exhumation processes during post collisional stage in the variscan belt revealed by detailed 40ar 39ar study tanneron massif se france detailed 40ar 39ar geochronology on single grains of muscovite was performed in the variscan tanneron massif se france to determine the precise timing of the post collisional exhumation processes thirty two plateau ages obtained on metamorphic and magmatic rocks sampled along an east west transect through the massif vary from 302 2 to 321 2 ma and reveal a heterogeneous exhumation of the lower crust that lasted about 20 ma during late carboniferous in the eastern part of the massif the closure of the k ar isotopic system is at 311 315 ma whereas in the middle part of the massif it closes earlier at 317 321 ma these cooling paths are likely to be the result of differential exhumation processes of distinct crustal blocks controlled by a major ductile fault the la moure fault that separates both domains in the western part of the massif the ages decrease from 318 to 303 ma approaching the rouet granite which provides the youngest age at 303 6 1 2 ma this age distribution can be explained by the occurrence of a thermal structure spatially associated to the magmatic complex these ages argue in favour of a cooling of the magmatic body at around 15 ma after the country rocks in the western tanneron the emplacement of the rouet granite in the core of an antiform is responsible for recrystallization and post isotopic closure disturbances of the k ar chronometer in the muscovite from the host rocks these new 40ar 39ar ages clearly outline that at least two different processes may contribute to the exhumation of the lower crust in the later stage of collision during the first stage between 320 and 310 ma the differential motion of tectonic blocks limited by ductile shear zones controls the post collisional exhumation this event could be related to orogen parallel shearing associated with crustal scale strike slip faults and regional folding the final exhumation stages at around 300 ma take place within the tectonic doming associated to magmatic intrusions in the core of antiformal structures local ductile to brittle normal faulting is coeval to upper carboniferous intracontinental basins opening

amphibole sponge in arc crust pressure temperature time paths followed by arc magmas ascending through the lithosphere dictate the phase assemblage that crystallizes and hence the compositions of liquid fractionates here we use la yb and dy yb versus sio 2 relationships from selected volcanoes to show that amphibole is an important mineral during differentiation of arc magma production of intermediate and silicic arc magmas occurs as magmas stall and cool in the mid lower crust where amphibole is stable because amphibole is rarely a phenocryst phase we term this cryptic amphibole fractionation if this process is as widespread as our investigation suggests then 1 amphibole cumulates may act as an effective filter for water dissolved in mantle derived magmas 2 amphibole cumulates may act as a fertile source of intracrustal melts and fluids and 3 recycling of amphibole cumulates has the potential to return incompatible trace elements and water to the mantle

thermokarst lake basin sediments tuktoyaktuk coastlands western arctic canada three stages of deposition are distinguished in thermokarst lake basin sequences in ice rich permafrost of the tuktoyaktuk coastlands western arctic canada 1 widespread retrogressive thaw slumping around lake margins that rapidly transports upland sediments into thermokarst lakes forming a distinctive basal unit of impure sand and or diamicton 2 a reduction or cessation of slumping because of the pinching out of adjacent ground ice slump stabilization or climatic cooling that reduces the input of clastic sediment permitting reworking of sediment around lake margins and suspension settling principally in basin centres 3 lakes drain and deposition may continue by gelifluction and accumulation of in situ peat or aeolian sand radiocarbon dating of detrital peat and wood from a progradational sequence basal unit defines a lateral younging trend in the direction of progradation a progradation rate is calculated to be 4 cm yr 1 consistent with rapid deposition during stage 1 above the nonuniform nature of the trend is attributed to episodic influxes of old organic material by slumping and reworking by waves and currents in comparison with thermokarst lake basin sequences previously described in alaska canada and siberia the middle unit of those in the tuktoyaktuk coastlands is similar whereas the basal unit is generally thicker and by contrast often contains diamicton these differences are attributed respectively to larger scale resedimentation of upland sediments by retrogressive thaw slumping and debris flow deposition in thermokarst lakes in the tuktoyaktuk coastlands compared with the sediments within supraglacial lakes in areas of moderate to high relief the middle unit of thermokarst lake basin sequences in the tuktoyaktuk coastlands lacks clastic varves and the basal unit is much thinner and texturally less variable these differences are attributed to higher relief and larger volumes of meltwater and glacigenic sediment in supraglacial lakes which promote more suspension settling and resedimentation of glacigenic sediment than in thermokarst lakes in the tuktoyaktuk coastlands it may be impossible to distinguish glacial and periglacial thermokarst lake basin sediments in permafrost areas of incomplete deglaciation not only is it often difficult to distinguish intrasedimental and buried glacier ice but the depositional processes associated with thaw of both ice types are presumably the same and the host sediments very similar

climate tectonics and the morphology of the andes large scale topographic analyses show that hemisphere scale climate variations are a first order control on the morphology of the andes zonal atmospheric circulation in the southern hemisphere creates strong latitudinal precipitation gradients that when incorporated in a generalized index of erosion intensity predict strong gradients in erosion rates both along and across the andes cross range asymmetry width hypsometry and maximum elevation reflect gradients in both the erosion index and the relative dominance of fluvial glacial and tectonic processes and show that major morphologic features correlate with climatic regimes latitudinal gradients in inferred crustal thickening and structural shortening correspond to variations in predicted erosion potential indicating that like tectonics nonuniform erosion due to large scale climate patterns is a first order control on the topographic evolution of the andes

developments in the characterization of complex rock slope deformation and failure using numerical modelling techniques recent advances in the characterization of complex rock slope deformation and failure using numerical techniques have demonstrated significant potential for furthering our understanding of both the mechanisms processes involved and the associated risk this paper illustrates how rock slope analyses may be undertaken using three levels of sophistication level i analyses include the conventional application of kinematic and limit equilibrium techniques with modifications to include probabilistic techniques coupling of groundwater simulations and simplistic treatment of intact fracture and plastic yield such analyses are primarily suited to simple translational failures involving release on smooth basal rear and lateral surfaces where the principle active damage mechanisms are progressive failure and or asperity breakdown level ii analyses involve the use of continuum and discontinuum numerical methods in addition to simple translation level ii techniques can be applied to complex translational rock slope deformations where step path failure necessitates degradation and failure of intact rock bridges along basal rear and lateral release surfaces active damage processes in this case comprise not only strength degradation along the release surface e g asperity breakdown but also a significant component of brittle intact rock fracture level iii analyses involve the use of hybrid continuum discontinuum codes with fracture simulation capabilities these codes are applicable to a wide spectrum of rock slope failure modes but are particularly well suited to complex translation rotational instabilities where failure requires internal yielding brittle fracturing and shearing in addition to strength degradation along release surfaces through a series of rock slope analyses the application of varied numerical methods are discussed particular emphasis is given to state of the art developments and potential use of level iii hybrid techniques d 2005 elsevier b v all rights reserved

orogen parallel tectonic transport in the variscan belt of northeastern sardinia italy implications for the exhumation of medium pressure metamorphic rocks a transpressive crustal scale dextral shear zone is documented in the variscan basement of northeastern sardinia it indicates the presence of a shear deformation parallel to the belt overprinting previous d1 structures related to nappe stacking and top to the s and sw thrusting the l2 stretch ing lineation points to an orogen parallel stretching and to a general change in the tectonic transport from d1 to d2 phase d1 developed during initial frontal collision whereas the d2 deformation was characterized by dextral shearing during the increasing curvature of the ibero armorican arc transpressional deformation developed in a regime of decreasing pressure it caused telescoping of the barrovian isograds and the exhumation of the low to medium grade metamorphic rocks in this sector of the variscan belt exhumation is due to continuing compression with an increasing compo nent of horizontal displacement the overall change of the shortening direction in a large sector of an orogenic belt with the occurrence of increasing orogen parallel displacement may be regarded as a general mechanism affecting the exhumation of rocks and preventing the thickened collisional crust from undergoing a generalized gravitational collapse

young late amazonian near surface ground ice features near the equator athabasca valles mars abstract a suite of four feature types in a 20 km 2 area near 10 n 204 w in athabasca valles is interpreted to have resulted from near surface ground ice these features include mounds conical forms with rimmed summit depressions flatter irregularly shaped forms with raised rims and polygonal terrain based on morphology size and analogy to terrestrial ground ice forms these athabascan features are interpreted as pingos collapsing pingos pingo scars and thermal contraction polygons respectively thermal infrared mapping spectrometer themis data and geological features in the area are consistent with a sedimentary substrate underlying these features these observations lead us to favor a ground ice interpretation although we do not rule out volcanic and especially glaciofluvial hypotheses the hypothesized ground ice that formed the mounds and rimmed features may have been emplaced via the deposition of saturated sediment during flooding an alternative scenario invokes magmatically cycled groundwater the ground ice implicit in the hypothesized thermal contraction polygons may have derived either from this flooding ground water or from atmospheric water vapor the lack of obvious flood modification of the mounds and rimmed features indicates that they formed after the most recent flood inundated the area analogy with terrestrial pingos suggests that ground ice may be still extant within the positive relief mounds as the water that flooded down athabasca valles emerged via a volcanotectonic fissure from a deep aquifer any extant pingo ice may contain evidence of a deep subsurface biosphere

direct observation of basal sliding and deformation of basal drift at sub freezing temperatures in a tunnel at the base of sub polar urumqi glacier no 1 china three new mechanisms of glacier flow at sub freezing temperatures have been observed taken individually or in combination these modes of flow can account for nearly all 60 80 of the overall glacier motion and yet they act only within the lowermost 1 2 of the effective glacier thickness these mechanisms are 1 enhanced deformation of the frozen and ice laden subglacial drift 2 motion across discrete shear planes or shear bands within the frozen drift or at the ice drift interface and 3 basal sliding at an ice rock interface at a temperature of nearly 5 c the ice laden drift has an effective viscosity of more than one hundred times less than that measured in the overlying ice thus allowing very rapid shear deformation the observed rate or basal sliding at the ice rock interface agrees favorably with that predicted by the recent work of shreve 1984 if proper account is taken of the measured surface roughness and reduced ice viscosity

permian evolution of sandstone composition in a complex back arc extensional to foreland basin the bowen basin eastern australia abstract the bowen basin is a permo triassic back arc extensional to foreland basin that developed landward of an intermittently active continental volcanic arc associated with the eastern australian convergent plate margin the basin has a complex polyphase tectonic history that began with limited back arc crustal extension daring the early permian this created a series of north trending grabens and half grabens which in the west accommodated quartz rich sediment derived locally from surrounding uplifted continental basement in the east coeval calc alkaline volcanolithic rich and volcaniclastic sediment was derived from the active volcanic arc this early extensional episode was followed by a phase of passive thermal subsidence accompanied by episodic compression during the late early permian to early late permian with little contemporaneous volcanism in the west quartzose sediment was shed from stable polymictic continental basement immediately to the west and south of the basin whereas volcanolithic rich sediment that entered the eastern side of the basin during this time was presumably derived from the inactive and possibly partly submerged volcanic arc during the late late permian flexural loading and increased compression occurred along the eastern margin of the bowen basin and renewed volcanism took place in the arc system to the east reactivation of this arc led to westward and southward spread of volcanolithic rich sediment over the entire basin accordingly areas in the west that were earlier receiving quartzose craton derived sediment from the west and south were overwhelmed by volcanolithic rich arc derived sediment from the east and north this transition from quartz rich craton derived sediments to volcanolithic rich arc derived sediments is consistent with the interpreted back arc extensional to foreland basin origin for the bowen basin

new insights into the weichselian environment and climate of the east siberian arctic derived from fossil insects plants and mammals multidisciplinary study of a key section on the laptev sea coast bykovsky peninsula east lena delta in 1998 2001 provides the most complete record of middle and late weichselian environments in the east siberian arctic the 40 m high mamontovy khayata cliff is a typical ice complex section built of icy silts with a network of large syngenetic polygonal ice wedges and is richly fossiliferous in combination with pollen plant macrofossil and mammal fossils a sequence of ca 70 insect samples provides a new interpretation of the environment and climate of the area between ca 50 and 12 ka the large number of radiocarbon dates from the section together with an extensive 14c database on mammal bones allows chronological correlation of the various proxies the bykovsky record shows how climate change and the last glacial maximum in particular affected terrestrial organisms such as insects and large grazing mammals both during the presumed karginsky interstadial mis 3 and the sartanian glacial mis 2 the vegetation remained a mosaic arctic grassland with relatively high diversity of grasses and herbs and dominance of xeric habitats the tundra steppe type this biome was supported by a constantly very continental climate caused by low sea level and enormous extension of shelf land variations within the broad pattern were caused mainly by fluctuations in summer temperature related to global trends but overprinted by the effect of continentality no major changes in humidity were observed nor were advances of modern type forest or forest tundra recorded suggesting a major revision of the karginsky interstadial paradigm the changing subtypes of the tundra steppe environment were persistently favourable for mammalian grazers which inhabited the shelf lowlands throughout the studied period mammal population numbers were lowered during the lgm especially toward its end and then flourished in a short but impressive peak in the latest weichselian just before the collapse of the tundra steppe biome throughout mis 3 and mis 2 the climate remained very favourable for the aggradation of permafrost no events of regional permafrost degradation were observed in the continuous bykovsky sequence until the very end of the pleistocene

climate variability over the last 9900 cal yr bp from a swamp forest pollen record along the semiarid coast of chile abstract we present a fossil pollen analysis from a swamp forest in the semiarid coast of chile 32 05 s 71 30 w at the northern influence zone of southern westerly wind belt a 10 000 cal yr bp calendar years before 1950 palynological sequence indicates a humid phase characterized by dense swamp forest taxa dated between 9900 and 8700 cal yr bp the presence of pollen starved sediments with only scant evidence for semiarid vegetation indicates that extreme aridity ensued until 5700 cal yr bp the swamp forest recovered slowly afterwards helped by a significant increase in moisture at 4200 cal yr bp a new swamp forest contraction suggests that another slightly less intense drought occurred between 3000 and 2200 cal yr bp the swamp forest expansion begins again at 2200 cal yr bp punctuated by a highly variable climate comparisons between the record presented here with other records across the region imply major variations in the extent of the southern westerlies during the holocene this variability could have been caused either by latitudinal displacements from the present mean position of southern westerlies wind belt or by changes in the intensity of the south pacific subtropical anticyclone both of which affect winter precipitation in the region

stratigraphy and palaeoclimatic significance of late quaternary loess palaeosol sequences of the last interglacial glacial cycle in central alaska abstract loess is one of the most widespread subaerial deposits in alaska and adjacent yukon territory and may have a history that goes back 3 ma based on mineralogy and major and trace element chemistry central alaskan loess has a composition that is distinctive from other loess bodies of the world although it is quartz dominated central alaskan loess was probably derived from a variety of rock types including granites metabasalts and schists detailed stratigraphic data and pedologic criteria indicate that contrary to early studies many palaeosols are present in central alaskan loess sections the buried soils indicate that loess sedimentation was episodic or at least rates of deposition decreased to the point where pedogenesis could keep ahead of aeolian input as in china loess deposition and pedogenesis are likely competing processes and neither stops completely during either phase of the loess soil formation cycle loess deposition in central alaska took place before and probably during the last interglacial period during stadials of the mid wisconsin period during the last glacial period and during the holocene an unexpected result of our geochronological studies is that only moderate loess deposition took place during the last glacial period our studies lead us to conclude that vegetation plays a key role in loess accumulation in alaska factors favouring loess production are enhanced during glacial periods but factors that favour loess accumulation are diminished during glacial periods the most important of these is vegetation boreal forest serves as an effective loess trap but sparsely distributed herb tundra does not thus thick accumulations of loess should not be expected where tundra vegetation was dominant and this is borne out by modern studies near the treeline in central alaska much of the stratigraphic diversity of north american loess including that found in the central lowlands the great plains and alaska is explained by a new model that emphasizes the relative importance of loess production factors versus loess accumulation factors

the sensitivity of paleocommunity sampling strategy at different spatiotemporal scales abstract one of the primary differences between paleoecological and modern ecological research is the added dimension of deep geological time the temporal dimension of paleoecological research can create added difficulties when determining the appropriate spatiotemporal sampling procedures required for any particular study previous paleocommunity studies have found that the spatial extent of sampling can have a grave impact on the multivariate analytical results here we expand spatially on the previous paleocommunity study of forcino et al 2010 to determine the importance lateral variation may have on the paleocommunity signal within the pennsylvanian finis shale spatial and temporal community gradients of bulk sediment shale samples from six localities were examined using ordinations and anosim the expanded spatial examination of the finis shale reveals the same two distinct communities separated at the mid point of each sampled stratigraphic section thus lateral variation did not have an effect on the primary multivariate result for the finis shale communities at the temporal scale of the complete stratigraphic section a temporal factor has the greatest influence on the community result however based on separation of samples in ordination space with respect to location and based on a significant difference between locality based groupings using anosim the primary influence on the paleocommunity result at a finer temporal scale containing 19 samples from only the lower half of each stratigraphic section is a spatial factor this minor variation in scale leading to a major change in the primary factor affecting the multivariate paleocommunity result is evidence that the paleocommunity results are extremely sensitive to the temporal scale of sampling thus this differs from previous research there are cases in which fewer laterally equivalent samples are required per stratigraphic horizon bed or unit because the temporal signal overwhelmed the spatial signal

pollen analysis and 14c age of moss remains in a permafrost core recovered from the active rock glacier murtel corvatsch swiss alps geomorphological and glaciological implications within the framework of core drilling through the permafrost of the active rock glacier murtel corvatsch in the swiss alps subfossil stem remains of seven different bryophyte species were found at a depth of 6 m below surface and about 3 m below the permafrost table in samples from massive ice the composition of the moss species points to the former growth of the recovered mosses in the nearest surroundings of the drill site a total of 127 pollen and spores captured by the mosses and representing 23 taxa were determined the local vegetation during deposition time must be characterized as a moss rich alpine grassland meadow rich in cyperaceae poaceae chenopodiaceae and asteraceae comparable to today s flora present around the study site for l4 c analysis accelerator mass spectrometry had to be used due to the small sample mass about 0 5 mg carbon content the mean conventional 14 c age of 2250 100 years 1 variability corresponds to ranges in the calibrated calendar age of 470 170 bc and 800 bc to ad 0 at statistical probabilities of 68 and 95 respectively this result is compared with the present day flow field as determined by high precision photogrammetry and with information about the thickness vertical structure and flow of the permafrost from borehole measurements total age of the rock glacier as a landform is on the order of 10 4 years the development of the rock glacier most probably started around the onset of the holocene when the area it now occupies became definitely deglaciated the bulk of the ice rock mixture within the creeping permafrost must be several thousand years old characteristic average values are estimated for 1 surface velocities through time cm a 1 2 long term ice and sediment accretion rates mm a 1 on the debris cone from which the rock glacier develops 3 retreat rates 1 2 mm a 1 of the cliff which supplies the debris to the debris cone and rock glacier and 4 ice content of the creeping ice rock mixture 50 90 by volume the pronounced supersaturation of the permafrost explains the steady state creep mode of the rock glacier

regional test of a model for shallow landsliding landslides mapped in 14 watershed analyses in oregon and washington provide a regional test of a model for shallow landsliding a total of 3224 landslides were mapped in watersheds covering 2993 km2 and underlain by a variety of lithologies including tertiary sedimentary rocks of the coast ranges volcanic rocks of the cascade range and quaternary glacial sediments in the puget lowlands gis geographical information system techniques were used to register each mapped landslide to critical rainfall values predicted from a theoretical model for the topographic control on shallow landsliding using 30 m dems digital elevation models a single set of parameter values appropriate for simulating slide hazards after forest clearing was used for all watersheds to assess the regional influence of topographic controls on shallow landsliding model performance varied widely between watersheds with the best performance generally in steep watersheds underlain by shallow bedrock and the worst performance in generally low gradient watersheds underlain by thick glacial deposits landslide frequency slides km2 varied between physiographic provinces but yielded consistent patterns of higher slide frequency in areas with lower critical rainfall values simulations with variable effective cohesion predicted that high root strength effectively limits shallow landsliding to topographic hollows with deep soils and locations that experience excess pore pressures but that low root strength leads to higher probabilities of failure across a greater proportion of the landscape 1998 john wiley sons ltd language en

tectonics and plate tectonics model for the variscan belt of europe abstract a plate tectonics model is presented to explain the tectonometamorphic characteristics of the european variscides after the closing of two oceanic domains by two sided subduction 500 420 ma and obduction 420 380 ma collision of the european and african continental plates occurred we propose that the subsequent complex intracontinental deformation 380 290 ma is the result of a double subduction of the continental lithosphere accompanied by crust mantle decollement this mechanism explains the progressive crustal thickening and migration of the deformation through time from the sutures toward the external parts of the variscan belt accounting for this model and for the relationships between the european variscides and the other paleozoic peri atlantic belts caledonides appalachian mauritanides and morocco we infer the relative positions of africa america and europe between the silurian and the permian

classification of debris covered glaciers and rock glaciers in the andes of central chile in the dry andes of chile 17 to 35 s debris covered glaciers and rock glaciers are differentiated from true glaciers based on the percentage of surface debris cover thickness of surface debris and ice content internal ice is preserved by an insulating cover of thick debris which acts as a storage reservoir to release water during the summer and early fall these landforms are more numerous than glaciers in the central andes however the existing legislation only recognizes uncovered or semicovered glaciers as a water resource glaciers debris covered glaciers and rock glaciers are being altered or removed by mining operations to extract valuable minerals from the mountains in addition agricultural expansion and population growth in this region have placed additional demands on water resources in a warmer climate as glaciers recede and seasonal water availability becomes condensed over the course of a snowmelt season rock glaciers and debris covered glaciers contribute a larger component of base flow to rivers and streams as a result identifying and locating these features to implement sustainable regional planning for water resources is important the objective of this study is to develop a classification system to identify debris covered glaciers and rock glaciers based on the interpretation of satellite imagery and aerial photographs the classification system is linked to field observations and measurements of ice content debris covered glaciers have three subclasses surface coverage of semi class 1 and fully covered class 2 glaciers differentiates the first two forms whereas debris thickness is critical for class 3 when glaciers become buried with more than 3 m of surface debris based on field observations the amount of ice decreases from more than 85 to 65 85 to 45 65 for semi fully and buried debris covered glaciers respectively rock glaciers are characterized by three stages class 4 rock glaciers have pronounced transverse ridges and furrows that arch across the surface which indicates flow produced via ice class 5 rock glaciers have ridges and furrows that appear linear in the direction of flow indicating reduced flow from limited internal ice and class 6 rock glaciers have subdued surface topography because the movement of the rock glacier has ceased ice content decreases from 25 45 to 10 25 to 10 from class 4 to 6 respectively examples from digital imagery aerial photographs and field photographs are provided for each class the classification scheme can be used to identify and map debris covered glaciers and rock glaciers to create an inventory this will help improve recognition of these landforms as an important water resource in the dry andes of chile which will aid in sustainable planning and development in basins that hold the majority of the population and support a large share of the economic activity in chile

above the weathering front contrasting approaches to the study and classification of weathered mantle abstract weathered mantle comprises the materials above bedrock and below the soil it can vary in thickness from millimeters to hundreds of meters depending primarily on climate and parent material study of the weathered mantle comes within the realms of four disciplines geology geomorphology soil science and civil engineering each of which uses a different approach to describe and classify the material the approaches of engineers geomorphologists and geologists are contrasted and compared using example papers from the published literature soil scientists rarely study the weathering profile as such and instead concentrate upon soil forming processes and spatial distribution primarily in the solum engineers including engineering geologists study the stability and durability of the weathered mantle and the strength of the materials using sophisticated procedures to classify weathered materials but their approach tends to be one dimensional furthermore they believe that the study of mineralogy and chemistry is not useful geomorphologists deal with weathering in terms of process how the weathered mantle is formed and with respect to landform evolution using a spatial approach geologists tend to ignore the weathered mantle because it is not bedrock or to study its mineralogy and or chemistry in the laboratory i recommend that the approaches of the various disciplines be integrated geomorphologists and geologists should consider using engineering weathering classifications and geologists should adopt a spatial perspective to weathering as should engineers and engineering geologists

early holocene climate change and human occupation along the semiarid coast of north central chile the brief terminal pleistocene archaeological site at santa julia sj 318 50 0 s 718 45 0 w is the only one with fluted projectile preforms and megafauna consumption known from the chilean semiarid coastline here we present the climatic history at sj during the early holocene reconstructed from pollen and charcoal analyses spanning 13 2 8 6 ka 10 3 calibrated 14 c yr bp elevated charcoal concentrations confirm human activity by 13 2 ka human occupation decreased in intensity and charcoal practically disappears from the record after 10 6 ka followed by wetland expansion at sj between 10 5 and 9 5 ka local dominance of coastal shrubland reveals that dry phases occurred between 11 2 10 5 and 9 5 9 0 ka overall these findings imply that by modulating available resources at both local and landscape levels climate change may have played an important role in explaining the peopling of semiarid coastal chile copyright 2010 john wiley sons ltd

isotopic and geochemical characteristics of laramide magmatic systems in arizona and implications for the genesis of porphyry copper deposits major element trace element and nd sm and rb sr isotope data are described from igneous rocks in 11 multiphase magmatic complexes of laramide age in arizona eight complexes contain barren stocks as well as productive plutons associated with the formation of porphyry base metal deposits whereas in three complexes porphyry orebodies have not been recognized most of the complexes evolved through similar stages early dominantly intermediate volcanic rocks were intruded by multiphase complexes temporally characterized by increases in sio 2 changes in the ferromagnesian mineral assemblage increasingly porphyritic textures and a progression from barren to subproductive to productive intrusions within complexes the sequence is independent of both the absolute age of initiation of local magmatism and its duration analytical data and field relationships are combined to show elements of the petrogenetic history of these complexes potential relationships between productive and barren magmas and factors which may have influenced formation of the characteristic magmatic hydrothermal sequence the isotopic composition of laramide igneous rocks forms an array from epsilon ndt and 87 sr 86 sr initial values of 0 and 0 704 to 14 and 0 710 respectively early volcanic rocks have a more primitive signature consistent with retention of a significant mantle component subsequent intrusions were derived predominantly from isotopically heterogeneous precambrian lower crust but probably also contain an undefined amount of mantle component individual complexes do not exhibit any consistent isotopic trends over time and unique types of source rocks are not indicated for productive magmas in contrast rare earth elements ree in several complexes display temporally systematic behavior progressively younger intrusions in a given complex follow a path of decreasing concentration of ree steepening profiles greater upward concavity in heavy ree profiles and changes in the eu anomaly from negative to either markedly less negative or positive the ree data from individual complexes suggest an increasing petrogenetic involvement of amphibole either in the restite of the source region or as a fractionating phase and similar paths of petrogenetic evolution in spite of chronologic and trace element evidence which argues against completely comagmatic development productive and barren intrusions cannot be clearly distinguished by the isotopic data but the systematic ree trends parallel increasing productivity of magmas in individual complexes models which reconcile isotopic variation systematic ree behavior protracted local but largely noncomagmatic magmatism and the increasing development of porphyry mineralization include 1 progressive metasomatism of the crustal component 2 increasing assimilation of amphibolitic crust by mantle basalts and 3 migration of crustal anatexis from deep anhydrous rocks to shallower amphibolites the relative importance of these processes cannot yet be clearly assessed from the data but a plausible metallogenic impact of each would be upon the concentration and possibly the composition of magmatic volatiles in the primary melts and or during subsequent fractionation in this light existing models which propose that the principal control upon intrusion productivity is a balance between crystal fractionation and the timing of saturation and release of magmatic hydrothermal fluids may be strongly influenced by processes operative either in their source regions or during their interaction with the crust initiation of such processes may be a response to abrupt changes in tectonic regime in the volcanic are environment

geotechnical and landslide aspects in weathered granitoid rock masses serre massif southern calabria italy abstract the weathering processes produce important chemical and physical transformations in rock masses producing a decay of their strength and then stability in this study different methodologies were employed to define the physical mechanical properties and the minero petrographical changes at each grade of weathering useful to determine a geological model of the weathered granitoids involved in mass movements the paper focuses on a multidisciplinary research on the weathering profiles of the paleozoic granitoid rocks surrounding the village of fabrizia located in the serre massif southern calabria italy fabrizia lies on an old erosion surface composed of basement rocks made up of weathered granitoids belonging to the serre massif granitoid complex and overlain by thin eluvial colluvial deposits the tectonic uplift of the area combined with mediterranean climatic conditions both active at least since the quaternary are the main causes of the deep weathering of the plutonic rocks the weathered profiles of the granitoid complex have been studied through field observations borehole explorations with geotechnical tests and seismic surveys coupled to minero petrographical analysis and laboratory tests weathered profiles are mainly composed by rock masses varying from completely weathered and residual soil classes v vi to moderately weathered rocks class iii characterized by a progressive increase of geotechnical properties e g seismic wave velocity rock quality designation internal friction angle uniaxial compressive strength with a decrease of weathering the weathered rocks display a wide variety of mass movement landslide types are rockfalls for the fresher rocks class iii translational slides occur between different weathering degrees classes iv and v and rotational slides dominate at the top of the slopes and generally involve the weathering grades from class iv to classes v vi the shallow horizons are composed of thin eluvial colluvial deposits and more weathered granitoids classes v vi that may generate dangerous debris flows or debris avalanches during intense and prolonged rainfall the landslide surface is usually at a depth lower than 2 m in the debris flow type while deeper landslides depth 2 m are rotational and translational types with sliding surfaces occurring mainly in the transition between the classes iv and v the field survey coupled to geotechnical geophysical and minero petrographical data allowed the recognition of the different weathered horizons and relative geotechnical properties useful to the reconstruction of the reliable geological model the model represents an important support for the study of the landslide processes and for a sustainable management of the territory the used approach provided results to set a general reference framework for establishing more precise correlations between mass movement phenomena and weathering processes

new insights on permafrost genesis and conservation in talus slopes based on observations at fluelapass eastern switzerland abstract the talus slope at fluelapass was the first mountain permafrost study site in switzerland in the 1970s and the presence of ice rich permafrost at the foot of the slope has been investigated in the context of several studies focusing on the role of snow cover distribution we review previously developed hypotheses and present new ones using various data sources such as temperature measurements in boreholes a subaquatic dem generated from unmanned aerial system uas photogrammetry terrestrial laser scan measurements of snow depth geophysical ground investigations and automatic time lapse photography from this combination of data sources together with observations in the field an interesting sequence of geomorphologic processes is established at fluelapass as a result we show how mass wasting processes can initiate the genesis and long term conservation of ice rich permafrost at the base of a talus slope

plutonic xenoliths from martinique lesser antilles evidence for open system processes and reactive melt flow in island arc crust the lesser antilles volcanic arc is remarkable for the abundance and variety of erupted plutonic xenoliths these samples provide a window into the deeper crust and record a more protracted crystallisation history than is observed from lavas alone we present a detailed petrological and in situ geochemical study of xenoliths from martinique in order to establish their petrogenesis pre eruptive storage conditions and their contribution to construction of the sub volcanic arc crust the lavas from martinique are controlled by crystal liquid differentiation amphibole is rarely present in the erupted lavas but it is a very common component in plutonic xenoliths allowing us to directly test the involvement of amphibole in the petrogenesis of arc magmas the plutonic xenoliths provide both textural and geochemical evidence of open system processes and crystal cargos all xenoliths are plagioclase bearing with variable proportions of olivine spinel clinopyroxene orthopyroxene and amphibole commonly with interstitial melt in martinique the sequence of crystallisation varies in sample type and differs from other islands of the lesser antilles arc the compositional offset between plagioclase an90 and olivine fo75 suggests crystallisation under high water contents and low pressures from an already fractionated liquid texturally amphibole is either equant crystallising early in the sequence or interstitial crystallising late interstitial amphibole is enriched in ba and lree compared with early crystallised amphibole and does not follow typical fractionation trends modelling of melt compositions indicates that a water rich plagioclase undersaturated reactive melt or fluid percolated through a crystal mush accompanied by the breakdown of clinopyroxene and the crystallisation of amphibole geothermobarometry estimates and comparisons with experimental studies imply the majority of xenoliths formed in the mid crust martinique cumulate xenoliths are inferred to represent crystal mushes within an open system through which melt can both percolate and be generated

high sr y magmas reflect arc maturity high magmatic water content and porphyry cu mo au potential examples from the tethyan arcs of central and eastern iran and western pakistan the temporal and geochemical evolution of arc magmatism that culminated in porphyry cu mo au deposit formation has been studied in three separate neo tethyan arc systems in central and eastern iran and western pakistan porphyry cu au deposits in the lut block of eastern iran formed in the middle eocene at the end of a period of extensive paleocene eocene volcanism porphyry cu mo deposits in the kerman belt of central iran formed in the middle miocene at the end of a period of voluminous eocene oligocene volcanism and porphyry cu au deposits in the chagai belt of western pakistan formed in four pulses during the eocene early miocene middle late miocene and late miocene pliocene after a prolonged period of arc magmatism that began in the late cretaceous and is still active in each region the late porphyry related magmas are more geochemically evolved and more hydrous as evidenced by the presence of hornblende phenocrysts than the preceding volcanic rocks we suggest that this reflects maturation of the arc magmatic system over a period of tens of millions of years leading to the generation of more evolved volatile rich magmas at later stages of the arc s history high magmatic water contents are a prerequisite for the shallow crustal emplacement of arc magmas and the subsequent generation of potentially ore forming subvolcanic magmatic hydrothermal systems it is thus suggested that the fertility of arc magmas within a given arc terrane can be assessed by observing the relative timing of plutonic suites later suites are more prospective noting the common presence of hornblende or biotite phenocrysts indicating high magmatic water contents and through lithogeochemical fingerprinting of magmatic fractionation processes relatively high sr y and la yb ratios and eun eu ratios 1 indicating abundant early hornblende fractionation and suppression of plagioclase crystallization in hydrous magmas

late quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern seward peninsula alaska a terrestrial sediment sequence exposed in an eroding pingo provides insights into the late quaternary environmental history of the northern seward peninsula alaska we have obtained the first radiocarbondated evidence for a mid wisconsin thermokarst lake demonstrating that complex landscape dynamics involving cyclic permafrost aggradation and thermokarst lake formation occurred over stadiale interstadial as well as glacialeinterglacial time periods high values of picea pollen and the presence of larix pollen in sediments dated to 50e40 ka bp strongly suggest the presence of forest or woodland early in mis 3 the trees grew within a vegetation matrix dominated by grass and sedge and there is indirect evidence of grazing animals thus the interstadial ecosystem was different in structure and composition from the holocene or from the preceding last interglacial period an early holocene warm period is indicated by renewed thermokarst lake formation and a range of fossil taxa multiple extralimital plant taxa suggest mean july temperatures above modern values the local presence of spruce during the early holocene warm interval is evident from a radiocarbon dated spruce macrofossil remain and indicates significant range extension far beyond the modern tree line the first direct evidence of spruce in northwest alaska during the early holocene has implications for the presence of forest refugia in central beringia and previously assumed routes and timing of post glacial forest expansion in alaska

ice flow and rock glaciers on mars several geologic features suggest the presence of rock glaciers on the surface of mars these features include lobate debris aprons concentric crater fill and lineated valley fill the lateral extent of these rock glaciers can range from 5 km to over 20 km a simple time marching model is developed and used here to demonstrate the ability of ice and ice rock mixtures to flow under martian conditions for temperatures lower than about 220 k even pure ice becomes too rigid to flow and a glacier 5 km long could not have formed results from this model indicate temperatures 20 to 40 k higher than present average midlatitude temperatures 210 k an ice content of no less than 80 and a net accumulation rate of at least 1 cm year 1 are required to produce rock glaciers of the size seen on mars

volcanic plutonic connections and metal fertility of highly evolved magma systems a case study from the herberton sn w mo mineral field queensland australia abstract understanding the connection between the highly evolved intrusive and extrusive systems is essential to explore the evolution of high silicic magma systems which plays an important role in discussions of planetary differentiation the growth of continents crustal evolution and the formation of highly evolved magma associated sn w mo mineral systems to discern differences between fertile and non fertile igneous rocks associated with sn w mo mineralization and reveal the genetic links between coeval intrusive and extrusive rocks we integrate whole rock geochemistry geochronology and hf isotope signatures of igneous zircons from contemporaneous plutonic and volcanic rocks from the world class herberton mineral field of queensland australia the 310 300 ma intrusive rocks and associated intra plutonic w mo mineralization formed from relatively oxidized magmas after moderate degrees of crystal fractionation the geochemical and isotopic features of the coeval volcanic succession are best reconciled utilizing the widely accepted volcanic plutonic connection model whereby the volcanic rocks represent fractionated derivatives of the intrusive rocks older intrusions emplaced at 335 315 ma formed from relatively low fo2 magmas that fractionated extensively to produce highly evolved granites that host sn mineralization coeval volcanic rocks of this suite are compositionally less evolved than the intrusive rocks thereby requiring a different model to link these plutonic volcanic sequences in this case we propose that the most fractionated magmas were not lost to volcanism but instead were effectively retained at the plutonic level which allowed further localized build up of volatiles and lithophile metals in the plutonic environment this disconnection to the volcanism and degassing may be a crucial step for forming granite hosted sn mineralization the transition between these two igneous regimes in herberton region over a 30 m y period is attributed to a change from an early compressive tectonic environment with a thickened crust to conditions of crustal thinning and lithospheric extension due to progressive slab rollback such tectonic transitions may provide favorable conditions for intrusion related mineralization given the common occurrence of volcanic and plutonic rocks associated with sn w mo mineralization worldwide we suggest that a combined understanding of temporal tectonic evolution and plutonic volcanic connections can assist in assessment of regional scale mineralization potential which in turn can aid strategies for future ore deposit exploration

the determination of statistical and deterministic hydrological landslide triggering thresholds hydrological landslide triggering thresholds separate combinations of daily and antecedent rainfall or of rainfall intensity and duration that triggered landslides from those that failed to trigger landslides they are required for the development of landslide early warning systems when a large data set on rainfall and landslide occurrence is available hydrological triggering thresholds are determined in a statistical way when the data on landslide occurrence is limited deterministic models have to be used for shallow landslides directly triggered by percolating rainfall triggering thresholds can be established by means of one dimensional hydrological models linked to the infinite slope model in the case of relatively deep landslides located in topographic hollows and triggered by a slow accumulation of water at the soil bedrock contact simple correlations between landslide occurrence and rainfall can no longer be established therefore real time failure probabilities have to be determined using hydrological catchment models in combination with the infinite slope model

interrogating the time and processes of development of the las liebres rock glacier central chilean andes using a numerical flow model the las liebres rock glacier is a large 2 2 km long andean rock glacier whose internal composition and kinematics are known from previous studies we investigate its development by posing and testing the following null hypothesis the rock glacier has developed from a constant supply of debris and ground ice in periglacial conditions and resulting creep of the ice rock mixture a rheological model was formulated based on recent advances in the study of ice rock mixture rheology and calibrated on the known surface velocities and internal composition of the rock glacier we show that the rock glacier viscosity is inversely related to both water and debris fractions in agreement with recent field and theoretical studies of ice rock mixture rheology taking into account the possible variations in water fraction the model was used to estimate the time spans of development 0 91 7 11 ka rates of rock wall retreat 0 44 4 18 mm a and rates of ground ice formation 0 004 0 026 m a for the rock glacier these results support the null hypothesis of a periglacial origin of the las liebres rock glacier copyright 2016 john wiley sons ltd

gondwana derived microcontinents the constituents of the variscan and alpine collisional orogens abstract the european variscan and alpine mountain chains are collisional orogens and are built up of pre variscan building blocks which in most cases originated at the gondwana margin such pre variscan elements were part of a pre ordovician archipelago like continental ribbon in the former eastern prolongation of avalonia and their present day distribution resulted from juxtaposition through variscan and or alpine tectonic evolution the well known nomenclatures applied to these mountain chains are the mirror of variscan resp alpine organization it is the aim of this paper to present a terminology taking into account their pre variscan evolution at the gondwana margin they may contain relics of volcanic islands with pieces of cadomian crust relics of volcanic arc settings and accretionary wedges which were separated from gondwana by initial stages of rheic ocean opening after a short lived ordovician orogenic event and amalgamation of these elements at the gondwanan margin the still continuing gondwana directed subduction triggered the formation of ordovician al rich granitoids and the latest ordovician opening of palaeo tethys an example from the alps external massifs illustrates the gradual reworking of gondwana derived pre variscan elements during the variscan and alpine tertiary orogenic cycles

landslides and climatic conditions in the barcelonnette and vars basins southern french alps france research into the climatic causes behind the triggering and reactivation of landslides has been carried out in two basins in the southern french alps where a great many landslides have occurred over more than a century correlations between landslides and climate are sometimes precise and closely related in time at other times imprecise and more distant the better known the type of landslide and the date of its occurrence the greater the correlation may appear be this as it may climate is never the sole cause this paper deals with the limits of the effects of climate

a 10 300 year old permafrost core from the active rock glacier lazaun southern otztal alps south tyrol northern italy two cores were drilled on rock glacier lazaun in the southern otztal alps n italy the average ice content of core lazaun i is 43 vol and of core lazaun ii is 22 vol radiocarbon dating of plant macrofossil remains of core lazaun i yielded ages ranging from 8960 cal yr bp at a depth of ca 23 5 m to 2240 cal yr bp at a depth of 2 8 m indicating that the ice near the base is approximately 10 300 yr old the rock glacier was intact since that time and the ice persisted even during warm periods of the holocene an ice free debris layer between 16 8 and 14 7 m separates the rock glacier into two frozen bodies inclinometer measurements indicate that both frozen bodies are active and that deformation occurs within a shear horizon at a depth of 20 25 m at the base of the lower frozen body and to a minor extent at a depth of approximately 14 m at the base of the upper frozen body the ice free debris layer in the middle of the lazaun rock glacier indicates a more than five centennial long drought period which dates to about 4300 3740 cal yr bp

micro sheeting of granite and its relationship with landsliding specifically after the heavy rainstorm in june 1999 hiroshima prefecture japan certain types of granite in mountainous areas are microscopically sheeted to a depth of 50 m due to unloading under the stress field that reflects slope morphology micro sheets generally strike parallel to major slope surfaces and gently dip downslope forming cataclinal overdip slopes the cataclinal overdip slope accelerates creep movement of micro sheeted granite which in turn loosens and disintegrates granite via the widening or neoformation of cracks probably in combination with stress release temperature change and changes in water content near the ground surface the surface portion of micro sheeted granite is thus loosened with a well defined basal front which finally slides in response to heavy rain innumerable landslides of this type occurred in hiroshima prefecture western japan following the heavy rainstorm of 29 june 1999 following such landslides the weathering of micro sheeted granite exposed on the landslide scar recommences setting the stage for future landslide

internal structure and composition of a rock glacier in the andes upper choapa valley chile using borehole information and ground penetrating radar this study uses boreholes ground temperature monitoring and ground penetrating radar gpr in order to understand the internal structure and composition of a rock glacier in the upper choapa valley northern chile the rock glacier is a small valley side feature 200 m long and ranging between 3710 and 3780 m a s l two boreholes were drilled down to depths of 20 and 25 m respectively using the diamond drillhole technique an ice rock mixture was encountered in the boreholes with heterogeneous ice content averaging 15 30 data from common midpoint cmp and constant offset co gpr surveys acquired respectively near the boreholes and across the whole rock glacier were processed to highlight the internal stratigraphy and variations in the radar wave velocity the gpr profiles depict a rock glacier constituted of stacked and generally concordant layers with a thickness ranging from 10 m in its upper part to 30 m towards its terminus the cmp analysis highlights radar wave velocities of 0 13 0 16 m ns 1 in the first 20 m of the structure larger vertical and lateral velocity variations are highlighted from co data reflecting the heterogeneous composition of the rock glacier and the likely presence of unfrozen water in the structure given the average air temperature registered at the site 0 58c the near melting point temperature registered in the boreholes over more than a year and the presence of locally high water content inferred from gpr data it is thought that the permafrost in the rock glacier is currently degrading

development of tongue shaped and multilobate rock glaciers in alpine environments interpretations from ground penetrating radar surveys abstract rock glaciers occur as lobate or tongue shaped landforms composed of mixtures of poorly sorted angular to blocky rock debris and ice these landforms serve as primary sinks for ice and water storage in mountainous areas and represent transitional forms in the debris transport system accounting for 60 of all mass transport in some alpine regions observations of active flowing alpine rock glaciers indicate a common association between the debris that originates from cirque headwalls and the depositional lobes that comprise them the delivery of this debris to the rock glacier is regulated primarily by the rate of headwall erosion and the point of origin of debris along the headwall these factors control the relative movement of individual depositional lobes as well as the overall rate of propagation of a rock glacier in recent geophysical studies a number of alpine rock glaciers on prins karls forland and nordenskioldland svalbard norway and the san juan mountains of southwest colorado usa have been imaged using ground penetrating radar gpr to determine if a relationship exists between the internal structure and surface morphology results indicate that the overall morphologic expression of alpine rock glaciers is related to lobate deposition during catastrophic episodes of rockfall that originated from associated cirque headwalls longitudinal gpr profiles from alpine rock glaciers examined in this study suggests that the difference in gross morphology between the lobate and tongue shaped rock glaciers can be attributed primarily but not exclusively to cirque geometry frequency and locations of debris discharge within the cirque and the trend and magnitude of valley gradient in relation to cirque orientation collectively these factors determine the manner in which high magnitude debris discharges which seem to be the primary mechanism of formation accumulate to form these rock glaciers

the effect of particles on creep rate and microstructures of granular ice the microstructures of particle free granular freshwater ice and ice containing 1 wt of 50 10 mm uniformly distributed particles were investigated before and after compressive creep to 10 strain with stresses of 1 45 mpa at 10 c and 0 4 mpa at 5 c creep rates of particle containing ice were always higher than those of particle free ice for an initial stress of 1 45 mpa at 10 c dynamic recrystallization occurred with new grains nucleating and growing along grain boundaries for both sets of specimens and the ice with particles showed a higher nucleation rate under creep with an initial stress of 0 4 mpa at 5 c dynamic recrystallization also occurred by the nucleation and growth of new grains along the grain boundaries for ice containing particles but recrystallization in the particle free ice occurred through grain boundary migration

circular cryogenic structures from the hirnantian deglaciation sequence anti atlas morocco abstract more than a hundred circular structures are observed at the topmost part of the late ordovician glaciogenic record in the central anti atlas southern morocco the structures were formed in the outer glaciated platform and characterize the hirnantian deglaciation sequence they are distributed within a 20 meter thick stratal interval and at present relicts of them still occupy several square kilometers in map view the circular to ovoidal structures which comprise fluvial sandstone beds and are sealed by shallow marine strata occur in closely spaced clusters they are 13 320 m in diameter with half of them in the 40 90 m range stratal wedging and bending as well as extensional and reverse centimeter to meter scale soft sediment fractures demonstrate that formation processes initially involved synsedimentary uplifts subsequent subsidence and collapse resulted in the formation of circular structures which essentially correspond to localized depocenters in the form of small scale sag basins regarding the overall deglaciation context the circular structures are interpreted as periglacial in origin with vertical movements ascribed to cryogenic processes involving the growth and then decay of bodies of segregation ice the size and diameter distributions which are comparable to the recent younger dryas and current lithalsa structures suggest that hirnantian circular features relate to similar genetic processes and can be referred to as lithalsa like structures a conceptual emplacement model is proposed which considers that a long term sedimentary aggradation over the fluvial plain prevented any significant landforms either a bump or a depression from being expressed at the depositional surface at the time of the circular structure formation the hirnantian lithalsa like structures constitute firm evidence for a late ordovician discontinuous permafrost during the deglaciation stage assuming that the late quaternary meridional zonation is valid it suggests the anti atlas was at latitudes in the 55 65 interval if combined with the rare pingo structures described in the literature which attest that coeval continuous permafrost conditions occurred at higher paleo latitudes the moroccan circular structures provide evidence for an alternate south pole position during the hirnantian 444 ma

geophysical geotechnical and hydrological investigations of a small landslide in the french alps abstract geophysical geotechnical and hydrological surveys were conducted in the french alps on a small landslide in black marl material to assess the stability the geophysical survey consisting of electromagnetic geo electric and relative differences in water content the data on the basal slip surface together with geotechnical parameters cohesion and angle of internal friction were used to make a stability analysis this analysis revealed that a groundwater level of 4 m below the ground surface is the critical threshold for reactivating the landslide the hydrological investigation which entailed measurements of saturated permeability and pressure heads indicated that instability depended on long term wet conditions with little evapotranspiration

multi method characterisation of an active landslide case study in the pays d auge plateau normandy france shallow landslides are among the most frequent natural hazards in the pays d auge plateau normandy france but no study has yet focused on the functioning of these phenomena at a detailed scale this study aims to identify the structure and mechanical properties of a representative case study in the region the main objective is to understand landslide dynamics and behaviour in order to assess triggering conditions and quantify triggering thresholds the results will help complement the regional landslide hazard mapping based on landslide statistical susceptibility mapping and quantification of triggering thresholds the landslide morphology and internal structure were identified using a multi method approach a morphodynamic map was produced in the field using car tographic gps to depict the surface morphology and map the estimated landslide activity these field measurements were completed by an analysis of all available aerial photo images from the french national geographic institute ign to identify the occurrence dates and possible landslide reactivations the landslide structure was defined using multiple electrical tomography profiles boreholes augerings and penetration tests despite the overall low electrical resistivity of the landslide materials i e b 80 m the electrical profiles showed good agreement with the interpreted structure based on direct observations augerings and penetration tests the landslide slip surface internal morphology and palaeotopography were identified a finite slope model was used to calculate the landslide safety factor based on the internal structure and geotechnical data the evolution of this safety factor according to the rainfall and the groundwater levels shows that the landslides are more likely to occur after long episodes of high cumulative precipitations with an important role being played by the preliminary conditions and the rise of the surficial groundwater table level

discrimination of productive and nonproductive porphyritic intrusions in the chilean andes a geochemical comparison between productive intrusions those associated with mineralization and nonproductive intrusions those unrelated to mineralization has been made on the basis of over 100 fresh granitoid rocks from the chilean porphyry copper belt the study was carried out on the scale of a mining district el salvador potrerillos then on the scale of a single traverse el salvador chilean coast and finally on the scale of the andes itself the productive intrusions are best characterized by large negative anomalies in y mn th and the heavy rare earth elements a discriminant diagram of y against mno is recommended for predicting whether an apparently fresh intrusion has associated peripheral mineralization the low values of y and mn in productive intrusions can be partly explained by the early crystallization of y and mn rich hydrous phases such as hornblende and by the loss of mn rich fluids from the magma the same elements make useful discriminants in other porphyry copper provinces although the exact position of the discriminant boundary varies from island arcs through continental margin to continental settings

the behaviour of trace and rare earth elements ree during hydrothermal alteration in the rangan area central iran the rhyolitic dome in the rangan area has been subjected to hydrothermal alterations by two different systems 1 a fossil magmatic hydrothermal system with a powerful thermal engine of a deep monzodioritic magma 2 an active hydrothermal system dominated by meteoric water based on mineralogical and geochemical studies three different alteration facies have been identified phyllic advanced argillic and silicic with notable differences in ree and other trace elements behaviour in the phyllic alteration zone with assemblage minerals such as sericite pyrite quartz kaolinite lree are relatively depleted whereas hree are enriched the advanced argillic zone is identified by the presence of alunite jarosite and pyrophyllite as well as immobility of lree and depletion in hree in the silicic zone most of lree are depleted but hree patterns are unchanged compared to their fresh rock equivalents all the ree fractionation ratios la yb cn la sm cn tb yb cn ce ce cn and eu eu cn are low in the phyllic altered facies eu eu cn in both advanced and silicic facies is low too in all alteration zones high field strength elements hfse e g ti zr nb are depleted whereas transition elements e g v cr co ni fe are enriched geochemically speaking trace and rare earth elements behave highly selective in different facies

permafrost evidence for severe winter cooling during the younger dryas in northern alaska 1 the younger dryas cold event a rapid reversion to glacial climate conditions at the pleistocene holocene transition has generally been attributed to the release of meltwater from the laurentide ice sheet to the north atlantic or arctic oceans the reaction of the north pacific region to this shutdown of the thermohaline circulation in the north atlantic during younger dryas is little understood in this paper we present the first radiocarbon dated centennial scale stable water isotope record from permafrost in northern alaska this late glacial winter climate reconstruction from barrow ice wedges demonstrates the existence of a younger dryas cold event formerly believed to be reduced or absent in this area our stable isotope data display a gradual change of the atmospheric moisture source conditions during the younger dryas likely associated with the successive opening of the bering strait

regional cooling in a warming world recent temperature trends in the southeast pacific and along the west coast of subtropical south america 1979 2006 1 while it is widely accepted that the global mean atmospheric temperature has increased in recent decades the spatial distribution of global warming has been complex in this study we comprehensively characterize the spatial pattern including vertical structure of temperature trends along the subtropical west coast of south america continental chile for the period 1979 2006 and examine their consistency with expectations based on the cmip 3 ensemble of coupled ocean atmosphere simulations for the late 20th century in central and northern chile 17 37 s the most notable feature is a strong contrast between surface cooling at coastal stations 0 2 c decade and warming in the andes 0 25 c decade only 100 200 km further inland coastal radiosonde data imply that the coast andes variation is largely due to strong vertical stratification of temperature trends in the atmosphere west of the andes the coastal cooling appears to form part of a larger scale la nina like pattern and may extend below the ocean mixed layer to depths of at least 500 m over continental chile the cmip 3 gcm ensemble predicts temperature trends similar to those observed in the andes the cooling along the chilean coast is not reproduced by the models but the mean sst warming is weaker there than any other part of the world except the southern ocean it is proposed that the intensification of the south pacific anticyclone during recent decades which is also a simulated consequence of global warming is likely to play a major role in maintaining cooler temperatures off the coast of chile

a late holocene 2600 bp glacial advance in the south central andes 29 s northern chile radiocarbon dates and relative ages of soils on moraines provide evidence of a substantial late holocene 2600 bp readvance of glaciers in the western part of the arid andes at 29 s the glacier in the encierro valley northern chile reached about 60 of its late pleistocene extent the equilibrium line altitude ela during this advance remained between 4250 and 4500 m which is above the modern 0 c isotherm of the free atmosphere during summer it is suggested that given the specific climate at high elevations in the extremely arid andes a substantial increase in effective moisture is sufficient to explain this advance whereas no significant temperature depression was needed this compares favourably with the regional late holocene climatic history when lake levels were higher and effective moisture greater than today between 3000 and 1800 bp judging from regional palaeodata we suggest that this late holocene humid spell was most likely related to increased westerly moisture sources from the pacific

weathering grade of rock masses as a predisposing factor to slope instabilities reconnaissance and control procedures weathering of rock masses often assumes importance as a predisposing factor to slope instability and it is possible to map it at various scales depending on the different purposes the effects of weathering processes are particularly intense on crystalline rocks plutonic and metamorphic these rocks are present in large areas of the globe and widespread in calabria the relationships between rock mass weathering grades and slope instabilities are analysed with reference to sectors 1 50 000 scale and areas 1 10 000 scale where crystalline rocks are strongly affected by weathering to this aim a reconnaissance procedure has been proposed to delimitate the zones with different weathering condition three macro classes at average scale 1 50 000 and six classes at detail scale 1 10 000 in this procedure first analysis of aerial photos and then field observations of representative situations have been used the reconnaissance procedure has been verified in a selected study area acri whose geological features are provided by the comparison with weathering maps obtained by means of a control procedure this last procedure consists of observations and index tests carried out in check points located in representative check sites discolouration sound when struck by geological hammer effect of the point of geological pick breaking with the hands rebound of schmidt hammer grain size analysis the results obtained confirm through quantitative data that the weathering of a rock mass can be assumed as a predisposing factor to slope instability at average scale 1 50 000 the reconnaissance procedure is able to give weathering maps representative for this type of evaluation the ratio between the landslides area in each weathering macro class and the whole landslide area goes from 67 to 14 for the macro class a and from 24 to 9 for the macro class b at detail scale 1 10 000 it is necessary to use a control procedure to obtain weathering maps indicative of predisposition to slope instabilities

possible submarine advanced argillic alteration at the basin lake prospect western tasmania australia the basin lake copper gold prospect lies in western tasmania s mount read volcanics and is hosted in a series of calc alkaline andesites quartz feldspar porphyries mudstones carbonates and sandstones between the tyndall group and the central volcanic complex alteration at the basin lake prospect occurs over a strike length of 1 4 km and includes thin strata bound pyrophyllite quartz paragonite kaolinite pyrite alunite alteration zones up to 12 m wide and containing up to 50 wt percent pyrophyllite with local fluorite veining these zones grade out to paragonite muscovite kaolinite quartz pyrite and muscovite carbonate chlorite alteration zones extensive propylitic alteration chlorite carbonate epidote affects most other rocks outside these zones mineralization consists of thin strata bound zones of massive and vein pyrite tennantite and chalcopyrite with trace covellite and galena hosted mainly within an intensely silicified core of the pyrophyllite quartzsericite alteration zone pyrite has 34s values of 1 4 to 6 9 per mil although marginal vein pyrite in the propylitic zone has 34s values around 12 4 per mil large silicified glacial erratic boulders at surface contain massive and vein pyrite enargite and tennantite with minor barite and trace covellite stannoidite and mawsonite pyrite and enargite have 34s values of 1 7 to 6 8 per mil barite has 34s values around 35 2 per mil with 87sr 86sr around 0 7108 the alteration and mineralization at the basin lake prospect is similar to that associated with high sulfidation copper gold systems formed by acidic relatively oxidized fluids a new geochemical vector here termed the advanced argillic alteration index aaai 100 sio2 sio2 10mgo 10cao 10na2o has been devised to help quantify the intensity of alteration the values of the aaai at basin lake are similar to those of several high sulfidation epithermal deposits the low sulfide 34s values are similar to those at other sulfide occurrences in the mount read volcanics that have previously been considered to be barren are lower than those of nearby volcanic hosted massive sulfide deposits and may indicate a magmatic fluid component however the 34s and 87sr 86sr values of basin lake barite at the assumed highest exposed level of the system and higher 34s values in pyrite from marginal veins are similar to those of cambrian volcanic hosted massive sulfide systems indicating the involvement of reduced seawater sulfate at these locations calcite carbon and oxygen isotope values silicate oxygen isotope values and the unusual abundance of carbonate close to advanced argillic alteration indicate fluid mixing and suggest that acidic magmatic fluids were likely neutralized by seawater this occurrence strengthens the case for prospecting the mount read volcanics and other similar submarine volcanic belts for copper gold and gold only deposits that formed by the actions of hyperacid oxidized fluids

exploration tools for linked porphyry and epithermal deposits example from the mankayan intrusion centered cu au district luzon philippines the mankayan mineral district of northern luzon philippines hosts several significant ore deposits and prospects of various types within an area of similar to 25 km 2 including the far southeast porphyry cu au deposit the lepanto high sulfidation epithermal cu au deposit the victoria intermediate sulfidation epithermal au ag vein deposit the teresa epithermal au ag vein deposit the guinaoang porphyry cu au deposit and the buaki old palidan porphyry cu au prospects all having formed in a period of about 2 m y from similar to 3 ma the geologic units include 1 a basement composed of late cretaceous to middle miocene metavolcanic rocks volcaniclastic rocks 2 the miocene 12 to 13 ma tonalitic bagon intrusive complex 3 the pliocene similar to 2 2 to 1 8 ma imbanguila dacite porphyry and pyroclastic rocks and 4 postmineralization cover rocks including die similar to 1 2 to 1 0 ma bato dacite porphyry and pyroclastic rocks and the similar to 0 02 ma lapangan tuff extensive advanced argillic alteration crops out for similar to 7 kin along the inconformity between the basement rocks and the imbanguila dacite formation consists of quartz alunite pyrophyllite or diaspore with local zones of silicic alteration and a halo of dickite kaolinite the alteration and its subhorizontal geometry indicate that it is a lithocap or coalesced lithocaps the northwest striking portion is similar to 4 km long and hosts the lepanto enargite au ore deposit also controlled by the lepanto fault the lepanto epithermal deposit is related to the underlying far southeast porphyry the quartz alunite alteration halo of lepanto is contemporaneous with the similar to 1 4 ma potassic alteration of the porphyry there are also silicic advanced argillic alteration patches similar to 600 m above the far southeast orebody at the present surface these are interpreted to be perched alteration there is no systematic mineralogical or textural zoning in the lepanto lithocap that indicates direction to the intrusive source most surface samples of the lithocap contain less than 50 ppb au despite many being less than a few hundred meters from underground cu au ore this study found that several characteristics of the lepanto lithocap change systematically with distance from the causative intrusion the alunite absorption peak at similar to 1 480 nm in the short wavelength infrared swir spectrum shifts to higher wavelengths where the sample is closer to the intrusive center due to higher na and lower k content in the alunite published experimental studies indicate that high na na k is related to higher formation temperature high ca alunite including huangite also occurs at locations proximal to the intrusive center alunite mineral composition analyzed by laser ablation inductively coupled plasma mass spectrometry la icp ms indicates that the pb content decreases toward the intrusive center whereas sr la sr ph and la pb increase markedly whole rock compositions using only nonmineralized taken as cu similar to 350 m above the upper extent of the veins an airborne geophysics survey indicates that the far southeast orebody is associated with a wide zone of demagnetization due to extensive magnetite destructive phyllic alteration such low magnetic anomalies on the margin of a large lithocap elsewhere may deserve attention the directional indicators and mineralization signatures found in this study have the potential to indicate direction to the intrusive center during exploration of similar porphyry epithermal districts

reconstruction of an early permian sublacustrine magmatic hydrothermal system mount carlton epithermal au ag cu deposit northeastern australia the mt carlton au ag cu deposit northern bowen basin northeastern australia is an uncommon example of a sublacustrine hydrothermal system containing economic high sulfidation epithermal mineralization the deposit formed in the early permian and comprises vein and hydrothermal breccia hosted au cu mineralization within a massive rhyodacite porphyry v2 open pit and stratabound ag barite mineralization within volcano lacustrine sedimentary rocks a39 open pit these orebodies are all associated with extensive advanced argillic alteration of the volcanic host rocks stable isotope data for disseminated alunite 34s 6 3 29 2 18oso4 0 1 to 9 8 18ooh 15 3 to 3 4 d 102 to 79 and pyrite 34s 8 8 to 2 7 and void filling anhydrite 34s 17 2 19 2 18oso4 1 8 5 7 suggest that early advanced argillic alteration formed within a magmatic hydrothermal system the ascending magmatic vapor 34sss 1 3 was absorbed by meteoric water 50 60 meteoric component producing an acidic ph 1 condensate that formed a silicic quartz alunite quartz dickite kaolinite zoned alteration halo with increasing distance from feeder structures the oxygen and hydrogen isotope compositions of alunite forming fluids at mt carlton are lighter than those documented at similar deposits elsewhere probably due to the high paleolatitude s60 of northeastern australia in the early permian veins of coarse grained banded plumose alunite 34s 0 4 7 0 18oso4 2 3 6 0 18ooh 10 3 to 2 9 d 106 to 93 formed within feeder structures during the final stages of advanced argillic alteration epithermal mineralization was deposited subsequently initially as fracture and fissure filling au cu rich assemblages within feeder structures at depth as the mineralizing fluids discharged into lakes they produced syngenetic ag barite ore isotope data for ore related sulfides and sulfosalts 34s 15 0 to 3 0 and barite 34s 22 3 23 8 18oso4 0 2 to 1 3 and microthermometric data for primary fluid inclusions in barite th 116 233 c 0 0 1 7 wt nacl are consistent with metal deposition at temperatures of 200 40 c for au cu mineralization in v2 pit and 150 30 c ag mineralization in a39 pit from a low salinity sulfur and metal rich magmatic hydrothermal liquid that mixed with vapor heated meteoric water the mineralizing fluids initially had a high sulfidation state producing enargite dominated ore with associated silicification of the early altered wall rock with time the fluids evolved to an intermediate sulfidation state depositing sphalerite and tennantite dominated ore mineral assemblages void filling massive dickite 18o 1 1 to 2 1 d 121 to 103 with pyrite was deposited from an increasingly diluted magmatic hydrothermal liquid 70 meteoric component exsolved from a progressively degassed magma gypsum 34s 11 4 19 2 18oso4 0 5 3 4 occurs in veins within postmineralization faults and fracture networks likely derived from early anhydrite that was dissolved by circulating meteoric water during extensional deformation this process may explain the apparent scarcity of hypogene anhydrite in lithocaps elsewhere while the mt carlton system is similar to those that form subaerial high sulfidation epithermal deposits it also shares several key characteristics with magmatic hydrothermal systems that form base and precious metal mineralization in shallow submarine volcanic arc and back arc settings the lacustrine paleosurface features documented at mt carlton may be useful as exploration indicators for concealed epithermal mineralization in similar extensional terranes elsewhere

the magnetite crisis in the evolution of arc related magmas and the initial concentration of au ag and cu the association of large au cu ag ore deposits with convergent margins is commonly attributed to the higher content of chalcophile elements in the parental magmas generated at subduction zones compared with mid ocean ridges we present new geochemical data for arc like relatively oxidized mantle derived basalt to rhyolite magmas from the pual ridge and vicinity eastern manus basin which show that the initial abundances of base and precious metals in the parental basalts are similar to those of mid ocean ridge basalt morb the contents of au cu and ag are built up in the evolving pual ridge liquids to levels considerably in excess of those in morb because unlike morb they are not saturated in a sulfide phase which is a consequence of their being more oxidized than morb the behaviour of s during the evolution of the pual ridge magmas is obscured by late stage so2 loss during eruption but we show that it may be inferred by using se as a proxy because this element follows s closely during magmatic evolution except it is not lost during low pressure near sea floor degassing the onset of magnetite fractionation at 60 wt sio2 and an mg number of 40 is accompanied by an abrupt decrease in the contents of au cu and ag previously attributed to separation of cu au rich fluid which is also shown by se implying that magnetite fractionation triggers sulfide saturation petrological modelling reveals that the amount of magnetite fractionation involved is sufficient to convert most of the s originally dissolved in the magma as sulfate so42 to sulfide s2 triggering saturation in a cu rich sulfide phase tentatively identified as bornite cu5fes4 this sulfide phase sequesters au and ag elements with the same valence as cu in sulfides but not other potentially chalcophile elements such as ni re and pt which suggests that the phase is crystalline rather than an immiscible sulfide melt the relatively high contents of cu and au characteristic of evolved convergent margin magmas requires no enrichment from subducted material instead the association of major cu au deposits with convergent margin magmatism results specifically from the process of magmatic evolution under oxidizing conditions this same property also leads to early magnetite fractionation triggering the abrupt saturation in the cu rich sulfide hence the easily recognizable trend of magmatic evolution under oxidizing conditions i e the sharp drop in chalcophile element concentrations may be an exploration guide to economic au ag cu provinces or a crucial pre enrichment step in the formation of such deposits the decrease in p2o5 and sr at the same stage in the fractionation sequence 60 wt sio2 indicates that saturation in apatite is concomitant with magnetite sulfide saturation in the eastern manus basin

landslides triggered in weathered crystalline rocks of moderate latitudes a case study in mediterranean environment the maures massif france abstract the main purpose of this study is to characterize shallow and moderately deep landslide prone materials in crystalline rocks at moderate latitudes the procedure is based by a four step approach coupling the geomorphological approach the geotechnical approach and slope stability analyses based on limit equilibrium equations firstly different weathering horizons were identified with different thicknesses and characteristics depending on the original lithology these observations led to the development of a weathering model with two steps a regional paleo weathering step and a geomorphological weathering step secondly conceptual models of weathered horizon thicknesses were created according to the lithological context these models led to the identification of three major weathering types thirdly slope stability models were computed for three types of weathered lithology favourable theoretically to slope failure granit micaschists gneiss for each case the different models properly computed landslide occurrences and their locations for highly saturated weathered materials that corresponded to field observations to finalize the study a first analysis of precipitation data was carried out to define some triggering trends for slope failures in this environment therefore based on this simple approach it is possible to define some trends for shallow and moderately deep landslides in weathered crystalline environment located in moderate latitudes with mediterranean climate finally the information can be used by end users and practitioners for public works management on these slopes

giant porphyry deposits characteristics distribution and tectonic controls more than half of the 25 largest known porphyry copper deposits defined in terms of contained copper metal formed during three time periods the paleocene to eocene eocene to oligocene and middle miocene to pliocene these giant deposits are clustered within three provinces central chile northern chile and southwest arizona northern mexico other giant deposits occur in montana utah panama peru argentina irian jaya mongolia and iran compressive tectonic environments thickened continental crust and active uplift and erosion were associated with the formation of many of these deposits calc alkalic magmas are most favorable for the formation of giant porphyry copper deposits although several of the largest systems are associated with high k calc alkalic intrusions the 25 largest gold rich porphyry deposits are concentrated in the southwest pacific and south america with other occurrences in eurasia british columbia alaska and new south wales many of the deposits formed in the last 13 m y the largest of the deposits are associated with high k calc alkalic intrusions many calc alkalic porphyritic intrusions have also produced giant gold rich porphyries in the last 20 m y the formation of giant porphyry copper molybdenum and copper gold deposits in the circum pacific region has been closely associated with subduction of aseismic ridges seamount chains and oceanic plateaus beneath oceanic island and continental arcs in several examples these tectonic perturbations have promoted flat slab subduction crustal thickening uplift and erosion and adakitic magmatism coeval with the formation of well endowed porphyry and or epithermal mineral provinces similar tectonic features are inferred to be associated with the giant porphyry copper molybdenum provinces of northern chile eocene oligocene and southwest united states cretaceous paleocene topographic and thermal anomalies on the downgoing slab appear to act as tectonic triggers for porphyry ore formation other factors such as sutures in the overriding plate permeability architecture of the upper crust efficient processes of ore transport and deposition and in some cases formation and preservation of supergene enrichment blankets are also vital for the development of high grade giant ore deposits a low grade geochemical anomaly may be the final product of mineralization if ore forming processes do not operate efficiently even in the most favorable geodynamic settings

on the persistence of weathering abstract the term weathering has been in use for a very long time but it has come to mean different things to different people and hence as scientific short hand it no longer functions here we question the tenets underpinning the most common usage of the term and note that the climate process linkage implicit to the term is often missing and amounts to misdirection rather than climate as the primary driver behind specific weathering processes it is argued that rock properties constitute the dominant control further a case is made for reconsideration of our present bipartite mechanical chemical division of weathering processes and of the weathering processes currently deemed to be those that occur as process studies become evermore reductionist in nature so the functionality of the term comes more and more into question the linkage between process and landform the scaling up attribute is seen as a current weakness and one that will become more confusing as reductionist approaches continue as a way forward it is suggested that weathering stripped of specific preconceived notions of specific processes be envisaged as a function of energy transfer and be investigated in that light identification of new processes as well as restructuring of known processes particularly when considering weathering on other planets is a potential outcome of such an approach with a process foundation rooted in energy transfer rock decay provides a better umbrella term and liberates researchers from the inescapable conceptual baggage implicit to the term weathering

landslide susceptibility in a mountainous geoecosystem tijuca massif rio de janeiro the role of morphometric subdivision of the terrain abstract the mountainous area of rio de janeiro is highly susceptible to landslides of creep translational and debris flow types these process operations are spatially non uniform due to local interactions of several controlling factors affecting the regolith formation and mechanical behavior including geomorphological geological geotechnical vegetation and land management variables this paper presents a methodology for morphometric subdivisions of the terrain based on hydro geomorphological parameters that may affect the landslide types indicated above it includes the so called hollow density h d and the strahler s drainage density parameters d d multiplied by the basin gradient g b to give the so called drainage efficiency index dei the range of dei values is classified so as to receive a legend for mapping the dei classes polygons are superposed to slope geometry and critical slope angles to produce the so called hydro geomorphological map the role played by these parameters in controlling landslide susceptibility is here evaluated by integrating this late map with relevant geological geotechnical vegetation and land use variables the final landslide susceptibility map 1 10 000 scale was successfully compared with the spatial distribution of several landslide scars originated during an extreme rainfall event in the western portion of tijuca massif february 1996 local morphometric controls over granite rocks with large in situ block formation together with forest degradation have controlled the occurrence of landslides in areas of medium to high susceptibility

reconsidering the glacier to rock glacier transformation problem new insights from the central andes of chile abstract the glacier to rock glacier transformation problem is revisited from a previously unseen angle a striking case in the juncal massif located in the upper aconcagua valley chilean central andes is documented there the presenteseracae debris covered glacier has advanced several tens of metres and has developed a rock glacier morphology in its lower part over the last 60 years the conditions for a theoretically valid glacier to rock glacier transformation are discussed and tested permafrost probability in the area of the studied feature is highlighted by regional scale spatial modelling together with on site shallow ground temperature records two different methods are used to estimate the mean surface temperature during the summer of 2014 and the sub debris ice ablation rates are calculated as ranging between 0 05 and 0 19 cm d 1 i e 0 04 and 0 17 m over the summer these low ablation rates are consistent with the development of a coherent surface morphology over the last 60 years furthermore the rates of rock wall retreat required for covering the former glacier at presenteseracae lie within the common 0 1 2 mm y 1 range assuming an average debris thickness and a range of debris covering time intervals the integration of the geomorphological observations with the numerical results confirms that the studied debris covered glacier is evolving into a rock glacier

comments on debris covered glaciers in the sierra nevada california and their implications for snowline reconstruction by d h clark m m clark and a r gillespie

paleoenvironmental reconstruction of the last glacial maximum inferred from insect fossils from a tephra buried soil at tempest lake seward peninsula alaska abstract sediments and vegetation dated 21 570 cal yr bp were buried under tephra on the northern seward peninsula this buried surface has yielded plant macrofossils in growth position as well as numerous insect fossils excellently preserved in permafrost it appears that many of the insects were buried alive by the volcanic ash the species composition and ecological affinities of this fossil fauna are typical of alaskan late pleistocene steppe tundra environments the assemblages are dominated by the weevil lepidophorus lineaticollis one of the most common species in eastern beringian pleistocene fossil assemblages many other members of the ancient steppe tundra insect community are preserved in these assemblages including the pill beetle morychus sp and weevils of the genus coniocleonus in alaska most of these species but not all of them survived the pleistocene holocene environmental transition but are restricted today to relict patches of steppe like vegetation faunal diversity is low in spite of the recovery of more than 1000 individual insects and mites including more than 600 beetles this reflects the small number of species adapted to the cold dry environments of the lgm in eastern beringia they represent an ecosystem which no longer exists

current transition from glacial to periglacial processes in the dolomites south eastern alps abstract a close relationship between glacial and periglacial landforms is frequently observed in alpine environments where a transition from glacial to periglacial processes often took place after the end of the little ice age lia understanding the origin of these landforms is challenging and assessing the current spatial domain of glacial and periglacial processes may be a difficult task in high relief areas where thick and widespread debris cover often characterize rapidly decaying glaciers here we present a comprehensive study of a composite landform located in the dolomites south eastern alps combining geomorphological geophysical and topographic surveys with ground surface temperature measurements results indicate that a debris covered glacier persists in the upper part rather large compared to the lia extent but currently inactive and rapidly losing mass an active rock glacier exists in the lower part surrounded by discontinuous permafrost a frozen body about 10 m thick was detected in the rock glacier and geomorphological evidence suggests that this ice mass is completely detached from the debris covered glacier our findings suggest that the lower part of the composite landform is probably a remnant of the ancient glacier tongue and is currently evolving under periglacial conditions periglacial processes are therefore replacing glacial processes which dominated in this site during the lia

assessing the rock glacier kinematics on three different timescales a case study from the southern swiss alps surface temperature increases since the 1990s have often been associated with an increase in the speed of rock glaciers evidence of similar links on the centennial to millennial scale are however still lacking due to less focus to date on the medium and long term kinematics of these landforms in order to assess palaeo climatic variations in rock glacier kinematics we analysed the movements of the stabbio di largario rock glacier in the southern swiss alps using three different timescales the schmidt hammer exposure age dating shd was applied to study long term kinematics in order to extrapolate the minimal age of the formation of the rock glacier which may have started its development after the mid holocene climate optimum and to detect possible accelerations of the horizontal surface velocity during the medieval warm period georeferentiation and orthorectification of six historical photographs of the rock glacier taken between ad 1910 and today were analysed using monoplotting to detect the rock glacier displacement on the decennial scale from the end of the little ice age finally differential global positioning system dgps monitoring data available since ad 2009 were used to assess annual and seasonal creep rates of the rock glacier at present our results show a link between the periods of increase in mean air temperature on different timescales and variations in rock glacier kinematics and provide important new insights into rock glacier development and evolution on the long term scale

south variscan terrane accretion sardinian constraints on the intra alpine variscides structural data are presented that show that the sardinian variscides form the boundary of the variscan intra alpine terrane thrust onto a gondwana foreland this model replaces the currently held hypothesis that the south armorican suture zone continues into the sardinian variscides the orogenic activity propagated toward the foreland in two distinct waves 1 thrusting burial and barrovian type metamorphism that reached the internal orogen in late devonian times and lasted in the external orogen until early carboniferous times transpressional strain partitioning is suggested by frontal thrusting in the external orogen and lateral displacement in the internal orogen 2 normal faulting exhumation and local buchan type metamorphism were superimposed on the internal orogen probably since early carboniferous times and reached the external orogen contemporaneously with the late carboniferous emplacement of voluminous granitic intrusions extensional doming and lateral displacement indicate a transtensional regime the sense of orogen parallel displacement during both stages was left lateral on inward dipping movement planes and right lateral on outward dipping movement planes the resulting left lateral displacement between the intra alpine terrane and the gondwana foreland is due to the bending of the variscan belt during which the sardinian segment underwent a bookshelf type movement within an overall right lateral displacement regime

a new model of rock glacier dynamics abstract rock glaciers have traditionally been described as periglacial landforms and thus associated genetically with the presence of permafrost and a seasonal active layer they have also been described as glacigenic in origin in which the main rock glacier body contains glacier ice at depth other rock glaciers can be considered as relict where they contain no interstitial ice and are functionally inactive although all rock glaciers are to some extent polygenic there is no clear simple test that can be used to distinguish between different rock glacier types this study proposes a simple and testable model for rock glacier classification based on their behaviour from evidence reported from the literature the study then proposes an interpretive evolutionary model describing the temporal evolution of rock glacier surface movement through the year that can inform on its dynamical controls this analysis provides an easily deployed interpretive framework for the origins of rock glaciers

age extent and climatic significance of the c 3400 bp aniakchak tephra western alaska usa tephra deposits at whitefish lake and cape espenberg on the northernmost seward peninsula of western alaska were derived from the aniakchak caldera on the alaska peninsula more than 1500 km to the south radiocarbon dates on the climactic caldera forming aniakchak eruption and on proximal and distal tephra indicate the aniakchak tephra was deposited about 3435 40 bp 3614 3815 cal bp and forms an isochronous marker horizon across much of western alaska the aniakchak tephra eruption and several other targe eruptions during the seventeenth century bc may have had widespread effects on climate

dominant weathering profiles of granite in southern peninsular malaysia abstract one of the most important challenges in the study of slope stability foundations and excavation of rocks is to understand their weathering states this issue is more important in tropical climates where severe weathering produces thick weathering profiles with different sequences of weathering thick weathering profiles are normally classified or graded based on field observation geological studies and the material properties of the rocks this paper presents the results of an extensive study of changes in the geological and morphological characteristics of granite in a tropical region due to severe weathering a total of 40 panels of rock exposure were studied in four active granite quarries located in johor southern peninsular malaysia the proposed dominant weathering profiles of granite are mainly based on the sequences of weathering zone topography and geological conditions joint characterization and the dominant color of rock material in addition two additional weathering subzones are introduced in the completely and the highly weathered zones based on the presence of corestones boulders it is believed that the proposed dominant weathering profiles can contribute to engineering design and the classification of weathered granitic rock in the tropical region

thermal and mechanical evolution of an orogenic wedge during variscan collision an example in the maures tanneron massif se france synthesis of structural petrological and geochronological data for the maures tanneron massif and its integration in the framework of adjacent massifs i e sardinia and corsica has allowed us to propose a new model of evolution for the southern variscan belt after siluro devonian subduction associated with high pressure low temperature hp lt metamorphism m 0 c 10 15 8c km 21 and subsequent carboniferous nappes stacking the belt underwent strong reworking related to back thrusting nappes stacking and back thrusting were associated with typical barrovian metamorphism m 1 c 20 30 8c km 21 starting at 360 ma that progressively evolved to higher temperature metamorphisms m 2 c 40 60 8c km 21 and m 3 c 60 80 8c km 21 during 330 300 ma in the internal part of the belt progressive increase of the thermal gradient is interpreted as a consequence of gravitational instabilities triggered in the partially molten orogenic root continuous compressive forces applied to the belt allowed vertical extrusion of the orogenic root in fold dome structures the mass transfer is accommodated by orogen parallel transpressive shearing synchronous with m 3 during late carboniferous time the orogenic wedge is characterized by two main tectono metamorphic units decoupled by a major shear belt an internal zone with migmatites and syntectonic granitoids where hp relicts have been exhumed and an external zone that escaped the late ht event and preserved precious structures

late quaternary pollen records from the kobuk and noatak river drainages northwestern alaska abstract pollen diagrams from joe and niliq lakes date to ca 28 000 and 14 000 yr b p respectively mesic shurb tundra grew near joe lake ca 28 000 to 26 000 yr b p with local populus populations prior to ca 27 000 yr b p shrub communities decreased as climate changed with the onset of itkillik ii glaciation 25 000 to 11 500 yr b p and graminoid dominated tundra characterized vegetation ca 18 500 to 13 500 yr b p herb tundra was replaced by shrub betula tundra near both sites ca 13 500 yr b p with local expansion of populus ca 11 000 to 10 000 yr b p and alnus ca 9000 yr b p mixed picea glauca p mariana woodland was established near joe lake ca 6000 yr b p these pollen records when combined with others from northern alaska and northwestern canada indicate 1 mesic tundra was more common in northwestern alaska than in northeastern alaska or northwestern canada during the duvanny yar glacial interval 25 000 to 14 000 yr b p 2 with deglaciation shrub betula expanded rapidly in northwestern alaska but slowly in areas farther east 3 an early postglacial thermal maximum occurred in northwestern alaska but had only limited effect on vegetation and 4 pollen patterns in northern alaska and northwestern canada suggest regional differences in late quaternary climates

mount st helens potential example of the partial melting of the subducted lithosphere in a volcanic arc mount st helens 50 km to the west of mount adams and the main cascade volcanic chain is only 80 km above the subducting oceanic lithosphere the elevated temperatures off the subducting slab because of the close proximity of the juan de fuca ridge to the trench may induce slab melting at a depth of 80 km dacites from mount st helens have geochemical compositions off magmas that are derived by direct partial melting of metamorphosed basalts at high pressure i e relatively high ai al2o3 15 at 70 sio2 low y and yb because of garnet and amphibole stability in the source low sc and high sr and eu trace element modeling of the partial melting of mid oceanic ridge basalt morb from the juan de fuca ridge that yields a hornblende eclogite residue can reproduce the mount st helens data results off the model are quite distinct from data derived from the mount adams volcanic rocks in contrast mount adams is 135 km above the subducting slab and is associated with normal arc magmatism believed to be derived from the mantle above the subducting plate the cascade are has been active in its present locality because of oblique subduction for the past 7 m y the major volcanoes along the arc have existed for at least 500 ka but mount st helens has existed for 40 ka we suggest that the subducting plate may have reached elevated temperatures because of the approach of north america to the juan de fuca ridge at 40 ka which initiated melting of the slab

deformation of debris ice mixtures mixtures of rock debris and ice are common in high latitude and high altitude environments and are thought to be widespread elsewhere in our solar system in the form of permafrost soils glaciers and rock glaciers these debris ice mixtures are often not static but slide and creep generating many of the landforms and landscapes associated with the cryosphere in this review a broad range of field observations theory and experimental work relevant to the mechanical interactions between ice and rock debris are evaluated with emphasis on the temperature and stress regimes common in terrestrial surface and near surface environments the first order variables governing the deformation of debris ice mixtures in these environments are debris concentration particle size temperature solute concentration salinity and stress a key observation from prior studies consistent with expectations is that debris ice mixtures are usually more resistant to deformation at low temperatures than their pure end member components however at temperatures closer to melting the growth of unfrozen water films at ice particle interfaces begins to reduce the strengthening effect and can even lead to profound weakening using existing quantitative relationships from theoretical and experimental work in permafrost engineering ice mechanics and glaciology combined with theory adapted from metallurgy and materials science a simple constitutive framework is assembled that is capable of capturing most of the observed dynamics this framework highlights the competition between the role of debris in impeding ice creep and the mitigating effects of unfrozen water at debris ice interfaces

computer simulation of rock glacier development under viscous and pseudoplastic flow the rock glacier debris transport system is mathematically linked to its bedrock cliff source area by combining expressions for debris input and rock glacier flow with a continuity equation numerical solutions are achieved by computer simulation given the initial conditions of a 295 m cliff and a 10 m basal talus resulting system configurations depend upon rockwall weathering rate and rock glacier flow resistance as well as the type viscous or pseudoplastic of rock glacier deformation steady state equilibrium is achieved more quickly under pseudoplastic flow but for given rates of rockwall retreat and flow resistance steady state rock glaciers tend to be larger and more powerful under viscous flow when rock glacier development is simulated under the assumption of cyclic climatic fluctuation resulting geometries are similar for viscous and pseudoplastic flow however the rock glacier output response to debris input is shown to be less lagged and less amplified under pseudoplastic flow

fast deformation of perennially frozen debris in a warm rock glacier in the swiss alps an effect of liquid water 1 surface movement internal deformation and temperature were monitored over 5 years on buz north rock glacier a small rock glacier located at the lower limit of the permafrost belt in the swiss alps the permafrost in the rock glacier mainly consists of pebbles and cobbles filled with interstitial ice two inclinometers installed at 4 and 5 m depths showed fast deformation with large seasonal and interannual variations while the permafrost temperatures remained almost at the melting point the movement of the inclinometers coincided with changes in the surface velocities the deformation rapidly accelerated during snowmelt periods whereas it gradually decelerated below a dry snow cover in winter the frozen debris was more deformable than typical glacier ice at the melting point these phenomena suggest that the frozen debris is permeable to snowmelt water the fast deformation should result from significant annual relocation of debris particles which probably creates a network of air voids in the frozen debris that eventually allows water infiltration the meltwater infiltration accelerates the deformation by reducing effective stress resulting in the reduced strength of the frozen debris the refreezing of the pore water which depends on the cooling intensity in winter decelerates the deformation the combination of these processes controls the temporal variations in the deformation

rock falls in high alpine rock walls quantified by terrestrial lidar measurements a case study in the mont blanc area 1 the global warming observed in recent decades and its future increase may affect permafrost distribution on high mountain faces with consequences for their stability in this paper we show that rock falls from high alpine rock walls can be computed with a decimetre resolution using lidar measurements a laser scanner was used to create point clouds and triangulated irregular network models on the east face of the tour ronde at 3792 m asl mont blanc massif comparison of the models realised from measurements of july 2005 and july 2006 enabled quantification of rock falls with reduced uncertainty the volume of rock fall reached a total of 536 m3 in the scanned area which matches an erosion rate of 8 4 mm yr 1 this rate slightly higher to the ones reported in former studies enable to assume that this rock fall may be the consequence of the permafrost degradation in this rock face

can economic porphyry copper mineralization be generated by a typical calc alkaline melt numerical simulation of chlorine and copper partitioning between a crystallizing melt and exsolving aqueous fluids indicates that typical calc alkaline magmas contain sufficient copper chlorine and water to produce economic porphyry copper mineralization neither an elevated copper content in the magma nor an additional large volume of magma are required to provide metals or volatiles the most important variables that determine the volume of melt necessary to produce sufficient copper are the degree of compatible behavior displayed by copper the ratio of initial water in the melt to the water saturation level and the initial chlorine water ratio of the melt the absolute values for initial water in the melt and water content at saturation are relatively unimportant in determining the required melt volume the bulk salinity of the exsolved fluid may vary from 2 0 wt nacl to saturation levels 84 wt nacl at 700 c indicating that boiling is not necessary to produce high salinity brines at appropriate p t xnacl conditions the magmatic aqueous fluid separates into a saline liquid which transports most of the copper and a low salinity vapor the salinities of the two immiscible phases are governed by the p t conditions while the bulk fluid salinity determines the mass fractions of liquid and vapor formed pressure quenching causes rapid crystallization of the aplitic groundmass in porphyritic rocks associated with copper mineralization and significantly reduces the amount of chlorine and copper partitioning to the aqueous fluid this results in abrupt and possibly large reductions in fluid salinity and causes copper to become concentrated in the melt as copper is transported from the melt by the earliest exsolving fluids in deep 2 0 kbar systems and by late exsolving fluids in shallow 0 5 kbar systems the relative timing of pressure quenching aplite formation and fluid transport of copper from the melt can vary significantly in systems produced under different confining pressures model results incorporating petrologic constraints determined for yerington nevada are in good agreement with observed mineralization

growth of ibyuk pingo western arctic coast canada and some implications for environmental reconstructions abstract ibyuk pingo which is 49 m high and 300 m in basal diameter is one of the largest pingos in the world precise surveys carried out for the 1973 to 1983 period indicate that the lower half of the pingo below a height of 25 m shows no perceptible growth from 25 m to the top the growth steadily increases to a maximum of 2 3 cm yr at the summit the source of growth is believed to lie at a depth of about 65 m below the highest peak evidence based upon the depth of permafrost near the pingo radiocarbon dating of wood in the pingo overburden heat conduction theory and the measured growth rate suggests an age of about 1300 200 yr ibyuk pingo is in an unstable state and collapse could be initiated by further slumping a thermal disturbance to the crater or erosion along a radial dilation crack a study of the potential collapse pattern of ibyuk pingo suggests a number of criteria that might be employed in the environmental reconstruction of large circular features that might be identified as collapsed pingo remnants

characteristics of weathering zones of granitic rocks in malaysia for geotechnical engineering design tropical climatic conditions cause severe weathering to rock masses resulting in thick weathering profiles consisting of different weathering zones with complex characteristics feasible geotechnical engineering design requires a detailed understanding of the characteristics of each weathering zone a typical weathering profile is usually characterized by field scale observation and geological study this paper presents the characteristics of weathering zones of various granitic rocks in the south of malaysia this region has a tropical climatic condition the study was carried out in four active quarries located in johor province malaysia and forty sections were investigated in the study areas a typical granitic weathering profile was characterized based on the geological and structural parameters i e joint characteristics corestone occurrence rock soil ratio mass homogeneity color of rock and discoloration at joints surfaces the profile includes common zones ranging from fresh to residual soil however two subzones are introduced based on corestone boulder occurrence in the highly weathered and completely weathered zones this study based on detailed field observations at the mentioned quarries followed by analysis presents an amalgamated picture of weathering zones in granitic profiles of a tropical region like malaysia moreover it is believed that the characterization of the typical weathering profile allows further classification of generally complex weathered rock masses for a specific geotechnical engineering design

debris covered glaciers in the sierra nevada california and their implications for snowline reconstructions abstract ice walled melt ponds on the surfaces of active valley floor rock glaciers and matthes little ice age moraines in the southern sierra nevada indicate that most of these landforms consist of glacier ice under thin ca 1 10 m but continuous covers of rock fall generated debris these debris blankets effectively insulate the underlying ice and greatly reduce rates of ablation relative to that of uncovered ice such insulation explains the observations that ice cored rock glaciers in the sierra actually debris covered glaciers are apparently less sensitive to climatic warming and commonly advance to lower altitudes than do adjacent bare ice glaciers accumulation area ratios and toe to headwall altitude ratios used to estimate equilibrium line altitudes elas of former glaciers may therefore yield incorrect results for cirque glaciers subject to abundant rockfall inadvertent lumping of deposits from former debris covered and bare ice glaciers partially explains an apparently anomalous regional ela gradient reported for the pre matthes recess peak neoglacial advance distinguishing such deposits may be important to studies that rely on paleo ela estimates moreover matthes and recess peak ela gradients along the crest evidently depend strongly on local orographic effects rather than latitudinal climatic trends indicating that simple linear projections and regional climatic interpretations of ela gradients of small glaciers may be unreliable

high sr y arc magmas and porphyry cu mo au deposits just add water porphyry cu mo au deposits are commonly associated with intermediate composition arc related igneous rocks with high sr y and la yb ratios and such rocks are equated by some researchers with melts derived from subducted oceanic crust undergoing eclogite facies metamorphism adakites however similar geochemical characteristics are readily developed in normal asthenospheric mantle wedge derived magmas by fractionation of amphibole and or garnet and or by interaction with crustal materials during ascent through the upper plate lithosphere while there is widespread evidence for such fractionation and contamination processes in porphyry magmas there is little direct evidence for an origin by slab melting the enhanced fertility of arc magmas relates primarily to their high water content which is required for the formation of magmatic hydrothermal systems upon shallow crustal emplacement magmatic water contents 4 wt percent h 2 o cause abundant amphibole garnet fractionation but suppression of plagioclase crystallization at deep crustal levels resulting in increasing sr y and la yb ratios with differentiation commonly into adakitic ranges but not reflecting slab melting additional factors that affect arc magma fertility are relatively high oxidation states and sulfur content but these are secondary to the requirement for sufficient water thus arc magmatic suites with high sr y ratios and evidence for the presence of hydrous phenocryst phases hornblende and or biotite are indeed prospective for porphyry cu mo au deposits but only because these parameters indicate high magmatic water content