experimental study of subsolidus phase relations and mixing properties of pyroxene in the system cao al2o3 sio2 abstract subsolidus phase relations in the system cao al2o3 sio2 cas were experimentally determined with tight reversals of several univariant curves and with 14 equilibration experiments containing the assemblage pyroxene anorthite where pyroxene is a binary solid solution of ca tschermak cats caal2sio6 and ca eskola caes ca0 5alsi2o6 endmembers reversals were obtained on the following reactions bar c 3an gr 2ky q p 22t 700 3an cor gr 3ky p 21 8t 950 3cats gr 2cor p 55t 53900 and 6cats 1 x caesx 2 1 2x gr 4 1 2x cor 9xan observed slopes indicate 9 8 j mol k of al si disorder in ca tschermak pyroxene and 5 3 j mol k of al si disorder in anorthite at 1300 c it is suggested that al si disorder in anorthite increases by 1 9 j mol k from 700 c to 1300 c compositions of cats caes pyroxene in equilibrium with anorthite and pbo rich liquid were experimentally determined at 1400 1430 c and 22 7 30 8 kbar microprobe measurements gave compositions which are consistent with an ideal pyroxene solution and the following parameters for the reaction 3an 2cats 2caes j bar k 2rtln xcats xcaes 60200 86 4t 5 06 13 10 7p p 0 resulting in h0j 39 8 kj mol and s0 461 8 j mol k for the ca eskola endmember at 1300 c the obtained properties of the ca eskola component are necessary for thermobarometry based on pyroxene bearing assemblages containing plagioclase quartz or kyanite

high pressure transformation of eclogite to garnetite in subducted oceanic crust the mineral composition of oceanic crust is a function of pressure and temperature and thus changes as a slab of crust descends a subduction zone a knowledge of the mineralogy of subducted material would provide important constraints on its geophysical characteristics we have sought by means of high pressure laboratory experiments in the pressure range 4 6 18 gpa on a synthetic mix with the composition of mid ocean ridge basalt morb to determine the sequence of mineralogical changes we find that at 1 200 c solid solution of pyroxene in garnet begins around 10 gpa and increases substantially between 12 and 15 gpa complete transformation of eclogite to garnetite is achieved at 15 gpa the garnetite has a zero pressure density of 3 76 g cm 3 and accordingly would be denser than the surrounding mantle throughout its stability field which extends to depths of 600 km if subducted to greater depths garnetite may transform to perovskitite

subaqueous delta of the ganges brahmaputra river system abstract the ganges brahmaputra is among the world s three largest river systems in terms of sediment load but until now no high resolution seismic data have been obtained to document the nature of the sediment deposit seaward of the rivers mouths the other two amazon huanghe discharge into energetic coastal environments and form subaqueous deltas with characteristic clinoform stratigraphy high resolution seismic reflection profiles of the bengal shelf reveal similar stratigraphy topset beds dip gently 0 036 and diverge offshore more steeply dipping foreset beds 0 190 converge farther seaward and relatively thin gently dipping bottomset beds 0 022 extend across the outer shelf overlying an erosional surface presumed to be of late pleistocene age sediment accumulation rates are highest in the foreset region 5 cm year and reduced in the bottomset region

nb in hawaiian magmas constraints on source composition and evolution abstract published th and nb data for basalts from 11 volcanoes from the hawaiian islands and emperor seamount chain yield a nearly uniform concentration ratio of nb th 15 2 1 7 the basalts include tholeiites with nb concentrations ranging down to 4 ppm and alkali basalts with a maximum nb concentration of 127 ppm however nephelinites and melilitites from the honolulu volcanic series have much lower nb th ratios and are excluded from this analysis using the average th u ratio of 3 2 for the five volcanoes of the island of hawaii this corresponds to a nb u 48 6 5 3 which is indistinguishable from the mean value of a worldwide sample of oib and morb nb u 47 10 given by direct nb and u analyses in contrast the earth s primordial mantle had a nb th ratio of 8 6 and a nb u ratio of 30 these data demonstrate that none of the hawaiian volcanoes not even the isotopically most nearly primitive koolau series from oahu has refractory elements derived from an undifferentiated or primordial portion of the mantle an even less likely source is recycled continental crust which has a mean nb u ratio of 10 a consideration of the chromatographic theory of metasomatism and comparison with metasomatic rocks observed in the continental crust show that large scale metasomatism in the mantle which would be needed to account for the very large total volume of hawaiian emperor magmas is expected to produce a strongly zoned mantle yielding chemically highly heterogeneous magmas unless the metasomatic column has reached a steady state the expected heterogeneity is difficult to reconcile with observed chemical homogeneity of the main stage tholeiitic magmas the late stage alkali basalts and the nephelinites must be excluded from this consideration because their isotopic composition shows that they are derived from the depleted lithosphere or asthenosphere the consequence of a steady state metasomatic column would be that the tholeiitic melt itself represents the metasomatic fluid the model of recycled oceanic crust and lithosphere is consistent with the chemical and isotopic data the mantle that originally produced this oceanic crust was already depleted and rehomogenized as a result of prior separation of continental crust uniform source ratios of nb u and ba rb were established during this rehomogenization process the general enrichment of the hawaiian source and the chemical and isotopic heterogeneities found in the present day lavas were produced during the differentiation into oceanic crust and lithosphere secondary pb 1bpb model ages indicate that this crust was probably produced 1 ga ago

measurement and analysis of depression storage on a hillslope a precise photogrammetric technique was used to determine the microtopography of seven 2 6 m 1 2 m experimental units located on a hillslope surface elevations were determined with an accuracy of better than 1 mm from which contours at 2mm intervals were interpolated these contour plots were then manually interpreted to define depressions and associated storage volumes analysis of the results highlighted the complex variability of depression storage over the hillslope for example there being little relation between depression storage volumes and unit slope this study also highlights the sampling problem for the measurement of depression storage on natural surfaces which appears not to have been formally recognized previously and also emphasizes the practical difficulty of achieving depression storage estimates with coefficients of variation less than ten per cent to 50 per cent much of this variability being due to problems of interpretation rather than measurement of the surface

the great tumaco colombia earthquake of 12 december 1979 southwestern colombia and northern ecuador were shaken by a shal low focus earthquake on 12 december 1979 the magnitude 8 shock located near tumaco colombia was the largest in northwestern south america since 1942 and had been forecast to fill a seismic gap thrust faulting occurred on a 280 by 130 kilometer rectangular patch of a subduction zone that dips east beneath the pacific coast of colombia a 200 kilometer stretch of the coast tectonically subsided as much as 1 6 meters uplift occurred offshore on the continental slope a tsunami swept inland immediately after the earthquake ground shaking intensity vi to ix caused many buildings to collapse and generated liquefaction in sand fills and in holocene beach lagoonal and fluvial deposits

the eclogite garnetite transformation at high pressure and some geophysical implications mineral assemblages displayed by morb and alkali poor olivine tholeiites have been investigated over the pressure interval 4 6 18 gpa at 1200 c both compositions crystallize to form normal eclogites between 4 6 and 10 gpa and there is little change in the relative proportions of garnet and pyroxene over this range however the proportion of garnet increases rapidly above 10 gpa as pyroxene dissolves in the garnet structure and pyroxene free garnetites stishovite are produced by 14 15 gpa dependent upon composition the garnetite facies for both compositions possess zero pressure densities of 3 75 g cm3 implying that subducted oceanic crust remains appreciably denser than surrounding mantle to depths exceeding 600 km it is demonstrated that the seismic velocity distributions in the mantle between 400 and 650 km are inconsistent with anderson s hypothesis that this region is of eclogitic composition

the late holocene gargano subaqueous delta adriatic shelf sediment pathways and supply fluctuations the gargano subaqueous delta formed on the eastern and southeastern sides of the gargano promontory in the western adriatic this subaqueous deposit represents the southernmost portion of the late holocene highstand systems tract hst growing along the western side of the adriatic as an extensive wedge of deltaic and shallow marine mud the late holocene hst rests above a regional downlap surface that marks the time of maximum landward shift of the shoreline attained around 5 5 cal kyr bp at the end of the late pleistocene holocene sea level rise high resolution seismic stratigraphic and tephra correlation indicate the presence of a thin basal unit recording condensed deposition between 5 5 and 3 7 cal kyr bp over much of the basin above this unit sediment accumulation rates increased to high values as much as 1 5 cm yr 1 reflecting the stabilisation of relative sea level and the forcing from high frequency climatic or anthropogenic changes affecting river dynamics the late holocene mud wedge of which the gargano subaqueous delta is a significant component reaches up to 35 m in thickness and has a volume of ca 180 km3 the shore parallel thickness distribution of the mud wedge reflects the dominant oceanographic regime of the basin and the asymmetric location of the mostly western sediment sources with a combined modern delivery of 51 7 106 t yr 1 of mean suspended load in sections perpendicular to the coast the late holocene mud wedge appears composed of forestepping clinoforms with gently dipping foresets typically 0 5 the gargano subaqueous delta is characterised by a submarine topset in water depths shallower than 25 28 m and accounts for about 1 7th of the total volume of the late holocene mud wedge despite the absence of direct river supply to the gargano area in the area of maximum interaction between shore parallel currents and basin morphology progradation occurs onto a flat and barren bedrock outcrop in about 50 80 m water depth the rapid transition from a thickness of 30 m of late holocene mud to nil is a good indication of the role of southward flowing bottom hugging shelf currents in causing the redistribution of sediment along the adriatic inner shelf additional evidence of this regime comes from 1 the most recent sigmoid defined at seismic stratigraphic scale deposited since the onset of the little ice age showing a shore parallel thickness distribution and a main depocentre to the southeast of the gargano promontory 2 the maximum values of sediment accumulation rates over the last century documented by 210pb measurements defining a narrow shore parallel belt immediately seaward of the depocentre of the most recent sigmoid the gargano subaqueous delta grows from the outbuilding of progressively younger progradational sigmoids that tend to parallel the previous ones the gargano subaqueous delta differs from other documented late holocene subaqueous deltas because its growth reflects 1 sediment transport dominated by bottom currents sub parallel to the strike of the composing clinoforms 2 a complex supply regime including the po delta 350 km to the north and several coalescing apennine rivers acting as line source 3 several alternating intervals of enhanced outbuilding and condensed deposition and 4 an in phase growth of the most recent sigmoid with the major progradation of the po delta during the little ice age

supersilicic clinopyroxene and silica exsolution in uhpm eclogite and pelitic gneiss from the kokchetav massif kazakhstan abundant exsolved quartz rods occur in matrix clinopyroxene of eclogite from the kokchetav massif kazakhstan these rocks are diamond grade ultrahigh pressure uhp metamorphic rocks that recrystallized at p 6 gpa and t 1000 c zircon is an excellent container which effectively protects peak uhp metamorphic phases from retrogression therefore to ascertain the pre exsolution composition of the clinopyroxene we analyzed clinopyroxene inclusions in zircon of the eclogite and a diamond bearing biotite gneiss clinopyroxene in zircon has an excess of fe 3 vi al over iv al na k and calculated cation totals significantly less than 4 0 per six o atoms the stoichiometry of these pyroxenes can be reconciled if the ca eskola end member ca 0 5 0 5 alsi 2 o 6 is considered the zircon hosted clinopyroxene in the eclogite contains up to 9 6 mol of the ca eskola component and in the biotite gneiss up to 18 2 mol whereas the matrix clinopyroxene contains much less 1 3 mol on average recalculation of the composition of the matrix clinopyroxene prior to exsolution of quartz rods yields 6 8 mol ca eskola component which is consistent with the composition of the clinopyroxene inclusions in zircon we conclude that the ca eskola component in the peak metamorphic clinopyroxenes broke down by a retrograde reaction 2 ca 0 5 square 0 5 alsi 2 o 6 rightarrow caal 2 sio 6 3 sio 2 resulting in exsolution of the quartz rods in the matrix clinopyroxene subducted crustal and supracrustal rocks form the ca eskola clinopyroxene at high pressures and temperatures the vacancy containing clinopyroxene may have an important bearing on the physico chemical properties of the subducted slab at upper mantle depth

ultrahigh pressure metamorphism in western tianshan china part i evidence from inclusions of coesite pseudomorphs in garnet and from quartz exsolution lamellae in omphacite in eclogites inclusions of coesite pseudomorphs in garnets have been found in type i eclogites interlayered with mafic blueschists and carbonate eclogites and quartz exsolution lamellae in omphacites have been recognized in type ii eclogites with pillow structure in western tianshan china based on mineralogy and petrology the metamorphic evolution of western tianshan eclogites can be divided into three stages 1 pre peak ultrahigh pressure uhp eclogite facies stage 356 443 c 8 10 kb 2 uhp eclogite facies stage 496 598 c 25 7 26 7 1 kbar and 3 retrograde epidote blueschist facies stage 500 530 c 10 12 kbar consequently the eclogites from the western tianshan region of china have undergone unambiguous uhp metamorphism

experimentally determined stability of clinopyroxene garnet corundum in the system cao mgo al 2 o 3 sio 2

silica precipitates in omphacite from eclogite at alpe arami switzerland evidence of deep subduction observations of oriented sio2 precipitates in omphacite from eclogite with tholeiitic basalt protolith bordering the alpe arami garnet peridotite massif ticino switzerland and petrological studies of the eclogitic mineral assemblages suggest that this rock was subjected to higher pressure metamorphism than previously realized we employed various calibrations of the fe2 mg exchange thermometer and calculations of equilibria with thermodynamic data considering the calcium tschermak s component caal2sio6 of garnet pyroxene pairs from these calculations it is concluded that the eclogitic lenses have recorded at least four stages of mineral growth corresponding to the following stage i prograde c 2 4 gpa 700 c stage iia maximum recorded grade c 7 0 gpa 1100 c stage iib retrograde c 3 7 gpa 900 c stage iii retrograde c 2 1 gpa 750 c because of the preservation of stage i a relatively rapid subduction and exhumation of alpe arami eclogite is suggested the exhumation path of the eclogitic rock is in good agreement with most exhumation paths inferred for the alpe arami garnet lherzolite proposed previously by several authors based upon a variety of different observations although the eclogite and peridotite exhumation paths may diverge at depths greater than 120 km

elasticity of diopside to 8 gpa and 1073 k and implications for the upper mantle abstract simultaneous measurements of elastic wave velocities and density have been conducted on diopside by a combined ultrasonic interferometry and x ray diffraction methods at pressure and temperature conditions relevant to the earth s upper mantle the current study not only yielded the first direct measurement of the shear modulus at high pressures but also enabled a simultaneous determination of the bulk and shear properties and their pressure and temperature derivatives from the measured density and velocities finite strain analysis of the experimental data results in ks0 116 4 7 gpa k s 0 4 9 1 ks t p 0 012 1 gpa gpa g 0 1 6 1 and g t p 0 011 1 gpa k with these results and the same finite strain equations the p and s wave velocities of diopsidic mantle clinopyroxene were calculated along a 1600 k adiabatic geotherm in comparison with other mantle minerals the seismic velocities of diopsidic clinopyroxene at upper mantle depths are 1 3 higher than those of orthopyroxene 1 2 and 6 8 lower than those of olivine and majoritic garnet respectively

seismicity structure and tectonics of the wellington region new zealand summary the wellington region lies on the border between the pacific and australian plates the former being subducted the plate interface lies at shallow depth under the region 10 60 km so that detailed and long term monitoring of the seismicity of the zone where large thrust earthquakes are expected to occur is possible hypocentres for events recorded by a 12 station seismic network for the period 1978 1982 7231 events have been refined by the use of a threedimensional velocity model derived from a simultaneous inversion of arrival time data from 129 local events for both hypocentres and velocity the hypocentres show that the subducting pacific plate is defined by a nw dipping zone of relatively intense activity the plate interface as given by the upper envelope of this activity is offset vertically by 7 km on average along a nw se line through cook strait parallel to the direction of absolute motion of the pacific plate rather than to the direction of convergence the strike of the interface at deeper levels also changes across this line this distortion may partly reflect effects of the transition to continent continent type convergence further south within the subducting pacific plate the seismic activity defines two parallel zones separated by about 20 km the lower zone being much less active and perhaps merging with the upper zone at a depth of 80 90 km composite focal mechanisms of events in the upper zone imply predominantly down dip tension with a compression axis perpendicular to the plate interface the mechanism in the lower zone also implies down dip tension but the compression axis has rotated to be horizontal and along strike indicating a component of lateral shearing within the plate these two types of mechanism correlate well with those found previously for events at depths of 150 km or more thus it seems that the large negative buoyancy of the subducted lithosphere dominates the internal stress field throughout the length of the seismically active region the lithosphere acting as a stress guide there is no evidence for a significant number of events with mechanisms indicating thrusting along the plate interface the seismic velocity in the region corresponding to the upper seismic band is close to that typical for oceanic crust which here is probably considerably thicker than normal there is no evidence for a substantial increase in velocity down

quartz exsolution in clinopyroxene is not proof of ultrahigh pressures evidence from eclogites from the eastern blue ridge southern appalachians u s a oriented quartz needles in clinopyroxene have become one of the diagnostic indicators of ultrahigh pressure uhp metamorphism the presence of apparently exsolved quartz is taken as evidence of decompression of a non stochiometric ca eskola component ca0 5 0 5alsi2o6 caes that is presumed to be stable only at uhp conditions eclogite from the eastern blue ridge north carolina contains clinopyroxene jd20cats5ac5caesdi65hd5 with oriented needles of quartz and calcic amphibole that appear to have exsolved together the quartz amphibole intergrowths are surrounded by 1 5 m haloes of neoformed pyroxene jd10cats10ac5caesdi70hd5 the modes of quartz amphibole and clinopyroxene haloes were determined using bse images and reintegrated with the host clinopyroxene viewing the quartz and amphibole needles down the c axis of the pyroxene host provides a better estimate of their proportions than in prismatic sections reintegrated pyroxene compositions were nearly identical to the analyzed host pyroxene with no caes component clinopyroxene with caes solid solution has been repeatedly synthesized at uhp conditions however examination of the phase equilibria usually cited as evidence for caes stability at conditions of 25 kbar shows that clinopyroxene with 10 mol caes is stable well within the quartz field and provides a pressure minimum similar to the albite jadeite quartz barometer exsolution of quartz and associated amphibole is commonplace in clinopyroxene from the blue ridge eclogite that lacks coesite or other evidence for uhp metamorphism the presence of a diluted 5 10 caes component in clinopyroxene does not require uhp conditions

sediment yield along the andes continental budget regional variations and comparisons with other basins from orogenic mountain belts abstract we assess the sediment yield at 119 gauging stations distributed from colombia to patagonia covering the different morphotectonic and morphoclimatic settings of the andes the most productive areas are the meta river basin within the northern andes and the bolivian and northern argentina chaco systems which produce an average of 3345 4909 and 2654 t km2 y 1 of sediment respectively the rivers of the northern and central andes excluding the pacific watersheds of peru northern chile and central argentina have a weighted mean sediment yield of 2045 t km 2 y 1 and produce 2 25 gty 1 of total sediment a major constraint estimating the andean continental budget of sediment yield lies in the lack of gauging data for the peruvian region using the available gauge stations the regional sediment yield appears underestimated assuming a higher value of sediment yield for the peruvian andes the total budget for the whole central andes could range between 2 57 gt y 1 and 3 44 gt y 1 a minimum of 0 55 gt y 1 and a probable maximum of 1 74 gt y 1 of sediment are deposited in the intramontane and surrounding proximal sedimentary basins the magnitude of sediment yield in the andes is comparable to other rivers draining orogenic belts around the world

morphodynamics of a high discharge tropical delta san juan river pacific coast of colombia abstract the san juan river has one of the most extensive and best developed deltas on the pacific coast of south america measuring 800 km 2 the river drainage basin measures 16 465 km 2 and is located in one of the areas with the highest precipitation in the western hemisphere the annual rainfall varies from 7000 to 11 000 mm and as a result the san juan river has the highest water discharge 2550 m 3 s 1 sediment load 16 10 6 t yr 1 and basin wide sediment yield 1150 t km 2 yr 1 on the west coast of south america the san juan delta growth began approximately 5000 years bp the structure of the delta is determined by the interactions between fluvial deposition and the effect of 1 7 m significant swells mostly from the sw and strong tidal currents analysis of delta progradation indicates that during 1848 1992 the morphology of the delta was characterized by beach ridge accretion spit growth narrowing of inlets and a general advance of the delta shoreline during the past decade processes such as rapid erosion of the delta shore narrowing of barrier islands and breaching of a new inlet are the result of a long term relative sea level rise of 2 6 mm yr 1 due to tectonically induced subsidence coupled with a eustatic rise of sea level the delta also experiences strong oceanographic manifestations associated with the el nino la nina cycle causing regional sea level elevation of 20 30 cm during el nino years recent coastal subsidence in the delta is evidenced by 1 increased occurrence of non storm washover events 2 increased erosion of barrier islands with average loss of 11 m yr 1 during 1993 1997 and 3 a relative sea level rise of 3 4 mm yr 1 during 1991 1999 the morphology and recent evolution of the san juan delta are unique when compared to other deltas of south america because of the singular combination of extreme climatic geologic and oceanographic conditions under which the delta has formed and the absence of human induced impact in the drainage basin

the evaluation of unmanned aerial system based photogrammetry and terrestrial laser scanning to generate dems of agricultural watersheds article i nfo agricultural watersheds tend to be places of intensive farming activities that permanently modify their microtopography the surface characteristics of the soil vary depending on the crops that are cultivated in these areas agricultural soil microtopography plays an important role in the quantification of runoff and sedi ment transport because the presence of crops crop residues furrows and ridges may impact the direction of water flow to better assess such phenomena 3 d reconstructions of high resolution agricultural watershed to pographyareessential fine resolutiontopographicdatacollectiontechnologiescanbeusedtodiscernhighlyde tailed elevation variability in these areas knowledge of the strengths and weaknesses of existing technologies used for data collection on agricultural watersheds may be helpful in choosing an appropriate technology this study assesses the suitability of terrestrial laser scanning tls and unmanned aerial system uas photogrammetry for collecting the fine resolution topographic data required to generate accurate high resolution digital elevation models dems in a small watershed area 12 ha because of farming activity 14 tls scans 25 points m 2 were collected without using high definition surveying hds targets whic ha re generally used to mesh adjacent scans to evaluate the accuracy of the dems created from the tls scan data 1098 ground control points gcps were surveyed using a real time kinematic global positioning system rtk gps linear regressions were then applied to each dem to remove vertical errors from the tls point elevations errors caused by the non perpendicularity of the scanner s vertical axis to the local horizontal plane and errors correlated with the distance to the scanner s position the scans were then meshed to generate a demtls with a1 1m spatial resolution the agisoft photoscan and micmac software packages were used to process the aerial photo graphsand generate a dempsc agisoftphotoscan anddemmcm micmac respectively with spatial resolutions of 1 1 m comparing the dems with the 1098 gcps showed that the demtls was the most accurate data prod uct with a root mean square error rmse of 4 5 cm followed by the demmcm and the dempsc which had rmse values of 9 0 and 13 9 cm respectively the dempsc had absolute errors along the border of the study area that ranged from 15 0 to 52 0 cm indicating the presence of systematic errors although the derived demmcm was accurate an error analysis along a transect showed that the errors in the demmcm data tended to increase in areas of lower elevation compared with tls uas is a promising tool for data collection because of its flexibility and low operational cost however improvements are needed in the photogrammetric processing of the aerial photographs to remove non linear distortions

granites and thermal structures in the lithosphere the production of melts of the granite clan on a significant scale requires participation of continental crust such crust will melt when heated from below by a mantle thermal anomaly or when thickend to 40 km or more sites of melting and the time sequences of melting associated with subduction and underplating processes and collision processes are complex in both these processes at least six melting sites may be involved the final chemical and isotopic composition of granitic melts depends on a very complex array of processes which include source composition composition of subducted materials magma mixing magma underplating assimilation fractionation cooling processes resolution of granite melt dynamics requires an integrated attack using modern seismic and electrical measurements in regions where the continental crust is abnormally thick or hot

matrix analysis of metamorphic mineral assemblages and reactions assemblage diagrams are widely used in interpreting metamorphic mineral assemblages in simple systems they can help to identify assemblages which may represent equilibrium states to determine whether differences between assemblages reflect changes in metamorphic grade or variations in bulk composition and to characterize isograd reactions in multicomponent assemblages these questions can be approached by investigating the rank composition space range and reaction space null space of a matrix representing the compositions of the phases involved singular value decomposition svd provides an elegant way of 1 finding the rank of a matrix and detemining orthonormal bases for both the composition space and the reaction space needed to represent an assemblage or pair of assemblages and 2 finding a model matrix of specified rank which is closest in a least squares sense to an observed assemblage although closely related to least squares techniques the svd approach has the advantages that it tolerates errors in all observations and is computationally simpler and more stable than non linear least squares algorithms models of this sort can be used to interpret multicomponent mineral assemblages by straightforward generalizations of the methods used to interpret assemblage diagrams in simpler systems svd analysis of mineral assemblages described by lang and rice 1985 demonstrates the utility of the approach

water discharge and sediment load from the western slopes of the colombian andes with focus on rio san juan abstract small rivers draining high rainfall basins and mountainous terrain west of the cordilleras in south america have disproportionately high water discharge and sediment load fifteen rivers in western colombia discharge a combined 254 km3 yr 1 or 8020 m3 s 1 of water into the pacific sediment yield is strongly correlated with basin area documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand textcyr cyr pagestyle empty declaremathsizes 10 9 7 6 begin document landscape r 2 0 97 end document and sediment load is correlated with water discharge documentclass aastex usepackage amsbsy usepackag

depressional storage for markov gaussian surfaces processes during rain events such as infiltration runoff soil erosion and crust formation are influenced in part by depressional storage and surface roughness if the surface topography is known its potential depressional storage can be calculated the objective of this paper was to relate the statistical parameters for quantifying surface roughness to depressional storage analysis of topographic data sets digitized at millimeter grids by a laser scanner showed that soil roughness can be quantified by a markov gaussian m g type random process a monte carlo simulation procedure was used to find the mean ponding characteristics from simulated m g surfaces depressional storages were found to be functions of two m g parameters two sample length scales and the slope steepness the markov parameters are the global variance 2 and the correlation length scale l and the sample length scales are grid spacing x and side length ls after proper scaling all storage functions collapsed into two nondimensional relationships 1 storage at zero slope as a function of relative sample length scale and 2 storage as a function of scaled slope when l 0 simulated surfaces followed the random gaussian model and the nondimensional storage was only a function of scaled slope storages calculated from digitized elevation data sets with m g type statistics agreed well with results obtained from simulated surfaces

on depressional storages the effect of dem spatial resolution depression storage can be a significant storage element on a watershed surface accounting for the retention of much water over the past decade many models were developed to derive landscape features however relatively little is known about the impact of changing the spatial and or temporal resolutions on subsequent features in this paper the surface topography was measured with the aid of a laser scanner with millimeter resolution emphasis was laid on quantifying the effect of changing spatial resolution upon geometric properties of depressional storages digital mapping allowed the visualization of the location and topology of potential water surfaces and the manner in which water might move from one depression to another from the pond analysis and associated spatial mapping it became clear that most geometric characteristics relating to size and spatial location of depression storage including area volume and depth are scale dependent the relationship between the contributing area of each depression and the surface area of the same depression at each pour depth was established and the organization inherent in such relationship was explored furthermore it was found that these geometric objects may best be described by resorting to fractal geometry a popular tool for quantifying variability across scales

assessing the effect of sea level change and human activities on a major delta on the pacific coast of northern south america the patia river abstract this paper presents the main physical and human induced stresses that have shaped the recent evolution of the patia river delta the largest and best developed delta on the western margin of south america during the holocene the patia delta moved southward and the northern part became an estuarine system characterized by large extensions of mangrove ecosystems however a major human induced water diversion starting in 1972 diverted the patia flow to the sanguianga river and shifted the active delta plain back to its former holocene location this discharge diversion has led to sediment starvation of the southern delta lobe and changed the northern estuarine system into an active delta plain in addition coastal areas of the patia delta subsided as a result of a devastating tsunami in 1979 morphological changes along the delta coast are evidenced by 1 coastal retreat along the whole delta front during the period 1986 2001 2 coastal retreat along the abandoned delta lobe for the period 2001 2008 56 of the southern delta shoreline is retreating and only 4 of the coast shows signs of accretion 3 progradation of the northern delta region during the period 2001 2008 the discharge diversion of the patia river to the sanquianga has apparently balanced the observed trends in coastal erosion and sea level rise 5 1 mm yr 1 for the period 1984 2006 after the 1979 tsunami 4 formation of transgressive barrier islands with exposed peat soils in the surf zone and 5 abandonment of former active distributaries in the southern delta plain with associated inlet closure in the northern delta lobe major geomorphic changes include 1 distributary channel accretion by morphological processes such as sedimentation also in crevasses overbank flow increasing width of levees inter distributary channel fill and colonization of pioneer mangrove 2 freshening conditions in the sanguianga distributary channel a hydrologic change that has shifted the upper estuarine region salinity max q min 3 spatial switch of delta distributaries related to tectonic movements and subsidence 4 a relative sea level rise of 5 1 mm yr 1 after the occurrence of the 1979 tsunami 5 episodes of sea level rise associated with the enso cycle and 6 human induced discharge diversion the information presented here is valuable evidence for understanding the role of extreme events versus normal conditions in creating and shaping deltas

effect of depression storage capacity on overland flow generation for rough horizontal surfaces water transfer distance and scaling overland flow triggering on rough surfaces was investigated using an understanding oriented model the model was based on conditioned walker technique and developed to simulate and analyse the evolution of puddle connection on numerically generated rough surfaces the percolation theory gave a theoretical framework to formalize model outputs and to study overland flow scaling overland flow triggering appeared consistent with a percolation process a scale change exponent was suggested new insights based on the concept of transfer distance of water were emphasized transfer distance enabled us to analyse the water redistribution inside a field and helped to define rainfall efficiency when infiltration occurred copyright 2002 john wiley sons ltd

evidence for immiscibility in ti rich garnet in a calc silicate hornfels from northeastern minnesota calcic garnet from a calc silicate hornfels from the contact metamorphic aureole of the duluth complex northeastern minnesota has ti02 compositions ranging from 0 to 13 wt the concentrations of fe mg ai ti and si are highly correlated and 93 of the total variance can be ascribed to three principal components formed by the additive component grossular and several exchange components the first is a combination of the exchangestisl i mgtial2 and mgca l the second represents the substitutions of al for fe and of fe for ca the third represents the substitution of cr for ai most of the variance occurs along a linear trend from ca3ai1 72feo 28si3012 to ca3m 33alo 67feo 67 ti1 0si2 33012 within this trend a gap in composition occurs between 6 and 12 wt ti02 separate grains of ti rich and ti poor garnet occur in contact with sharp boundaries no exsolution lamellae were observed however immiscibility appears to be blocked by the presence of cr

human induced discharge diversion in a tropical delta and its environmental implications the patia river colombia summary the patia river the number one in terms of sediment yield 1500 t km 2 yr 1 draining the western south america has the most extensive and well developed delta on the pacific coast measuring 1700 km 2 during the holocene nature forced the patia delta to the south however a major water diversion starting in 1972 diverted the patia flow to the sanguianga river the latter a small stream draining internal lakes from the pacific lowlands this human induced discharge diversion shifted the active delta plain back to the north and changed the northern estuarine system into an active delta plain overall major environmental consequences of this discharge diversion in terms of morphological changes along the delta coast and distributary channels are evidenced by 1 coastal retreat along the abandoned delta lobe 63 of the southern shoreline is retreating at maximum rates of 7 m yr 1 with a corresponding coastal land loss of 106 m yr 1 2 transgressive barrier islands with exposed peat soils in the surf zone 3 abandonment of former active distributaries in the southern delta plain with associated closing of inlets and formation of ebb tidal deltas 4 breaching events on barrier islands and 5 distributary channel accretion in the northern delta plain by morphological processes such as sedimentation also in crevasses overbank flow increasing width of levees interdistributary channel fill and colonization of pioneer mangrove the sanguianga mangrove national park smnp the largest mangrove reserve in colombia measuring 800 km 2 lies in this former estuary where major hydrologic and sedimentation changes are occurring observed environmental changes in the smnp include 1 seaward advance of the sub aqueous delta front at the sanquianga inlet evidenced by an increase in tidal flat area from 5 4 mm 2 in 1986 to 14 mm 2 in 2001 2 freshening conditions in the sanguianga distributary channel a hydrologic change that has shifted the upper estuarine region salinity 1 for the 1984 2006 yr period after the devastating tsunami of 1979 in the patia catchment erosion rates have been more pronounced during the 1970 1980 and 1990 2000 decades as a result of land degradation and deforestation preliminary results indicate that relative resent anthropogenic influences on the patia river drainage basin have altered the deltaic environment and beyond significantly

late holocene evolution of the mahakam delta east kalimantan indonesia abstract the late holocene mahakam delta located along the tropical eastern shore of kalimantan indonesia is considered to be a textbook example of a mixed tide fluvial dominated delta system the delta prograded about 60 km during the past 5000 years which led to the development of a distinct network of distributary and tidal channels wave action is low due the limited fetch in the narrow strait of makassar mahakam river discharge is about a quarter of the mississippi river discharge and is characterized by absence of flood surges therefore natural levees crevasse splays and avulsions are absent in the delta plain for the past four decennia both modern and ancient mahakam delta deposits have been studied in detail in order to better understand subsurface miocene and tertiary mahakam deposits which host large volumes of hydrocarbons this study focuses on the dynamics and stratal patterns of delta plain delta front platform deposits and suspended sediments due to the predominance of semi diurnal tides and the associated flow reversals depositional patterns are highly variable which has resulted in the formation of characteristic sand mud couplets the distribution of the sand mud couplets found in this study differs from previously proposed conceptual models they are limited to the fluvial domain and form in the distributary channels lateral channel bar or at the fluvial dominated delta front platform which flanks the mouth bar deposits in offshore direction the sand mud couplets which formed as delta front platform and lateral channel bar deposits are similar and can only be identified based on their 14 c age the sand content decreases significantly towards the tidal dominated areas due to limitation in transport capacity turbidity measurements taken in front of the river mouth also show rapid settlement of river plume sediments some 22 new ams 14 c dates show that late holocene sea level history resembles the eustatic sea level curve giving a first approximation of the late holocene sea level history for east kalimantan the dates suggest that the progradational delta system evolved under conditions of slowly rising sea level which compares well to the eustatic sea level curve in addition calculated averaged deposition rates of the sand mud couplets indicate that deposition is driven by the spring neap tide cycles instead of the daily tidal cycle

relict coesite exsolution in omphacite from western tianshan eclogites china exsolution rods of relict coesite together with quartz were identified in omphacite in eclogites from western tianshan china they are oriented along the c axis of the host clinopyroxenes and have grain size up to 30 m long and 2 3 m wide raman spectra of exsolved lamellae yield consistent but weak bands at 521 270 181 151 and 118 cm 1 typical for coesite in addition to those of quartz and the host omphacite such occurrences together with textured observations suggest a two stage evolution of sio 2 exsolution rods in omphacite lamellae of coesite were apparently exsolved from supersilicic omphacite at p 5 0 gpa and the transformation from coesite to quartz occurred during retrograde metamorphism

an experimental investigation of the pyroxene garnet transformation in a pyrolite composition and its bearing on the constitution of the mantle abstract the pyroxene garnet transformation in a model pyrolite composition has been investigated over the pressure interval 4 0 to 17 5 gpa at temperatures of 1200 1400 c the transformation is largely completed in the pressure interval 14 16 gpa and a single phase aluminum deficient garnet majorite becomes stable above 16 gpa the mineral assemblages and the density and seismic velocity distributions for pyrolite are calculated as a function of depth on the basis of this and other recent experimental data density and seismic velocity profiles calculated for pyrolite are consistent with models based on seismic observations to a depth of 550 km if the existence of a high density velocity gradient between 550 km and 650 km is confirmed the presence of further phase transformations in majorite and or some degree of chemical heterogeneity in this depth interval would be indicated

transformation of enstatite diopside jadeite pyroxenes to garnet the high pressure stability of enstatite en diopside di jadeite jd pyroxenes has been investigated experimentally with a split sphere anvil apparatus ussa 2000 on the enstatite pyrope join the compositions of garnet coexisting with enstatite were determined at 100 165 kbar and 1450 1850 c the results indicate complete solubility between enstatite and pyrope in the system cao mgo al2o3 sio2 cmas the compositions of coexisting pyroxenes and garnet were determined at 100 165 kbar and 1250 1750 c at 157 kbar 1650 c garnet with the composition en79di21 mol forms on the en di join in the system na2o mgo al2o3 sio2 nmas the compositions of coexisting pyroxenes and garnet were determined at 60 160 kbar and 1200 1850 c on the en jd join the first garnet has the composition en48jd52 at 135 kbar 1650 c and en53jd47 at 140 kbar 1500 c on the di jd join the first garnet with the composition di63jd37 forms around 170 kbar 1650 c in the en di jd system the first appearance of garnet with the composition en42di9jd49 is estimated at 133 kbar 1650 c the new pyroxene with the composition namg0 5si2 5o6 napx transforms to garnet at 154 kbar 1650 c the experimental results indicate that the transformation of a twopyroxene assemblage to garnet and residual pyroxene in the en di jd system could occur at pressures consistent with the 400 km seismic discontinuity and in a pressure interval of 0 3 kbar

power law scaling of topographic depressions and their hydrologic connectivity topographic depressions areas of no lateral surface flow are ubiquitous characteristics of the land surface that control many ecosystem and biogeochemical processes high density of depressions increases the surface storage capacity whereas lower depression density increases runoff thus influencing soil moisture states hydrologic connectivity and the climate soil vegetation interactions with the widespread availability of high resolution lidar based digital elevation model ldem data it is now possible to identify and characterize the structure of the spatial distribution of topographic depressions for incorporation in ecohydrologic and biogeochemical studies here we use ldem data to document the prevalence and patterns of topographic depressions across five different landscapes in the united states and quantitatively characterize the probability distribution of attributes such as surface area storage volume and the distance to the nearest neighbor through the use of a depression identification algorithm we show that these probability distributions of attributes follow scaling laws indicative of a structure in which a large fraction of land surface areas can consist of high number of topographic depressions of all sizes and can account for 4 to 21 mm of depression storage this implies that the impacts of small scale topographic depressions in the landscapes on the redistribution of material fluxes evaporation and hydrologic connectivity are quite significant

three dimensional landscape process modelling the effect of dem resolution many landscape models have been developed over the past decades however relatively little is known about handling the effects of changing spatial and temporal resolutions therefore resolution effects remain a factor of uncertainty in many hydrological and geomorphological modelling approaches in this paper we present an experimental multi scale study of landscape process modelling emphasis was laid on quantifying the effect of changing the spatial resolution upon modelling the processes of erosion and sedimentation a simple single process model was constructed and equal boundary conditions were created using artificial digital elevation models dems eliminated effects of landscape representation the only variable factors were dem resolution and the method of flow routing both steepest descent and multiple flow directions our experiments revealed an important dependency of modelled erosion and sedimentation rates on these main variables the general trend is an increase of erosion predictions with coarser resolutions an artificial mathematical overestimation of erosion and a realistic natural modelling effect of underestimating resedimentation cause this increasing the spatial extent eliminates the artificial effect while at the same time the realistic effect is enhanced both effects can be quantified and are expected to increase within natural landscapes the modelling of landscape processes will benefit from integrating these types of results at different resolutions

the eclogite garnetite transformation in the morb h2o system abstract to decipher phase relations of oceanic crust in the coldest slab at the mantle transition zone multi anvil experiments were conducted in the morb h 2 o system at pressures of 10 19 gpa and temperatures of 700 1500 c garnet and stishovite were recognized in all run charges above 15 gpa garnet drastically increases nasi na 2 msi 5 o 12 component m ca mg fe 2 jadeite occurs instead of omphacite na k hollandite containing 7 mol naalsi 3 o 8 and ca perovskite with 60 mol catio 3 were observed at p 17 gpa with decomposition of omphacite and increase of modal ratio of garnet there is a sharp increase of density at 440 km the density increase due to appearance of ca perovskite at 570 km is estimated approximately 100 km shallower than that of previous estimation

improved hydrologic modeling for depression dominated areas abstract modeling of overland flow for a depression dominated area is a difficult task due to the spatial distribution of depressions particularly the hierarchical relationships of depressions and their variable contributing areas make the hydrologic modeling more complicated in traditional hydrologic modeling however digital elevation models dems that are used to represent surface topography are often edited by filling depressions before delineation and the impacts of depressions are considered by using certain simplified and lumped approaches due to such flaws these hydrologic models fail to account for the actual dynamic influences of surface depressions the objective of this study is to improve hydrologic modeling for depression dominated regions by developing a new modeling framework to quantify the influence of spatially distributed depressions to achieve this objective a new puddle based unit pbu probability distributed model pbu pdm is developed and coupled with the existing soil and water assessment tool swat the pbu pdm facilitates separate simulations for non depressional and depressional areas and accounts for the hierarchical relationships of depressions their filling and spilling processes and the dynamic variations in their contributing areas the pbu pdm enhanced swat was applied to the upper maple river watershed in north dakota and calibrated and validated using the observed data in particular it was also compared with the original swat model which demonstrated the abilities of pbu pdm to mimic the filling spilling overland flow dynamics and the threshold behavior the pbu pdm provides improved watershed scale hydrologic modeling especially for depression dominated areas

experimentally determined compositions of diopside jadeite pyroxene in equilibrium with albite and quartz at 1200 1350 c and 15 34 kbar abstract equilibrium compositions of diopside jadeite pyroxene coexisting with albite and quartz were experimentally determined at 25 different p t conditions using an electron microprobe for analysis the new data and the 600 c data of holland 1983 provided the following mixing properties of the diopside di jadeite jd solid solution j k g xs x jd x di 12600 9 45 t 12600 7 6 t x jd x di 21400 16 2 t x jd x di 2 the di jd solution is close to ideal above 1000 c but immiscible below 565 c the di jd solvus is slightly asymmetric with the crest at composition di 42 4 jd 57 6 excess enthalpy is positive but smaller than indicated by the enthalpy of solution measurements of wood et al 1980 disorder in the di jd solution is significantly smaller than complete disorder implied by the ionic two site model

soil roughness slope and surface storage relationship for impervious areas summary the study of the relationships between surface roughness local slope gradient and maximum volume of water storage in surface depressions is a fundamental element in the development of hydrological models to be used in soil and water conservation strategies good estimates of the maximum volume of water storage are important for runoff assessment during rainfall events some attempts to link surface storage to parameters such as indices of surface roughness and more rarely local gradient have been proposed by several authors with empirical equations often conflicting between them and usually based on a narrow range of slope gradients this suggests care in selecting any of the proposed equations or models and invites one to verify the existence of more realistic experimental relationships based on physical models of the surfaces and valid for a larger range of gradients the aim of this study is to develop such a relation for predicting estimating the maximum volume of water that a soil surface with given roughness characteristics and local slope gradient can store experimental work has been carried out in order to reproduce reliable rough surfaces able to maintain the following properties during the experimental activity a impervious surface to avoid biased storage determination b stable un erodible surfaces to avoid changes of retention volume during tests c absence of hydrophobic behaviour to meet the conditions a c we generate physical surfaces with various roughness magnitude using plasticine emulsion of non expansible clay and oil the plasticine surface reproducing surfaces of arable soils was then wetted and dirtied with a very fine timber sawdust this reduced the natural hydrophobic behaviour of the plasticine to an undetectable value storage experiments were conducted with plasticine rough surfaces on top of large rigid polystyrene plates inclined at different slope gradient 2 5 10 20 30 roughness data collected on the generated plasticine surfaces were successfully compared with roughness data collected on real soil surfaces for similar conditions a set of roughness indices was computed for each surface using roughness profiles measured with a laser profile meter roughness indices included quantiles of the abbot firestone curve which is used in surface metrology for industrial application to characterize surface roughness in a non parametric approach whitehouse 1994 storage data were fitted with an empirical equation double negative exponential of roughness and slope several roughness indices resulted well related to storage the better results were obtained using the abbot firestone curve parameter p100 beside this storage empirical model sem a geometrical model was also developed trying to give a more physical basis to the result obtained so far depression geometry was approximated with spherical cups a general physical model was derived storage cup model scm the cup approximation identifies where roughness elevation comes in and how it relates to slope gradient in defining depression volume moreover the exponential decay used for assessing slope effect on storage volume in the empirical model of eqs 8 9 emerges as consistent with distribution of cup sizes

excess silica in omphacite and the formation of free silica in eclogite silica lamellae in eclogitic clinopyroxene are widely interpreted as evidence of exsolution during decompression of eclogite however mechanisms other than exsolution might produce free silica and the possible mechanisms depend in part on the nature and definition of excess silica excess silica may occur in both stoichiometric and non stoichiometric pyroxene although the issue has been debated we show that all common definitions of excess silica in non stoichiometric clinopyroxene are internally consistent interchangeable and therefore equivalent the excess silica content of pyroxene is easily illustrated in a three component condensed composition space and may be plotted directly from a structural formula unit or recalculated end members in order to evaluate possible mechanisms for the formation of free silica in eclogite we examined the net transfer reactions in model eclogites using a thompson reaction space we show that there are at least three broad classes of reactions that release free silica in eclogite i vacancy consumption in non stoichiometric pyroxene ii dissolution of ti phases in pyroxene or garnet iii reactions between accessory phases and either pyroxene or garnet we suggest that reliable interpretation of the significance of silica lamellae in natural clinopyroxene will require the evaluation not only of silica solubility but also of titanium solubility and the possible roles of accessory phases and inclusions on the balance of free silica

ultradeep greater than 300 kilometers ultramafic upper mantle xenoliths geophysical discontinuities in earth s upper mantle and experimental data predict the structural transformation of pyroxene to garnet and the solid state dissolution of pyroxene into garnet with increasing depth these predictions are indirectly verified by omphacitic pyroxene exsolution in pyropic garnet bearing xenoliths from a diamondiferous kimberlite conditions for silicon in octahedral sites in the original garnets are met at pressures greater than 130 kilobars placing the origin of these xenoliths at depths of 300 to 400 kilometers these ultradeep xenoliths support the theory that the 400 km seismic discontinuity is marked by a transition from peridotite to eclogite

dynamic puddle delineation and modeling of puddle to puddle filling spilling merging splitting overland flow processes 1 surface microtopography affects overland flow infiltration soil erosion pollutant transport and other fundamental hydrologic and environmental processes across scales under the influence of surface depressions overland flow essentially features a series of progressive puddle to puddle p2p filling spilling merging and splitting processes the objectives of this study are to characterize puddles and their hierarchical relationships and model the microtopography controlled p2p processes we proposed a new modeling framework for simulating the p2p overland flow dynamics through cell to cell c2c and p2p routing for a set of puddle based units pbus in a well delineated cascaded p2p drainage system testing of the p2p model demonstrated its potential to improve overland flow modeling and hydrologic connectivity analysis by explicitly incorporating the hydrologic roles of depressions and quantifying the real microtopography controlled p2p dynamics

subduction of the eastern panama basin and seismotectonics of northwestern south america spreading along the cocos nazca plate boundary since the breakup of the farallon plate in the miocene has resulted in the formation of the panama basin and a complex interaction of plates in and near northwestern south america current plate boundaries have been defined and segments of subducted lithosphere identified through selection of hypocentral locations of earthquakes considering only well located events and through focal mechanism determinations the existence of relict plate boundaries bathymetric features and the panamanian isthmus has affected the subduction process of the nazca plate beneath south america and determined the present day configuration of the subducting lithospheric plate there is no single triple junction separating the caribbean south american and nazca plates instead the panamanian isthmus and surrounding areas are accommodating east west compression and a lesser degree of north south compression along a series of thrust faults striking nw to ne and the andean ranges of ecuador colombia and venezeula are moving as a block nne relative to the rest of the south american plates along a system of faults following the front of the eastern cordillera the subducted portions of the panama basin and old farallon plate have become segmented into three pieces recognized in this study from north to south they are 1 a bucaramanga segment continuous with the caribbean seafloor northwest of colombia 2 a cauca segment continuous with oceanic crust nazca plate currently being subducted beneath south america at the colombia ecuador trench and 3 an ecuador segment at the northern end of the subducted lithospheric plate which is dipping at a small angle to the east beneath northern peru the segmentation of the subducted plate can be explained by the buoyancy of bathymetric features which have been partially subducted