foreland shortening and crustal balancing in the andes at 30 s latitude excellent surface exposures known benioff zone geometry a dynamic morphology and the availability of industry seismic reflection data all make the andes at 30 s an excellent transect for investigating crustal scale balanced sections 150 170 km of horizontal shortening has occurred in three major belts located between the trench and the foreland the thin skinned east verging precordillera of western argentina accounts for 60 75 of the total shortening and formed mostly since major volcanism ceased at 10 ma industry seismic reflection data show that the decollement of the precordillera belt is located anomalously deep at 15 km the belt is dominated by fault propagation folds and contains several prominent out of sequence thrust faults seismic stratigraphie analysis shows that miocene strata in the iglesia valley located between the precordillera and the crest of the andes accumulated in a piggy back basin onlap relations on the western side indicate that the high cordillera was uplifted as a major fault bend fold over a buried ramp thrusting in the two western belts both in the high cordillera of chile formed during the waning stages of arc volcanism 11 16 ma and account for 25 40 of the shortening the observed shortening is probably greater than can be accounted for with reasonable crustal thicknesses indicating the possibility of continental truncation or erosion along the plate margin or an anomalously thick root held down by the nearly flat subducted nazca plate our preferred crustal geometry puts the ramp between upper and lower crustal deformation west of the high topography requiring crustal scale tectonic wedging to thicken the crust beneath the crest of the andes this non unique model provides a simple explanation of the first order morphology of the andes at this latitude

the mechanism of ascent and emplacement of granite magma during transpression a syntectonic granite paradigm we propose a model for syntectonic ascent and emplacement of granite magma based on structural relations in part of the northern appalachians in the study area in western maine strain was distributed heterogeneously during devonian acadian transpression metasedimentary rocks migmatites at high grades record two contrasting types of finite strain in zones that alternate across strike rocks in both types of zones have a penetrative moderately to steeply ne plunging mineral elongation lineation defined by bladed muscovite fibrolite sillimanite at high grades in straight belts of enhanced deformation rocks have s l fabrics that record apparent flattening to plane strain apparent flattening zones afzs but rocks between these belts have l s fabrics that record apparent constriction apparent constriction zones aczs at metamorphic grades above the contemporary solidus rocks in afzs developed stromatic structure in migmatite which suggests that percolative flow of melt occurred along the evolving flattening fabric stromatic migmatites are intruded by concordant to weakly discordant m scale composite sheet like bodies of granite to suggest magma transport in planar conduits through the afz rocks inhomogeneous migmatite is found in the intervening aczs which suggests migration of partially molten material through these zones en masse probably by melt assisted granular flow inhomogeneous migmatites are intruded by irregular m scale bodies of granite that vary from elongate to sub circular in plan view and seem cylindrical in three dimensions these bodies apparently plunge to the northeast parallel to the regional mineral elongation lineation to suggest magma transport in pipe like conduits through the acz rocks we postulate that the form of magma ascent conduits was deformation controlled and was governed by the contemporaneous strain partitioning magma ascent in planar and pipe like conduits through migmatites is possible because oblique translation during contraction displaces isotherms upward in the orogenic crust to form a thermal antiform within this hot corridor it is the difference in temperature between melt producing reactions in the anatectic zone and the wet solidus for granite melt that enables magma to migrate pervasively up through the orogenic crust without congealing heat advected with the migrating melt promotes amplification of the thermal antiform in a feedback relation that extends the zone of plastic deformation and pervasive melt migration to shallower levels in the crust at the wet solidus we suggest melt flows obliquely toward axial culminations in the thermal antiform which are sites of melt accumulation and perturbations from which magma may escape to form plutons batches of melt that escape from these perturbations may be trapped by tectonic structures higher in the crust or ascent may become inhibited with decreasing depth by thermal arrest and solidification if the rate of arrival of subsequent melt batches exceeds the rate of crystallization at the site of pluton construction melt pressure ultimately may lead to sub horizontal magma fracture or viscous flow of wall rocks may allow lateral spreading the resultant plutons have sub horizontal tabular geometries with floors that slope down to the ascent conduit as the thermal antiform decays the height of sub solidus crust that separates the deepest part of the pluton from the anatectic zone increases consequently pluton inflation declines and solidification leads to infilling of the magma feeder channel to form a root zone that passes downward into migmatite which may explain the difficulty of determining precisely the floor to these deeper segments of large plutons using gravimetry

variability in sediment delivery and storage along river courses in bega catchment nsw australia implications for geomorphic river recovery in many catchments in southeastern australia alluvial stores have been the dominant source of sediments mobilised in the period since european settlement in bega catchment on the south coast of new south wales nsw this has been reflected by dramatic changes to river morphology extensive volumes of material have been released and efficiently flushed to the lowland plain with a sediment delivery ratio of almost 70 however only 16 of these alluvial sediments have been flushed through to the estuary as antecedent controls on valley width have resulted in the lowland plain acting as a large sediment sink the changing nature of sediment source transfer and accumulation zones has varied markedly from subcatchment to subcatchment the volume of material supplied to the lowland plain from differing subcatchments is not related to subcatchment area rather the pattern of river types dictates the spatial variability in storage and transfer over 67 of sediment released has been sourced from just 25 of the catchment from subcatchments characterised by large valley fills cut and fill river style that previously stored extensive volumes of material at the base of the escarpment these parts of bega catchment were especially sensitive to disturbance sediment exhaustion from these parts of the catchment and from river courses elsewhere has major implications for the geomorphic recovery potential of rivers constraining what can be realistically achieved in terms of river rehabilitation

kinematic setting and structural control of arc volcanism abstract the evaluation of the kinematic setting and the structural control of volcanic arcs are important in defining the tectono magmatic processes along convergent plate boundaries however our knowledge is fragmented and the available data highlight different behaviours this study analyzes the kinematic setting the structural control and the volcanic productivity of 16 arcs these arcs are characterized by predominant extensional compressional strike slip or oblique motions there is an overall coupling between the normal vs parallel motions along the arc and those of the underlying slab therefore the higher the trench normal or parallel component of the subduction rate the higher is the amount of arc normal or parallel motion this relation confirms that strain partitioning is in general feasible at many convergent settings involving also the volcanic arc portion the arc normal motion may be characterized by extension or compression as a function of the increase in the trench normal convergence or subduction velocity the lack of an evident relation between the subduction rate or convergence rate and the volcanic productivity of the arc is partly inconsistent with previous studies which highlight a relation between the subduction rate and melt production below arcs this discrepancy mainly suggests that different processes control the generation rise and eruption of magma at different depths varying the intrusive extrusive ratio along arcs the structure of the arc does not control the distribution of the volcanoes however it does control the volcanic output through different processes even though regional or local extension associated with strike slip or compressive structures is the ultimate requisite in any setting in general the higher the amount of extension the higher is the output rate along the arc

el morro caldera 33 10 s 66 24 w san luis argentina an exceptional case of fossil pre collapse updoming abstract volcanism at sierra del morro represents the final stages of the flat slab related magmatism in the easternmost san luis neogene volcanic belt this 80 km long nw wnw trending belt tracks the episodic inland migration of both magmatism and tectonic deformation since 18 ma the sierra del morro stands out in the eastern sierras pampeanas as a metamorphic block uplifted during the late miocene pleistocene by a combination of magma injection and tectonic deformation although sequences that preserve stages of basement updoming are not often preserved exposures in sierra del morro are exception in providing key evidence and insight into the involved processes based on the comprehensive study of volcanic stratigraphy and structures the reconstruction of the volcanic architecture has been carried out we infer a three stage evolution of the el morro caldera as follows 1 pre collapse updoming and volcanism 2 collapse caldera formation and 3 post caldera volcanism the ascent of magma is recorded in small tumescence sites strongly controlled by oblique transtensional wnw nw and ene striking brittle ductile megashear zones even though the area affected by tumescence was large magma injection progressed only locally at cerros guanaco and pampa metamorphic rocks were updomed and strongly brecciated whereas at sierra del morro magma was emplaced as pre collapse domes with associated block and ash flows ignimbrite caldera forming eruptions and post caldera lava domes and dykes the caldera is located in the intersection of two major oblique transtensional wnw nw and ene trending brittle ductile megashear zones where the highest positive dilatation occurred

late cenozoic tectonism collapse caldera and plateau formation in the central andes abstract the evolution of andean volcanism including the formation of late miocene to recent collapse calderas on the puna plateau is generally interpreted in terms of the kinematic framework of the nazca and south american plates we present evidence that caldera dynamics and associated ignimbrite volcanism are genetically linked to the activity of first order nw se striking zones of left lateral transtension on the local and regional scales consequently ages of collapse calderas indicate activity of these fault zones which initiated at about 10 ma on the puna plateau the onset of such faulting points to a change in the deformation regime from dominantly vertical thickening to orogen parallel stretching upon reaching maximum crustal thickness and critical surface elevation horizontal magma sheets that formed at mid crustal level possibly due to heat advection by volume increase of asthenospheric mantle below thickened crust were tapped by sub vertical faults this accounts well for the observed tectono magmatic phenomena at surface it follows that formation of collapse calderas and eruption of voluminous ignimbrites appear to be related to the mechanical evolution of the andean plateau rather than to changes in the geometry of the wadati benioff zone or plate boundary kinematics

granite and gabbrodiorite associated skarn deposits of nw iran abstract field and laboratory studies show that there are two types of skarn deposits in nw iran granite associated type i and gabbrodiorite associated type ii granite associated deposits are accompanied by cu and fe mineralisation whereas mn and fe are the main ore metals in gabbrodiorite associated skarn deposits there are some differences in the mineralogy of these skarn deposits bixbyite piemontite and cr bearing garnet are found only in gabbrodiorite associated skarns whereas idocrase occurs only in granite associated deposits type ii skarns show exoskarn features whereas some type i skarns have developed endoskarn as well evidence of boiling of hydrothermal fluid can be seen in both types and seems to be a common mechanism of mineral deposition gabbrodiorite associated skarns show higher f o 2 than granite associated deposits based on mineralogical and textural evidence mineralisation in both groups has started from about 550 c early formed anhydrous minerals have begun to be replaced by hydrous minerals from about 400 c it seems that due to low fluid content in the gabbrodioritic magma heated meteoritic water in the surrounding volcanoclastic and tuffaceous rocks was the main source of hydrothermal solution in the gabbrodiorite associated skarn system

stress transfer among en echelon and opposing thrusts and tear faults triggering caused by the 2003 mw 6 9 zemmouri algeria earthquake stress transfer among en echelon and opposing thrusts and tear faults triggering caused by the 2003 m w 6 9 zemmouri algeria earthquake 1 the essential features of stress interaction among earthquakes on en echelon thrusts and tear faults were investigated first through idealized examples and then by study of thrust faulting in algeria we calculated coseismic stress changes caused by the 2003 m w 6 9 zemmouri earthquake finding that a large majority of the zemmouri afterslip sites were brought several bars closer to coulomb failure by the coseismic stresses while the majority of aftershock nodal planes were brought closer to failure by an average of 2 bars further we calculated that the shallow portions of the adjacent thenia tear fault which sustained 0 25 m slip were brought 2 bars closer to failure we calculated that the coulomb stress increased by 1 5 bars on the deeper portions of the adjacent boumerdes thrust which lies just 10 20 km from the city of algiers both the boumerdes and thenia faults were illuminated by aftershocks over the next 6 years the entire south dipping thrust system extending 80 km to the southwest experienced an increased rate of seismicity the stress also increased by 0 4 bar on the east sahel thrust fault west of the zemmouri rupture algiers suffered large damaging earthquakes in a d 1365 and 1716 and is today home to 3 million people if these shocks occurred on the east sahel fault and if it has a 2 mm yr tectonic loading rate then enough loading has accumulated to produce a m w 6 6 6 9 shock today thus these potentially lethal faults need better understanding of their slip rate and earthquake history among en echelon and opposing thrusts and tear faults triggering caused by the 2003 m w 6 9 zemmouri algeria earthquake

seismicity and shape of the subducted nazca plate an updated compilation of earthquake locations and focal mechanism solutions from the international seismological centre and preliminary determination of earthquakes is the basis of a comprehensive study of the geometry of the wadati benioff zone beneath western south america the new data support previous mapping of a sharp flexure rather than a tear in the subducted nazca plate beneath southern peru and provide evidence for a similar flexure in the southward transition from nearly horizontal subduction to a slab with 30 dip at latitude 33 s in contrast the transition from 30 slab dip beneath bolivia to a nearly horizontal dip in the region between 28 s 32 s is more gradual occurring over several hundred kilometers of along strike distance between 20 s and 32 s this southward flattening corresponds to a broadening of a horizontal benchlike part of the subducted plate formed between 100 and 125 km depth the transition in continental tectonic style near 27 s 28 s from a wide volcanically active plateau to a narrow nonvolcanic cordillera appears not to be associated with the main slab flattening which begins to the north of these latitudes but with a more abrupt change in curvature of the subducted slab from convex upward to concave upward immediately below the plate boundary interface the concept of gaussian curvature is applied to slab bending to explain how subduction geometry is affected by the shape of the south american plate we hypothesize that the polarity of vertical curvature in the subducting slab is governed by the orientation of lateral curvature of the plate margin focal mechanism solutions for intermediate and deep earthquakes are grouped by geographic region and inverted for the orientation and relative magnitudes of the principal stresses results of the inversion indicate that downdip extension dominates in the slab above 350 km while downdip compression dominates at greater depths

effects of vertical wind shear on the intensity and structure of numerically simulated hurricanes a series of numerical simulations of tropical cyclones in idealized large scale environments is performed to examine the effects of vertical wind shear on the structure and intensity of hurricanes the simulations are performed using the nonhydrostatic pennsylvania state university national center for atmospheric research fifth generation mesoscale model using a 5 km fine mesh and fully explicit representation of moist processes when large scale vertical shears are applied to mature tropical cyclones the storms quickly develop wavenumber one asymmetries with upward motion and rainfall concentrated on the left side of the shear vector looking downshear in agreement with earlier studies the asymmetries develop due to the storm s response to imbalances caused by the shear the storms in shear weaken with time and eventually reach an approximate steady state intensity that is well below their theoretical maximum potential intensity as expected the magnitude of the weakening increases with increasing shear all of the storms experience time lags between the imposition of the large scale shear and the resulting rise in the minimum central pressure while the lag is at most a few hours when the storm is placed in very strong 15 m s21 shear storms in weaker shears experience much longer lag times with th e5ms 21 shear case showing no signs of weakening until more than 36 h after the shear is applied these lags suggest that the storm intensity is to some degree predictable from observations of largescale shear changes in all cases both the development of the asymmetries in core structure and the subsequent weakening of the storm occur before any resolvable tilt of the storm s vertical axis occurs it is hypothesized that the weakening of the storm occurs via the following sequence of events first the shear causes the structure of the eyewall region to become highly asymmetric throughout the depth of the storm second the asymmetries in the upper troposphere where the storm circulation is weaker become sufficiently strong that air with high values of potential vorticity and equivalent potential temperature are mixed outward rather than into the eye this allows the shear to ventilate the eye resulting in a loss of the warm core at upper levels which causes the central pressure to rise weakening the entire storm the maximum potential vorticity becomes concentrated in saturated portions of the eyewall cloud aloft rather than in the eye third the asymmetric features at upper levels are advected by the shear causing the upper portions of the vortex to tilt approximately downshear the storm weakens from the top down reaching an approximate steady state intensity when the ventilated layer can descend no farther due to the increasing strength and stability of the vortex at lower levels

westward shift of western north pacific tropical cyclogenesis tropical cyclones tcs in the western north pacific or typhoons account for one third of all tcs in the world and the change of the mean tc genesis location can affect billions of people in pacific islands and asian countries the annual mean tc genesis longitude is generally controlled by the east west shift of the tropical upper tropospheric trough tutt a pronounced westward shift in the tutt is found in all of the available reanalysis data sets during 1979 2012 suppressing tc genesis in the eastern portion east of 145 e of the western north pacific basin due to the enhanced vertical wind shear associated with the tutt shift as a result the annual mean tc genesis longitude has significantly shifted westward since 1979 the westward shifting trends in the tutt and tc genesis are associated with the enhanced tropical tropospheric warming which is consistent with the response of the tropospheric temperature to global warming

the character and age structure of valley fills in upper wolumla creek catchment south coast new south wales australia extensive valley fills at the base of the escarpment in upper wolumla creek on the south coast of new south wales australia have formed from a combination of cut and fill processes the valley fills comprise series of alternating horizontally bedded sand and mud units reflecting reworking of detritus from deeply weathered granites of the bega batholith sand units are deposited as sand sheets or splays on floodplain surfaces or in floodouts that form atop intact valley fill surfaces downstream of discontinuous gullies alternatively sands are deposited from bedload and form bars or part of the valley floor within channel fills organic rich mud units are deposited from suspension in swamps or in seepage zones at the distal margin of floodouts within 5 km of the escarpment valley deposits grade downstream from sand sheet and splay deposition in floodouts to mud deposition in swamp and seepage zones radiocarbon dates indicate that virtually the entire valley fill of upper wolumla creek was excavated prior to 6000 years bp remnant terraces are evident at valley margins the valley subsequently filled between 6000 years bp and 1000 years bp producing valley fills around 12 m deep but no greater than 300 m wide reincision into the valley fill on a scale smaller than the present incision phase is indicated at around 1000 years bp following which the channel refilled portion plans dated from 1865 refer to the study area as wolumla big flat and show large areas of swampy terrain suggesting that the valley fill had re established by this time within a few decades of european settlement the valley fill incised once more upper wolumla creek now has a channel over 10 m deep and 100 m wide in places draining a catchment area of less than 20 km2 1998 john wiley sons ltd

the recent history of erosion and sedimentation on the southern tablelands of southeastern australia sediment flux dominated by channel incision abstract as in other regions colonised from europe within the last few centuries australia s vegetation and soils have been dramatically changed by clearing cropping and grazing in southeastern australia particularly on the southern tablelands the impacts of european settlement are clearly manifested by channel incision by using stratigraphic and documentary evidence in conjunction with aerial photographs sediment budgets for the post settlement period have been constructed to define the fluxes and stores of sediment for each of the major geomorphic components of the 136 km2 catchment of jerrabomberra creek near canberra using these budgets and some plausible assumptions it has been possible to approximate the history of both the sediment delivery ratio and sediment yield for this catchment while the quantities estimated in this analysis are approximations the trends through time are credible sediment yield increased rapidly to a peak after european settlement and has returned to a level between the peak and the pre european value the delivery ratio has followed a similar trend the most general conclusion to emerge is that in this landscape both the total sediment flux and the sediment yield of the catchment have been dominated by channel erosion this result is contrary to the findings in many parts of the world where sheet and rill erosion dominates the fluxes the soil conservation implication of these results is clear to control off site effects of erosion the focus must be on the channels

the negra muerta volcanic complex southern central andes geochemical characteristics and magmatic evolution of an episodically active volcanic centre abstract this petrologic analysis of the negra muerta volcanic complex nmvc contributes to understanding the magmatic evolution of eruptive centres associated with prominent nw striking fault zones in the southern central andes specifically the geochemical characteristics and magmatic evolution of the two eruptive episodes of this complex are analysed the first one occurred as an explosive eruption at 9 ma and is represented by a strongly welded fiamme rich andesitic to dacitic ignimbrite deposit the second commenced with an eruption of a rhyolitic ignimbrite at 7 6 ma followed by effusive discharge of hybrid lavas at 7 3 ma and by emplacement of andesitic to rhyodacitic dykes and domes both explosive and effusive eruptions of the second episode occurred within a short time span but geochemical interpretations permit consideration of the existence of different magmas interacting in the same magma chamber our model involves an andesitic recharge into a partially cooled rhyolitic magma chamber pressurising the magmatic system and triggering explosive eruption of rhyolitic magma chemical or mechanical evidence for interaction between the rhyolitic and andesitic magma in the initial stages are not obvious because of their difference in composition which could have been strong enough to inhibit the interaction between the two magmas after the initial explosive stages of the eruption at 7 6 ma the magma chamber become more depressurised and the most mafic magma settled in compositional layers by fractional crystallisation restricted hybridisation occurred and was effective between adjacent and thermally equivalent layers close to the top of the magma chamber at 7 3 ma increments of caldera formation were accompanied by effusive discharge of hybrid lavas through radially disposed dykes whereby andesitic magma gained in importance toward the end of this effusive episode in the central portion of the caldera assimilation during turbulent ascent ata is invoked to explain a conspicuous reversed isotopic signature 87sr 86sr and 143nd 144nd in the entire volcanic series therefore the 7 6 to 7 3 ma volcanic rocks of the nmvc resulted from synchronous and mutually interacting petrological processes such as recharge fractional crystallization hybridisation and assimilation during turbulent ascent ata geochemical characteristics of both volcanic episodes show diverse type and or depth in the sources and variable influence of upper crustal processes and indicate a recurrence in the magma forming conditions similarly other minor volcanic centres in the transversal volcanic belts of the central andes repeated their geochemical signatures throughout the miocene

holocene valley aggradation and gully erosion in headwater catchments south eastern highlands of australia late quaternary stratigraphy of a 50 km2 catchment on the south eastern highlands of australia reveals processes and history of denudation and helps resolve a long standing debate about factors controlling episodic valley aggradation and degradation during holocene times valley sedimentation occurred when swampy vegetation fully colonized valley floors and obliterated all channels promoting aggradation for periods of several thousand years with most incoming sediment being trapped in swampy meadows much of the sediment was reworked from late pleistocene alluvial fan and valley fill deposits and primary hillslope erosion was minor during the holocene differing sedimentation patterns between the late pleistocene holocene and post european settlement periods reflect regional changes in sediment supply and transport capacity as a result of major environmental change within the holocene however valley fill stratigraphy is controlled by massive episodic gully erosion terminating aggradation gully initiation appears to be controlled more by thresholds of incision into vegetated valley floors than by changes to sediment supply whether the thresholds are exceeded because of climatic change autonomous change or extreme events cannot yet be determined overall the holocene history represents continuing complex response to events of the late pleistocene and does not support the k cycle concept which has strongly influenced late quaternary geomorphology in australia

tectonic evolution of a continental magmatic arc from transpression in the upper crust to exhumation of mid crustal orogenic root recorded by episodically emplaced plutons the central bohemian plutonic complex bohemian massif the central bohemian plutonic complex cbpc consists of episodically emplaced plutons the internal fabrics of which recorded tectonic evolution of a continental magmatic arc the 354 350 ma calc alkaline plutons were emplaced by multiple processes into the upper crustal tepla barrandian unit and their magmatic fabrics recorded increments of regional transpression multiple fabrics of the younger 346 ma blatna pluton recorded both regional transpression and the onset of exhumation of mid crustal orogenic root moldanubian unit continuous exhumation related deformation during pluton cooling resulted in the development of a wide zone of sub solidus deformation along the se margin of the cbpc finally syn exhumation tabular durbachitic pluton of ultrapotassic composition was emplaced atop the intrusive sequence at 343 340 ma and the ultrapotassic tabor pluton intruded after exhumation of the orogenic root 337 ma we suggest that the emplacement of plutons during regional transpression in the upper crust produced thermally softened domain which then accommodated the exhumation of the mid crustal orogenic root and that the complex nature of the tepla barrandian moldanubian boundary is a result of regional transpression in the upper crust the enhancement of regional deformation in overlapping structural aureoles the subsequent exhumation of the orogenic root domain and post emplacement brittle faulting

stream response to quaternary climate change evidence from the shoalhaven river catchment southeastern highlands temperate australia abstract luminescence ages from a flight of four paired alluvial terraces in the upper catchment of the shoalhaven river southeast highlands australia provide a record of stream behaviour throughout the late quaternary ages ranging from 7 ka in the modern floodplain to nearly 500 ka for the uppermost dated terrace allow comparisons to be made of the response of streams throughout southeastern australian to late quaternary climatic perturbations the alluvial record of the shoalhaven river highlights the broad regional synchronicity of episodes of heightened fluvial activity during oxygen isotope stage ois 5 terminating 75 ka 60 40 30 25 and 20 15 ka the shoalhaven record also shows an absence of fluvial activity during the last glacial maximum suggesting that southeastern australia was most likely dry at this time as compared to northern australia which was probably wet fluvial activity while still significant decreased substantially after approximately 60 ka suggesting a general drying of climate towards the present

is the poleward migration of tropical cyclone maximum intensity associated with a poleward migration of tropical cyclone genesis a recent study showed that the global average latitude where tropical cyclones achieve their lifetime maximum intensity has been migrating poleward at a rate of about one half degree of latitude per decade over the last 30 years in each hemisphere however it does not answer a critical question is the poleward migration of tropical cyclone lifetime maximum intensity associated with a poleward migration of tropical cyclone genesis in this study we will examine this question first we analyze changes in the environmental variables associated with tropical cyclone genesis namely entropy deficit potential intensity vertical wind shear vorticity skin temperature and specific humidity at 500 hpa in reanalysis datasets between 1980 and 2013 then a selection of these variables is combined into two tropical cyclone genesis indices that empirically relate tropical cyclone genesis to large scale variables we find a shift toward greater smaller average potential number of genesis at higher lower latitudes over most regions of the pacific ocean which is consistent with a migration of tropical cyclone genesis towards higher latitudes we then examine the global best track archive and find coherent and significant poleward shifts in mean genesis position over the pacific ocean basins

topographically associated but chronologically disjunct late quaternary floodplains and terraces in a partly confined valley south eastern australia the bellinger river catchment in the new england fold belt on the mid north coast of new south wales is characterized by an assemblage of stepped late quaternary alluvial units late pleistocene terraces were formed by large more competent rivers that eroded almost entire valley floors however a decline in discharge prior to the holocene has resulted in the abandonment of these deposits as elevated terraces or residual alluvium onlapped by contemporary floodplains intrinsic controls on floodplain formation appear to be superimposed over an early mid holocene climatic signature a fluvially active period known as the nambucca phase from 10 to 4 5 ka eroded late pleistocene terraces two floodplain surfaces one higher than the other both started to accrete vertically from 4 ka but with some valley locations remaining vulnerable to episodes of erosion resulting in substantial units of even younger basal alluvium the high floodplain is dominated by horizontally laminated vertically accreted sequences while the low floodplain which overlaps in age is characterized by pronounced cut and fill stratigraphy terraces and floodplains in partly confined settings can have similar elevations but be polycyclic with very different basal ages in such landscapes the classical assumption that individual terrace or floodplain profiles along a valley represent periods of coeval formation is shown to be frequently invalid copyright 2007 john wiley sons ltd

plate reconstructions aseismic ridges and low angle subduction beneath the andes low angle subduction segments beneath peru and chile are believed to represent interaction of the subduction zone with the aseismic nazca and juan fernandez ridges on the basis of symmetric sea floor spreading models and plate hotspot reconstructions predicted continuations of the relatively buoyant ridges correspond well with the limits of the low angle subduction segments further the history of interaction of the aseismic ridges with the subduction zone as predicted by plate reconstructions is not inconsistent with available information on volcanic episodes of the andes if the contemporary correlation of volcanic gaps and low angle subduction is also applicable to the rest of the late cenozoic the occurrence of deep seismicity beneath the eastern flanks of the andes is also believed to reflect the effects of low angle subduction the deep seismic segments are adjacent to segments which are presently or were recently experiencing low angle subduction thus the deep seismicity is interpreted as representative of remnants of normal oceanic lithosphere subducted before interaction of aseismic ridges with the subduction zone other geologic phenomena are associated with low angle subduction beneath south america including landward shift in loci of tectonism surficial subsidence and laramide style deformation the aseismic ridge buoyancy hypothesis appears to be a valuable predictive tool for the interpretation of such geologic effects

geomorphic evidence for tear faults accommodating lateral propagation of an active fault bend fold wheeler ridge california abstract wheeler ridge is the topographic expression of an actively growing fault bend fold developed in the hanging walls of a system of mostly north vergent blind thrusts the eastern tip of the fold system has migrated laterally by approximately 3 km during the last 120 ka perpendicular to the regional shortening direction comparison of surface topography and structural cross sections indicates that eastern wheeler ridge comprises three fold segments whose topographic expression steps southward towards the eastern end of the structure lateral propagation of the fold is associated with numerous tear faults expressed as fault scarps that face towards the eastern end of the fold we suggest that these tear faults accommodate earthquake related processes that collectively build plunge of the fold and lateral propagation on blind thrusts we envisage that the fold will grow primarily by thrust faulting events with similar displacement s along strike that are terminated abruptly at tear faults build displacement over multiple earthquake cycles and then step eastward to form a new tear fault formation of especially large tear faults is inferred to be in response to an increase in rock strength governed by lithology the high fault displacement vs length d l for wheeler ridge may be related to high strain rates across a restraining bend in the nearby san andreas strike slip fault system

late quaternary dynamics of a south african floodplain wetland and the implications for assessing recent human impacts abstract knowledge of the long term geomorphological dynamics of wetlands is limited so currently there is an inadequate scientific basis for assessing anthropogenically induced changes and for developing conservation remediation and or sustainable management guidelines for these fragile ecosystems along the upper klip river eastern south africa geomorphological and sedimentological investigations geochronology and remote sensing have been used to establish the late quaternary dynamics of some internationally important floodplain wetlands thus providing a reference condition against which to assess the extent of recent human impacts optically stimulated luminescence dating reveals that the wetlands have developed over at least the last 30 ky as a result of slow meander migration 1 irregular cutoff events and infrequent avulsions approximately one every 3 6 ky that have occurred autogenically as a natural part of meander belt development following european settlement in the klip valley late nineteenth century however modifications to local flora and fauna as well as the initiation of local wetland drainage schemes have had major impacts in particular proliferation of exotic willows and associated debris jams and the artificial excavation of a 1 2 km long channel section across the wetlands have initiated an ongoing avulsion that is characterised by failure gradual abandonment of the main channel and rapid incision of a headcutting channel compared to the pre settlement condition little change in lateral migration activity has occurred but this avulsion provides a clear example of anthropogenically accelerated change occurring only 1 ky after the last natural avulsion and in a part of the wetlands where avulsions have not occurred previously subsequent human interventions have included installing weirs in an attempt to control the resulting erosion and promote reflooding but ongoing maintenance has been required in areas that were not glaciated during the quaternary many other floodplain wetlands may be of similar antiquity but the klip river illustrates their sensitivity to direct and indirect human impacts

the holocene evolution and geomorphology of a chain of ponds southeast australia establishing a physical template for river management abstract chains of ponds are a discontinuous river type found in australia their unusual morphology important ecological functions and increasing rarity make them a priority for conservation and yet very little research has investigated their physical structure behaviour and evolution this paper reconstructs the holocene evolution and environmental history of crisp s creek a headwater chain of ponds in the southern tablelands of nsw australia this history establishes baseline information on the physical template that can be used to assess a range of other biophysical processes and design appropriate river rehabilitation and management strategies for these rivers sedimentary aggradation began in the late holocene at least 3 7 1 3 ka broadly synchronous with aggradation phases at other sites in southeast australia since european arrival in the nineteenth century parts of the river incised destroying intact ponds and smothering formerly swampy floodplains with post incision alluvium however sections unaffected by incision provide a rare opportunity to examine the evolutionary trajectory of an intact variant of these rivers this research deepens our understanding of the evolutionary context for contemporary river behaviour as relevant for designing appropriate and effective conservation and rehabilitation strategies for chains of ponds

pre existing cross structures and active fault segmentation in the northern central apennines italy abstract the multideformed axial zone of the apennines provides a great opportunity to explore the influence of pre existing cross structures inherited from pre quaternary tectonic phases on the segmentation of quaternary active seismogenic extensional faults detailed geological and structural data and their comparison with seismological data show that although the attitudes strike and dip of oblique pre existing faults are certainly an important factor in determining a segment boundary the size of the inherited oblique structures seems to be more crucial pre existing cross structures with lengths ranging from several kilometers to a few tens of kilometers show a twofold behavior they can act as segment barriers during the rupture of a single fault segment or they can be reactivated as transfer zones inducing the activation of two adjacent segments that belong to the same fault system regional basement crustal oblique pre existing cross structures with lengths ranging from several tens of kilometers to hundreds of kilometers commonly nne striking may act as persistent structural barriers that halt both fault segment and fault system propagation thus determining their terminations and maximum sizes in the northern central apennines the nne striking ancona anzio valnerina and ortona roccamonfina tectonic lineaments although having been repeatedly reactivated since the mesozoic represent the most important examples of these structures moreover probably due to their misorientation with respect to the present extensional stress field regional nne striking pre existing structures appear to be less likely to produce strong magnitude events no surface evidence for quaternary faulting has been found thus far and historical and instrumental seismicity shows only m m 7 event on the other hand is more likely to occur along the n nw s se trending normal fault systems lastly we propose a model that can explain the different sizes of fault segments and fault systems on the basis of their location with respect to the persistent structural barriers and their spacing in this view our results may contribute to a more reasonable assessment of the nature and size of future surface ruptures in the northern central apennines which are of critical importance to estimating seismic hazard

late quaternary river evolution of floodplain pockets along mulloon creek new south wales australia valley confinement along upper middle reaches of mulloon creek in the upper shoalhaven catchment of southern new south wales australia restricts floodplain development to a series of distinct pockets these pockets comprise a downstream thinning wedge of vertically accreted fine grained deposits atop basal gravels some time before 12500 years ago a bedload dominated river was transformed into a suspended load system in the mid late holocene swamps developed in the middle lower part of each floodplain pocket within a few decades of european settlement of this region circa ad 1820 discontinuous watercourses in some floodplain pockets had incised to form a low sinuosity gravel bed channel wedge shaped units of post incisional alluvium that thicken downstream overlie the swamp and floodplain deposits in the downstream part of these pockets in the downstream most pocket incision commenced prior to colonization while upstream swamps retain a continuous swamp across the valley floor the late quaternary evolution of this variant of discontinuous watercourse is summarized in a schematic model

thick skinned and thin skinned thrusting in the la ramada fold and thrust belt crustal evolution of the high andes of san juan argentina 32 sl abstract the cenozoic structural evolution of the la ramada fold and thrust belt in the high andes of argentina between 32 00 s and 32 30 s shows in time and space the interaction of thin skinned and thick skinned deformations based on geometric and kinematic constraints three different deformation stages have been recognized the first began with thin skinned nnw trending structures detached in upper jurassic gypsum in the second stage the basement was involved by tectonic inversion of triassic normal faults producing a thick skinned fold and thrust belt this inversion combined with the ductile rheology of the jurassic gypsum resulted in refolding of older structures the uplift of the basement by high angle reverse faults at the ramada espinacito massif produced a sticking point in the foreland propagation of the thrust belt this was responsible for the third stage of deformation characterized by thin skinned nnw out of sequence thrusts developed in the westernmost sector the total andean shortening calculated in the area was 21 24 km near 30 the structure of the la ramada fold and thrust belt was integrated into a crustal scale cross section at 32 s latitude based on gravimetric models and surface geology a crustal model is proposed for the andes of chile and argentina a shortening of 180 km was calculated between the chile trench and the sierra de pie de palo this implies a mean deformation rate of 2 8 mm year 1 during cenozoic times an initial crustal thickness of ca 33 km was computed a two layer model with a middle detachment level is proposed to explain the spatial decoupling between maximum shortening at the surface and maximum crustal thickening the upper layer was balanced based on surface structural information the lower layer is interpreted to have been constructed by an imbricate thrust system controlled by the mercedario rift master shear and the precordillera chilenia suture

the cerro aguas calientes caldera nw argentina an example of a tectonically controlled polygenetic collapse caldera and its regional significance article i nfo polygenetic silicic collapse calderas are common in the central andes here we describe in detail the cerro aguas calientes caldera in nw argentina which comprises two caldera forming episodes that occurred at 17 15 ma and 10 3 ma we analyse the significance of its structural setting composition size and the subsidence style of both caldera episodes we find that the caldera eruptions had a tectonic trigger in both cases an homogeneous dacitic crystal rich n60 vol of crystals reservoir of batholithic size became unstable due to the effect of increasing regional transpression which favoured local dilation through minor strike slip faults from which ring faults nucleated and permitted caldera collapse both calderas are similar in shape location and products the 17 15 ma caldera has an elliptical shape 17 14 km elongated in a n30 trend both intracaldera and extracaldera ignimbrites covered an area of around 620 km 2 with a minimum volume estimate of 140 km

deformation partitioning in flat subduction setting case of the andean foreland of western argentina 28 s 33 s 1 the andean foreland of western argentina 28 s 33 s corresponds to back arc deformations associated with the ongoing flat subduction of the nazca plate beneath the south american lithosphere in this paper short and long term tectonic regimes for this andean region are investigated and compared to nuvel 1 and the new gps derived velocity field for the andes mountains from this comparison it appears that 1 the slight convergence obliquity at the plate boundary is accommodated by the subduction zone itself precluding any deformation partitioning at lithospheric scale 2 clockwise rotation of 1 and p axes within the andean foreland of western argentina suggests that plio quaternary deformation partitioning may occur in the upper plate at crustal scale and 3 comparison of seismic rates of shallow deformations determined from moderate to large earthquakes localized between 22 s and 36 s shows that the amount of shortening is about the same 2 4 cm yr 1 between the forearcs of the 30 dipping slab segments and the back arc of the flat segment all together those observations are in close agreement with the idea that interplate coupling in flat subduction settings may play a key role in the present day transfer of plate boundary forces consequently the andean back arc of western argentina might be regarded as an obliquely converging foreland where plio quaternary deformations are partitioned between strike slip and thrust motions that are localized in the east verging thin skinned argentine precordillera and west verging thick skinned pampean ranges respectively

geological controls on the formation of alluvial meanders and floodplain wetlands the example of the klip river eastern free state south africa tooth s mccarthy t s brandt t hancox p j morris r 2002 geological controls on the formation of alluvial meanders and floodplain wetlands the example of the klip river eastern free state south africa earth surface processes and landforms 27 8 797 815

magma emplacement in transpression the santa olalla igneous complex ossa morena zone sw iberia the santa olalla igneous complex a late variscan group of intrusions located in the ossa morena zone sw iberia has been the focus of a gravity and structural study the structure outlined by the foliation map is complex showing two different structural domains one characterized by vertical and the other by horizontal magmatic foliations the vertical fabrics are restricted to the ne half of the complex which is in direct contact with a variscan sinistral strike slip fault cherneca fault whereas the horizontal fabrics are developed in the sw half of the complex which is characterized by a horizontal tabular geometry gravity modeling indicates that the deeper floor of the plutons is closely related to the ne margin and the cherneca fault an emplacement and structural evolution model for this igneous complex is proposed following these structural and gravity results 1 magma ascent was favored by releasing bends in the trace of the cherneca fault 2 when magma reached the present level it intruded to the sw with a horizontal sheet geometry generating the subhorizontal foliation domain 3 after emplacement the ne half of the complex suffered the external tectonic stress field provoked by sinistral motion along the cherneca fault subsequently generating the subvertical magmatic foliation domain

magmatic evidence for neogene lithospheric evolution of the central andean flat slab between 30 s and 32 s abstract geochemical data from andean miocene magmas erupted through the now volcanically inactive flat slab between 30 s to 32 s coupled with geological and geophysical data illuminate details on magmatic and continental lithospheric evolution over a progressively shallowing subduction zone pb sr and nd isotopic and trace element data show that main cordilleran precordilleran and pampean magmas were contaminated in both the mantle and crust and that the nature of the contaminants varied in time and space reflecting tectonic events contaminants included both enriched high lil element high sr and pb and low nd isotopic ratios and depleted low lile element low sr and pb and high nd isotopic ratios types in the western region main cordilleran earlier miocene lavas had contaminants with less enriched signatures than later miocene lavas progressive enrichment is attributed to a increasing amounts of sediment and tectonically eroded crust being subducted into the mantle wedge and b contamination in a thickening main cordilleran lower crust whose composition was progressively enriched this enrichment occurred through addition of upper crust by an intracrustal mixing process driven by a propagating wedge tip associated with westward wedging heating and deformation of crust from beneath the shortening precordillera thrust belt to the east further east magmas erupted through back arc crust have more depleted signatures those erupted in the central part through the evolving precordilleran thrust belt were contaminated by an older thinner grenville 1100 ma basement whose depleted signature is unique among central andean terranes late miocene pocho lavas erupted further east in conjunction with uplift of the sierras pampeanas show enrichment through time arguably these magmas could contain a component mechanically removed from the base of the thinning continental lithosphere to the west and progressively incorporated into the convecting asthenosphere first order mass balance calculations comparing the lithospheric geometry proposed for 20 ma with that today suggests that 60 of the lithosphere within 600 km of the trench at 20 ma has been lost this lithospheric loss is required to accommodate simultaneous shallowing of the oceanic slab and thickening and shortening of the crust continental lithosphere recycled into the asthenosphere could contribute to the sources of the enriched em1 and em2 mantle components in oceanic island basalts

landscape preservation under post european settlement alluvium in the south eastern australian tablelands inferred from portable osl reader data human land use changes leading to widespread erosion and gully incision have been well studied but the effects that erosion and sediment mixing which accompany the deposition of post european settlement alluvium psa have in valley bottoms and wetlands receive considerably less attention psa overlying pre disturbance swampy meadow sm wetland sediments is commonly exposed along incised stream channel gully walls throughout the south eastern australian tablelands providing an ideal setting in which to assess and understand better how psa deposition affects valley bottoms and the wetland environments that often occupy them portable optically stimulated luminescence posl reader data were measured on bulk sediment samples from sm psa stratigraphies at 16 locations throughout the south eastern australian tablelands to assess the effects of erosion and sediment mixing at the sm psa boundary trends of posl data with depth at each profile were used in conjunction with visual profile descriptions to identify the stratigraphic boundary between sm and psa sediment and to infer the degree of valley bottom erosion and sediment mixing during psa deposition at most sites sm sediments experienced minimal if any disturbance during psa deposition and we refer to these as non eroded sites many sites however experienced a significant degree of erosion and sediment mixing eroded sites often corresponding to visually diffuse sedimentary boundaries between the two stratigraphic units our findings demonstrate that sm landscapes in the tablelands can be preserved with minimal disturbance under psa at non eroded sites and are preserved beneath a mixing zone at all eroded sites copyright 2016 john wiley sons ltd

wetting and drying of australia over the past 300 ka alternately dry and wet climatic episodes across central and eastern australia during the past 300 ka have greatly affected australia9s rivers lakes and dune fields evidence of widespread climate and flow regime changes has been provided by 75 thermoluminescence tl dates and 18 u th dates from alluvial and eolian sediments fluvial conditions dominated part of the last two interglacials stage 5 and 7 resulting in large sand loads in rivers in the present simpson desert and southeastern australia during the last interglacial fluvial activity in central australia peaked at 110 ka stage 5 pluvial probably 5 10 ka behind world temperature and sea level maxima following the last late interglacial wet phase aridity associated with dune building spread from central australia toward its margins achieving greatest intensity during the last glacial maximum a less widespread wet phase identified at about 55 35 ka stage 3 subpluvial is associated with high lake levels and paleochannel activity in southeastern australia this tl record of variable continental aridity in australia correlates well with global changes including the variable eolian dust flux into central china the northern pacific ocean and antarctica

structural controls of volcanism in transversal chains resheared faults and neotectonics in the cordon caulle puyehue area 40 5 s southern andes abstract the nature of the relationship between tectonics and volcanism in a specific area is the result of the interaction between the crustal structures of the basement and ongoing regional stress field in the southern andes different kinematic environments represented by two nearly orthogonal active fissure systems show apparently incompatible arrays of volcanic chains moreover a local quaternary compressive regime is inferred from basement faults however these mutually orthogonal chains which are also oblique to the volcanic front have contrasting magma evolution and eruptive styles that can be related with their tectonic setting whereas northeast trending monogenetic cones carran los venados can be interpreted as resulting from magma upwelling along regional tension cracks in a quaternary dextral transpressive compressive domain northwest striking fissure system cordon caulle volcanic complex can be the result of extensional fault reactivation and long magma residence in the upper crust different kinematic environments cause contrasting magma evolution and eruptive styles a two way coupling mechanism is suggested for to explain local depart of the regional stress field geometric array of extensional features and final magmatic evolution in these volcanic domains of the southern andes

the long term control of vegetation and woody debris on channel and flood plain evolution insights from a paired catchment study in southeastern australia abstract numerous case studies have demonstrated that alluvial and semi alluvial rivers in se australia have undergone dramatic metamorphosis in historical times however very few studies place these changes within a long term evolutionary context as a consequence the magnitude of and ultimate controls on the changes to river form and processes are not fully appreciated in this study a paired catchment analysis is undertaken between two moderate sized sand bed rivers in east gippsland australia from the thurra river direct insight is gained into the predisturbance control exerted by riparian vegetation and wood in a lowland alluvial river this river is effectively in the same condition today as it was at the time of the arrival of europeans in australia in contrast the adjacent cann river which has been settled by europeans for 150 years but was previously very similar to the thurra river exhibits stark differences today channel morphodynamics observed within the thurra river when coupled with historical and geomorphic evidence for the former condition of the cann river provide a detailed reference by which the recent changes to the cann river are measured chronostratigraphic evidence from both flood plains places recent channel behavior within an evolutionary context extending well into the pleistocene since european settlement the study reach of the cann river has experienced a 360 increase in channel depth a 240 increase in channel slope a 700 increase in channel capacity and up to a 150 fold increase in the rate of lateral channel migration the contemporary condition of the cann river channel differs profoundly to that which has prevailed over at least the previous 27 ka the first order control on the historical channel metamorphosis is the removal of riparian vegetation and woody debris wd numerous thresholds have been crossed as a result of historical channel changes particularly the relationship between average length of woody debris pieces and channel width consequently channel recovery will not simply be achieved by reintroducing the pre existing riparian vegetation and woody debris load devising sound management strategies and realistic management targets for the cann river or any similarly altered river requires an understanding of the long term channel and flood plain evolutionary history as well as the underlying controls on historical changes

approximating edges of source bodies from magnetic or gravity anomalies cordell and grauch 1982 1985 discussed a technique to estimate the location of abrupt lateral changes in magnetization or mass density of upper crustal rocks the final step of their procedure is to identify maxima on a contoured map of horizontal gradient magnitudes we attempt to automate their final step our method begins with gridded magnetic or gravity anomaly data and produces a plan view of inferred boundaries of magnetic or gravity sources the method applies to both local surveys and to continent wide compilations of magnetic and gravity data e g zietz 1982 simpson et al 1983a kane et al 1982

mind the gap an absence of valley fill deposits identifying the holocene hypsithermal period of enhanced flow regime in southeastern australia the holocene sedimentary record in southeastern australia is present in a range of landscape settings such as upland swamps dells internally drained lake basins alluvial fans and mid catchmen

deformation structures and processes within the continental crust an introduction the collection of research papers in this volume provides an overview of current trends in the study of deformation structures and deformation processes in rocks from the continental crust the volume has been divided into three sections to reflect the current interest in structures and processes shear zones and folds the interactions between magmatism and structure and the relationship between microstructure and rheology the range of topics includes the geometry of natural structures from field observations the detailed analysis of the microstructure of deformed rocks the timing of deformation by various geochronological techniques the modelling of deformation processes to constrain the development of structures in rocks and the use of labora tory experimentation to reproduce deformation fabrics in rocks the mixture of techniques and methods treated illustrate the broad and multidisciplinary approach to the study of rock defor mation in the continental crust

european impacts on downstream sediment transfer and bank erosion in cobargo catchment new south wales australia abstract upland valley fills in cobargo catchment on the south coast of new south wales represent substantial sediment source zones contemporary channels within these fills are up to 8 m deep and 50 m wide for catchment areas 2 virtually all banks are eroding downstream of this sediment source zone sediment transfer zones are characterised by sinuous channels that are partially choked by sands released from upland valley fills coarse sands stored in point bars deflect flow to outer banks where colluvial footslopes are eroded approximately 50 of banks are eroding in this section of the catchment other than the 10 km river reach upstream of the river mouth the remainder of the catchment is a bedrock confined sediment throughput zone characterised by fluctuations in channel bed elevation the downstream 10 km of the catchment is a sediment accumulation zone in which erosion is restricted to occasional concave banks prior to european settlement of cobargo catchment upland valley fills were largely unincised and middle transfer reaches of the catchment comprised swamps vegetation clearance along with disturbance and drainage of swamps transformed discontinuous water courses into continuous channels working from a base point of intact upland valley fills almost 50 of available material has been removed from the upper catchment sediment source zone contributing 2 9 10 6 m 3 of material to the lower catchment of this roughly 65 has been stored along the channel bed and floodplain this gives a total sediment contribution to the delta of 1 0 10 6 m 3 sufficient materials are stored in transient storage units along transfer zones to maintain current rates of sediment throughput to the delta for several decades cobargo catchment experienced dramatic acceleration of channel incision and bank erosion processes within a few decades following european settlement of the catchment i e around 1830 transition in landscape form and associated sediment delivery were rapid with a negligible lag interval i e within a few decades of disturbance however given the extensive volume of sediment released from upland valley fills landscape recovery i e refilling of upland valleys will likely take thousands of years

can slab melting be caused by flat subduction slab melting has been suggested as a likely source of adakitic arc magmas i e andesitic and dacitic magmas strongly depleted in y and heavy rare earth elements existing numerical and petrologic models however restrict partial melting to very young 5 ma oceanic crust typically at 60 80 km depth paradoxically most of the known pliocene quaternary adakite occurrences are related to subduction of 10 45 ma lithosphere which should not be able to melt under normal subduction zone thermal gradients we propose an unusual mode of subduction known as flat subduction occurring in 10 of the world s convergent margins that can produce the temperature and pressure conditions necessary for fusion of moderately old oceanic crust of the 10 known flat subduction regions worldwide eight are linked to present or recent 6 ma occurrences of adakitic magmas observations from chile ecuador and costa rica suggest a three stage evolution 1 steep subduction produces a narrow calc alkaline arc typically 300 km from the trench above the asthenospheric wedge 2 once flat subduction begins the lower plate travels several hundred kilometers at nearly the same depth thus remaining in a pressure temperature window allowing slab melting over this broad distance and 3 once flat subduction continues for several million years the asthenospheric wedge disappears and a volcanic gap results as in modern day central chile or peru the proposed hypothesis which reconciles thermal models with geochemical observations has broad implications for the study of arc magmatism and for the thermal evolution of convergent margins

influence of track changes on the poleward shift of lmi location of western north pacific tropical cyclones abstractthe annual mean latitude at which tropical cyclones tcs reach their lifetime maximum intensity lmi over the western north pacific ocean basin has shifted northward since the early 1980s

cross strike structures controlling magmatism emplacement in a flat slab setting precordillera central andes of argentina fil oriolo sebastian universidad de buenos aires facultad de ciencias exactas y naturales departamento de geologia argentina consejo nacional de investigaciones cientificas y tecnicas argentina

multi scalar controls on channel geometry of headwater streams in new zealand hill country abstract catchment reach and local scale controls upon channel geometry are examined for small headwater streams in adjacent sub catchments with variable land use histories in a typical hill country area of the north island of new zealand although systematic downstream increase in channel cross sectional area is evident in one sub catchment a result of catchment scale controls on geometry including discharge and slope marked local variability in channel geometry in the two other sub catchments reflects non systematic patterns of reach scale controls including the distribution of floodplain pockets and associated bank materials and local scale controls such as bedrock outcrops and wood land use change exerts a primary control upon these relationships for a given catchment area streams in native forest are wider and shallower than streams that flow within pasture or pinus plantations increased hillslope erosion following land clearance has instigated the accumulation of post settlement alluvium psa which has altered the boundary conditions and bank materials within which streams flow significant psa accumulation following native forest clearance in one of the sub catchments has allowed the stream to flow entirely within its own alluvial deposits in this instance catchment scale controls on channel geometry are dominant in contrast local scale controls on channel geometry are more important in the other sub catchments where lesser accumulation of psa reflects differences in land clearance these findings indicate that place based understandings which consider the spatial and historical contexts of landscape settings are required to interpret patterns of channel geometry and to inform river rehabilitation initiatives

confirming geomorphological interpretations based on portable osl reader data portable optically stimulated luminescence osl readers are increasingly being used in geomorphological and archaeological investigations but information regarding data reproducibility and the reliability of interpretations based on portable osl reader data has not yet been presented to the wider geomorphological community this letter addresses these two issues by returning to grabben gullen creek in the southeastern australian tablelands where we remeasure a sediment profile that was first measured by other researchers 3 years earlier we also compare portable osl reader data measured on sediment interpreted to have been deposited in swampy meadow wetlands and flood alluvium settings with data measured on known swampy meadow and flood deposits our data show that portable osl reader data are reproducible moreover we confirm the earlier interpretation that stratigraphies commonly exposed in southeastern australian tablelands valley bottoms reflect pre european swampy meadow wetlands and flood alluvium copyright 2015 john wiley sons ltd

surface ruptures on cross faults in the 24 november 1987 superstition hills california earthquake sequence left lateral slip occurred on individual surface breaks along northeast trending faults associated with the 24 november 1987 earthquake sequence in the superstition hills imperial valley california this sequence included the m s 6 2 event on a left lateral northeast trending cross fault between the superstition hills fault shf and brawley seismic zone which was spatially associated with the left lateral surface breaks six distinct subparallel cross faults broke at the surface with rupture lengths ranging from about formula to 10 km and maximum displacements ranging from 30 to 130 mm about half a day after the m s 6 2 event an m s 6 6 earthquake nucleated near the intersection of the cross faults with the shf and rupture propagated southeast along the shf whereas right lateral slip on the shf occurred dominantly on a single trace in a narrow zone the cross fault surface slip was distributed over several stands across a 10 km wide zone also whereas afterslip accounted for a large proportion of total slip on the shf there is no evidence for afterslip on the cross faults we present documentation of these surface ruptures a simple mechanical model of faulting illustrates how the foreshock sequence may have triggered the main rupture displacement on other cross faults could trigger an event on the southern san andreas fault by a similar mechanism in the future