mountain evaporation profiles on the island of hawai i evaporation was measured along three altitudinal transects on mauna loa on the island of hawai i stations lie between 70 and 3400 m a s l and included environments ranging from tropical rainforest with 6 m year 1 annual rainfall to barren subalpine lava fields in a dry environment above a persistent subsidence temperature inversion average daily evaporation decreased with elevation between sea level and about 1200 m and then increased with elevation above that level evaporation minima ranged from 1 9 to 2 2 mm day 1 the maximum evaporation rate 6 1 mm day 1 was at the highest site mauna loa observatory at 3400 m analysis of pan evaporation data collected at 3400 m showed that standard formulae based on other meteorological variables provided good approximations of measured evaporation transect data were also compared with similar measurements from mountains on other hawaiian islands

paleoproterozoic granitoids of the don terrane east sarmatian orogen age magma source and tectonic implications abstract the pavlovsk complex granitoid plutons and associated gabbro diorites are confined to the east sarmatian orogen eso that compose the western part of the junction between the sarmatian and volgo uralia segments of the east european craton the plutons form the largest batholiths with an area of up to 2000 km2 and a total length of more than 330 km the conditions for their emplacement and crystallization sources of melts and tectonic position remain debatable here we present new results on geochronological geochemical and isotope data on the pavlovsk complex granitoids and associated gabbro diorites and discuss these in conjunction with previously published data the geochemical characteristics such as elevated concentrations of mg k sr and ba usually 500 ppm ratios la yb n 25 73 and sr y 23 223 in the absence of eu anomalies of the pavlovsk type plutons are similar to high mg archean granites zircon u pb data indicate the formation of the granitoids and associated gabbro diorites during a short span at 2060 2075 ma the magma emplacement occurred in a transitional environment from late collisional to post collisional after the collision of two crustal segments sarmatia and volgo uralia we identify a significant ancient archean continental crust in the magma source for the northern plutons and leucogranites including the presence of archean zircon cores and archean model tnd dm ages all the plutons are dominated by a mixed magma source generated through the interaction of juvenile lower crustal and enriched mantle components the nd isotopic composition of the studied plutons is significantly more radiogenic as compared with the host archean rocks end t from 0 3 to 4 2 our geochemical data suggest that that the mantle source of the gabbro diorites and granitoids were modified metasomatized by subduction related processes the contrasting geochemical and isotopic features of the granitoids in the eso as compared to the pavlovsk granitoids suggest different sources for the parent melts

world class ni cu pge deposits key factors in their genesis magmatic ni cu sulfide deposits form as the result of segregation and concentration of droplets of liquid sulfide from mafic or ultramafic magma and the partitioning of chalcophile elements into these from the silicate melt sulfide saturation of a magma is not enough in itself to produce an ore deposit the appropriate physical environment is required so that the sulfide liquid mixes with enough magma to become adequately enriched in chalcophile metals and then is concentrated in a restricted locality so that the resulting concentration is of ore grade the deposits of the noril sk region have developed within flat elongate bodies 15 2 0 2 km that intrude argillites evaporites and coal measures adjacent to a major trans crustal fault and immediately below the centre of a 3 5 km thick volcanic basin studies of the overlying basalts have shown that lavas forming a 500 m thick sequence within these have lost 75 of their cu and ni and more than 90 of their pge overlying basalts show a gradual recovery in their chalcophile element concentrations to reach normal values 500 m above the top of the highly depleted zone the ore bearing noril sk type intrusions correlate with those basalts above the depleted zone that contain normal levels of chalcophile elements the high proportion of sulfide 2 10 wt associated with the noril sk type intrusions the high pge content of the ores the extensive metamorphic aureole 100 400 m around the bodies and the heavy sulfur isotopic composition of the ores 8 12 34s are explicable if the ore bearing bodies are exit conduits from high level intrusions along which magma has flowed en route to extrude at surface the first magma to enter these intrusions reacted with much evaporitic sulfur at a low r value and thus gave rise to sulfides with low metal tenors successive flow of magma through the system progressively enriched the sulfides in the conduits losing progressively less of their chalcophile metals and thus accounting for the upward increase in metals in successive lava flows above the highly depleted flows the voisey s bay deposit lies partly within a 30 100 m thick sheet of troctolite interpreted as a feeder for the 1 334 ga voisey s bay intrusion and partly at the base of this intrusion where the feeder adjoins it studies of olivine compositions indicate that an early pulse of magma through the feeder and into the intrusion was ni depleted but that subsequent pulses were much less depleted trace element re os and s and o isotope data and mineralogical studies indicate that the magma pulses interacted with country gneiss probably principally in a deeper level intrusion extracting sio2 na2o k2o and possibly sulfur form the gneiss which accounts for the magma becoming sulfide saturated the jinchuan deposit of north central china occurs within a 6 km long dyke like body of peridotite the compositions of olivine within the dyke the igneous rocks themselves and the ore are all inconsistent with derivation of the body from ultramafic magma as originally supposed and indicate that the structure forms the keel of a much larger intrusion of magnesian basalt magma flow of magma into the intrusion has resulted in olivine and sulfide being retained where the keel was widening out into the intrusion the west australian komatiite related deposits occur in thermal erosional troughs which have developed due to the channelisation of magma flow and the resulting thermal erosion of underlying sediments and basalt by the hot komatiite magma the sediments are sulfide rich and may have contributed substantially to the sulfide of the ores the mineralisation in the duluth complex occurs in troctolitic intrusions along the western margin of the complex as a result of magma interacting with and extracting sulfur from the underlying graphite and sulfide bearing sediments no magma flow channels have been identified so far and the lack of magma flow subsequent to the development of sulfide immiscibility is regarded as the reason why these deposits are not of economic grade when most major ni cu sulfide deposits are compared they prove to have a number of features in common olivine rich magma proximity to a major crustal fault sulfide bearing country rocks chalcophile element depletion in related intrusive or extrusive rocks field and or geochemical evidence of interaction between the magma and the country rocks and the presence of or proximity to a magma conduit the features are thought to explain the three key requirements sulfide immiscibilty adequate mixing between sulfides and magma and localisation of the sulfides discussed and have important implications with respect to exploration

the effects of precipitation gradients on river profile evolution on the big island of hawai i to better understand how climate affects bedrock river incision and long term landscape evolution in the absence of tectonic forcing we quantify differences in the longitudinal profiles of eroding bedrock channels across the kohala peninsula on the northern tip of the big island of hawai i an orographic rainfall gradient causes mean annual precipitation rates to vary by over an order of magnitude from greater than 4000 mm yr on the wet side to less than 250 mm yr on the dry side of the peninsula channels on the wet side are relatively deeply incised into the surrounding landscape and have developed profiles in which slope increases downstream in upstream reaches convex form and decreases downstream in downstream reaches concave form wet side river channels have relatively large 10 30 m vertical steps or knickpoints in the convex zone in contrast channels on the dry side of the peninsula are more shallowly incised have developed nearly straight longitudinal profiles in which channel slope does not significantly change from upstream to downstream and have smaller knickpoints channel profile form changes from straight to convex concave at a watershed averaged mean annual precipitation rate of between 1300 and 1750 mm yr suggesting a climatic threshold in this landscape above which bedrock incision rates are enhanced valley depth used as a proxy for the magnitude of channel incision increases with increasing mean annual precipitation and is consistent with a similar fluvial incision threshold while the lithology is entirely basalt incision patterns also appear to be affected by spatial differences in bedrock weathering due to both local climate and basalt flow age the older and more weathered polol basalts 260 450 ka are capped by the younger haw basalt series 120 260 ka and we interpret that heterogeneous weathering of these units influences channel form relief sediment production and knickpoint development

tectonic setting of post collisional magmatism in the palaeoproterozoic svecofennian orogen sw finland abstract five bimodal post collisional intrusions in southwestern finland have been investigated geochemically the mafic rocks are shoshonitic monzodiorites which are highly enriched in fe p ti f lree and in incompatible trace elements the felsic rocks are garnet bearing peraluminous s type anatectic granites new data on the mafic and the felsic intrusions yielded the same u pb zircon age of 1815 ma therefore the mafic and felsic intrusions are coeval but not cogenetic narrow contact metamorphic aureoles around the mafic intrusions contain garnet orthopyroxene bearing assemblages and thermobarometry indicates an intrusion depth of at least 15 km hence there was little or no unroofing after peak regional metamorphism at 4 6 kbar the geochemical characteristics of the mafic rocks suggest that they were derived from subcontinental lithospheric mantle that was previously enriched by fluids released during svecofennian subduction it is suggested here that hot upwelling asthenosphere convectively removed subcontinental lithospheric mantle and triggered partial melting of the enriched parts of the mantle uprising mafic melts increased the already high temperatures at mid crustal levels and caused granulite facies metamorphism crustal anatexis and production of granitic melts

the scourie dyke suite petrogenesis and geochemical nature of the proterozoic sub continental mantle the petrogenesis of bronzite picrite olivine gabbro norite and quartz tholeiite dykes which make up the 2 39 b y scourie dyke swarm cutting the archaean lewisian gneisses of n w scotland is interpreted on the basis of their major and trace element geochemistry most of the dykes bear primary amphibole and or phlogopite and with one exception are all hypersthene or quartz normative apart from one tholeiite dyke which shows relative light rare earth element depletion all the dykes show enrichment in light rare earths and large ion lithophile elements they do not however show an equivalent enrichment in other incompatible high field strength ions such as nb and ta and in this respect resemble island arc and calc alkaline basalts the different dyke types have distinctive rare earth patterns and other trace element ratios which are maintained over a range of major element compositions

the kalatongke magmatic ni cu deposits in the central asian orogenic belt nw china product of slab window magmatism the permian kalatongke ni cu deposits in the central asian orogenic belt are among the most important ni cu deposits in northern xinjiang western china the deposits are hosted by three small mafic intrusions comprising mainly norite and diorite its tectonic context petrogenesis and ore genesis have been highly contested in this paper we present a new model involving slab window magmatism for the kalatongke intrusions the origin of the associated sulfide ores is explained in the context of this new model minor amounts of olivine in the intrusions have fo contents varying between 71 and 81 5 mol which are similar to the predicted values for olivine crystallizing from coeval basalts in the region analytic modeling based on major element concentrations suggests that the parental magma of the kalatongke intrusions and the coeval basalts represent fractionated liquids produced by 15 of olivine crystallization from a primary magma itself produced by 7 8 partial melting of depleted mantle peridotite positive end values 4 to 10 and significant negative nb anomalies for both intrusive and extrusive rocks can be explained by the mixing of magma derived from depleted mantle with 6 18 of a partial melt derived from the lower part of a juvenile arc crust with a composition similar to coeval a type granites in the region plus up to 10 contamination with the upper continental crust our model suggests that a slab window was created due to slab break off during a transition from oceanic subduction to arc arc or arc continent collision in the region in the early permian decompression melting in the upwelling oceanic asthenosphere produced the primary magma when this magma ascended to pond in the lower parts of a juvenile arc crust it underwent olivine crystallization and at the same time triggered partial melting of the arc crust mixing between these two magmas followed by contamination with the upper crust after the magma ascended to higher crustal levels formed the parental magma of the kalatongke intrusions the parental magma of the kalatongke intrusions was saturated with sulfide upon arrival primarily due to olivine fractional crystallization and selective assimilation of crustal sulfur sulfide mineralization in the kalatongke intrusions can be explained by accumulation of immiscible sulfide droplets by flow differentiation gravitational settling and downward percolation which operated in different parts of the intrusions platinum group element pge depletion in the bulk sulfide ores of the kalatongke deposits was due to depletion in the parental magma which in turn was likely due to depletion in the primary magma pge depletion in the primary magma can be explained by a relatively low degree of partial melting of the mantle and retention of coexisting sulfide liquid in the mantle

petrogenetic relationship between palaeoproterozoic tholeiitic dykes and associated high mg noritic dykes labrador canada abstract trace element and sr nd isotopic studies of the palaeoproterozoic 2235 ma kikkertavak dyke swarm in labrador provide information on early sub continental lithosphere development there are three distinct chemical dyke types two are tholeiitic the third of high mg norite composition petrogenetically it is not possible to relate any of the chemical groups one to another by simple fractional crystallisation processes nor can they be derived by contaminating asthenospheric magmas with local crustal components from their sr nd isotopic characteristics in relation to their rare earth and multielement patterns it is clear that significant heterogeneity existed in the source regions of the dyke magmas at the time they were generated and that the mantle processes responsible can be linked with the phase of crustal growth in the region at 3 0 ga modelling suggests that the observed compositions can be accounted for by lower lithosphere asthenosphere mantle sources which have been variably depleted by previous episodes of basalt magma extraction and then re enriched by a lamproitic melt component and possibly by progressive infiltration of melts from a subducted sediment or subduction component high mg noritic dykes are relatively common worldwide in the palaeoproterozoic and are often broadly coeval with tholeiitic dykes but are much less common in younger dyke suites most have compositions which require a refractory major element composition coupled with significant re enrichment in incompatible lithophile elements recent models for cyclic mantle overturns with related deep mantle plumes begin to provide the right thermal and compositional environment beneath immature lithosphere which can generate the dyke types observed

a review of the cu ni sulphide deposits in the chinese tianshan and altay orogens xinjiang autonomous region nw china principal characteristics and ore forming processes abstract several cu ni sulphide deposits and occurrences have recently been discovered along parallel deep faults in the chinese tianshan and altay orogenic belts xinjiang province nw china the kalatongke and several other cu ni mineralized intrusions are located along the irtysh fault which separates the altay orogenic belt from the junggar basin the huangshan huangshandong xiangshan tudun erhongwa tula ergen and hongling deposits occur along the kanggurtag suture which separates the jueluotage orogenic belt from the turpan hami tuha basin the baishiquan tianyu and tianxiang deposits are located along the arqikekuduke fault which separates the jueluotage orogenic belt from the central tianshan precambrian terrane the poyi poshi and luodong deposits are located along the baidiwa fault which separates the central tianshan precambrian terrane from the beishan paleozoic rift re os dating of cu ni sulphide ores reveals that these cu ni ore belts formed in a narrow age range of 298 282 ma this age range is about the same as those of associated intrusions and dykes dated by the shrimp zircon u pb method tectonic and geochronological constraints suggest that the amalgamation of continental blocks mainly occurred during the late carboniferous in the central asian orogenic belt large scale hydrothermal and magmatic metallogenesis in the region occurred during post collisional stages of latest carboniferous to early permian age the cu ni sulphide deposits are part of this metallogenic event the cu ni orthomagmatic sulphide deposits in northern xinjiang are represented by 1 net textured type deposits by segregation of a cu ni metal sulphide melt and 2 magma conduit type some mafic ultramafic suites exhibit lithological zoning caused by strong differentiation stratiform orebodies are hosted by ultramafic rocks at the base of the magma chamber good examples are the kalatongke huangshandong and poshi deposits others such as the xiangshan baishiquan tianyu and tula ergen deposits are hosted by magma conduits consisting of peridotite troctolite and pyroxenite these ultramafic rocks either occur within faults or are surrounded by gabbroic and dioritic intrusions these two types of orthomagmatic cu ni sulphide deposits are also distributed along the same ore belts for instance the differentiated sill related huangshandong deposit co exists with the magma conduit type tula ergen deposit in the jueluotage orogenic belt orthomagmatic cu ni sulphide deposits in northern xinjiang formed during post collisional extension and are possibly related to a late carboniferous early permian mantle plume event the mafic ultramafic suites and associated cu ni deposits are commonly accompanied by dyke swarms and are characterized by elongated outcrops occurring along parallel e w trending regional faults these mafic ultramafic suites and accompanying dyke swarms are generally fractionated implying that they were feeders of presently eroded flood basalts

a physically based model for the topographic control on shallow landsliding a model for the topographic influence on shallow landslide initiation is developed by coupling digital terrain data with near surface through flow and slope stability models the hydrologic model topog o loughlin 1986 predicts the degree of soil saturation in response to a steady state rainfall for topographic elements defined by the intersection of contours and flow tube boundaries the slope stability component uses this relative soil saturation to analyze the stability of each topographic element for the case of cohesionless soils of spatially constant thickness and saturated conductivity the steady state rainfall predicted to cause instability in each topographic element provides a measure of the relative potential for shallow landsliding the spatial distribution of critical rainfall values is compared with landslide locations mapped from aerial photographs and in the field for three study basins where high resolution digital elevation data are available tennessee valley in marin county california mettman ridge in the oregon coast range and split creek on the olympic peninsula washington model predictions in each of these areas are consistent with spatial patterns of observed landslide scars although hydrologic complexities not accounted for in the model e g spatial variability of soil properties and bedrock flow control specific sites and timing of debris flow initiation within areas of similar topographic control

noritic dykes of southern west greenland early proterozoic boninitic magmatism two major swarms of early proterozoic ca 2 1 ga basic dykes occur within the archaean craton of southern west greenland one swarm comprises ophitic and sub ophitic tholeiitic dolerites while the other the bn dyke swarm constitutes mainly norites in which pyroxenes and olivine are enclosed by plagioclase oikocrysts the close geochemical similarity between a quenched norite and the coarser grained varieties indicates that the composition of the latter type has not been significantly modified by crystal accumulation the bn dykes are geochemically distinctive most having high mgo ca 16 cr and ni contents in conjunction with relatively high sio2 light rare earth ree and large ion lithophile lil element concentrations the texture mineral chemistry and petrochemistry of the quenched noritic dyke all bear strong resemblances to those features in modern boninitic lavas the bn dykes also correspond to proposed parental liquids of the bushveld complex and other major layered basic igneous intrusions the two dyke swarms are petrogenetically distinct the tholeiitic dolerites were derived from a relatively undepleted primordial mantle while the noritic dykes originated from a metasomatized harzburgitic source the wide spread distribution of similar proterozoic intrusions suggests crustal underplating by harzburgitic mantle on a world wide scale at this time

u pb zircon geochronology and geochemistry of paleoproterozoic magmatic suite from east sarmatian orogen tectonic implications on columbia supercontinent abstract extensive paleoproterozoic magmatism occurred in the east sarmatian orogen eso located at the junction of the sarmatian and volga ural segments of the east european craton generating numerous felsic to mafic ultramafic complexes here we report geochemical and zircon u pb age data from a suite of ultramafic mafic and diorite granodiorite intrusive rocks from this orogen shrimp u pb dating of zircons yielded the following concordant ages for the magmatic suites 1 2085 17 to 2093 20 ma sub volcanic high mg intrusions of shmb like melanorite melaquartz diorite melagranodiorites and quartz diorite tonalite granodiorites 2 2072 4 8 2073 8 3 and 2068 13 ma ultramafic mafic diorite layered intrusions 3 2053 14 to 2058 22 ma magnesian ferroan quartz diorite tonalite granodiorite intrusions and 4 2035 18 ma ferroan norite diorite intrusions the trace and rare earth element geochemistry indicate arc related features the enrichment in lree and lile in the mafic ultramafic and diorite granodiorite suites is correlated with melting of metasomatised lithosphere mantle along with involvement of crustal components in their petrogenesis the third magmatic event conforms to the age of the post collision s and a granitoids of the region our data indicate two major magmatic events in the post collisional setting the former immediately after metamorphism with the formation of schistosity in the host rocks and the latter two during the culmination of the orogenic cycle in the voronezh crystalline massif the duration of the paleoproterozoic orogeny during the collision of the sarmatian and volga ural segments of the east european craton is estimated to be approximately 100 million years from 2140 to 2035 ma we propose that the layered orogenic plutons were derived from relatively deeper mantle source whereas the sub volcanic rock series are derivatives of the slightly shallow mantle source the paleoproterozoic collision in the region broadly coincides with timing of amalgamation of the global supercontinent columbia

paleohydrology of arid southeastern maui hawaiian islands and its implications for prehistoric human settlement abstract arid slopes on the southeastern side of maui are densely covered with archaeological remains of hawaiian settlement from the late prehistoric to early postcontact period ca a d 1500 1860 permanent habitation sites agricultural features and religious structures indicate perennial occupation and farming in a subregion called kahikinui yet there is presently no year round water source we explore the possibility that postcontact deforestation led to the loss of either 1 perennial channel flow or 2 perennial springs or seeps to investigate the first possibility we estimated ancient peak flows on 11 ephemeral channels in kahikinui using field measurements and paleohydrology peak flow estimates 3 230 m3 s for a given drainage area are smaller than those for current perennial maui streams but are equivalent to gauged peak flows from ephemeral and intermittent streams in the driest regions of hawai i and maui islands this is consistent with the long term absence of perennial channel flow in kahikinui on the other hand others have shown that canopy fog drip in hawai i can be greater than rainfall and thus a large part of groundwater recharge using isolated live remnants and snags we estimate the former extent of the forest upstream from archaeological sites we use rough estimates of the loss of fog drip recharge caused by deforestation and apply a simple steady state hydrologic model to calculate potential groundwater table fall these order of magnitude estimates indicate that groundwater could have fallen by a minimum of several meters abandoning perennial seeps this is consistent with archaeological evidence for former perennial seeps such as stonewalls enclosing potential seeps to protect them although longer term reductions in rainfall cannot be ruled out as a factor deforestation and loss of fog drip recharge are obvious and more immediate reasons for a recent loss of perennial water in kahikinui maui

archaean boninite like rocks in an intracratonic setting abstract boninites and high mg norites show considerable compositional overlap while the petrogenesis of both may involve large ion lithophile element lile replenishment of a mantle source boninites appear restricted to convergent margin settings while many high mg norite suites intrude intracratonic rifts rocks with boninitic compositions are extremely rare in archaean terranes where they are also interpreted to have formed at convergent margins high mg lile enriched basaltic rocks form a ca 2950 ma sub volcanic sill within the 3010 2935 ma mallina basin of the pilbara craton northwest australia they are spatially associated with low ti tholeiitic intrusions and a high mg diorite sanukitoid suite they have a strong boninitic affinity with high sio 2 52 54 wt mg 62 67 and al 2 o 3 tio 2 62 73 low tio 2 0 24 0 28 wt and strong lile enrichments primitive mantle normalised la gd and gd yb ratios of 4 5 and 0 6 respectively produce prominent u shaped normalised trace element patterns despite such close compositional affinity to boninite these rocks probably formed more than 40 myr after regional magmatism and 60 myr after the last regional event linked to subduction geological evidence suggests that the mallina basin formed in an intracontinental setting not at a convergent margin and so high mg norite provides a more realistic analogy for the mallina boninite like rocks in terms of tectonic setting in old terranes the tectonic setting of rocks with boninite like compositions must be interpreted with caution trace element modelling shows that contamination by felsic crust is a plausible explanation for lile enrichments in the mallina boninite like rocks but the scarcity of suitable contaminants makes this explanation unlikely petrogenesis of the boninite like rocks was closely associated with that of the high mg diorite sanukitoid suite lile enrichments in high mg diorite require that the mantle beneath the entire mallina basin was variably metasomatically enriched by an earlier subduction event at or before ca 3015 ma the refractory source for the boninite like rocks may have also been enriched during this event

thermal constraints on the emplacement rate of a large intrusive complex the manaslu leucogranite nepal himalaya the emplacement of the manaslu leucogranite body nepal himalaya has been modelled as the accretion of successive sills the leucogranite is characterized by isotopic heterogeneities suggesting limited magma convection and by a thin 100 m upper thermal aureole these characteristics were used to constrain the maximum magma emplacement rate models were tested with sills injected regularly over the whole duration of emplacement and with two emplacement sequences separated by a repose period additionally the hypothesis of a tectonic top contact with unroofing limiting heat transfer during magma emplacement was evaluated in this latter case the upper limit for the emplacement rate was estimated at 3 4 mm year or 1 5 myr for 5 km of granite geological and thermobarometric data however argue against a major role of fault activity in magma cooling during the leucogranite emplacement the best model in agreement with available geochronological data suggests an emplacement rate of 1 mm year for a relatively shallow level of emplacement granite top at 10 km uninterrupted by a long repose period the thermal aureole temperature and thickness and the isotopic heterogeneities within the leucogranite can be explained by the accretion of 20 60 m thick sills intruded every 20 000 60 000 years over a period of 5 myr under such conditions the thermal effects of granite intrusion on the underlying rocks appear limited and cannot be invoked as a cause for the formation of migmatites

manaslu leucogranite a collision signature of the himalaya a model for its genesis and emplacement the manaslu pluton is one of 10 leucogranites that formed in the overthrusted higher himalaya after the indo eurasian collision field and analytical data indicate that the underlying migmatites of the tibetan slab may be where the leucogranitic melts were generated the himalayan crustal thrusting of a hot slab over a rather cold volcano sedimentary pile le fort 1975a provides the necessary release of fluids these fluids cross the main central thrust mct induce the partial anatexis of the overheated tibetan slab and produce a leucogranitic magma the emplacement of the magma at first is located along the main disharmonic plane above the mct between the infrastructure and the superstructure there it generates a convective hydrothermal system extending very far laterally according to the stratification of permeabilities progressive emplacement of the granite proceeds as the convected fluids including the fluids released by the saturated magma dissolve the mainly calcareous host rocks of tibetan sedimentaries a frozen image of this caving out progression is given by the extensive network of granitic dikes outside the pluton the two quite independant fluid cycles of the generation and of the emplacement were triggered or guided by the tectonics due to collision this two fold model dominated by fluid activity may be of importance for other leucogranites and granites

the sarmatian crustal segment precambrian correlation between the voronezh massif and the ukrainian shield across the dniepr donets aulacogen abstract sarmatia is the southernmost crustal segment of the east european precambrian craton the phanerozoic dniepr donets aulacogen dda subdivides it into unequal halves the ukrainian shield in the south and the voronezh massif in the north correlation between the ukrainian shield and the voronezh massif is reviewed the overall structure and age province subdivision of sarmatia are assessed and constraints are imposed on displacement along the dda it is shown that differences in the trends of the principal basement structures highlighted by magnetic anomalies outlining palaeoproterozoic banded iron formations are a consequence of the heterogeneous structure of the archaean palaeoproterozoic basement rather than the kinematics of the opening of the dda only minor right lateral displacement along the dda has occurred the main crustal units of the ukrainian shield i e the azov middle dniepr and ingul ingulets blocks correlate excellently with the oskol sumy and sevsk blocks of the voronezh massif which allows the definition of three coherent oskol azov sumy dniepr and sevsk ingulets crustal domains presently available radiometric datings show that these three domains all have archaean crustal ages of 3 65 3 0 3 2 3 1 and 3 1 2 8 ga respectively the inter domain boundaries appear largely to have existed already in the archaean but were subsequently masked by palaeoproterozoic deformation and overlain by proterozoic cover and nappe piles amongst the three crustal domains of central and eastern sarmatia the oskol azov and sevsk ingulets ones have been reworked substantially in the palaeoproterozoic while the sumy dniepr domain acted as a stable cratonic unit although apparently rotating anti clockwise between 2 3 and 2 1 ga ago the palaeoproterozoic banded iron belts of sarmatia can be subdivided into the cratonic margin krivoy rog type and the interior intra domain oskol type the former outline the cratonic sumy dniepr domain while the latter associate with nw se continental rifting that followed archaean zones of weakness inside the oskol azov domain the bryansk block in the northwestern part of the voronezh massif is a part of the large bryansk bragin granulite domain which was formed between ca 2 2 and 2 1 ga ago and extends into the northwestern ukrainian shield in the east the lipetsk losev volcanic belt and the east voronezh turbidite schist province follow the boundary between the sarmatian and volgo uralian crustal segments together these two crustal units appear to represent a palaeoproterozoic orogenic environment ca 2 1 2 0 ga in age

assembling north china craton within the columbia supercontinent the role of double sided subduction abstract an evaluation of recent s wave receiver functions s wave velocities and two versions of p wave tomographic images along various transects in the north china craton provides some clues on the subduction collision history of the different crustal blocks and their final amalgamation within the paleoproterozoic columbia supercontinent interpretation of a n s seismic section of the craton suggests thick slab debris sinking to various depths in the mantle the w e seismic corridors show the preservation of a thick 200 km lithospheric root tectosphere beneath the ordos block and its variable and extensive erosion towards the yanliao block eastern block this zone is characterized by layers with marked velocity contrast and suggests repeated stacking of the remnants of underplated and accreted paleoproterozoic oceanic lithosphere the present day lithosphere asthenosphere boundary beneath this region probably marks the erosional plane along which decratonization occurred through subduction erosion from the east and thermal and material erosion by upwelling asthenosphere from below resulting in the partial destruction of the tectosphere and its thinning towards the east within the asthenosphere below the yanliao block younger and thinner slabs predominate in the absence of any prominent thick high velocity layers these younger slabs define a westward polarity and constitute a mega scale duplex formed by underplating through phanerozoic subduction process particularly the pacific plate subduction from the east the lithologic associations within the inner mongolia suture zone dividing the yinshan block to the north and ordos block to the south correspond to an accreted ocean plate stratigraphic sequence with the tonalite trondhjemite granodiorite ttg gneisses charnockites and calc alkaline granites representing a continental arc built up through subduction from the north the seismic transects bring out a contrasting polarity in the subduction regime with an oblique east to southward subduction of the yinshan block and a westward subduction of the yanliao block here i propose a double sided subduction history for the ncc similar to the ongoing subduction process in the western pacific such double sided subduction is considered to promote rapid amalgamation of continental fragments within supercontinents and the subduction polarities and mantle dynamics of ncc are therefore considered to be critical in evaluating the final assembly of the paleoproterozoic supercontinent columbia

paleohydraulic reconstruction of flash flood peaks from boulder deposits in the colorado front range nine watersheds in the colorado front range with steep bedrock channels were used to test the accuracy of paleohydraulic reconstruction of large flash floods using boulder deposits the nine basins consist of eight small ungauged basins ranging in size from 1 6 to 29 km2 and the big thompson river at the mouth of the big thompson canyon draining 790 km2 between 1923 and 1976 all nine basins had had one catastrophic flash flood the magnitude of which has been estimated by the conventional slope area method in each basin coarse boulder deposits of the large flash floods were identified and three axes of the five largest boulders were measured along with at least two profiles of the valley cross section a simple arithmetic average of two theoretical and two empirical relationships was used to estimate average flood velocity using boulder size and shape average depth was estimated as the arithmetic average of four values computed from the manning equation a regression equation for boulder size and unit stream power a relative smoothness equation and a modified shields relationship the appropriate flood width for the estimated average depth was found by iteration using the valley cross sections the paleohydraulic discharges thus computed generally underestimate conventional slope area discharge estimates on small streams by as much as 75 although the average amount is only 28 too low and the reconstructed discharge in one stream was 31 too large the big thompson river flood of 1976 was overestimated by 76 reasons for discrepancy in reconstructed peaks could include 1 the possibility that floods may have been able to move boulders larger than those available to be moved 2 overestimation of the slope area discharge because high water marks were set prior to erosion of the channel 3 underestimation of original roughness coefficients and 4 macroturbulent effects during fast deep flows the paleohydraulic technique is applied to two other streams in colorado with sedimentological evidence of large flash floods but no conventional indirect discharge estimates a small tributary to the big thompson river draining 1 8 km2 has a paleohydraulic reconstructed flood peak of about 60 m3 s from a flood in 1976 using boulders excavated from a foundation site in holocene alluvium along boulder creek in boulder colorado a paleohydraulic reconstructed flood peak of between 860 and 1 512 m3 s is calculated this is 1 4 to 2 4 times the magnitude of the estimated 500 yr flood

petrology geochemistry and la icp ms u pb geochronology of paleoproterozoic basement rocks in bangladesh an evaluation of calc alkaline magmatism and implication for columbia supercontinent amalgamation abstract the paleoproterozoic 1 7 ga basement rocks from maddhapara bangladesh show a large range of chemical variations e g sio2 50 7 74 7 and include diorite quartz diorite monzodiorite quartz monzonite and granite the pluton overall displays metaluminous calc alkaline orogenic suite mostly i type suites formed within subduction related magmatism the observed major elements show general trends for fractional crystallization trace element contents also indicate the possibility of a fractionation or assimilation explain the entire variation from diorite to monzonite even granite the pluton may have evolved the unique chemical features by a process that included partial melting of calc alkaline lithologies and mixing of mantle derived magmas followed by fractional crystallization and by assimilation of country rocks the pluton shows evidence of crystal fractionation involving largely plagioclase amphibole and possibly biotite some of the fractionated magmas may have mixed with more potassic melts from distinct parts of the continental lithosphere to produce granites and or pegmatites new geochronological results of granitic pegmatite 1722 10 ma are indisputably consistent with diorite and tonalite and those data showing credible geochronological sequence i e diorite tonalite granitic pegmatite identical paleoproterozoic age 1 7 ga with distinctive magmatism of the maddhapara basement rocks have agreeable relationship with the citz india the consistent magmatism is also common in the transamazonian of south america trans hudson orogeny in north america bohemian massif and the svecofennian poland have identified the sequential growth of the continent through the amalgamation of juvenile terrains succeeded by a major collisional orogeny such paleoproterozoic subduction related orogens in australia have similar counterparts in antarctica and other part of the world these types of paleoproterozoic magmatism dominantly contributed to assemble amalgamation and breakup of the enormous columbia supercontinent

a late quaternary pollen record from ka au crater o ahu hawai i abstract a pollen record from ka au crater o ahu hawai i contains evidence for changes in vegetation and climate since about 28 000 14c yr b p zone 1 ca 28 100 ca 22 800 14c yr b p has pollen of dry to mesic forest species including pipturus type dodonaea viscosa acacia koa chenopodium oahuense claoxylon sandwicense myrsine and metrosideros type in zone 2 ca 22 800 ca 16 200 14c yr b p myrsine and coprosma increase with herbs fern allies and grammitidaceae suggesting open canopies zone 3 ca 16 200 ca 9700 14c yr b p has pollen of wet forest species including freycinetia arborea abundant pritchardia and metrosideros type zone 4 ca 9700 ca 7000 14c yr b p is similar with less pritchardia and more metrosideros type climate reconstruction was based on modern climatic ranges of flowering plants and an index derived from abundance of pollen in surface samples both methods agree on a qualitative reconstruction although the ages are poorly constrained 28 000 25 000 14c yr b p cool and dry 25 000 23 000 14c yr b p dry and warmer 23 000 20 000 14c yr b p moderately dry with declining temperature 20 000 16 000 14c yr b p moderately dry and cool 16 000 9000 14c yr b p warm and wet 9000 7000 14c yr b p warm and possibly drier lower precipitation at ka au crater during the late glacial period and last glacial maximum is consistent with the interpretation that the north pacific subtropical anticyclone was south of its present position the pollen derived temperature index yields an estimate of 3 5 c temperature depression during the last glacial maximum

acadian synorogenic mafic intrusions in the maine appalachians two belts of syn acadian mafic intrusions the central maine belt is progressively more altered and metamorphosed toward the southwest at the northeast end the moxie pluton represents the least altered and most important example in the belt forsterite contents of the most primitive olivines are consistent with the derivation of the earliest magma from a largely unfractionated mantle melt the coastal maine belt is spatially associated with the siluro devonian coastal volcanics the age difference however between the volcanics and plutonics suggests that they may not be directly related the important pocomoonshine gabbro appears to represent the well layered roof zone of a major fractionated body mineral compositions are similar to those in the moxie pluton and suggest a similar primary magma intrusions in both belts have complex contacts pronounced contact aureoles and were all deformed by late acadian deformation modified journal abstract

petrogenetic and tectonic significance of young leucogranites from the northwestern himalaya pakistan in the himalaya of northwestern pakistan small discordant bodies of leucogranite intrude metamorphosed basement of the indian crust as the first step in assessing the tectonic significance of these granites we have used the shrimp ion microprobe to obtain u pb dates on zircon zircons of igneous appearance are scarce in the leucogranites and with one exception are associated with xenocrystic components which occur as discrete grains and as cores rimmed by young zircon zircons of igneous appearance are high in u 5000 to 40 000 ppm low in th u 0 01 to 0 05 and frequently colored a distinct blue xenocrystic components give a range of proterozoic ages consistent with ages previously reported for indian crust in sharp contrast zircons of igneous appearance yield clusters of concordant tertiary ages two leucogranite dikes from southern localities yield rather old emplacement ages of about 35 ma swat and about 50 ma naran together with previously determined 40ar 39ar and fission track cooling ages these ages document immediate and rapid metamorphism and denudation following eocene collision three leucogranite dikes from northern localities within the nanga parbat haramosh massif are very young having emplacement ages of about 2 3 ma 5 ma and 7 ma the formation and emplacement of these leucogranites during the rapid late tertiary denudation of the nanga parbat region suggests to us that decompression melting may be a viable mechanism for leucogranite genesis

high magnesian granitoids in the precambrian continental crust implication for the continuum between ferro potassic and magnesio potassic rock suites abstract ferro potassic fe k to magnesio potassic mg k hornblende biotite granitoids hbgs with a wide range of sio2 from 52 to 77 wt are typical of precambrian continental crust and are generally related to late and post collisional orogenic events despite their broadly uniform mineralogy and tectonic environment the chemical compositions of these granites suggest different sources from lower crust for the fe k suites to enriched mantle for the mg k counterparts here we propose a classification of the magnesian rocks into moderate mg high mg and ultra mg with corresponding examples from various parts of the world such as the closepet type sanukitoids and their high mg counterparts of the elan type the elan type granitoids are characterized by the highest mgo cr ni end t and lowest tio2 feot feot mgo contents among all the precambrian hbgs and are hence close to a true end member the precambrian hbgs show common features such as a wide range of sio2 contents enrichment in lile k ba sr lree nb ti negative primitive mantle normalized anomalies and weak negative or no eu anomalies in intermediate suites the mg of magmatic and cumulus relict amphiboles displays a compositional array of ultra mg to fe granites and shows positive correlation with the whole rock mg continuum between the compositions of mg k and fe k granitoids is reflected in a gradual decrease in mg cr ni of the rocks and mg of the mafic silicates increase in ti p zr y zn u total ree and decrease of the nd initial isotopic composition together with a change in the paragenesis of fe ti oxides we interpret these features to result from mixing of metasomatized mantle and crustal magmas and their homogenization at the lower crust level the lower crustal source component increases from the mg k to fe k series during their passage to higher crustal levels the magmas underwent fractional crystallization and crustal contamination leading to the wide range in silica content

late paleozoic mafic ultramafic intrusions in southern central asian orogenic belt nw china insight into magmatic ni cu sulfide mineralization in orogenic setting abstract the mafic ultramafic intrusions hosting magmatic ni cu sulfide ore deposits usually present within the precambrian cratons and on their margin have been extensively studied whereas those occurring within the phanerozoic orogenic belts have received little attention the southern margin of the central asian orogenic belt is a region of late paleozoic mafic ultramafic intrusions emplaced during post orogenic stage in order to recognize the mineralization features this study compares barren or weakly mineralized mafic ultramafic intrusions in the beishan with those hosting ni cu sulfide ore deposit in the altay and eastern tianshan in petrology mineralogy and geochemistry aspects several mineralization features can be recognized with respects to petrology mineralogy and geochemistry from comprehensive comparisons among the mineralization indicators we highlight strong alteration accompanying sulfide emplacement post erosion exposure of magma conduit abundant primary hydrous minerals and potential transportation mechanism of ore forming elements other indicators are the presence of orthopyroxene and pyroxenite for potential sulfide formation through crystal fractionation restricted fo and ni ranges in olivines for sulfide segregation and some other special geochemical characteristics related to crustal contamination the variation in mineralization could be ascribed to different degrees of partial melting crustal assimilation and subduction related modification of a mantle source we suggest that the ni cu sulfide mineralization of mafic ultramafic intrusions within orogenic belts is remarkably different from that of cratonic and continental marginal settings in respects of petrogenesis and mineralizing mechanism magmatic conduit type ni cu sulfide ore deposit is a target for future prospecting and exploration for mafic ultramafic intrusions in the orogenic belts

geochemical investigations of the origin of the manaslu leucogranite himalaya nepal the himalayan orogeny is characterized by an intraplate subduction zone the thrusting of the tibetan slab over the foreland is probably responsible for the origin of the manaslu type leucogranites this geochemical study tries to examine the crustal origin of the granite to verify whether the paragneisses of the tibetan slab are the most probable parent material and to determine the subsequent petrogenetic processes the rb sr systematics suggest that 1 1 the scatter of data points in the 87sr86srvs 87rb86sr diagram may be due to the heterogeneity of the initial 87sr86sr ratios 2 2 the initial isotopic ratios are very high 0 730 0 760 and are in agreement with those of the gneisses of the tibetan slab at the time of the melting pb isotopic ratios are homogeneous they are also consistent with a crustal prehistory the ree and th contents are unexpectedly low in comparison with the much higher contents of the parent material monazite left in the residue of melting or more probably extracted in an early stage of the magmatic history may explain the observed ree and th abundances alternatively field observations show that the emplacement of the granite has been accompanied by a very strong hydrothermal activity in consequence the low ree and th contents of the granite could also be due to the loss by solution during prolonged fluid circulation throughout the granitic melt and the sr and pb isotope distribution to the effect of late to post magmatic fluids the isotopic character of which was determined by the underlying tibetan slab

early precambrian crustal development changing styles of mafic magmatism the work of sutton watson 1951 was one of the cornerstones in the interpretation of the evolution of early precambrian archaean and early proterozoic gneiss complexes and in the documentation of mafic dyke swarms that intruded recently accreted archaean cratons since then the concept of geological terranes and terrane accretion has been extended back to the archaean and different events can be distinguished by increasingly precise isotopic dating techniques there is growing evidence that with certain clear provisos the principle of uniformitarianism can be applied as equally to the early precambrian as it can through the rest of the geological record in terms of mafic magmatism there are similarities between some ancient and modern suites both intrusive and extrusive but there are also some major differences such as the presence of komatiites in the archaean and the formation of large scale layered intrusions and extensive dyke swarms at the end of the late archaean and in the early proterozoic the mantle has evolved continuously with the progressive extraction of mafic magmas but allowing for this continental tholeiites appear to have changed little with time ancient mid ocean ridge basalts are elusive because of their poor preservation record the geochemistry of mafic volcanics occurring in many greenstone belts commonly suggests a continental contamination component and that these volcanic rocks are most closely akin to those from present day arc systems the relative abundance of early precambrian intrusive mafic suites parallels the crustal growth curve reflecting the global crustal accretion differentiation superevent towards the close of the archaean bimodal tholeiitic noritic mafic magmatism associated with many of these intrusive suites stems from this rapid turnover in the mantle mafic crust continental crust system this in turn gives a possible link between the respective evolutions of archaean to recent komatiitic noritic and boninitic suites

modeling the influence of rainfall gradients on discharge bedrock erodibility and river profile evolution with application to the big island hawai i motivated by convex concave bedrock river profiles developed across a climate gradient on the wetside of the kohala peninsula of the big island of hawai i we numerically model how rainfall gradients may influence longitudinal fluvial incision patterns first we model transient profile adjustment with two tectonic boundary conditions subsidence and uplift in this generalized analysis we assume that rainfall gradients only influence incision by modifying the relation between upstream drainage area and local discharge using a detachment limited model downstream increases in rainfall lead to profile convexities during transient adjustment in both tectonic settings and this is the opposite of the predicted increase in profile concavity that would develop in a steady state uplifting profile a transport limited erosion model develops only concave channel profiles without clear signatures of the rainfall pattern second we model the development of convex concave transient profiles and incision patterns on kohala using a detachment limited model if rainfall gradients only influence incision through the local discharge reasonable rainfall gradients can only develop channel convexities that are much smaller than those observed instead we hypothesize that local bedrock erodibility increases with the degree of rainfall dependent chemical weathering when local erodibility is assumed to scale with local rainfall rate the model can produce convex concave profiles similar to those observed in kohala our results suggest that changes in local bedrock erodibility due to local climate dependent weathering may be an important mechanism by which climate influences landscape form and rates of evolution this hypothesis requires further testing in this study area and beyond

geochemistry of the permian kalatongke mafic intrusions northern xinjiang northwest china implications for the genesis of magmatic ni cu sulfide deposits the kalatongke cu ni sulfide deposit in northern xinjiang northwest china is located on the southern side of the regional irtysh fault zone which is the boundary between the early paleozoic altai orogenic belt to the north and the late paleozoic junggar terrane to the south in the kalatongke region there are 11 mafic intrusions which were emplaced in lower carboniferous strata economic ni cu sulfide ores are found within three of these intrusions which are well differentiated and compositionally zoned four rock types are recognized which from top to base of the three mineralized intrusions include biotite diorite biotite hornblende norite biotite hornblende olivine norite and biotite hornblende dolerite the biotite hornblende olivine norites and biotite hornblende norites are the most favorable host rocks for ni cu mineralization the initial 87sr 86sr t t 280 ma ratios of the intrusions vary from 0 70375 to 0 70504 and end t from 6 3 to 8 2 implying that the magmas originated from depleted asthenospheric mantle however the strong enrichment of lithophile elements such as k rb th u and lree the negative nb and ta anomalies and the high 18o values of whole rocks 5 4 10 6 suggest significant crustal contamination these patterns are present in almost all samples from the intrusions indicating that the contamination took place before the magma was emplaced at its present level in the crust crustal contamination is interpreted to have driven the magma to s saturation and brought orthopyroxene onto the liquidus convection or perhaps flow differentiation of the crystal bearing magma during ascent caused the dense sulfide melt with entrained olivine and orthopyroxene crystals to become concentrated in the center of the intrusions whereas the fractionated magmas formed other less mafic intrusions which intrude the nearby strata