unusual bulk rock compositions in eclogite facies rocks from syros and tinos cyclades greece implications for u pb zircon geochronology low temperature eclogite facies rocks from syros and tinos cyclades greece include meta ophiolitic blocks of unclear origin meta olistostrome or tectonic melange these blocks occur in a matrix of altered serpentinite and or semipelitic to tuffitic schists some samples are characterized by very high trace element concentrations for example eclogites from tinos contain up to 4950 ppm zr and up to 480 ppm y understanding of the geochemical controls on the petrogenesis of these rocks has important consequences for interpretation of geochronological results the emphasis of this study is on the behaviour of zr under eclogite facies p t conditions due to remarkably high modal amounts of zircon some samples from the meta ophiolite suite are suitable for u pb zircon chronology the geological significance of zircon ages can only be correctly interpreted by assessing whether zircon crystallized from a melt or formed during subsequent hydrothermal or metamorphic processes the results of this study lead us to conclude that infiltration of trace element enriched fluids during eclogite facies metamorphism caused local scale compositional changes textural observations document the presence of a fracture network favouring fluid infiltration under high pressure conditions such a system of microfractures might have provided infiltration paths for trace element enriched fluids during earlier stages of high pressure metamorphism in most cases subsequent recrystallization erased any evidence of the early infiltration channels but inclusion of high pressure phases in zircon provide evidence for this model suggesting metasomatic alteration in a subduction zone environment the original fluid source and the conditions e g high f environment highly saline brines under which commonly immobile elements were mobilized remain unclear it is speculated that eclogitization of closely associated metagabbros may have released zr and other trace elements the results of this contribution suggest that new zircon formed during high pressure metamorphism cretaceous u pb zircon ages are interpreted to date subduction metamorphism and not magmatic crystallization

tectonic evolution of the qinling orogenic belt central china new evidence from geochemical zircon u pb geochronology and hf isotopes abstract the qinling orogenic belt qob located between the north china craton ncc and the yangtze craton yzc is composed of the northern qinling belt nqb and the southern qinling belt sqb this study presents new geochemical data zircon u pb ages and hf isotopes from a suite of metamorphic rocks from the kuanping qinling danfeng douling and wuguan groups in the nqb and the sqb our results suggest that the qinling group in the nqb formed in an active continental margin related to the subduction of the songshugou ocean under the southern ncc during grenvillian period the kuanping group in the northern nqb was deposited in the within plate extension basin during late neoproterozoic to early paleozoic the detritus of sedimentary rocks of the kuanping group were mainly sourced from the nqb and subordinately from the basement rocks of the ncc the danfeng group in the southern nqb formed later than 827 ma with the sediments derived mainly from the qinling terrane the nqb witnessed multiphase tectono thermal events from mesoproterozoic to early paleozoic including several magmatic events and the early paleozoic metamorphic event the original douling group in the sqb represents the basement complex of the sqb which is composed of rocks with different formation ages the oldest rock in the complex is represented by 3 0 ga granitic gneiss which underwent at least two periods of metamorphism at 2 5 ga and 0 97 0 91 ga in this study the douling group is redefined as a suite of neoproterozoic 860 750 ma rocks formed in an extensional setting after the subduction of the songshugou ocean the wuguan group in the sqb formed in the middle late neoproterozoic later than 740 ma and was subjected to early paleozoic metamorphism our data indicate that the sqb experienced early neoproterozoic 970 865 ma and early paleozoic 444 ma metamorphism and strong middle neoproterozoic 870 730 ma magmatism the age spectra of zircons from the nqb trace major tectono thermal events at 1462 ma 927 ma and 412 ma which are different from those recorded in the southern ncc and northern yzc suggesting that the nqb had a distinct evolution during mesoproterozoic to early neoproterozoic grenvillian the hf isotopic compositions of zircons from the various rocks suggest that the nqb probably developed on the basement of the southern ncc the rocks in the sqb show zircon age spectra and hf isotope compositions similar to those in the northern yzc suggesting a close affinity we therefore interpret the sqb to have developed on the basement of the northern yzc integrating the new data in this study with those from previous works we propose a new tectonic model for the formation and evolution of the qob during late mesoproterozoic to early paleozoic involving the following major events 1 late mesoproterozoic to early neoproterozoic grenvillian northward subduction of the songshugou ocean 2 early middle neoproterozoic 870 800 ma bidirectional subduction and collision 3 middle neoproterozoic 800 710 ma post collision extension 4 middle late neoproterozoic 710 600 ma within plate extension 5 late neoproterozoic early paleozoic 600 520 ma opening of the shangdan ocean and 6 early paleozoic 520 420 ma subduction collision we thus trace at least two distinct wilson cycles in the qob

zoisite and clinozoisite segregations in metabasites tauern window austria as evidence for high pressure fluid rock interaction high pressure zoisite and clinozoisite bearing segregations are common in garnet and albite bearing amphibolites of the palaeozoic part of the lower schieferhulle south central tauern window austria the zoisite segregations primary assemblage zo qtz cal formed during an early to pre hercynian high pressure event p 0 6 gpa t 500 550 c by hydrofracturing as a result of protolith dehydration zoisite is growth zoned from fe3 poor cores al 2 fe 9 mol to fe3 rich rims 17 mol and has high sr pb and ga contents and lree enriched ree patterns controlling the trace element budget of the segregations hercynian deformation at c 0 7 gpa 600 c kinked and cracked primary zoisite and enhanced breakdown into secondary zoisite 13 mol al 2 fe clinozoisite 40 55 mol al 2 fe albite an 20 calcite and white mica during an eoalpine high pressure event at 0 9 1 2 gpa 400 500 c the clinozoisite segregations primary assemblage czo qtz omp ttn chl cal are mm to cm wide vein like bodies cross cutting fabric elements of the host garnet amphibolite they formed during the eoalpine high pressure event at 0 9 1 2 gpa 400 500 c during alpine exhumation omphacite was pseudomorphed by amphibole albite quartz and clinozoisite oxygen isotope data suggest equilibrium between host metabasite and zoisite segregations and indicate an internal fluid source and fluid buvering by the protolith mobility of p nb and lree changed the protolith s trace element composition in the vicinity of the zoisite segregations mobilization of lree is evidenced by decreasing modal amounts of lree rich epidote and decreasing lree contents in lree rich epidote towards the segregations chang ing the ree patterns of the host metabasite from lree enriched to lree depleted tectonic discrimi nation diagrams based on the trace element content of metabasites should be applied with extreme caution

tectonic significance of 400 ma zircon ages for ophiolitic rocks from the lachlan fold belt eastern australia new shrimp ion microprobe data provide constraints on the age of formation of ophiolitic rocks from the tumut region of the lachlan fold belt southeastern australia magmatic zircons from plagiogranites within both the coolac serpentinite belt and wambidgee serpentinite belt give 206 pb 238 u ages of about 400 ma this devonian age is considerably younger than those previously proposed for these ophiolitic rocks cambrian ordovician to early silurian and provides important tectonic data for this region of the lachlan fold belt we suggest that these rocks formed within a narrow marginal basin akin to those of cretaceous age within the chilean andes of south america the dates presented are within the 420 390 ma range assigned to most of the granitic bodies of the lachlan fold belt we therefore suggest that the generation of both the ophiolitic rocks and granitic magmas of the lachlan fold belt were part of the same major tectonothermal event

sulfur in serpentinized oceanic peridotites serpentinization processes and microbial sulfate reduction the mineralogy contents and isotopic compositions of sulfur in oceanic serpentinites reflect variations in temperatures and fluid fluxes serpentinization of 1 ma peridotites at hess deep occurred at high temperatures 200 400 c and low water rock ratios oxidation of ferrous iron to magnetite maintained low o2 and produced a reduced low sulfur assemblage including nife alloy small amounts of sulfate reduction by thermophilic microbes occurred as the system cooled producing low 34s sulfide 1 5 to 23 7 in contrast serpentinization of iberian margin peridotites occurred at low temperatures 20 200 c and high water rock ratios complete serpentinization and consumption of ferrous iron allowed evolution to higher o2 microbial reduction of seawater sulfate resulted in addition of low 34s sulfide 15 to 43 and formation of higher sulfur assemblages that include valleriite and pyrite the high so4 total s ratio of hess deep serpentinites 0 89 results in an increase of total sulfur and high 34s of total sulfur mean 8 in contrast iberian margin serpentinites gained large amounts of 34s poor sulfide mean total s 3800 ppm and the high sulfide total s ratio 0 61 results in a net decrease in 34s of total sulfur mean 5 thus serpentinization is a net sink for seawater sulfur but the amount fixed and its isotopic composition vary significantly serpentinization may result in uptake of 0 4 14 1012 g s yr 1 from the oceans comparable to isotopic exchange in mafic rocks of seafloor hydrothermal systems and approaching global fluxes of riverine sulfate input and sedimentary sulfide output

estimates of three dimensional rupture surface geometry of deep seated landslides using landslide inventories and high resolution topographic data abstract deep seated landslides cause significant damage to the built environment characterizing the shear surface and volume of these features is often limited to intensive site specific monitoring or at a larger scale generalized empirical relationships developed from change analysis however there is limited means of generalizing regional scale rupture surface information for deep seated landslides where deposits still overlay much of the failure surface herein a method is proposed that uses high resolution bare earth digital elevation models with an inventory of mapped landslide extents to gather first order estimates of three dimensional rupture surface geometries and volumes for rotational and compound landslide features at a regional scale this approach is first calibrated to a suite of well characterized landslides and then applied to over eight hundred deep seated landslides in three different geologic regimes estimates of landslide area volume relationships are proposed that are consistent with previous empirical assessments the aforementioned relationships describe mean landslide thickness added relationships relating landslide area to maximum landslide thickness are proposed the presented results suggest limits on magnitudes of depth with landslide classification and relief between geologic settings consistent with prior research it is observed that landslide area exhibits a first order control on maximum and mean landslide thickness but further insight is provided towards the influence of a limited set of landslide classification which exhibit controls on the range of magnitudes observed for maximum landslide depth associated with failure lastly the implications and limitations of the developed three dimensional mapping approach is discussed

significance of geomorphological and subsurface drainage controls on failures of peat covered hillslopes triggered by extreme rainfall on 19 september 2003 40 landslides of 140 18 000 m3 volume occurred within 2 5 km2 on the slopes of dooncarton mountain republic of ireland during a storm that may have exceeded 90 mm within 90 minutes the landslides were investigated to determine the reasons for such a high density of slope failures all of the landslides were surveyed within four months and nine of them were investigated in detail the six largest landslides all peat failures accounted for 57 of the more than 100 000 m3 of material displaced during the event a consistent sequence of superficial materials was found on the failed hillslopes including an extensive iron pan at the base of a buried soil horizon 0 3 m below the base of the peat morphologically almost all of the landslides occurred on steep planar slopes or around sharp convexities with the latter failures developing retrogressively upslope the only significant relationship found from analysis of 371 subsurface pipes and 142 seepage cracks defined here as contiguous fissures conducting concentrated subsurface flow across all the failures was that the thinner the peat cover the deeper the pipes and seepage cracks occurred below the base of peat it is concluded that most of the landslides were probably caused by a combination of excess water pressures in the buried soil horizon and the thinner overburden of peat or peaty soil associated with the steeper slope segments pipes and seepage cracks formed on the iron pan probably existed prior to the failure event and may have contributed to the high water pressures as rainwater inputs exceeded their discharge capacities one large peat slide was probably triggered by excess water pressures developed within and between artificial tine cuts the properties of the blanket peat were generally of little consequence in the occurrence of the landslides but relict desiccation cracks and other structural weaknesses through the peat mass were probably highly significant although several aspects of the peat failures correspond to previously published examples the context of these failures in terms of the topography and upland catena is distinctive copyright 2007 john wiley sons ltd

zircon hf isotope signature of the depleted mantle in the myanmar jadeitite implications for mesozoic intra oceanic subduction between the eastern indian plate and the burmese platelet article i nfo this study systematically investigated the lu hf isotope signatures of zircons in jadeitite from the north myanmar which was formed from jadeite forming hydrothermal fluids and is always sourced in serpentinite as a mark for the subduction zone results show that the three group zircons have positive ehf t values group i zircons 163 2 3 3 ma have relatively higher 176 lu 177 hf ratios n0 0004 and the corresponding ehf t values range from 15 5 to 20 0 at t 163 ma in contrast group ii zircons 146 5 3 4 ma exhibit highly variable 176 lu 177 hf ratios from 0 000027 to 0 001398 but still have ehf t values of 15 6 to 18 5 at t 147 ma which resemble to those of the group i zircons the group iii zircon 122 2 4 8 ma has a 176 lu 177 hf ratio of 0 000578 and a ehf t value of 15 8 at t 122 ma such highly positive ehf t values for all jadeitite zircons indicate that they were derived from rapid reworking of the very juvenile crust therefore zircon in jadeitite can be used as a valuable mineral to constrain the age of serpentinization rodingitization and even the age of formation of ultramafic rock within ophiolites the results also suggest the presence of the mesozoic intra oceanic subduction within the indo burman range and further suggest that the hydrothermal fluids were derived from dehydration of seawater altered oceanic juvenile crust that had been hydrated during and or after the formation of the oceanic crust and additionally from serpentine minerals at greater depth consequently the fluids carry the hf isotope signature of the depleted mantle that can be later imparted to the jadeitite zircons

intense ch4 plumes generated by serpentinization of ultramafic rocks at the intersection of the 15 20 n fracture zone and the mid atlantic ridge abstract as part of the fara french us program designed to study the mid atlantic ridge mar between 15 n and the azores twenty three dives with the submersible nautile were conducted during the french us faranaut 15n cruise on the eastern and western parts of the 15 20 n fracture zone ridge axis intersection south of the eastern ridge transform fault intersection nine nautile dives were made within the rift valley and along the western rift valley wall ch4 concentrations in the bottom waters reach 53 2 nmol kg along faulted zones on top and on the east flank of the ultramafic inner corner high 15 05 n 44 59 w where serpentinized rocks outcrop no 3he anomaly is associated with methane ruling out any primary mantle component fourteen dives were also made in the rift valley to the north close to the western intersection of the 15 20 n transform high ch4 anomalies up to 22 nmol kg are also present in the bottom waters of the rift valley northern segment on both the western and eastern valley walls and on the inner high adjacent to the eastern wall where ultramafic rocks outcrop seven vertical hydrocasts carried out in the axial valley 4500 m deep show an intense ch4 anomaly with a maximum 35 8 nmol kg at 3200 m depth this ch4 concentration is among the highest found along the mid atlantic ridge charlou and donval 1993 charlou et al 1997 ch4 concentrations of 9 9 14 9 nmol kg are also present on the western wall along the 3200 m isobath the high ch4 concentrations correspond to only weak 3he anomalies this ch4 rich plume is also associated with active fault zones that expose peridotite rocks ch4 output from ultramafic outcrops on the western and eastern intersections of the 15 20 n fracture zone with the mar is believed to reflect ongoing serpentinization these results associated with many other ch4 anomalies measured in the water column above ultramafic outcrops found between 12 n and the azores most likely reflect serpentinization processes extending along the whole slow spreading mid atlantic ridge

the palaeozoic variscan oceans revisited abstract geological evidence supported by biogeographical data and in accord with palaeomagnetic constraints indicates that one ocean models for the variscides should be discarded and confirms instead the existence of three gondwana derived microcontinents which were involved in the variscan collision avalonia north armorica franconia and thuringia subdivided by a failed vesser rift and south armorica central iberia armorica bohemia all divided by small oceans in addition parts of south eastern europe including adria and apulia are combined here under the new name of palaeo adria which was also peri gondwanan in the early palaeozoic oceanic separations were formed by the break up of the northern gondwana margin from the late cambrian onwards most of the oceans or seaways remained narrow but much like the alpine cenozoic oceans gave birth to orogenic belts with hp uhp metamorphism and extensive allochthons the saxo thuringian ocean between north and south armorica and the galicia moldanubian ocean between south armorica and palaeo adria only the rheic ocean between avalonia and peri gondwana was wide enough to be unambiguously recorded by biogeography and palaeomagnetism and its north western arm closed before or during the emsian in europe ridge subduction under the northernmost part of armorica in the emsian created the narrow and short lived rheno hercynian ocean it is that ocean and not the rheic whose opening and closure controlled the evolution of the rheno hercynian foldbelt in south west iberia south west england germany and moravia czech republic devonian magmatism and sedimentation set within belts of early variscan deformation and metamorphism are probably strike slip related the first arrival of flysch on the forelands and or the age of deformation of foreland sequences constrains the sequential closure of the variscan seaways galicia moldanubian in the givetian saxo thuringian in the early famennian rheno hercynian in the tournaisian additional mid to late devonian and partly early carboniferous magmatism and extension in the rheno hercynian saxo thuringian and galicia moldanubian basins overlapped with variscan geodynamics as strictly defined the early carboniferous episode was the start of episodic anorogenic heating which lasted until the permian and probably relates to tethys rifting

assessment of sediment delivery from successive erosion on stream coupled hillslopes via a time series of topographic surveys in the central high mountain range of taiwan abstract landslides play an important role in the evolution of mountain topography and are a major source of sediment in tectonically active mountain belts for the active orogeny of taiwan erosion rates have been assessed by various methods the discrepancies observed between erosion rates integrated over modern and quaternary time scales may result from various effects related to surface processes more process oriented research on the spatio temporal distribution of hillslope processes and coupling relationships with the fluvial system is needed to reconcile the temporally heterogeneous data in the future this paper assesses and describes the processes of subsequent erosion on hillslopes via a time series of topographic surveys of hillslopes after the initial failure in order to better understand the temporal and spatial variability of landslide erosion sediment fluxes and storage of landslide sediment within channels the results demonstrate that hillslope channel coupling is controlled by the relative frequency of erosive flooding events and the magnitude of rainfall driven hillslope processes the latter is assumed to be disproportionately high on larger failures in periods with less rainfall mass wasting may only affect part of the total failure s area volumes of eroded sediment from gullies on the landslide scar may be as high as the volume estimated for the initial failure the geometry of the sliding masses eroded after the initial failure appears to be uniform and their depths average 6 1 2 2 m

zircon u pb hf isotopic and whole rock geochemical studies of paleoproterozoic metasedimentary rocks in the northern segment of the jiao liao ji belt china implications for provenance and regional tectonic evolution abstract this study examines the original nature tectonic setting and evolution of paleoproterozoic metasedimentary rocks of the north liaohe and laoling groups of the northern segment of the jiao liao ji belt in the northeastern margin of the eastern block of the north china craton using new petrological whole rock geochemical geochronological and lu hf isotope data zircons in the metasediments are magmatic and metamorphic in origin yielding peak ages of 2 03 ga for the deposition of the protoliths of the metasedimentary rocks and 1 90 and 1 85 ga for their metamorphism geochemical analyses indicate the protoliths contained sandy wacke and claystone material with minor shale derived from paleoproterozoic granites coeval acidic meta volcanic rocks meso and neo archean basement granites and paleoproterozoic meta mafic rocks using regional geological and new lu hf isotopic data we propose that the protoliths of the metasedimentary rocks of the north liaohe and laoling groups in the northern segment of the jiao liao ji belt were deposited in a back arc basin setting this region experienced two crustal growth events at 2 57 2 46 and 2 28 2 08 ga as well as two metamorphic events at ca 1 90 and 1 85 ga

isotope geochemistry and revised geochronology of the purrido ophiolite cabo ortegal complex nw iberian massif devonian magmatism with mixed sources and involved mesoproterozoic basement abstract in the purrido ophiolite cabo ortegal complex new u pb zircon dating of the amphibolite g03 8 by laser ablation inductively coupled plasma mass spectrometry confirms the existence of a dominant mesoproterozoic zircon population with a refined age of 1155 14 ma however the u pb zircon dating of two more amphibolite samples by sensitive high resolution ion microprobe has provided new ages of 395 3 ma and 395 2 ma respectively interpreted as the crystallization age hf isotope data for zircon show that most of the devonian zircons crystallized from a juvenile depleted mantle source the mesoproterozoic zircons have relatively juvenile hf isotopic composition reflecting some influence of an older component a few devonian zircon crystals show evidence of mixing with an older component represented by the mesoproterozoic zircons the whole rock sm nd isotope data indicate an important heterogeneity in the composition of the purrido amphibolites only compatible with the generation of their protoliths from two sources we interpret these puzzling data as resulting from the mixing of a devonian mantle derived magma with a mesoproterozoic basement these new data provide new perspectives in the interpretation of the most common ophiolites across the variscan suture in europe supplementary material analytical methods zircon u th pb shrimp analytical data zircon u th pb la icp ms analytical data zircon lu hf la mc icpms analytical data and whole rock sm nd isotope data are available at http www geolsoc org uk sup18449

u pb dating of serpentinization hydrothermal zircon from a metasomatic rodingite shell sudetic ophiolite sw poland abundant zircon grains were found within a metasomatic chlorite corrensite trioctahedral regularly interstratified chlorite smectite shell that surrounds rodingite from the jordanow gogolow jg serpentinite massif sudetic ophiolite bohemian massif the zircon grains bear two types of primary fluid inclusions containing either liquid co2 or aqueous solutions the inclusions were used to assign the p t conditions of the zircon formation 270 300 c ca 1 kbar using the crossed isochore method abraded single zircon grains give a u pb age of 400 4 3 ma which is interpreted as the age of zircon crystallization this zircon formed during rodingitization i e a metasomatic process directly connected with the serpentinization and thus provides the opportunity of direct dating of the early serpentinization process the zircon age from the jordanow gogolow massif is consistent with the crystallization age of metagabbro protoliths from the sudetic ophiolite as determined by oliver et al j geol soc lond 150 1993 355 a ce anomaly combined with the mineralogical record of greenschist facies metamorphism of the mafic rocks from sudetic ophiolite suggests that the sm nd whole rock isotopic data of pin et al lithos 21 1988 195 353 21 ma possibly characterize the age of later metamorphic event

spatial and temporal analysis of hillslope channel coupling and implications for the longitudinal profile in a dryland basin author s michaelides katerina hollings rory singer michael bliss nichols mary h nearing mark a

the origin of rodingites from cassiar british columbia and their use to estimate t and p h2o during serpentinization abstract the cassiar serpentinite located in north central british columbia is a low grade alpine type serpentinite within the sylvester allochthon two stages of rodingitization have occurred at cassiar and these correlate with two stages of serpentinization that have occurred in the ultramafic rock the first stage is characterised by an increase in ca activity and decreases in mg and sio 2 activities in the rodingite culminating in the crystallization of grossular in the rodingite and by the formation of lizardite in the serpentinite at a later time a second event occurred characterised by a decrease in ca activity and increases in mg and sio 2 activities both in the rodingite and the serpentinite this was marked by the crystallization of diopside prehnite and lizardite in the rodingite and by the recrystallization of lizardite to chrysotile and antigorite in the serpentinite the serpentine recrystallization and the development of the second stage rodingite minerals indicate that the changes in rodingite and serpentine mineral assemblages were driven by similar changes in the bulk rock compositions this suggests that the second stage event in both rodingite and serpentinite was caused by an externally derived fluid measurements on fluid inclusions in the rodingite minerals clinozoisite grossular and diopside of the second event indicate that the externally derived fluid was co 2 poor but relatively saline 8 1 5 equiv wt nacl by combining the pressure dependant temperature measurements from fluid inclusions with the pressure independant temperature measurements on 18 o in coexisting serpentine magnetite pairs the pressure of formation can be estimated the second event of serpentine recrystallization and rodingitization was an isothermal process at 300 c 36 c p h 2 o

unraveling alteration histories in serpentinites and associated ultramafic rocks with magnetite u th he geochronology serpentinization is a widespread process that affects large scale geodynamic processes along plate boundaries including continental breakup seafloor spreading and subduction documenting the timing of serpentinization is critical for our understanding of these processes but direct dating of serpentinites has been challenging or impossible we present the first application of magnetite u th he chronometry to date stages of alteration and cooling in ultramafic rocks in order to demonstrate the viability of magnetite he dating in these lithologies magnetite ages were obtained from two ultramafic lithologies of the kampos melange belt a high pressure low temperature subduction complex on the island of syros greece magnetite u th he measurements of internal fragments from large grains within a chlorite schist and a serpentinite record miocene exhumation related cooling ages whereas smaller grains from the serpentinite record mineral growth associated with hydrothermal fluid flow along pliocene normal faults these age results with magnetite trace element geochemistry reveal evidence for multiple episodes of fluid rock alteration which has implications for the cooling history and local geochemical exchanges of this high pressure low temperature terrane this method provides a new tool that may be expanded to investigate the processes and time scales of serpentinization from a variety of tectonic settings

solution to the volume problem in serpentinization kernel pattern consists of a rim of completely serpentinized peridotite surrounding a core of partly serpentinized or unserpentinized peridotite it is found adjacent to shear zones in some serpentinites kernels are commonly rectangular with length width ratios of 1 to 3 the boundary between the completely serpentinized rim and the unserpentinized core is commonly cut at a high angle by cross fractures the cross fractures which contain either picrolite or chrysotile asbestos taper out in the core and widen in the rim they are almost always perpendicular to the core rim boundary and point into the core of the kernel in this sense they are radially distributed in the rim the kernel pattern can be observed in thin section in outcrop and on the megascopic scale of tens of metres cross fractures represent expansion fractures in serpentinite in the rim of the kernel caused by an increase in volume acompanying serpentinization of the peridotite in the core of the kernel as the serpentinization front penetrates into the kernel the serpentinized peridotite expands however the serpentinite in the rim cannot expand and must fracture to accommodate the increase in volume as serpentinization proceeds more expansion occurs extending the fractures farther into the core and requiring the fractures in the existing serpentinite to widen these fractures are subsequently filled by serpentine minerals the resulting pattern consists of a rim of serpentinite cut by serpentine veins that surrounds a core of peridotite measured densities of cross fractures in the rims of kernels are consistent with those expected from the magnitude of the volume change accompanying serpentinization of peridotite

time lapse video observation of erosion processes on the black marls badlands in the southern alps france in order to clarify the erosion processes on a marly bare slope in the southern alps the erosion processes in a steep and erodible slope composed of the black marls formation were observed by a time lapse video camera the observations revealed that miniature debris flows mdfs occurred at the time of the rainfall runoff event in which the most severe erosion took place in the whole observation period of 3 months analysis of the camera images showed some characteristics of the mdfs and these are discussed in the context of real rainfall runoff phenomena observed at the outlet of a small experimental basin including the visually observed slope the following results were obtained 1 a rough estimation of the total amount of sediment discharge by the mdfs showed that it was not negligible quantitatively 2 the mdfs occurred only during the rising limb of the hydrograph during 6 minutes 3 based on this observation and a review of the literature in a very steep and highly erodible slope mdfs or similar phenomena might play an important role in the erosion and transport processes copyright 2008 john wiley and sons ltd

sediment transport by runoff on debris mantled dryland hillslopes 1 hillslopes supply sediment to river channels and therefore impact drainage basin functioning and evolution the relationship between hillslope attributes and sediment flux forms the basis of geomorphic transport laws used to model the long term topographic evolution of drainage basins but their specific interactions during individual storm events are not well understood runoff driven erosion of coarse particles prevalent in dryland environments presents a particular set of conditions for sediment transport that is poorly resolved in current models in order to address this gap we developed a particle based force balance model for sheetwash sediment transport on coarse debris mantled hillslopes within a rainfall runoff model we use the model to examine how the interplay between hillslope attributes gradient length and grain size distribution and runoff characteristics affects sediment transport grain size changes on the hillslope and sediment supply to the slope base the relationship between sediment flux and hillslope gradient was found to transition from linear above a threshold to sigmoidal depending on hillslope length initial grain sizes and runoff characteristics grain sizes supplied to the slope base vary in a complex manner with hillslope attributes but an overall coarsening of the hillslopes is found to occur with increasing gradient corroborating previous findings from field measurements intense short duration storms result in within hillslope sediment redistribution and equifinality in sediment supply for different hillslope characteristics which explain the lack of field evidence for any systematic relationships our model findings provide insights into hillslope responses to climatic forcing and have theoretical implications for modeling hillslope evolution in dry lands

garnetite xenoliths and mantle water interactions below the colorado plateau southwestern united states garnetite xenoliths from ultramafic diatremes in northeastern arizona provide insights into hydration and metasomatism in the mantle the garnetites contain more than 95 garnet some of which has complex compositional zonation related to growth in fractures within grains accessory minerals include rutile ilmenite chlorite clinopyroxene and zircon zircon grains in one rock were analyzed in situ to determine u pb ages and hf isotopic compositions most u pb analyses plot on or near concordia in the range 60 85ma but a few are discordant the range in 176 hf 177 hf is about 0 2818 0 2828 with grains zoned to more radiogenic hf from interiors to rims the garnetite protolith contained zircons at least 1 8ga in age and garnet and additional zircon crystallized episodically during the interval 85 60ma the garnetites are interpreted as mantle analogues of rodingites formed in metasomatic reaction zones caused by water rock interactions in proterozoic mantle during late cretaceous and cenozoic subduction of the farallon plate associated eclogite xenoliths may have been parts of these same reaction zones the rodingite hypothesis requires serpentinization in the mantle wedge 700km from the trench beginning 5 10myr before tectonism related to low angle subduction

u pb ages from sw poland evidence for a caledonian suture zone between baltica and gondwana faunal and palaeomagnetic evidence suggests the existence of a c 3000 km wide tornquist sea between gondwana and baltica in early ordovician times which narrowed to 50 2 ma an unmetamorphosed ophiolite gives a 420 20 2 ma age whilst in two other terranes amphibolite facies island arc lavas have fossiliferous lower ludlow 424 415 ma sequences all are unconformably overlain by unmetamorphosed upper devonian conglomerates a sinistral transpressive regime is observed in regionally extensive mylonite zones titanite and zircon ages 338 2 3 and 339 4 ma record variscan magmatism the data suggest considerable narrowing of the tornquist sea during the ordovician continuing ocean floor and island arc activity in the silurian and final sinistral transpressive closure by the mid devonian

age origin and geodynamic significance of plagiogranites in lherzolites and gabbros of the piedmont ligurian ocean basin abstract u pb zircon dating sr nd isotope tracing and major trace re element analyses were performed to constrain the age origin and geodynamic significance of plagiogranites that intrude lherzolites and gabbros in the ligurian alps and the northern apennines in addition a host fe diorite was investigated samples from the ligurian alps were collected from the voltri group and the sestri voltaggio zone whereas the plagiogranites from the northern apennines were taken in the bracco unit all these units have been affected by alpine metamorphism reaching eclogite facies in the voltri group blueschist degree in the sestri voltaggio samples and prehnite pumpellyite facies in the bracco unit which has additionally been affected by rodingitization u pb zircon ages of 150 1 153 1 and 156 ma were obtained respectively for two plagiogranites and the host fe diorite in the ligurian alps and an age of 153 1 ma was determined for the plagiogranite in northern apennines inherited components in zircon and initial pb in plagioclase indicate mixing of variously differentiated basaltic magmas with small amounts of roughly 1 7 2 1 ga old continental crust material ree patterns in both the plagiogranites and the host diorite are characterized by high ree abundance and moderate lree enrichment nd isotopic compositions lie in the range of n morb sources yielding initial epsilon nd values between 8 8 and 9 7 whereas sr is isotopically heterogeneous the geochemical pattern of the plagiogranites and the host fe diorite requires melting of a morb type mantle source that experienced lree enrichment shortly before melting the most likely explanation for such enrichment is the injection of melts derived by small degrees of melting from an adjacent mantle region the basaltic lree enriched parent magmas generated from this enriched domain have probably undergone up to about 72 of low pressure fractional crystallization prior to their emplacement into the gabbro peridotite complex the 156 150 ma magmatism occurred in close relation to normal faulting sedimentation of breccias and detachment of the mantle complex from its overlying continental crust followed by exposure on the ocean floor this tectono magmatic event in the ligurian alps and the northern apennines reflects rifting of the adriatic iberian continental plate segment preceding wider opening of the piedmont ligurian ocean basin and pillow basalt deposition

the application of zircon cathodoluminescence imaging th u pb chemistry and u pb ages in interpreting discrete magmatic and high grade metamorphic events in the north china craton at the archean proterozoic boundary abstract two distinct late neoarchean to early paleoproterozoic magmatic events are recognized at the northern margin of the eastern block of the north china craton based on interpretation of zircon structure cathodoluminescence signature th u pb chemistry and age the first event is represented by emplacement of the chaihe trondhjemite and xianjinchang tonalite with magmatic zircon core ages ranging from 2559 2553 7 ma respectively these rocks experienced a subsequent high grade metamorphic event constrained by partial recrystallization of primary magmatic zircon and growth of new zircon rims between 2517 and 2490 ma a second magmatic episode generated by partial melting of crustal rocks during this metamorphic event is represented by the hongshilazi syenogranite with an age of 2502 11 ma the short time interval between initial magmatism and high grade regional metamorphism signifies they were related to the same major tectonothermal event when considered along with evidence of a similar sequence of events at this time 800 km to the south in eastern hebei and the previously established 2500 ma age of granulite facies metamorphism in mafic rocks across the craton it is proposed that a large mantle plume developed beneath the north china craton at the close of the archean

connecting source and transport suspended sediments in the nepal himalayas understanding the dynamics of sediment fluxes is a key issue to constrain modern erosion rates in mountain belts and determine the still debated level of control exerted by precipitation topography and tectonics the well defined monsoon seasonality in the himalayas together with active tectonics and strong relief provide an ideal environment to assess these possible interactions for this purpose we present a new compilation of daily suspended sediment data for 12 stations of the major rivers of the nepal himalayas we analyze the relationships of sediment transport with daily river discharge and precipitation data as well as with morphometric parameters we show that suspended sediment concentrations vary systematically through the seasons and asynchronously to river discharge displaying a hysteresis effect this clockwise hysteresis effect disappears when suspended sediment fluxes are directly compared with direct storm discharge therefore we attribute the hysteresis effect to groundwater dilution rather than a sediment supply limitation we infer a rating model to calculate erosion rates directly from long river discharge chronicles we show that when normalized by drainage area and mean sediment flux all rivers exhibit the same trend this similarity implies that all river basins have the same erosion behavior independent of location size and catchment characteristics erosion rates calculated from suspended sediment fluxes range between 0 1 and 2 8 mm yr the erosion rates of the three main basins of nepal are in the range 0 9 1 5 mm yr erosion rates in the higher himalayas are relatively low 0 5 mm yr except for kali gandaki while in the lesser himalayas they range from 0 2 to 2 mm yr we propose that material transport in the rivers depends on hillslope sediment supply which is in turn controlled by those rainfalls producing direct runoff in other words the rivers in the nepal himalayas are supply limited and the hillsopes as a contributing source are transport limited we also show that erosion processes are not as much controlled by infrequently occurring extreme precipitation events than by moderate ones with a high recurrence interval

mobilization of ree during crustal aging in the troodos ophiolite cyprus ree data for secondary minerals from low and high temperature alteration environments in the troodos ophiolite have been determined using a combined mass spectrometry neutron activation technique smectite and analcime ree mimic fresh rock profiles and have concentrations ranging from 1 5 times chondritic values celadonite is depleted in lree and total ree relative to the rocks groundmass replacing chlorite and epidote are similar to or enriched in ree relative to fresh rocks in contrast fault related chlorite and void filling epidote are lree enriched with large positive eu anomalies and yield comparable ree profiles to those of hydrothermal fluids venting at mid ocean ridges the zeolites clinoptilolite and laumontite are also lree enriched with ree contents significantly lower than rock values carbonate is enriched in hree relative to lree and concentrations vary from 0 2 to 18 times chondritic values ree data for these minerals indicate that seawater ree contents are modified by seawater rock interaction in volcanic sequences and sheeted dykes in oceanic crust during axial hydrothermal alternation and subsequent crustal aging the absolute and relative abundances of ree in seawater derived solutions evolve in response to the precipitation of secondary minerals and the prevailing water rock ratios rocks altered at low temperatures will show no change or a decrease in ree content the lree hree ratio will reflect the proportion of smectite celadonite and carbonate in the groundmass assemblage in contrast rocks altered at high temperatures will show no change or an increase in ree the lree hree ratio will reflect the proportion of void filling and groundmass replacing chlorite and epidote in the rock

contemporary versus long term denudation along a passive plate margin the role of extreme events short term contemporary and long term denudation rates were determined for the blue mountains plateau in the western sydney basin australia to explore the role of extreme events wildfires and catastrophic floods in landscape denudation along a passive plate margin contemporary denudation rates were reconstructed using 40 years of river sediment load data from the nattai catchment in the south west of the basin combined with an analysis of hillslope erosion following recent wildfires long term denudation rates 10 kyr 10 myr were determined from terrestrial cosmogenic nuclides apatite fission track thermochronology and post basalt flow valley incision contemporary denudation rates average several times lower than the long term average 5 5 4 mm kyr 1 versus 21 5 7 mm kyr 1 erosion of sediment following wildfires accounts for only a small proportion 5 of the contemporary rate most post fire sediment is stored on the lower slopes and valley floor with the amount transported to the river network dependent on rainfall run off conditions within the first few years following the fire historical catastrophic floods account for a much larger proportion 35 of the contemporary erosion rate and highlight the importance of these events in reworking stored material evidence for palaeofloods much larger than those experienced over the past 200 years suggests even greater sediment export potential mass movement on hillslopes along valleys incised into softer lithology appears to be a dominant erosion process that supplies substantial volumes of material to the valley floor it is possible that a combination of infrequent mass movement events and high fluvial discharge could account for a significant proportion of the discrepancy between the contemporary and long term denudation rates copyright 2006 john wiley sons ltd

reduced sediment supply in a fast eroding landscape a multi proxy sediment budget of the upper rhone basin central alps alpine water and sediment supply influence the sediment budget of many important european fluvial systems such as the rhine rhone and po rivers in the light of human induced climate change and landscape modification it becomes increasingly important to understand the mechanisms of sediment production and supply in alpine sediment systems this study aims to investigate the modern sediment budget of the upper rhone basin one of the largest alpine intramontane watersheds located in the central alps of southwestern switzerland major areas of sediment generation are fingerprinted by framework petrography heavy mineral concentrations and bulk geochemistry the relative contributions of the three major sources to the sediment of the trunk rhone river are identified by compositional mixing modelling concentrations of the terrestrial cosmogenic nuclide 10be measured in quartz separated from fluvial sediments provide spatially averaged denudation rates for selected tributary basins results from sediment fingerprinting and mixing modelling suggest that tributaries located in the north and the east of the catchment are generating most of the sediment transported by the rhone river to its primary sedimentary sink in lake geneva despite having some of the highest denudation rates within the basin tributaries located in the southern area of the rhone basin are relatively underrepresented in the sediment budget of the rhone river these tributaries are severely affected by human activities for example through sediment mining as well as water and sediment abstraction in large hydropower reservoirs together these processes reduce the basin wide sediment discharge by about 50 thereby explaining most of the observed compositional pattern in addition there is evidence suggesting that large amounts of glaciogenic sediments are currently supplied by retreating glaciers glaciogenic material with its low 10be concentrations can lead to a significant overestimation of denudation rates and thus limit the applicability of cosmogenic nuclide analysis in such glaciated settings

the mobility of zirconium and other immobile elements during hydrothermal alteration abstract development of zircon and other zr phases in hydrothermal deposits indicates that zr can be highly mobile in these systems mobility is most common in but not restricted to f rich hydrothermal systems related to alkalic f rich igneous suites these suites can range from peralkaline through metaluminous to peraluminous a few examples are neither alkalic nor f rich three locations in the trans pecos magmatic province texas u s a demonstrate this hydrothermal zr mobility all three igneous systems are alkalic and f rich but vary in alkali al ratios peralkaline rhyolites and trachytes in the christmas mountains contain as much as 2100 ppm zr mostly in aegirine or arfvedsonite zircon is rare or absent fluorspar replacement deposits in limestone at contacts with the rhyolites contain as much as 38 000 ppm zr occurring as small disseminated zircons the deposits also are enriched in a variety of incompatible elements including be rare earth elements ree y nb mo hf pb th and u the sierra blanca intrusions a series of mildly peraluminous f rich rhyolite laccoliths contain as much as 1000 ppm zr mostly as zircon hydrothermal zircon occurs as overgrowths on magmatic grains as veinlets connected to overgrowths and in fluorspar replacement bodies in adjacent limestone the highest zr concentrations in fluorspar are 200 ppm metaluminous quartz monzonite from the infiernito caldera contains 400 600 ppm zr mostly as zircon euhedral zircon in quartz fluorite veins in the quartz monzonite indicates mobility of zr zirconium concentrations in the veins are unknown but the paucity of zircon suggests little zr enrichment relative to the host zircon and more rarely zirconolite occur in skarn in the ertsberg district of irian jaya indonesia unlike in texas related igneous rocks are metaluminous and the hydrothermal system was f poor worldwide hydrothermal zircon other zr phases and ti and al bearing phases occur in skarn epithermal precious metal veins volcanogenic massive sulfide deposits and mylonites we propose that differences in zr mineralogy of igneous source rocks is an important factor in determining the availability of zr to hydrothermal fluids although zr concentrations in the sierra blanca and christmas mountains rhyolites are similar zr enrichment in fluorspar was much greater in the christmas mountains we suggest that hydrothermal solutions could easily break down aegirine and arfvedsonite to release zr but that zircon was only moderately attacked therefore far more zr was available for transport and subsequent deposition in the christmas mountains than at sierra blanca availability of other trace elements probably is also governed by their mineral host although zr mobility is most common in f rich hydrothermal systems related to alkalic and f rich igneous systems mobility at ertsberg may have been promoted by sulfate complexing

tectonic evolution of the north qinling orogen from subduction to collision and exhumation evidence from zircons in metamorphic rocks of the qinling group abstract the north qinling block nqb is an important segment of the qinling orogen in central china here we report the results from sims geochronology and oxygen isotopes as well as la mc icpms hf isotopic analyses on zircon grains from a suite of metamorphic rocks felsic gneisses garnet plagioclase amphibolites and retrograde eclogite dikes in the qinling group of the nqb the age data show that these rocks underwent at least two episodes of metamorphism with the peak at 483 501 ma followed by 454 470 ma retrograde metamorphism these results are generally coeval with the periods of 500 480 ma for peak metamorphism and 460 420 ma for retrograde metamorphism previously obtained from the hp uhp metamorphic rocks of the nqb during the prograde and retrograde metamorphism widespread fluid and melt circulation within the block has been identified from the geochemical features of the metamorphic zircons the fluids that circulated in the felsic gneisses and retrograde eclogite dikes originated from the dehydration of altered oceanic basalts as inferred from the exceedingly low th u ratios positive ehf t 5 and extremely 18o 10 01 13 91 values in metamorphic zircons in contrast the melt involved in the formation of garnet plagioclase amphibolites appears to have been derived from continental sediments interlayered with the oceanic basalts since zircons crystallized during the peak and retrograde metamorphism show typical magmatic features with high u and th contents and th u ratios and enriched hf ehf t 5 42 to 0 18 and oxygen isotope composition 18o around 8 geochronological and geochemical features of the magmatic cores of the clear core rim textured zircons demonstrate that the protoliths of the gneisses were intermediate acid volcanic rocks erupted before neoproterozoic 800 ma which is further supported by the intrusion of basaltic magma of asthenospheric origin as represented by protoliths of retrograde eclogite dikes with the oldest magmatic zircon formed at 789 ma the protoliths of garnet plagioclase amphibolites appear to be altered oceanic basalts but had been significantly affected by the melt during the metamorphism combined with the previous studies the qinling group experienced overall subduction in the early paleozoic the nqb as represented by the qinling group was most likely a discrete micro block in the neoproterozoic and underwent deep subduction in the cambrian 483 501 ma and exhumation in ordovician 454 470 ma we propose that the nqb preserves a complete cycle of tectonic evolution of an orogen from an oceanic basin spreading and micro continent formation to deep subduction and exhumation

hillslope channel sediment transfer in a slope failure event wet swine gill lake district northern england this paper describes and analyses a hillslope channel slope failure event that occurred at wet swine gill lake district northern england this comprised a hillslope slide 180 m3 c 203 36 t which coupled with the adjacent stream resulting in a channelized debris flow and fluvial flood the timing of the event is constrained between january and march 2002 the hillslope failure occurred in response to a rainfall snowmelt trigger on ground recently disturbed by a heather moorland fire and modified by artificial drainage slide and flow dynamics are estimated using reconstructed velocity and discharge values along the sediment transfer path there is a rapid downstream reduction in both maximum velocity from 9 8 to 1 3 m s 1 and maximum discharge ranging from 33 5 to 2 4 m3 s 1 a volumetric sediment budget quantified a high degree of coupling between the hillslope and immediate channel 92 167 m3 but virtually all of the sediment was retained in the first order tributary channel approximately 44 81 m3 of the slide volume was retained in the run up deposit and termination of the debris flow prior to the main river meant that the remainder did not discharge into the fluvial system downstream these results suggest poor transmission of sediment to the main river at the time of the event but importantly an increase in available material for post event sediment transfer processes within the small upland tributary

palaeoproterozoic metasedimentary rocks of the ji an group and their significance for the tectonic evolution of the northern segment of the jiao liao ji belt north china craton in this paper we present new petrological and whole rock geochemical data for the palaeoproterozoic metasedimentary rocks in the upper part of the ji an group within the jiao liao ji belt china as well as zircon u pb age dates and in situ lu hf isotope data the new data improve our understanding of the original nature of the metasedimentary rocks further providing insights into their tectonic setting and the evolutionary history of the northern segment of the jiao liao ji belt the zircons can be divided into two groups viz one of magmatic origin and the other of metamorphic origin zircon u pb dating gave mean or statistical peak ages for the magmatic zircons at 2035 2082 2178 2343 2421 2451 2545 2643 2814 and 2923 3446 ma and mean peak ages for the metamorphic zircons at 1855 and 1912 ma which indicate a maximum depositional age of 2 03 ga and two stage metamorphic events at c 1 91 and 1 85 ga for the metasedimentary rocks geochemical data show that 1 the protoliths of these rocks were mainly sandstones greywackes and claystones together with some shales 2 the main sources of the sedimentary material were palaeoproterozoic granites and acid volcanic rocks with minor contributions from archaean granitic rocks and 3 the sediments were deposited in an active continental margin setting moreover along the northeastern margin of the eastern block of the north china craton there is evidence of ancient crustal materials as old as 3 76 ga and multiple crustal growth events at 3 23 3 05 2 80 2 65 2 54 2 45 and 2 28 2 08 ga

ion microprobe zircon u pb age and geochemistry of the myanmar jadeitite combined geochemistry and geochronology of the myanmar jadeitite were determined bulk rock trace element compositions display u shaped ree patterns with pronounced positive eu anomalies the total ree abundances are very low less than half chondritic and the high field strength elements and some large ion lithophile elements are moderately enriched these features indicate a metasomatic origin there are three groups of zircons with different interior characteristics cathodoluminescence mineral inclusions chemical compositions and sensitive high resolution ion microprobe u pb ages group i zircons with a mean age of 163 2 3 3 ma mostly have distinct oscillatory zoning highest u and th contents and na free mg rich mineral inclusions and thus indicate an igneous formation of oceanic crust or hydrothermal serpentinization and or rodingitization event in the middle jurassic group ii zircons with a mean age of 146 5 3 4 ma have bright luminescence without oscillatory zoning and include jadeite and jadeitic pyroxene inclusions suggesting that formation of the myanmar jadeitites as well as subduction of the eastern indian oceanic plate occurred in the late jurassic group iii zircons have an age of 122 2 4 8 ma which represents a later unknown thermal event discovery of the middle jurassic zircons provides geochronological constraint on the tectonic evolution of the eastern indo burman range

the hofðaholar rock avalanche sturzstrom chronological constraint of paraglacial landsliding on an icelandic hillslope the hof aholar rock avalanche in the skagafjor ur area of northern iceland was investigated on the basis of a geomorphological analysis of its landforms and close surrounding environment thanks

sediment erosion dynamics of a gullied debris slide a medium term record medium term post event sediment flux investigations are rare for headwater catchments and particularly sparse for gullied hillslope failures repeat field observation ground photography and cross section measurements of a debris slide scar at the wet swine gill headwater catchment 0 65 km2 in the english lake district uk provide evidence of erosion and deposition dynamics over the medium term 2002 2014 these data are compared to site topographic and meteorological conditions to evaluate potential process response linkages rill and gully erosion networks establish soon after the slide failure 1 february 2002 thereafter gully enlargement proceeds rapidly first by vertical downcutting prior to lateral expansion and gully wall angle decline changes in cross sectional width depth and area 2002 2013 are characterised by statistically significant p 0 05 negative exponential growth models r2 width 0 88 0 97 depth 0 71 0 86 area 0 87 0 93 gully walls were dominated by erosion but the gully bed was characterised by episodic sediment production storage and transfer often leading to temporary deposition specific erosion rates on the gully wall exceeded those on the adjacent slide scar by up to 764 maximum values wall 0 0084 scar 0 0011 m2 m 1 d 1 upslope contributing runoff area and slope gradient are generally important for erosion although linear regression analysis demonstrates weak or insignificant relationships between meteorological conditions and gully scar sediment flux a general conceptual model of slide scar evolution integrating gully growth and capture summarises activity at this site however transferability to locations with terrain characteristics land management practices and climate conditions different to those existing in the uk uplands remains to be tested this investigation adds to growing appreciation of the complexities of sediment dynamics in headwater catchments and provides clear evidence for the potential of early management intervention to counter detrimental post failure sediment erosion which at this site would have been most effective up to 3 4 years following gully initiation

dissolved rare earth elements in the southern ocean cerium oxidation and the influence of hydrography abstract analysis of dissolved ree distributions in the southeastern atlantic ocean has revealed that progressive oxidative removal of dissolved ce from deepwater 1 km occurs over the mixing time of the oceans ce anomaly ce ce values measured in deep waters from the southeastern atlantic are similar to but slightly higher than those from deep ocean stations throughout the indian and pacific oceans typically falling in the range 0 08ce ce 0 12 only deepwater samples from the north atlantic exhibit values greater than ce ce 0 12 with the exception of southeastern atlantic bottomwaters which are influenced by antarctic bottomwater covariation of dissolved ree concentrations with salinity and or dissolved si concentrations at this site has allowed dissolved ree compositions for various southern ocean water masses to be predicted end member concentrations for antarctic bottom water aabw derived in this way indicate high dissolved ree concentrations similar to average pacific deep water but with significantly enhanced dissolved ce concentrations and less pronounced hree enrichment this result is consistent with the proximity of our study site to active aabw deepwater formation and evolution of that water mass during transport to the pacific ocean

epigenetic gorges in fluvial landscapes epigenetic gorges form when channels that have been laterally displaced during episodes of river blockage or aggradation incise down into bedrock spurs or side walls of the former valley rather than excavating unconsolidated fills and reinhabiting the buried paleovalley valley filling events that promote epigenetic gorges can be localized such as a landslide dam or an alluvial debris flow fan deposit at a tributary junction or widespread such as fluvial aggradation in response to climate change or fluctuating base level the formation of epigenetic gorges depends upon the competition between the resistance to transport strength and roughness of valley filling sediments and a river s ability to sculpt and incise bedrock the former affects the location and lateral mobility of a channel incising into valley filling deposits the latter determines rates of bedrock incision should the path of the incising channel intersect with bedrock that is not the paleovalley bottom epigenetic gorge incision by definition post dates the incision that originally cut the valley strath terraces and sculpted bedrock walls that form in relation to epigenetic gorges should not be used to directly infer river incision induced by tectonic activity or climate variability rather they are indicative of the variability of short term bedrock river incision and autogenic dynamics of actively incising fluvial landscapes the rate of bedrock incision associated with an epigenetic gorge can be very high 1 cm yr typically orders of magnitude higher than both short and long term landscape denudation rates in the context of bedrock river incision and landscape evolution epigenetic gorges force rivers to incise more bedrock slowing long term incision and delaying the adjustment of rivers to regional tectonic and climatic forcing copyright 2008 john wiley sons ltd

seafloor slopes at mid ocean ridges from submersible observations and implications for interpreting geology from seafloor topography abstract observations from 145 submersible dives are used to create a database of mid ocean ridge scarp topography and lithology seafloor lithologies are classified into extrusives basaltic talus dykes gabbros and serpentinites and the dive locations are broadly classified according to whether they are close to transform valleys and as a function of ridge spreading rate the database is used to determine whether there is any difference in the maximum slope for each rock type which might relate to differences in rock jointing cohesion or friction properties there is a common perception that lower crustal rocks form steeper slopes than shallower crustal rocks but until now there has been little evidence to support or refute this idea from our analysis we find a tendency for gabbro and dykes to form steeper slopes than serpentinite the 90th percentile of each lithology slope distribution used as a measure of limiting slope is 43 39 and 32 for gabbro dykes and serpentinite respectively lithologic control on slope is weak however compared to overall slope variability in these mid ocean ridge settings so seafloor relief is likely to be a poor guide to underlying geology we speculate on the structure of eroding fault scarps outline the implications for attempts to infer active faults from talus ramp activity and discuss more generally factors affecting the geomorphology of mid ocean ridge slopes

development of rodingite in basaltic rocks in serpentinites east liguria italy hydrogrossular replacement of plagioclase in basaltic rocks enclosed in serpentinite and relationships between hydrogrossular pumpellyite vesuvianite are described rogingitic rocks are dominated by mixed layer chlorite smectite chlorite pumpellyite hydrogrossular and vesuvianite in these rocks pumpellyite attains maximal mg contents and chemical analysis shows extreme removal of na2o k2o tio2 and sio2 from the basalts and increase in the fe3 fe2 ratio leaching during serpentinization by extremely alkaline solutions dominated by ca mg oh may explain removal of components but the oxidation may suggest that at an earlier stage dykes may have acted as input aquifers

re interpreting the devonian ophiolites involved in the variscan suture u pb and lu hf zircon data of the moeche ophiolite cabo ortegal complex nw iberia new u pb zircon data of a mylonitic greenschist from the moeche ophiolite one of the mafic units involved in the variscan suture in the cabo ortegal complex nw of the iberian massif yielded an age of 400 3 ma consequently this unit can be considered one of the devonian ophiolites the most extended group of oceanic units in the variscan belt the mafic rocks show transitional compositions between n morb and island arc tholeiites although lu hf isotope signatures of its zircons clearly indicate contribution from an old continental source ehf values in the analysed zircons are negative generally below ehf 5 and thence they are not compatible with their generation from a juvenile mantle source accordingly the igneous protoliths were generated in a setting where juvenile mafic magmas interacted with an old continental crust the devonian ophiolites from the variscan suture have been repeatedly interpreted as remnants of the rheic ocean however the presence of a continental source in the origin of the mafic rocks of the moeche ophiolite allows discarding an intraoceanic setting for their generation at least for the nw iberian counterparts the tectonic setting for the devonian ophiolites of nw iberia is very likely represented by an ephemeral oceanic basin opened within a continental realm herein the real rheic ocean suture could only be located west of the terrane represented by the upper units of the allochthonous complexes apparently that suture is not represented in nw iberia

upper paleozoic oceanic crust in the polish sudetes ndsr isotope and trace element evidence the two main mafic ultramafic complexes outcropping in the polish sudetes around the sowie gory high grade massif mt sleza and nowa ruda have been studied for trace elements and nd sr isotopes upper paleozoic sm nd whole rock isochron ages are obtained for both massifs 353 21 ma 2 with i 8 8 0 1 mt sleza and 351 16 ma with i 8 5 0 1 nowa ruda the high initial nd point to a source characterized by a strong time integrated lree depletion and along with incompatible trace element patterns they substantiate the oceanic derivation of these massifs although a subduction related marginal basin setting cannot be totally precluded trace element and isotopic data rather suggest a normal mid ocean ridge origin for the sudetic ophiolites while these results are in marked contrast with previously inferred precambrian or early paleozoic ages remnants of oceanic crust as young as the early carboniferous are consistent with the local sedimentary record of pelagic facies from the frasnian to the tournaisian and they may provide a suitable explanation for the contrasted evolution displayed by different domains of the sudetes the sudetic ophiolites might tentatively be correlated with the upper paleozoic prasinites of the saxon lineament if a late hercynian ca 150 km dextral offset is assumed along the elbe fracture in that case they might represent the latest stage remnants of an oceanic suture zone between the saxo thuringian and moldanubian zones together with several other examples throughout europe these ophiolites provide compelling evidence for the involvement of oceanic crust and plate tectonic processes in the variscan belt

interpreting erosion rates from cosmogenic radionuclide concentrations measured in rapidly eroding terrain a combination of numerical analysis and 10be concentrations measured in sediment samples from the high relief torrente catchment southern spain allows us to investigate the sampling requirements for determining erosion rates using cosmogenic nuclides in high relief landslide dominated terrain we use simple modelling to quantify the effect of particle spalling and or landsliding on erosion rates determined using a cosmogenic in situ produced isotope analytical results show that the cosmogenic nuclide concentration of a surface experiencing regular detachment of a grain or block may be considered to be in steady state and in situ erosion rates estimated when an appropriate number of spatially independent samples are amalgamated we present equations that enable calculation of the number of bedrock samples that must be amalgamated for the estimation of mean erosion rates on an outcrop experiencing regular detachment of a grain or chip of thickness l every t years our findings confirm that mean catchment erosion rates may be reliably estimated from 10be concentrations in fluvial sediment in high relief rapidly eroding terrain these catchment wide integrated erosion rates can be calculated where erosion is primarily accomplished through shallow 3 m landslides are the dominant mode of erosion only minimum erosion rates can be determined lastly we present erosion rate measurements from the torrente catchment that reveal variation of two orders of magnitude 0 03 1 6 m ka 1 quantifying the high degree of spatial variation in erosion rates expected within rapidly uplifting catchments copyright 2006 john wiley sons ltd

continental breakup by detachment faulting field evidence and geochronological constraints tasna nappe switzerland the lower tasna detachment ltd is a low angle fault contact between serpentinized peridotite below and continental basement above it was formed during jurassic to early cretaceous rifting of a tethyan continental margin and later captured in a thrust nappe during tertiary plate convergence foliated gabbro gabbro mylonite and granitoid mylonite occurring along the ltd record shearing under decreasing temperatures u pb dating of zircon from the gabbro mylonite yielded a permian age interpreted as the age of gabbro intrusion whereas the breakup of the passive margin occurred as late as early cretaceous this suggests that the gabbro belongs to a prerift lower to middle crustal intrusion smeared out along the detachment by extensional faulting the juxtaposition of mantle and upper crust along the lower tasna detachment may serve as a model for several seismic reflectors observed in distal passive continental margins e g s reflector of the galicia margin

titanium mobility in metamorphic systems a review abstract titanium is a dispersed lithophile element commonly regarded as chemically immobile at sub magmatic temperatures however a growing number of field studies demonstrate that ti is somewhat mobile in certain environments this review examines the current state of knowledge concerning the mobility of ti during alteration and metamorphism of crustal rocks also considered are relevant ti oxide solubility data from experiments and determinations of ti concentrations in natural waters where ti mobility is well documented its length scale is 10 m however ti may move greater distances in deep crustal shear zones the solubility of ti oxides in geologic fluids is strongly temperature dependent under low to medium grade metamorphic conditions ti mobility is limited by the low solubility of ti oxides in the associated fluids under eclogite conditions ti mobility is probably limited not by ti oxide solubility which reaches 1 ti but by restricted fluid flow in low permeability rocks

rb sr and u pb geochronology of migmatitic gneisses from the gory sowie west sudetes poland the importance of mid late devonian metamorphism the gory sowie block west sudetes sw poland consists of a gneiss migmatite complex with minor amphibolites calc silicate rocks ultrabasic rocks and granulites migmatitic gneisses underwent a complex polyphase history of deformation and metamorphism each deformation phase d1 to d5 being associated with synkinematic amphibolite facies metamorphism m1 to m5 for a better understanding of the p t t deformation path three types of gneisses which represent distinct stages of deformation and metamorphism d2 m2 d3 m3 and d5 m5 have been studied by means of the rb sr and u pb isotopic systems u pb monazite and xenotime ages of c 380 ma for rocks migmatized and deformed during the d3 m3 and d5 m5 stages constrain the timing of the last metamorphic migmatitic event in the gory sowie block rb sr thin slab and mica whole rock dating for samples with d2 d3 and d5 characteristics provide ages between 362 and 375 ma which overlap within error 2o no correlation between deformational characteristics and apparent rb sr ages was recognized the rb sr data are interpreted as time constraints for post peak metamorphic cooling the new geochronological data indicate the significance of devonian high temperature metamorphism in the sudetes and support a similar interpretation of earlier studies the isotopic results are also consistent with the interpretation based on field structural and petrological data that at least four d2 d5 structural episodes occurred in devonian times within a very short time interval the details of which cannot be further resolved with the methods used

geological investigation of a lineated massif at the kane transform fault implications for oceanic core complexes recently available new perspectives on the morphology of the sea floor near the mid atlantic ridge reveal the widespread development of dome like massifs with lineated upper surfaces in form and dimensions these features resemble continental metamorphic core complexes developed in regions of large magnitude extension and thus may be oceanic core complexes excellent examples of these features occur south of the kane transform fault where high resolution geological data from side looking sonar deeply towed cameras and manned submersibles are available the geological data from two different massifs representing somewhat different types of crustal structure provide important constraints on the development of these oceanic core complexes inferences from these direct geological investigations of oceanic core complexes are a first step toward understanding the processes by which these features form in slow spread crust specific relationships in these massifs and nearby areas suggest that these structures have formed over significant lengths of ridge axis tens of kilometres and are not necessarily confined to any specific setting with respect to morphologic segmentation patterns in some cases they are developed in thick gabbroic crust but elsewhere have formed in crust composed serpentinite riddled with gabbroic intrusions ductile stretching and thinning of these sections is recorded in extensive mylonites and shear zones syntectonic gabbroic intrusions are widespread and contradict the notion that the massifs develop during intervals of amagmatic spreading cataclastic fault zones in gabbros and serpentinites developed during uplift cooling and hydration of the stretched crust and may have been localized as major detachment faults sparse diabase dikes and basaltic lavas are the latest magmatic additions to these areas numerous joints and steeply dipping small offset faults are the youngest observed structures across part of the top surface of one massif small scale faults appear to bound elongated ridges of fractured basement rocks creating the lineated terrain thus the extensive lineated surfaces nearby need not reflect prolonged displacement along a continuous detachment fault surface geological relationships developed in the dome like massifs along the kane transform fault hint at a complex array of processes involved in the evolution of these features and raise new questions regarding their origin and analogies with continental core complexes

thellier palaeointensity experiments on faroes flood basalts technical aspects and geomagnetic implications based on palaeomagnetic and rock magnetic results 108 samples from 27 flows from palaeogene flood basalts of faroe islands were chosen for whole rock thellier palaeointensity experiments altogether 90 samples were rejected due to either chemical alterations or typical multidomain md behaviour evidenced by ptrm tails af pre treatment was used to reduce the effect of md grains on thellier experiments only five flows 18 samples yielded acceptable palaeointensity estimates with flow mean vdms ranging from 3 5 to 7 4 10 22 am 2 modest selection criteria imposed on all published 5 160 ma palaeointensity data left only 15 palaeomagnetic dipole moments eight from whole rock samples six from submarine basaltic glass and one from single plagioclase crystals more data are needed before the intriguing differences between results from different materials can be put into a geomagnetic context 2002 elsevier science b v all rights reserved

evidence for a caledonian amphibolite to eclogite facies pressure gradient in the middle allochthon lindas nappe sw norway the proterozoic anorthosite mangerite charnockite complex dominating the lindas nappe in the scandinavian caledonides was locally eclogitized in the southwestern part of the nappe during the caledonian orogeny whereas only amphibolite facies assemblages are recorded in the rest of the nappe sveconorwegian granulites of anorthositic to jotunitic composition in the northernmost eclogite free exposures of the nappe exhibit large garnet phenoblasts ca 900 c that are fractured and partly replaced by a caledonian symplectitic amphibolite facies assemblage ca 515 c metamorphic zircon attributed to this garnet breakdown is dated by id tims u pb at 430 3 ma suggesting that the amphibolite facies overprint was coeval with the formation of eclogite 30 km further south probably implying that the section across the nappe represents a caledonian pressure gradient the rocks also preserve a complex sveconorwegian history including an age of 969 6 ma which we interpret as dating magmatic emplacement of jotunitic anorthositic portions of the complex 936 12 ma reflecting the granulite facies metamorphism and 908 16 ma representing a late generation of zircon best explained as having formed by metasomatic processes caledonian shearing severely deformed zircon grains in an amphibolite facies shear zone resetting their u pb systems and forming new ones hereby also demonstrating a case of resetting and recrystallization of low u zircon our data gained from diverse lithologies illustrate several processes involved in making and resetting zircon as well as indicate the contemporaneous evolution and similar origin of the lindas nappe and the jotun nappe complex

linking landslides hillslope erosion and landscape evolution this virtual issue highlights 10 recent innovative unconventional or otherwise significant contributions to earth surface processes and landforms that help advance the state of the art in research on linkages between landslides hillslope erosion and landscape evolution the selected studies address this feedback within a temporal spectrum that ranges from the event to the millennial scale thus underscoring the importance of detailed field observations high resolution digital topographic data and geochronological methods for increasing our capability of quantifying landslide processes and hillslope erosion copyright 2009 john wiley sons ltd

paleosols identified by rock magnetic properties indicate dam outburst events of the min river eastern tibetan plateau abstract river terrace sediments are archives of past fluvial processes and they may also reflect a wide range of additional environmental processes detailed studies of river terrace sediments are important for understanding the role of tectonics climate and extreme geomorphological events in fluvial evolution here we present a sedimentary reconstruction using the combination of field description magnetic measurements and optically stimulated luminescence and ams 14c dating of the maoxian mx section in the third terrace of the min river in the eastern margin of the tibetan plateau the section is mainly composed of clastic deposits and spans the interval from the last glacial to late holocene apart from the silt at the bottom and the gravel layer in the middle it is difficult to determine whether other clastic deposits were exposed sub aerially multiple magnetic proxies indicate that the mx section contains three layers of pedogenic production of fine grained magnetite maghemite which correspond to paleosol layers the paleosol layers indicate the occurrence of at least three intervals of exposure to the atmosphere the three paleosol layers were likely caused by dam outburst events the results demonstrate that rock magnetic methods are a useful approach for identifying paleosol layers in fluvial sediments

careon ophiolite nw spain suprasubduction zone setting for the youngest rheic ocean floor the careon ophiolite galicia nw iberian massif shows lithological and geochemical features suggestive of an origin in a suprasubduction zone setting as with other devonian ophiolites in the european variscan belt it was generated within a contracting rheic ocean this setting and the general absence of large silurian devonian volcanic arcs on both of the rheic ocean margins strongly suggest that this ocean was closed by intraoceanic subduction directed to the north this subduction removed the older normal n mid oceanic ridge basalt morb oceanic lithosphere and gave rise to a limited volume of new suprasubduction zone oceanic lithosphere the careon ophiolite is a key element in understanding the evolution of the rheic ocean which was the main oceanic domain that closed during the paleozoic convergence of gondwana and laurussia preceding the assembly of pangea

dissolved zirconium and hafnium distributions across a shelf break in the northeastern atlantic ocean abstract dissolved zr and hf distributions have been determined for five stations located across the shelf break in the northeastern atlantic ocean on the celtic approaches for stations in deep water the range in zr concentrations has been found to be 70 180 pmol kg and the range in hafnium concentrations 0 4 1 1 pmol kg the distributions with depth are indicative of a nutrient like scavenging regeneration behavior in seawater although the dissimilarity with silicate and nitrate for samples below the nutricline suggest that other mechanisms are also important in defining the oceanic distribution of these elements in contrast the concentrations of zr and hf at the station located closest to land are highest in surface waters and decrease with depth although salinity does not indicate dilution of seawater with freshwater with high zr and hf concentrations the ratio of dissolved zr to hf in seawater is higher and more variable than is found for the majority of terrestrial rocks or predicted from thermodynamic considerations fractionation due to small differences in their interactions with particulate material is implicated

subduction of water into the mantle history of an alpine peridotite the erro tobbio peridotite western alps is a slice of subcontinental mantle that underwent pre jurassic passive rifting followed by sea floor hydration and cretaceous alpine subduction analysis of its extension and subduction related structures and metamorphism suggest the dip below the adria plate of both the extensional detachments and the subduction plane high pressure boudinage structures of rigid metarodingite within ductile antigorite serpentinite prove that antigorite survived subduction and remained stable at eclogite facies conditions subduction of serpentinized peridotites from ophiolite slabs is here considered the most effective mechanism of bringing water to great depth within the mantle

a multi parameter field monitoring system to investigate the dynamics of large earth slides earth flows in the northern apennines italy abstract large earth slides and rocks lides evolving into earth flows are quite widespread in the northern italian apennines despite being simply referred to as landslides many of them are in fact large complexes of landslides they evolved through multiple and or successive movements undergoing partial and or total reactivations the reactivation of pre existing landslide bodies is the prevalent mechanism for the known landslide events as the historical records and the technical reports indicate landslide reactivation is indeed a relevant topic from the perspective of risk assessment and mitigation a multi parameter monitoring system was installed on a large complex of landslides that underwent partial or total reactivations after heavy rainfall events causing damages to buildings and infrastructures two clusters of automatic piezometers each coupled with an inclinometer and a time lapse resistivity deployment were the core of the monitoring system a weather station collecting data from subsurface thermometers and a water content probe completed the system after the construction of a new geological model of the slope this study aimed at understanding the possible mechanisms leading to the reactivation of the landslide this goal was achieved by gaining insights into the process of rainfall infiltration into the landslide deposits by determining the groundwater flow and evaluating the landslide displacements the monitoring system captured the processes that took place in the landslide bodies and the bedrock in response to a rainfall event in early february 2017 which followed a dry period of eight months the recorded data provided indications on the variation of the hydraulic head in the groundwater within the landslide and the bedrock particularly at the sliding surfaces the electrical conductivity of the groundwater and the resistivity of the terrain varied across the failure surfaces in particular a sudden increase in the electrical conductivity was related to the locations of the main sliding surfaces the joint analysis of time lapse resistivity hydraulic heads and groundwater electrical conductivity helped identify the locations of weaker levels within the landslide masses which were confirmed by data from inclinometers this study improved the knowledge of the hydrogeological behaviour of a complex of landslides in heterogeneous low permeability media moreover the obtained results contributed to the understanding of the role played by different portions of the landslide complex in the evolution of the movement

use of lidar derived images for mapping old landslides under forest large deep seated landslides are common features in the flemish ardennes belgium as most of these old 100 years landslides are located under forest in this hilly region aerial photograph interpretation is not an appropriate landslide mapping method this study tested the potential of lidar light detection and ranging images for mapping old landslides under forest landslide inventory maps were created for a 125 km2 area by applying the expert knowledge of seven geomorphologists to lidar derived hillshade slope and contour line maps in a gis environment each of the seven lidar based landslide inventories was compared i with the other six ii with a detailed field survey based inventory and iii with a comparable study in which topographic data were extracted from a topographical map the combination of the percentage of field landslides indicated by an expert and the percentage of positional discrepancies expressed in terms of positional mismatch were used to evaluate the quality of the lidar based inventory maps high quality lidar derived landslide inventory maps contain more than 70 per cent of the landslides mapped during the field survey and have positional discrepancies smaller than 70 per cent when compared with the field survey based inventory map four experts and the combination map of all experts satisfied these criteria together the seven experts indicated all landslides mapped in the field importantly lidar enabled the experts to find ten new landslides and to correct the boundaries of eleven of the 77 landslides mapped during the field survey hence this study showed that large scale lidar derived maps analysed by experienced geomorphologists can significantly improve field survey based inventories of landslides with a subdued morphology in hilly regions copyright 2006 john wiley sons ltd

the central sudetic ophiolites sw poland petrogenetic issues geochronology and palaeotectonic implications abstract the central sudetic ophiolites cso including the largest and best studied leza ophiolite are relatively well preserved complete palaeozoic ophiolitic sequences at the ne margin of the bohemian massif near the eastern edge of the variscan belt in central europe despite a detailed study and a well documented morb type affinity the geochemical complexity of these ophiolites has only recently been appreciated allowing construction of petrogenetic models we review here petrological and geochemical data indicating a contrast between the plutonic and volcanic members of the leza ophiolite this contrast was previously interpreted in terms of a model of two stage incremental melting of a depleted asthenospheric source producing basaltic magmas and subsequent melts crystallizing as gabbros however we argue that the geochemical differences between the plutonic and volcanic members can be explained by differentiation and cumulation processes of broadly similar parental magmas preliminary interpretation of new shrimp zircon age data from plutonic and volcanic members are consistent with earlier u pb zircon ages and provide evidence for magmatic crystallization of the leza ophiolite at c 400 ma the cso interpreted as traces of the rheic ocean are key for reconstructing the early to mid palaeozoic rifting processes distinct similarities exist with time equivalent ophiolitic units in the western variscan segment of the nw iberian massif the cso represent c 400 ma oceanic crust fragments and their structural position delineates likely major variscan tectonic sutures and tectonic mosaic domains within the variscan accretionary prism

modeling sediment movement and channel response to rainfall variability after a major earthquake abstract the 2008 wenchuan ms 8 0 earthquake caused severe destruction in the mountainous areas of sichuan province china landslips and mass movements led to substantial amounts of loose sediment accumulating in valleys that subsequently led to widespread riverbed aggradation in addition to erosion and deposition hazards this aggradation produced rivers in earthquake affected areas that were more susceptible to flash floods under extreme rainfall events however fluvial processes and sediment movement after a major earthquake as well as the re working of sediments in future events are not well studied in this paper we investigate the response of sediment and river channel evolution due to different rainfall scenarios after the wenchuan earthquake by using the caesar lisflood model this is the first time that this landscape evolution model has been employed to explore material migration processes in a post earthquake area and to test its applicability to real landform changes in the studied catchment the caesar lisflood model is well suited to simulate sediment movement particularly the fluvial processes driven by severe rainfall after an earthquake we calibrated the model parameters to the 2013 extreme rainfall event using high resolution satellite images under rainfall scenarios of different intensity and frequency over a 10 yr period landform evolution and sediment migration in the post earthquake area were simulated the results showed that the sediment yield could be significantly increased under enhanced and intensified rainfall scenarios compared to a normal rainfall scenario these findings are of importance for the planning of post earthquake rehabilitation and regional sustainable development which considers risk prevention and mitigation

comparative fe and sr isotope study of nephrite deposits hosted in dolomitic marbles and serpentinites from the sudetes sw poland implications for fe as au bearing skarn formation and post obduction evolution of the oceanic lithosphere abstract nephrites belonging to both the dolomite related and serpentinite related genetic types from the zloty stok deposit and jordanow l ski and naslawice prospects in the leza ophiolite respectively were analyzed for fe and sr isotope compositions these deposits in the central sudetes sw poland are unusually situated relatively close to each other this study is a first attempt to perform combined fe and sr isotope study of nephrites our results show that fe in the fe as au bearing skarn samples from zloty stok 2 77 7 00 wt fe 56fe 0 07 to 0 14 and 57fe 0 12 to 0 21 to which the dolomite related nephrite belongs is not inherited from the host dolomitic marbles ca 0 4 wt fe 56fe 0 08 to 0 07 and 57fe 0 12 to 0 09 but derived from the nearby ca 340 ma granite intrusion 2 64 5 64 wt fe in contrast iron in the serpentinite related nephrites 2 06 3 88 wt fe 56fe 0 41 to 0 45 and 57fe 0 59 to 0 66 was likely inherited from host serpentinites 5 27 4 81 wt fe rather than metasomatically derived from adjacent granite intrusions 0 13 0 45 wt fe moreover both the marble transformation into a dolomite related nephrite and fe as au bearing skarn and the abyssal serpentinite through ophiolite towards serpentinite related nephrite transformation are accompanied by a progressive increase of 56fe and 57fe this increase is regardless of changes in the bulk fe content increasing during the dolomite related nephrite formation and decreasing during serpentinite related nephrite formation this phenomena may be caused by one of the below listed factors or combinations a preferential incorporation of heavy iron by tremolite and diopside b preferential incorporation of the heavy iron in the fe3 bearing phases crystallizing during nephrite formation c preferential incorporation of the heavy fe from migrating granite derived fluids positive fractionation between aqueous fe bearing fluid and tremolite diopside d positive isotope fractionation between dolomite antigorite precursor and newly formed amphibole clinopyroxene e change of the fe oxidation state furthermore fe in the rock forming tremolite from the serpentinite related nephrites is isotopically heavier than fe in tremolite from the dolomite related ones in contrast to the iron the isotopic composition of strontium combined with its content and structural evidence suggest multiple sources for this element in the case of the dolomite related nephrite ca 3 4 ppm sr initial 87sr 86sr 0 7085 sr inheritance from the host dolomitic marble ca 90 ppm sr initial 87sr 86sr 0 7081 as well as its derivation from intrusions of both the syn to late tectonic ca 340 ma granites ca 400 440 ppm sr and post tectonic 305 ma granites 86 4 ppm sr is suggested in the case of the serpentinite related nephrite 6 3 61 7 ppm sr initial 87sr 86sr 0 7037 to 0 7081 the situation is similar i e sr in the most primitive samples tends to be sourced from ophiolitic rocks up to 2 4 ppm sr in serpentinite whereas in the more evolved types it was likely delivered from the adjacent ca 340 ma 8 8 102 6 ppm sr partially rodingitized granites as well as 305 ma granites ca 80 ppm sr moreover these granites caused the fluid flow responsible for sr bearing clinozoisite vein formation these veins are likely related with nephrite formation and with a metallic mineralization

metamorphic zirconology of continental subduction zones abstract zircon is widely used to date geological events and trace geochemical sources in high pressure hp to ultrahigh pressure uhp metamorphic rocks of continental subduction zones however protolith zircons may be modified by three different types of metamorphic recrystallization via mechanisms of solid state transformation metasomatic alteration and dissolution reprecipitation new zircon growth may be induced by dehydration reactions below the wet solidus of crustal rocks metamorphic zircon or peritectic reactions above the wet solidus peritectic zircon as a consequence there are different origins of zircon domains in high grade metamorphic rocks from collisional orogens thus determining the nature of individual zircon domains is substantial to correct interpretation of their origin in studies of isotopic geochronology and geochemical tracing we advocate an integrated study of zircon mineragraphy internal structure and external morphology u pb ages mineral inclusions trace elements and lu hf and o isotope compositions only in this way we are in a position to advance the simple zircon applications to metamorphic zirconology enabling discrimination between the different origins of zircon and providing constraints on the property of fluid activity at subduction zone conditions the metamorphic recrystallization of protolith zircons and the new growth of metamorphic and peritectic zircons are prominent in hp to uhp metamorphic rocks of collisional orogens these different types of recrystallized and grown zircons can be distinguished by their differences in element and isotope compositions while the protolith nature of metamorphosed rocks dictates water availability the p t conditions of subduction zones dictate the property of subduction zone fluids the fluids of different properties may be produced at different positions of subducting and exhuming crustal slices and they may physically and chemically mix with each other in continental subduction channels such fluids can act as an important agent not only for the physical transport of protolith zircons but also for the chemical transport of element zr and other fluid mobile incompatible trace elements from the subducted crust to the mantle wedge therefore the discrimination between the different types of zircons provides a powerful means to decipher the role of fluids in subduction zone processes