces and scarps bounding the plateau geomorphological analysis through morphometric indices extracted from a dem 90 m and its derived maps as well as field observations supported by the literature data permit the demonstration that tectonics climate and base level are the main factors that control the formation and evolution of the planation surfaces and scarps that separate them from west to east the south namibian plateau consists of four main morphological provinces the coastal province and the intermediate upper and kalahari provinces in the interior plateau these provinces include five cenozoic planation surfaces that are differentiated by their elevations regional slopes relative reliefs and erosion processes these surfaces have been formed by etchplanation and pediplanation the drainage pattern and river length profiles show that the coastal province evolved differently than the interior plateau the development of the coastal province is controlled by eustasy and tectonics whereas climate related processes and tectonics control that of the interior plateau the presence of several scarps separating these surfaces the most degraded and older of which are inside the plateau reflects a polyphase evolution this evolution can be highlighted by two models 1 an eastward migration mantle dynamics causing a slight uplift and rejuvenation of the system by destabilizing the coupled weathering erosion equilibrium and 2 an internal propagation of isostatic rebound induced by the retreat of the western scarp leading to a significant flattening in the central part of the plateau

late neoarchean thick skinned thrusting and paleoproterozoic reworking in the macquoid supracrustal belt and cross bay plutonic complex western churchill province nunavut canada abstract in the western churchill province canadian shield neoarchean supracrustal and plutonic rocks intruded by paleoproterozoic mafic dykes and granitic rocks comprise the macquoid supracrustal belt and the structurally overlying cross bay plutonic complex they form part of the northwestern hearne subdomain that occupies an intermediate position between the continental rae domain to the north and west and the oceanic central hearne subdomain to the south and east new geological mapping and supporting geoscience are compatible with the presence of 2550 2500 ma southeast directed mid crustal thick skinned thrusting that juxtaposed the plutonic complex over the supracrustal belt the structural contact between the macquoid supracrustal belt and the cross bay plutonic complex potentially represents a fundamental boundary between isotopically distinct crustal blocks the 2190 ma macquoid mafic dyke swarm cuts across neoarchean deformation fabrics but records 1 9 ga deep crustal regional metamorphism that affected both the supracrustal belt and the plutonic complex other paleoproterozoic deformation events that occurred at 1850 1810 ma are of local extent and appear to be relatively minor manifestations of more important events elsewhere related to the trans hudson orogen

river incision or diversion in response to bedrock uplift introductionmany researchers have examined the long term behavior of alluvialrivers i e schumm et al 1987 snow and slingerland 1990 paola et al 1992 on long time scales alluvial rivers act as sediment transport systemsthat broadly deposit sediment over low areas in their basins i e tucker andslingerland 1996 the behavior of bedrock rivers is less well understood although most workers agree that bedrock erosion is some function of streampower howard and kerby 1983 seidl and dietrich 1992 howard et al 1994 accordingly researchers addressing a river s response to bedrock up lift equate incision with relatively high stream power and diversion with rela tively low stream power e g burbank et al 1996 however these studiesassume that the erosion rate of the bedrock channel across the mountainrange controls the eventual outcome they have not examined the behavior ofthe alluvial river upstream and downstream of the uplift we propose to lookat the entire erosional and depositional river system and examine the long term response of a coupled alluvial bedrock river system to tectonic uplift our motivation is general and aims at a greater understanding offluvial and tectonic interactions but our model is necessarily both specificand simplified the tectonic uplift of a bedrock massif into the path of a later ally unconstrained alluvial river such a scenario has two possible out comes either the river maintains its original course and incises through theuplift or the river diverts and forms a new course around the uplift a sig nificant complication in the analysis of this scenario is that the evolvingriver system is partial alluvial and partial bedrock channeled because thebehaviors of these two river types are different modeling requires couplingdiverse systems we construct an analytical model to perform a first orderanalysis of this coupled system our objective is to identify the specific fac tors that determine the final outcome of river diversion or incision our model focuses on long time scales 10

geochemistry and origin of organic rich sediment veins in fractured granitic basement helmsdale sutherlandshire uk abstract black sediment veins up to 2 cm width penetrate the caledonian helmsdale granite in the vicinity of the helmsdale fault onshore moray firth the black colour and geochemistry of the veins reflect a high content of organic carbon both devonian and jurassic shales are conceivable available sources but sterane compositions relate the organic matter to the jurassic shales a content of extractable organic matter higher than in the shales suggests that the carbon in the veins represents oil rather than mechanically mobilized shale the oil was present during sediment vein emplacement the veins were emplaced forcefully which may reflect high fluid pressure associated with post jurassic movement on the helmsdale fault

response of alluvial rivers to slow active tectonic movement alluvial rivers respond to valley slope deformation caused by active tectonics in various ways depending on the rate and amount of surficial deformation and on the type of river on the basis of experimental results and field examples hypothetical models of river response to anticlinal uplift and synclinal subsidence were developed for different types of alluvial rivers an experimental braided channel responded to anticlinal uplift across the channel with degradation and terrace formation in the central part of the uplift with subsidence aggradation in the central reach was the main response transverse bars developed downstream of the subsidence axis an experimental meandering channel responded to slope steepening with a sinuosity increase bank erosion and point bar growth occurred downstream of the anticlinal axis and upstream of the synclinal axis upstream of the uplift axis and downstream of the subsidence axis where the slope was flattened water flooded over bars local convexity in longitudinal profiles of the middle rio grande new mexico is considered to be formed by a domal uplift local aggradation and degradation could be explained by the effect of uplift the san joaquin river california which is now highly controlled does not show clear adjustment to the rapid subsidence due to ground water withdrawal it shows however a channel pattern adjustment to active tectonic subsidence that has been occurring for a long time the san antonio and guadalupe rivers in texas both increase their sinuosity significantly where monoclinal movements steepen valley slopes

longitudinal profile development into bedrock an analysis of hawaiian channels analysis of topographic maps of rivers incised into dated hawaiian lava flows shows that the long term average bedrock erosion rate along certain reaches is linearly related to stream power field observations suggest that two processes may control hawaiian channel downcutting 1 stream power dependent erosion including abrasion of the channel bed by transported particles and 2 step wise lowering caused by knickpoint propagation modeling results indicate that a simple stream power dependent erosion law predicts the straight to weakly convex longitudinal profiles characteristic of kauai channels but is insufficient to predict two other characteristic features the upslope propagation of knickpoints and the straight 5 8 channel slopes below the knickpoints thus more than this single transport law is apparently required to model bedrock channel incision field surveys also indicate that significant portions of the channel lengths below the knickpoints are mantled with large boulders we propose that

tectonic influences on the quaternary drainage evolution on the north western margin of the french central massif the creuse valley example abstract this work examines the links between tectonics and fluvial dynamics on the north western margin of the french central massif geomorphological and sedimentological analyses of detrital deposits were carried out as the basis for correlating the different formations and for reconstructing the palaeodrainage in the creuse basin cross sections of the valleys longitudinal profiles of terraces and glacis indicate post depositional deformation of about 50 m amplitude uplift north and south of gueret and in the eguzon district these deformations are related to the central massif uplift of 50 m above the paris basin since 1 1 ma ois 32 the creuse incision varies from 140 m in the crozant anticline to 60 m in the paris basin an upper pliocene palaeochannel located on the sedelle ardentes issoudun lineament is evidenced by andalusite coming from the fougeres unit the reactivation of the transverse faults between le pin and le menoux has distorted the middle terraces the main knick points are mainly due to tectonics and have been persistent in the landscape since the upper pliocene their recession rate is controlled both by discharge and lithology tributary streams exhibit strong convexities indicating that the erosional response to pliocene uplift has not yet propagated into upland surfaces

magnetotelluric investigations of the lithosphere beneath the central rae craton mainland nunavut canada new magnetotelluric soundings at 64 locations throughout the central rae craton on mainland nunavut constrain 2 d resistivity models of the crust and lithospheric mantle beneath three regional transects responses determined from colocated broadband and long period magnetotelluric recording instruments enabled resistivity imaging to depths of 300 km strike analysis and distortion decomposition on all data reveal a regional trend of 45 53 but locally the geoelectric strike angle varies laterally and with depth the 2 d models reveal a resistive upper crust to depths of 15 35 km that is underlain by a conductive layer that appears to be discontinuous at or near major mapped geological boundaries surface projections of the conductive layer coincide with areas of high grade archean metasedimentary rocks tectonic burial of these rocks and thickening of the crust occurred during the paleoproterozoic arrowsmith 2 3 ga and trans hudson orogenies 1 85 ga overall the uppermost mantle of the rae craton shows resistivity values that range from 3000 m in the northeast beneath baffin island and the melville peninsula to 10 000 m beneath the central rae craton to 50 000 m in the south near the hearne domain near vertical zones of reduced resistivity are identified within the uppermost mantle lithosphere that may be related to areas affected by mantle melt or metasomatism associated with emplacement of hudsonian granites a regional decrease in resistivities to values of 500 m at depths of 180 220 km increasing to 300 km near the southern margin of the rae craton is interpreted as the lithosphere asthenosphere boundary

palaeoecology and sedimentology across a jurassic fault scarp ne scotland a detailed palaeoecological and sedimentological analysis of the kimmeridgian coastal outcrops around helmsdale northeast scotland has been related for the first time to a detailed biostratigraphical scheme allowing the depositional history of this important area adjacent to some north sea oilfields to be elucidated a broad shallow marine sub tropical shelf was disrupted by the onset of normal faulting along the helmsdale fault in earliest kimmeridgian times initially water depths remained shallow on the hanging wall reflected by a normal benthic fauna but a rapidly steepening southeast directed palaeoslope produced frequent sediment sliding shoreface sands developed immediately to the west of the fault and were transferred to the hanging wall via a fault transfer zone where they now constitute the allt na cuile formation continued rapid subsidence during the remainder of the kimmeridgian and the portlandian produced deep poorly oxygenated to anoxic benthic conditions on the hanging wall in which a combination of rock slide debris flow turbidity current deposition alternated with hemipelagite deposition to produce the helmsdale boulder bed formation the eathie locality cromarty previously regarded as a deeper more distal setting than helmsdale contains a slightly more diverse benthic fauna implying shallower water the deepest waters were immediately adjacent to the fault scarp as predicted by the standard half graben depositional model

alluvial river response to neotectonic deformation in louisiana and mississippi repeat geodetic surveys show uplift of the monroe and wiggins anticlines in louisiana and mississippi there are deformed quaternary terraces which indicate long term deformation in the valleys of the alluvial rivers that cross these structures and there are floodplain and channel convexities that provide evidence of modern deformation in addition the channels show significant variations of morphology sinuosity gradient and depth and behavior appropriate to reaches of increased and decreased valley slope these alluvial rivers are adjusting to modern deformation and their adjustment confirms two geodetic leveling anomalies

the contact uranium prospect kiggavik project nunavut canada tectonic history structural constraints and timing of mineralization uranium mineralization in the kiggavik area on the eastern border of the thelon basin nunavut canada hosts significant uranium resources within the basement and its understanding is critical to comprehending the genesis of unconformity related deposits structural controls and therefore exploration of these types of deposits in this prospective district this article deciphers the complex multiphase fracture network associated with uranium mineralization of the most recently discovered basement hosted prospect in the kiggavik area named contact the contact prospect is located along the andrew lake fault alf a major ne sw fault corridor in the area this study combines field work drillcore logging sampling and macro to micro petro structural analyses key results from this study highlight that the ne trending alf along with the ene trending thelon tf and judge sissons jsf faults formed early during intracratonic rifting and deposition of the baker lake and wharton groups ca 1850 1750 ma in response to the thelon and trans hudsonian orogeny the alf was affected by a strong silicification brecciation event that likely developed at ca 1750 ma and partitioned later deformation and fluid circulation in the contact prospect the alf was reactivated multiple times and mineralized in three stages with distinctive secondary fracture patterns alteration and mineralization types ten fracture stages have been identified at the contact prospect f1 to f10 the first stage of mineralization coeval with f5 is related to fluids of unconstrained origin that circulated through e w faults in the area that locally reactivated quartz veins of the brecciation event at the intersection with the alf mineralization at this stage is polymetallic and associated with weak clay alteration the second stage of uranium mineralization occurred coeval with transtensional reactivation of the ne sw trending alf f6c and in relation to circulation of oxidizing basinal brines within the fault zone mineralization at this stage is monometallic and associated with illite and sudoite alteration later reactivation of the inherited fracture network f8 led to strong illitization and bleaching of the host rock with local reworking of the ore body finally reactivation of the fracture network during f9 and 10 lead to circulation of meteoric fluids that remobilized mineralization in a third stage of uranium re concentration along redox fronts with strong illitization and bleaching of the host rock unlike the classic unconformity related uranium deposits in the athabasca basin where clay alteration halos occur around the ore bodies related to mineralizing processes in the contact prospect the strongest clay alteration event f8 postdates both main stages of mineralization along with uranium remobilization the basement hosted contact prospect is likely a relict of what was once a larger deposit

eclogites of the snowbird tectonic zone petrological and u pb geochronological evidence for paleoproterozoic high pressure metamorphism in the western canadian shield eclogite occurs within the southern domain of the east athabasca mylonite triangle in northern saskatchewan situated at the boundary between the archean rae and hearne provinces of the western canadian shield the east athabasca mylonite triangle is a fundamental exposure of the 3 000 km long snowbird tectonic zone the eclogite occurs in association with a variety of lower crustal high pressure granulites that record a complex metamorphic history from 2 6 to 1 9 ga temperatures of the eclogite facies metamorphism are constrained by garnet clinopyroxene exchange thermometry at 920 1 000 c minimum pressure conditions are recorded by the jadeite quartz albite geobarometer at 1 8 2 0 gpa a near isothermal decompression path to granulite facies conditions is inferred from retrograde reaction textures involving the formation of granulite facies assemblages such as orthopyroxene plagioclase and pargasite plagioclase u pb idtims zircon geochronology of the eclogite yields a weighted mean 207pb 206pb date of 1 904 0 0 3 ma which we interpret as the time of peak eclogite facies metamorphism shrimp in situ analyses of metamorphic zircons included within omphacitic clinopyroxene support this interpretation with a weighted mean 207pb 206pb date of 1 905 19 ma inclusion suites of high pressure phases and the petrographic setting of zircon are a direct link between zircon growth and eclogite facies metamorphism zircon from one eclogite sample has older cores that are 2 54 ga which is a minimum age for the emplacement or earliest metamorphism of the gabbroic protolith u pb rutile data indicate slow cooling at 1 c ma below 500 c from 1 88 to 1 85 ga the formation and exhumation of the eclogites at ca 1 9 ga has important implications for the tectonic significance of the snowbird tectonic zone during the paleoproterozoic the eclogites described here are consistent with transport of continental crust to mantle depths during the paleoproterozoic followed by rapid buoyancy driven exhumation to normal lower crustal depths

geochronology and genesis of the bong uranium deposit thelon basin nunavut canada the thelon basin nunavut shares many similarities with the uranium producing athabasca basin saskatchewan however the uranium deposits associated with the thelon basin are still poorly understood the kiggavik project area areva resources canada is located near the northeastern terminus of the thelon basin and comprises multiple uranium deposits hosted exclusively in basement rocks the bong deposit is hosted dominantly by neoarchean metagraywacke of the woodburn lake group a five phase metallogenetic model is proposed for the bong deposit with three stages of uraninite identified the premineralization phase is characterized by host rock silicification mineralization is separated into three main stages stage 1 uraninite u1 ca 1500 ma is preserved in highly fractured and altered disseminated grains that are overgrown by later stages of uraninite stage 2 uraninite u2 ca 1100 ma forms veinlets parallel to d 1 foliation and coats and fills fractures in organic matter nodules and blebs stage 2 uraninite is associated with pervasive illite that formed from 190 c fluids 18 o 6 4 2 h 97 which remobilized much of stage 1 uraninite and completely overprinted stage 1 alteration at 1000 ma an oxidizing fluid deposited uraninite along redox fronts u3 while altering and remobilizing stage 1 and 2 uraninite post uranium oxide minerals include drusy quartz calcite and illite accompanied by uranyl phases e g uranophane ca u

alluvial eolian and lacustrine sedimentology of a paleoproterozoic half graben baker lake basin nunavut canada the northeast trending baker lake sub basin was a volcanically active half graben during deposition of ca 1 85 1 76 ga baker lake group drainage was oriented along transverse and axial directions with flow to playa lake and deeper perennial lacustrine depocentres basin marginal streamflow dominated alluvial fans were concentrated along the southern margin and provided sediment from archean crystalline basement rocks these fed transverse gravel and sand bed braided streams alluvial dynamics were characterized by channel aggradation and abandonment abandoned channel belts were sites of floodplain and eolian deposition basin axial braided streams fed northeast and southwest to a depocentre near christopher island where eolian playa and lacustrine environments were intimately linked felsic minette flows were initially erupted from localized centres contemporaneous sedimentary deposits typically contain minor volcaniclastic components that increase in abundance basinward voluminous and widespread younger minette flows prograded outward from volcanic centres contributing significant additional basin infill

u pb detrital zircon geochronology and provenance of the late paleoproterozoic dubawnt supergroup linking sedimentation with tectonic reworking of the western churchill province canada u pb sensitive high resolution ion micro probe shrimp analysis of detrital zircon in 11 sandstone samples from the late paleo proterozoic dubawnt supergroup of the baker lake and thelon basins are presented here alluvial fan and braided stream facies of the ca 1 84 1 78 ga baker sequence yield age spectra with significant groupings at 2 70 and 2 60 ga reflecting provenance chiefly from local sources in the northwestern hearne domain of the western churchill province age spectra are consistent with sed imentological and stratigraphic information which indicate provenance from the proximal uplifted shoulders of an intracontinental rift that developed in response to inboard effects of the hudsonian orogeny collision of superior craton into western churchill province the unconformably overlying 1 76 1 74 ga whart sequence exhibits a more varied provenance and has an abundance of 2 0 1 9 ga detrital zircon these ages match those of synorogenic plutons in the taltson thelon orogen collision of slave craton into the western churchill province provenance from the taltson thelon orogen is supported by easterly paleocurrents and rb sr cooling ages from mafic dikes that indicate reactivated collision of the slave craton and related uplift and denudation coeval with deposition of the whart sequence the depositional age of the whart sequence is constrained by intercalated rhyolite flows with conventional 207 pb 206 pb crystallization ages of 1757 6 3 4 ma and 1753 0 1 7 ma 2 the thermal effects of this collision also are recorded in isotopic data from basement rocks throughout the western churchill province and in syndepositional to postdepositional faults that parallel the main boundary faults of the slave indentor late reactivation and associated metamorphism faulting and basin development could be the result of the inboard effects of subduction and related collision along the southern margin of laurentia the detrital zircon geochronology of the barrens sequence supports recycling of local supracrustal sequences and weathering of underlying granitic gneisses zircons of hudsonian affinity ca 1 9 1 8 ga are nearly absent which argues against a distant eastern source region for the barrens sequence the dubawnt supergroup detrital zircon age data set shows concentrations ca 2 75 2 6 ga 2 1 1 9 ga and 1 85 1 75 ga which are concordant with the known ages of major juvenile crust forming events leading up to final amalgamation of late archean and paleoproterozoic supercontinents detritus of this age was shed cratonward and captured by interior basins such as the baker lake and thelon basins during major collisional events that reworked the margins of the western churchill province e g hudsonian and thelon taltson orogenies

longitudinal profile evolution of valleys on coastal terraces under the compound influence of eustasy tectonism and marine erosion abstract on the coast of tosa bay southwestern japan there is a wide coastal terrace which was formed in the last interglacial and has been uplifted to altitudes of 150 200 m above the present sea level by crustal movement many valleys dissect the terrace surface with upwardly convex profiles in downstream reaches numerical simulations were conducted to investigate the development of longitudinal profiles of the valleys under the influence of baselevel change and marine erosion the basic equation used for the calculation had been derived theoretically from the hydraulic mechanism of river erosion the independent variables are the gradient and curvature of the valley floor and the distance from the divide drainage area per unit basin width the parameter in the sediment transport equation is determined based on the results of laboratory experiments a time sequence of seashore migration which has been caused by marine erosion and relative sea level change due to crustal uplift and glacial eustasy since the last interglacial was given as a boundary condition numerical calculations were conducted using a finite difference method starting from 125000 years ago when the shoreline was located at the upper end of the terrace surface and progressive changes in the valley profiles over time were simulated the present profiles obtained from the calculation fit quite closely to actual valley profiles which demonstrates the validity of the equation and at the same time suggests a formation process for wide coastal terraces

nonlinear dynamical systems in geomorphology revolution or evolution abstract geomorphic systems typically exhibit complex apparently random behaviors and patterns in both spatial and temporal domains this complexity can arise from the cumulative impacts of individual process response mechanisms which are far too numerous to be accounted for in individual detail or due to multiple controls over process response relationships which operate over a range of spatial and temporal scales stochastic complexity nonlinear dynamical systems nds theory which includes specific techniques and concepts such as chaos dissipative structures bifurcation and catastrophe theory and fractals shows that extreme complexity can also arise due to the nonlinear dynamics and couplings of relatively simple systems represented by relatively small equation systems deterministic complexity while emphasis in earth science has been largely on stochastic complexity geomorphologists have long recognized the presence of deterministic complexity as well recent developments in the study of nonlinear dynamical systems have implications for the ability to make reliable long term predictions and therefore applications of nds in geomorphology may be revolutionary to some extent however virtually all the basic conceptual underpinnings of nds theory can be mapped onto existing and even traditional theoretical concepts in geomorphology in this sense the use of nds concepts in understanding earth surface processes and landforms is evolutionary the link between traditional and nds based concepts is illustrated by analyzing a generalized geomorphic mass flux system it is shown that the system is in most cases unstable consistent with chaos or deterministic complexity however the three attractor states of the system correspond exactly to the states of aggradation degradation and steady state

effects of syndepositional faulting and folding on early cretaceous rivers and alluvial architecture lakota and cloverly formations wyoming u s a abstract quantitatively reconstructed paleochannel hydraulics e g channel discharges slopes velocities geometries e g widths depths sinuosities channel patterns and alluvial architecture record the local effects of syndepositional faults and folds these effects are evaluated from lower cretaceous rocks in three areas 1 the northern black hills where the axes of syndepositional folds trend roughly perpendicular to paleoflow 2 the northwestern black hills where the trend of a syndepositional fault is oblique to paleoflow and 3 the wind river basin where the trends of syndepositional faults are nearly parallel to paleoflow in each area channel belt deposits are laterally and vertically connected where local subsidence rates were high producing thick laterally extensive sandstones areas of lower subsidence rates are characterized by isolated or laterally connected channel belt deposits and thinner sandstones surface deformation controlled the positions of some rivers because of the development of antecedent drainages or by directing rivers toward areas of maximum subsidence some reconstructed channel slopes which range from 0 62 10 4 to 5 43 10 4 record surface deformation the three dimensional alluvial architecture was simulated using the model of mackey and bridge 1995 together with quantitatively reconstructed paleochannel parameters in order to provide quantitative insight as to possible conditions and processes that produced the observed alluvial architecture the effects of deformation on channel slopes together with depositional topography were important in controlling avulsion and resultant alluvial architecture the most important condition that governed the alluvial architecture was comparable rates of local subsidence and sediment accumulation paleochannel reconstructions indicate that the rivers were 48 180 m wide and 4 4 13 6 m deep and had discharges of 64 1073 m3s 1 channel deposits all appear to represent point bars and associated channel fills of meandering rivers sinuosities were comparable ranging from 1 1 to 1 4 and show no consistent trends with other channel parameters hence with the exception of two paleochannels out of the thirteen that were reconstructed differences in hydraulic parameters such as slope and sediment transport rate had no discernible effect on channel pattern or sinuosity

rapid and widespread response of the lower mississippi river to eustatic forcing during the last glacial interglacial cycle the lower mississippi valley provides an exceptional fi eld example for studying the response of a continental scale alluvial system to upstream and downstream forcing associated with the large orbitally controlled glacialinter glacial cycles of the late quaternary however the lack of a numerical chronology for the widespread pleistocene strata assemblage known as the prairie complex which borders the holocene fl oodplain of the lower mississippi river has so far precluded such an analysis here we apply optically stimulated luminescence osl dating mainly on silt sized quartz from prairie complex strata in total 27 osl ages indicate that the prairie complex consists of multiple allostratigraphic units that formed mainly during marine isotope stages 7 5e and 5a thus the aggradation of the prairie complex is strongly correlated with the sea level highstands of the last two glacialinterglacial cycles fluvial incision during the sea level fall associated with the mis 5a mis 4 transition extended as far inland as 600 km from the present day shoreline testifying to the dominant downstream control of fl stratigraphic architecture in the lower mississippi valley in addition the short reaction time of the lower mississippi river suggests that large fl uvial systems can respond much more rapidly to allogenic forcing than is commonly believed

multiple burial exhumation episodes revealed by accessory phases in high pressure granulite facies rocks rae craton nunavut canada the big lake shear zone blsz is a 60 km long deep crustal structure adjacent to the northern segment of the snowbird tectonic zone stz nunavut canada in a region characterized by intensely sheared high pressure granulite facies rocks the units exposed here provide an exceptional record of the lower crust that preserves crucial evidence bearing on interpretation of superimposed neoarchean and paleoproterozoic tectono metamorphic events deformation along the blsz postdates 2650 ma the age of a mylonitized monzogranite and predates 2190 ma the age of cross cutting macquoid mafic dykes metamorphic assemblages and p t modeling suggest crustal thickening in the neoarchean with peak conditions of 800 c and 14 15 kbar at ca 2530 ma mylonitic fabrics developed at ca 2505 ma t 800 c p 10 c ma and partial exhumation post ca 2505 ma followed by re burial at 1900 ma rather than slower isobaric cooling at depth these results indicate that the long term residence models proposed by several authors for domains in the central stz are not applicable to the blsz region and are more compatible with a ca 1 9 ga collisional setting

paleoproterozoic reworking of an archean thrust fault in the hearne domain western churchill province u pb geochronological constraints the nature timing and control of archean crustal architecture on the distribution of proterozoic reworking in western churchill province are investigated in the yathkyed lake area central nunavut the tyrrell shear zone tsz marks the boundary between the northwestern and central hearne subdomains respectively in the hanging wall and footwall metamorphism and deformation in the hanging wall are ca 2 66 2 50 ga two episodes of metamorphism are recorded in a foliated granodiorite in the footwall at 1818 5 2 and 1827 5 6 ma the latter age is interpreted as the time of amphibolite facies metamorphism and deformation in the footwall a crosscutting dyke provides a minimum age of 1818 2 ma for this metamorphism and deformation the tsz is dominated by dextral oblique slip shear fabrics a suite of leucogranite dykes provide a maximum age of 1816 2 ma for dextral shearing dextral deformation is bracketed between 1815 2 and 1811 1 ma the ages of two other granitoid dykes in an area of low d

u pb geochronological constraints on neoarchean tectonism multiple compressional events in the northwestern hearne domain western churchill province canada in the yathkyed lake area the tyrrell shear zone tsz marks the boundary between the northwestern and central hearne subdomains of the western churchill province the tsz is dominated by proterozoic dextral strain but in areas of low dextral strain older shear fabrics are consistent with an earlier thrusting event four syntectonic granite sheets from within low dextral strain zones in the tsz and contiguous shear zones at the base of the yathkyed belt have ages of 2636 2629 2652 8 2665 2639 and 2644 3 ma the yathkyed belt occurs in the hanging wall of these shear zones and comprises a greenschist to amphibolite grade overturned panel that is overlain by an upper amphibolite grade polydeformed panel the geometry is consistent with a thrust imbricated stack two episodes of deformation in the hanging wall are bracket between ca 2660 and 2616 6 4 ma and between 2616 6 4 ma and ca 2 60 ga the yathkyed belt is interpreted to have initially been emplaced as a thick skinned thrust nappe alon

organic geochemistry petrology and palynofacies of middle devonian lacustrine flagstones in the orcadian basin scotland depositional environment thermal history and petroleum generation potential during middle devonian time a thick succession of organic rich mainly lacustrine flagstones developed within the orcadian basin these petroleum source rocks crop out in northern scotland nineteen samples were studied using organic petrology palynology and organic geochemistry in order to characterize kerogen type depositional environment thermal maturity and petroleum generation potential c org carbonate and sulphur content as well as hydrogen index hi values are quite variable e g hi from 79 to 744 mg hc g c org based on biomarker data organic material mainly originates from aquatic organic matter deposited under lacustrine conditions with oxygen depleted but not permanently anoxic bottom waters petrography reveals small quantities of vitrinite particles indicating minor input of terrestrial material this is supported by biomarker data and the palynofacies which is characterized by a high amount of oil prone amorphous organic matter aom and generally few miospores maturity of the succession studied in caithness and orkney is between immature and oil mature one dimensional basin modelling shows that a significant remaining hydrocarbon generation potential exists within the middle devonian succession in contrast to the low hydrocarbon generation in the onshore area offshore oil generation was significant especially after deposition of thick upper jurassic upper cretaceous sediments at the end of cretaceous time hydrocarbon generation ceased due to uplift the contribution to known oil fields from the devonian flagstones is a realistic scenario including a contribution to the beatrice oil field in the south of the modelled area

a statistic for testing the elevation characteristics of landscape simulation models there is an urgent need to test recently constructed conceptual models of landscape evolution and geomorphology against field data many statistics that have commonly been used such as strahler statistics are poorly suited to this testing being unable to potentially falsify the models when applied in controlled conditions the relations between these statistics and catchment mass movement processes are in many cases indirect moreover they are sensitive to unknowable inputs e g initial conditions one of the main differences among the competing landscape evolution models is their representation of mass movement and erosion processes so that statistics that are directly linked to these processes or their geomorphic signature are needed this paper examines the use of a log log linear relation between catchment area slope and elevation this relation has been previously derived quantitatively from the catchment erosion and hydrologic processes for dynamic and declining geomorphic equilibria using a catchment evolution model this paper shows that the relation is robust against deviations from the assumptions of spatial and temporal homogeneity of erosion climate and tectonic uplift made in its derivation the sensitivity of the geomorphology to time varying tectonic uplift and climate and spatially variable soil erodability is examined it is thus asserted that the relation between area slope and elevation is suitable for testing of models against field data where spatial and temporal homogeneity of erosion climate and tectonic uplift are only approximately true in the case of variable soil erodability planar drainage patterns exhibit self organization with the high elevation regions of the catchment having low soil erodability consequently a downstream increasing erodability of the soil material consistent with a downstream fining type of behavior is observed it is further argued that the equilibria relation is fundamental and uniquely defines the elevation form of catchments so that all other elevation statistics are derived from it

petrological and geochronological constraints on high pressure high temperature metamorphism in the snowbird tectonic zone canada the upper deck of the east athabasca mylonite triangle eamt northern saskatchewan canada contains mafic granulites that have undergone high p t metamorphism at conditions ranging from 1 3 to 1 9 gpa 890 960 c coronitic textures in these mafic granulites indicate a near isothermal decompression path to 0 9 gpa 800 c the godfrey granite occurs to the north adjacent to the upper deck high p t domain well preserved corona textures in the godfrey granite constrain igneous crystallization and early metamorphism in the intermediate pressure granulite field opx pl at 1 0 gpa 775 c followed by metamorphism in the high pressure granulite field grt cpx pl at 1 2 gpa 860 c u pb geochronology of zircon in upper deck mafic granulite yields evidence for events at both c 2 5 ga and c 1 9 ga the oldest zircon dates are interpreted to constrain a minimum age for crystallization or early metamorphism of the protolith a population of 1 9 ga zircon in one mafic granulite is interpreted to constrain the timing of high p t metamorphism titanite from the mafic granulites yields dates ranging from 1900 to 1894 ma and is interpreted to have grown along the decompression path but still above its closure temperature indicating cooling following the high p t metamorphism from c 960 650 c in 4 10 myr zircon dates from the godfrey granite indicate a minimum crystallization age of 2 61ga without any evidence for 1 9 ga overgrowths the data indicate that an early granulite facies event occurred at c 2 55 2 52 ga in the lower crust c 1 0 gpa but at 1 9 ga the upper deck underwent high p t metamorphism then decompressed to 0 9 1 0 gpa juxtaposition of the upper deck and godfrey granite would have occurred after or been related to this decompression in this model the high p t rocks are exhumed quickly following the high pressure metamorphism this type of metamorphism is typically associated with collisional orogenesis which has important implications for the snowbird tectonic zone as a fundamental boundary in the canadian shield

age and evolution of the lower crust beneath the western churchill province u pb zircon geochronology of kimberlite hosted granulite xenoliths nunavut canada abstract zircon from granulite facies xenoliths can preserve unique geodynamic records of deep and mostly inaccessible levels of the continental crust within archean cratons we present the first such records from beneath two archean crustal blocks that were affected by multiple episodes of regional scale proterozoic metamorphism and are located within the western churchill province nunavut canada zircon u pb geochronology and trace element analysis were carried out on samples that originated in the deep crust at the time of kimberlite eruption as confirmed with raman spectroscopy zircon was recovered from four metabasites grt cpx plg from the rankin inlet area of the chesterfield block and five metabasites grt cpx plg hbl opx and three metatonalite anorthosites plg cpx plg hbl opx from the repulse bay area of the rae craton sem cl imaging reveals several types of growth zoning diagnostic of igneous and metamorphic zircon crystallization the latter are related to local high temperature recrystallization and micro fracturing and are spatially associated with zones of apparent pb loss and or intracrystalline pb variability evidence for the formation of paleoarchean mesoarchean to neoarchean crust is preserved in oscillatory zoned igneous cores having 207pb 206pb ages of ca 3 5 ga and ca 3 0 2 6 ga two periods of paleoproterozoic metamorphism and zircon growth followed with the oldest episode at ca 2 0 1 9 ga in the chesterfield block metamorphic zircon rims from all twelve xenoliths have an age range of ca 1 75 to 1 70 ga the trace element compositions of the metamorphic rims differ from those of older igneous and metamorphic cores with the rims characterized by lower hree contents and low lu gd n suggesting that garnet crystallization occurred syn to pre rim growth at ca 1 75 ga the archean and paleoproterozoic ages correspond broadly to the upper crustal histories of the western churchill province however the prevalence of ca 1 75 1 70 ga metamorphic rims indicates regional scale metamorphic reworking of the lower crust across the region during a period of intracratonic extension and associated magmatism regional magmatic underplating and or remobilization of the lithosphere at ca 1 75 1 70 ga to an extent not widely appreciated represents a terminal stage in western churchill cratonization including stabilization of reworked archean crust relative to underlying diamondiferous mantle

implications of sediment flux dependent river incision models for landscape evolution 1 developing a quantitative understanding of the factors that control the rate of river incision into bedrock is critical to studies of landscape evolution and the linkages between climate erosion and tectonics current models of long term river network incision differ significantly in their treatment of the role of sediment flux we analyze the implications of various sediment flux dependent incision models for large scale topography in an attempt 1 to identify quantifiable and diagnostic differences between models that could be detected from topographic data or from the transient responses of perturbed systems and 2 to explain the apparent ubiquity of mixed bedrock alluvial channels in active orogens although certain forms of the various models can be discarded as inconsistent with morphological data we find that the relative intrinsic concavity indices of detachment and transport limited systems defined herein largely dictate whether the various models can be tied to distinctive steady state morphologies preliminary data suggest that no such diagnostic differences may exist and other methods must be developed to test models accordingly we develop and explore differences in the scaling behavior of topographic relief and the extent of detachment versus transport limited channels as a function of rock uplift rate that may allow discrimination among various models further we explore potentially diagnostic differences in the rates and patterns of transient channel response to changes in rock uplift rate in addition to general differences between detachment and transport limited systems our analysis identifies an interesting hysteresis in landscape evolution hybrid channels at the threshold between detachment and transport limited conditions are expected to act as detachment limited systems in response to an increase in rock uplift rate or base level fall and as transport limited systems in response to a decrease in rock uplift rate especially during postorogenic topographic decline the analyses presented set the stage for field studies designed to test quantitatively the various river incision models that have been proposed

evidence for neoarchean ni cu bearing mafic intrusions along a major lithospheric structure a case study from the south rae craton canada abstract deformed and metamorphosed mafic to ultramafic intrusive rocks are common along and adjacent to the snowbird tectonic zone a major paleoproterozoic structure separating the rae and hearne cratons on the rae side of this major lithospheric structure we investigated a series of mafic bodies that intrude high grade paragneiss and are associated with ni cu pge mineralization by linking field observations geochronology and metamorphic petrology our results indicate archean 2 63 ga crystallization ages for these mafic intrusions over a minimum along strike extent of 500 km and a later high temperature 820 c and 7 5 kbar paleoproterozoic metamorphic overprint at t

the evolution of the danube gateway between central and eastern paratethys se europe insight from numerical modelling of the causes and effects of connectivity between basins and its expression in the sedimentary record abstract the pannonian and dacic basins in se europe are presently connected by the danube river across the south carpathians to which they are in a back arc and foreland position respectively part of the paratethys realm during the neogene open water communication between the basins was interrupted by the late miocene uplift of the carpathians different mechanisms have been proposed for the formation of the danube gateway capture of the upstream lake or an upstream river or incision of an antecedent river estimates on its age range from late miocene to quaternary a related issue is the effect of the large mediterranean sea level fall related to the messinian salinity crisis on the paratethys subbasins specifically the isolated pannonian basin in a synthetic numerical modelling study using a pseudo 3d code integrating tectonics surface processes and isostasy we addressed the causes and effects of changes in connectivity between two large sedimentary basins separated by an elevated barrier specifically we aimed to find the expression of connectivity events in the sedimentary record in general and the consequences for the evolution of the pannonian dacic area in particular we studied a range of parameters including the geometry and uplift rate of the barrier downstream sea level change and lithosphere rigidity we found that changes in connectivity are expressed in the sedimentary record through their effect on base level in the upstream basin and supply in the downstream basin the most important factors controlling the response are the elevation difference between the basins and the upstream accommodation space at the time of reconnection the most pronounced effect of reconnection through lake capture is predicted for a large elevation difference and limited upstream accommodation space downstream increase in sediment supply is dependent on the latter rather than the reconnection event itself of the parameters we tested the rigidity of the lithosphere was found to be of major importance by its control on sediment loaded subsidence and generation of accommodation space a downstream sea level change is unlikely to induce capture but may affect the upstream lake level by enhancing incision in a pre existing gateway in the pannonian dacic region the mechanically weak continuously subsiding pannonian lithosphere allowed accommodation of significant volumes of continental sedimentation and as a consequence transfer of excess sediment to the downstream dacic basin was only gradual the messinian sea level fall in the dacic basin could have been recorded in the pannonian basin only if a connection between the basins already existed more detailed modelling of river incision taking into account lateral differences in erodibility in the south carpathians will be required to give better time constraints on the formation of the danube gateway