disequilibrium dihedral angles in layered intrusions a microstructural record of fractionation the dihedral angle formed at junctions between two plagioclase grains and a grain of augite is only very rarely in textural equilibrium in gabbros from kilometre scale crustal layered intrusions the median of a population of these disequilibrium angles cpp varies systematically within a single layered intrusion remaining constant over large stretches of stratigraphy with significant increases and decreases associated with the addition or reduction respectively of the number of phases on the liquidus of the bulk magma the stepwise changes in cpp are present in the upper zone of the bushveld complex the megacyclic unit i of the sept iles intrusion and the layered series of the skaergaard intrusion the plagioclase bearing cumulates of rum have a bimodal distribution of cpp dependent on whether the cumulus assemblage includes clinopyroxene the presence of the stepwise changes is independent of the order of arrival of cumulus phases and of the composition of either the cumulus phases or the inferred composition of the interstitial liquid the only parameter that behaves in an exactly analogous manner to cpp is the rate of change in enthalpy with temperature h t during crystallization both h t and cpp increase with the addition of a liquidus phase and decrease with the removal of a liquidus phase the replacement of one phase by another has little effect on h t and no discernible effect on cpp an increase of h t results in an increase in the fraction of the total enthalpy budget that is the latent heat of crystallization the fractional latent heat it also increases the mass crystallized in each incremental temperature drop the crystal productivity these increases of both fractional latent heat and crystal productivity are likely to cause an increase in the time taken to form three grain junctions in the mush via thermal buffering of a thickened mushy layer we suggest these are the underlying causes of stepwise increases in cpp stepwise changes in the geometry of three grain junctions in fully solidified gabbros thus provide a clear microstructural marker for the progress of fractionation down the liquid line of descent in layered intrusions

a new interpretation of the structure of the sept iles intrusive suite canada the layered mafic intrusion at sept iles canada is one of the largest intrusions in the world a new interpretation of its structure is proposed based on a review of its geology and a comparison with the skaergaard intrusion greenland several different magmatic components are recognized hence the name sept iles intrusive suite siis is proposed emplacement of the suite may have been preceded by eruption of flood basalts the first magmas of the suite rose in the crust to accumulate beneath the density filter afforded by the basalts the largest component is the sept iles mafic intrusion simi the lower series of the simi is dominated by leucotroctolites and leucogabbros above it lie the layered series which is largely comprised of gabbro and troctolite both these units are unchanged from earlier interpretations the anorthosites s l gabbros and monzogabbros formerly called the transitional series are now considered to be the upper border series developed by floatation of plagioclase common autoliths in the layered series are parts of the hydrothermally altered upper border series from towards the interior of the intrusion which have foundered and settled through the magma the contamination of the magma that accompanied this event oxidised iron in the magma and led to the precipitation of magnetite around the periphery of the intrusion the subsequent depletion of fe3 and or increase in sio2 cao and p2o5 may have induced apatite saturation and accumulation to form two layers rich in apatite near the base and at top of the layered series granitic magma was developed by fractional crystallisation and was emplaced along the roof of the chamber where it acquired large quantities of xenoliths these were probably derived from the flood basalts their evolved members and fragments of mafic dykes chilled by the granitic magma accumulations of monzonite pillows in this unit testify to another magmatic event and a floor to the granitic magma chamber indicating lateral transport of magma chemically distinct syenites in the upper part of the intrusion are part of the point du criade intrusion a large late composite sill diabase and leucogabbro components show a close link with the simi and all the acidic magmas may have originally formed by differentiation of the main magma in cupolas towards the centre of the intrusion a series of late gabbro intrusions that cut the simi may represent a rejuvenation of magmatism the border zone is a mass of fine grained rocks that occurs along the border of the simi it may be another magmatic component or just the lateral border series of the simi

nature of sub volcanic magma chambers deccan province india evidence from quantitative textural analysis of plagioclase megacrysts in the giant plagioclase basalts sub volcanic magma chambers might be a widespread component of flood basalt provinces and their presence can be revealed in some cases by plagioclase megacrystic basalts in at least four levels within the deccan flood basalt sequence the generally low abundance of small plagioclase crystals increases to 5 25 with some as large as 30 mm long these giant plagioclase basalt gpb flows were formed by mixing of megacryst rich and megacryst poor magmas the crystal size distributions csd of these megacrysts mostly plot as almost straight lines on a classic csd diagram for a plagioclase growth rate of 10 10 mm s steady state magma chamber models and simple continuous growth suggest residence times of 500 1500 years however the lack of crystals smaller than 2 mm suggests that coarsening may have been involved and crystal shape can help define the environment where this happened plagioclase megacrysts are very tabular and commonly form clusters of sub parallel crystals characteristics that are also found in the plagioclase of anorthosites formed by flotation at the top of shallow magma chambers and crystallization in a high peclet number regime e g skaergaard sept iles a possible history is as follows 1 plagioclase megacrysts crystallize in a convecting magma chamber just below the lava pile 2 currents sweep the crystals to the top of the chamber where they accumulate as a result of their buoyancy the crystals coarsen in response to the continuous supply of hot magma 3 new magma sweeps through the plagioclase mush mingles and mixes then erupts to form the gpbs the residence time recorded by the megacrysts in the gpbs is that of the magma chamber where the megacrysts formed not that of the magmas that make up the megacryst poor part of the gpbs or the other megacryst poor lavas lavas with megacrysts similar to the gpbs are uncommon but widespread galapagos surtsey etc and suggest the presence of sub volcanic magma chambers elsewhere

origin of the early permian wajilitag igneous complex and associated fe ti oxide mineralization in the tarim large igneous province nw china abstract the wajilitag igneous complex is part of the early permian tarim large igneous province in nw china and is composed of a layered mafic ultramafic intrusion and associated syenitic plutons in order to better constrain its origin and the conditions of associated fe ti oxide mineralization we carried out an integrated study of mineralogical geochemical and sr nd hf isotopic analyses on selected samples the wajilitag igneous rocks have an oib like compositional affinity similar to the coeval mafic dykes in the bachu region the layered intrusion consists of olivine clinopyroxenite coarse grained clinopyroxenite fine grained clinopyroxenite and gabbro from the base upwards fe ti oxide ores are mainly hosted in fine grained clinopyroxenite forsterite contents in olivines from the olivine clinopyroxenite range from 71 to 76 mol indicating crystallization from an evolved magma reconstructed composition of the parental magma of the layered intrusion is fe ti rich similar to that of the bachu mafic dykes syenite and quartz syenite plutons have end t values ranging from 1 4 to 2 9 identical to that for the layered intrusion they may have formed by differentiation of underplated magmas at depth and subsequent fractional crystallization magnetites enclosed in olivines and clinopyroxenes have cr2o3 contents higher than those interstitial to silicates in the layered intrusion this suggests that the cr rich magnetite is an early crystallized phase whereas interstitial magnetite may have accumulated from evolved fe ti rich melts that percolated through a crystal mush low v content in cr poor magnetite

the conformable emplacement of the bushveld mafic rocks along a regional unconformity in the transvaal succession of south africa abstract a previously unrecognized regional unconformity occurs in the proterozoic transvaal succession of the kaapvaal province of southern africa the predominantly marine and siliciclastic rocks of the lower two thirds of the pretoria group are unconformably overlain by a terrestrial and largely volcanic sequence the most voluminous portion of which is the rooiberg felsite if the bushveld complex is mentally subtracted from map patterns the rooiberg felsite also locally overlies pre pretoria sequences and the archean crystalline basement the bushveld complex is not lopolithic as commonly supposed instead regionally condordant emplacement of the complex along the unconformity explains both the seemingly discordant footwall features and the lack of pretoria and older strata other than a few xenoliths in the hanging wall the lack of any geochemical evidence for major crustal contamination of bushveld magmas precludes disposing of any such hanging wall strata by wholesale assimilation the bushveld complex the unconformity and the enclosing strata are synformally folded making the bushveld appear to be lopolithic due to this folding and multiple periods of erosion the original extents of the bushveld complex the unconformity and the enclosing strata are now much reduced other smaller mafic intrusions along or immediately below the same regional unconformity probably are bushveld related

trace elements in magnetite as petrogenetic indicators we have characterized the distribution of 25 trace elements in magnetite mg al si p ca sc ti v cr mn co ni cu zn ga ge y zr nb mo sn hf ta w and pb using laser ablation icp ms and electron microprobe from a variety of magmatic and hydrothermal ore forming environments and compared them with data from the literature we propose a new multielement diagram normalized to bulk continental crust designed to emphasize the partitioning behavior of trace elements between magnetite the melt fluid and co crystallizing phases the normalized pattern of magnetite reflects the composition of the melt fluid which in both magmatic and hydrothermal systems varies with temperature thus it is possible to distinguish magnetite formed at different degrees of crystal fractionation in both silicate and sulfide melts the crystallization of ilmenite or sulfide before magnetite is recorded as a marked depletion in ti or cu respectively the chemical signature of hydrothermal magnetite is distinct being depleted in elements that are relatively immobile during alteration and commonly enriched in elements that are highly incompatible into magnetite e g si and ca magnetite formed from low temperature fluids has the lowest overall abundance of trace elements due to their lower solubility chemical zonation of magnetite is rare but occurs in some hydrothermal deposits where laser mapping reveals oscillatory zoning which records the changing conditions and composition of the fluid during magnetite growth this new way of plotting all 25 trace elements on 1 diagram normalized to bulk continental crust and elements in order of compatibility into magnetite provides a tool to help understand the processes that control partitioning of a full suit of trace elements in magnetite and aid discrimination of magnetite formed in different environments it has applications in both petrogenetic and provenance studies such as in the exploration of ore deposits and in sedimentology

experimental effects of pressure and fluorine on apatite saturation in mafic magmas with reference to layered intrusions and massif anorthosites apatite is a cumulate phase in the upper parts of some mafic layered intrusions and anorthositic complexes we investigated the effect of pressure and fluorine on apatite saturation in mafic magmas to better understand under which conditions this mineral crystallizes apatite saturation gives information about the formation of silicate rocks and is of interest in explaining the formation of apatite oxide rich rocks e g nelsonites comprising approximately one third apatite and two third fe ti oxide two models of formation are proposed for this rock type crystal fractionation followed by accumulation of apatite and fe ti oxides and liquid immiscibility new experiments carried out with mafic compositions at 500 mpa confirm that the most important variables on phosphate saturation are sio2 and cao fluorine addition leads to apatite saturation at lower sio2 and higher cao concentrations comparison of our results with those of previous experimental studies on liquid liquid immiscibility at upper to mid crustal conditions allows us to investigate the relative importance of apatite saturation versus liquid liquid immiscibility in the petrogenesis of nelsonites and similar rocks the liquid line of descent of three natural examples studied the sept iles intrusive suite the anorthositic complex of the lac st jean and the skaergaard layered intrusion do not cross the liquid liquid immiscibility field before they reach apatite saturation thus the apatite oxide rich rock associated with these three intrusive suites are best explained by crystal fractionation followed by accumulation of apatite and fe ti oxides

monzo anorthosite from the taguei ring complex air niger a hybrid rock with cumulus plagioclase and an infiltrated granitic intercumulus liquid an unusual hybrid rock composed of cumulus plagioclase with the interstices occupied by abundant quartzo feldspathic material occurs in the taguei ring complex niger the monzo anorthosite consists of about 75 plagioclase in large tabular to elongate crystals with interstices occupied in two stages firstly by clinopyroxene titanomagnetite and apatite and then by an intergrowth of quartz and alkali feldspar associated with brown green amphibole and zircon secondary green amphibole chlorite epidote and calcite may occur four stages in the crystallization history were identified 1 cumulus stage represented by the cores of the plagioclase laths an56 an66 with reversed oscillatory zoning and rare clinopyroxene t 1 150 c 2 early intercumulus stage with a wide overgrowth zone on plagioclase an62 an15 with oscillatory zoning and increase in or clinopyroxene apatite titanomagnetite t 1 150 1 050 c 3 late intercumulus stage with alkali feldspar quartz opaque oxide brown green amphibole apatite and zircon t 750 700 c alkali feldspar gave cryptoperthite on further cooling 4 deuteric stage with development of turbidity in the alkali feldspar and plagioclase rims and formation of patch perthite with microcline and secondary minerals t 400 c

differentiation of tholeiitic basalt to a type granite in the sept iles layered intrusion canada the undeformed 564 ma sept iles layered intrusion quebec canada is a large igneous body of c 20 000km3 from the base to the top it consists of a layered series dominated by troctolite and gabbro an anorthositic upper border series and a dominantly granitic upper series the parent magma of the layered series is inferred to be an iron rich tholeiitic basalt 48 wt sio2 15wt feot whole rock compositions from the chilled margin dykes cross cutting the layered series and silicic rocks from the upper series display continuous major and trace element geochemical trends ranging from basalts to ferroan metaluminous a type granites 77 wt sio2 initial 143nd 144nd 0 51201 0 51207 and 87sr 86sr 0 70353 0 70548 indicate a juvenile mantle source and minimal contamination by old crust 1 2 during crystallization geochemical modeling using the melts thermodynamic calculator combined with equations predicting mineral melt equilibria from experiments on tholeiitic basalts indicate that basaltic to monzonitic melt compositions are in equilibrium with the troctolites and gabbros of the layered series fe ti oxides saturate early in the layered series after 14 fractionation of plagioclase olivine cumulates further fractionation of fe ti oxide bearing gabbros drives the residual liquids toward silica enrichment and iron depletion major and trace element modeling indicates that the a type granites from the upper series were produced by protracted fractional crystallization of an iron rich basaltic parent magma at a fraction of residual liquid of only 8 the observed relative volumes of mafic cumulates and silicic rocks in the intrusion are in agreement with the calculations most of the intermediate compositions correspond to magmatic mafic enclave bearing granitoids and display geochemical evidence of hybridization intermediate compositions produced by fractional crystallization are scarce and a daly gap occurs from 57 to 67 wt sio2 this gap could result either from the fractional crystallization process or from silicate liquid immiscibility during that compositional interval

importance of different types of marine particles for the scavenging of heavy metals in the deep sea bottom water abstract in experiments of 7 days duration using voltammetric and radiotracer measurement techniques the role of different particle types in the sorption of dissolved metal species in a disturbed deep sea bottom seawater system were investigated resuspension of oxic to suboxic surface sediment into the bottom water in the deep sea either by natural events or industrial activities like mn nodule mining has been shown to be followed quickly by scavenging of dissolved heavy metals e g released from interstitial water on the resuspended particles compared to other deep sea particles like clay minerals calcite and apatite mn and fe oxides and oxyhydroxides were found to be by far the most important phases in scavenging many dissolved heavy metals only pb was sorbed strongly on all particles used with highest affinity to carbonate fluorapatite caesium was significantly scavenged only by clay minerals like illite the sorption experiments support a simple electrostatic model hydrated cations and labile cationic chloro complexes in seawater like mn2 mncl co2 ni2 cu2 zn2 ba2 and pbcl are preferentially adsorbed or ion exchanged on the negatively charged surfaces of mn oxides in contrast oxyanions and neutrally or negatively charged complexes like hvo42 moo42 haso42 uo2 co3 22 and pbco30 associate with neutral to slightly positive amphoteric fe oxyhydroxide particles metals forming strong chloro complexes in seawater like cd cdcl20 are less readily sorbed by oxides than others a comparison of the results of voltammetric and radiotracer techniques revealed that after fast sorption within the first hour isotopic exchange dominated reactions on mno2 rich particles in the following days this was especially pronounced for mn and co which are bound to the mn oxide surface via a redox transformation

a stable ediacaran earth recorded by single silicate crystals of the ca 565 ma sept iles intrusion the archetypical example of inertial interchange true polar wander iitpw the rapid rotation of the entire solid earth by 90 is based on two nearly orthogonal directions seen in paleomagnetic studies of the sept iles ca 565 ma intrusion quebec canada this motion has also been proposed as the driving force for the early cambrian explosion of life others have challenged these interpretations linking the data instead to flips between an axial and equatorial dipole field configuration we examine this enigma using single silicate crystal paleomagnetic analyses we conclude that only one of the previously reported magnetic directions is carried by single domain magnetic grains and can be considered primary thus the ediacaran diversification occurred on a rotationally stable earth driven by biotic and longer term abiotic forcing whether iitpw ever occurred in the past on earth remains uncertain

new textural and mineralogical constraints on the origin of the hongge fe ti v oxide deposit sw china the hongge magmatic fe ti v oxide deposit in the panxi region sw china is hosted in a layered mafic ultramafic intrusion this 2 7 km thick lopolith like intrusion consists of the lower middle and upper zones which are composed of olivine clinopyroxenite clinopyroxenite and gabbro respectively abundant fe ti oxide layers mainly occur in the middle zone and the lower part of the upper zone fe ti oxides include cr rich and cr poor titanomagnetite and granular ilmenite cr rich titanomagnetite is commonly disseminated in the olivine clinopyroxenite of the lower parts of the lower and middle zones and contains 1 89 to 14 9 wt cr2o3 and 3 20 to 16 2 wt tio2 whereas cr poor titanomagnetite typically occurs as net textured and massive ores in the upper middle and upper zones and contains much lower cr2o3 0 4 wt but more variable tio2 0 11 to 18 2 wt disseminated cr rich titanomagnetite in the ultramafic rocks is commonly enclosed in either olivine or clinopyroxene whereas cr poor titanomangetite of the net textured and massive ores is mainly interstitial to clinopyroxene and plagioclase the lithology of the hongge intrusion is consistent with multiple injections of magmas the lower zone being derived from a single pulse of less differentiated ferrobasaltic magma and the middle and upper zones from multiple pulses of more differentiated magmas cr rich titanomagnetite in the disseminated ores of the lower and middle zones is interpreted to represent an early crystallization phase whereas clusters of cr poor titanomagnetite granular ilmenite and apatite in the net textured ores of the middle and upper zones are thought to have formed from an fe ti p rich melt segregated from a differentiated ferrobasaltic magma as a result of liquid immiscibility the dense fe ti p rich melt percolated downward through the underlying silicate crystal mush to form net textured and massive fe ti oxide ores whereas the coexisting si rich melt formed the overlying plagioclase rich rocks in the intrusion

the sept iles anorthosite complex field relationships geochronology and petrology the sept iles anorthosite complex is located in the grenville structural province of the canadian shield geochronological studies of both the basic and acidic portions of the complex show that i

a paleomagnetic study of the layered mafic intrusion at sept iles quebec a paleomagnetic study of gabbroic and anorthositic members of the sept iles layered mafic intrusion has isolated a remanence with direction d 333 i 29 remanence a and a corresponding pole of 141 e 20 n the rocks are cut by numerous diabase dykes of unknown age the remanence carried by the dykes has direction d 188 i 85 remanence b with a corresponding pole of 116 e 59 s another remanence statistically identical to b d 186 i 85 is found at dyke contacts and in the local host rock its associated pole 115 e 61 s is identical to the one derived from the dykes this overprint is significantly different from remanence a and is obviously related to dyke emplacement the location of the pole derived from remanence a is in excellent agreement with many other cambrian poles from a variety of locations throughout cratonic north america the rocks at sept iles have been previously dated radiometrically at 540 ma thus all evidence indicates that remanence a is an original

sequential leaching of marine ferromanganese precipitates genetic implications abstract sequential leaching experiments were carried out on twenty one hydrogenetic crust samples from different locations in the central pacific and the results are compared with four crust and nodule samples of different genetic origin fe vernadite mno2 is the most important minor and trace metal bearing mineral phase and shows high concentrations of co ni cd ti ba zn and cu which are present in seawater mainly as hydrated and labile complexed cations elements forming carbonate and hydroxide complexes and oxyanions in seawater like pb mo v and minor proportions of cu and zn are bound in the fe00h fraction the ca carbonate phase and the residual fraction which consists of aluminosilicates and crystalline oxides show only minor heavy metal associations e g cu and zn only a small part of the high ti concentrations in hydrogenetic crusts is of detrital origin ti mainly forms a hydrogenetic phase probably consisting of ti02 2h20 intergrown with the amorphous fe00h phase analyses of different sample types and crust layers show that aging and diagenetic effects can change the phase associations of some elements the most notable change was observed for pb which during phosphatization of crusts is transferred from the mn fe oxide fraction to the apatite fraction a colloid chemical model for the hydrogenetic precipitation of ferromanganese crusts on seamounts is proposed in the first stage mn2 rich water from the oxygen minimum zone is mixed with oxygen rich deep water and oxidized mn iv and other metals like fe ti al and si form oxide and hydroxide colloids these form mixed colloidal phases and scavenge trace metals by sorptive processes which are dominated by coulombic and chemical interactions between colloid surfaces and dissolved metal species in stage two the colloidal phases precipitate on the substrate rocks of the seamounts as ferromanganese oxide encrustations incorporating the sorbed heavy metals into the mineral phases

microstructures and late stage magmatic processes in layered mafic intrusions symplectites from the sept iles intrusion quebec canada replacive symplectites vermicular intergrowths of two or more minerals are an important feature of layered igneous intrusions recording evidence of late stage reactions between interstitial liquid and crystals they are common throughout the layered series of the 564 ma sept iles layered intrusion in quebec canada and fall into three types oxy symplectites type i symplectites and type ii symplectites oxy symplectites are comprised of magnetite and orthopyroxene nucleate on olivine primocrysts and form via the reaction olivine o2 orthopyroxene magnetite type i symplectites of which there are 3 distinct categories are comprised of anorthitic plagioclase with pyroxene amphibole or olivine vermicules grow from primocryst oxide grains and replace primary plagioclase and type ii symplectites of which there are 2 distinct categories are comprised of anorthitic plagioclase with orthopyroxene amphibole vermicules grow from primocryst olivine

the sept iles layered mafic intrusion geophysical expression eighty eight percent of the cambrian sept iles layered mafic intrusion possibly the second largest on earth lies under the estuary of the st lawrence river a marine geophysical cruise in 1986 t

crystallization sequence and magma chamber processes in the ferrobasaltic sept iles layered intrusion canada the sept iles layered intrusion quebec canada 564 ma is a large plutonic body with a diameter of 80 km and a thickness of 6 km made up from its base to top of a layered series with troctolite and gabbro and an upper border series with anorthosite capped by cupolas of a type granite chilled margin compositions suggest a ferrobasaltic parental magma close to that of the skaergaard intrusion but much richer in iron and titanium samples from drill cores and surface sampling of the 4 7 km thick layered series reveal a succession of massive troctolites and layered gabbros that contain 24 fe ti oxide layers cm to m thick and many anorthositic autolithic blocks the sequence of crystallization in the layered series is plagioclase an72 34 and olivine fo75 21 followed by magnetite and ilmenite then ca rich pyroxene and finally apatite an olivine gap is observed between fo66 and fo59 the saturation of fe ti oxides before ca rich pyroxene is interpreted to be the result of the high feot and tio2 contents and the low cao content of the parental magma contamination by old continental crust has occurred during crystallization of the layered series as indicated by sr isotopic compositions 87sr 86sr564 0 70360 0 70497 the differentiation trend of the intrusion is interrupted by two large and many small reversals to more primitive compositions of cumulus phases cr content of magnetite and lower sr isotope ratios these reversals and the intermittent disappearance of some phases are interpreted as resulting from magma chamber replenishments by undifferentiated primitive basaltic magma and mixing with the resident magma the author 2010 published by oxford university press all rights reserved for permissions please e mail journals permissions oxfordjournals org

stream network modelling using lidar and photogrammetric digital elevation models a comparison and field verification a conventional photogrammetrically derived digital elevation model dem 10 m resolution and a light detection and ranging lidar derived dem 1 m resolution were used to model the stream network of a 193 ha watershed in the swan hills of alberta canada stream networks modelled using both hydrologically corrected and uncorrected versions of the dems and derived from aerial photographs were compared the actual network mapped in the field was used as verification the lidar dem derived network was the most accurate representation of the field mapped network being more accurate even than the photo derived network this was likely due to the greater initial point density accuracy and resolution of the lidar dem compared with the conventional dem lidar dems have great potential for application in land use planning and management and hydrologic modelling the network derived from the hydrologically corrected conventional dem was more accurate than that derived from the uncorrected one but this was not the case with the lidar dem copyright 2007 john wiley sons ltd

the role of fe ti oxide crystallization in the formation of a type granitoids with implications for the daly gap an example from the permian baima igneous complex sw china abstract the baima igneous complex bic is a member of the permian emeishan large igneous province sw china and is composed of a layered gabbroic unit and an isotropic syenitic unit the gabbroic unit consists of four distinct zones 1 lower cumulate zone 2 massive fe ti v oxide ore zone 3 olivine gabbro zone and 4 upper gabbro zone shrimp zircon u pb dating results yield an age of 261 2 ma for the gabbroic unit contemporaneous with the spatially associated syenitic unit the gabbroic rocks show slightly lree enriched patterns with la yb n values between 1 6 and 12 1 and positive eu anomalies eu eu 1 1 3 6 in contrast the syenites display stronger enrichments of lree la ybn 6 8 51 3 and negative eu anomalies eu eu 0 3 1 1 rocks of the syenitic unit are chemically similar to the ferroan alkalic a type granitoids k2o na2o 0 58 0 80 feot feot mgo 0 80 0 91 and have a within plate geochemical signature both units have similar trace element ratios zr nb th u ni co cu ni hf ta and zn ga resembling an ocean island basalt source the end t values for the gabbroic unit end t 1 6 4 2 and syenitic unit end t 2 5 3 2 are within the range of the high ti emeishan flood basalts the geochemical and geochronological data indicate that the gabbroic and syenitic units are comagmatic and cogenetic geochemical modeling suggests that the two units originated by fractional crystallization of a common parental magma that resembles the high ti emeishan flood basalts the formation of the two units by fractional crystallization was likely responsible for the enrichment of fe ti v oxide minerals in the gabbroic unit and thus the development of the daly gap the results of this study indicate that silica saturated peralkaline a type granitoids can be formed by fractionation of mantle derived mafic magmas

compositional changes of surface sediments and variability of manganese nodules in the peru basin abstract two types of manganese nodules were observed in the peru basin large botryoidal nodules in basins and small ellipsoidal nodules on slope positions the sediment in areas with large botryoidal nodules contains a thinner and weaker oxidation zone than the sediment under small ellipsoidal nodules indicating that diagenetic processes in the sediment which supply manganese nodules with metals for their growth are stronger in sediments on which large botryoidal nodules grow organic matter which activates remobilization of metals occurs mostly in the form of refractory lipidic compounds in the inner capsule of radiolaria this material needs bacterial degradation to act as a reducing agent easily oxidizable organic components could not be found in the sediments other changes in sediment composition do not have a link to manganese nodule growth biogenous components radiolarians organogenic barite and apatite increase towards the equatorial high productivity zone authigenous clay minerals nontronite as well as montmorillonite with high fe 3 incorporation on positions of ochtaedral al increase with distance from the continent the assessment of environmental impacts will have to take into account the regional differences in sediment composition and the small scale variability of manganese nodules

anorthosite formation by plagioclase flotation in ferrobasalt and implications for the lunar crust abstract the sept iles layered intrusion quebec canada is dominated by a basal layered series made up of troctolites and gabbros and by anorthosites occurring 1 at the roof of the magma chamber 100 500 m thick and 2 as cm to m size blocks in gabbros of the layered series anorthosite rocks are made up of plagioclase with minor clinopyroxene olivine and fe ti oxide minerals plagioclase displays a very restricted range of compositions for major elements an 68 an 60 trace elements sr 1023 1071 ppm ba 132 172 ppm and sr isotopic ratios 87 sr 86 sr i 0 70356 0 70379 this compositional range is identical to that observed in troctolites the most primitive cumulates of the layered series whereas plagioclase in layered gabbros is more evolved an 60 an 38 the origin of sept iles anorthosites has been investigated by calculating the density of plagioclase and that of the evolving melts the density of the feo rich tholeiitic basalt parent magma first increased from 2 70 to 2 75 g cm 3 during early fractionation of troctolites and then decreased continuously to 2 16 g cm 3 with fractionation of fe ti oxide bearing gabbros plagioclase an 69 an 60 was initially positively buoyant and partly accumulated at the top of the magma chamber to form the roof anorthosite with further differentiation plagioclase 60 became negatively buoyant and anorthosite stopped forming blocks of anorthosite autoliths even fell downward to the basal cumulate pile the presence of positively buoyant plagioclase in basal troctolites is explained by the low efficiency of plagioclase flotation due to crystallization at the floor and or minor plagioclase nucleation within the main magma body dense mafic minerals of the roof anorthosite are shown to have crystallized from the interstitial liquid the processes related to floating and sinking of plagioclase in a large and shallow layered intrusion serve as a proxy to refine the crystallization model of the lunar magma ocean and explain the vertically stratified structure of the lunar crust with gabbro noritic rocks at the base and anorthositic rocks at the top we propose that the lunar crust mainly crystallized bottom up this basal crystallization formed a mafic lower crust that might have a geochemical signature similar to the magnesian suite without kreep contamination while flotation of some plagioclase grains produced ferroan anorthosites in the upper crust

a flower like glomerophyric diorite porphyry from central china constraints on the unusual texture abstract an unusual texture with plagioclase phenocrysts clustered as flower like glomerocrysts has been discovered in the wulong diorite porphyry at the southern margin of north china craton the rock consists mainly of plagioclase and amphibole with the former as dominant phenocryst two groups of the plagioclase phenocrysts have been distinguished flower like glomerocrysts fg type and single isolated phenocrysts sp type chemical compositions of both fg and sp type plagioclases are similar in anorthite contents an35 45 which are slightly higher than the matrix an25 35 calculation of the plagioclase crystallization time based on crystal size distribution csd program shows that the fg type crystals have been formed within a longer timescale 226 2782 years than the sp type crystals 98 1910 years the concave down csds and lack of small crystals for fg type plagioclases suggest that coarsening may have been involved in contrast a concave up csd within the size of 3 10 mm plagioclase indicating that a rejuvenation kinetic process after coarsening a possible formation history for the unusual flower like plagioclase glomerocrysts was proposed as follows 1 initial nucleation and growth of single crystals in a confined environment 2 ascent of early crystals with magma upwelling and radial coarsening at the roof layer of magma chamber 3 remobilization of dense crystal mush and final emplacement at shallow level of crust 4 rapid cooling and extensive nucleation and growth of matrix 5 post magmatic alteration and metamorphism it is likely that the morphologic diversity of plagioclase glomerocrysts are largely influenced by variation of undercooling degrees the second step is the most important for the formation of the flower like glomerophyric texture which requires an environments of relatively low undercooling degree

key factors controlling the accumulation of the fe ti oxides in the hongge layered intrusion in the emeishan large igneous province sw china abstract the hongge layered intrusion hosts the largest fe ti v oxide ore deposit in the central part of the emeishan large igneous province sw china it is divided into lower zone lz middle zone mz and upper zone uz from the bottom to the top for the lz relatively higher cr 250 3000 ppm and ni 50 200 ppm contents of clinopyroxene lower end259ma and higher 87sr 86sr 259ma values 2 82 to 0 07 and 0 7057 0 7076 respectively and plenty of hornblende demonstrate a more primitive parental hydrous magma in contrast relatively low cr

large scale silicate liquid immiscibility during differentiation of tholeiitic basalt to granite and the origin of the daly gap the dearth of intermediate magmatic compositions at the earth s surface referred to as the daly gap remains a major issue in igneous petrology the initially favored explanation invoking silicate liquid immiscibility during evolution of basalt to rhyolite has lost support because of the absence of any firm geological evidence for separation of fe and si rich liquids in igneous rocks this work presents a record of large scale magmatic differentiation due to immiscibility in the tholeiitic sept iles intrusion canada one of the largest layered plutonic bodies on earth gabbroic cumulate rocks from the critical zone of this intrusion show a bimodal distribution in density and p2o5 content despite identical major element chemistry of the principal magmatic phases immiscibility is supported by the presence of contrasting fe rich and si rich melt inclusions trapped in cumulus apatite phase diagrams and well documented occurrences of small scale immiscibility confirm that liquid liquid unmixing and the separation of fe rich and si rich liquids may contribute significantly to the daly gap along the tholeiitic liquid line of descent

geospatial resources for the geology community the usgs national map abstractgeospatial data are a key component of investigating interpreting and communicating the geological sciences locating geospatial data can be time consuming which detracts from time spent on a study because these data are not obviously placed in central locations or are served from many disparate databases the national map of the us geological survey is a publicly available resource for accessing the geospatial base map data needs of the geological community from a central location the national map data are available through a viewer and download platform providing access to eight primary data themes plus the us topo and scanned historical topographic maps the eight themes are elevation orthoimagery hydrography geographic names boundaries transportation structures and land cover and they are being offered for download as predefined tiles in formats supported by leading geographic information system software data tiles are periodically refreshed to capture the most current content an

the plagioclase magma density paradox re examined and the crystallization of proterozoic anorthosites intermediate composition plagioclase an40 60 is typically less dense than the relatively evolved basaltic magmas from which it crystallizes and the crystallization of plagioclase produces a dens residual liquid thus plagioclase should have a tendency to float in these magmatic systems there is however little direct evidence for plagioclase flotation cumulates either in layered intrusions or in proterozoic anorthosite complexes the layered series of the poe mountain anorthosite southeast wyoming contains numerous anorthosite leucogabbro blocks that constrain density relations during differentiation all blocks are more mafic than their hosting anorthositic cumulates their plagioclase compositions are more calcic and each block is in strong sr isotopic disequilibrium with its host cumulate associated structures disrupted and deformed layering indicate that 1 a floor was present during crystallization and that plagioclase was accumulating and or crystallizing on the floor 2 compositional layering and plagioclase lamination formed directly at the magma crystal pile interface and 3 the upper portions of the crystal pile contained significant amounts of interstitial melt liquid densities are calculated for proposed high al olivine gabbroic parental magmas and fe enriched ferrodioritic and monzodioritic residual magmas of the anorthosites taking into account pressure oxygen fugacity p2o5 estimated volatile contents and variable temperatures of crystallization for all reasonable conditions calculated block densities are greater than those of the associated melt the liquid densities however are greater than those for an40 60 plagioclase which cannot have settled to the floor plagioclase must either have been carried to the floor in relatively dense packets of cooled liquid plus crystals or have crystallized in situ a sloping floor possibly produced by diapiric ascent of relatively light plagioclase rich cumulates is required to allow for draining and removal of the dense interstitial liquid produced in the crystal pile and may be a characteristic feature during the crystallization of many proterozoic anorthosites and layered intrusions

high resolution multiproxy records of sedimentological changes induced by dams in the sept iles area gulf of st lawrence canada abstract a multiproxy approach was performed on two sediment box cores sampled in the nw gulf of st lawrence in order to better understand the impacts of recent climatic or land use changes on the sedimentary regime in the proximal offshore zone multibeam and seismic surveys allowed for the careful selection of coring sites the chronology of the cores was established by 210 pb measurements and validated with coinciding historical weather events recorded in both cores confirming that the sediments are recent last 370 years the lithological variations in the cores were quantified using 1 stratigraphic markers and grain size measurements 2 high resolution x ray micro fluorescence xrf and 3 physical and magnetic tracers the grain size measurements allowed the identification of a major flood around ad 1844 4 years whereas a drastic decrease in variations and in the median grain size d50 occurred around ad 1900 highlighting the offshore impact of the sm1 dam construction on the sainte marguerite river in the early 1900s sedimentological variations have been investigated by wavelet analysis using xrf data and the sharp disappearance of high frequencies

petrogenesis and tectonic implications of the iron rich tholeiitic basalts in the hutuo group of the wutai mountains central trans north china orogen abstract the hutuo group located in the wutai mountains area is characteristic of paleoproterozoic strata in the north china craton and plays an important role in establishing evolutionary processes in the trans north china orogen we present petrological observations along with geochemical and nd isotopic data for basalts in the qingshicun and hebiancun formations of the hutuo group these basalts are enriched in tfeo 11 97 18 01 wt consistent with occurrences of iron rich basalt world wide they also display relatively high mgo 4 95 12 25 wt ni 79 121 ppm and cr 37 101 ppm and low in sio 2 41 37 51 95 wt therefore the iron rich character of the hutuo group basalts originated with their parental magma rather than via shallow crustal fractionation at low oxygen fugacity as inferred for many high iron basalts the hutuo group basalts exhibit weak to moderate differentiation of light ree over heavy ree la lu cn 2 61 6 79 with minor or slight eu anomalies eu eu 0 77 1 41 and also show the nb and ti troughs without obvious zr and hf anomalies the nd t values of the basalts range from 1 23 to 0 81 with t dm of 2489 2664 ma the basalts most plausibly originated from the fertile subcontinental lithosphere mantle and in the case of the qingshicun formation basalts also underwent the crustal contamination basalts in the hutuo group also have the high zr hf ratios and present high ti v values of 24 55 and zr y ratios ranging from 4 6 to 13 6 suggesting that they were emplaced in a within plate setting considering the sedimentary associations and detrital fragments in the hutuo and gantaohe groups and bimodal magmatism along the trans north china orogen we propose that 2 2 2 0 ga geological events within the orogen were rift related but did not result from subduction or island arc processes

dual origin of fe ti p gabbros by immiscibility and fractional crystallization of evolved tholeiitic basalts in the sept iles layered intrusion we present a detailed study of two ca 200 m thick apatite bearing ferrogabbro horizons of the sept iles layered intrusion canada these rocks are the most evolved cumulates of the megacyclic units mcu i and ii and mark the transition between basaltic and silicic magmatism they are made up of plagioclase an55 34 olivine fo66 21 clinopyroxene mg 75 55 ilmenite magnetite apatite pigeonite and are a significant source of fe ti p ore ferrogabbros have relatively uniform bulk rock compositions in mcu i but are bimodal in mcu ii the liquid lines of descent for major elements in equilibrium with cumulates of mcu i and ii have been calculated using a forward model formalism both trends evolve towards sio2 enrichment and feot depletion after saturation in fe ti oxides however because of magma mixing in mcu ii they do not follow the same path evolved liquids from mcu ii are shown to enter the experimentally determined two liquid stability field while mcu i liquids do not immiscibility in mcu ii and its absence in mcu i are supported by the presence of contrasted reactive symplectites in cumulate rocks apatite bearing ferrogabbros in mcu ii have crystallized from distinct immiscible fe rich and si rich silicate melts which have physically segregated in the slow cooling magma chamber two different types of cumulate rocks are thus produced leucocratic and melanocratic gabbros this is consistent with the presence of si rich and fe rich melt inclusions in apatite in contrast homogeneous ferrogabbros from mcu i were produced by simple fractional crystallization of a homogeneous liquid our data suggest that immiscibility could also explain the large geochemical variability of ferrogabbros in the upper zone of the bushveld complex south africa

plagioclase preferred orientation and induced seismic anisotropy in mafic igneous rocks fractional crystallization and crystal segregation controlled by settling or floating of minerals during the cooling of magma can lead to layered structures in mafic and ultramafic intrusions in continental and oceanic settings in the lower crust thus the seismic properties and fabrics of layered intrusions must be calibrated to gain insight into the origin of seismic reflections and anisotropy in the deep crust to this end we have measured p and s wave velocities and anisotropy in 17 plagioclase rich mafic igneous rocks such as anorthosite and gabbro at hydrostatic pressures up to 650 mpa anorthosites and gabbroic anorthosites containing 80 vol plagioclase and gabbros consisting of nearly equal modal contents of plagioclase and pyroxene display distinctive seismic anisotropy patterns vp z vp y 1 and vp z vp x 1 for anorthosites while 0 8 vp y than the gabbros laminated anorthosites with vp x vp y vp z display a strong crystal preferred orientation cpo of plagioclase whose 010 planes and 100 and 001 directions parallel to the foliation for the gabbros and amphibolites characterized by vp x vp y vp z and vp x vp y vp z respectively pyroxene and amphibole play a dominant role over plagioclase in the formation of seismic anisotropy the poisson s ratio calculated using the average p and s wave velocities from the three principal propagation polarization directions x y and z of a highly anisotropic anorthosite cannot represent the value of a true isotropic equivalent the cpo induced anisotropy enhances and decreases the foliation normal incidence reflectivity at gabbro peridotite and anorthosite peridotite interfaces respectively

the age of the sept iles layered mafic intrusion canada implications for the late neoproterozoic cambrian history of southeastern canada the large sept iles layered mafic intrusion of eastern canada has been precisely dated by u pb zircon methods at 565 4 ma consideration of other magmatic events at that time in southeastern canada reveals three different phases of magmatism the first phase was composed of two tholeiitic dike swarms at 615 ma and 590 ma the second including the sept iles intrusion comprised a widespread series of mostly alkaline intrusions emplaced around 575 565 ma along the rift faults of the st lawrence graben the last phase was composed predominantly of alkali and transitional basalts now exposed in the appalachians erupted during the latest neoproterozoic and early cambrian the second and third phases are best accounted for by the arrival of a major mantle plume near the town of sept iles 565 million years ago the widespread but volumetrically minor alkali magmatism that peaked 10 m y earlier is typical of other plumes elsewhere the plume model is reinforced by sedimentological evidence for a crusta

rare earth element geochemistry and strontium isotopic composition of a massif type anorthositic charnockitic body the hidra massif rogaland sw norway abstract the hidra massif rogaland complex sw norway mainly consists of plagioclase cumulates anorthosites and leuconorites which grade progressively into a fine grained 200 m locally porphyritic jotunitic rock towards the contact with the granulite facies gneisses the massif is cross cut by thin 10 cm up to 1 m charnockitic dykes the petrographical and geochemical evolution of the hidra massif can be explained by fractional crystallization of a jotunitic parental magma major and trace element constraints indicate that mafic phases are underabundant in the exposed levels of the massif most likely as a result of plagioclase flotation in the early stages of solidification partitioning into the cumulate minerals mainly plagioclase and orthopyroxene governs the trace element contents of the leuconoritic adcumulates however the trace element geochemistry of the apparently early formed anorthositic orthocumulates largely depends upon the amount of a trapped intercumulus liquid on the basis of trace element abundances high ree rb th u negative eu anomalies the silicic charnockitic dykes can be considered as the residual liquid of the anorthositic fractionation trend the higher initial 87 sr 86 sr ratios 0 7086 0 0006 vs 0 7055 0 0004 for the plagioclase cumulates and jotunites point to contamination of the charnockitic liquids by surrounding gneissic material

the origin of laminated and massive anorthosite sept iles layered intrusion quebec canada well laminated plagioclase rich rocks anorthosite occur as layers in mineralogically similar but massive rocks in the sept iles intrusion several phases of crystallization of poikilitic clinopyroxene have preserved the intermediate stages in the production of these rocks plagioclase nucleated and initially grew in random orientations in the stationary part of the boundary layer there in the absence of other events crystallization produced the massive anorthosite the laminated anorthosite may have been produced by episodic increases in the velocity of the magma adjacent to the boundarylayer induced by magmatic density currents such currents would have caused the zone of simple shear of the boundary layer to migrate outwards into the previously stationary part this simple shear would then have rotated the existing plagioclase crystals as well as crystals that nucleated at that time towards the shear plane some rocks show evidence of several periods of enhanced flow velocities the production of the lamination may have weakened the crystal mush and enabled slumping to occur producing folds and contorted layers finally compaction liberated large quantities of intercumulus magma of which some was trapped as granophyric segregations and some escaped by overturing and churning the crystal pile earlier formed granophyric segregations and laminated layers were disrupted during this process to produce a range of more complex rocks including igneous breccias

remote sensing and geomorphometry for studying relief production in high mountains mountain topography is the result of highly scale dependent interactions involving climatic tectonic and surface processes no complete understanding of the geodynamics of mountain building and topographic evolution yet exists although numerous conceptual and physical models indicate that surficial erosion plays a significant role mapping and assessing landforms and erosion in mountain environments is essential in order to understand landscape denudation and complex feedback mechanisms this requires the development and evaluation of new approaches in remote sensing and geomorphometry the research herein evaluates the problem of topographic normalization of satellite imagery and demonstrates the use of terrain analysis using a digital elevation model dem to evaluate the relief structure of the landscape in the western himalaya we specifically evaluated the cosine correction and minnaert correction methods to reduce spectral variation in imagery caused by the topography semivariogram analyses of the topography were used to examine the relationships between relief and surface processes remote sensing results indicate that the minnaert correction method can be used to reduce the topographic effect in satellite imagery for mapping although extreme radiance values are the result of not accounting for the diffuse skylight and adjacent terrain irradiance geomorphometry results indicate that river incision and glaciation can generate extreme relief although the greatest mesoscale relief is produced by glaciation at high altitudes at intermediate altitudes warm based glaciation was found to decrease relief our results indicate that glaciation can have a differential influence on the relief structure of the landscape collectively our results indicate that scale dependent analysis of the topography is required to address radiation transfer issues and the polygenetic nature of landscape denudation and relief production

geochemical constraints on the differentiation processes that were active in the sept iles complex major and trace element abundances in the major units gabbro anorthosite monzonite syenite and granite of the unmetamorphosed sept iles complex have been evaluated to determine if these rocks can be related by simple magmatic processes or if it is necessary to invoke separately derived magmas major element mass balance and trace element distribution calculations indicate that the diorite and quartz syenite were produced by fractional crystallization of plagioclase and augite together with minor hypersthene and ilmenite from a parental gabbroic magma the sr depletion of the granite as compared with the quartz syenite cannot be developed readily by partial melting and is better explained by fractional crystallization models major element mass balance solutions indicate that the granite was formed by removal of alkali feldspar plagioclase amphibole and ilmenite from a quartz syenitic magma depletion of ree in the granite was probably the result of amphibole or ree rich accessory mineral fra

the corossol structure a possible impact crater on the seafloor of the northwestern gulf of st lawrence eastern canada we report on a 4 1 0 2 km diameter and 185 m deep circular submarine structure exposed on the seabed in 40 m water depths in the northwestern gulf of st lawrence eastern canada from the analysis of high resolution multibeam bathymetric and seismic data the presence of a circular form characterized by a central uplift and concentric rings resembles the morphology and geometry of complex meteorite impact structures also other origins such as kimberlites intrusions karsts or diapirs can be eliminated on geological criteria a single 4 cm long breccia fragment recovered from the central uplift has numerous glassy droplets of fluorapatite composition assumed to be impact melts and a single quartz grain with planar intersection features thought to be shock induced planar deformation features pdfs the absolute age of this possible impact structure is unknown but its geological setting indicates that it was formed long after the mid ordovician and before regional pre quaternary sea level lowstands present results outline the need for further examination to confirm an impact origin and to precisely date the formation of the structure

formation of the late permian panzhihua plutonic hypabyssal volcanic igneous complex implications for the genesis of fe ti oxide deposits and a type granites of sw china the late permian 260 ma emeishan large igneous province of sw china contains numerous magmatic fe ti oxide deposits the fe ti oxide deposits occur in the lower parts of evolved layered gabbroic intrusions which are spatially and temporally associated with a type granitic rocks the 260 ma panzhihua layered gabbroic intrusion hosts one of the largest magmatic fe ti oxide deposits in china and is coeval with a peralkaline a type granitic pluton the granite has intruded the overlying emeishan flood basalts and fed at least one dyke which erupted onto the surface producing columnar jointed trachytes the presence of syenodiorite between the layered gabbro and granite is evidence for compositional evolution from mafic to intermediate to felsic rocks the syenodiorites have intermediate to felsic composition with sio2 61 to 65 wt mgo 0 27 to 0 6 wt and cao 1 0 to 2 5 wt as compared to the granite sio2 65 to 72 wt mgo 0 1 to 0 4 wt cao 1 eu eu 1 1 to 2 6 in the gabbroic intrusion to 1 in the syenodiorite eu eu 0 75 to 0 83 granites and trachytes eu eu 0 55 0 87 previously published end t values from clinopyroxenes end t 1 1 to 3 2 of the gabbroic intrusion match the whole rock values of the syenodiorite end t 2 1 to 2 5 granite and trachyte end t 2 2 to 2 9 suggesting that all rock types originated from the same mantle source melts and trace element modeling confirm that all rock types can be generated by fractional crystallization of high ti emeishan basalt the jump in sio2 from the gabbro to the syenodiorite is attributed to the en masse crystallization of the fe ti oxides the geological and geochemical data indicate that fractional crystallization of a common parental magma produced the layered gabbroic intrusion and fe ti oxide deposit the syenodiorite granites and trachyte of the panzhihua region which thus form a genetically related plutonic hypabyssal volcanic complex other granite gabbro complexes in the region likely formed in a similar manner

a plume generated segment of the rifted margin of laurentia southern canadian appalachians seen through a completed wilson cycle the southern part of the canadian appalachians and the adjacent parts of the craton show a range of distinctive features pertaining to the evolution of the rift and rift drift transition stages of a segment of the continental margin of laurentia despite the effects of a completed wilson cycle several lines of evidence point to an initial lithospheric rupture in the form of a three pronged rift possibly induced by a rising mantle plume the earliest synrift igneous products to penetrate the crust in the area are represented by a swarm of tholeiitic diabase dykes intruded at ca 590 ma the swarm is more than 700 km long and radiates from the inferred location of the rrr triple junction dyke emplacement and the initiation of rifting were probably synchronous approximately 35 m y later a rapid outburst of volcanism occurred at the triple junction probably as a harbinger of sea floor spreading the volcanic products are predominantly basalts of mildly alkaline to transitional character but with a minor comenditic component the voluminous nature of the volcanic outburst and the compositional characteristics of its products indicate higher than normal asthenospheric temperatures coupled with thinning of the lithosphere suggesting continued mantle plume activity the volcanic sequence is overlain by rift facies elastics that are locally interrupted and augmented by a deltaic deposit representing the delta of a river that drained the failed arm into the nascent lapetus ocean the rift facies elastics and the associated deltaic deposits are overlain by rocks of marine origin signalling the beginning of the drifting stage possibly at ca 550 ma

analysis of lidar derived topographic information for characterizing and differentiating landslide morphology and activity abstract this study used airborne laser altimetry lidar to examine the surface morphology of two canyon rim landslides in southern idaho the high resolution topographic data were used to calculate surface roughness slope semivariance and fractal dimension these data were combined with historical movement data global positioning systems gps and laser theodolite and field observations for the currently active landslide and the results suggest that topographic elements are related to the material types and the type of local motion of the landslide weak unconsolidated materials comprising the toe of the slide which were heavily fractured and locally thrust upward had relatively high surface roughness high fractal dimension and high vertical and lateral movement the body of the slide which predominantly moved laterally and consists mainly of undisturbed older canyon floor materials had relatively lower surface roughness than the toe the upper block consisting of a down dropped section of the canyon rim that has remained largely intact had a low surface roughness on its upper surface and high surface roughness along fractures and on its west face unrelated to landslide motion the upper block also had a higher semivariance than the toe and body the topographic data for a neighboring older and larger landslide complex which failed in 1937 are similarly used to understand surface morphology as well as to compare to the morphology of the active landslide and to understand scale dependent processes the morphometric analyses demonstrate that the active landslide has a similar failure mechanism and is topographically more variable than the 1937 landslide especially at scales 20 m weathering and the larger scale processes of the 1937 slide are hypothesized to cause the lower semivariance values of the 1937 slide at smaller scales