geochronology and geochemistry of late cretaceous igneous intrusions and mo cu w mineralization in the southern yidun arc sw china implications for metallogenesis and geodynamic setting abstract the sanjiang tethyan metallogenic domain stmd is an important part of the tethyan giant metallogenic belt the yidun arc is a part of the stmd in the eastern tibetan plateau recently four newly discovered mo cu w ore deposits related to granitic intrusions were found distributed along the north south strike in the southern yidun arc which are identified as the xiuwacu relin hongshan and tongchanggou deposits herein these four deposits formed along high angle north northwest or north west strike slip faults with vein type and porphyry type mo cu mineralization developed in the intrusions molybdenite re os and zircon u pb dating together with zircon hf isotopes and whole rock geochemistry of the intrusions were studied to discern the relationship between mineralization and magmatism metallogenesis and tectonic settings molybdenite from skarn type mineralization at the hongshan deposit has a re os isochron age of 81 2 2 6 ma mswd 1 3 n 5 consistent with previously published zircon u pb ages and re os ages of porphyry type mo mineralization these results indicate that the hongshan is a late cretaceous porphyry skarn cu mo deposit zircon u pb ages of the granitic intrusions in the xiuwacu relin and tongchanggou deposits varying from 87 4 ma to 82 7 ma combined with published molybdenite re os age spectrum 85 ma to 81 2 ma it is proposed that the mo cu w mineralization in the shangri la region is spatially temporally and probably genetically related to the late cretaceous granitic intrusions the relin hongshan and tongchanggou intrusions have high sio 2 65 2 70 0 wt sr 363 905 ppm sr y 22 72 and la yb 37 69 ratios and low y 11 6 17 0 ppm and yb 0 97 1 59 ppm which displayed adakitic affinities their low mgo 0 66 1 44 wt mg 25 46 variable negative zircon e hf t values 7 9 to 2 3 and proterozoic two stages hf model ages t dm2 1 13 1 62 ga suggest that they were probably dominantly derived from partial melting of thickened lower continental crust according to the tectonic evolution of the bangong meso tethys ocean during the late mesozoic the late cretaceous igneous event and mineralization in the yidun arc likely formed under a late or post collision extensional environment probably related to the collision between the lhasa and qiangtang terranes during the late cretaceous

chemical composition genesis and exploration implication of garnet from the hongshan cu mo skarn deposit sw china abstract in this study we present new mineral chemical data on the garnet from the hongshan cu mo deposit one of the largest skarn deposits in the sanjiang tethyan tectonic domain in sw china the aims are to unravel the formation mechanism of the oscillatory zoned garnet at hongshan and to explore possible applications using garnet trace element to distinguish different types of skarn deposits two generations of garnets i e poorly zoned garnet i grt i and the well zoned garnet ii grt ii are identified from the endoskarn and exoskarn at hongshan based on field and petrographic observations epma and la icp ms analyses show that grt i contains a narrow compositional range adr40 07 61 25 grs36 65 57 08 and chondrite normalized hree enriched and lree depleted patterns with minor positive eu anomalies in contrast grt ii shows a wide compositional range adr27 78 67 53 grs30 67 70 92 to almost pure andradite adr94 41 99 99 grs0 00 4 21 with interlayered al rich and fe rich zones in grt ii its al rich zone is chemically similar to grt i whereas its fe rich zone exhibits chondrite normalized lree enriched and hree depleted patterns with distinct positive eu anomalies the positive ree3 vs mg correlations and the poor ree3 vs y and ca correlations altogether indicate that the ree3 incorporated into garnet was co influenced by the menzerite type substitution mechanism c a 2 1 v i i i r e e 3 1 v i i i a l 3 1 v i m g 2 1 v i fluid chemistry and the physicochemical conditions of precipitation the higher u contents and hree enriched patterns of grt i suggest that it was formed under a relatively reducing and near neutral ph condition varying u contents and ree patterns across different oscillatory zones indicate that grt ii was probably formed under alternating physicochemical fluctuations led by repeating crack seal cycles in the hydrothermal system besides chemical data compilation suggests that the garnet from different types of skarn deposits has different compositions and can be used as mineral prospecting tools we suggested that discrimination plots such as eu vs v and ce vs u can distinguish cu skarn deposit from other skarn deposit types whilst the u vs w plot can discriminate between cu w w sn and w mo skarn deposits

quaternary fluvial systems of tropics major issues and status of research abstract fluvial systems in tropical regions are not only the lifeline for modern civilizations there but also form an important continental archive for reconstructing quaternary palaeoclimates and palaeoenvironments tropical rivers drain through a variety of geological and geomorphological settings across the world and have been studied for their hydrology sediment transport characteristics facies models stratigraphic development and flood hazards this paper presents an overview of the research on tropical rivers globally and identifies major gaps and unanswered research questions as a part of the igcp 582 on tropical rivers the participants of this project are continuing to tackle many of these issues the collection of papers in this special issue is an outcome of this activity and presents new data on processes and alluvial stratigraphy of the tropical rivers from china india south america and northern australia

multiple mesozoic porphyry skarn cu mo w systems in yidun terrane east tethys constraints from zircon u pb and molybdenite re os geochronology abstract porphyry cu mo au deposits typically formed in volcanoplutonic arcs above subduction zones however there is increasing evidence for the occurrence of porphyry deposits related to magmas generated after the underplating arc has ceased post subduction lithospheric thickening lithospheric extension or mantle lithosphere delamination could trigger the remelting of subduction modified arc lithosphere and lead to the formation of post subduction porphyry deposits the nnw trending yidun terrane located in the eastern tethys experienced subduction of garze litang oceanic plate a branch of the paleotethys in the late triassic and witnessed two mineralization events respectively associated with the ca 215 ma arc related intermediate felsic porphyries and the 88 79 ma mildly alkaline granitic porphyries it is therefore an ideal place to investigate the genetic linkage between the subduction related porphyry deposits and post subduction porphyry deposits our new in situ zircon u pb dating of the two granitic intrusions biotite granite 213 4 0 9 ma monzogranite porphyry 86 0 0 4 ma in the xiuwacu district the molybdenite re os age 84 7 0 6 ma of the mineralization and previously published geochronological data together show the spatially overlapping distribution of the multiple mesozoic porphyry systems in the late triassic yidun arc system furthermore the arc like elemental signatures and the mixed sr nd hf isotopic signatures of the late cretaceous ore related porphyries i e originating from a mixed components between the 215 ma juvenile arc crust and the mesoproterozoic mafic lower crust indicate a genetic linkage between the late triassic and late cretaceous porphyry systems this suggests that the remelting of underplated arc related mafic rocks formed during the subduction of the garze litang ocean could be responsible for the mixing between the mantle derived components and the mesoproterozoic lower crustal materials when post subduction transtension occurred in the late cretaceous the formation of the late cretaceous porphyry skarn cu mo w deposits could most likely be related to the remelting of late triassic residual sulfide bearing cu rich cumulates in the subduction modified lower crust that triggered by the late cretaceous transtension

reconciling the roles of tectonism and climate in quaternary alluvial fan evolution tectonism and climate are the primary variables considered in conceptual models of alluvial fan evolution and basin fill architecture yet their roles and relative importance are far from resolved the madison range and madison river valley southwestern montana were affected during late quaternary time by varying degrees of tectonic activity as well as by climate change through multiple glaciations we are thus able to evaluate the impact of tectonism and climate on fan evolution two primary fan deposits were correlated along the range front they were deposited as proglacial outwash fans during glacial periods of increased sediment and water discharge during the present interglacial period these deposits were entrenched and secondary fans formed on lower fan areas temporal and stratigraphic relations indicate that climate was largely responsible for driving both fan aggradation and entrenchment in contrast stratigraphic relations between fan deposits and surface faults do not support a direct relation either spatial or temporal between local faulting and fan deposition because tectonism produces and maintains the relief necessary for fans to form its primary role is long term controlling the duration over which fan deposition may occur along a mountain front if quaternary alluvial fan evolution is representative of ancient alluvial fan evolution this study has important implications for interpreting primary controls on deposition of the ancient alluvial fan sequences

extensional tectonic activity in the cratonward parts peripheral bulge of the ganga plain foreland basin india flexural subsidence of the indian lithosphere created the foreland basin in front of the emerging himalayan mountain belt the continued northward push of the indian plate and thrust sheet loading in the himalayan orogen caused an up warping along its cratonward margin in the form of a regional gentle bulge in the cratonward peripheral bulge small scale to moderate size deformation features e g gentle folds up arching of the sediment layers extensional normal faults and uplifted tilted blocks and incised river channels with 20 60 m high cliffs developed cliff sections of many rivers in this cratonward part of the foreland basin expose deposits of latest pleistocene holocene age and show evidences of active tectonics in the last few thousand years vertical uplift leading to deep incision of the river system development of prominent fractures cutting through the sedimentary succession bending and tilting of the strata and tilted blocks in the late quaternary relaxation phase of the himalayan orogen foreland there is increased vertical tectonic activity in the region of the peripheral bulge the vertical uplift in this part of the ganga plain foreland basin caused the rivers including the axial rivers to make further deep incision without shifting from their courses during periods of increased tectonic activity in the himalayan region i e the addition of thrust slices more rapidly probably caused the maximum down bending in the proximal part of the ganga plain foreland basin the high amplitude and asymmetric nature of this foreland basin is partly controlled by extensional tectonism

geochronology of the hongniu hongshan porphyry and skarn cu deposit northwestern yunnan province china implications for mineralization of the zhongdian arc abstract the hongniu hongshan porphyry and skarn copper deposit is located in the triassic zhongdian island arc northwestern yunnan province china single zircon laser ablation inductively coupled plasma mass spectrometry u pb dating suggests that the diorite porphyry and the quartz monzonite porphyry in the deposit area formed at 200 ma and 77 ma respectively a re os isotopic date of molybdenite from the ore is 78 9 ma which indicates that in addition to the known triassic cu au porphyry systems a late cretaceous porphyry cu mo mineralization event also exists in the zhongdian arc the quartz monzonite porphyry shows characteristics of a magnetite series intrusion with a high concentration of al k rb ba and pb low amount of ta ti y and yb and a high ratio of sr y average 26 42 the cretaceous porphyry also shows a strong fractionation between light and heavy rare earth elements average la yb n 37 9 which is similar to those of the triassic subduction related diorite porphyry in the hongniu hongshan deposit and the porphyry hosting the pulang copper deposit however in contrast to the older intrusions the quartz monzonite porphyry contains higher concentrations of large ion lithophile elements and co and lesser sr and zr therefore whereas the triassic porphyry cu au mineralization is related to slab subduction slab in an arc setting the quartz monzonite porphyry in the hongniu hongshan deposit formed by the remelting of the residual oceanic slab combined with contributions from subduction modified arc lithosphere and continental crust which provided the metals for the late cretaceous mineralization

a note on the extent of glaciation throughout the himalaya during the global last glacial maximum abstract quantitative chronologies for the impressive glacial successions that occur throughout the himalaya have until recently been almost totally lacking within the last decade two new techniques have promised to remedy this situation these techniques optically stimulated luminescence and cosmogenic nuclide surface exposure dating enable the age of many glacial features to be determined and have allowed us to study the extent and timing of himalayan glaciation in the late quaternary new data show that the local last glacial maximum lgm occurred during the early part of the last glacial cycle in most areas during marine isotope stage 3 mis 3 mis 3 was a time of increased insolation when the south asian summer monsoon strengthened and penetrated further north into the himalaya the concomitant increased precipitation occurring as snow at high altitudes produced positive glacier mass balances thereby allowing glaciers to advance on the other hand during the global lgm 18 24 ka himalayan glaciation was very restricted in extent generally extending

glacial to interglacial contrasts in the northern indian ocean differences between the 18o 16o ratios of planktonic foraminifera deposited during the last glacial maximum about 18 000 yr ago and those deposited during the holocene show that in the indian ocean the south west monsoon was weaker than today but that the north east monsoon was stronger the upwelling observed in modern conditions along the southern coast of arabia had disappeared because of the low speed of the southwestern winds during glacial summers the reduction in rainfall and runoff over the continent caused a reduction of the salinity gradient in the bay of bengal and along the western coast of india increased precipitation fell on the sea south of 10 n while strong evaporation over the northernmost arabian sea produced an enhanced salinity gradient in that area

integrated analysis of structures and landforms of an intermontane longitudinal valley pinjaur dun and its associated mountain fronts in the nw himalaya abstract frontal regions of the himalaya associated with topographic recesses are commonly marked by the development of intermontane valleys locally referred to as duns the relationship between structural evolution and landform development of an intermontane longitudinal valley pinjaur dun is explored to understand the role of tectonic processes on landform development the pinjaur dun has a length of 180 km it is divisible into a wider 20 km northwestern and a narrower 6 8 km southeastern segment the barsar thrust the nalagarh thrust and the himalayan frontal thrust form the mountain fronts in the area the proposed structural model integrates the transverse structures for e g ghaggar tear fault with the sequential development of imbricates in front of the main boundary thrust the pinjaur dun formed as a consequence of the fold thrust related uplift that formed the outermost siwalik hills most of the geomorphic units formed within the dun are the result of interactions between the imbricates such as the pinjaur thrust jhajara thrust and pinjaur garden fault these interactions also resulted in the development of a significant and prominent drainage divide between the jhajjara and the sirsa rivers of the pinjaur dun landform development and landscape evolution in this frontal region of the himalaya are a consequence of the interaction of thrust fold and transverse fault zone tectonics and constitute a record of transient 102

geochemical and nd pb isotopic characteristics of the tethyan asthenosphere implications for the origin of the indian ocean mantle domain abstract it is unclear why the pb nd and sr isotopic composition of the modern mid ocean ridge basalts morb from the indian ocean is different from that of the north atlantic and pacific oceans a possible explanation for this is that the indian morb type isotopic signature is a long lived regional feature of the mantle as evidently shown by the isotopic composition of the 350 ma morb like mian lue northern ophiolite which was formed in the same region presently occupied by the indian ocean however this hypothesis is in conflict with the lack of indian morb type isotopic signature in a number of 150 ma tethyan and indian ocean crusts to further constrain the origin of the indian morb type isotopic signature we analyze the geochemical and pb nd and sr isotopic composition of representative mafic rocks from four tethyan ophiolites ranging in age from 90 to 360 ma the sr isotopic composition of the samples is unreliable due to alteration but the age corrected nd and pb isotopic ratios and geochemical data indicate that these tethyan rocks were derived from a geochemically depleted asthenospheric source that had a clear indian morb type isotopic signature we therefore conclude that the bulk of the indian suboceanic mantle was most probably inherited from the tethyan asthenosphere a few regions in both the tethyan and indian oceans however are most probably underlain by pacific and north atlantic morb type mantle and vice versa because of the flow of the asthenosphere in response to tectonic plate reorganizations that lead to openings and closures of ocean basins the indian morb type isotopic signature of the western pacific marginal basin crusts could be due to either flow of the indian ocean mantle into the western pacific or to endogenous production of such an isotopic signature from delaminated east asian sublithospheric materials during closure of the tethys ocean

exploring the roles of climate and tectonics in the geomorphic evolution of the chitwan intermontane valley central himalaya abstract the himalayan front exhibits varying convergence rates along its length this study examines the morphotectonic evolution of the landforms in an intermontane valley viz chitwan dun present in a relatively rapidly converging segment of the himalaya using field investigations geomorphic analysis and geochronology we demonstrate that five geomorphic levels have developed in the past 112 ka four major phases of aggradation occurred in the chitwan i e 112 ka 112 70 ka 70 25 ka and 18 11 ka tectonic activity on the jharahi jht and belani thrusts bt at 112 ka and 70 ka respectively resulted in the uplift of the geomorphic units to level 5 and level 4 continuous aggradation in the valley occurred between 70 and 25 ka level 3 the tectonic activity during this period is marked by the reactivation of the west chitwan thrust wct and the central churia thrust cct the level 3 surfaces were abandoned during the lgm 25 18 ka and subsequently incised enhanced monsoon in the post lgm period favored aggradation of the level 2 and 1 geomorphic units the level 2 surfaces were abandoned due to activity on the danda dt and shaktikhor thrusts st whereas the level 1 landforms were incised due to climatic changes in the holocene comparing the results of this study with other parts of the himalaya we infer that despite variable tectonic convergence rates major aggradation and incision cycles are uniform this suggests that late quaternary climatic perturbations have strongly influenced the fluvial systems across the himalaya however the role of tectonics is also manifested in the form of multiple levels of surfaces and terraces

garnets in porphyry skarn systems a la icp ms fluid inclusion and stable isotope study of garnets from the hongniu hongshan copper deposit zhongdian area nw yunnan province china abstract the late cretaceous hongniu hongshan porphyry skarn copper deposit is located in the zhongdian area of northwestern yunnan province china garnets from the deposit have compositions that range from adr14grs86 to almost pure andradite adr98grs2 and display two different styles of zoning the garnets are predominantly of magmatic hydrothermal origin as is evidenced by their 18ofluid 5 4 6 9 and low dfluid 142 to 100 values both of which likely result from late stage magmatic open system degassing three generations of garnet have been identified in this deposit 1 al rich garnets grt i adr22 57grs78 43 are anisotropic have sector dodecahedral twinning are slightly enriched in light rare earth elements lrees compared with the heavy rare earth elements hrees have negative or negligible eu anomalies and contain high concentrations of f fluid inclusions within these al rich garnets generally have salinities of 12 39 wt nacl eq and have liquid vapor homogenization temperatures th of 272 331 c the grt i are most likely associated with low to medium salinity fluids that were generated by the contraction of an ascending vapor phase and that formed during diffusive metasomatism caused by pore fluids equilibrating with the host rocks at low w r water rock ratios these garnets formed as a result of the high f activity of the system which increased the solubility of al within the magmato hydrothermal fluids in the system 2 fe rich garnets adr75 98grs25 2 have trapezohedral faces and are both anisotropic with oscillatory zoning and isotropic these second generation fe rich garnets grt ii have high ree concentrations are lree enriched and hree depleted and generally have positive but variable eu anomalies all of the fe rich garnets contain high salinity fluid inclusions with multiple daughter minerals with salinities of 33 80 wt nacl eq some of them show higher temperatures of halite dissolution 465 591 c than liquid vapor homogenization temperatures 319 473 c and several fe rich garnets contain inclusion groups indicative of boiling the grt ii are associated with high temperature hypersaline fluids that were segregated from magma at a depth of at least 5 6 km and reacted with carbonates at depths shallower than 2 0 km 3 al rich garnet veins adr14 60grs86 40 contain allotriomorphic crystals have lower hfse high field strength element and ree concentrations than the other garnets and have hree enriched and lree depleted patterns with small eu anomalies that are typical of the majority of garnets the grt iii most likely formed from residual metasomatic fluids

zircon u pb geochronology and elemental and sr nd hf isotopic geochemistry of the daocheng granitic pluton from the yidun arc sw china abstract the garze litang suture zone located in the eastern part of the tethyan tectonic domain is notable for widespread late triassic granitic plutons which are genetically associated with the evolution of the paleo tethys ocean the daocheng granitic pluton in the eastern yidun arc sw china is located in the middle of the garze litang suture zone and has an outcrop area of 2800 km 2 in the present study we report zircon u pb ages and elemental and sr nd hf isotopic data for the daocheng granitic intrusion secondary ion mass spectrometry and laser ablation inductively coupled plasma mass spectrometry u pb analyses on zircons yield consistent ages of ca 216 ma for three samples from the pluton all the daocheng granitic rocks are enriched in si sio 2 68 1 76 4 and large ion lithophile elements but depleted in high field strength elements e g nb ta and ti mineralogical and geochemical features indicate that these are high k and calc alkaline and i type granites they are characterized by relatively variable initial 87 sr 86 sr ratios 0 7059 0 7102 negative e nd t values 5 7 to 7 8 wide ranging e hf t values 9 8 to 3 4 and two stage hf model ages of 1 04 to 1 88 ga these isotopic signatures indicate that the source for the daocheng granite was probably derived from partial melting of a late paleoproterozoic to early mesoproterozoic mafic intermediate lower crust with a variably minor addition

foreland sedimentation in himalayan tectonic regime a relook at the orogenic process by raiverman v 2002 bishen singh mahendra pal singh publishers 23 a connaught place p o box 137 dehradun 248 001 india 378 pp price us 125

titanite major and trace element compositions as petrogenetic and metallogenic indicators of mo ore deposits examples from four granite plutons in the southern yidun arc sw china major minor and trace element abundances in titanite crystals from four granitic plutons in southern yidun arc sw china have been determined using electron microprobe and laser ablation inductively coupled plasma mass spectrometry the selected plutons are the cretaceous xiuwacu cxwc pluton with quartz vein type mo mineralization economic mo the tongchanggou tcg pluton with porphyry type mo mineralization economic mo the triassic pulang pl pluton with porphyry type cu mineralization subeconomic mo and the triassic xiuwacu txwc pluton without any mo mineralization mo barren our study reveals that the chemical compositions of titanite crystals from these plutons such as ree sr ga delta eu delta ce fe2o3 al2o3 halogens and mo can be used to track magma compositions oxidation states metal fertility and crystallization history the data from this study also show that titanite crystals from these plutons with different potential of mo mineralization have similar mo contents and exhibit an irregular variation between mo and sr abundances indicating non mo enrichment in the residual melt during the progressive crystallization for some mo mineralized plutons our new observations support the recent hypothesis that high initial mo contents in magma and the enrichment of mo in residual melts formed by fractional crystallization are not the only requirements to form a granite related mo ore deposit efficient extraction of the residual melts possibly facilitated by high concentrations of magmatic f is also critical to the ore formation evidence for high f concentration in felsic magma which facilitates melt and fluid separation and economic mo mineralization during magma evolution may be traced by the presence of f rich titanite crystals in the two mo mineralized granite plutons cxwc and tcg these new findings from this study confirm that titanite is indeed a good petrogenetic and metallogenic indicator however in light of the limited contribution of metal fertility to mo mineralization we suggest that titanite mo concentrations should be used along with other crucial proxies such as titanite f contents and fe2o3 al2o3 ratios to better evaluate the mo mineralized potential of granites

seismic imaging of the main frontal thrust in nepal reveals a shallow decollement and blind thrusting abstract because great earthquakes in the himalaya have an average recurrence interval exceeding 500 yr most of what we know about past earthquakes comes from paleoseismology and tectonic geomorphology studies of the youngest fault system there the main frontal thrust mft however these data are sparse relative to fault segmentation and length and interpretations are often hard to validate in the absence of information about fault geometry here we image the upper two km of strata in the vicinity of the fault tip of the mft in central nepal around the town of bardibas applying a pre stack migration approach to two new seismic reflection profiles that we interpret using quantitative fault bend folding theory our results provide direct evidence that a shallow decollement produces both emergent patu thrust and blind bardibas thrust fault strands we show that the decollement lies about 2 km below the land surface near the fault tip and steps down to a regional 5 km deep decollement level to the north this implies that there is significant variation in the depth of the decollement we demonstrate that some active faults do not reach the surface and therefore paleoseismic trenching alone cannot characterize the earthquake history at these locations although blind these faults have associated growth strata that allow us to infer their most recent displacement history we present the first direct evidence of fault dip on two fault strands of the mft at depth that can allow terrace uplift measurements to be more accurately converted to fault slip we identify a beveled erosional surface buried beneath quaternary sediments indicating that strath surface formation is modulated by both climate related base level changes and tectonics together these results indicate that subsurface imaging in conjunction with traditional paleoseismological tools can best characterize the history of fault slip in the himalaya and other similar thrust fault systems

sedimentary processes and facies of the waterlaid anvil spring canyon alluvial fan death valley california the anvil spring canyon fan of the panamint range piedmont in central death valley was built entirely by water flow processes as revealed by an analysis of widespread 2 to 12 m high stratigraphic cuts spanning the 9 7 km radial length of this 2 5 5 0 sloping fan two facies deposited from fan sheetfloods dominate the fan from apex to toe the main one 60 95 of cuts consists of sandy granular fine to medium pebble gravel that regularly and sharply alternates with cobbly coarse to very coarse pebble gravel in planar couplets 5 25 cm thick oriented parallel to the fan surface the other facies 0 25 of cuts comprises 10 to 60 cm thick wedge planar and wedge trough beds of pebbly sand and sandy pebble gravel in backsets sloping 3 28 both facies are interpreted as resulting from rare sediment charged flash floods from the catchment and were deposited by supercritical standing waves of expanding sheetfloods on the fan standing waves were repeatedly initiated enlarged migrated and then terminated either by gradually rejoining the flood or by more violent breakage and washout the frequent autocyclic growth and destruction of standing waves during an individual sheetflood resulted in the deposition of multiple coarse and fine couplet and backset sequences 50 250 cm thick across the active depositional lobe of the fan erosional intensity during washout of the standing wave determined whether early phase backset bed deposits or washout phase sheetflood couplet deposits were selectively preserved in a given cycle two minor facies are also found in the anvil fan pebble cobble gravel lags 0 20 of cuts are present above erosional scours into the sheetflood couplet and backset deposits they consist of coarse gravel concentrated through fine fraction winnowing of the host sheetflood facies by sediment deficient water flows this reworking occurred during recessional flood stage or from non catastrophic discharge during the long intervals between major flash floods this facies is common at the surface giving rise to a braided stream appearance however it is stratigraphically limited present as thin continuous to discontinuous beds or lenses that bound 50 to 250 cm thick sheetflood sequences the other minor facies of the anvil fan consists of clast supported and imbricated thickly stratified pebbly cobbly boulder gravel present in narrow radially aligned ribbons nested within sheetflood deposits this facies is interpreted as representing deposition in the incised channel of the fan a subenvironment characterized by greater flow competence resulting from maintained depth from channel wall confinement and by more frequent water flows and winnowing events caused by its direct connection with the catchment feeder channel

distribution of porphyry deposits in the eurasian continent and their corresponding tectonic settings in the eurasian continent there are three huge metallogenic belts of cu and mo porphyry deposits comprising the paleozoic central asian ore belt in the north the tethyan eurasian ore belt of jurassic to cenozoic age in the southwest and the east margin ore belt of the eurasian continent of jurassic to cretaceous age in the east the latter is considered to be part of the vast circum pacific ore belt some of the main features of the spatial temporal distribution of cu and mo porphyry systems and related geodynamic processes of the three metallogenic belts are described in particular the key role of postsubduction related porphyry ore systems is emphasized comprising collisional and post collisional cu mo porphyry deposits during the geological history of the eurasian continent the recurrent feature of these ore systems and related felsic rocks is their derivation from partial melting of stagnant or residual oceanic slabs and mixing with a variable amount of crustal material during magma ascent to shallower levels 2013 published by elsevier ltd

geochronology geochemistry and sr nd isotopes of the granitic rocks associated with tungsten deposits in beishan district nw china central asian orogenic belt petrogenesis metallogenic and tectonic implications abstract the beishan orogenic belt is an important tectonic unit and a suitable target to investigate and understand the paleozoic tectonic framework of the central asian orogenic belt paleozoic granitic rocks are widely distributed in the area and closely related to the tungsten deposits at hongjianbingshan guoqing yingzuihongshan and yushan to understand the petrogenesis of the intrusions we performed sims zircon u pb o and whole rock major trace element contents and sr nd isotopic analyses two major suites of granitic intrusions associated with tungsten mineralization have been recognized during 424 314 ma and 286 244 ma the former suite shows variable sr nd and o compositions average 87sr 86sr i 0 7149 or 0 7034 end t 6 3 or 7 6 t2dm 1 68 or 0 41 ga 18o 9 3 or 5 9 indicating an ancient crust or a juvenile lower crust origin whereas the latter suite shows a type affinity and the sr nd and o compositions average 87sr 86sr i 0 7125 end t 4 5 t2dm 1 42 ga 18o 6 9 suggest the precambrian metasedimentary strata may have exerted a significant role in the magma source the proposed magma sources combined with the geochemical differences between these two suites of intrusions indicating the silurian carboniferous mineralization such as hongjianbingshan guoqing and yingzuihongshan are closely associated with subduction accretion and generation of gongpoquan arc accretionary system while the permian mineralization including yushan deposit are attributed to continuing accretion and subsequent post collision these tungsten related granitic rocks are enriched in lree and depleted in hree and ba sr nb p eu and ti suggesting they may have experienced advanced fractional crystallization furthermore a spectacular tetrad effect in their ree distribution patterns has been discovered showing the granites are highly evolved rocks with strong hydrothermal interaction the prolonged fractional crystallization and magmatic hydrothermal interactions have contributed to the formation of the silurian permian tungsten mineralization

late triassic granitoids of the eastern margin of the tibetan plateau geochronology petrogenesis and implications for tectonic evolution abstract late triassic granitoids in the songpan garze fold belt sgfb on the eastern margin of the tibetan plateau formed at 230 to 220 ma and can be divided into two groups group 1 are high k calc alkaline rocks with adakitic affinities k adakites with sr 400 ppm y n 32 105 and high k 2 o na 2 o 1 group 2 are ordinary high k calc alkaline i types with lower sr 18 ppm and weakly fractionated ree patterns la yb n 0 50 to 0 94 and initial 87 sr 86 sr 0 70528 to 0 71086 but group 1 rocks have higher e nd t 1 01 to 4 84 than group 2 3 11 to 6 71 calculated initial pb isotope ratios for both groups are 206 pb 204 pb 18 343 to 18 627 207 pb 204 pb 15 610 to 15 705 and 208 pb 204 pb 38 269 to 3759 group 1 magmas were derived through partial melting of thickened and then delaminated ttg type eclogitic lower crust with some contribution from juvenile enriched mantle melts group 2 magmas were generated by partial melting of shallower lower crustal rocks the inferred magma sources of both groups suggest that the basement of the sgfb was similar to the exposed kangding complex and that the sgfb was formed in a similar manner to the south china basement here passive margin crust was greatly thickened and then delaminated all within a very short time interval 20 myr such post collisional crustal thickening could be the tectonic setting for the generation of many adakitic magmas especially where there is no spatial and temporal association with subduction

microfossil evidence for changing salinity patterns in the bay of bengal over the last 20 000 years the monsson climate characterizing the northern indian ocean produces salinity gradients that are large compared with those in other open ocean areas these gradients are substantially independent of thermal and other ecologically important gradients this situation makes it possible not only to isolate the effect of salinity on sea bed distribution patterns of planktonic foraminifera but also to investigate past salinity changes along a north south transect of piston cores in the bay of bengal analysis of 152 surface sediment samples reveals that at least three factors other than salinity are important in controlling foraminiferal distribution sea bed dissolution surface productivity and surface temperature of these dissolution is the most important therefore in order to reconstruct past salinity patterns in the bay of bengal faunal indices need to be developed that isolate the effect of salinity we have developed two independent approaches the first uses ternary diagrams of the three dominant dissolution resistant species globoquadrina dutertrei globorotalia menardii pulleniatina obliquiloculata high values of g dutertrei are associated with low surface salinities the second approach uses dissolution buffered salinity transfer functions based on the total foraminiferal fauna in the 152 surface samples from the northern indian ocean applied to downcore samples these methods show the same basic historical pattern of salinity variation which is in turn consistent with independent inferences based on preliminary oxygen isotope data duplessy 1980 historical changes in the bay of bengal salinity are reconstructed along a north south transect of seven cores at 90 e the stratigraphy of the transect is controlled by oxygen isotope profiles that are similar to the generalized patterns observed in other areas over the past 20 000 yr salinity gradients are reconstructed for three time intervals 1 the last glacial maximum lgm 2 the mid termination mt and 3 the holocene during the lgm interval salinity was highger in the bay of bengal particularly in the north thus reducing the north south salinity gradient during the mt the middle of the transition from glacial to interglacial global climatic regimes northern bay of bengal surface salinity was considerably reduced while salinity to the south was generally similar to today thus the salinity gradient between 10 n and 15 n was considerably steeper than today in contrast the holocene gradient was approximately the same as the modern gradient with absolute values along the transect being slightly but uniformly higher these changes in the pattern of salinity are explained in terms of changes in the local patterns of precipitation and river run off during the lgm the salinity pattern probably results from decreased precipitation and decreased run off by the ganges brahmaputra river system during the mt decreased salinity in the northern bay of bengal is caused by increased precipitation and run off rather than by the influx of glacial meltwater the steeper mt salinity gradient in the central bay of bengal suggests increased eastward advection of equatorial surface waters by a southwest monsoon current somewhat more vigorous than today these patterns can be correlated with faunal evidence from the western arabian sea that suggest decreased upwelling during the lgm and increased upwelling during the mt this coupling of events may be associated with changes in the pattern or intensity of circulation during the southwest monsoon decreased intensity at the lgm 18 000 b p and increased intensity at the mt 10 500 to 12 500 b p

the giant dexing porphyry cu mo au deposit in east china product of melting of juvenile lower crust in an intracontinental setting the dexing porphyry cu mo au deposit in east china 1 168 mt at 0 45 cu is located in the interior of the south china craton scc made up of two lithospheric blocks the yangtze and cathaysia blocks the cu mo au mineralization is associated with mid jurassic granodioritic porphyries with three high level intrusive centers controlled by a series of lineaments at the southeastern edge of the yangtze block available age data define a short duration 172 170 ma of the felsic magmatism and the mineralization 171 1 ma the deposit shows broad similarities with deposits in volcanoplutonic arcs although it was formed in an intracontinental setting porphyries associated with mineralization are mainly granodiorites which contain abundant phenocrysts 40 60 and carry contemporaneous microgranular mafic enclaves mmes they are mainly high k calc alkaline and show geochemical affinities with adakite characterized by relatively high mgo cr ni th and th ce ratios the least altered porphyries yielded relatively uniform end t values from 0 9 to 0 6 and wide 87sr 86sr i range between 0 7046 and 0 7058 partially overlapping with the sr nd isotopic compositions of the mmes and mid jurassic mafic rocks in the scc zircons from the porphyries have positive ehf t values 3 4 to 6 9 and low 18o values 4 7 to 6 3 generally close to those of depleted mantle all data suggest an origin by partial melting of a thickened juvenile lower crust involving mantle components e g neoproterozoic mafic arc magmas triggered by invasion of contemporaneous mafic melts at dexing the mmes show textural mineralogical and chemical evidence for an origin as xenoliths formed by injection of mafic melts into the felsic magmas these mmes usually contain magmatic chalcopyrite and have original variable contents of cu up to 500 ppm their geochemical characteristics suggest that they were derived from an enriched mantle source metasomatized by proterozoic slab derived fluids and supplied a part of cu au and s for the dexing porphyry system during their injection into the felsic magmas the 171 1 ma magmatic hydrothermal event at dexing is contemporaneous with the mid jurassic extension in the scc followed by 160 90 ma arc like magmatism in southeastern china with respect to the tectono magmatic evolution of the scc the emplacement of cu bearing porphyries and the associated cu mineralization occurred in response to the transformation from a tensional regime related to mid jurassic extension to a transpressional regime related to the subduction of the paleo pacific oceanic lithosphere

re os dating of molybdenite from tongchanggou mo polymetallic deposit in northwest yunnan and its metallogenic environment the tongchanggou mo polymetallic deposit lies in the western margin depression belt of the yangtze landmass and is adjacent to yidun island arc and garze litang suture zone it is a representative ore deposit in studying yanshanian mineralization and shows bright future for further prospecting some intrusions or apophyses have been wholly mineralized and hydrothermal metasomatism in the upper part mainly displays skarn type and hydrothermal vein type mineralization in wall rocks forming a porphyry minerogenetic series the ore deposit is a large size or even a superlarge deposit re os isotopic dating technique was applied and six molybdenite samples were analyzed for re os isotopic compositions and the model ages obtained are from 82 34 1 28 to 88 27 1 23 ma with the isochron age being 85 10 ma the result suggests that mo mineralization occurred in yanshanian period during which zhongza block and yangtze landmass collided intensively and gradually turned into post collision stage because of the thickening of the crust crustal melting or crustal mantle melting resulted in the formation of s type granite and granite porphyry accompanied by molybdenum polymetallic mineralization the re content of the molybdenite is 6 440 43 530 ng g suggesting that the metallogenic material originated from a source mixed with crust and mantle components field investigation shows that concealed granite intrusions may exist in the depth and mineralization was related to magmatic intrusion acid intrusions in the area extend from north to south and the belt passes through yidun arc and enters the western margin of yangtze landmass in northwestern yunnan a number of large middle molybdenum polymetallic deposits were formed in the belt accordingly they are scattered from north to south represented by xiuwacu relin hongshan and tongchanggou the research on metallogenic background and ore prognosis is of great significance for ore exploration in this area

sedimentology paleoflow dynamics and flood history of jokulhlaup deposits paleohydrology of holocene sediment sequences in southern iceland sandur deposits abstract this paper examines the sedimentology of a series of deposits associated with catastrophic floods caused by subglacial volcanic eruptions in southern iceland a simple model is proposed for the interpretation of the sediments in terms of changes in flow characteristics of the fluid sediment mix a range of sediment types characteristic of these flood flows is identified the predominant one being thick massive homogeneous poorly structured black pumice fine gravels with 65 p rcent silt clay type e and single lithology boulder deposits type f these flood deposits alternate with or are channeled into more normal sandur deposits comprising heterogeneous poorly sorted clast supported imbricated rounded cobble and pebble gravels type g the dominant sediment sequences are interpreted as representing hyperconcentrated fluid sediment mixtures with dispersive stresses acting to create massive poorly sorted nongraded or inversely graded sediments the latter characterized by large surface boulders the vertical changes in sediment type reflect significant changes in flow conditions during transport and subsequent deposition with an initial massive flood surge followed by flow deceleration sediment freezing and dewatering producing a more fluid series of flows the more fluid phases were associated with extensive erosion and channelization cutting deep scour channels marked by residual streamlined hummocks boulder lags and fields of megaripples leading downstream to a washed sandur plain the paper examines some of the problems associated with the application of paleoflow models for determining former flow dynamics the models adopted suggest that most of the flows occurred as relatively mobile low viscosity flows with little internal resistance to shear while sediment concentrations are estimated to have reached about 50 percent by weight with maximum yield strengths between 2 9 103 and 4 2 105 dn cm 2 maximum viscosities ranged between only about 2 and 8 102 poises a range of paleovelocity models applied to the flood sediment indicates flow rates of between abo t 4 and 13 ms 1 with peak discharges reaching a maximum of 3 3 105 m3 s 1 dating of the deposits by 14c dating and tephrochronology indicates that at least 8 major sediment producing jokulhlaups occurred over a 4 000 year period between c 4500 yr bp and 1357 ad hence although relatively rare the effects of these floods still dominate the proglacial landscape probably producing 85 percent of the total thickness of proglacial sandur sediments

controls on fan development evidence from fan morphometry and sedimentology sierra nevada se spain abstract we have studied the morphology and the morphometric relations between alluvial fans and drainage basins in a bajada system including more than 20 coalescent fans developed since the late pleistocene as a result of the recent uplift of the sierra nevada betic cordillera spain three allocycles of tectonic origin were recognised across which there is a clear evolution from debris flow to sheet flow dominated fans in connection with a decrease in the volume of fines available in the source areas the larger volume of accommodation space created by higher tectonic subsidence in the northern sector favoured vertical accumulation of sediment with the appearance of less elongated fans in the rest of the system where subsidence is less more elongated fans appear with the development of incised channels and irregular distribution of sediment in depositional lobes this involves the appearance of markedly asymmetric transverse profiles as well as lengthy recurrence between the sedimentation events on particular sectors of the fans where headward eroding gullies develop the lithology of the source area where intensely fractured rocks are found is responsible for an important sediment supply and a significant degree of clast sorting from the source area consequently a weak longitudinal trend in particle size can be recognised which influences the predominance of longitudinal constant slope profiles and anomalous relations between both fan area and fan slope and their drainage areas recent intense tectonic activity has caused the appearance of abnormally low slopes in upper sectors of some catchments where mass flows are trapped and the fans present a subsequently higher proportion of sheet flows recent piracy phenomena can be recognised in some of the drainage basins which indicate rejuvenation of the source area in which case the fan presents a rapid increase in the proportion of mass flows with the development of a segmented longitudinal profile due to the recent nature of the processes the morphometric relations in the fan fed by the basin affected by capture do not coincide with the other fans in the area

the trollheim alluvial fan and facies model revisited widely held fundamental alluvial fan facies concepts generated in past literature based on the trollheim fan deep springs valley california are inconsistent with the actual characteristics of this fan previous publications have established mostly without field study that the trollheim fan consists of debris flow sieve lobe sheetflood and channel facies debris flow and sieve deposits comprise the proximal area giving way to channel or sheetflood deposits distally contrary to these views clayey and gravelly matrix supported debris flow deposits dominate all parts of the trollheim exposures suggesting that this fan has been built almost exclusively by mass wasting events channel fill deposits constitute only a small component of the fan and most are restricted to the proximal area where they have an inset relationship with debris flow sequences the channel facies consists of laterally restricted clast supported gravel lenses formed primarily through the winnowing of debris flow fines by streamflow the most widespread facies on the surface of the fan is a mantle of varnished matrix free pebbles cobbles and boulders that commonly are distributed in radially oriented lobes or levees characteristic of debris flow deposits this mantle was produced by the surficial winnowing of the fine fraction from debris flow deposits primarily by overland water flow in contrast to previous conclusions sheetflood and sieve deposits were not identified anywhere on the fan additionally many of the facies depicted in the widely cited trollheim vertical profile including ripple bedded sand cross bedded sand and overbank mud are not present on or in stratigraphic cuts of the fan after which the profile was named

porphyry cu mo au deposits related to melting of thickened mafic lower crust examples from the eastern tethyan metallogenic domain abstract most porphyry cu deposits in the world occur in magmatic arc settings and are formed in association with calc alkaline arc magmas related to subduction of oceanic lithosphere this contribution reviews a number of significant porphyry cu deposits in the eastern tethyan metallogenic domain they widely occur in a variety of non arc settings varying from post late collisional transpressional and extensional environments to intracontinental extensional environments related to orogenic and anorogenic processes their spatial temporal localization is controlled by strike slip faults orogen transverse normal faults lineaments and their intersections in these non arc settings these deposits are dominated by porphyry cu mo deposits with minor porphyry cu au and epithermal au deposits and exhibit a broad similarity with those in magmatic arcs the associated magmas are generally hydrous relatively high fo2 high k calc alkaline and shoshonitic and show geochemical affinity with adakites they are distinguished from arc magmas and or oceanic slab derived adakites by their occurrence as isolated complexes high k2o contents 1 2 8 5 and much wider range of end t values 10 to 3 and positive ehf t values 4 6 to 6 9 these potassic magmas are most likely formed by partial melting of thickened juvenile mafic lower crust or delaminated lower crust but also involving various amounts of asthenospheric mantle components key factors that generate hydrous fertile magmas are most likely crust mantle interaction processes at the base of thickened lower crust in non arc settings rather than oceanic slab dehydration as in arc settings breakdown of amphibole in thickened lower crust e g amphibole eclogite and garnet amphibolite during melting is considered to release fluids into the fertile magmas leading to an elevated oxidation state and higher h2o content necessary for development of porphyry cu mo au systems copper and au in hydrous magmas are likely derived from mantle derived components and or melts which either previously underplated and infiltrated at the base of the thickened lower crust or were input into the primitive magmas by melt mantle interaction in contrast mo and part of the s in the fertile magmas are probably supplied by old crust during melting and subsequent ascent

the role of the indian summer monsoon and the mid latitude westerlies in himalayan glaciation review and speculative discussion new dates for late quaternary glaciations in the himalayas show that during the last glacial cycle glaciations were not synchronous throughout the region rather in some areas glaciers reached their maxima at the global glacial maximum of c 18 20 ka bp whereas in others glaciers were most extensive at c 60 30 ka bp comparison of these data with palaeoclimatic records from adjacent regions suggest that on millennial timescales himalayan glacier fluctuations are controlled by variations in both the south asian monsoon and the mid latitude westerlies

structural evidence for the permo triassic tectonic evolution of the yidun arc eastern tibetan plateau abstract deformation across the yidun arc occurred as a two phase process i early triassic deformation of paleozoic sequences resulting from closure of the jinsha jiang suture and ii late triassic deformation of middle to late triassic rocks as a result of final basin closure deformation in the western yidun arc is dominantly west vergent a north south striking west directed thrust the jinsha thrust forms the boundary between the western yidun arc and the eastern qiangtang block the jinsha thrust incorporates within it ophiolitic material of the jinsha jiang suture and the structural geometry across the jinsha thrust suggests that early triassic subduction was east dipping along the jinsha jiang suture deformation within middle to late triassic sequences of the eastern yidun arc eastern qiangtang block and western songpan garze fold belt is thin skinned being restricted largely to a single generation of upright folds and associated thrusts late triassic westwards subduction underneath the combined western yidun arc qiangtang block resulted in arc volcanism in the eastern yidun arc coeval arc volcanics in the northern margin of the qiangtang block suggest that the suture along the northern margin of the qiangtang block may be correlated with the garze litang suture rather than the jinsha jiang suture

luminescence chronometry and late quaternary geomorphic history of the ganga plain india abstract flexing of the indian lithosphere due to the continent continent collision and thrust fold loading produced the gangetic foreland basin during the middle miocene the basin attained its present configuration during the late quaternary neotectonics and climate change since the last interglacial influenced the evolution of the present landscape of the gangetic ganga plains the regional geomorphic surfaces in these plains are 1 upland interfluve surface t2 2 marginal plain upland surface mp 3 megafan surface mf 4 piedmont fan surface pf 5 river valley terrace surface t1 6 active flood plain surface t0 minor geomorphic features comprise ponds alluvial ridges and small channels which occur on the upland interfluve surfaces the present contribution reviews geomorphic processes that sculpted the basin landscape and then using the blue green stimulated luminescence bgsl and infrared stimulated luminescence irsl ages provides a first order chronological framework for the relationship of major and minor geomorphic features to climate and tectonics luminescence dating of the upland interfluve surface t2 shows that formation of this surface started before 51 ka and continued at least up to 7 ka deposition in the marginal plain mp began at least at 76 ka and continued after 32 ka bracketing the evidence of a more humid climate during 50 40 ka sedimentation on the t2 and mp surfaces was synchronous the top of these surfaces gives variable ages ranging from 48 to 7 ka due to differential erosion of an undulatory topography caused by tectonic activity age upper bound for the initiation and termination of the final building phase of ganga megafan can be placed at 26 ka and 22 ka respectively deposition on piedmont fan surface continued between 8 and 3 ka the river valley terrace surface t1 of ganga river shows the activity of yazoo type channels during 3 1 1 ka the last phase of active accretion on the narrow poorly developed youngest active flood plain surface t0 was after 1 5 ka the ponds of t2 surface formed due to cessation of fluvial activity sometime during 8 6 ka a prominent tectonic activity at 7 5 ka and dry climate at 5 ka produced undulatory topography and high siltation rates in the lakes and ponds the peripheral bulge southern ganga plain has been tectonically active causing deep incision of rivers and a 40 ka seismic event and mid late holocene tectonic activity can be inferred

a genetic linkage between subduction and collision related porphyry cu deposits in continental collision zones the genesis of continental collision related porphyry cu deposits pcds remains controversial the most common hypothesis links their genesis with magmas derived from subduction modified arc lithosphere however it is unclear whether a genetic linkage exists between collision and subduction related pcds here we studied jurassic subduction related cu au and miocene collision related cu mo porphyry deposits in south tibet the jurassic pcds occur only in the western segment of the jurassic arc which has depleted mantle like isotopic compositions e g 87 sr 86 sr i 0 7041 0 7048 e nd t as high as 7 5 and e hf t as high as 18 by contrast no jurassic pcds have been found in the eastern arc segment which is isotopically less juvenile e g 87 sr 86 sr i 0 7041 0 7063 e nd t 4 5 and e hf t 12 these results imply that incorporation of crustal components during underplating of jurassic magma induced copper accumulation as sulfides at the base of the eastern jurassic arc inhibiting pcd formation at this time miocene pcds are spatially confined to the jurassic arc and the giant miocene pcds cluster in its eastern segment where no jurassic pcds occur this suggests that the arc segment barren for subduction related pcds could be fertile for collision related pcds miocene ore forming porphyries have young hf model ages and sr nd hf isotopic compositions overlapping with those of the jurassic rocks in the eastern segment whereas contemporaneous barren porphyries outside the jurassic arc have abundant zircon inheritance and crustlike sr nd hf isotopic compositions these data suggest that remelting of the lower crustal sulfide bearing cu rich jurassic cumulates triggered by cenozoic crustal thickening and or subsequent slab break off led to the formation of giant miocene pcds the spatial overlap and complementary metal endowment between subduction and collision related magmas may be used to evaluate the mineral potential for such deposits in other orogenic belts

aggradation and dissection sequences on spanish alluvial fans influence on morphological development abstract similarities in quaternary alluvial fan development are identified throughout southeast spain pre wurm aggradation phases culminate in calcrete crusted upper fan surfaces which are followed by wurm dissection phases producing deep fanhead or through trenches deposits of the aggradation phases reflect source area size relief and geology and in addition to proximal distal facies variations show vertical decreases in debris flow and increases in gravel deposition the dissection phases were complicated by cut and fill sequences forming within trench terraces which show a southward decrease in complexity the sequences are expressed in progressive changes in fan terrace and channel slopes and intersection point location fan morphological development during the quaternary reflects long term progressive change complicated by short term responses to climatic fluctuations and further comolicated by the locally variable effectiveness of trenching thresholds

the role of base level change in the dissection of alluvial fans case studies from southeast spain and nevada abstract tectonics climate and base level are the underlying controls of alluvial fan development on many fans base level is stable but where base level change occurs it may itself be a response to tectonics or climatic change tectonically induced base level change will be temporally independent of climatic change and will show spatial variability depending on the rate of propagation of tectonically induced regional dissection this is illustrated by the tabernas fans southeast spain the timing of climatically induced base level change follows the timing of climatic change itself and will show more consistency of spatial relationships within groups of fans affected alluvial fans which toe out in coastal zones or at lake shorelines may be influenced by climatically controlled base level changes conventionally a fall in base level would be expected to cause dissection of the distal fan zone however the reverse may occur with fan progradation taking place in response to a base level fall and dissection occurring in response to a base level rise two contrasted case studies are considered based in part on previously published work from dry region alluvial fan zones the coastal cabo de gata fans in southeast spain and the stillwater and cold springs fans in nevada usa in these areas base level changes occurred in response to late quaternary eustatic changes of sea level and changes in the levels of pluvial lakes respectively within both areas there are fans not affected by base level change cabo de gata west coast and inland fans cold springs fans and others where base level change has been important in fan evolution cabo de gata east coast fans stillwater fans the differences in geomorphic regime between those fans influenced by base level changes and those not are expressed in morphometric contrasts and different fan profile and plan characteristics within those fans influenced by base level changes the different mechanisms have influenced the location and elevation of the zone of incision the differences can be attributed in part to the temporal interactions of base level change with climatically induced changes in sediment supply and in part to differences in gradients of the foreshore exposed by the falling sea or lake base levels

constraining the timing of alluvial fan response to late quaternary climatic changes southern tunisia the evolution of the oued es seffaia alluvial fan during the last 50 000 years is analyzed in the light of chronometric data derived from ams radiocarbon and optical dating techniques these ages have enabled the temporal constraint of the distalward progression of the intersection point the upper limit of the locus of deposition which has resulted in the telescopic segmentation of the fan comparison of these data with the late quaternary climatic history of the maghreb highlights several problems of interpretation due both to our limited knowledge of regional palaeoclimates and of the response of dryland fluvial systems to climate changes however our data provide some evidence to suggest that fan incision and formation of telescopic segments occurs in response to changes from arid to less arid conditions supporting the conclusions of some of the work from other areas

lateral erosion toe cutting of alluvial fans by axial rivers implications for basin analysis and architecture abstract we document the neglected phenomenon of lateral erosion toe cutting of alluvial fans by non incising axial river channels field examples from the holocene of the big lost river basin idaho and the plio pleistocene of the rio grande rift new mexico help to establish architectural models with more general application to basin analysis the process of toe cutting can lead to complete fan destruction and may be a response to climate change tectonic tilting fault propagation or a combination of these variables it gives rise to near horizontal erosion surfaces cut in fan sediment steep fan margin scarps progressive up fan incision from the scarp by a network of channels soil formation up fan away from the incised channel network a deposit of axial alluvium that overlies the erosion surface and onlaps the scarp once avulsion occurs to take the axial channel away from the bajada margin distinctive healing wedges of fan alluvium prograde across abandoned axial river channel and floodplain deposits gradually onlapping the eroded scarp and its upstream network of incised channels toe cutting has important stratigraphic basin analysis and economic consequences bajada deposits subject to the process exhibit appreciable extra groundwater and petroleum reservoir potential in the intercalations of more porous and permeable axial fluvial sediments

late cretaceous metallogeny in the zhongdian area constraints from re os dating of molybdenite and pyrrhotite from the hongshan cu deposit yunnan china abstract the zhongdian area in yunnan southwestern china located at the southern end of the yidun volcano magmatic arc that was formed during the triassic westward subduction of the gaze litang ocean hosts numerous triassic large porphyry and skarn deposits the arc suffered jurassic to cretaceous arc continental orogenic collision and cenozoic intracontinental strike slip shearing the hongshan cu mo pb zn deposit is potentially a large deposit and contains two ore types 1 predominant layered skarn cu pb zn ores along marble hornfels contacts and 2 minor crosscutting vein type cu mo mineralization previous research forwards a two stage genetic model without sufficient dating evidence supposing the skarn mineralization is related to the triassic calc alkalic intrusions and the vein type mineralization related to cretaceous quartz monzonite porphyries re os dating of molybdenite from vein type ores and quartz monzonite porphyries and that of pyrrhotite from skarn ores are presented here to constrain the mineralization age and rebuild the genetic model analyses of eight molybdenite samples yield an isochron age of 79 7 3 1 ma mswd 9 2 for the vein type mineralization and a model age of 81 9 1 1 ma for the quartz monzonite porphyries isotope data on seven pyrrhotite samples from the skarn ores yield an isochron age of 79 16 ma z mswd 8 4 the re os ages for the two ore types are concordant within analytical errors indicating that the hongshan deposit was formed in the late cretaceous elevated re contents in molybdenite 13 65 to 63 91 g g and extremely radiogenic initial 187 os 188 os ratios in pyrrhotite 0 7673 to 0 8184 weighted average 0 796 0 038 together with elevated os values in pyrrhotite 507 to 547 average 528 imply a significant crustal component in the ore forming materials that was likely derived from a lower crustal reservoir combined with the tectonic evolution of the zhongdian area and geochemical characteristics of corresponding intrusions the ages of mineralization obtained in this study indicate that the hongshan deposit was formed in a post collision setting with a genetic relationship to the emplacement of the quartz monzonite porphyry these results provide significant new information for the study and exploration of the late cretaceous metallogeny in the zhongdian area

two phase stratigraphic model of foreland basin sequences application of flexural models to nonmarine foreland basin evolution indicates that two different stratigraphic styles of basin fill may develop over time basin subsidence is most rapid during times of thrust load emplacement associated sedimentation is coarse grained immediately adjacent to the thrust front and grades rapidly into fine grained deposits that cover most of the basin the distal part of the basin may also contain deposits derived from streams that flow from beyond the basin toward the thrust belt subsequent removal of the thrust load by erosion and other processes results in flexural rebound of the thrust belt and adjacent foreland basin during this postorogenic phase of adjustment a regional unconformity develops in the proximal part of the foreland basin proximal deposits along with thrust derived sediment are redeposited in the distal foreland basin and beyond this two phase model of foreland sedimentation predicts that coarsening upward sequences in the proximal and distal parts of the basin have reciprocal significance the proximal sequence represents thrust belt advance whereas the distal sequence represents thrust belt cessation

petrogenesis of late cretaceous i type granites in the southern yidun terrane new constraints on the late mesozoic tectonic evolution of the eastern tibetan plateau abstract the collision between the lhasa and qiangtang terranes prior to the indo asian collision is a critical aspect in terms of development of the tibetan plateau it has been demonstrated that the occurrence of the late cretaceous granites 110 80 ma in the yidun terrane eastern tibetan plateau etp associates with the lhasa qiangtang collision the xiuwacu late cretaceous pluton in the southern yidun terrane consists three phases including biotite granitic porphyry phase 1 monzogranite phase 2 and alkali feldspar leucogranite phase 3 which have zircon u pb ages ranging from 85 5 ma to 84 4 ma all these three phases are metaluminous or slightly peraluminous granites a cnk 0 96 1 07 with high sio2 70 0 76 0 wt k2o na2o 7 5 10 7 wt and ga al 2 5 4 7 and relatively low cao 0 39 1 67 wt mgo 0 01 0 57 wt and p2o5 0 01 0 17 wt the granites are enriched in light rare earth elements lrees rb th u and ta but depleted in heavy rees hrees ba sr p and ti with significantly negative eu anomalies eu eu 0 24 0 59 comparing to classic a type granites these samples present higher sr 10 1 256 ppm mostly 100 ppm and lower feo mgo ratios 1 2 9 9 and zr nb ce y 248 483 ppm mostly

the pulang porphyry copper deposit and associated felsic intrusions in yunnan province southwest china the pulang porphyry copper deposit recently discovered in northwestern yunnan province china is located at the south end of the triassic yidun island arc to date 15 mineralized porphyry deposits have been defined in the pulang area and the copper resource is estimated to exceed 10 mt the pulang deposit as currently defined is made up of five ore bearing porphyry deposits covering an area of approximately 9 km2 intermediate acidic porphyritic intrusions composed of quartz diorite monzodiorite quartz monzonite and granodiorite are widespread in the pulang area the alteration zones identified with the porphyry deposits include silicic potassium silicate quartz sericite and propylitic zones the porphyry deposits have hornfels at the contact with slate sandstone and andesite re os ages of molybdenite and ar ar and k ar dating of biotite indicate that the pulang porphyry copper deposit formed during the indosinian tectonic episode with the main ore formation taking place from 216 to 213 ma late triassic norian however the whole process of hydrothermal activity including overprinting may have extended from 235 to 182 5 ma

paleoseismic investigation along nalagarh thrust evidence of late pleistocene earthquake in pinjaur dun northwestern sub himalaya abstract the present article is the first time reporting of a paleoearthquake that occurred during late pleistocene time along the nalagarh thrust nt in the pinjaur dun in northwestern sub himalaya using corona satellite photographs multi spectral irs satellite data and aerial photographs a prominent active fault has been identified at nalagarh in pinjaur dun this fault in the alluvial fan is located very close to the nt which borders the topographic front of the tertiary rocks against quaternary deposits a trench excavation survey was carried out at nalagarh for detailed paleoseismic studies across this thrust fault displacing all the lithologic units of the fan sequence the fault plane has an average dip of 30 due ene and a vertical displacement of 1 6 m and slip of 2 5 m along the fault the lithological units consisting of alternating sand and gravel show back tilting and asymmetrical tight folding based on optically stimulated luminescence osl ages the oldest litho unit in the trench is 85 83 7 2 ka and the youngest is 67 05 8 4 ka the osl age of the sample collected from the easterly exposure of the fault shows an age of 20 ka the faulting and associated induced deformation features suggest occurrence of a late pleistocene large magnitude earthquake along nt in the nalagarh region of the pinjaur dun following the deposition of the quaternary sedimentary units the late pleistocene fault substantiates the seismic potential of pinjaur dun and calls for more exhaustive study of paleoearthquakes in this fast developing industrial belt and highly populous mountainous region

postsubduction porphyry cu au and epithermal au deposits products of remelting of subduction modified lithosphere porphyry cu mo au and some epithermal au deposits are formed from hydrothermal fluids exsolved from cooling water rich calc alkaline magmas emplaced in volcanoplutonic arcs above subduction zones these magmas originate by partial melting of the metasomatized asthenospheric mantle wedge however there is increasing evidence for the existence of a suite of porphyry cu au and epithermal au deposits related to magmas generated after subduction beneath the arc has ceased associated magmas tend to be mildly alkaline relatively sulfur poor and emplaced as isolated complexes rather than in voluminous volcanoplutonic arcs they are likely formed by remelting of previously subduction modified arc lithosphere triggered by postsubduction lithospheric thickening lithospheric extension or mantle lithosphere delamination metasomatized mantle lithosphere or hydrous lower crustal cumulates residual from first stage arc magmatism contain small amounts of chalcophile and siderophile element rich sulfides and constitute a fertile source for hydrous au rich but relatively sulfur poor magmas during later remelting the recognition that porphyry cu au and related epithermal au systems can also form in postsubduction and collisional tectonic settings expands the range of geological environments and geographical terranes that are prospective for such deposits

differential features of alluvial fans controlled by tectonic or eustatic accommodation space examples from the betic cordillera spain abstract the creation of accommodation space in subaerial sedimentary environments is closely linked to uplift the source area along basin margin faults or to a rise in base level depending amongst others on the relative importance of these two factors the margins of terrestrial sedimentary basins where alluvial fans develop produce aggradational progradational or retrogradational stratigraphic architecture we studied a total of 43 quaternary alluvial fans in the granada and bajo segura basins betic cordillera spain the analysis of their stratigraphic architecture and sedimentary facies has revealed the existence of three groups characterised by distinct stratal stacking patterns which is the result of differences in eustasy and tectonics the qualitative and quantitative analysis of these alluvial fans and their drainage basins has allowed us to define certain characteristic geomorphological patterns related in each case to the main mechanism operative in the creation of accommodation space these patterns are described as follows 1 alluvial aggradation is the main result of high tectonic subsidence with the development of quite open but small fans with a constant steep slope lacking incised channels and headward eroding gullies 2 in contrast when the principal mechanism in creating accommodation space is low tectonic subsidence progradation occurs and the fans are narrower and larger moreover the slopes of such fans are less steep in relation to the drainage area than in the above case being constant or even concave in longitudinal profile they also have short deep incised channels culminating downfan in a depositional lobe in inactive zones long deep headward eroding gullies develop 3 areas of extremely low tectonic subsidence and base level rise produce very open fans in the sedimentary basin although with a pronounced mountain embayment which gives them a characteristic mushroom shape in plan view in the latter case retrogradation is the typical stratigraphic stacking pattern and the fans are quite extensive with respect to their drainage areas usually showing a segmented longitudinal profile with a low gradient the feeder channels do not surpass stream order 3 and various extremely long and shallow incised channels can appear 4 contrary to the case of fans developing under a regime of subsidence when the accommodation is due to base level rise the fan slopes bear no relation to the extent of the catchment basins in such a case the overall fan slope is strongly influenced by the extent of the mountain embayment because it determines the distributions of debris and sheet flows over the alluvial surface

a model of alluvial megafan sedimentation ganga megafan abstract ganga megafan is one of several megafans developed in the northern and central part of the ganga plain that formed during the middle late pleistocene under conditions of higher sediment water discharge and higher regional slopes than today incision by the ganga river exposes 15 30 m thick megafan deposits in the valley walls and cliffs ganga megafan deposits can be separated into four zones zone i gravelly braided streams zone ii sandy braid plain zone iii anastomosing channel plain and zone iv meandering channels with broad interfluve areas deposits of each zone show distinct facies associations palaeocurrents fan from sw to se and e while the grain size decreases from proximal to distal fan at present fan building activity is highly subdued and is restricted only to the northernmost 5 10 km wide belt of piedmont plain

interplay between faulting and base level in the development of himalayan frontal fold topography 1 fold topography preserves a potentially accessible record of the structure and evolution of an underlying thrust fault system provided we understand the factors that shape that topography here we examine the morphology and fault geometry of two active folds at the northwest himalayan front the chandigarh and mohand anticlines show the following patterns 1 most 60 70 growth in catchment size and relief across multiple scales is accomplished within 5 km of the fault tips 2 range scale relief is divided unevenly between the fold flanks because of base level contrasts 3 mean gradients of the uplifting catchments correspond to different flank averaged rock uplift rates 4 high hillslope scale relief coincides with areas of fast rock uplift and stronger lithologies and 5 existing relief represents only 15 of the total rock eroded since faulting began implying significant erosion the first order fold topography is developed quickly and asymmetrically as a result of fault generated rock uplift which sets the space available for the fold and the distribution of rock uplift rates with some modulation by base level which affects the erosional response of the landscape to the uplift a linear rate of growth in catchment relief with range half width correlates with catchment averaged rock uplift rate suggesting that this metric may be used to infer variations in fault dip at depth in these frontal fold settings high slip rates weak uplifting rocks and rapid erosion may combine to quickly limit the topographic growth of emerging folds and disconnect their morphology from the displacement field

uplift and convergence along the himalayan frontal thrust of india along the himalayan thrust front in northwestern india terrace deposits exposed 20 to 30 m above modern stream level are interpreted to have been uplifted by displacement on the underlying himalayan frontal thrust a radiocarbon age limits the age of the terrace to 1665 215 calendar bc 3663 215 radiocarbon years before present yielding a vertical uplift rate of 6 9 1 8 mm yr in combination with published studies constraining the dip of the himalayan frontal thrust fault to about 30 in the study area the observed uplift rate equates to horizontal shortening across the himalayan frontal thrust of 11 9 3 1 mm yr and the slip rate of the himalayan frontal thrust of 13 8 3 6 mm yr this is similar to previously reported rate estimates along the himalayan arc based on displacement of older plio miocene age rocks or the much shorter records of geodesy and historical seismicity the similarity is consistent with the idea that convergence across the himalayan front has occurred at a relatively steady rate through time the seismic expression of this deformation includes several great m 8 historical earthquakes which due to lack of surface rupture during those events have been attributed to their occurrence on blind thrusts yet the occurrence of a possible fault scarp in the field area indicates that past earthquakes have been sufficiently large to rupture to the surface and produce coseismic scarps these observations suggest a potential for earthquakes along the himalayan frontal thrust larger than those observed historically

geomorphic evolution of glacier fed baspa valley nw himalaya record of late quaternary climate change monsoon dynamics and glacial fluctuations abstract in glacier fed baspa river valley late quaternary climatic changes are archived in the terraces fan and landslide deposits an initial optically stimulated luminescence osl based stratigraphy of these deposits is developed to deduce geomorphic evolution and palaeoclimatic changes the data show large alluvial fan progradation around sangla till c 45 ka middle of marine isotope stage 3 or mis 3 due to glacial retreat and readjustment of glacigenic sediment under warm and humid conditions followed by incision during the end phase of mis 3 23 ka intensified precipitation blocked the river course near sangla and kharogla by rock avalanches and imposed lacustrine conditions which recorded sedimentation until the beginning of holocene c 11 4 ka reduced sedimentation in these lakes during the last glacial maximum lgm c 23 18 ka suggests a cold and arid climate whereas increased sedimentation during c 18 11 5 ka indicates a warm and humid climate post lgm a palaeolake breach occurred during early holocene and incision continued throughout the holocene with a pulse of fluvial aggradation during c 9 1 6 5 ka over lacustrine remnant in the upper reach of the valley chitkul area coeval aggradation continued from 28 ka until c 19 ka mis 3 to lgm under cold and relatively arid conditions this study emphasizes that late quaternary geomorphic evolution of baspa valley is well synchronous with glacial fluctuations and the rapid response of the glacifluvial system to indian summer monsoon ism dynamics

response of the ganges dispersal system to climate change a source to sink view since the last interstade the forcing of sediment dispersal systems by climate is widely accepted but there remains disagreement on the general responses to climate change such as how resulting signals propagate downstream and ultimately how they are preserved in the stratigraphic record towards a better understanding of these issues this paper presents a comprehensive overview of ganges dispersal system behavior since the last interstade which reveals major coeval responses to changes in the south asian monsoon at 3000 km from its mountain headwaters to deep sea fan the ganges dispersal system is immense and yet shows tight coupling between source area catchment basin and coastal and marine depocenters furthermore system wide responses and downstream transfer of the signal appear to occur at least as fast as current temporal resolution of 1 2 ky this tight linkage of source to sink components is considered a function of the southwest summer monsoon s overwhelming control on regional hydrology about 80 of the ganges discharge and 95 of its sediment load are delivered to the margin during only 4 months making the system extremely sensitive to this seasonal forcing in addition the regional scale and distribution of the monsoon weather system means that changes in atmospheric circulation affect the entire drainage basin rather than local subcomponents finally despite its present intensity strength of the summer monsoon has varied significantly over the past 150 ky under orbitally driven changes in insolation and global glacial boundary conditions the resulting changes in precipitation both well above and below modern values have forced system wide responses ranging from glacier advance retreat to sediment fluxes to the margin and deep sea fan the overall conclusions are 1 that this immense dispersal system responds to multimillennial scale 104 years climate change in a system wide and largely contemporaneous manner and 2 that major sedimentary signals can be transferred rapidly from source to sink with little apparent attenuation furthermore these acute responses to climate change have produced sedimentary stratigraphic features that diverge from traditional sequence models in their nature and timing

evaluating major controls on basinal stratigraphy pine valley nevada implications for syntectonic deposition the interpretation of prograded gravel as an indicator of tectonic uplift that is syntectonic deposition is not necessarily correct increases in sediment supply induced by tectonic uplifting did not control the progradation of gravel in the pine valley basin an actively subsiding half graben in northeastern nevada rather the distribution of lithofacies in the pine valley basin is primarily controlled by the uneven distribution of subsidence within the basin differences in subsidence along the axis of the basin indicate a strong inverse relationship between the long term subsidence rate since late miocene time and the distance of gravel transport out into the basin differential progradation of alluvial gravel into the basin from various drainages along the footwall is not related to uplift or lithology of the source area size of the catchment area or climate in addition the relatively fixed location of the topographic low within the basin through time as indicated by the distribution of lacustrine deposits and the position of the modern axial drainage suggests that a balance between basin subsidence and sediment supply to the basin has been generally maintained through time thus if subsidence rates are a measure of tectonic activity gravel progradation may record times of reduced not increased tectonism

late cenozoic uplift in southern asia and the american west rationale for general circulation modeling experiments geologic evidence suggests significant increases in uplift rates and absolute elevation in several areas during the late cenozoic especially in the last 10 m y regions of major uplift include the tibetan plateau and himalayan mountains of southern asia and the sierra nevada colorado plateau basin and range rocky mountains and high plains of the american west uplift occurred at a scale large enough to affect regional and global climate in a number of ways several of which we evaluate by general circulation model experiments in accompanying papers

high sr y and la yb ratios the meaning of the adakitic signature abstract the name of adakite is used to describe a far too large group of rocks whose sole common feature is high sr y and la yb ratios however such a signature can be achieved via different processes melting of a high sr y and la yb source deep melting with abundant residual garnet fractional crystallization or afc or interactions of felsic melts with the mantle causing selective enrichment in lree and sr over hree a database of the compositions of adakitic rocks including high silica and low silica adakites martin h smithies r h rapp r p moyen j f champion d c 2005 an overview of adakite tonalite trondhjemite granodiorite ttg and sanukitoid relationships and some implications for crustal evolution lithos 79 1 2 1 24 continental adakites and archaean adakites was assembled geochemical modeling of the potential processes is used to interpret it and reveals that 1 the classical model of slab melting provides the best explanation for the genesis of high silica adakites 2 low silica adakites are explained by garnet present melting of an adakite metasomatized mantle i e at depths greater than 2 5 gpa 3 continental adakites is a term encompassing a huge range of rocks with a corresponding diversity of petrogenetic processes and most of them are different from both low and high silica adakites 4 archaean adakites show a bimodal composition range with some very high sr y examples similar to part of the ttg suite reflecting deep melting 2 0 gpa of a basaltic source with a relatively high sr y while lower sr y rocks formed by shallower 1 0 gpa melting of similar sources comparison with the archaean ttg suite highlights the heterogeneity of the ttgs whose composition spreads the whole combined range of hsa and archaean adakites pointing to a diversity of sources and processes contributing to the ttg suite

zircon u pb ages hf o isotopes and whole rock sr nd pb isotopic geochemistry of granitoids in the jinshajiang suture zone sw china constraints on petrogenesis and tectonic evolution of the paleo tethys ocean the jinshajiang suture zone located in the eastern part of the tethyan tectonic domain is noticeable for a large scale distribution of late jurassic to triassic granitoids these granitoids were genetically related to the evolution of the paleo tethys ocean beiwu linong and lunong granitoids occur in the middle zone of the jinshajiang suture zone and possess similar geochemical features indicating that they share a common magma source sims zircon u pb dating reveals that the beiwu linong and lunong granitic intrusions were emplaced at 233 9 1 4 ma 2 233 1 1 4 ma 2 and 231 0 1 6 ma 2 respectively all of these granitoids are enriched in abundances of si sio2t 65 2 73 5 wt and large ion lithophile elements liles but depleted in high field strength elements contents hfses e g nb ta and ti in addition they have low p2o5 contents 0 06 0 11 wt a cnk values molecular al2o3 cao na2o k2o mostly 1 1 and 10 000 ga al ratios 1 7 2 2 consistent with the characteristics of i type granites in terms of isotopic compositions these granitoids have high initial 87sr 86sr ratios 0 7078 0 7148 pb isotopic compositions 206pb 204pb t 18 213 18 598 207pb 204pb t 15 637 15 730 and 208pb 204pb t 38 323 38 791 zircon 18o values 7 3 9 3 and negative end t values 5 1 to 6 7 suggesting they were predominantly derived from the continental crust their nb ta ratios average value 8 6 are consistent with those of the lower continental crust lcc however variable ehf t values 8 6 to 2 8 and the occurrences of mafic microgranular enclaves mmes suggest that mantle derived melts and lower crustal magmas were involved in the generation of these granitoids moreover the high pb isotopic ratios and elevated zircon 18o values of these rocks indicate a significant contribution of the upper crustal composition we propose a model in which the beiwu linong and lunong granitoids were generated under a late collisional or post collisional setting it is possible that this collision was completed before late triassic decompression induced mantle derived magmas to be underplated and provided the heat for the anatexis of the crust hybrid melts including mantle derived and the lower crustal magmas were then generated the hybrid melts thereafter ascended to a shallow depth and resulted in some degree of sedimentary rock assimilation such three component mixing magma source and subsequent fractional crystallization could be responsible for the formation of the beiwu linong and lunong granitoids

tectonic evolution of the qinghai tibet plateau abstract the qinghai tibet plateau composed of several continental slivers within the eastern tethyan domain is one of the pivotal sites to examine to better understand the theory of plate tectonics and the orogenic evolution on earth this plateau is generally inferred to be a collage of several continental blocks that rifted from gondwanaland and subsequently accreted to the asian continent however recent recognition of over twenty ophiolite melange zones and their associated island arcs indicates that the traditional model of tectonic evolution requires revision based on 177 recently finished 1 250 000 scale geological maps and related studies we summarize the main tectonic context of the qinghai tibet plateau and propose a new integrated model to account for the new findings the complex orogen of the immense qinghai tibet plateau consisting of multiple island arc basin systems that developed at different stages while surrounded by the north china yangtze tarim and indian plates is emphasized the entire orogen surrounded by suture zones that mark the locations of oceanic closure is investigated by examining i the first order tectonic units and ophiolitic melanges including arc arc continent collision zones and ii their internally enclosed blocks as the second order tectonic units therefore the qinghai tibet plateau is divided into three major orogenic systems namely from northeast to southwest the early paleozoic qinling qilianshan kunlunshan qin qi kun the late paleozoic triassic qiangtang sanjiang and the late paleozoic to cenozoic gangdese himalaya orogenic systems which are separated by the kangxiwa muzitagh maqin mianxian and the bangong shuanghu changning menglian sutures respectively we propose that the formation and evolution of the qinghai tibet plateau to have been intrinsically related to those of the eastern tethys recorded by the longmu co shuanghu ophiolite melange zone the southern qiangtang paleozoic accretionary arc basin system the bangong nujiang suture zone and their associated composite island arc basin systems the present day bangong shuanghu changning menglian suture system marks the final closure of the tethyan ocean the yarlung zangbo ocean opened as a back arc basin in response to the southward subduction of the tethyan ocean lithosphere in the middle triassic and closed as a result of the india asia collision at the end of cretaceous followed by the northward indention of the indian plate that resulted in significant intra continental deformation and plateau uplift in the cenozoic

an overview of timing and structural geometry of gold gold antimony and antimony mineralization in the jiangnan orogen southern china abstract the jiangnan orogen located between the yangtze and cathaysia blocks in southern china hosts significant gold and antimony resources long standing controversies over the number and precise timing of gold gold antimony and antimony mineralization event s and the genesis of these deposits limit the understanding and exploration of this giant gold and antimony system together with geological evidence a critical review of the published geochronological data of these deposits suggest that there were two gold events in the triassic 235 ma and early cretaceous 142 130 ma two gold antimony events in the early devonian 402 ma and late triassic middle jurassic 224 163 ma possibly equivalent to the two gold events and one antimony event in the early cretaceous 130 ma there are other possible gold events in the neoproterozoic or at an even older age and ordovician to early devonian which are constrained only by limited geological evidence and a few non robust isotopic ages the regional distribution of the gold gold antimony and antimony districts and deposits therein reveal a first order control on the mineralization by crustal scale faults which acted as ore forming fluid pathways connected to deep fluid and metal source areas second and third order faults that are situated along the jogs of the first order faults especially fault corridors defined by nne ne trending second order faults and third order nw to e w trending discontinuous oblique faults provided favorable locations for pre cretaceous gold antimony mineralization in addition ne trending open anticlines linked to deep crustal levels by first order faults host significant antimony and minor gold mineralization and the curvilinear fanjingshan detachment fault hosts some gold and antimony deposits locally at deposit to orebody scales pre ore barren quartz veins and magmatic dikes were the loci for mineralization in some gold antimony deposits the structural geometry of the pre cretaceous gold and gold antimony deposits suggests an early devonian orogenic gold antimony mineralization event during a transpressional tectonic regime related to coeval intracontinental orogeny between the yangtze and cathaysian blocks in contrast triassic orogenic gold and triassic middle jurassic orogenic gold antimony events are interpreted to relate to distal effects of the collision between the north and south china blocks the structurally contrasting major early cretaceous epizonal antimony mineralization event together with contemporaneous hydrothermal gold mineralization is interpreted to have been controlled by normal faults and pre ore open folds in an extensional tectonic regime related to the distal effects of rollback of the paleo pacific plate after 135 ma for future geoscience based exploration in the orogen documentation and interpretation of critical structural geometries of gold gold antimony and antimony deposits is a vital step towards successful target generation

debris flow deposits in alluvial fans on the west flank of the white mountains owens valley california u s a abstract sections measured in incised channels on 10 alluvial fans show that debris flow beds mostly 30 200 cm thick are more important than stream flow deposits in construction of fans along the west flank of the white mountains the debris flow beds have a matrix supported fabric with a sandy mud matrix that comprises about 40 of individual beds complete grain size analyses of 19 debris flow beds show that they average 50 gravel 25 sand 11 silt and 4 clay inverse grading at the base of most beds is interpreted as due to a layer of high shear stress beneath an overlying semi rigid high strength plug that supported cobbles and boulders sticks and logs embedded in the plugs are oriented parallel with flow directions reflecting the laminar viscous motion of the plugs in the shear layer the average inclination of discoidal clasts is subhorizontal varying from 2 to 7 in the up flow direction in the plugs discoidal clasts have a subhorizontal fabric with average dips of 5 13 compared to the shear layer plugs have more scatter in clast orientation with numerous clasts dipping at 60 90 levees along the margins of debris flow lobes contain concentrations of the larger clasts in the flows in the leeves discoidal clasts have an average up flow dip of 21 31 with substantial variability in orientation similar to the plugs maximum clast size in individual debris flow beds is fairly constant down fan until the flows spread and thinned on the sandflat at the fan toe clast lithologies show that debris flows originate on steep slopes underlain by granitic and metavolcanic rocks at high elevations in the canyons in contrast stream flows obtained most of their clasts from talus slopes on metasedimentary rocks near the apices of the fans debris flows are generated during intense rainstorms in the spring and summer when landslides in the water saturated regolith move down slope shear dilate and by adding water are transformed into debris flows which then move with surging laminar motion along canyon flows to the fans the recurrence interval for debris flows is about 320 years as evidenced by 14c dates on plant material buried beneath debris flow beds

the influence of climate regime shift on enso observations indicated that for the el nino southern oscillation enso there have been eastward displacements of the zonal wind stress ws anomalies and surface heat flux short wave heat flux and latent heat flux anomalies during el nino episodes in the 1981 1995 regime relative to the earlier regime of 1961 1975 without corresponding displacements during la nina episodes our numerical experiments with the zebiak cane coupled model generally reproduced such displacements when the model climatological fields were replaced by the observed climatologies of sea surface temperature sst surface ws and surface wind atmospheric divergence and simulated climatologies of oceanic surface layer currents and associated upwelling for the 1981 1995 regime sensitivity tests indicated that the background atmospheric state played a much more important role than the background ocean state in producing the displacements which enhanced the asymmetry between el nino and la nina in the later regime the later regime climatology state resulted in the eastward shifts in the enso system ws and sst only during el nino through the eastward shift of the atmosphere convergence heating rate in the coupled model the enso period and enso predictability were also enhanced in the coupled model under the later regime climatology that the change in the mean state of the tropical pacific atmosphere and ocean after the mid 1970s could have produced the observed changes in enso properties is consistent with our findings

terminal fans and the ganga plain tectonism a study of neotectonism and segmentation episodes of the indo gangetic foreland basin india abstract the study of spatial and temporal distribution of holocene terminal inland fans in the indo gangetic foreland basin suggests that the segmentation of the basin was initiated at 9 3 ka and continued up to 0 75 ka in three distinct episodes the earliest episode 9 3 7 3 ka was exclusively confined in the upper gangetic plain this episode covers 29 of total time span and contributes 13 of total faults including their reactivations development of six faults associated with terminal fans having large age gaps indicate relatively slow rate of faulting activities in the early holocene the second faulting episode was started at 6 4 ka and continued up to 2 3 ka covering 60 time of the total time span and contributed 69 of total faults including their reactivations though in most of the time the faulting events were confined in the upper gangetic plain but development of few faults in the middle gangetic plain in the middle of this episode shows a transitional shift of tectonic front from the upper to the middle gangetic plain the third faulting episode 1 5 0 75 ka is mainly confined in the middle gangetic plain this episode covers 11 time of the total time span and contributes 18 of faults out of the eight faults seven of them are in the middle gangetic plains though these three episodes have contributed in segmentation of the gangetic plains but the second episode was responsible for major segmentation of the region two major tectonically stable periods 7 3 6 4 ka and 2 3 1 5 ka and three minor periods in duration of 0 5 ka have been observed in the region episodic development of faults in individual tectonic blocks indicates that the stress distribution along the plains is non uniform which can also be correlated to the adjacent corresponding segments of the himalayan tectonics it has been observed that in each fault bounded block the faulting events start slowly and later becomes more frequent previous work pointed out four tectonically active episodes between the ghaghara and kosi rivers with the oldest faulting event at 7 89 ka however the region west of it i e between the ghaghara and ghaggar rivers which includes rest of the upper gangetic plain shows that neotectonic activities are earlier than 7 89 ka the oldest faulting event observed by previous study the youngest faulting episode of the present study coincides with that of previous study and suggests that the region between the gandak and kosi rivers is tectonically most active at present the tectonically stable periods pointed out in the previous study between the ghaghara kosi region is occupied by the faulting events in the upper gangetic plains hence instead of four tectonically active episodes the whole ganga plain witnesses three segmentation episodes with two major intervening stable periods the change of orientation of the faults in the plain may be correlated to directional change of indian plate motion differential convergence and upliftment rates along the himalayan front and the spatial extension of subsurface precambrian basement ridges into the plains

quantifying long term catchment changes of alluvial fan systems in mountain areas affected by uplift significant reorganization of drainage networks can occur through river capture this modification can dramatically affect sediment flux and routing into adjacent sedimentary basins it is thus important to obtain information on rates and direction of changes in catchment areas in such environments this can be achieved where the original precapture catchments can be compared with the postcapture scenario this paper examines three modern mountain catchments from southeast spain that were affected by river capture and that fed relict pliocene pleistocene alluvial fan systems morphometric data have been collated for complete quaternary mountain catchment piedmont fan systems these data are used to establish regressions to determine catchment area and basin relief from a combination of fan characteristics area and gradient these relationships are then used to predict the original catchment characteristics for the three pliocene pleistocene relict fans and compared with the modern catchments to quantify the magnitude and direction of changes which have affected the drainage basins since fan abandonment in the early pleistocene the figures suggest that the catchment areas are responding to regional uplift most significantly by drainage net expansion facilitated by river capture rather than lowering of surface relief as a result sediment routing into the sedimentary basins has been radically altered

tropical climate instability the last glacial cycle from a qinghai tibetan ice core an ice core record from the guliya ice cap on the qinghai tibetan plateau provides evidence of regional climatic conditions over the last glacial cycle 36 cl data suggest that the deepest 20 meters of the core may be more than 500 000 years old the 18 o change across termination i is 5 4 per mil similar to that in the huascaran peru and polar ice cores three guliya interstadials stages 3 5a and 5c are marked by increases in 18 o values similar to that of the holocene and eemian 124 000 years ago the similarity of this pattern to that of ch 4 records from polar ice cores indicates that global ch 4 levels and the tropical hydrological cycle are linked the late glacial stage record contains numerous 200 year oscillations in 18 o values and in dust nh 4 and no 3 levels

late cretaceous granitic intrusions and associated deposits in the yidun arc of the eastern tibetan plateau abstract the yidun arc is an important tectonic unit and polymetallic metallogenic belt in the sanjiang tectono magmatic belt in which many cretaceous 138 75 ma granites and associated polymetallic deposits are distributed along a nw trending belt the queershan cuomolong rongyicuo and genie granitic intrusions and the associated sn pb zn ag polymetallic deposits are distributed in the changtai and xiangcheng arcs whereas the xiuwacu relin hongshan and tongchanggou granitic intrusions and the associated cu mo w deposits are mainly distributed in the geza arc this study presents new zircon u pb hf o isotopic data for the queershan cuomolong rongyicuo genie xiuwacu and tongchanggou granitic intrusions combined with the structural analysis of the xiuwacu granitic complex to discuss the differences in the petrogenesis and metallogenesis of these granitic intrusions as well as the geodynamic processes that controlled the formation of the late cretaceous intrusions and related deposits hf o isotopic characteristics indicate that the highly fractionated granites hfg in the changtai and xiangcheng arcs were mainly derived from the partial melting of metasedimentary crustal materials with a minor input from mantle components while the i type granites ig in the geza arc were predominantly derived from the partial melting of ancient lower crustal material the spatial distributions of the different types of deposits in the yidun arc were probably controlled by the magma sources reduced magmas produced by the partial melting of the sedimentary crust in the changtai and xiangcheng arcs are favorable for w sn pb and zn mineralization whereas oxidized magmas produced by the partial melting of the lower crust in the geza arc are conducive to the enrichment of cu au and mo the geochronological data indicate that the emplacement ages of the late cretaceous granites in the yidun arc gradually decrease from north to south ranging from 106 to 73 ma reflecting the southward lateral tectonic migration the structural analysis of the xiuwacu w mo deposit in combination with previous studies demonstrated that the late cretaceous granites in the yidun arc were likely formed in a regional extensional setting which was probably related to the slab break off of the bangong nujiang oceanic slab or the subduction of the yarlung zangbo oceanic slab

tethys tectonic evolution and its bearing on the distribution of important mineral deposits in the sanjiang region sw china abstract the sanjiang region in se tibet plateau and nw yunnan is known to have formed by amalgamation of gondwana derived continental blocks and arc terranes as a result of oceanic subduction followed by continental collision from paleozoic to mesozoic in this paper we provide a synthesis of tectonic evolution magmatism and metallogeny in the region based on data from literatures early paleozoic ophiolites 473 439 ma in the changning menglian belt indicate the existence of a proto tethys ocean in this region two episodes of subduction related magmatism in the early paleozoic one occurred in the baoshan and tengchong blocks at 502 455 ma and the other occurred in the simao block at 421 401 ma are regarded as evidence for two different events of subduction of the proto tethys ocean at different locations the proto tethys was succeeded in early devonian by the paleo tethys which comprised the main ocean and three branches ailaoshan jinshajiang and garze litang the changning menglian main ocean existed from middle devonian to middle triassic the remnants of the oceanic crust are preserved in a few places in the longmu tso shuanghu suture as well as in the changning menglian ophiolite belt the eastward subduction of the main oceanic plate from early permian to early triassic formed a prominent arc terrane stretching 1500 km from yunnan to eastern tibet from the waning stage of subduction to post subduction numerous s type granite plutons with ages varying between 230 and 219 ma such as the lincang batholith in yunnan were emplaced at or close to the suture this event produced several hydrothermal w sn deposits in the region the tectonic evolution and associated magmatism of the jinshajiang and ailaoshan branch oceans are generally comparable to those of the main ocean however the branch oceans were subducted westward instead the garze litang branch ocean also underwent westward subduction from middle devonian to late triassic arc related high sr y porphyry intrusions and associated porphyry skarn cu mo au deposits are common in the jinshajiang ailaoshan region especially in the yidun arc which formed prior to jurassic the vms deposits in the sanjiang region formed in diverse tectonic settings including middle silurian back arc basins carboniferous oceanic islands paleozoic subduction zones and triassic post subduction rifting environments the mesozoic and early cenozoic evolution of the baoshan and tengchong blocks was largely influenced by eastward oceanic subduction of the meso and neo tethys from late permian to middle cretaceous and from late cretaceous to 50 ma respectively abundant early cretaceous granitoids and associated skarn type pb zn and sn fe deposits in the baoshan and tengchong blocks were produced in the background of the shan boundary oceanic slab subduction to the west and the break off of the nujiang bitu oceanic slab to the north the subduction of the neo tethys oceanic plate beneath the tengchong block from late cretaceous to paleogene formed abundant s type granitoids and many skarn type and greisen type sn w deposits granitoids formed at 105 to 81 ma and contemporaneous hydrothermal w mo ag and au deposits which temporally coincided with the subduction of the neo tethys are common in the yidun arc terrane

geology geochronology and geochemistry of granitic intrusions and the related ores at the hongshan cu polymetallic deposit insights into the late cretaceous post collisional porphyry related mineralization systems in the southern yidun arc sw china abstract the hongshan cu polymetallic deposit is located in the southern yidun arc in southwestern china where both subduction related late triassic and post collisional late cretaceous porphyry skarn epithermal mineralization systems have been previously recognized in this study two distinct magmatic events represented by diorite porphyry and quartz monzonite porphyry have been revealed in the hongshan deposit with zircon shrimp u pb ages of 214 2 ma and 73 4 0 7 ma respectively the 73 ma age is comparable to the re os ages of 77 to 80 ma of ore minerals from the hongshan deposit indicating that the mineralization is related to the late cretaceous quartz monzonite porphyries rather than late triassic diorite porphyries the late triassic diorite porphyries belong to the high k calc alkaline series and show arc magmatic geochemical characteristics such as enrichment in rb ba th and u and depletion in hfses indicating that they were formed during the westward subduction of the garze litang ocean in contrast the late cretaceous quartz monzonite porphyries show shoshonitic i type geochemical characteristics with high sio 2 k 2 o lile low hree y and yb contents and high lree hree and la yb ratios these geochemical characteristics together with the sr nd pb isotopic compositions average 87 sr 86 sr i 0 7085 e nd t 6 0 206 pb 204 pb 19 064 207 pb 204 pb 15 738 208 pb 204 pb 39 733 suggest that the quartz monzonite porphyries originated from the partial melting of the ancient lower crust in response to underplating of mafic magma from subduction metasomatized mantle lithosphere possibly triggered by regional extension in the post collisional tectonic stage the s isotopic compositions 34 s v cdt 3 81 to 5 80 and pb isotopic compositions 206 pb 204 pb 18 014 to 18 809 207 pb 204 pb 15 550 to 15 785 and 208 pb 204 pb 38 057 to 39 468 of ore sulfides indicate that the sulfur and metals were derived from mixed mantle and crustal sources it is proposed that although the late triassic magmatic event is not directly related to mineralization it contributed to the late cretaceous mineralization system through the storage of large amounts of sulfur and metals as well as water in the cumulate zone in the mantle lithosphere through subduction metasomatism re melting of the mantle lithosphere including the hydrous cumulate zone and ancient lower crust during the post collisional stage produced fertile magmas which ascended to shallow depths to form quartz monzonite porphyries hydrothermal fluids released from the intrusions resulted in porphyry type mo cu ores in and near the intrusions skarn type cu mo ores in the country rocks above the intrusions and hydrothermal pb zn ores in the periphery

coarse grained nonmarine volcaniclastic sediment terminology and depositional process modern and ancient volcaniclastic sedimentary sequences contain depositional units whose features cannot be attributed to fully turbulent dilute stream flow or viscous debris flow the characteristics of these poorly sorted sediments suggest rapid deposition from high concentration dispersions but not en masse sedimentation thus appears related to high discharge flows intermediate in sediment water ratio between stream flow and debris flow the term hyperconcentrated flood flow is proposed for describing this intermediate condition hyperconcentrated flood flow deposits are distinguished from debris flow deposits by lack of matrix support or reverse grading and instead exhibit distribution normal grading and horizontal stratification these deposits are distinguished from normal dilute stream flow deposits by lack of cross stratification in sand facies and by very poor sorting poor imbrication and numerous clasts with long axes oriented parallel to flow direction in gravel facies the horizontal bedding that dominates sandy hyperconcentrated flood flow deposits consists of sediment too coarse grained and strata too thick to have been produced in the boundary layer of the upper flow regime and should not be confused with the more familiar thin graded laminae of fine to medium grained sand often associated with parting lineation hyperconcentrated flood flow deposits are not unique to volcanic settings they also occur in arid alluvial fan sequences debris flow and hyperconcentrated flood flow deposits however are much thicker and more extensive in volcanic regions than on alluvial fans because explosive volcanism leads to rapid mobilization of large volumes of sediment and water on a scale unparalleled in nonvolcanic settings in volcanic regions therefore these deposits have greater preservation potential show greater lateral variability and are more voluminous transformation of channelized debris flow to hyperconcentrated flood flow by dilution with stream water recently observed at mount st helens is recorded in ancient volcaniclastic sequences and may serve as the primary mechanism for generating hyperconcentrated flood flow

luminescence studies on neotectonic events in south central kumaun himalaya a feasibility study abstract results of a feasibility study on luminescence dating of neotectonic events as recorded in fault gouges and buried soils formed on landslide debris are reported it is suggested that clay mineralogical data on illite and chlorite can provide a reasonable estimate on the thermal excursion and hence on resetting of the luminescence clock during faulting the thermoluminescence ages are consistent with the available radiocarbon ages and have been used to infer that naini lake was formed at ca 40 50 ka

climatic and tectonic controls on the sedimentary processes of an alluvial fan of the western ganga plain india detailed facies analysis and morphotectonic investigations of the malin river9s alluvial fan in the western ganga plain india reveal that the morphology of the fan is largely tectonically controlled whereas the sedimentary processes are mainly climatically controlled the sedimentation occurred in two distinct evolutionary cycles which are separated by a time gap the older cycle deposited thick gravelly units up to the distal fan area whereas the sediment fill of the younger cycle is gavel dominated in the proximal fan area gravel sand dominated in the middle fan area and sand mud dominated in the distal fan area the gravels of the older cycle were emplaced by intense sediment gravity flows during periods of strengthened monsoon and steeper regional gradient during the younger cycle the proximal to distal parts of the fan were dominated by different sedimentary processes this was a time of relatively weaker monsoon and gentler regional slopes when gravels could travel only up to the middle fan area the gravels in the proximal fan area have mainly been deposited by sediment gravity flows and channel processes in the middle fan area channel processes sheetfloods and sediment gravity flows have been the main sedimentary processes and in the distal fan area fluvial processes of channel migration and overbank deposition have been the main sedimentary processes

controls on sedimentation in distal margin palaeovalleys in the early tertiary alpine foreland basin south eastern france the influence of palaeodrainage characteristics palaeogeography and tectonic setting are rarely considered as controls on stratigraphic organization in palaeovalley or incised valley systems this study is an examination of the influence of source region vs downstream base level controls on the sedimentary architecture of a set of bedrock confined palaeovalleys developed along the distal margin of the alpine foreland basin in south eastern france three distinct facies associations are observed within the palaeovalley fills fluvial facies association a is mainly dominated by poorly sorted highly disorganized clast to matrix supported cobble to boulder conglomerates that are interpreted as streamflood deposits facies association b comprises mainly yellow siltstones and is interpreted as recording deposition in an estuarine basin environment estuarine marine facies association c comprises interstratified estuarine siltstones and clean well sorted washover sandstones the sedimentary characteristics of the valley fill successions are related to the proximity of depositional sites to sediment source areas palaeovalleys located proximal to structurally controlled basement palaeohighs are entirely dominated by coarse fluvial streamflood deposits in contrast distal palaeovalley segments which are located several kilometres downstream contain successions showing upward transition from coarse fluvial facies into estuarine central basin fines and finally into estuarine marginal marine facies facies distributions suggest that the fluvial deposits form wedge shaped downstream thinning sediment bodies whereas the estuarine deposits form an upstream thinning wedge the vertical stacking of fluvial to estuarine to marginal marine depositional environments records the fluvial aggradation and subsequent transgression of relatively small bedrock confined river valleys which drained a rugged upland terrain facies geometries suggest that a fluvial sediment wedge initially prograded downvalley in response to high bed load sediment yields subsequently palaeovalleys became drowned during the passage of a marine transgression with the establishment of estuarine conditions initial fluvial aggradation and subsequent marine flooding of the palaeovalleys is a consequence of the interaction of high local rates of sediment supply and relative sea level rise driven by flexural subsidence of the basin

sedimentologic and geomorphic variations in storm generated alluvial fans howgill fells northwest england in june 1982 a storm with a return period greater than 100 yr but lasting less than 2 5 hr destabilized hillslopes and produced a suite of geomorphologically and sedimentologically diverse alluvial fans thirteen major fans were deposited at the tributary junctions between small 2 catchments and two north flowing headwater streams of the river lune northwest england storm generated fans spread over or became inset into older stable fans and produced localized vertical accretion of as much as 3 m and lateral accretion of as much as 100 m sedimentary processes operating during deposition involved debris flow transitional flow and streamflow six facies types are recognized on the basis of depositional topography sedimentary texture and fabric and matrix content viscous debris flow d1 dilute debris flow d2 transitional flow t1 fluvial bars and lobes s1 s2 and fluvial sheet gravels s3 regionally streamflow deposition prevails over debris flow deposition and type s3 facies has the greatest areal extent temporal and spatial variations in facies deposition during the storm however resulted from water sediment ratio variations fan deposition involved an early phase of debris flow to transitional flow due to large inputs of sediment from hillslope failures this was followed by a systematic change to more dilute conditions resulting in streamflow deposition and eventually in channel incision a significant amount of geomorphic work and complex variations in sedimentary processes during the storm resulted in part from extensive overland flow and hillslope destabilization discriminant analyses indicate that catchment size channel gradient and percentage of area eroded during the storm controlled whether debris flow or streamflow facies dominated a fan sequence smaller steeper catchments had a greater percentage of the area yielding sediment and are dominanted by debris flows whereas larger catchments produced more runoff resulting in dilution and streamflow the results indicate that the facies sequences and fan entrenchment in the howgill fells which are typically considered products of longer term climatic change or tectonics in other localities are here primarily affected by thresholds related to catchment geomorphology by the type of sediment available and by the position within the storm cell

new zircon fission track analysis constraints on tectonic mineralization epochs in the ganzi litang gold belt eastern qinghai tibet plateau abstract the ganzi litang gold belt as a part of the sanjiang tethys orogen is located between the yidun block and songpan ganzi block terrane in the eastern qinghai tibetan plateau and experienced oceanic slab subduction continent arc collision and intracontinental convergence since the indosinian orogeny a series of gold ore deposits have been found within the region this paper describes the tectonic evolution and episodes of gold mineralization within this belt using zircon fission track ft thermochronology a total of 15 zircon ft analysis results were obtained that can be divided into four age groups 217 213 ma 190 160 ma 155 93 ma and 72 67 ma representing four distinct episodes of gold mineralization of which the middle two episodes predominate eruption of the auriferous volcanic rocks that comprise the belt started at 217 213 ma when the ganzi litang meso tethys ocean began to subduct the mineralization episode at 190 160 ma corresponds to the formation of auriferous volcanic rocks during intracontinental collisional convergence of the ganzi litang belt finally the episodes at 155 93 ma and 72 67 ma are respectively related to the closing times of the bangong nujiang and yarlung zangbu oceans corresponding to tectonic quiet episodes

pleistocene geomorphological and sedimentary development of the akaki river catchment northeastern troodos massif in relation to tectonic uplift versus climatic change the uplift of the troodos ophiolite is reflected in the development of the akaki river catchment in the northeast troodos massif four main stages f1 f4 of geomorphological terrace development and related deposits are recognised using satellite imagery and field observations the geomorphological terraces have been tectonically uplifted during the pleistocene so that they dip northwards from the troodos mountains until they merge with the mesaoria plain lithology e g hard diabase versus soft extrusive rock has exerted an important control on the geomorphology of the akaki river channel the f1 terraces and related deposits are well preserved in the lower reaches of the catchment the f2 terraces are more widely preserved but with few preserved deposits the f3 erosional surfaces e g strath terraces and related deposits are widespread up into the higher reaches of the catchment the f4 to recent geomorphological surfaces and deposits are confined to near the modern river channel the f1 to f3 aged deposits each include very high energy mass flow deposits and somewhat lower energy traction flow deposits with minimal sand preservation stages of fluvial aggradation were followed by soil development e g terra rossa the f1 to f4 aged terraces and related deposits mainly formed in response to a combination of very long term tectonic uplift and climatic related change long term and short term tectonic uplift was the dominant driver related to the updoming of the troodos ophiolite especially during the earlier time period f1 and f2 whereas climate related effects appear to have dominated more recently f3 and f4 sedimentary aggradation is likely to have predominated during interglacial periods while interglacial glacial transitions when climate fluctuated are seen as times of increased incision previous correlations of the f1 f4 fluvial deposits with similar deposits elsewhere in cyprus including coastal marine carbonate deposits suggest that the f1 and f2 deposits are likely to be of middle pleistocene age and the f3 f4 deposits of late pleistocene to holocene age

the role of alluvial fans in the mountain fluvial systems of southeast spain implications of climatic change the mountain fluvial systems of southeast spain involve sediment supply from steep mountain slopes into headwater channels alluvial fans often occur where these headwater channels emerge from the mountain areas and may influence the connectivity of the sediment transport system from the mountain source areas to the main lowland drainages critical in this role is whether the alluvial fans are aggrading or dissecting and whether there is a break or continuity in the channel through the fan environment previous work has identified some of the factors influencing the behaviour of the alluvial fans in southeast spain this paper deals with the mountain front alluvial fans in the semi arid areas of murcia and almeria provinces it attempts by mapping the location of alluvial fans then their classification into aggrading or dissecting fans to identify the extent to which the mountain fluvial systems are buffered by aggrading alluvial fans or exhibit channel continuity through the mountain front environment it further considers the implications of climatically induced changes between aggradational and dissectional behaviour on alluvial fans

early cretaceous adakitic granites in the northern dabie complex central china implications for partial melting and delamination of thickened lower crust abstract to date few adakitic rocks have been reported in direct association with contemporary intra continental extensional structures which has cast doubt on genetic models involving partial melting of the lower crust this study presents early cretaceous 143 129 ma new sensitive high resolution ion microprobe shrimp zircon u pb ages adakitic granites which are directly associated with a contemporary metamorphic core complex i e the northern dabie complex in the dabie area these granites exhibit relatively high sr contents negligible to positive eu and sr anomalies high la yb and sr y ratios but very low yb and y contents similar to subducted oceanic crust derived adakites they are also characterized however by very low mgo or mg and ni values and nd sr isotope compositions end t 14 6 to 19 4 and 87sr 86sr i 0 7067 0 7087 similar to triassic continent derived eclogites subducted in the dabie sulu orogen additionally late granitic dikes in the adakitic intrusions exhibit low sr contents clearly negative eu and sr anomalies low la yb and sr y ratios but relatively high yb and y contents similar to 118 105 ma granites in the northern dabie complex based on composition and geochronology data of neoproterozoic amphibolites and orthogneisses triassic high to ultra high pressure metamorphic rocks and early cretaceous mafic ultramafic intrusive rocks and the constraints provided by experimental melt data for tonalites metabasaltic rocks and eclogites we suggest that the adakitic granites were most probably generated by partial melting of thickened amphibole or rutile bearing eclogitic lower crust as a consequence of triassic middle jurassic subduction and thrusting the late dikes probably originated from plagioclase bearing intermediate granulites moreover we suggest that late mesozoic delamination or foundering of thickened eclogitic lower crust is also a more plausible mechanism for the petrogenesis of early cretaceous mafic ultramafic intrusive rocks in the dabie area and probably involved partial melting of a mixed source comprising eclogitic lower crust that had delaminated or foundered into upper lithospheric or asthenospheric mantle peridotite asthenospheric upwelling in response to post collisional delamination of lithospheric mantle was likely to have provided the heat source for the cretaceous magmatism

structure and shortening of the kangra and dehra dun reentrants sub himalaya india surface geology oil well seismic reflection and magnetostratigraphic data are integrated to evaluate the structural style and the shortening rate at the himalayan front sub himalaya of northwest india the sub himalaya between the main boundary thrust and the himalayan frontal fault is the primary surface expression of shortening between the himalaya and the indian plate at certain locations the himalayan frontal fault is a blind thrust beneath anticlines of siwalik tertiary molasse parallel to the himalayan orogen the main boundary thrust is sinuous so the width of the sub himalaya ranges from 30 to 80 km where the sub himalaya is narrow nahan salient tertiary rocks are exposed in imbricate thrust sheets where the sub himalaya is broad kangra and dehra dun reentrants alluvium fills wide synclinal valleys duns seismic reflection data reveal that surface anticlines form in association with south vergent thrusts that root in a decollement at the base of the tertiary section reflection profiles and well data also indicate that the basement lithology changes northward from precambrian crystalline rocks beneath the indo gangetic plains to precambrian and cambrian metasedimentary rocks beneath the sub himalaya the sub himalayan decollement dips 2 5 northward beneath the kangra reentrant but it is steeper 6 beneath the dehra dun reentrant the kangra and dehra dun reentrants display fault propagation folds having steep limbs in the north and fault propagation and fault bend folds that have gently north dipping limbs in the south a balanced cross section of the kangra reentrant shows that a minimum of 23 km shortening has occurred since 1 9 1 5 ma yielding a shortening rate of 14 2 mm yr shortening has occurred at a rate of 6 16 mm yr across the dehra dun reentrant these data are similar to other published shortening rates and indicate that approximately 25 of the total india eurasia convergence at this longitude is accommodated within the sub himalaya given continued convergence and the presence of overpressured wells in the kangra reentrant the region is likely at risk from moderate and or great earthquakes in the future

evolution of quaternary alluvial fans and terraces in the intramontane pinjaur dun sub himalaya nw india interaction between tectonics and climate change quaternary alluvial fans in the tectonically active pinjaur dun an intramontane valley in the sub himalaya were deposited in front of the nalagarh thrust and were influenced both by tectonics and glacial climate fluctuations the surface morphology indicates that an earlier set of first order fans qf1 became entrenched and onlapped by a series of second order fans qf2 the younger fan segments were then cut by a pair of terraces t1 and t2 quartz optically stimulated luminescence dating establishes that the qf1 aggradational phase was initiated before 96ae 5 2 5ae3 ka and terminated after 83ae 7 1 6ae3 ka this was followed by a period of incision before qf2 fan deposition started at 72ae 4 1 3ae4 ka and continued until 24ae 5 4 ae 9k a sediment was deposited on the t1 upper and t2 lower terraces at 16ae 3 2 ae1 and 4ae5 ka respectively recording a return to overall degradation punctuated by minor deposition on terraces the period of incision separating the younger and older fan deposits coincided with enhanced sw monsoon precipitation the subsequent development of the qf2 fans and their progradation until 20 ka suggest erosional unloading of the thrust hangingwall during a tectonically quiescent phase toe cutting deposition of axial river and lacustrine facies and retreat of qf2 around 45 ka indicate fanward shift of the axial river due to tilting of the valley towards the ne in response to reactivation of the nalagarh thrust the cessation of qf2 deposition around 20 ka and the onset of through fan entrenchment suggest reduced sediment supply but relatively high stream power during the last glacial maxima lgm the prolonged stream incision since the cessation of qf2 deposition with only minor depositional phases at 16ae 3 2 ae1 and 4ae 5k a resulted from high water discharge and low sediment input during intensification of the sw monsoon and vegetation changes in the hinterland

porphyry cu deposits in collisional orogen setting a preliminary genetic model porphyry cu deposits pcds as the primary source of copper are usually thought to be formed in a magmatic arc setting they can also occur in collisional orogen or intraplate settings the classic pcds model proposed by lowell and guilbert 1970 has been widely accepted by economic geologists because of its practical value in the exploration of pcds in the arc setting especially in the circum pacific belt however lowell and guilbert s model fails to give a reasonable explanation of the pcds in the collisional orogen setting the authors therefore give a detailed description of geological setting tectonic control magma source general characteristics of the ore deposit source and enrichment mechanism of metals fluid source and evolutionary path of pcds in the qinghai tibetan collisional orogen setting and propose a preliminary genetic model several points are emphasized in this model mineralization related porphyry intrusions in the collisional orogen setting are geochemically adakitic rocks which originaue from the newly formed lower crust and are triggered by the upwelling of asthenosphere and or the transition of structure mechanism from extrusion to extension the enrichment of cu and other metals in the adakitic magmas results from the relatively high oxidation state of the source in which the bulk of the sulfur is dissolved in the sulfate form with the result that sulfide compatible elements such as cu and au can also behave as incompatible elements and will be retained in the evolving magmas the ascent of the adakitic magmas is usually constrained by large sized strike slip fault systems triggered by oblique collision or by large sized normal faults induced by lithosphere removal whereas the emplacement of the adakitc magmas is generally controlled by mine scale structures the magma chamber usually exists below large sized and especially giant deposits in these deposits cu s and magmatic fluids which are essential for the formation of porphyry cu deposits generally originate directly from the magma chamber the deposits reinforce most of the generalized characteristics of porphyry cu deposits in continental arc settings except for the fact that they show relatively strong k silicate alteration due to high k h value in the high k adakitic magma dominated ore forming fluid sulfide precipitation mainly occurs during k silicate alteration usually in response to the change of temperature pressure salinity f o2 and ph value especially to the change of temperature and pressure

petrogenesis of mesozoic granitoids and genesis of au polymetallic mineralization in the sonchon district dpr korea abstract the au polymetallic deposit in the sonchon district is located in the western parts of north pyongan province dpr korea here we present a detailed study of the petrogenesis magma source of the mesozoic granitoids and the sources of ore forming materials and fluids mesozoic granitoids consist of diorite granodiorite and biotite granite these rocks are alkali enriched k2o na2o 5 02 7 75 wt and classified as high k calc alkaline the diorite is metaluminous while the granodiorite and biotite granite are weakly peraluminous and peraluminous respectively the samples show high cao na2o ratios of 1 66 2 16 for the diorite and 0 74 1 35 for the granodiorite indicating a derivation from clay poor psammite derived melt source and the biotite granite has low cao na2o ratios of 0 14 0 38 indicating a derivation from clay rich pelite derived melt source the biotite granite belongs to fractionated m i and s type granites fg whereas the granodiorite and the diorite belong to unfractionated m i and s type granites ogt these rocks are typically arc related the similar ree distribution patterns of these rocks show that they are relatively uniform with partial melting processes playing an important role in their generation the ree distribution patterns of ore bearing quartz are similar to those of granodiorite rather than diorite biotite granite and wall rocks suggesting that they were mainly inherited from the granodiorite the barren quartz has more negative eu anomalies than the ore bearing quartz the histogram of sulfur isotopic composition shows that the 34s values are mainly distributed around 5 to 10 and indicate the sulfur within sulfide was derived from a magmatic source the absence of sulfates in ore bodies indicates that the low fo2 and high ph of ore forming fluid system fluid inclusions in quartz have only aqueous gas phases without co2 rich phase and daughter minerals indicating that ore forming fluids was homogenous magmatic and had low salinity according to the values of x na x k ratios x na x ca2 mg2 ratios and x f x cl ratios the ore forming fluids could be interpreted as a mixture of magmatic and meteoric water microthermometric analyses indicate that these inclusions have medium temperature 223 5 286 3 c and low salinity 1 39 4 01 wt nacl and are nacl h2o or nacl kf h2o systems all these data in this study suggest that the sonchon au polymetallic deposit is mesothermal and related to the granodiorite

facies and depositional model of alluvial fan dominated by episodic flood events in arid conditions an example from the quaternary poplar fan north western china

atmospheric summer circulation and coastal upwelling in the arabian sea during the holocene and the last glaciation accumulation rates of biogenic and lithogenic components were studied in 39 turbidite free well dated sediment cores from the northern indian ocean to define the proportions of fluvial and eolian input and to reconstruct quaternary patterns of coastal upwelling the majority of dust deposited in the western arabian sea during the holocene about 100 106 t yr 1 is advected from arabia by northwesterly winds which overlie the low level southwest monsoon the glacial increase in dust flux to 160 106 t yr 1 culminated in the northern arabian sea most probably due to i entrainment of dust rich in chlorite dolomite and lithogenic carbonate in the then dry persian gulf and ii a southward shift of the mean position of the southwest monsoon during glacial summer this shift is recorded in reduced accumulation rates of biogenic opal and increased rates of marine carbonate off somalia and oman both the terrigenous and biogenic sediment records show that the northwesterly winds and the southwest monsoon persisted over the last 27 000 yr as well as the asian continental summer heat low however the glacial seasonal time span of the southwest monsoon season was much reduced most likely because of a delay in the seasonal onset of the southwest monsoon

discontinuity bounded alluvial sequences of the southern gangetic plains india aggradation and degradation in response to monsoonal strength abstract discontinuity bounded late quaternary sequences in the southern gangetic plains himalayan foreland basin reflect floodplain aggradation and degradation in response to forcing by the powerful southwest indian monsoon the major himalayan and cratonic rivers in this area occupy narrow incised valleys and do not inundate the adjoining broad interfluves which display soil development small plains fed rivers lakes eolian deposits and badland ravines however these areas formerly experienced active alluviation because thick floodplain muds underlie the interfluve an age model suggests that interfluve areas near the major rivers aggraded periodically between about 27 ka and 90 ka marine oxygen isotope stages 3 5 they subsequently degraded or accumulated sediment only locally probably reflecting decreased monsoonal precipitation around the last glacial maximum marine isotope stage 2 when major river valleys moved to an underfit condition increased precipitation during the 15 to 5 ka period of monsoon recovery probably increased discharge and promoted incision and widespread badland formation discontinuities at deeper levels reflect earlier degradation phases and are marked by reworked gravel lenses thin channel bodies and carbonate cemented surfaces carbonate veins infilled joints that cut strata below but not above one discontinuity suggest some local tectonic influence there is no evidence that sea level fluctuations influenced stratal patterns in this elevated inland region discontinuity bounded sequences linked to climate change may characterize alluvial successions in many continental settings especially along the cratonic margins of foreland basins where subsidence rates are modest