volcanism and faulting of the campania margin eastern tyrrhenian sea italy a three dimensional visualization of a new volcanic field off campi flegrei by means of information technology 3d digital geologic models are increasingly the best methods of constraining interpretations of geology at depth visualization in three dimensions has allowed us to develop solutions that explain the stratigraphic and structural complexity of the campania margin of the eastern tyrrhenian sea especially the lateral relationships among volcanoes and underlying normal faults using seismic and sequence stratigraphy and structural geology approaches in a dedicated gis environment we interpreted a seismic grid and investigated a subsurface volcanic field in gaeta bay off campi flegrei located within the campania margin the gaeta bay basin fill is characterized by several volcanic units that were analyzed using 2d structure contour maps and isochron maps these volcanoes are comparable in size to the edifices of campi flegrei vesuvius and the submerged volcanoes of the bay of naples their age spans from the lower pleistocene for the isolated v0 volcano sited in central gaeta bay to 0 4 0 1 ma for the volcanic field of southern gaeta bay the study of the interplay between volcanic units and faults allowed us to distinguish 1 the oldest fault buried by the lower pleistocene v0 volcano in central gaeta bay 2 a normal fault swarm ne sw that in the middle pleistocene gave rise to a half graben filled by the v1 v5 volcanic field in southern gaeta bay and 3 post 0 4 ma normal faults that downthrow the v1 and v3 volcanoes we correlated the 1 500 m thick late quaternary volcanoes of southern gaeta bay to the buried lava volcanoes interlayered with volcanoclastic deposits drilled at campi flegrei geothermal wells

three dimensional implicit stratigraphic model building from remote sensing data on tetrahedral meshes theory and application to a regional model of la popa basin ne mexico remote sensing data provide significant information to constrain the geometry of geological structures at depth however the use of intraformational geomorphologic features such as flatirons and incised valleys often calls for tedious user interaction during 3 d model building we propose a new method to generate 3 d models of stratigraphic formations based primarily on remote sensing images and digital elevation models this method is based on interpretations of the main relief markers and interpolation of a stratigraphic property on a tetahedral mesh covering the domain of study the tetrahedral mesh provides a convenient way to integrate available data during the interpolation while accounting for discontinuities such as faults interpretive expert input may be provided through constrained interactive editing on arbitrary cross sections and additional surface or subsurface data may also be integrated in the modeling we demonstrate this global workflow on a structurally complex basin in the sierra madre oriental northeastern mexico

40ar 39ar and k ar geochronology of the dykes from the south indian granulite terrain abstract 40ar 39ar and conventional k ar data on mafic dykes and a felsic dyke together with previous data have been used to constrain the ages of the dyke magmatism in the south indian granulite terrain the age of the mainly ene wsw trending agali anaikatti swarm is estimated to be 1980 25 ma with a very limited occurrence of upper cretaceous 80 90 ma dykes in the area the nw se dharmapuri swarm is dated as at least 1800 ma possibly 1855 9 ma both the nw se and the ne sw dyke swarms of tiruvannamalai are dated at 1650 10 ma only a few dykes in north kerala are of middle proterozoic ca 1700 1650 ma age furthermore the 40ar 39ar results of dharmapuri dykes exhibit age spectrum characteristic of partial degassing they provide strong evidence of latest proterozoic overprinting by a thermal event probably related to the pan african orogeny most of the phanerozoic dykes are confined to the coastal region in kerala province the dolerites of central kerala and the majority of north kerala dolerites intruded during the 70 65 ma period whereas a large gabbro and a felsic dyke in central and north kerala respectively are of upper cretaceous age ca 85 ma and the mean 81 1 5 ma age from these dykes may represent cooling age the oldest phanerozoic upper jurassic 144 6 ma dyke intrusions have a restricted occurrence in south kerala very close to the southern tip of india the proterozoic dykes are interpreted as being lateral intrusions from under plating igneous bodies beneath the eastern shield region the geological record of the terrain does not show indications of significant pre magmatic extension and rifting but dyke magmatism may have led to extension rifting and the consequent development of the india antarctica sri lanka proterozoic high grade terrain the data are also interpreted to suggest that the south indian granulite terrain is an early proterozoic tectono metamorphic terrane with strong thermal imprints of neoproterozoic early palaeozoic age it is difficult to reconcile its extensions into proterozoic sri lanka or antarctica where tectono metamorphism is dated to be of neoproterozoic age the late phanerozoic dykes are predominantly related to the deccan trap event and are associated with mantle plume decompressional tectonics that gave rise to ocean floor spreading between the seychelles and the indian continent the few older ca 145 ma dykes in south kerala may be related to the rift tectonics that preceded the separation of australia antarctica and india

the environmental significance of the remobilisation of ancient mass movements in the atbara tekeze headwaters northern ethiopia abstract old landslides are prominent features in the landscape around hagere selam tigray highlands ethiopia the available evidence suggests their late pleistocene to middle holocene age and conditions of soil humidity the affected geological layers often silicified lacustrine deposits prone to sliding rest upon or above the water holding amba aradam sandstone aquifer three examples of present day remobilisation of old mass movements are illustrated and discussed the aims of the study were to unravel the environmental conditions of the present day remobilisation of ancient flows as well as those of first time landslides the first two mass movements discussed are slumps located in areas with vigorous regeneration of grassy vegetation their activation is thought to be the consequence of an increase in infiltration capacity of the soils under regenerating vegetation one of these slumps had a horizontal movement of the order of 10 20 m in 1 day the other case is the remobilisation of the may ntebteb debris flow below the amba aradam sandstone cliff the debris flow presently creeps downslope at a rate of 3 6 cm year 1 palynological evidence from tufa shows that the reactivation of the flow started 70 years ago shear resistance measurements indicate the danger for continuous or prefailure creep from the soil mechanics point of view the reactivation of the debris flow is due to the combination of two factors 1 the reduction of flow confining pressures as a result of gully incision over the last hundred years and 2 the increase of seepage pressure as a consequence of the cumulative effect of this incision and the increase in infiltration rates on the lobe since grazing and woodcutting have been prohibited 8 years ago the role of such exclosures as possible landslide triggers is discussed from the geomorphological point of view the ancient movements and their present day reactivation cannot be compared the ancient movements led to the development of debris flows whereas the reactivations relate to the dissection of these mass movement deposits

well documented travel history of mesozoic pelagic chert in japan from remote ocean to subduction zone the mino tanba belt in southwest japan a segment of the cordilleran type orogenic chain of jurassic east asia is composed mainly of a middle upper jurassic subduction accretion complex in which triassic and lower jurassic bedded radiolarian cherts occur as large allochthonous units structurally interlayered with middle upper jurassic clastic rocks high resolution microfossil conodont and radiolaria research has identified very low average sedimentation rates of about 0 5 g cm 1000 yr in the chert units similar to those of modern pelagic sediments accumulated in open ocean environments judging from the low average sedimentation rate high purity of biogenic silica long duration of continuous deposition 50 m y and wide along strike extent 1000 km the bedded radiolarian cherts in the mino tanba belt are best understood as ancient pelagic sediments that accumulated in open ocean environments accordingly the alleged origin in smaller marginal basins is untenable upward lithologic change from bedded chert to overlying siliceous mudstone in the uppermost portion of chert sequences suggests the gradual landward approach of the oceanic plate toward a trench the tectonic interlayering of these cherts and coarse grained terrigenous elastics is a secondary feature that was added through duplexing underplating in the subduction zone on the basis of the primary stratigraphy and field occurrence of triassic bedded chert in the mino tanba belt newly proposed are an idealized oceanic plate stratigraphy and a generalized travel history of a cordilleran type bedded chert from its birth at a mid oceanic ridge to its demise at a subduction zone

pleistocene paleosol development and paleoenvironmental dynamics in east africa a multiproxy record from the homo bearing aalat pedostratigraphic succession dandiero basin eritrea abstract the climatic changes during the early middle pleistocene transition are a key to understand the ecosystem dynamics that involved the homo erectus ergaster distribution the aalat pedostratigraphic succession represents a continental archive in the african rift valley eritrea where remains of homo around 1 ma were identified high resolution magnetostratigraphy dated this succession between the base of the jaramillo subchron and the lower brunhes chron despite the present arid desert climate the aalat section records a persistence of water driven fluvio lacustrine environments which suggests a major tectonic control on sedimentation although climate changes are clearly overprinted macro and micromorphological physico chemical mineralogical and geochemical features up to now poorly available for pleistocene paleosols in east africa depict a poor to moderate degree of development although calcic and petrocalcic petrogypsic horizons at different stratigraphic heights indicate phases of geomorphic stability the concurrent alternation of these horizons with iron stained layers suggests cyclical changes from dry to wet conditions which fit well with aeolian dust fluxes and marine isotope stages of glacials and interglacials at higher latitudes stable isotope data are consistent with these climatic cycles and suggest a succession of monsoonal and non monsoonal conditions the homo erectus settlement lasted apparently for a short time span because a long high discharge fluvial sedimentation and or an aridity phase at the base of the fluvial facies could have made the area less suitable for human settling and could have hindered preservation of fossils and artifacts

soils of the main ethiopian rift valley escarpment a transect study abstract the mountainous environment of the ethiopian highlands has a great variety of ecotopes and thus demands great flexibility in land management different climatic conditions and landscape positions induce different soil forming processes leading to various soil types with specific risks and potentials the present study portrays a soil sequence of the central section of the main ethiopian rift valley from the footslopes of the eastern escarpment to the marginal volcano structures six profiles under natural vegetation are described for classification according to the usda soil taxonomy and world reference base for soil resources classification systems and special site characteristics are discussed the acacia savannah of the footslopes 1900 m a s l is characterized by vertisols mazic vertisols aridic haplusterts with often pronounced effects of seasonal waterlogging all other soils are well drained and reflect the general increase in rainfall with elevation and slope causing a decline in topsoil ph and a change from cation rich clay soils of the podocarpus dominated forest at 2300 m a s l mollic nitisols typic palehumults to strongly leached humic umbrisols humic dystrudepts of the hagenia dominated forest around 2600 m a s l the highland savannah plain 2700 m a s l with a drier and cooler environment has typically mollic cambisols dystric haplustepts which are less leached and have a rather brownish colour at 2900 m a s l niti umbric alisols andic hapludalfs are found in the hypericum forest at the midslopes of the marginal volcanoes receiving high rainfall whereas soil development is at a more initial state in the erica dominated forest at 3200 m a s l umbric andosols alic hapludands clay mineral composition is kaolinite dominated for the upper five profiles with a high proportion of poorly crystalline components in the upper savannah and the volcano upslopes the lowermost profile probably has a polygenetic origin indicated by an abrupt change from a smectitic to a kaolinitic composition in the subsoil soil development on quite homogeneous bedrock appears essentially controlled by relief and climate underlining the suitability of the region as a model area for in depth gradient studies on ecosystem processes and land use

a review of the western part of the altaids a key to understanding the architecture of accretionary orogens abstract the altaids is one of the largest accretionary collages in the world and the tectonic styles of the accretionary processes have been interpreted in several ways including as an amalgamation of multiple terranes as a result of oroclinal bending of a long single arc or as a caledonian continental collision based on recent tectonostratigraphic analyses together with paleomagnetic data the tectonic styles of the neoproterozoic to paleozoic accretionary processes of the altaids are discussed the western altaids is the main focus of the study which was mainly composed of several independent linear components such as arcs and microcontinents with proterozoic basement and cover rocks various kinds of arcs existed in the paleo asian ocean including a complicated type of arc alaskan type which is a combination of the japan and mariana type intra oceanic arcs and the cordillera type continental arcs these linear components rotated and collided with each other with multiple subduction polarities which could have been an important result of multiple linear element amalgamation and which has contributed greatly to the architecture of the eurasian continent the basic tectonic styles of the altaids can be summarized as arc arc collision oroclinal bending and large scale rotation and multiple subductions with a complicated archipelago paleogeography these basic features of accretionary orogens in general can be attributed to the amalgamation of complicated multiple linear elements some mesozoic to cenozoic accretionary orogens in the world are also characterized by processes of multiple linear element amalgamation more attention should be paid to the multiple linear element amalgamation of ancient accretionary orogens which will shed light on lateral and vertical continental growth

geologic stereo mapping of geologic structures with spot satellite data geologic note 1 the spot imaging system launched in 1986 by the french national space agency cnes provides two significant advances for mapping geological structures from satellite imagery increased spatial resolution of key structural and stratigraphic elements and stereoscopic capabilities for making strike and dip measurements quantitative stereo mapping with spot data may be done using hard copy images and conventional equipment such as stereo plotters or by displaying images on a video monitor in stereo viewing format the latter method is a new remote sensing technique particularly relevant to the exploration community this technique allows development with minor expenditure and training of an effective stereo mapping capability on existing image processing systems or o stand alone personal computers spot stereo data is particularly useful for mapping low amplitude and highly deformed structures surface structure maps generated from stereo imagery data can be applied to exploration at two levels at early stages such maps can be used to establish the style trend size and spatial distribution of structures in a basin and to investigate key tectonic elements at more advanced prospecting stages these maps can be used to constrain subsurface mapping of structures located in areas of poor seismic data quality this latter technique however may require the support of higher resolution stereo aerial photography

ophiolite genesis and global tectonics geochemical and tectonic fingerprinting of ancient oceanic lithosphere ophiolites and discussions on their origin and significance in earth s history have been instrumental in the formulation testing and establishment of hypotheses and theories in earth sciences the definition tectonic origin and emplacement mechanisms of ophiolites have been the subject of a dynamic and continually evolving concept since the nineteenth century here we present a review of these ideas as well as a new classification of ophiolites incorporating the diversity in their structural architecture and geochemical signatures that results from variations in petrological geochemical and tectonic processes during formation in different geodynamic settings we define ophiolites as suites of temporally and spatially associated ultramafic to felsic rocks related to separate melting episodes and processes of magmatic differentiation in particular tectonic environments their geochemical characteristics internal structure and thickness vary with spreading rate proximity to plumes or trenches mantle temperature mantle fertility and the availability of fluids subduction related ophiolites include suprasubduction zone and volcanic arc types the evolution of which is governed by slab dehydration and accompanying metasomatism of the mantle melting of the subducting sediments and repeated episodes of partial melting of metasomatized peridotites subduction unrelated ophiolites include continental margin mid ocean ridge plume proximal plume distal and trench distal and plume type plume proximal ridge and oceanic plateau ophiolites that generally have mid ocean ridge basalt morb compositions subduction related lithosphere and ophiolites develop during the closure of ocean basins whereas subduction unrelated types evolve during rift drift and seafloor spreading the peak times of ophiolite genesis and emplacement in earth history coincided with collisional events leading to the construction of supercontinents continental breakup and plume related supermagmatic events geochemical and tectonic fingerprinting of phanerozoic ophiolites within the framework of this new ophiolite classification is an effective tool for identification of the geodynamic settings of oceanic crust formation in earth history and it can be extended into precambrian greenstone belts in order to investigate the ways in which oceanic crust formed in the archean

cryogenian 830 ma mafic magmatism and metamorphism in the northern madurai block southern india a magmatic link between sri lanka and madagascar abstract the northern madurai block southern india lies directly south of and partly deformed by the palghat cauvery shear zone system pcss a potential suture of the neoproterozoic mozambique ocean the kadavur gabbro anorthosite complex lies south of the pcss in the northern madurai block and crystallized at 829 14 ma la icpms zircon data in a supra subduction zone setting the complex contains zircon e hf t values of 12 5 to 8 6 that represent palaeoproterozoic t dm model ages 2 3 2 5 ga these broadly agree with a whole rock neodymium t dm model age of 2287 ma oxygen isotope 18 o ratios range from 5 82 and 6 74 the parental magma for the gabbro anorthosites are interpreted to be derived from a juvenile neoproterozoic mantle contaminated by mesoarchaean igneous infra crustal sources the gabbro anorthosites intrude quartzites with dominantly palaeoproterozoic detrital zircons that contain neoarchaean and mesoarchaean hafnium model ages these quartzite zircons contain metamorphic rims that yield an age of 843 23 ma demonstrating the autochthonous nature of the gabbro anorthosite complex later felsic magmatism is recorded by the 766 8 ma crystallisation age of the protolith of a felsic gneiss cryogenian magmatism in the madurai block is interpreted to form part of an extensive arc magmatic province within the southern east african orogen that can be traced from central madagascar through southern india to the wanni complex of sri lanka this province is interpreted to have formed above a south west dipping subduction system as the mozambique ocean was subducted under the neoproterozoic continent azania

coexistence of allophane gibbsite kaolinite and hydroxy al interlayered 2 1 clay minerals in a perudic andosol allophane and halloysite are the most common secondary aluminosilicate minerals in andosols developed in pyroclasts in humid tropical areas we studied the composition and the charge properties of the clays extracted from the weathered b horizon of a perhydrated andosol developed in andesitic ash in guadeloupe french west indies by selective dissolution x ray diffraction xrd thermal analysis and characterization of ion exchange properties the bw horizon contained weatherable minerals and exhibited an allophane content of 25 its clay fraction contained gibbsite allophane kaolinite and hydroxy al interlayered 2 1 clay minerals the occurrence of gibbsite allophane and kaolinite was linked with intense leaching of silica after oxalate dissolution of allophane the cation exchange capacity cec was 11 8 cmol c kg 1 clay i e a typical value for low activity clays subsequent citrate treatment completely dissolved gibbsite but partly extracted al interlayers from the hydroxy al interlayered phase this extraction led to a 5 6 fold increase of the cation exchange capacity 62 3 cmol c kg 1 clay and a 2 3 fold increase in k selectivity the 2 1 clay minerals involved a combination or continuum of high charge beidellite and vermiculite from our data we believe that the 2 1 clay minerals first acted as a sink for aluminium and might have expressed an anti gibbsitic effect after substantial al interlayering of 2 1 clay minerals mimicking low activity clay gibbsite might have formed in a second stage c 2003 elsevier science b v all rights reserved

abrupt post glacial climate events in west asia and north africa monsoon domains regions beyond the present or past penetration of the indian and african monsoons have experienced several large and abrupt climatic fluctuations over the past 13 14c kyr pollen and lake records from west asia western tibet and rajasthan east africa ethiopia and west africa western sahara sahel and subequatorial africa were selected on the basis of chronological control sensitivity of both site and environmental indicators to climate change the continuity of the record and interdisciplinary control of the palaeoclimatic interpretation conditions wetter than those of today prevailed during the early mid holocene period but major dry spells are recorded at all sites during the intervals 11 0 9 5 kyr bp 8 7 kyr bp and 3 4 kyr bp several records also suggest dry events of minor amplitude around 6 kyr bp potential boundary forcings of insolation and sea surface and tropical land surface conditions are discussed the solar radiation accounts for the general envelop of the post glacial monsoon fluctuations but explains neither the timing nor the amplitude of the short term changes in spite of apparent covariation between fluctuations in sea surface conditions in the north atlantic and the monsoon record no direct mechanism could be found relating the intensity of the oceanic thermohaline conveyor belt to the monsoon strength changes in tropical land surface conditions soil moisture negative feedback and changes in ch4 production from wetlands provide a more satisfactory hypothesis for explaining abrupt reversal events

zircon u pb geochronology and hf isotope of felsic volcanics from attappadi southern india implications for neoarchean convergent margin tectonics abstract the attappadi area on the south western flanks of the archean dharwar craton in southern india is located along the e w trending bhavani shear zone which marks the trace of a neoarchean suture zone the dominant rock types in the area include meta ultramafics amphibolites ttg tonalite trondhjemite granodiorite gneisses metapelites and sulphidic banded iron formation bif here we report the occurrence of felsic volcanic rocks preserving primary textures from the anaikatti area in eastern attappadi the felsic volcanics are interbanded with the bif amphibolite metapelite metapyroxenite and hornblende gneisses the felsic volcanics are divided into two types based on their textures the type 1 rock is medium grained with gneissic texture and lack unequivocal primary volcanic textures type 2 felsic volcanics are thinly laminated fine grained and at places preserve relict soft sediment deformation structures they also contain relict volcanic clasts or lapilli and are interpreted as felsic tuff geochemically the attappadi felsic volcanics are rhyolitic in composition and have arc related trace element signatures they also possess a calc alkaline volcanic affinity we report la icpms u pb ages from zircons in four samples of the felsic tuffs which show weighted mean ages of 2567 18 ma and mswd 1 4 2499 19 ma mswd 0 57 2555 24 ma mswd 1 7 and 2576 64 ma mswd 5 8 the late neoarchean early paleoproterozoic ages obtained in our study correlate well with the zircon u pb ages reported in recent studies from ophiolites and other suprasubduction suites from attappadi and surrounding regions the zircon ehf values range from 11 1 to 7 6 suggesting heterogeneous source material involving both juvenile and older reworked components we build a tectonic model for the sw margin of the dharwar craton with an oceanic realm characterized by island arcs and widespread submarine tholeiitic as well as komatiitic ultramafic and mafic volcanism during the neoarchean this predominantly mafic volcanism on the ocean floor is represented by primitive komatiitic lavas oxide and sulphide facies bif the birth of volcanic arc at the convergent margin is marked by felsic volcanism and the deposition of felsic volcanics and volcano sedimentary successions in the final stage of ocean closure the ocean plate and continental arc assemblages were brought in juxtaposition including the accretion of the ophiolitic fragments our study confirms the recent models of arc arc and arc continental accretion to the southern margin of the dharwar craton and major continental growth at the end of the archean

3 d modeling of geologic maps from surface data recent discoveries in earth sciences are mostly related to technologies allowing graphical representations of volumes we present a way to produce mathematically and geometrically correct three dimensional 3 d geologic maps consisting of the volume and shape of all geologic features of a given area the method is innovative in that it only uses surface information based on the combination of a standard geologic map a satellite image and a digital elevation model it is based on a modeling algorithm that only uses surfaces calculated from scattered data points and that intersects them following a series of geologically sound rules the major advantage of using such technology is that it provides the user with a way to quantify geology to illustrate how a 3 d geologic map can be computed we explain the steps taken to build a dummy model with simple faulting and depositional sequencing the case study chosen to illustrate the method is the beirut watershed lebanon an area with relatively simple geology the 3 d visualization and cross sections help in the understanding of the geometrical relationship between the different geologic features allowing a reexamination of the tectonic history of the area during the late mesozoic

soft sediment deformation structures in the earth s oldest seismites abstract the chaibasa formation in eastern india which was deposited between 2100 and 1600 million years ago shows deformations that must have formed when the sediments were not yet consolidated some of these deformation structures have never been described before here they are described depicted and their origin is analysed we show that they must be the result of shocks which can only be explained satisfactorily as triggered by earthquakes the layers containing these deformation structures are termed seismites they are among the earliest records of earthquakes known in the earth s history

recognition of ocean plate stratigraphy in accretionary orogens through earth history a record of 3 8billion years of sea floor spreading subduction and accretion abstract ocean plate stratigraphy ops is a term used to describe the sequence of sedimentary and volcanic rocks deposited on oceanic crust substratum from the time it forms at a spreading center to the time it is incorporated into an accretionary prism at a convergent margin in this study we review the major geological characteristics of relict cenozoic to early archean oceanic crust and ops persevered in alaska japan california franciscan complex central asia british isles canada slave province australia pilbara craton and greenland isua and ivisaartoq belts an assessment of ops in accretionary orogens spanning the duration of earth s rock record shows remarkable similarities between ops of all ages in terms of structural style major rock components sequence of accretion and trace element geochemical signatures volcanic rocks preserved in the orogenic belts are characterized predominantly by oceanic island arc basalts island arc picrites mid ocean ridge basalts back arc basalts oceanic plateau basalts ocean island basalts and boninites with extremely rare komatiites this demonstrates that sea floor spreading lateral movement of oceanic plates with accompanying sedimentation over the oceanic substratum and accretion at convergent margins have been major earth processes since at least 3 8 ga ago there have been some secular changes in the rock types in ops such as changes in carbonates and radiolarian cherts whose sources were in the biota in existence in phanerozoic times but absent in the precambrian but overall there have been few changes in the style of ops accretion with time komatiites and banded iron formations occur predominantly in archean orogenic belts reflecting higher mantle temperatures and less oxic seawater composition respectively before 2 5 ga this is clear documentation that plate tectonics including the lateral movement of oceanic lithosphere has been a major heat loss mechanism on earth since the early precambrian

the cauvery shear zone southern granulite terrain india a crustal scale flower structure abstract the cauvery shear zone csz is a crustal scale shear system within the southern granulite terrain along the southern margin of the archaean dharwar craton structural interpretation of satellite data and field observations reveal four major shear zones within the csz system they show dextral shear kinematics synchronous with a major neoproterozoic tectono metamorphic event d2 associated with intracrustal melting and migmatisation the disposition geometry and contemporaneity of shear fabrics of the csz system are modelled in terms of a crustal scale flower structure akin to transpressional and collisional orogens in the light of recent seismic evidence for a displaced moho structure and a mid to lower crustal low velocity zone the flower structure across the csz may extend to mantle depths

extensive ash falls in and around the sea of japan from large late quaternary eruptions abstract five widespread ashes of late quaternary age have been recognized on land and also in deep sea sediments in and around the sea of japan all are favorable for determining the magnitude and type of the great eruptions and for establishing a quaternary chronology around japan accurate determination of refractive indices of volcanic glass shards and phenocrysts together with chemical data have enabled successful characterization of the tephra layers and correlation between land and sea of the five tephras two are alkalic and are the products of major eruptions of two korean volcanoes the baegdusan tomakomai ash b tm and the ulreung oki ash u oki the b tm ash is recognized at the top of most cores in the northern part of the sea of japan and also on hokkaido and the northern part of honshu where a reliable archeological age is given around the 11th century the u oki ash occurs between the kikai akahoya and aira tn ashes in cores from adjacent to the ulreung do to central honshu where three radiocarbon ages of around 9300 yr b p were obtained the other three tephras are subalkalic and are correlated with large scale eruptions producing voluminous pyroclastic flows and calderas in kyushu the kikai akahoya k ah aira tn at and aso 4 ashes the former two have been well described already but their fallout areas are partly revised in this manuscript the at ash is the most prominent marker recognized not only on land of japan but also in cores from the whole area of the sea of japan and part of the pacific ocean the airfall aso 4 ash simultaneous with the aso 4 pyroclastic flow eruption is also described it mantles very extensive areas and serves as an important time marker about 70 000 years ago

genesis of lavas of the taupo volcanic zone north island new zealand the taupo volcanic zone forms part of the taupo hikurangi subduction system and comprises five volcanic centres tongariro taupo maroa okataina and rotorua tongariro volcanic centre is formed almost entirely of andesite while the other four centres contain predominantly rhyolitic volcanics and later fissure eruptions of high al basalt estimated total volume of each lava type are as follows 2 km3 of high al basalt 10 000 km3 of rhyolite and ignimbrite 97 4 the location of the andesites and vent alignments suggest a source from a subduction zone underlying the area however the lavas differ chemically from island arc andesites such as those of tonga in particular by having higher contents of the alkali elements light ree and sr and pb isotopes this suggests some crustal contamination and it is considered that this may occur beneath the wide accretionary prism of the subduction system amphibolite of the subduction zone will break down between 80 and 100 km and a partial melt will rise a multi stage process of magma genesis is then likely to occur high al basalts are thought to be derived from partial melting of a garnet free peridotite near the top of the mantle wedge overlying the subduction zone locations of the vents controlled largely by faults within the crust rhyolites and ignimbrites were probably derived from partial melting of mesozoic greywacke and argillite under the taupo volcanic zone initial partial melting may have been due to hydration of the base of the crust the water having come from dehydration of the downgoing slab the partial melts would rise to form granodiorite plutons and final release of the magma to form rhyolites and ignimbrites was allowed because of extension within the taupo graben dacites of the bay of plenty probably resulted from mixing of andesitic magma with small amounts of rhyolitic magma but those on the eastern side of the rotorua taupo area were more likely formed by a higher degree of partial melting of the mesozoic greywacke argillite basement this may be due to intrusion of andesite magma on this side of the taupo volcanic zone

biological and mineralogical features of andisols in the mexican volcanic higlands abstract in the montane grasslands of mexico perennial grass and black andisols are linked in a complex mechanism of soil formation in which both biogenic and mineral products interact in this ecosystem typical of the volcanic highlands a sequence of profiles has been studied by macro and micro morphology scanning and transmission electron microscopy tem infra red spectroscopy of soil samples and humic acid ha extracts radiocarbon dating and pollen record soil moisture and available water determinations and soil water analyses the grass muhlennberrgia macroura is important in the soil forming process as it is the host of micro and meso fauna which produce abundant organic micro aggregates soil formation began 7550 years ago and continued through several climatic and vegetation changes the soil thickens as its age increases mineral neoformation is oriented towards allophane and halloysite rather than al rich minerals such as imogolite and gibbsite and high si contents are observed in the soil water the black andisols have high water and carbon storage capacities and play a prominent role in regulating drainage presentday destruction of the grassland for potato cultivation will decrease the waterer reserve of these volcanic highlands

late glacial holocene diatom record of water chemistry and lake level change from the tropical east african rift lake abiyata ethiopia abstract diatom study of a 12 6 m long sediment core ab95ii from lake abiyata ethiopian rift 8 n revealed large amplitude changes in the water level and chemistry over the past 13 4 cal kyr bp past water conductivity ph and water chemical facies reflected by ionic ratios are quantitatively reconstructed based on diatom transfer functions previously established conductivity has varied from 400 to 21 500 s cm 1 ph from 8 to 10 5 the anion hco 3 co 3 2 cl so 4 2 and cation na k ca 2 mg 2 ratios ranged between 0 9 4 and 0 5 275 respectively a high water salinity oscillation is recorded at the base of the sequence the extrapolated age of this interval 12 7 12 0 cal kyr bp corresponds to the younger dryas chronozone the early middle holocene registers a high stand freshwater lake between 12 and 5 4 cal kyr bp changes in diatom assemblages suggest minor changes in water depth lake mixing and or nutrient content during this interval post 5 4 cal kyr bp shallow saline conditions generally predominate short term regressive events are recorded at 5 6 and 3 0 cal kyr bp our results are roughly consistent with previous works in the region they refine the timing of the hydrochemical changes and quantify their amplitude thus providing inputs for modelling approaches

gold mineralization in kottathara prospect attappadi valley kerala india a preliminary appraisal abstract the kottathara gold prospect of attappadi valley in kerala is located within the southern indian granulite terrain comprising charnockite and gneisses with enclaves of high grade supracrustals the gold mineralization associated with the basic members of the attappadi supracrustals and the quartz veins traversing them are confined within the bhavani shear zone primarily the gold quartz lode is emplaced in rheologically preferred zones along the contact of the basic members with the enclosing gneisses subsequent to a period of retrogression and shearing ore mineralogical studies reveal that gold got remobilized and this remobilization is identified with the regional bhavani shear sem studies indicate that gold occurs in free state and also within sulphides especially pyrite variation in grain morphology is clearly discernible in gold occurring within oxidised and in non oxidised zones sequencing of deformational events with associated emplacements of known ages suggests the age of gold mineralization of attappadi area as between 2 ga and 2 5 ga the secondary mobilization has to be

formation of an archean tectonic melange in the schreiber hemlo greenstone belt superior province canada implications for archean subduction accretion process the late archean circa 2750 2670 ma schreiber hemlo greenstone belt superior province canada is composed of tectonically juxtaposed fragments of oceanic plateaus circa 2750 2700 ma oceanic island arcs circa 2720 2695 ma and siliciclastic trench turbidites circa 2705 2697 ma following juxtaposition these lithotectonic assemblages were collectively intruded by synkinematic tonalite trondhjemite granodiorite ttg plutons circa 2720 2690 ma and ultramafic to felsic dikes and sills circa 2690 2680 ma with subduction zone geochemical signatures overprinting relations between different sequences of structures suggest that the belt underwent at least three phases of deformation during d1 circa 2695 2685 ma oceanic plateau basalts and associated komatiites arc derived trench turbidites and oceanic island arc sequences were all tectonically juxtaposed as they were incorporated into an accretionary complex fragmentation of these sequences resulted in broken formations and a tectonic melange in the schreiber assemblage of the belt d2 circa 2685 2680 ma is consistent with an intra arc right lateral transpressional deformation fragmentation and mixing of d2 synkinematic dikes and sills suggest that melange formation continued during d2 the d1 to d2 transition is interpreted in terms of a trenchward migration of the magmatic arc axis due to continued accretion and underplating the d2 intra arc strike slip faults may have provided conduits for uprising melts from the descending slab and they may have induced decompressional partial melting in the subarc mantle wedge to yield synkinematic ultramafic to felsic intrusions a similar close relationship between orogen parallel strike slip faulting and magmatism has recently been recognized in several phanerozoic transpressional orogenic belts suggesting that as in phanerozoic counterparts orogen parallel strike slip faulting in the schreiber hemlo greenstone belt played an important role in magma emplacement

halloysite as a kinetically controlled end product of arid zone basalt weathering abstract mineralogical and isotope results paired with field observations suggest that halloysite is the favored albeit metastable aluminosilicate end product of arid zone basalt weathering on kohala hawai i and that the formation of smectite has been inhibited by kinetic factors soils sampled on constructional lava flows having ages ranging from 4 to 350 ka provide a chronosequence that has had minimal physical disturbance thus allowing us to interpret chemical and mineralogical changes as the result of a time dependent process the halloysite content of the soil increases with increasing soil age its growth is at the expense of allophane which in turn forms at the expense of primary minerals these mineral relationships suggest that halloysite has been forming continuously throughout the lifetime of the soil smectite the thermodynamically stable phyllosilicate phase predicted by soil solution composition is not found in these arid soils we determined that our soil system is controlled by kinetic factors and that therefore thermodynamic predictions do not reflect reality the main factors favoring kinetic control of halloysite formation are intense but short wet periods followed by prolonged extremely dry seasons and microenvironmental conditions leading to immediate uptake of released al by the halloysite precursor mineral allophane the 18o relationship between present day soil water and halloysite formed over the last 170 ka was used as a tracer of past soil conditions results from a reconstruction of paleo climate and soil conditions combined with 18o data observed mineral relationships along the 350 ka chronosequence and field evidence for long term aridity rule out the possibility that the arid side of kohala was affected by prolonged periods of higher rainfall that could have produced more dilute soil waters and therefore altered mineralogical stabilities we conclude that pedogenic halloysite has been continually forming from the early stage of soil formation and that it has consistently formed under isotopic equilibrium conditions indicating that halloysite 18o compositions imply paleoclimatic conditions over the time of its formation that are similar to today s

upper plate deformation as marker for the northern step fault of the ionian slab tyrrhenian sea central mediterranean abstract the eastern tyrrhenian margin etm the active boundary of the tyrrhenian sea backarc basin is the key for understanding the geodynamics of the central mediterranean numerous seismic tomography studies have been carried out in this region proposing different reconstructions of the lower subducting plate and cause of the slab break off existing beneath the southern apennines however the area and mode of the recent deformation of the tyrrhenian sea are still not fully defined and understood in this study we combine the analysis of a recent seismic tomography model and geological data in order to understand the relationship between the subducting lower plate and the tectonic evolution of the sedimentary basins formed on the upper plate with this aim we interpreted a large data set of seismic reflection profiles and several well logs the results consist in 2d and 3d geological models of the basins sedimentary infill and fault networks taking into account the geological data of the etm and those of the adjacent inner flank of the apennines we observe i a system of linked sedimentary basins developed on a narrow deformation belt bounded by transform fault zones ii a polyphase rifting within the upper plate iii an abrupt change of the direction of extension 90 from ne oriented in the lower pleistocene to se oriented in the middle pleistocene since these etm features are not the typical expressions of the current backarc extensional models we propose a link between the evolution of upper plate and the onset and development of a step subduction transform edge propagator fault along the northern margin of the ionian slab

proterozoic orogens in southern peninsular india contiguities and complexities abstract the precambrian terranes of southern peninsular india have been central to discussions on the history of formation and breakup of supercontinents of particular interest are the proterozoic high grade metamorphic orogens at the southern and eastern margins of the indian shield skirting the 3 4 ga dharwar craton which not only preserve important records of lower crustal processes and lithospheric geodynamics but also carry imprints of the tectonic framework related to the assembly of the major neoproterozoic supercontinents rodinia and gondwana these proterozoic orogens are described as southern granulite terrane sgt in the southern tip and the eastern ghats mobile belt egmb in the eastern domains of the peninsula the contiguity of these orogens is broken for a distance of 400 km and disappears in the bay of bengal these orogens expose windows of middle to lower crust with well preserved rock records displaying multiple tectonothermal events and multiphase exhumation paths recent studies in these orogens have led to the recognition of discrete crustal blocks or terranes separated by major shear zone systems some of which represent collisional sutures the sgt and egmb carry several important features such as fold thrust tectonics regional granulite facies metamorphism of up to ultrahigh temperature conditions in some cases multiple p t paths development of lithospheric shear zones emplacement of ophiolites presence of alkaline and anorthositic complexes development of crustal scale flower structures transpressional strains and reactivation tectonics a heterogeneous distribution of different metamorphic and magmatic assemblages with distinct spatial and temporal strain variations in shaping the fabric elements in different blocks is identified both egmb and sgt share a common transpressional deformation history during the latest neoproterozoic characterized by the steepening of the initial low angle crustal scale structures leading to a subvertical grain conducive to reactivation tectonics our synthesis of the spatial distribution geometry kinematics and the transpressional strain of the shear zone systems provides insights into the tectono metamorphic history of the proterozoic orogens of southern india and their contiguity and complexities recent understanding of subduction accretion and collisional history along these zones together with a long lived transpressional tectonic regime imply that these orogens witnessed identical tectonic regimes at different times in earth history although the major and common structural architecture was built during the final assembly of the gondwana supercontinent

human impact on the environment in the ethiopian and eritrean highlands a state of the art abstract this review analyses the environmental evolution of the ethiopian highlands in the late quaternary the late pleistocene 20 000 12 000 14c years bp was cold and dry with 1 low lake levels in the rift valley 2 large debris fans on the flanks of lake abhe basin and 3 the blue nile transporting coarse bedload then a period with abundant and less seasonal rains existed between 11 500 and 4800 14c years bp as suggested by increased arboreal pollen high river and lake levels low river turbidities and soil formation around 5000 4800 14c years bp there was a shift to more arid conditions and more soil erosion many phenomena that were previously interpreted as climate driven might however well be of anthropic origin thick sediment deposits on pediments as well as an increase of secondary forest scrub and ruderal species in pollen diagrams are witnesses of this human impact one important aspect of the late quaternary palaeoenvironment is unclear changes in nile flow discharges and rift valley lake levels have been linked to changes in precipitation depth most authors do not take into account changes in land use in the highlands nor changes in the seasonality of rain both of which can lead to a change in runoff coefficients tufa and speleothem deposition around 14 000 years ago tend to indicate that at the end of the last glacial maximum lgm conditions might have been wetter than generally accepted the most important present day geomorphic processes are sheet and rill erosion throughout the country gullying in the highlands and wind erosion in the rift valley and the peripheral lowlands based on existing sediment yield data for catchments draining the central and northern ethiopian highlands an equation was developed allowing to assess area specific sediment yields sy 2595a 0 29 n 20 r 2 0 59 where sy area specific sediment yield t km 2 year 1 and a drainage area km2 with respect to recent environmental changes temporal rain patterns apart from the catastrophic impact of dry years on the degraded environment cannot explain the current desertification in the driest parts of the country and the accompanying land degradation elsewhere causes are changing land use and land cover which are expressions of human impact on the environment deforestation over the last 2000 3000 years was probably not a linear process in ethiopia studies on land use and land cover change show however a tendency over the last decades of increasing removal of remnant vegetation which is slowed down or reversed in northern ethiopia by a set aside policy ongoing land degradation requires urgent action at different levels of society soil and water conservation swc structures are now widely implemented local knowledge and farmer s initiatives are integrated with introduced swc techniques at various degrees impact assessments show clear benefits of the soil conservation measures in controlling runoff and soil erosion in high rain areas runoff management requires greater emphasis during the design of soil conservation structures in such areas investment in swc might not be profitable at farm level although benefits for society are positive this pleads in favour of public support the present land degradation in the ethiopian highlands has a particular origin which includes poverty and lack of agricultural intensification causes of these are to be found in the nature of past and present regional social relations as well as in international unequal development this review strengthens our belief that under improved socio economic conditions land husbandry can be made sustainable leading to a reversal of the present desertification and land degradation of the ethiopian highlands

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

three dimensional reconstruction of geological surfaces an example of growth strata and turbidite systems from the ainsa basin pyrenees spain the external and internal geometry of four turbidite systems outcropping around the buil syncline ainsa basin spanish pyrenees has been reconstructed with reservoir scale resolution in three dimensions 3 d the irregular geometry of the syncline and the resolution required for the reconstruction cannot be resolved with cross sections therefore reconstruction has been carried out with a new methodology that applies a 3 d dip domain geometrical model and 3 d restoration techniques to achieve reservoir scale resolution in kilometric scale reconstructions this methodology is aimed at resolving 3 d geometries in folded areas and regions with variable thickness stratigraphy the 3 d reconstruction of the buil syncline reveals the synsedimentary growth of an intrabasinal anticline and the foreland lithospheric flexure associated with tectonic loading north of the ainsa basin

senonian basin inversion and rejuvenation of rifting in africa and arabia synthesis and implications to plate scale tectonics abstract the late paleozoic to tertiary stratigraphic record of much of the african plate reflects the effects of continental rifting and passive margin development several short lived but widespread and tectonically important compressional or wrench dominated events occurred however during the permian to recent evolution of africa we focus here on the best documented of these events which occurred during the late santonian at that time older sedimentary basins mostly ene wsw trending were folded and inverted including some basins along the tethyan margin from morocco to the syrian arc and the intraplate benue southern chad basins and the lugh mandera basin in oman ophiolites were obducted following the santonian tectonism an extensive phase of rifting occurred in central and north africa and northern arabia spanning from campanian to maastrichtian or paleocene times rejuvenation or acceleration of subsidence occurred in several basins located along the tethyan margin along the atlantic and indian ocean margins as well as within the intraplate domain rifting was sometimes accompanied by magmatic activity especially in offshore northern libya and along the indian ocean margin compressional deformations rejuvenated or developed by latest maastrichtian times along the tethyan margin and locally within the intraplate domain one of the most remarkable attributes of the santonian tectonic event which we consider representative of the major trans african stress field changes is the rapidity with which the change was reflected stratigraphically across north and central africa and its short duration the cause of the santonian compressional event is directly linked to the change in poles of rotation for the opening of the atlantic at 83 85 ma the end of the cretaceous normal magnetic quiet zone this was also synchronous with the obduction of ophiolites along the northeast margin of arabia oman the onset of separation between india and madagascar with formation of the mascarene oceanic basin and the development of the european alpine chain we interpret these phenomena as causally related aspects of a global tectonic event the santonian compressional event as well as the campanian maastrichtian rifting event and the end cretaceous compressional event illustrate the critical connection between intraplate tectonic histories and processes occurring at sometimes very distant plate boundaries

groundwater visualisation system gvs a software framework for integrated display and interrogation of conceptual hydrogeological models data and time series animation summary management of groundwater systems requires realistic conceptual hydrogeological models as a framework for numerical simulation modelling but also for system understanding and communicating this to stakeholders and the broader community to help overcome these challenges we developed gvs groundwater visualisation system a stand alone desktop software package that uses interactive 3d visualisation and animation techniques the goal was a user friendly groundwater management tool that could support a range of existing real world and pre processed data both surface and subsurface including geology and various types of temporal hydrological information gvs allows these data to be integrated into a single conceptual hydrogeological model in addition 3d geological models produced externally using other software packages can readily be imported into gvs models as can outputs of simulations e g piezometric surfaces produced by software such as modflow or feflow boreholes can be integrated showing any down hole data and properties including screen information intersected geology water level data and water chemistry animation is used to display spatial and temporal changes with time series data such as rainfall standing water levels and electrical conductivity displaying dynamic processes time and space variations can be presented using a range of contouring and colour mapping techniques in addition to interactive plots of time series parameters other types of data for example demographics and cultural information can also be readily incorporated the gvs software can execute on a standard windows or linux based pc with a minimum of 2 gb ram and the model output is easy and inexpensive to distribute by download or via usb dvd cd example models are described here for three groundwater systems in queensland northeastern australia two unconfined alluvial groundwater systems with intensive irrigation the lockyer valley and the upper condamine valley and the surat basin a large sedimentary basin of confined artesian aquifers this latter example required more detail in the hydrostratigraphy correlation of formations with drillholes and visualisation of simulation piezometric surfaces both alluvial system gvs models were developed during drought conditions to support government strategies to implement groundwater management the surat basin model was industry sponsored research for coal seam gas groundwater management and community information and consultation the virtual groundwater systems in these 3d gvs models can be interactively interrogated by standard functions plus production of 2d cross sections data selection from the 3d scene rear end database and plot displays a unique feature is that gvs allows investigation of time series data across different display modes both 2d and 3d gvs has been used successfully as a tool to enhance community stakeholder understanding and knowledge of groundwater systems and is of value for training and educational purposes projects completed confirm that gvs provides a powerful support to management and decision making and as a tool for interpretation of groundwater system hydrological processes a highly effective visualisation output is the production of short videos e g 2 5 min based on sequences of camera fly throughs and screen images further work involves developing support for multi screen displays and touch screen technologies distributed rendering gestural interaction systems to highlight the visualisation and animation capability of the gvs software links to related multimedia hosted online sites are included in the references

environmental changes in a tropical lake lake abiyata ethiopia during recent centuries lake abiyata is a small closed saline alkaline lake located in the central part of the ethiopian rift valley east africa a multi proxy study of a sediment core 116 cm long and with undisturbed mud water interface was performed to test the sensitivity of the lake system and of different proxies to the changes in climate and human activities that occurred in the catchment during the past few centuries the 210pb analyses suggest that the upper 80 cm of the core represent the past 200 years this study complements millennial scale environmental records available in the region the main freshwater climatic and biological features of the modern lake system and their variations over the past decades as known from observations are first summarised results derived from individual proxies analysed along the core are then presented successively major physical and chemical properties of bulk sediments diatoms and pollen uncertainties on the chronological framework are discussed major limnological stages are finally identified based on the multi proxy interpretation of our record our record shows large variations in the lake water and salt balances in the sediment sources and in the vegetation distribution in the basin using our 210pb chronology major changes observed in the core are tentatively compared with environmental events known from instrumental and historical records the upper 41 cm of the core 210pb age 1940 1998 ad reveal several fluctuations in diatom inferred water depth and salinity which seem to be consistent with known changes in water level human impact on vegetation clearly appears since about 30 years the interval 85 41 cm suggests a period of overall water deficit lake abiyata experienced episodes shallower and more saline than over the past decades especially around 68 66 cm 210pb dated at ca 1890 ad this level may coincide with one of the worst droughts known in the ethiopian history during 1888 1892 the lower part of the core includes a stage 108 85 cm of lake level much higher than today and which ended before 1800 ad although its base is undated so far this stage suggests that conditions much wetter than today have prevailed in the region during at least part of the 18th century lake abiyata appears to be a suitable site for a detailed environmental reconstruction over the recent past although further work is needed to reduce the uncertainties on our record as discussed in the conclusions

remote surface mapping using orthophotos and geologic maps draped over digital elevation models application to the sheep mountain anticline wyoming remote mapping of surface structures can be conducted by draping digital orthophotos and geologic maps over digital elevation models in geographic information systems formational contacts can be mapped by viewing the intersections of these contacts with the topography on a true to scale three dimensional image bedding orientations can be determined from 1 the trends and slopes of dip slopes or 2 best fit planes to multiple points of intersection of a bedding surface with the topography the methods are tested against mapped formation contacts and bedding attitudes for the sheep mountain anticline in the bighorn basin wyoming detailed mapping of formation contacts is improved by careful observations of the contacts on three dimensional images interpreted bedding attitudes from slope and multiple point solutions show strong positive correlations with field measurements this mapping method provides an efficient and accurate alternative to stereoscopic mapping using aerial photographs and satellite images particularly for remote and inaccessible areas

geologic stereo mapping of geologic structures with spot satellite data reply the spot imaging system launched in 1986 by the french national space agency cnes provides two significant advances for mapping geological structures from satellite imagery increased spatial resolution of key structural and stratigraphic elements and stereoscopic capabilities for making strike and dip measurements quantitative stereo mapping with spot data may be done using hard copy images and conventional equipment such as stereo plotters or by displaying images on a video monitor in stereo viewing format the latter method is a new remote sensing technique particularly relevant to the exploration community this technique allows development with minor expenditure and training of an effective stereo mapping capability on existing image processing systems or on stand alone personal computers spot stereo data is particularly useful for mapping low amplitude and highly deformed structures surface structure maps generated from stereo imagery data can be applied to exploration at two levels at early stages such maps can be used to establish the style trend size and spatial distribution of structures in a basin and to investigate key tectonic elements at more advanced prospecting stages these maps can be used to constrain subsurface mapping of structures located in areas of poor seismic data quality this latter technique however may require the support of highermore resolution stereo aerial photography less

some outstanding issues in the geology of lebanon and their importance in the tectonic evolution of the levantine region abstract the concept of pervasive and disruptive late neogene quaternary strike slip tectonics in lebanon has made establishing a satisfactory pre neogene palaeogeographic and palaeotectonic history for the area difficult research has allowed clarification of three fundamental issues that permit the setting of lebanon against its adjacent regions to be more firmly assigned the first issue is the identification of the significance of the 100 km long nne ssw trending monocline of the western lebanon flexure this feature is interpreted as a modified and rejuvenated early mesozoic hinge line that is presumed to be the northern continuation of the carmel sinai hinge line to the south the second issue is the correlation of the mount lebanon bekaa and anti lebanon complex with the adjacent intracontinental palmyride fold belt of syria through recognition in each of common divisions in structural style between a higher northern zone dominated by broadly spaced box folds and a lower southern zone with more numerous closely spaced and more internally complex folds the third issue involves the identification of major two stage late cretaceous to palaeogene syrian arc tectonism within lebanon resolution of these issues suggests a tectonic model for the region whereby the levantine region formed in two main phases the first of these was the multiphase late palaeozoic early mesozoic rifting of the area which imposed a fundamental extensional fabric over much of the region the second tectonic phase was the subsequent inversion of these extensional structures in the two stage syrian arc deformation of senonian and late palaeogene age which gave rise to the main lebanon structures it is this syrian arc tectonism rather than the late cenozoic strike slip that was probably the main structuring agent which affected the lebanon area the transpression from the braided dead sea fault motion although locally complex is an essentially neotectonic overprint on an already existing fabric offset of syrian arc structures in lebanon suggests that the total sinistral motion of the yammouneh fault segment of the dead sea fault is around 47 km

sulfur fractions in particle size separates of the sub humid ethiopian highlands as influenced by land use changes abstract extensive deforestation of natural forests in the ethiopian highlands and their conversion to low input agriculture and plantations have caused severe soil degradation and significant changes in the ecosystem we investigated the influence of land use changes on the amount form and distribution of sulfur s in bulk soils and size separates of the sub humid highlands of southern ethiopian surface soil samples 0 10 cm were collected from natural forest tea plantation and 25 years cultivated fields at wushwush and from podocarpus dominated natural forest cupressus plantation and 30 years cultivated fields at munesa sites the total s contents ranged from 635 to 1082 mg kg 1 soil and from 520 to 1040 mg kg 1 soil at wushwush and munesa respectively organic s represented on the average 98 of the total s while inorganic so 4 s accounted for only 2 c bonded s was the dominant organic s fraction at both sites comprising 77 84 of the total organic s pool whereas ester so 4 s constituted merely for 16 23 total s and c bonded s were highly significantly correlated p 4 s and total s soc and n were weak the c s and n s ratios ranged from 58 to 99 and from 5 7 to 7 9 respectively and decreased generally in the order sand silt clay continuous cropping resulted in 41 and 50 depletion of total s at wushwush and munesa respectively in contrast losses from the tea 34 and cupressus 13 plantations were low sulfur depletions due to cultivation were lower than losses from soc 55 wushwush 63 munesa and n 52 wushwush 60 munesa suggesting that s was more resistant to mineralization compared to soc and n c bonded s accounted for 88 and 73 of the total s depletion whereas ester so 4 s accounted only for 11 and 26 at wushwush and munesa respectively these results indicate that most of the s depletion occurred from c bonded s based on our results it is possible to conclude that s deficiency might occur in a foreseeable future if the current depletion rate of som continues therefore integrated soil and crop management practices have to be developed which involve the use of organic materials of farm and non farm origins and inorganic fertilizers to combat the ongoing nutrient depletion in the sub humid highlands agroecosystems of southern ethiopia

chemical trends in a perhumid soil catena on the turrialba volcano costa rica abstract the variation in chemical composition of soil samples xrfs data from a soil catena of 14 soil profiles on the northern slope and foot slope of the andesitic turrialba volcano 3300 m has been analysed to test the two hypotheses which underlie our interpretation that this catena is a weathering sequence the first hypothesis is that all parent material is chemically homogeneous and the second hypothesis is that development of chemical variation is the net result of progression of weathering and of diversity of weathering which both depend on altitude via gradients in temperature and precipitation the aim of this purely chemical approach is to find out if trace elements are significant tracers for different weathering paths leading to different amorphous or crystalline products for example imogolite allophane halloysite gibbsite and ferrihydrite the results show that volcanic ash is sufficiently homogeneous to detect the well known dominance of a general weathering trend with relative depletion of mobile elements mg k si etc and relative enrichment of less mobile elements ti fe al ce cr v zr etc the least mobile elements were ti v and zr from their contents a weathering index for all samples has been derived that describes 95 of their total variance hypothesis 1 in addition to this general trend ti v and zr showed systematic deviations that could be defined as a chemical differentiation factor in combination with the general weathering trend this explained 99 of the total variation of ti v and zr hypothesis 2 the contents of other major minor and trace elements used can only partially be described by the ti v zr derived weathering index and chemical differentiation the level of explanation decreases roughly with increasing mobility of the chemical element in the system triangular plots of element ratios suggest that contents of mobile elements are influenced by too many weathering processes trace elements did not show a more specific chemical differentiation than major and minor oxides the leaching pattern of mg indicates the presence of three different processes 1 short term preferential leaching of basic cations at high altitude 2 subsequent allophane formation between 660 and 1220 m altitude and 3 long term loss of basic oxides and not of silica upon ageing of fluvio volcanic sediments in the foot plain below 240 m fe shows anomalous depletion redistribution due to oxidation and reduction and al shows extra depletion in two of the allophanic profiles

arc generated blocks with crustal sections in the north atlantic craton of west greenland crustal growth in the archean with modern analogues abstract the ca 700 km long archean craton of west greenland consists of six meso neoarchean ca 3000 2720 ma shear zone bounded crustal blocks that display similar cross sections from south to north ivittuut kvanefjord bjornesund sermilik fiskefjord maniitsoq each block has a southerly upper and a northerly lower zone thus each faces upwards to the south upper zones have prograde amphibolite facies mineralogy and have never been in the granulite facies whereas lower zones reached granulite facies and were partly retrogressed to amphibolite facies upper and lower zones consist predominantly of tonalite trondhjemite granodiorite ttg orthogneisses geochemistry suggests generation by slab melting in subduction settings of island arcs and active continental margins the gneisses contain km thick metavolcanic amphibolite layers typically bordered by km thick layers containing anorthosite and leucogabbro most upper zones contain upper greenschist to amphibolite facies metavolcanic belts including volcaniclastic andesitic rocks the two most prominent metavolcanic belts in the fiskefjord block at qussuk andesitic volcaniclastic rocks garde a a 2007 a mid archaean island arc complex in the eastern akia terrane godthabsfjord southern west greenland journal of the geological society london 164 565 579 and ivisaartoq mafic ultramafic rocks and anorthosite leucogabbro from upper and lower parts of a supra subduction zone system polat a frei r appel p w u dilek y fryer b ordonez calderon j c yang z 2008 the origin and compositions of mesoarchean oceanic crust evidence from the 3075 ma ivisaartoq greenstone belt sw greenland lithos 100 293 321 have island arc geochemical signatures the 2 km thick fiskenaesset complex bjornesund block comprises chromite layered anorthosites leucogabbros and gabbros and local pillow bearing roof pendants from overlying metavolcanic amphibolite the style of deformation changes downwards within crustal blocks upper zones are characterised by linear metavolcanic belts deformed by mostly one major phase of isoclinal folding and lower zones by kilometre scale double triple fold interference patterns everywhere ttg protoliths have intruded anorthositic and volcanic rocks typically along ductile shear zones often so extensively that only anorthositic or amphibolitic lenses are preserved the meso neoarchean crust was thickened by a combination of thrusting isoclinal folding and continued ttg injection dissimilarities in the proportions of anorthositic and metavolcanic rocks in the six blocks suggest that they evolved in several different microcontinents but by similar processes these crustal blocks provide an exceptional example of how continents evolved in the meso neoarchean comparable archean examples in kapuskasing and pikwitonei canada and modern analogues in fiordland new zealand kohistan himalayas southern california batholith peruvian andes and hidaka japan demonstrate that processes of continental growth from island arc to continental arc magmatism and by implication to continental collision were broadly similar throughout most of earth history

a neoarchean dismembered ophiolite complex from southern india geochemical and geochronological constraints on its suprasubduction origin abstract ophiolites the remnants of ancient oceanic lithosphere have been described from collisional sutures of various ages with only few examples from archean terranes here we report the discovery of a neoarchean ophiolite suite from the southern margin of the dharwar craton in india tectonically intercalated within a neoproterozoic suture zone the metamorphosed and variably dismembered ophiolite suite exposed around devanur comprises altered ultramafic units websterite gabbros mafic dykes amphibolites trondhjemites and pegmatites associated with ferruginous metachert structural and petrographic studies indicate that the rocks represent a highly sheared and metamorphosed suite emplaced as a thrust sheet the major and trace element geochemistry of the mafic dykes indicate derivation from basaltic andesitic magmas with tholeiitic to calc alkaline characteristics the rocks display negative nb anomalies with enrichment of lile k rb ba th and depletion in hfse ti nb hf tb the tectonic discrimination of these rocks based on various geochemical plots suggests that they were generated in a suprasubduction zone setting we present new shrimp zircon u pb data for two trondhjemite samples from this complex which yield 238u 206pb ages of 2528 61 and 2545 56 ma the neoarchean age from the trondhjemites obtained in our study is closely comparable to similar ages obtained in recent studies from magmatic zircons in charnockites and orthogneisses in the area the suprasubduction zone assemblages and arc magmas suggest a neoarchean ocean closure along the southern margin of the dharwar craton

paleozoic multiple accretionary and collisional tectonics of the chinese tianshan orogenic collage abstract subduction related accretion in the junggar balkash and south tianshan oceans paleo asian ocean mainly in the paleozoic gave rise to the present 2400 km long tianshan orogenic collage that extends from the aral sea eastwards through uzbekistan tajikistan kyrgyzstan to xinjiang in china this paper provides an up to date along strike synthesis of this orogenic collage and a new tectonic model to explain its accretionary evolution the northern part of the orogenic collage developed by consumption of the junggar balkash ocean together with paleozoic island arcs northern ili issyk kul and chatkal located in the west which may have amalgamated into a composite arc in the paleozoic in the west and by addition of another two roughly parallel arcs dananhu and central tianshan in the east the western composite arc and the eastern dananhu and central tianshan arcs formed a late paleozoic archipelago with multiple subduction zones the southern part of the orogenic collage developed by the consumption of the south tianshan ocean which gave rise to a continuous accretionary complex kokshaal kumishi which separated the central tianshan in the east and other paleozoic arcs in the west from cratons tarim and karakum to the south cross border correlations of this accretionary complex indicate a general southward and oceanward accretion by northward subduction in the early paleozoic to permian as recorded by successive southward juxtaposition of ophiolites slices of ophiolitic melanges cherts island arcs olistostromes blueschists and turbidites which are mainly paleozoic in age with the youngest main phase being late carboniferous permian the initial docking of the southerly tarim and karakum cratons to this complicated late paleozoic archipelago and accretionary complexes occurred in the late carboniferous early permian in the eastern part of the tianshan and in the late permian in the western part which might have terminated collisional deformation on this suture zone the final stages of closure of the junggar balkash ocean resembled the small ocean basin scenario of the mediterranean sea in the cenozoic in summary the history of the altaids is characterized by complicated multiple accretionary and collisional tectonics

quantitative structural analysis with stereoscopic remote sensing imagery we employ powerful stereoscopic methods with satellite imagery to obtain surface bedding attitude measurements these data are used to constrain geologic structures in three dimensions using quantitative structural models we document a numerical method for measuring the strike and dip of bedding using stereoscopic pairs of air photos as well as landsat thematic mapper and spot images in examples from the north american and andean cordilleras these remote measurements prove consistent with direct surface control and subsurface structures imaged in seismic reflection profiles remotely derived measurements are combined with subsurface data to generate balanced structural interpretations that define complex structural traps using fault related folding theory these remote sensing methods can provide a low cost and rapid means of delineating prospects and leads

deep electrical signatures across the achankovil shear zone southern granulite terrain inferred from magnetotellurics abstract two parallel magnetotelluric mt traverses across the achankovil shear zone aksz in southern india using a wide band 1 khz 1 ks data acquisition system reveal the regional geo electric average strike direction of n 40 w consistent with the geological strike direction of the aksz the derived model shows distinct high electrical resistivity 1000 m for the upper crust below the madurai granulite block mgb with a gentle dip towards south and a northerly dip below the kerala khondalite block kkb the lower crust is resistive below both mgb and kkb while it is moderately conductive

recognizable primary volcanic and sedimentary features in a low strain domain of the highly deformed oldest known 3 7 3 8 gyr greenstone belt isua west greenland a low strain domain has been identified in the metamorphosed mostly highly deformed volcanic and sedimentary rocks of the early archaean isua supracrustal belt this domain contains well preserved volcanic and sedimentary features including basaltic pillow lavas pillow breccia heterogeneous volcanic breccia amygdules in metabasalt and polymict conglomerate dominated by recrystallized chert and volcanic clasts the low strain domain is bounded by highly deformed rocks mostly derived from basalt chert and banded iron formation these discoveries demonstrate that some primary features have escaped the pervasive metasomatism dominant in other parts of the belt and furthermore strengthen the characterization of the isua supracrustals as a typical greenstone belt

intracrustal controls on the coexistence of tholeiitic and calc alkaline magma series at aso volcano sw japan aso caldera sw japan was formed incrementally over a period of 300 kyr by the eruption of four basaltic to dacitic pyroclastic flow and fall deposits aso 1 4 these units are collectively referred to as the aso pyroclastic flow deposit apfd in which tholeiitic and calc alkaline magmas have been erupted in close temporal and spatial proximity detailed petrological and geochemical studies indicate that a major shift in magmatic composition occurred between aso 1 and 4 as the caldera forming stage evolved changing from a predominantly tholeiitic to a calc alkaline signature the mineralogical and geochemical characteristics of aso 1 4 suggest that magmatic evolution within each unit is controlled by fractional crystallization associated with magma mixing crustal assimilation by altering the fractional crystallization mineral assemblage as well as the relative amounts of fractional crystallization magma mixing and crustal assimilation the systematic shifts in differentiation trends and magmatic series observed between the four eruptive units can be reproduced this suggests that the coexistence of tholeiitic and calc alkaline magma series can be attributed to shallow level intracrustal processes

geomorphological investigation on gully erosion in the rift valley and the northern highlands of ethiopia abstract gully erosion phenomena are very common in ethiopia they affect large areas with different morphological pedological and climatic characteristics the amount of soil loss due to gullying has become a very serious problem in the recent decades as it was associated to remarkable depletion of cultivated land field investigations on gully morphology and its genetic processes were carried out in two study areas of ethiopia representative of different geo environmental conditions the lakes region in the rift portion north of shashamene and the area surrounding the town of mekele in tigray two main types of gullies were identified on the basis of their morphological and hydraulic geometry characteristics 1 discontinuous gullies which generally develop on low gradient slopes 1 5 on average and the hydraulic radius of which increases from an upstream minimum to a maximum at approximately their mid length and decreases again to a relative minimum at their downstream end and 2 stream gullies formed by deep erosion processes typically migrating upslope in order to investigate the main causes originating the different types of gullies shear stress data were collected in the field from their hydraulic geometry hypotheses on the mechanisms responsible for both discontinuous and stream gullies development and for their different characteristics are discussed considering the pattern of shear stress variation in the downstream direction

weathering and soil forming processes under semi arid conditions in two mexican volcanic ash soils abstract weathering and neoformation of allophane imogolite and halloysite in volcanic ash soils have been studied extensively in humid climates but little data are available on these soils in arid and semi arid conditions weathering and soil formation under semi arid conditions on acid pyroclastics have been investigated in two profiles both at the micro site scale and on bulk samples xr microdiffractions and sem edx microanalysis were performed on soil thin sections chemical particle size xrd and mineral identification analysis were performed on conventional soil samples results show the interplay of various sub processes a intense division of the coarse minerals into small fragments 50 200 m in size b diagenesis of noncrystalline products in the zone of contact with the parent minerals c transformation of noncrystalline minerals into halloysite in the compact soil microstructures and preservation of the noncrystalline minerals in the topsoil d desiccation and condensation of the crystalline and noncrystalline minerals into microaggregates in the topsoil the results of these interacting weathering processes are silty loam soils with no cohesion and high susceptibility to wind erosion differences appearing between different analytical methods at different sampling scales need special precautions in explaining the results

andosol to luvisol evolution in central mexico timing mechanisms and environmental setting abstract surface and buried andosols and buried luvisols of the nevado de toluca late quaternary tephra paleosol sequence central mexico were studied to show whether these soils present an evolutionary sequence and to determine the pedogenic mechanisms and environmental factors involved in the evolutionary process micromorphological observations and mineralogical composition of fine sand and clay fractions were used to detect type and succession of soil forming process some of the buried andosols defined as intergrade andosols have a predominantly blocky structure humus depleted areas redoximorphic features and thin clay coatings in ah horizons clay fractions of buried andosols contain halloysite besides amorphous components whereas in modern andosols allophane is dominant luvisols have micro areas with granular structure and abundant phytoliths in the groundmass of bt horizons assumed to be the relict andosol features luvisol clay fractions are dominated by halloysite and kaolinite primary minerals show micromorphological weathering features in all studied soils being stronger in luvisols however even in luvisols sand fractions consist mostly of unstable volcanic silicates we hypothesise that the studied profiles form an evolutionary sequence andosols intergrade andosols luvisols the soil transformation is supposed to be linked to progressive crystallisation of 1 1 clay minerals comparing the nevado de toluca paleosol properties with the existing data on volcanic soil climo and chronesequences and assessing the regional paleopedological and lacustrine records of quaternary paleoclimates we concluded that wet dry climatic oscillations took place during the formation of the studied paleosols rapid crystallisation of 1 1 minerals occurred during dry phases which speeded up the andosol to luvisol transformation and made it independent from the primary mineral weathering status the andosol to luvisol transformation accelerated by climatic fluctuations is thought to be a common soil evolutionary pathway in the subtropical and tropical regions of recent volcanism which suffered contrasting precipitation oscillations in the quaternary

soil elevation relationships on a volcanic plateau in the southern cascade range northern california usa summary the main features of an altitudinal sequence were determined from mapping soils on a late cenozoic volcanic plateau west southwest of lassen peak and from the analyses of 27 pedons sampled from 270 to 2030 m above sea level this sequence is characterized by thermic rhodoxeralfs in oak grassland below 500 m through mesic palexeralfs mesic xeric haplohumults frigid andic haplohumults and haplocryands in conifer forest soil depth and clay content are greatest in the lower part of the conifer forest but soils in the oak grassland are slightly redder the characteristic not necessarily predominant clay minerals from low to high altitude are smectite kaolinite halloysite hydrated halloysite and allophane soil reaction ranges from slightly acid at all depths in the oak grassland to strongly acid in the surface and very strongly acid in the subsoil at higher altitude the soil organic carbon content increases from about 9 kg m2 m in the oak grassland to about 11 in the lower part and 25 kg m2 m or more in the upper part of the conifer forest soil organic carbon to total nitrogen ratios range from 11 to 14 in the oak grassland and from 25 to 35 in the surface horizons in the conifer forest increase with elevation in the forest being relatively small compared to the abrupt increase in c n ratio from grassland to forest

the building blocks of continental crust evidence for a major change in the tectonic setting of continental growth at the end of the archean abstract oceanic arcs are commonly cited as primary building blocks of continents yet modern oceanic arcs are mostly subducted also lithosphere buoyancy considerations show that oceanic arcs even those with a felsic component should readily subduct with the exception of the arabian nubian orogen terranes in post archean accretionary orogens comprise 50 produced in continental arcs felsic igneous rocks in oceanic arcs are depleted in incompatible elements compared to average continental crust and to felsic igneous rocks from continental arcs they have lower th yb nb yb sr y and la yb ratios reflecting shallow mantle sources in which garnet did not exist in the restite during melting the bottom line of these geochemical differences is that post archean continental crust does not begin life in oceanic arcs on the other hand the remarkable similarity of incompatible element distributions in granitoids and felsic volcanics from continental arcs is consistent with continental crust being produced in continental arcs during the archean however oceanic arcs may have been thicker due to higher degrees of melting in the mantle and oceanic lithosphere would be more buoyant these arcs may have accreted to each other and to oceanic plateaus a process that eventually led to the production of archean continental crust after the archean oceanic crust was thinner due to cooling of the mantle and less melt production at ocean ridges hence oceanic lithosphere is more subductable widespread propagation of plate tectonics in the late archean may have led not only to rapid production of continental crust but to a change in the primary site of production of continental crust from accreted oceanic arcs and oceanic plateaus in the archean to primarily continental arcs thereafter

the impact of climate on the biogeochemical functioning of volcanic soils abstract rainfall and the amount of water available to leach ions from soil are among the most important features determining mineral weathering secondary mineral synthesis and soil chemical properties along an arid to humid climosequence on kohala mountain hawaii we sampled 16 soil profiles and found that weathering and soil properties change in a nonlinear fashion with increased rainfall the lavas are influenced by a strong rain shadow with mean annual precipitation map averaging 160 mm near the coast and rising to 3000 mm near the summit a temperature decline from 24 to 15 c with increasing elevation is matched by lower potential evapotranspiration et a water balance model monthly precipitation minus monthly et defines three broad climate zones along the sampling transect an arid zone with moisture deficit in every month an intermediate zone with moisture deficit during low rainfall summer months and moisture surplus during high rainfall winter months and a humid zone with moisture surplus during every month the annualized water balance can be ratioed with the integrated porosity of the top meter of soil to provide a leaching index the index reaches 1 total filling of the pore space on an annual basis at about 1400 mm map index values 1 imply intense leaching conditions because of pore water replacement in these 170 ka soils leaching losses of soluble base cations and si are nearly complete at index values 1 whereas only 60 of al has been lost at index values 1400 mm soil buffering capacity has been totally exhausted leading to low ph and low ecec the nonlinear decline in ecec is irreversible under natural conditions base cation depleted soils will remain so even if the climate shifts to drier conditions in contrast a climate shift to wetter conditions can drastically modify surface chemical properties existing in the drier soils as weathering depletes primary minerals elements are lost to leaching and surface chemistry is modified there is a time dimension implied in climate gradient studies soils forming in recently rejuvenated landscapes contain more primary minerals and should experience loss of buffering capacity at higher rainfall loss of buffering capacity means that biological acidity will move more deeply into the vadose zone or into the aquatic system the details of this transfer depend on present and past climate and the age and erosional stability of landscapes

neoarchean suprasubduction zone arc magmatism in southern india geochemistry zircon u pb geochronology and hf isotopes of the sittampundi anorthosite complex abstract the sittampundi anorthosite complex sac in southern india is one of the well exposed archean layered anorthosite gabbro ultramafic rock associations here we present high precision geochemical data for the various units of sac coupled with zircon u pb geochronology and hf isotopic data for the anorthosite the zircon ages define two populations the older yield a concordia age of 2541 13 ma which is interpreted as the best estimate of the magmatic crystallization age for the sittampundi anorthosite a high grade metamorphic event at 2461 15 ma is suggested by the upper intercept age of the younger zircon population a neoproterozoic event at 715 180 ma resulted in pb loss from some of the metamorphic zircons the magmatic age of the anorthosite correlates well with the timing of crystallization of the arc related 2530 ma magmatic charnockites in the adjacent salem block while the metamorphic age is synchronous with the regional metamorphic event the geochemical data suggest that the rocks were derived from a depleted mantle source sub arc mantle metasomatism of slab derived fluids and subsequent partial melting produced hydrous aluminous basalt magma the magma fractionated at depth to produce a variety of high alumina basalt compositions from which the anorthositic complex with its chromite rich and amphibole rich layers formed as cumulates within the magma chamber of a supra subduction zone arc the coherent initial176hf 177hf ratios and positive ehf values 1 7 4 5 of the magmatic zircons in the anorthosite are consistent with derivation of a rather homogeneous juvenile parent magma from a depleted mantle source our study further confirms that the southern part of the dharwar craton was an active convergent margin during the neoarchean with the generation and emplacement of suprasubduction zone arc magmas which played a significant role in continental growth

analysis of the hydrological response of a tropical terminal lake lake abiyata main ethiopian rift valley to changes in climate and human activities integrated dynamic water and chloride balance models with a catchment scale hydrological model prms are used to investigate the response of a terminal tropical lake lake abiyata to climate variability and water use practices in its catchment the hydrological model is used to investigate the response of the catchment to different climate and land use change scenarios that are incorporated into the lake model lake depth area volume relationships were established from lake bathymetries missing data in the time series were filled using statistical regression techniques based on mean monthly data the lake water balance model produced a good agreement between the simulated and observed levels of lake abiyata for the period 1968 83 from 1984 onwards the simulated lake level is overestimated with respect to the observed one while the chloride concentration is largely underestimated this discrepancy is attributed to human use of water from the influent rivers or directly from the lake the simulated lake level and chloride concentration are in better agreement with observed values r2 0 96 when human water use for irrigation and salt exploitation are included in the model a comparison of the simulation with and without human consumption indicates that climate variability controls the interannual fluctuations and that the human water use affects the equilibrium of the system by strongly reducing the lake level sensitivity analysis based on a mean climatic year showed that after prolonged mean climatic conditions lake abiyata reacts more rapidly to an abrupt shift to wetter conditions than to dry conditions this study shows the significant sensitivity of the level and salinity of the terminal lake abiyata to small changes in climate or land use making it a very good recorder of environmental changes that may occur in the catchment at different time scales copyright 2004 john wiley sons ltd

hf isotopic compositions of the standard zircons and baddeleyites used in u pb geochronology abstract zircon and baddeleyite u pb geochronological dating is widely used in solid earth sciences and the advent of rapid in situ methods of analysis such sims and icp ms has re emphasized the importance of having uniform standards recently it has been shown that hf isotopic data can provide important information on these minerals since they contain high concentrations of hf but have low lu hf ratios which results in negligible age correction however the complex internal structures that result from multiple thermal events such as inherited cores and metamorphic overgrowths require that the hf isotopic data be measured with high spatial resolution however the isobaric interferences of 176 yb and 176 lu on 176 hf hamper the precise determination of the 176 hf 177 hf ratio during in situ laser ablation mc icpms analysis it is shown here that mass biases of yb yb and hf hf change with time during analyses and behave differently for solutions and solid material therefore it is suggested that the mean yb value of the individual spot be used to obtain the precise isotopic composition for in situ zircon and baddeleyite hf isotopic analyses for low yb hf 176 yb 177 hf yb value have little effect on the accuracy of the hf isotopic composition however the appropriate yb isotopic abundance is necessary for high yb hf 176 yb 177 hf 0 001 zircons and baddeleyites since the interference of 176 yb on 176 hf is significant using the mean yb value of the individual spot and newly published yb isotopic abundance data six standard zircons and two standard baddeleyites have been investigated using a neptune mc icpms with 193 nm laser for zircons the obtained 176 hf 177 hf ratios are 0 282307 31 2sd for 91500 0 282680 31 2sd for temora 0 281729 21 2sd for cz3 282177 17 2sd for cn92 1 0 282983 17 2sd for fm0411 and 281234 11 2sd for phalaborwa the baddeleyites from phalaborwa and sk10 2 have 176 hf 177 hf ratios of 0 281238 12 and 0 282738 13 2sd these results agree well with the values obtained by the solution method and indicate that these standards have different hf isotopic compositions in which the extremely low 176 lu 177 hf and 176 yb 177 hf values of cz3 zircon and phalaborwa baddeleyite make them excellent standards for machine calibration during in situ zircon hf isotopic measurement with the other standards being more suitable for the development of the correction method