slip rate measurements on the karakorum fault may imply secular variations in fault motion beryllium 10 surface exposure dating of offset moraines on one branch of the karakorum fault west of the gar basin yields a long term 140 to 20 thousand year right lateral slip rate of 10 7 0 7 millimeters per year this rate is 10 times larger than that inferred from recent insar analyses 1 3 millimeters per year that span 8 years and sample all branches of the fault the difference in slip rate determinations suggests that large rate fluctuations may exist over centennial or millennial time scales such fluctuations would be consistent with mechanical coupling between the seismogenic brittle creep and ductile shear sections of faults that reach deep into the crust

kinematic model of active deformation in central asia the velocity field of present day deformation in central asia is modelled using a set of four rotating blocks siberia tarim tibet india on a spherical earth a best fit is inverted on the basis of estimated shortening rates across the main thrust zones himalayas tien shan and measured slip rates along the principal strike slip faults altyn tagh and karakorum separating those blocks the fit to the data implies that nearly all the present convergence between india and asia can be accounted for by slip partitioning on these four zones with as much as 50 absorbed by northeastwards extrusion of tibet this suggests that localised deformation governs the present mechanical behaviour of the central asian lithosphere

indian punch rifts tibet the strikes of late cenozoic normal faults in tibet fan systematically from a northwesterly to northeasterly direction from west to east they exhibit an axis of symmetry that bisects the himalayan arc and trends subparallel to india asia motion the two dimensional stress field inferred from the spatial pattern of normal fault orientations can be explained solely by collisional stresses localized along a southern part of the himalayan arc continued insertion of indian crust into tibet can explain the persistence of extension and may be increasing plateau crustal thickness and elevation coeval with rifting

the neotectonics of the tibetan plateau part of the continuing northward convergence between india and eurasia is probably taken up by strike slip displacement with tibet as a whole moving eastward away from the collision zone and undergoing east west extension molnar and tapponnier 1975 ni and york 1978 on the basis of our interpretation of landsat images we propose that strike slip faulting occurs throughout the tibetan plateau such that its north south cross section is being shortened with little contemporary folding or thrusting

southward propagation of the karakoram fault system southwest tibet timing and magnitude of slip the net slip on the southern portion of the karakoram fault system in southwest tibet is estimated by restoring a piercing line defined by two key surfaces in the south kailas thrust system a regional counter thrust along the indus yalu suture assuming that the thrust system is planar across the karakoram fault we calculate 66 5 5 km of normal right slip documentation of the south kailas thrust active at 13 ma implies that the karakoram fault in southwest tibet did not initiate until after the cessation of motion on the thrust however field investigations of the central portion of the karakoram fault system document the fault to have been active at 17 ma and to have accumulated a maximum of 150 km of right slip we suggest that these along strike variations in the magnitude of slip and timing constraints are best explained by southward propagation of the karakoram fault system this is inconsistent with major right lateral slip on the fault system which was used in support of extrusion models for tibet

microfracturing paleostress and the growth of faults abstract we have analyzed the microfractures in samples taken near one thrust fault and five normal faults of known displacement to test the dependence of microfracture density and distribution on fault slip we have also recorded the orientation of microfractures as a function of distance from the associated fault surface in order to control as many parameters as possible shallow faults with similar lithologies were chosen they showed the same kind of deformation namely microfracturing without block rotation recrystallization extensive granulation or crystal plasticity the results of over 8000 microfracture measurements suggest that maximum microfracture density is independent of net slip we interpret this relationship as indicating that the preponderance of microfracturing occurs in proximity to the propagating fault tip the angular relationship between the shear plane and microfractures was commonly found to be between 5 and 20 significantly less than the 30 expected between the far field maximum principal stress and the shear surface this low angle between microfracture orientation and shear plane orientation is predicted for a local stress field associated with a propagating mode ii fault tip other possible explanations for the small angle for tensional microfractures and the shear surface are 1 the effective confining pressure was very low or 2 shear strength at failure was much larger than expected

geochronology of unconformity related uranium deposits in the athabasca basin saskatchewan canada and their integration in the evolution of the basin the importance of geochronology in the study of mineral deposits in general and of unconformity type uranium deposits in particular resides in the possibility to situate the critical ore related processes in the context of the evolution of the physical and chemical conditions in the studied area the present paper gives the results of laser step heating 40ar 39ar dating of metamorphic host rock minerals pre ore and syn ore alteration clay minerals and laser ablation inductively coupled plasma mass spectrometer la icp ms u pb dating of uraninite from a number of basement and sediment hosted unconformity related deposits in the athabasca basin canada post peak metamorphic cooling during the trans hudson orogen of rocks from the basement occurred at ca 1 750 ma and gives a maximum age for the formation of the overlying athabasca basin pre ore alteration occurred simultaneously in both basement and sandstone hosted mineralizations at ca 1 675 ma as indicated by the 40ar 39ar dating of pre ore alteration illite and chlorite the uranium mineralization age is ca 1 590 ma given by la icp ms u pb dating of uraninite and 40ar 39ar dating of syn ore illite and is the same throughout the basin and in both basement and sandstone hosted deposits the mineralization event older than previously proposed as well as several fluid circulation events that subsequently affected all minerals studied probably correspond to far field continent wide tectonic events such as the metamorphic events in wyoming and the mazatzal orogeny ca 1 6 to 1 5 ga the berthoud orogeny ca 1 4 ga the emplacement of the mckenzie mafic dyke swarms ca 1 27 ga the grenville orogeny ca 1 15 to 1 ga and the assemblage and break up of rodinia ca 1 to 0 85 ga the results of the present work underline the importance of basin evolution between ca 1 75 ga basin formation and ca 1 59 ga ore deposition for understanding the conditions necessary for the formation of unconformity type uranium deposits

east west extension in the nw indian himalaya explaining the presence of normal faults in overall compressive settings is a challenging problem in understanding the tectonics of active mountain belts the himalayan tibetan orogenic system is an excellent setting to approach this problem because it preserves one of the most dramatic records of long term contemporaneous shortening and extension over the past decades several studies have described extensional features not only in the tibetan plateau but also in the himalaya for a long time the favored model explained the function of the southern tibetan detachment system a major fault zone in the himalaya as a decoupling horizon between the regime of crustal shortening forming the himalayan wedge to the south and the extensional regime of the tibetan plateau to the north however in recent years increasing evidence has shown that n s trending normal faults in the central himalaya crosscut not only the southern tibetan detachment system but also the main central thrust here we present new structural data and geologic evidence collected within the nw indian himalaya and combine them with previously published seismicity data sets in order to document pervasive e w extension accommodated along n s trending faults extending as far south as the footwall of the main central thrust we conducted a kinematic analysis of fault striations on brittle faults documented and mapped fault scarps in quaternary sedimentary deposits using satellite imagery and made field observations in the greater sutlej region spiti lahul kinnaur and the garhwal himalaya studies of extensional features within the regionally nw se trending nw indian himalaya provide the advantage that arc parallel and e w extension can be separated in contrast to the central himalaya therefore our observations of e w extension in the indian nw himalaya are well suited to test the applicability of current tectonic models for the whole himalaya we favor the interpretation of e w extension in the nw indian himalaya as a propagation of extension driven by collapse of the tibetan plateau

large scale geometry offset and kinematic evolution of the karakorum fault tibet the total offset lifespan and slip rate of the karakorum fault zone kfz western tibet are debated along the southern fault half ongoing oblique slip has exhumed dextrally sheared gneisses intruded by synkinematic leucogranites whose age v23 ma u pb on zircon indicates that right lateral motion was already in progress in the late oligocene ar ar k feldspar thermochronology confirms that rapid cooling started around 12 ma likely at the onset of the present dextral normal slip regime correlation of suture zones across the fault requires a total offset greater than 250 km along the active northern fault branch an average long term slip rate of 1 0 3 cm yr is inferred assuming that this offset accrued in a time span of 23 34 ma southwest of the ladakh karakorum range the large scale boudinage of ophiolitic units suggests that an offset of several hundreds of kilometers exists along another southern branch of the kfz towards the southeast in the mount kailas region the fault zone does not end at gurla mandatha but continues eastwards as a transpressive flower structure along the indus tsangpo suture our new data thus suggest that the kfz contributed to absorb hundreds of kilometers of india asia convergence

petrogenesis of the proterozoic athabasca basin northern saskatchewan canada and its relation to diagenesis hydrothermal uranium mineralization and paleohydrogeology abstract in the athabasca basin proterozoic sandstones unconformably overlie archean and aphebian rocks multiple fluid events involving isotopically and chemically distinct fluids which have migrated laterally for considerable distances and along fault zones have produced a paragenetically identifiable assemblage of clay silicate and oxide minerals in the basin and basement rocks altered sandstones and the underlying metasedimentary rocks proximal to fault zones host high grade u ni co unconformity type uranium ore deposits and contain an alteration assemblage of highly crystalline 2m 3t illite 1m kaolinite clinochlore and sudoite hematite dravite and euhedral quartz in the sandstones 18o values of coeval quartz hematite quartz illite quartz dravite illite hematite and kaolinite hematite fluid inclusion temperatures in diagenetic quartz and d values of 1m kaolinite 2m 3t illite dravite and in fluid inclusions in the quartz indicate formation from a basinal fluid that had d values of 60 10 and which underwent salinity temperature and 18o increases from 5 to 34 wt nacl 120 to 240 c and 5 to 3 respectively as a result of increasing burial depth and sustained water rock interactions with the basinal sediments over substantial time periods 18 o 16 o and d h ratios of sudoite and clinochlore in meta sedimentary basement rocks within the alteration haloes indicate formation from a basement derived fluid with 18o and d values of 4 4 and 30 10 respectively that was isotopically distinct from the basinal fluids 18o and d values of late kaolinites in reactivated fault zones indicate formation mainly from low temperature 50 25 c fluids having 18o and d values of 16 and 130 respectively similar to relatively modern meteoric waters in the area some kaolinites have 18o and d values which suggest they formed from meteoric waters at mid latitudes and have experienced varying degrees of oxygen and hydrogen isotope exchange with relatively modern meteoric waters in the re activated faults illite sudoite and dravite have d values that vary by 100 without concurrent changes to their 18o values indicating preferential hydrogen isotope exchange with relatively modern meteoric waters at low temperatures and under conditions of high integrated water rock ratios rb sr isochron and model ages of 1477 57 and 952 ma respectively for the crystalline 2m 3t illites indicate the timing of the high temperature basinal fluid events associated with fluid mixing rb sr and k ar ages on illites with the lowest d values are as young as 300 ma and indicate late stage resetting of their radiogenic isotope systematics as a result of substantial interactions with relatively modern meteoric waters the evolution of sr isotopic compositions of fluids in the basin and basement rocks as reflected by the 87 sr 86 sr ratios of chlorite illite and dravite indicates that mixing of two isotopically distinct fluids in the vicinity of faults was the process by which uranium was precipitated similar to that suggested by oxygen and hydrogen isotope systematics in the clays and silicate minerals nd ratios in the high temperature diagenetic and hydrothermal clay and silicate minerals and the cogenetic uranium ores suggest they all have formed from similar fluids which have interacted substantially with the basin sediments in general the isotopic chemical microthermometric and petrologic data indicate that the athabasca basin has had a protracted fluid history comparable to that documented for more modern sedimentary basins the data clearly show that the major sandstone aquifers have been affected by widespread lateral flow of diagenetic fluids over distances of hundreds of kilometers and also that these fluid migration paths have been modified by cross formational fluid flow near active fault zones

transtensional deformation in the central himalaya and its role in accommodating growth of the himalayan orogen 1 field mapping structural analysis and geochronologic data from northwestern nepal reveal major normal right slip motion along a previously unrecognized west northwest striking system of shear zones that we term the gurla mandhata humla fault system gmh the gmh obliquely cuts across the greater himalayan crystalline sequence and into the lesser himalayan imbricate thrust belt via two right step over structures the average slip direction on the gmh parallels the strike of the himalayan orogen motion along this fault system has resulted in an apparent left separation of the south tibet detachment main central thrust zone and lesser himalayan imbricate thrust belt along a north striking segment of the fault system we estimate a minimum of 21 km of net slip on the southern branch of the gmh by restoring the trace of the main central thrust zone parallel to the average slip direction on the fault taking into account slip estimates from the northern branch of the gmh yields a minimum net slip estimate of 24 4 to 32 4 km for the gmh the 232th 208pb ion microprobe monazite ages from leucogranite bodies indicate that motion on the gmh occurred after 15 ma its initiation immediately followed crustal thickening between the main central thrust zone and indus yalu suture zone motion on the gmh is contemporaneous with arc normal contraction in the southernmost himalayan orogen these observations can be explained by a model that involves foreland propagating structural systems facilitating arc normal contraction in the foreland and arc parallel extension in the hinterland that work together to maintain the arcuate shape of the himalayan orogen

geological evidence against large scale pre holocene offsets along the karakoram fault implications for the limited extrusion of the tibetan plateau two end member models proposed to accommodate the convergence between india and asia north of the himalaya are 1 homogeneous crustal thickening of the tibetan plateau and 2 continental escape or extrusion of tibet and southeast asia away from the indenting indian plate foremost among the arguments supporting the latter would be large scale 1000 km offsets and high present day slip rates along the major strike slip faults bounding the postulated extruding crust notably the altyn tagh fault along the northern margin of tibet and the karakoram fault along the sw margin satellite photographic interpretation and field mapping in the karakoram mountains in pakistan the nubra siachen area of north ladakh and the pamirs in xinjiang show that although the karakoram fault is extremely active today geological offsets along the right lateral fault are probably less than 120 km the 21 0 5 ma baltoro monzogranite leucogranite batholith has been rotated clockwise about a vertical axis 35 40 into nw se alignment parallel with the karakoram fault east of the siachen glacier with a maximum offset of 90 km across the fault the bangong shyok suture zone similarly has a dextral offset of 85 km the course of the indus river which was antecedent to the rise of the ladakh karakoram and himalayan ranges has been offset dextrally by 120 km south of pangong lake if present day slip rates approximately 32 mm yr avouac and tapponnier 1993 are correct only 4 ma are required to obtain a 120 km offset there is no geological evidence for any larger scale pre holocene offsets and it is suggested that the karakoram fault cannot have accommodated major eastward lateral motion of tibetan crust the fault has also exerted little or no influence on surface topographic uplift cutting obliquely across the highest peaks of the karakoram dextral motion along the central part of the karakoram fault has been transferred in the north to the rangkul murghab and karasu transpressional faults in the central pamir north of tashkurgan the karakoram fault shows mainly normal motion around the kongur and mustagh ata gneiss domes metamorphic core complexes and the extensional muji graben minor dextral displacement has occurred along the shiquanhe fault but this motion cannot be linked to the jiale fault of east tibet the southern end of the karakoram fault merges with the indus yarlung suture zone near mount kailas and does not cut across the himalaya the lack of large scale geological offsets along the karakoram fault together with its very recent initiation 5 or 4 ma suggests that it is related to the pliocene quaternary northward indentation of the pamir and not to any long term extrusion of tibetan crust following the indian collision

basin formation in the high himalaya by arc parallel extension and tectonic damming zhada basin southwestern tibet 1 the late miocene pleistocene zhada basin in southwestern tibet provides a record of subsidence and basin formation within an active collisional thrust belt the 800 m thick basin fill is undeformed and was deposited along an angular unconformity on top of tethyan strata that were previously shortened in the himalayan fold thrust belt modal sandstone petrographic data conglomerate clast count data and detrital zircon u pb age spectra indicate a transition from detritus dominated by a distal northern source to a local southern source this transition was accompanied by a change in paleocurrent directions from uniformly northwestward to basin centric at the same time the depositional environment in the zhada basin changed from a large braided river to a closed basin lake sedimentation in the zhada basin was synchronous with displacement on the qusum and gurla mandhata detachment faults which root beneath the basin and exhume midcrustal rocks along the northwestern and southeastern flanks of the basin respectively these observations indicate that accommodation for zhada basin fill was produced by a combination of tectonic subsidence and damming as midcrustal rocks were evacuated from beneath the zhada basin in response to arc parallel slip on crustal scale detachment faults

magmatic and metamorphic uraninite mineralization in the western margin of the trans hudson orogen saskatchewan canada a uranium source for unconformity related uranium deposits the genetic model for the giant unconformity related uranium deposits of the athabasca basin is still being debated with one of the main issues being the source of the uranium concentrated by mesoproterozoic era ca 1 60 1 00 ga diagenetic hydrothermal events at the interface between the athabasca basin and the underlying archean paleoproterozoic basement rocks currently accessory minerals like monazite zircon and or apatite from the sedimentary basin and basement rocks are proposed as the primary uranium source for these high grade uranium deposits numerous occurrences of u mineralization of hudsonian age have been documented for decades all around the athabasca basin however so far these have not been regarded as viable u sources here a systematic and detailed study of two areas of basement rocks near the eastern part of the athabasca basin is presented i e the way lake property lying outside the current margin of the basin and the moore lakes property currently covered by the basin this study highlights the significant and widespread occurrence of hudsonian ca 1 81 1 76 ga uranium oxide uo2 mineralization in these zones two types of mineralization are identified and documented here magmatic uranium oxides related to granitic pegmatites and leucogranites which are more common and high temperature vein hosted uranium oxides which have the highest grades the two types were formed during the peak 1 82 1 81 ga and or postthermal peak 1 81 1 72 ga events related to the evolution of the trans hudson orogeny the magmatic uranium oxides formed by partial melting of wollaston group metasedimentary rocks the origin of the vein type occurrences is unclear but their high thorium and rare earth element ree contents suggest a high temperature process associated with ca and or na metasomatism the uranium oxides are associated with other u th and reebearing accessory minerals like u rich thorite thorite zircon and or monazite adding to the exceptional u contents 100 2 460 ppm of these uo2 bearing rocks up to 200 times more primarily enriched in u than other basement or basin rock types a 3 d model of a 1 300 630 200 m basement zone from the way lake property indicates that uraninite bearing granitic pegmatites and leucogranites represent 7 of the total volume of crystalline rock within this rock volume are approximately 8 121 assuming a mean u content of 250 ppm to 16 242 assuming a mean u content of 500 ppm tonnes u the u tonnage of this limited rock volume contained mainly by the hudsonian age uo2 corresponds to between 4 for mcarthur river and 103 for rabbit lake of the u tonnage of known unconformity related u deposits of the basin some of the studied rock samples even macroscopically fresh and located far away from any known unconformity related u deposit present clear evidence of alteration including clay minerals aluminophosphatesulfate aps minerals and uo2 dissolution indicating the percolation of the brines associated with the formation of unconformity related uranium deposits when the basin was far more geographically extensive due to geologic similarities between the studied zones and the basement domains from the eastern part of the athabasca basin i e the hearne province it is proposed that these domains hosted widespread hudsonianage uranium oxide protores these protores provided easily leachable uranium for the metal enrichment of basinal brines during their percolation within the basement and the formation of the unconformity related u deposits these observations bring new insight to the debate about the genetic model of unconformity related u deposits and reinforce the metal source potential of the basement compared to that of the sedimentary basin

active tectonics of the western tethyan himalaya above the underthrusting indian plate the upper sutlej river basin as a pull apart structure fault bounded blocks and structural elements were mapped in the eastern ladakh spiti and upper sutlej river basin located within the tethyan himalaya and to the southwest of the karakorum fault zone mainly using landsat multispectral scanner mss band 5 band 7 near infrared images with detailed analysis of smaller areas by interactive digital processing of false color images and returned beam vidicon rbv imagery in conjunction with available topographical geological and seismological data for the first time the leo pargil horst and other nearby fault bounded blocks located at the northwestern end of the upper setlej river basin were clearly revealed on the landsat color composites shallow crustal seismicity is systematically related to the nne trending and n trending normal faults of the leo pargil and nearby regions some of the aftershocks of the kinnaur earthquake of january 19 1975 ms 6 8 appear to be associated with movement along the nne trending westbound fault of the leo pargil horst and the nearby kaurik chango fault the main shock however is teleseismically located at about 30 km to the northwest of the kaurik chango fault fault plane solutions of the main shock and two aftershocks indicate a large component of normal faulting in map view the upper sutlej river basin has an approximately rhomboidal shape and is located to the southwest of the karakorum fault system we suggest that this basin is a pull apart between the nw se oriented right lateral strike slip karakorum fault system and the high angle faults near the southern boundary of the tethyan himalaya the leo pargil horst is the northwestern bounding fault block of this pull apart the active tectonic features in this part of the tethyan himalaya appear to reflect right shear within the crust and this is probably a consequence of oblique underthrusting of the indian continental plate beneath the western himalaya and southwestern tibet during the neogene and quaternary times nw trending right lateral strike slip faults in the lesser himalaya and in southwestern tibet may reflect the same right shear

mantle fluids in the karakoram fault helium isotope evidence abstract the karakoram fault kkf is the 1000 km long strike slip fault separating the western himalaya from the tibetan plateau from geologic and geodetic data the kkf is argued either to be a lithospheric scale fault with hundreds of km of offset at several cm a or to be almost inactive with cumulative offset of only a few tens of kilometers and to be just the upper crustal localization of distributed deformation at depth here we show 3he 4he ratios in geothermal springs along a 500 km segment of the kkf are 3 100 times the normal ratio in continental crust providing unequivocal evidence that a component of these hydrologic systems is derived from tectonically active mantle mantle enrichment is absent along the indus yarlung suture zone isz just 35 km southwest of the kkf suggesting that the mantle fluids flow only within the kkf within the last few ma the kkf must have accessed tectonically active tibetan mantle northeast of the mantle suture which we therefore locate vertically beneath the kkf very close to the surface trace of the isz hence in southwestern tibet indian crust may not now be underthrusting substantially north of the isz even though miocene underthrusting may have placed indian crust north of the isz in the lower half of the tibetan plateau crust this is in significant contrast to central and eastern tibet where underthrust indian material not only forms the lower half of the tibetan crust but is also currently underthrusting for 200 km north of the isz our new constraint on kkf penetration to the mantle allows an improved description of the continuously evolving karakoram fault as a tectonically significant yet perhaps geologically ephemeral lithospheric structure

gps measurements from the ladakh himalaya india preliminary tests of plate like or continuous deformation in tibet observations of relative motion in a geodetic network in ladakh india and across southern tibet indicate slow shear on the karakorum fault rapid east west extension across the whole of southern tibet and constant arc normal convergence between india and southern tibet along the himalayan arc measurements of ten campaign style and six permanent sites with global positioning system gps precise geodesy provide these bounds on the style and rates of the large scale deformation in the tibet himalaya region divergence between sites at leh ladakh india and shiquanhe western tibet as well as slow relative motion among sites within the ladakh network limit right lateral slip parallel to the karakorum fault to only 3 4 5 mm yr this low rate concurs with a recent estimate of 3 4 mm yr for late holocene time but disagrees with the much higher rate of 30 35 mm yr that has been used to argue for plate like behavior of the tibetan plateau convergence between ladakh and the indian subcontinent at 18 8 3 mm yr at 224 17 1 differs little from estimates of convergence across the central segment of the himalaya finally lengthening of the baseline between leh ladakh and lhasa in southeastern tibet at 17 8 1 mm yr or between leh and bayi farther to the southeast at 18 3 mm yr is consistent with an extrapolation of rates of east west extension of the tibetan plateau based both on shorter gps baselines e g lhasa simikot and on diverging slip vectors of earthquakes in the himalaya we interpret these results to indicate that tibet behaves more like a fl uid than like a plate

crustal evolution and age of thermotectonic reworking in the western hinterland of the trans hudson orogen northern saskatchewan abstract the hearne province in northern saskatchewan forms the western hinterland of the trans hudson orogen it is a fault bounded terrane lying structurally and geographically between the rae province to its west and the wathaman batholith and orogenic internides to its east the hearne province is comprised primarily of high grade metamorphic archean rocks structurally overlain by archean or proterozoic metasedimentary rocks and intruded by paleoproterozoic granites whereas the rae terrane on its west boundary is comprised primarily of still higher grade archean rocks the calc alkaline wathaman batholith was intruded at ca 1 855 ga and the orogenic internides to the east of it include mostly high grade mafic and intermediate volcanic rocks crystallized between 1 92 and 1 86 ga terminal collision and orogenesis in the internides have been constrained to be later than 1 82 ga and earlier than 1 78 ga mineral u pb data presented here unequivocally demonstrate that high grade metamorphism and large volume anatexis across the southern hearne province were approximately synchronous with terminal collision and high grade metamorphism across the trans hudson orogen zircon data for most samples form complex arrays in concordia space but demonstrate a high grade metamorphic overprint at 1810 1800 ma zircons typically have inherited components of archean age suggesting the presence of extremely old material in the hearne and a potential archean connection with the rae province sm nd data indicating ca 3500 ma model ages for similar parageneses in both terranes further support the proposed archean connection between hearne and rae province and the great antiquity of hearne crust sm nd data also elucidate the similarity of the ca 1 80 ga anatectic granites of the hearne to the 1 82 ga junction granite which intruded the virgin river shear zone and constrains the timing of final motion on that structure monazite 207 pb 206 pb ages are not older than 1812 ma or younger than 1769 ma and rutile 207 pb 206 pb ages and u pb ages are tightly constrained at about 1750 ma these data in combination with results of standard thermobarometric analysis permit determination of post orogenic cooling and denudation rates high cooling 7 c ma and denudation 240 m ma rates suggest fault accomodated uplift during post orogenic collapse

thermochronologic constraints on the late cenozoic exhumation history of the gurla mandhata metamorphic core complex southwestern tibet how the tibetan plateau is geodynamically linked to the himalayas is a topic receiving considerable attention the karakoram fault plays key roles in describing the structural relationship between southern tibet and the himalayas in particular considerable debate exists at the southeastern end of the karakoram fault where its role is interpreted in two different ways one interpretation states that slip along the dextral karakoram fault extends eastward along the indus yalu suture zone bypassing the himalayas the other interprets that fault slip is fed southward into the himalayan thrust belt along the gurla mandhata detachment gmd to evaluate these competing models the late miocene history of the gmd was reconstructed from thermokinematic modeling of zircon u th he data three east west transects reveal rapid cooling of the gmd footwall from 8 0 1 3 ma to 2 6 0 7 ma model simulations show a southward decrease in slip magnitude and rate along the gmd in the north initiation of the gmd range between 14 and 11 ma with a mean fault slip rate of 5 0 0 9 mm yr the central transect shows an initiation age from 14 to 11 ma with a mean fault slip rate of 3 3 0 6 mm yr in the south initiation began between 15 and 8 ma with a mean fault slip rate of 3 2 1 6 mm yr the initiation ages and slip rates match the karakoram fault across several timescales supporting the idea that the two are kinematically linked specifically the data are consistent with the gmd acting as an extensional stepover with slip transferred southward into the himalayas of western nepal

present day crustal deformation in china constrained by global positioning system measurements global positioning system gps measurements in china indicate that crustal shortening accommodates most of india s penetration into eurasia deformation within the tibetan plateau and its margins the himalaya the altyn tagh and the qilian shan absorbs more than 90 of the relative motion between the indian and eurasian plates internal shortening of the tibetan plateau itself accounts for more than one third of the total convergence however the tibetan plateau south of the kunlun and ganzi mani faults is moving eastward relative to both india and eurasia this movement is accommodated through rotation of material around the eastern syntaxis the north china and south china blocks east of the tibetan plateau move coherently east southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year respectively with respect to the stable eurasia

rift flank uplift in tibet evidence for a viscous lower crust analysis of high resolution digital topography across 21 plio pleistocene grabens in central and southern tibet shows that high topography occurs along the graben margins profiles across these marginal highlands fit curves describing the flexure of an elastic plate under vertical loading we interpret the features as flexural rift flank uplifts resulting from regional isostatic compensation of low density grabens the short wavelengths of the uplifts 30 40 km imply a low flexural rigidity for the plateau d 2 6 1020 n m similar to values inferred for the basin and range of western north america in addition the grabens themselves are extremely narrow compared to typical continental rifts taken together these observations suggest the existence of a low viscosity lower crust and suggest that isostatic compensation is taking place within this ductile lower crust simple channel flow calculations suggest that crustal viscosities below 1022 pa s are necessary to accommodate this compensation over reasonable timescales

reconstruction of the deformed collision zone between india and asia by backward motion of lithospheric blocks 1 on the basis of a synthesis of tectonic data available on the india asia collision we present a first attempt to reconstruct the evolution of the collision zone assuming that the deformation of the lithosphere is localized along narrow shear zones and that the interiors of mantle blocks in between remain relatively undeformed we define block contours from the fault pattern and move back the blocks along their boundary faults along convergent or extensional boundaries the crust is assumed to shorten or stretch coherently step by step we go backward in time to finally reach the collision onset for each time step we find a solution compatible with the data set available and the position of the adjacent blocks for each block the search for compatibility at the scale of the entire collision zone allows for solving the kinematics of regions with fewer data and suggests plausible scenarios for regions where data is lacking for each step we calculate large scale displacement maps and determine euler poles for each block for the most recent time step the map proposed is compared to gps motions the deformation budget implies that extrusion absorbed 30 of the convergence between india and siberia during the entire collision span but varied with time accounting for as little as 3 or as much as 60 of this convergence at different epochs

oxygen and carbon isotope patterns archived in shells of the aquatic gastropod radix hydrologic and climatic signals across the tibetan plateau in sub monthly resolution abstract the tibetan plateau tp including its surrounding mountain ranges represents the largest store of ice outside the polar regions it hosts numerous lakes as well as the head waters of major asian rivers on which billions of people depend and it is particularly sensitive to climate change the moisture transport to the tp is controlled by the indian and pacific monsoon and the westerlies understanding the evolution of the interaction of these circulation systems requires studies on climate archives in different spatial and temporal contexts the objective of this study is to learn more about the interannual variability of precipitation patterns across the tp and how different hydrologic systems react to different climatic factors aragonite shells of the aquatic gastropod radix which is widely distributed in the region may represent suitable archives for inferring hydrologic and climatic signals in particularly high resolution therefore sclerochronological studies of 18 o and 13 c ratios in radix shells from seven lakes were conducted each representing a different hydrologic and climatic setting on a transect from the pamirs across the tp the shell patterns exhibit an increasing influence of precipitation and a decreasing influence of evaporation on the isotope compositions from west to east 18 o values of shells from lakes on the eastern and central tp donggi cona yamdrok yumco tarab co mirror monsoon signals indicated by more negative values and higher variabilities compared to the more western lakes karakul bangong nyak manasarovar in yadang co located on the central southern tp the monsoon rains did not reach the lake in the sampling year although it is located in a region which is usually affected by monsoon circulation the 18 o values are used to differentiate the annual hydrological cycle into ice cover period melt water period precipitation period and evaporation period 13 c compositions in the shells particularly depend on specific habitats which vary in biological productivity and in carbon sources 18 o and 13 c patterns show a positive covariance in shells originating from large closed basins the results show that radix shells mirror general climatic differences between the seven lake regions these differences reflect both regional and local climate signals in sub seasonal resolution without noticeable dependence on the particular lake system

mesozoic and cenozoic tectonic evolution of the shiquanhe area of western tibet 1 in the shiquanhe area of far western tibet mid cretaceous strata lie unconformable on ophiolitic melange and jurassic flysch associated with the bangong nujiang suture zone on the basis of our mapping and geochronologic studies we suggest that these cretaceous strata were shortened by 57 over a north south distance of 50 km during late cretaceous early tertiary time the late cretaceous narangjiapo thrust placed permian strata 20 km over ophiolitic melange and cretaceous strata north of the narangjiapo thrust 40 km of shortening was accommodated by the late cretaceous early tertiary south directed jaggang thrust system that involves jurassic flysch and cretaceous strata and roots into a decollement within ophiolitic melange the most recent shortening was accommodated to the south of the narangjiapo thrust along the north dipping shiquanhe thrust the shiquanhe thrust cuts flat lying 22 6 0 3 ma volcanic rocks and underlying folded tertiary nonmarine strata in its footwall and was likely active during slip along the oligocene gangdese thrust system of southern tibet ophiolitic melange and structurally overlying jurassic flysch near shiquanhe are interpreted to represent remnants of a subduction accretion complex and forearc basin respectively that were obducted southward onto the margin of the lhasa terrane during late jurassic early cretaceous closure of the bangong nujiang ocean subsequent imbrication of the obducted sheet could have produced the two east west trending belts of ophiolitic melanges separated by 100 km in western tibet late cretaceous early tertiary thin skinned shortening may have been accommodated in the deeper crust by northward underthrusting and duplexing of lhasa terrane rocks beneath the obducted ophiolitic melange and the qiangtang terrane to the north

the evolution of yarlung tsangpo river constraints from the age and provenance of the gangdese conglomerates southern tibet abstract cenozoic conglomerates are exposed discontinuously along the length of the yarlung tsangpo suture zone on the southern margin of the gangdese arc these conglomerates the gangdese conglomerates herein record a crucial stage in the uplift and erosion histories of the southern tibet after the initial india asia collision in the mt kailas area the gangdese conglomerates strata consist of multiple sedimentary cycles and each cycle is a fining upward sequence that was deposited by alluvial fan braided river and delta systems whereas in the xigaze area the gangdese conglomerates strata comprise a coarsening upward sequence that was deposited by delta braided river and alluvial fan systems based on the detrital and igneous zircon u pb ages the depositional ages of the gangdese conglomerates are late oligocene to early pliocene ca 26 5 ma in the mt kailas area late oligocene to middle miocene ca 26 15 ma in the xigaze area and late oligocene to early miocene ca 26 19 ma in the zedong area paleocurrent measurements and provenance data i e conglomerate clast composition sandstone petrology and detrital zircon age indicate that the initial detritus of the gangdese conglomerates were entirely derived from the north mainly from the gangdese arc sediment resulting from denudation to the south the xigaze forearc basin the yarlung tsangpo suture zone and the northern margin of the indian plate first appeared by the early miocene ca 19 ma and subsequently increased in abundance gradually our new results together with previous data from the xigaze area reveal 3 major stages in the evolution of the yarlung tsangpo river system 1 the southward flowing stage ca 26 19 ma featured southward draining transverse rivers that transported materials from the gangdese arc southward southward paleocurrents in the gangdese conglomerates indicate a northern source 2 the westward flowing stage ca 19 15 ma developed due to the uplift of the suture zone and tethys himalaya to the south northward draining rivers began to develop and lakes resembling a string of beads formed and finally connected together initiating the westward flowing paleo yarlung tsangpo river westward paleoflows were recorded in the gangdese conglomerates 3 the eastward flowing stage ca 15 ma present resulted from differential uplift and denudation of the southern tibet which reversed the direction of the young yarlung tsangpo river by ca 15 ma the deposition of the gangdese conglomerates was controlled by eastward paleoflows at this point the modern eastward flowing yarlung tsangpo river system was established

spatially constant slip rate along the southern segment of the karakorum fault since 200 ka abstract determining the slip rate history along the right lateral karakorum fault kf is fundamental to understanding its present day kinematic role in the deformation of tibet geodetic and geologic studies suggest slip rates of 0 11 mm yr along this structure whether slip rate variability exists along strike and or time or simply results from different measuring techniques timescales remains unknown in order to constrain slip rates within a timescale of 200 ka we studied fluvial and glacial geomorphic features that are right laterally or vertically offset by the fault by varying amounts from 7 1 m to 430 30 m and up to 53 5 m respectively we constrained their ages using 10be surface exposure dating on 141 quartz rich samples collected on 4 lateral moraines and at 3 alluvial sites along the southernmost segment of the kf menshi kailas basin and along the gurla mandhata detachment fault in the pulan graben from the 30 fault bend at baer 80 5 e to mount kailas area the slip rate along the kf is 7 1 3 2 1 7 mm yr at menshi and 7 9 3 2 2 5 mm yr at kailas slip on two parallel fault strands in the pulan graben the normal fault slip rate is 1 6 0 4 0 3 mm yr our data suggest that the quaternary slip rate along the southern kf does not decrease eastward but is constant along strike for at least 200 km from 5 11 mm yr in the gar basin further north to 7 8 mm yr in the menshi kailas basin because no expected along strike slip rate gradient is observed it implies that the kf does not end at the kailas but must extend where the slip rate decreases i e eastward along the yarlung zangbo suture and southward along the gurla mandhata humla fault system

geochemical isotopic and geochronlologic constraints on the formation of the eagle point basement hosted uranium deposit athabasca basin saskatchewan canada and recent remobilization of primary uraninite in secondary structures the athabasca basin hosts many world class unconformity related uranium deposits recently uranium reserves for the eagle point basement hosted deposit have increased with the discovery of new mineralized zones within secondary structures a paragenetic study of eagle point reveals the presence of three temporally distinct alteration stages a pre athabasca alteration a main alteration and mineralization comprised of three substages and a post main alteration and mineralization stage that culminated in remobilization of uraninite from primary to secondary structures the pre athabasca alteration stage consists of minor amounts of clinochlore followed by dolomite and calcite alteration in the hanging wall of major fault zones and kaolinitization of plagioclase and k feldspar caused by surface weathering the main alteration and uranium mineralization stage is related to three temporally distinct substages all of which were produced by isotopically similar fluids a major early alteration substage characterized by muscovite alteration and by precipitation ca sr lree rich aluminum phosphate sulfate minerals both from basinal fluids at temperatures around 240 c prior to 1 600 ma the mineralization substage involved uraninite and hematite precipitated in primary structures the late alteration substage consists of dravite uranophane beta veins calcite veins and sudoite alteration from mg ca rich chemically modified basinal fluids with temperatures around 180 c the post main alteration and mineralization stage is characterized by remobilization of main stage uraninite from primary to secondary structures at a minimum age of ca 535 ma u pb resetting events recorded on primary and remobilized uraninites are coincident with fluid flow induced by distal orogenies remobilizing radiogenic pb to a distance of at least 225 m above the mineralized zones

the obliquely convergent plate boundary in the south island of new zealand implications for ancient collision zones abstract the alpine fault of new zealand forms the western boundary of a zone of distributed deformation formed by the oblique convergence of continental crust belonging to the pacific and australian plates structural and geodetic data from the alpine fault show that a large proportion of the total plate displacement is accommodated by rapid oblique slip on the fault the remaining displacement is distributed over a 200 km wide zone to the east the collision may be modelled as a two sided deforming orogen with the partitioning of deformation being controlled by erosional differences between the narrow high strain inboard and broad low strain outboard sides in ancient collision zones little evidence may remain of the nature and amount of displacement on the inboard side partitioning of deformation among pre existing structures complicates interpretation of the outboard zone radiometric ages may post date collision by several tens of millions of years and indicate slow isostatic uplift and unroofing collision ages if preserved may be recognized by high uplift rates calculated from muscovite biotite pairs

structural complexity resulting from pervasive ductile deformation in the karakoram shear zone ladakh nw india 1 the nw se trending 800 km long dextral karakoram shear zone bounds southwest tibet we investigate an area immediately nw of the pangong lake where midcrustal rocks sections of the shear zone are exposed here the dominant shear zone is characterized by dextral mylonitic rocks sheared at amphibolite facies and partly retrogressed to greenschist facies these rocks define a kilometric se plunging inclined to recumbent fold in the footwall of a north directed oblique dextral thrust that exhumed anatectic rocks of the pangong range argon cooling ages reveal that the pangong range cooled from 700 c to 300 c between 18 15 and 10 ma contemporaneously with overthrusting toward the se closer to the pangong lake this kilometric fold is rotated from its nw se trend to an e w trend and the sense of shear changes to sinistral with a broadly north directed thrusting component the documented structures contradict predictions of normal movement in this area derived from considerations of rigid block behavior of the crust and support the interpretation that the system records dextral transpression thrusting and exhumation of the deeper and hot rocks exposed in the pangong range folding of the thrust footwall and the development of a sinistral e w trending shear zone are all compatible with transpression caused by a northward push by a rigid indenter such as the ladakh batholith

distributed deformation in southern and western tibet during and after the india asia collision field and radiometric data are used to describe and date strain and stress states in southern longitude 88 o to 91oe latitude 28 o to 30on and western tibet longitude 79 o to 82oe latitude 30 o to 34on we factorize deformation into syncollisional and postcollisional and we present stretching lineation and displacement orientation maps two sections across the indian shelf sequence and stress orientations calculated from mesoscale fault slip data in southern tibet syncollisional stretching and displacement directions trend 90 46 o and displacement is top to south synkinematic low grade metamorphism is dated at 50 ma at one locality in the indian shelf sequence underlying the main mantle thrust of the indus yarlung suture this implies paleocene onset of continental collision for the investigated section postcollisional structures comprise a backthrust group which includes foreland and hinterland directed thrusts reverse and strike slip faults and folds it dominates postcollisional deformation is concentrated along the indus yarlung suture and portrays n s compression otrend of 8o 17 o o2 of 97o 17o a strike slip group consists of conjugate strike slip faults is concentrated in east trending narrow highly deformed zones and indicates that n s compression is locally compensated by e w extension oof 15o 29 o o3 of 103o 30o synkinematic muscovite dates postcollisional deformation as late early miocene 17 5 ma at one locality at the suture strike slip and oblique normal 03 of 600 23 o oof 144o 21 o and normal o3 114o 16 o faulting dated between late miocene and recent and including active deformation represents dominant e w and minor n s extension due to e w stretching of southern tibet and oroclinal bending along the himalayan arc restoring syncollisional and postcollisional deformation yields a minimum of 67 258 km shortening across the indian shelf sequence incorporating recently published contraction estimates across the eastern himalaya yields minimum shortening between undeformed india and the indus yarlung suture of 66 536 km the himalaya tibet orogenic system south of the indus yarlung suture had an initial width of 811 km in the southern tibetan section in western tibet imbrication of an ophiolite sequence of the bangong nujiang suture is top to south stretching lineation trend of 15o 18o and o3 of active deformation trends ese faulting along the shiquanhe fault zone which transfers displacement from the northern part of the karakorum fault to a system of rifts in western central tibet indicates dextral strike slip alternating with sinistral oblique normal faulting and block rotations around vertical axes during a prolonged shearing history the indian shelf sequence south of mount kailas shows top to south imbrication stretching lineation trend of 52o 60o both indian shelf rocks and oligocene miocene kailas conglo merates record backthrusting and backfolding oof 33 o and recent e w extension 03 of 85o 28o

sinistral strike slip shearing along the jiali shear zone around the eastern himalaya syntaxis region evidences for oligocene eastward limited translation of tibet abstract in and around the eastern himalaya syntaxis ehs the metamorphic complex and its structural boundaries are key tectonics to investigate the kinematics and thermal evolution of the continental collision we provide new structural kinematic and geochronological data along the northeastern boundary of the ehs namely the jiali strike slip shear zone structures and various kinematic indicators record sinistral strike slip shearing in the zone based on the microstructural features crystallographic preferred orientation patterns of quartz and their slip systems coupled with raman spectroscopy of carbonaceous materials rscm geothermometry the ductile sinistral shearing fabrics formed at upper greenschist and amphibolite facies 500 c two hornblende one muscovite and five biotite separates from the mylonites in the shear zone were dated by the 40ar 39ar method a hornblende plateau age of 23 7 ma is interpreted as representing or being close to the time of sinistral movement muscovite and biotite 40ar 39ar ages from 22 9 to 16 9 ma represent cooling ages following sinistral shearing it is concluded on the basis of these data that the jiali sinistral strike slip shear zone was active in latest oligocene this sinistral movement on the jiali shear zone is considered to link with the ailao shan red river shear zone and form a unique continuous structural boundary around the ehs the jiali ailao shan red river sinistral shear zone and gaoligong dextral shear zone formed a huge conjugate strike slip shear pair around the ehs to accommodate the n s shortening corresponding to northward indentation of the folded indian continent the conjugate strike slip shear systems also contribute to transporting tibet southeastward in a limited scale

mesozoic cenozoic geological evolution of the himalayan tibetan orogen and working tectonic hypotheses the himalayan tibetan orogen culminated during the cenozoic india asia collision but its geological framework and initial growth were fundamentally the result of multiple previous ocean closure and intercontinental suturing events as such the himalayan tibetan orogen provides an ideal laboratory to investigate geological signatures of the suturing process in general and how the earth9s highest and largest orogenic feature formed in specific this paper synthesizes the triassic through cenozoic geology of the central himalayan tibetan orogen and presents our tectonic interpretations in a time series of schematic lithosphere scale cross sections and paleogeographic maps we suggest that north dipping subducting slabs beneath asian continental terranes associated with closure of the paleo meso and neo tethys oceans experienced phases of southward trench retreat prior to intercontinental suturing these trench retreat events created ophiolites in forearc extensional settings and or a backarc oceanic basins between rifted segments of upper plate continental margin arcs this process may have occurred at least three times along the southern asian margin during northward subduction of neo tethys oceanic lithosphere from 174 to 156 ma 132 to 120 ma and 90 to 70 ma at most other times the tibetan terranes underwent cordilleran style or collisional contractional deformation geological records indicate that most of northern and central tibet the hoh xil and qiangtang terranes respectively were uplifted above sea level by jurassic time and southern tibet the lhasa terrane north of its forearc region has been above sea level since 100 ma stratigraphic evidence indicates that the northern himalayan margin of india collided with an asian affinity subduction complex forearc arc system beginning at 60 ma both the himalaya composed of indian crust and tibet show continuous geological records of orogenesis since 60 ma as no evidence exists in the rock record for a younger suture the simplest interpretation of the geology is that india asia collision initiated at 60 ma plate circuit paleomagnetic and structural reconstructions however suggest that the southern margin of asia was too far north of india to have collided with it at that time seismic tomographic images are also suggestive of a second more southerly neo tethyan oceanic slab in the lower mantle where the northernmost margin of india may have been located at 60 ma the geology of tibet and the india asia suture zone permits an alternative collision scenario in which the continental margin arc along southern asia the gangdese arc was split by extension beginning at 90 ma and along with its forearc to the south the xigaze forearc rifted southward and opened a backarc ocean basin the rifted arc collided with india at 60 ma whereas the hypothetical backarc ocean basin may not have been consumed until 45 ma a compilation of igneous age data from tibet shows that the most recent phase of gangdese arc magmatism in the southern lhasa terrane initiated at 70 ma peaked at 51 ma and terminated at 38 ma cenozoic potassic adakitic magmatism initiated at 45 ma within a 200 km wide elliptical area within the northern qiangtang terrane after which it swept westward and southward with time across central tibet until 26 ma at 26 to 23 ma potassic adakitic magmatism swept southward across the lhasa terrane a narrow 20 km width orogen parallel basin developed at low elevation along the axis of the india asia suture zone the kailas basin and greater himalayan sequence rocks began extruding southward between the south tibetan detachment and main central thrust the kailas basin was then uplifted to 4 km elevation by 20 ma after which parts of the india asia suture zone and gangdese arc experienced 6 km of exhumation between 20 and 16 ma between 16 and 12 ma slip along the south tibetan detachment terminated and east west extension initiated in the northern himalaya and tibet potassic adakitic magmatism in the lhasa terrane shows a northward younging trend in the age of its termination beginning at 20 to 18 ma until volcanism ended at 8 ma we interpret the post 45 ma geological evolution in the context of the subduction dynamics of indian continental lithosphere and its interplay with delamination of asian mantle lithosphere

fault terminations and barriers to fault growth abstract field observations of strike slip faults in jointed granitic rocks of the central sierra nevada california combined with a mechanical analysis of fault interaction provide insight into how fault terminations vary with scale we document here a strike slip fault system 2 3 km long clustered about the west end of the fault system are several dozen faults that parallel the three main fault zones in the system we interpret this cluster of small faults as a barrier that inhibited growth of fault zones in the fault system a two dimensional mechanical analysis shows that a cluster of small faults flanking the tip of a large fault zone will tend to diffuse the stress concentration near the fault zone tip an analogous effect in engineering is known as crack tip shielding near tip stress concentrations promote fault growth and processes that decrease these stress concentrations inhibit fault growth as faults lengthen and grow they interact with features at greater distances and over a broader area so the potential for tip shielding effects will increase as fault length increases this effect can account for why the mechanisms and character of fault terminations would tend to vary as a function of scale

active displacement transfer and differential block motion within the central walker lane western great basin velocities determined for 50 global positioning system sites within the central walker lane indicate differential motion among tectonic blocks forming a boundary zone between the great basin extensional province and the sierra nevada the velocity field is related to displacement transfer from the owens valley and furnace creek fault systems of east ern california to transtensional structures of the walker lane and extensional faults of the central nevada seismic belt block boundaries are sharp and appear to be inherited from pre tertiary crustal structure the block geometries exert strong influence on dif ferential displacements concentrated along boundaries as belts of divergent transcurrent and convergent motion the aggregate velocity accounts for about 25 of the relative motion between the pacific and north american plates about 5 mm yr of the motion is localized along the eastern margin of the sierra nevada whereas about 10 mm yr is stepped 100 km east along a belt of east northeast trending transtensional faults that merge with northwest trending transcurrent structures of the walker lane about 6 mm yr of the velocity field is transferred to north northeast trending extensional faults of the central nevada seismic belt the heterogeneous distribution of motions is consistent with partitioning of a regional velocity field formed by westward extension and n408w directed shear

brine rock interaction in the athabasca basement mcarthur river u deposit canada consequences for fluid chemistry and uranium uptake terra nova 22 303 308 2010 abstract the nature of uranium source rocks transport conditions and deposition processes are still highly controversial for world class unconformity related u deposits this article presents the first detailed chemistry of brines associated with the giant mcarthur river u deposit canada la icp ms analysis of individual fluid inclusions suggests mixing between a na ca mg k sr ba brine and a ca mg na k sr ba brine the brines share a common origin evaporated seawater and show evidence for contrasting interaction with basement rocks the na rich brine lost mg and k in alteration haloes around u ores while the ca rich brine results from na ca exchange and sr ba gain u concentrations 0 3 530 g g 1 are anomalously high compared with usual basinal fluids this indicating that u uptake occurred within basement rocks the two brine end members have mixed within the main u deposit area which could be one of the major driving forces for u deposition

mineral chemistry and oxygen isotopic analyses of uraninite pitchblende and uranium alteration minerals from the cigar lake deposit saskatchewan canada abstract the cigar lake unconformity type u deposit is one of the largest and highest grade u deposits in the proterozoic athabasca basin northern saskatchewan canada cigar lake has recently been the focus of an international 3 a collaborative program in which this u deposit was studied as a natural analogue for a spent nuclear fuel repository the deposit is located near the eastern margin of the athabasca basin 430 m below the surface at the intersection between hudsonian age faults and the unconformity between athabasca group sandstones and aphebian metasediments three stages of u mineralization have been identified based on cross cutting relationships and textures observed in thin section and back scattered electron bse images o isotope data and chemical compositions all stages of u mineralization have been variably altered to ca rich u hydrate minerals or uranyl oxide hydrate minerals and coffinite u pb chemical ages of the 3 stages of u mineralization from cigar lake coincide with the 3 major fluid events that precipitated clay and silicate minerals at 1500 ma 950 ma and 300 ma throughout the entire athabasca basin stage 1 and 2 uraninite and pitchblende have the lowest 18o values that range from 30 1 to 15 2 whereas stage 3 uraninite has 18o values ranging from 10 0 to 3 4 uranyl oxide hydrate minerals have 18o values that range from 11 3 to 8 2 whereas uranyl minerals have much higher 18o values based on u pb chemical ages 18o values and petrographic relationships of u alteration minerals associated with primary u mineralization the cigar lake u ore is similar to u ore from other unconformity type u deposits in the athabasca basin therefore the cigar lake ore deposit although surrounded by clay and sandstone barriers has been effected by the same fluid events that have altered other unconformity type u deposits in the athabasca basin the 3 stages of ore formation and associated alteration minerals permit the detailed study of fluids responsible for u deposition and alteration this information provides the necessary context for the evaluation of the cigar lake deposit as a natural analogue for the disposal of spent nuclear fuel in underground vaults in rocks of the canadian shield

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

palaeoclimatic interpretation of a topographic profile across middle holocene regressive shorelines of longmu co western tibet most lakes and closed basins in tibet are surrounded by abandoned shorelines attesting for high water levels in the past two such lakes longmu co and sumxi co western tibet were the focus of detailed palaeoclimatic work during the 1989 sino french expedition based on the study of lake sediments and analysis of a piston core here it is shown that additional information may be deduced from the abandoned shorelines around longmu co a 1800 m long topographic profile was levelled from 75 m up to 230 m above the present lake elevation 5008 m on which the shorelines form a flight of horizontal terraces separated by more or less degraded scarps the elevations of the terraces were spaced regularly about 1 35 m except for 3 5 m high lacunae reccurring every 15 16 m the potential annual evapo transpiration was computed based on meteorological data collected at tien shui hai from 13 08 89 to 11 09 90 using a modified penman formula a value of 1 60 0 3 m yr was obtained under close system conditions no outlet and a synthetic curve of lake regression was derived which appears to be consistent with the measured shoreline heights it is concluded that the 1 35 m terraces represent annual regression of the lake level by contrast the 3 5 m high lacunae might reflect the periodic return about every 9 12 yr of particular climatic conditions responsible for a perturbation of the annual process of shoreline formation all the shorelines of this profile have formed probably within one century during a continuous and abrupt regression of the lake such evolution has also been identified in the sediments of a piston core collected at sumxi co and dated at about 6 5 5 kyr b p the lake level must have been at its highest stand shortly before that major regression the mechanism responsible for this middle holocene high stand and for the major sudden drop of the lake level remains uncertain

role of the brittle ductile transition on fault activation abstract we model a fault cross cutting the brittle upper crust and the ductile lower crust in the brittle layer the fault is assumed to have stick slip behaviour whereas the lower ductile crust is inferred to deform in a steady state shear therefore the brittle ductile transition bdt separates two layers with different strain rates and structural styles this contrasting behaviour determines a stress gradient at the bdt that is eventually dissipated during the earthquake during the interseismic period along a normal fault it should form a dilated hinge at and above the bdt conversely an over compressed volume should rather develop above a thrust plane at the bdt on a normal fault the earthquake is associated with the coseismic closure of the dilated fractures generated in the stretched hangingwall during the interseismic period in addition to the shear stress overcoming the friction of the fault the brittle fault moves when the weight of the hangingwall exceeds the strength of the dilated band above the bdt on a thrust fault the seismic event is instead associated with the sudden dilation of the previously over compressed volume in the hangingwall above the bdt a mechanism requiring much more energy because it acts against gravity in both cases the deeper the bdt the larger the involved volume and the bigger the related magnitude we tested two scenarios with two examples from l aquila 2009 italy and chi chi 1999 taiwan events gps data energy dissipation and strain rate analysis support these contrasting evolutions our model also predicts consistently with data that the interseismic strain rate is lower along the fault segment more prone to seismic activation

geology and thermotectonic evolution of the western margin of the trans hudson orogen evidence from the eastern sub athabasca basement saskatchewan in the cree lake zone of northern saskatchewan reworked archean orthogneisses are overlain by a highly deformed supracrustal sequence the paleoproterozoic wollaston group this package of rocks was deformed and metamorphosed during the ca 1 8 ga continent continent collision of the trans hudson orogen tho forming the wollaston fold thrust belt that underlies the eastern athabasca basin the hudsonian structural metamorphic and magmatic evolution of the wollaston fold thrust belt in the eastern athabasca area involved six major stages 1 early collisional stage dp1 at 1860 1835 ma involved burial of wollaston group metasediments from surface to depths equivalent to 3 5vkbar 1 kbar 100 mpa by thrust pile stacking or imbrication tectonics prograde metamorphism with garnet growth and development of early leucosomes and emplacement of ca 1840 ma grey granite suite 2 collisional stage dp2a at 1835 1820 ma involved continued deeper burial of wollaston group metasediments along a prograde

geometry kinematics and landscape characteristics of an active transtension zone karakoram fault system southwest tibet abstract we investigate the style of active transtensional deformation and characteristics of the landscape along the southern segment of the karakoram fault system through field mapping structural analysis and examination of digital topography srtm aster multi spectral aster landsat 7 and panchromatic corona photography imagery our data suggests that wrench dominated transtension is occurring within a 90 km wide zone simple shear within the zone is accommodated by right lateral r and p shears as well as left lateral r shears vertical shortening is accommodated by north striking extensional shear zones and horizontal shortening is accommodated by east west trending transtension related corrugations drainage divides strike at high angles and subparallel to the transtension zone those that strike at high angles to the zone can be explained by movement along north striking extensional fault systems while the geometry of drainage divides subparallel to the zone are consistent with uplift of corrugations as well as rapid uplift of mountain ranges by normal right slip faulting

u redox fronts and kaolinisation in basement hosted unconformity related u ores of the athabasca basin canada late u remobilisation by meteoric fluids proterozoic basement hosted unconformity related uranium deposits of the athabasca basin saskatchewan canada were affected by significant uranium redistribution along oxidation reduction redox fronts related to cold and late meteoric fluid infiltration these redox fronts exhibit the same mineralogical and geochemical features as the well studied uranium roll front deposits in siliclastic rocks the primary hydrothermal uranium mineralisation 1 6 1 3 ga of basement hosted deposits is strongly reworked to new disseminated ores comprising three distinctly coloured zones a white green zone corresponding to the previous clay rich alteration halo contemporaneous with hydrothermal ores a uranium front corresponding to the uranium deposition zone of the redox front brownish zone rich in goethite and a hematite rich red zone marking the front progression the three zones directly reflect the mineralogical zonation related to uranium oxides pitchblende sulphides iron minerals hematite and goethite and alumino phosphate sulphate aps minerals the zoning can be explained by processes of dissolution precipitation along a redox interface and was produced by the infiltration of cold 50 c meteoric fluids to the hydrothermally altered areas u fe ca pb s ree v y w mo and se were the main mobile elements in this process and their distribution within the three zones was for most of them directly dependent on their redox potential the elements concentrated in the redox fronts were sourced by the alteration of previously crystallised hydrothermal minerals such as uranium oxides and light rare earth element lree rich aps the uranium oxides from the redox front are characterised by lree enriched patterns which differ from those of unconformity related ores and clearly demonstrate their distinct conditions of formation uranium redox front formation is thought to be linked to fluid circulation episodes initiated during the 400 300 ma period during uplift and erosion of the athabasca basin when it was near the equator and to have been still active during the last million years a major kaolinisation event was caused by changes in the fluid circulation regime reworking the primary uranium redox fronts and causing the redistribution of elements originally concentrated in the uranium enriched meteoric related redox fronts

late cenozoic right lateral strike slip faulting in southern tibet field observations collected during the sino french himalaya tibet cooperation project 1980 1982 show that right lateral faulting between southern and northern tibet roughly along the chord joining the eastern and western syntaxes of the himalayan arc is a major component of the active tectonics north of the himalayas just north of the well developed rifts of southern tibet we studied three right lateral 100 200 km long strike slip faults forming an en echelon array along that chord evidence for earthquake surface breaks was found on each of these faults for the m 8 beng co or damxung strike slip earthquake of november 18 1951 rupture parameters could be constrained to be 8 2 m and l 90 km offset glacial and postglacial morphological markers 105 years and 104 years b p imply displacement rates of the order of 1 2 cm yr on the three faults the en echelon fault zone appears to extend westward 2000 km across the plateau to the karakorum fault and is thus referred to as the karakorum jiali fault zone kjfz fast rates of slip on it and on faults along the northern rim of tibet appear to contrast with the slower rates of deformations in the interior of the plateau our estimates of slip rates on the strike slip and normal faults of southeastern tibet suggest that eastward extrusion of north tibet between the right lateral kjfz and the left lateral altyn tagh and kun lun faults absorbs at least 30 of the present convergence between india and asia we propose an instantaneous velocity model of the active tectonics of asia compatible with such faulting rates and geometries evidence for tertiary right lateral strike slip movements in southern tibet and around the eastern syntaxis of the himalayas is also found in the structural record offsets of various large scale geological features imply that these movements have been large

the millennium uranium deposit athabasca basin saskatchewan canada an atypical basement hosted unconformity related uranium deposit the millennium uranium basement hosted unconformity related deposit is one of the most recent discoveries of basement hosted deposits and may hold as much as 46 8 million pounds 18 000 metric tonnes u at an average grade of 4 53 percent u3o8 the alteration zone associated with the deposit is atypical as it consists predominantly of muscovite rather than the chlorite and muscovite commonly found in the other basement hosted deposits of the athabasca basin the preore stage consists of early minor clinochlore alteration at temperatures of about 275 c interpreted to result from retrograde metamorphism of the basement rocks prior to the deposition of the athabasca basin this clinochlore event is followed by an extensive 1mc muscovite alteration of the basement rocks by na k fe rich basinal brines at temperatures of about 250 c creating up to 25 percent void space in the basement rocks subsequently a weak chamoisite alteration resulted from fe mg ca rich fluids with temperatures of about 300 c that evolved from reactions between the basinal brines and the basement rocks ore stage uraninite has an extrapolated chemical age of 1590 ma and is contemporaneous with synore 1mc muscovite and iron oxide deposited at temperatures near 250 c from fluids with similar 18o but lower d values to preore basinal fluids the low d values indicate postdepositional exchange of h isotopes with cenozoic fluids postore alteration consists of dravite and sudoite precipitated from mg ca rich fluids from the same evolved basinal brines that precipitated preore chamoisite at temperatures of about 185 c filling voids created during the preore stage our results indicate that the pre and synore minerals were formed dominantly by basinal fluids with no contribution from basement fluids which differ from some other basement hosted deposits in the athabasca basin where basement derived fluid influx was more significant several u pb and ar ar resetting events recorded on preore muscovite and on uraninite are coincident with fluid flow induced by distal orogenies remobilizing radiogenic pb from the deposit the radiogenic pb remobilization events were not widespread as the presence of radiogenic pb is restricted to basement rocks proximal to the deposit and along the unconformity

hydrothermal alteration of monazite in the precambrian crystalline basement of the athabasca basin saskatchewan canada implications for the formation of unconformity related uranium deposits microanalytical studies of basement rocks below the athabasca sandstone basin indicate that monazite is the dominant uranium bearing mineral in the study area drill core samples of hydrothermally altered basement show that monazite is commonly altered to a th silicate phase and uranium has been significantly mobilized on average 75 of the uranium bound to monazite is leached out during monazite alteration in contrast no substantial mobilization of uranium from detrital minerals e g zircon has yet been observed in the athabasca sandstones it is suggested that hydrothermal alteration of granitic rocks especially potassic pegmatoids and potassic orthogneisses of the sub athabasca basement represents the most important uranium source for the unconformity type deposits

structural evolution of the neogene gar basin western tibet implications for releasing bend development and drainage patterns we investigated the interaction among basin bounding faults basin fi ll and geomorphic features of the southern gar basin one of only two known releasing double bend basins along the karakoram fault to better understand their structural evolution and role in basin development the southern gar basin is bounded by an 44 km long n20 wstriking central fault segment fl anked by two n40 w striking segments that parallel the regional strike of the karakoram fault system the central fault segment is composed of a system of strike slip and normal faults that young basinward and incorporate basin fi ll in their uplifted footwalls the oldest faults along the extensional portion of the bend are dominantly strike slip and they strike 15 w from the main strike of the karakoram fault basin fi ll is broadly folded about a nnwtrending axis and can be explained by e se directed slip along a listric normal fault cross sections across the basin and associated faults suggest the geometry is best described as an extensional fl ower structure forward structural modeling of the intrabasinal faults shows that the system has accommodated 8 km of east west extension we interpret the bend to have formed from linking of r and p shears into a through going principal displacement zone at shallow levels in the crust low confi ning pressures r shears are exploited at deeper levels these faults merge with the principal displacement zone forming the extensional fl ower structure geometry we estimate that the shear zone is 50 35 km wide based on the aerial distribution of p and r shears restoration of r shears on the west and east sides of the gar valley indicates 55 km of right lateral separation along the karakoram fault which is a minimum slip estimate for the karakoram fault system

conjugate strike slip faulting along the bangong nujiang suture zone accommodates coeval east west extension and north south shortening in the interior of the tibetan plateau this is the published version copyright 2002 american geophysical union all rights reserved

3d computational shape and cooling process modeling of magmatic intrusion and its implication for genesis and exploration of intrusion related ore deposits an example from the yueshan intrusion in anqing china abstract computational modeling is a promising method for investigating the spatial topographic characteristics and geodynamic processes of complex geological systems involving irregularly shaped geological bodies the ore deposits in the anqing orefield are of skarn type and show close association with the cooling process of the irregularly shaped intrusion yueshan intrusion in this paper we apply the methods of 3d geometric shape and geodynamic process modeling to investigate the yueshan intrusion related mineralization systems in the anqing orefield china we have developed a c program to transform a 3d geometric solid model to the 3d geodynamic discrete model for simulating the geodynamic process of irregular geological bodies the 3d geometric shape modeling is used to simulate the spatial and topographic features of the yueshan intrusion and its association with the cu orebodies while the geodynamic modeling is used to reconstruct the cooling process of the intrusion and to investigate the controlling mechanism of intrusion on orebodies the modeling results demonstrate that the orebodies are located in some specific places where the intrusion boundary is concave and in contact with its carbonate rocks these mineralized zones are also the high dilation zones where the fluids from different sources are focused as a result of the coupled mechano thermo hydrological mth processes during the syn extensional cooling of the intrusion the modeling results provide a useful guide for selecting further exploration targets which has led to the discovery of a new mineralization zone in dilation zones close to the intrusion contact

structural controls on fluid flow during compressional reactivation of basement faults insights from numerical modeling for the formation of unconformity related uranium deposits in the athabasca basin canada the unconformity related uranium deposits in the athabasca basin canada are generally associated with reactivated basement faults crosscutting the basin basement unconformity two dimensional 2 d numerical modeling of coupled compression and fluid flow in a reverse fault system was carried out with varying dip angles preexisting offsets and degrees of deformation the results indicate that the fluid flow pattern associated with structural reactivation is sensitive to the degree of bulk shortening at a low bulk shortening stage fluid is driven up along the fault zone into the sandstone in the basin whereas at a relatively high bulk shortening stage fluid tends to flow down into the fault zone and the basement this is interpreted to indicate that the fluid pressure within the fault zone increases at the early stage of deformation due to pore volume decreases in relation to shortening whereas the fluid pressure within the fault zone decreases at later stages of deformation due to dilation in relation to fracturing and reverse displacement variation of the dip angles and preexisting offsets of the faults shows little effect on the strain distribution and fluid flow patterns the simulation results demonstrate that both unconformity contact and basement hosted orebodies may be generated at different stages of deformation within the same fault system under a unified compressional stress regime

structural constraints and numerical simulation of strain localization in the bendigo goldfield victoria australia strain localization and fluid flow patterns adjacent to the massive quartz hosted reefs of the bendigo gold field have been investigated using new structural observations three dimensional geometry of fold fault relationships and gold distribution quartz reef and vein formation in the bendigo goldfield is associated with an initial e w compression event that produced a penetrative upright cleavage and n s trending fold hinges in the immediate hanging wall of quartz reefs with high gold grades the s1 cleavage is locally deformed by an e w trending s2 cleavage that is attributed to a low strain n s oriented compressive event further evidence of this low strain event is provided by gently s plunging quartz carbonate slickenline lineations on s1 cleavage surfaces and the reef margin surfaces and visible gold within the outer portions of the reef the reefs are commonly situated on or immediately to the south of a left flex sinistral change in strike of the axial surface of the folds and the flexure occurs close to an anticlinal culmination defined by the double plunging n s striking folds the folds become deformed with meter to decimeter wavelengths which generally affect the stiff units in a disharmonic style accompanying this is a reactivation of reef margins by oblique slip and the formation of dilational sites and tensional vein arrays that provide the conduits for fluid flow and gold deposition numerical models that best simulate the observed distribution of strain based upon the location of quartz reefs involve nw se oriented contraction with a significant sinistral strike slip component this contraction event has an overall n s sense orientation and is therefore consistent with deformation features in the immediate hanging wall of quartz reefs the models also demonstrate a geometrical dependence on the localization of strain and thus the potential localization of fluid flow volume and shear strain increase with the flex angle and variations in the magnitude of strain are also associated with variations in the strike angle of the flexure this analysis highlights that the modification of preexisting fold structures and quartz veins by a low strain event may enhance the localization of dilation sites within individual quartz reefs where there are subtle changes in the orientation of the reef margins such numerical modeling can also improve ranking of exploration targets based on fold geometry and provide a better understanding of fluid flow in hydrothermal mineral systems

the age of unconformity related uranium mineralization in the athabasca basin northern saskatchewan age data are presented for major athabasca basin uranium deposits at cigar lake cluff lake collins bay dawn lake eagle point mcarthur river midwest and rabbit lake as well as for several minor or undeveloped deposits including hughes lake and nisto the best constrained data indicate that almost all the deposits formed in a restricted time interval between about 1330 and 1380 ma this range of ages is believed to be real and not the result of uncertainties in the calculation of ages based on discordant data the one major exception is the recently discovered nias free deposit at mcarthur river for which a well determined age of 1514 18 ma 2 has been obtained even this deposit yields an age in the1330 1380 ma range for some material periods of reworking redeposition occurred at 1280 1000 575 and 225 ma these may be basin wide affecting to some degree all the deposits that we have studied other times of redeposition are less well determined but may be present as well no ages tha

age constraints on ductile deformation and long term slip rates along the karakoram fault zone ladakh the dextral karakoram fault zone that bounds the southwestern margin of tibet is widely regarded as one of the major strike slip faults that accommodates the eastward extrusion of the thickened crust of tibet in northern ladakh the karakoram fault bounds the pangong transpressional zone with the active fault trace following the eastern margin of the range exhumation within this zone reveals mylonites that have absorbed much of the deformation along the fault two sets of dikes are evident within the main fault strand that bounds the transpressional zone whilst one dike set is concordant with the dominant foliation and shows mylonitic fabric the youngest dike set are less deformed and cross cut the shear zone fabric using u pb id tims data from five shear zone samples deformed by differing degrees we infer that fault initiation occurred between 15 68f0 52 and 13 73f0 28 ma since absolute offset is difficult to determine we couple these age constraints with suggested minimum and maximum offsets of the baltoro type granites the offset range of 40 150 km reveals that the karakoram fault has a longterm average slip rate in the range 2 7 10 2 mm year the lower rate being compatible with gps insar and cosmogenic data for the fault the small range of offset and low slip rates do not support rapid large scale extrusion of tibet along lithosphericscale faults and strengthens the argument that tibet does not behave in a rigid plate like manner d 2004 elsevier b v all rights reserved

mechanical controls on fluid flow during regional metamorphism some numerical models the control of fluid flow by plastic deformation during metamorphism is critical to our understanding of metamorphic processes various geological observations and field studies demonstrate the consequences of fluid flow control by deformation so that the concept appears to be accepted at least for small scale public for example faults and vein public however the concept appears to be less well recognized at regional scales considered here are examples of simple conceptual models based on fully coupled mechanical fluid flow concepts they include deformation of a section of fluid saturated crust containing a block or a layer of material of different properties from its surrounds in particular rheological and permeability contrasts between rock types during deformation associated with regional metamorphism are sufficient to control the form of fluid flow over the range of a few kilometres low contrasts and small strains allow pervasive fluid flow whereas greater contrasts and increasing strains cause focusing of the flow such focusing is generally associated with localization of the deformation especially for a strongly dilatant elastic plastic material however a rate of fluid flow much greater than the rate of deformation may result in pervasive flow although for most models pervasive flow is difficult to attain over regional distances furthermore lateral and downward fluid flow may occur demonstrated here by simple models for folding and for deformation of regions containing plutons therefore such modelling may be used as a means of testing the various hypotheses concerning the volumes of fluid predicted to have passed through some rock volumes numerical models of the future will become increasingly complex and powerful allowing greater coupling of thermal mechanical chemical and fluid flow effects and based more on the physical processes involved combined field and laboratory studies will provide correspondingly greater understanding and will permit the determination of the timing of fluid flow and structural controls on fluid flow patterns

fluid flow in extensional environments numerical modelling with an application to hamersley iron ores the mechanical feasibility of focusing both surface and basinal derived fluids towards sites of iron ore genesis during proterozoic deformation in the hamersley province is tested here by computer simulation finite difference modelling of porous media flow during extensional deformation of a mountain range shows that surface fluids are drawn towards areas of failure and focus into the centre of the mountain the addition of permeable structures such as a normal fault provides focused fluid pathways in which mechanical and geological conditions are particularly conducive to both upward and downward flow upward flow from the base of the fault within the model overall is favoured by low permeability basement materials and supra hydrostatic pore pressures downward migration of fluids becomes more prominent as extension progresses and upward fluid flow from the base diminishes the introduction of sedimentary layering into the models allows lateral fluid flow such that sites of potential fluid mixing may then occur within permeable iron formation units close to the fault zone allowing parts of the stratigraphy to become more permeable as a function of high fluid flux simulates permeability enhancement by silica dissolution as a mechanism for iron ore genesis the involvement of both basinal and surficial fluids in the genesis of the ore deposits is supported by the mechanical models and in addition provides an explanation for a progression from relatively reduced to oxidised conditions at the mt tom price deposit and possibly other large deposits with time

late quaternary intensified monsoon phases control landscape evolution in the northwest himalaya the intensity of the asian summer monsoon circulation varies over decadal to millennial time scales and is reflected in changes in surface processes terrestrial environments and marine sedi ment records however the mechanisms of long lived 2 5 k y intensified monsoon phases the related changes in precipitation distribution and their effect on landscape evolution and sedimen tation rates are not yet well understood the arid high elevation sectors of the orogen correspond to a climatically sensitive zone that currently receives rain only during abnormal i e strength ened monsoon seasons analogous to present day rainfall anom alies enhanced precipitation during an intensified monsoon phase is expected to have penetrated far into these geomorphic threshold regions where hillslopes are close to the angle of failure we as sociate landslide triggering during intensified monsoon phases with enhanced precipitation discharge and sediment flux leading to an increase in pore water pressure lateral scouring of rivers and ov ersteepening of hillslopes eventually resulting in failure of slopes and exceptionally large mass movements here we use lacustrine deposits related to spatially and temporally clustered large land slides 0 5 km 3 in the sutlej valley region of the northwest him alaya to calculate sedimentation rates and to infer rainfall patterns during late pleistocene 29 24 ka and holocene 10 4 ka inten sified monsoon phases compared to present day sediment flux measurements a fivefold increase in sediment transport rates re corded by sediments in landslide dammed lakes characterized these episodes of high climatic variability these changes thus em phasize the pronounced imprint of millennial scale climate change on surface processes and landscape evolution

slip rates of the karakorum fault ladakh india determined using cosmic ray exposure dating of debris flows and moraines most recent major glacial advance occurred at 90 15 ka this is consistent with the inference of others that alpine glaciers in this region have not necessarily expanded in concert with northern hemisphere continental ice sheets if features including lateral moraines that liu inferred to have been offset 300 350 m by the karakorum fault date from the same period they too imply a slip rate of 3 4 mm yr 1 this slip rate is comparable to rates of extension across grabens within tibet with recent evidence that slip along the altyn tagh fault occurs at 10 mm yr 1 our rate suggests that slip along the boundaries of tibet is not significantly more rapid than extension within the plateau hence plate tectonics in the strictest sense ought not be applied to tibet because tibet does not behave as a rigid plate index terms 1824 hydrology geomorphology 1625 1035 geochemistry geochronology 9320 information related to geographic region asia 8107 tectonophysics continental neotectonics keywords karakorum fault slip rate cosmic ray exposure age beryllium 10

syncollisional extension along the india asia suture zone south central tibet implications for crustal deformation of tibet abstract crustal deformation models of the tibetan plateau are assessed by investigating the nature of neogene deformation along the india asia suture zone through geologic mapping in south central tibet 84 30 e our mapping shows that the suture zone is dominated by a system of 3 to 4 ene striking south dipping thrust faults rather than strike slip faults as predicted by models calling upon eastward extrusion of the tibetan plateau faults along the suture zone are not active as they are cut by a system of nnw striking oblique slip normal faults referred to herein as the lopukangri fault system fault slip data from the lopukangri fault system shows that the mean slip direction of its hanging wall is n36w we estimate the net slip on the lopukangri fault by restoring components of the thrust system we estimate that the fault has accommodated 7 km of right slip and 8 km of normal dip slip yielding a net slip of 10 5 km and 6 km of horizontal east west extension the lopukangri fault system is active and geomorphic offsets indicate right separations and westside down dip separation the mapview curviplanar geometry and geomorphic expression of the lopukangri fault system is similar to faults and rift basins to its east and west these extensional faults are en echelon in map view and encompass a region that is 200 km long east west and 95 km wide north south assuming our results for the lopukangri fault are applicable to the entire system we estimate a maximum of 18 extension across the zone all active faults in the system terminate southward adjacent to the india asia suture zone because the individual rift geometries are similar and suggest a common kinematic relationship we propose that the extensional system formed as a trailing extensional imbricate fan at the southern termination of the central tibet conjugate fault zone alternatively the extensional system may terminate to the north and represent a group of isolated crustal tears both kinematic interpretations imply a semi smooth north south variation in the magnitude of east west extension in southern tibet with higher magnitudes in the north along the bangong nujiang suture zone than in the south along the india asia suture zone our results from southern tibet show that deformation between southern tibet and the himalayas is broad 95 km wide and best described as a continuum possibly since the late miocene conversely the structural boundary between western tibet and the himalayas which is defined by the karakoram fault is presently a discrete boundary and probably has been since the middle miocene we think this variation in the displacement gradient and age of these structural boundaries within the interior of tibet is best explained by the fault patterns and strain history describing wholesale e w stretching and n s shortening of the tibetan crust

electrical conductivity of dense hydrous magnesium silicates with implication for conductivity in the stagnant slab abstract electrical conductivities of dense hydrous magnesium silicates dhms phase a super hydrous phase b sub and phase d were measured by means of impedance spectroscopy in the frequency range of 10 1 106 hz at temperatures up to 775 700 and 700 k and pressures of 10 18 and 22 gpa respectively for all phases the increase in electrical conductivity with temperature follows the arrhenian formula 0 exp h k t the pre exponential factors 0 and activation enthalpies h of phase a sub and phase d yield values of 7 28 0 82 s m and 0 77 0 01 ev 292 48 s m and 0 83 0 01 ev and 1342 154 and 0 75 0 01 ev respectively higher pressure dhms phases show higher conductivity values the electrical conductivities of phase d and super hydrous phase b are about two and one orders of magnitude higher than that of phase a in the same temperature range respectively although the proton conduction is considered to be a dominant mechanism there is no clear relationship between water content and conductivity rather the conductivity of dhms phase is closely related to the o o distance the conductivity depth profiles for a cold subduction zone were constructed based on the phase proportion predicted in the descending slab the results show distinctly lower conductivity values than those geophysically observed beneath the northeastern china and the philippine sea where the cold slab stagnates in the mantle transition zone consequently the dhms phases themselves cannot be a main contributor to enhance the conductivity in the stagnant slab dehydration of the stagnant slab would strongly enhance the conductivities in the transition zone beneath northeastern china and philippine sea

neotectonics of the western nepal fault system implications for himalayan strain partitioning oblique convergence at the himalayan margin is hypothesized to be partitioned by orogen normal thrusting and orogen parallel strike slip faulting we conducted field mapping and remote sensing in the dhaulagiri range of nepal and the results reveal an active regional fault system termed the western nepal fault system wnfs right and normally offset quaternary deposits and brittly deformed bedrock demarcate dextral slip along two strike slip faults striking n40 50 w linked via an extensional right step over striking n10 20 e the strike slip attitudes subparallel bedrock foliation while the step over cuts at a high angle 70 fault slip data along the strike slip segments trend n70 w with minor dip component top to north fault slip data and observed kinematics along the wnfs support our interpretation that the wnfs formed via arc parallel stress on the basis of geometry kinematics and structural position we correlate the wnfs to active faults between the karakoram and bari gad faults this suggests an 350 km long dextral fault system extending obliquely across the western nepal himalaya which appears to intersect the main frontal thrust mft near 83 30 e coinciding with a large gradient in the arc parallel component of gps velocities we interpret the wnfs to represent a class of orogen parallel strike slip faults working with subduction to accommodate obliquely convergent plate motion our observations support the hypothesis that the region lying between the mft and the wnfs is a continental version of a fore arc sliver bounded at its base by the main himalayan thrust