present day south american climate abstract this paper documents the main features of the climate and climate variability over south america on the basis of instrumental observations gathered during the 20th century it should provide a modern reference framework for paleoclimate research in south america targeting high resolution proxies over the past few centuries several datasets suitable for present day climate research are first described highlighting their advantages as well as their limitations we then provide a basic physical understanding of the mean annual cycle of the precipitation and atmospheric circulation over the continent and the adjacent oceans in particular the diversity of precipitation temperature and wind patterns is interpreted in terms of the long meridional extent of the continent and the disruption of the large scale circulation caused by the andes cordillera the contrasting oceanic boundary conditions and the landmass distribution similarly the intensity and timing of the interannual and interdecadal climatic fluctuations exhibit considerable geographical dependence as some regions are more influenced by large scale phenomena rooted in the tropical oceans while others are more influenced by high latitude phenomena the impact of these large scale phenomena over south america is documented by a regression analysis between selected atmospheric indices and the precipitation and temperature fields we have included a discussion on the seasonality and long term stability of such impacts and complemented our general description by an updated review of the literature on climate variability over specific regions

relative contributions of crustal temperature and composition to controlling the depth of earthquakes in southern california 1 control of the 13 km range of the maximum depth of earthquakes in southern california has been attributed previously to lateral variations in either crustal temperature or crustal rock composition here i compare heat flow a proxy for crustal temperature local maximum depths of earthquakes d95 and best guess crustal rock compositions plotting heat flow versus d95 produces distinct trends for each rock composition with each trend representing an isotherm marking the onset of plastic behavior offsets between the trends measure the differences in the plastic behavior temperatures of each rock composition these offsets are comparable to the d95 variations with heat flow thus crustal temperature and composition contribute about equally to the control of the maximum depths of earthquakes the observed isotherm slopes imply vertical variations in crustal composition in addition to the lateral variations

the evolution of the patagonian ice sheet from 35 ka to the present day patice abstract we present patice a gis database of patagonian glacial geomorphology and recalibrated chronological data patice includes 58 823 landforms and 1 669 geochronological ages and extends from 38 s to 55 s in southern south america we use these data to generate new empirical reconstructions of the patagonian ice sheet pis and subsequent ice masses and ice dammed palaeolakes at 35 ka 30 ka 25 ka 20 ka 15 ka 13 ka synchronous with the antarctic cold reversal 10 ka 5 ka 0 2 ka and 2011 ad at 35 ka the pis covered of 492 6 x103 km2 had a sea level equivalent of 1 496 mm was 350 km wide and 2090 km long and was grounded on the pacific continental shelf edge outlet glacier lobes remained topographically confined and the largest generated the suites of subglacial streamlined bedforms characteristic of ice streams the pis reached its maximum extent by 33 28 ka from 38 s to 48 s and earlier around 47 ka from 48 s southwards net retreat from maximum positions began by 25 ka with ice marginal stabilisation then at 21 18 ka which was then followed by rapid irreversible deglaciation by 15 ka the pis had separated into disparate ice masses draining into large ice dammed lakes along the eastern margin which strongly influenced rates of recession glacial readvances or stabilisations occurred at least at 14 13 ka 11 ka 6 5 ka 2 1 ka and 0 5 0 2 ka we suggest that 20th century glacial recession a 1 is occurring faster than at any time documented during the holocene

an interlinked system of folds and ductile shear zones late stage svecokarelian deformation in the central fennoscandian shield finland abstract the svecokarelian deformation of the karelian and svecofennian provinces in finland involved four main phases isoclinal folding and associated thrusting were the main processes of d 1 which was followed by more open folding in d 2 subsequent deformation was localized during d 3 and d 4 this paper focuses on the late stage d 4 svecokarelian deformation that created most of the ductile shear zones in the central fennoscandian shield and was the last penetrative deformational event to affect the entire palaeoproterozoic domain deformation during d 4 occurred approximately from 1 85 1 80 ga and left a greater imprint in the rocks than has commonly been supposed the shear zones formed during d 4 are referred to collectively as the finlandia shear system the karelian province is composed of archaean basement and its autochthonous allochthonous palaeoproterozoic sedimentary cover svecokarelian tectonics split the basement into separate complexes the rheological properties of which differed markedly from those of the adjacent proterozoic supracrustal units on the northern and southern margins of the archaean complexes folding with steep e w trending axial surfaces was the main response to d 4 deformation whereas on the eastern and western margins of the complexes the response to d 4 was the development of sinistral and dextral shear zones trending ne sw and nw se respectively on a large scale these areas of folding and of shearing form an interlinked system the changes from one style of deformation to the other being gradual the principal d 4 elements in the area of juvenile svecofennian crust are folds with e w trending axial surfaces

response and feedback of the indian summer monsoon and the southern westerly winds to a temperature contrast between the hemispheres during the last glacial interglacial transitional period abstract the hypothesis that an interhemispheric thermal gradient or a temperature contrast between the hemispheres tcbh drives shifts in the latitudinal position of the intertropical convergence zone itcz and the southern westerly winds sww is considered one of the most important climate change mechanisms proposed in the last few decades however the controversy over the shifting magnitude and direction of the itcz and the sww brings uncertainty to the hypothesis here we further examine the shifting characteristics of the itcz and its relationship with the intensity variation of the indian summer monsoon ism based on synthesis and summary of previously published literature data in particular we evaluate regional distribution patterns of the dry and wet climatic changes in southern south america during the last glacial interglacial transitional period including the heinrich event 1 the antarctic cold reversal and the younger dryas the results show that in response to the northern hemisphere wide cooling and the southern hemisphere wide warming the northern hemisphere wide warming and the southern hemisphere wide cooling during the period the itcz over the asian and northern south american continents and the sww shift poleward equatorward while the intensity of the ism decreases increases however the shifting characteristics of the itcz over the vast pacific ocean remain unclear which implies that the relationship between the tcbh and the el nino southern oscillation in the tropical pacific ocean needs to be studied in addition there may be a relatively stable core region in the sww this core region is located in central patagonia at approximately 47 s where the local climate is wetter during the all transition period showing the continuous influence of the sww on this region the position shift of the sww in response to the tcbh phase changes seems to behave as a swing process with an axis of approximately 47 s the poleward swing of the sww may trigger the self repairing process of the global climate system after the catastrophic impacts of the meltwater including the pulling effect of the enhanced upwelling on the atlantic meridional overturning circulation the influence of co2 released from the deep sea and the impact of the gradual strengthening of the ism these results support and reinforce the hypothesis that the tcbh drives global climate change highlight the global teleconnection characteristics of the key physical processes in the earth s climate system and the important role of the sww in this teleconnection and provide a basis for further simulating the climate connections in the two hemispheres especially the impact of the sww on the global climate change

a 3d study of aligned porphyroblast inclusion trails across shear zones and folds inclusion trails si within 741 equant garnet porphyroblasts show a consistent orientation across a 100 m2 outcrop of precambrian metapelite with later d2 folds and shear zones in posio finland variation in si orientations is not systematic with respect to these later folds and shear zones but instead represents microfolding and warping of s1 before the formation of d2 structures the development of the d2 folds and shear zones is investigated by comparing the pattern of si in the outcrop to those predicted for porphyroblasts in tangential longitudinal strain axial slip flexural flow pure shear partitioned flexural flow and partitioned pure shear folds si patterns are also compared with models for non coaxial and coaxial shear zones along with corroborating evidence from structures in the outcrop and matrix the comparisons indicate that d2 folds and shear zones in the outcrop formed in response to nw se axially symmetric shortening during which garnet porphyroblasts did not rotate relative to each other the axial plane of f2 folds and d2 shear zone boundaries

abrupt vegetation changes during the last glacial to holocene transition in mid latitude south america a pollen record from the huelmo site ca 41 30 s shows that vegetation and climate changed at millennial time scales during the last glacial to holocene transition in the mid latitude region of western south america the record shows that a nothofagus parkland dominated the landscape between 16 400 and 14 600 14c yr bp along with magellanic moorland and cupressaceous conifers evergreen north patagonian rainforest taxa expanded in pulses at 14 200 and 13 000 14c yr bp following a prominent rise in nothofagus at 14 600 14c yr bp highly diverse closed canopy rainforests dominated the lowlands between 13 000 and 12 500 14c yr bp followed by the expansion of cold resistant podocarps and nothofagus at ca 12 500 and 11 500 14c yr bp local disturbance by fire favoured the expansion of shade intolerant opportunistic taxa between 10 900 and 10 200 14c yr bp subsequent warming pulses at 10 200 and 9100 14c yr bp led to the expansion of thermophilous summer drought resistant valdivian rainforest trees until 6900 14c yr bp our results suggest that cold and hyperhumid conditions characterised the final phase of the last glacial maximum lgm between 16 400 and 14 600 14c yr bp the last ice age termination commenced with a prominent warming event that led to a rapid expansion of north patagonian trees and the abrupt withdrawal of andean ice lobes from their lgm positon at ca 147 000 14c yr bp hyperhumid conditions prevailed between 16 400 and 13 000 14c yr bp what we term the extreme glacial mode of westerly activity this condition was brought about by a northward shift and or intensification of the southern westerlies the warmest driest conditions of the last glacial interglacial transition occurred between 9100 and 6900 14c yr bp during this period the westerlies shifted to an extreme interglacial mode of activity via a poleward migration of stormtracks our results indicate that a highly variable climatic interval lasting 5500 14c years separate the opposite extremes of vegetation and climate during the last glacial interglacial cycle i e the end of the lgm and the onset of the early holocene warm and dry period copyright 2003 john wiley sons ltd

thermodynamic projection and extrapolation of high variance mineral assemblages a procedure is described whereby the effect of extra components on the plotting positions of minerals in projected phase diagrams may be accounted for rigorously the method employs the equilibrium constraints of the mineral assemblage to extrapolate the compositions of the minerals to where the values of the extra components approach 0 the same procedure may also be used to extrapolate the compositions of natural assemblages over isothermal isobaric composition diagrams or polythermal polybaric diagrams

climatic and lacustrine morphometric controls of diatom paleoproductivity in a tropical andean lake abstract the coupling of lake dynamics with catchment biogeochemistry is considered the key element controlling primary production in mountain lakes at time scales of a few decades to millennia yet little is known on the impacts of the morphometry of lakes throughout their ontogeny as lake chungara central andean altiplano northern chile experienced long term lake level fluctuations that strongly modified its area volume ratio it is an ideal system for exploring the relative roles that long term climatic shifts and lake morphometry play on biosiliceous lacustrine productivity in this paper we review previous data on the percent contents of total organic carbon total inorganic carbon total nitrogen total biogenic silica isotopic composition of organic matter carbonates and diatom frustules as well as data on the abundance of the chlorophycean botryococcus braunii in this lake for the period 12 400 1300 cal yr bp we also include new data on organic carbon and biogenic silica mass accumulation rates and the diatom assemblage composition of an offshore core dated using 14 c and u th biosiliceous productivity in lake chungara was influenced by shifts in allochthonous nutrient inputs related to variability in precipitation humid phases dated at approx 12 400 to 10 000 and 9600 to 7400 cal yr bp coincide with periods of elevated productivity whereas decreases in productivity were recorded during arid phases dated at approx 10 000 to 9600 and 7400 to 3550 cal yr bp andean mid holocene aridity period however morphometry related in lake controls led to a lack of a linear response of productivity to precipitation variability during the late glacial to early holocene lowstands facilitated complete water column mixing prompting episodic massive blooms of a large centric diatom cyclostephanos cf andinus thus moderate productivity could be maintained regardless of aridity by this phenomenon of morphometric eutrophy during the early history of the lake the subsequent net increase in lake level introduced modifications in the area of the epilimnion sediments versus the total volume of the epilimnion preventing complete overturn surpassing a certain depth threshold at approx 8300 cal yr bp caused cessation of the morphometric eutrophy conditions associated with cyclostephanos cf andinus superblooms after 7300 cal yr bp the lake experienced a decrease in biosiliceous productivity and a change of state that involved a stronger dependence on precipitation variability with a lesser contribution of diatoms to the total primary productivity our results show that the interpretation of lacustrine paleoproductivity records as paleoclimatic archives needs to take into account the effects of changes in the epilimnion sediment area to epilimnion volume ratio in association with lake ontogeny

an oxygen buffer for some peraluminous granites and metamorphic rocks the mineral assemblage biotite garnet muscovite magnetite quartz and its subsets are common in many peraluminous granites schists and gneisses if the biotite and garnet are reasonably iron rich then the system is a useful buffer for oxygen fugacity available thermochemical data indicate that in temperature oxygen fugacity space the buffer curve is located between the hematite magnetite curve and the quartz magnetite fayalite curve in a region that previously had no buffer curve applicable to peraluminous rocks the buffer equation partially taking into account the departures of biotite garnet and muscovite compositions from their end member formulae is logfo2 10 29 262847 t 0 148 p l r atog x3l 3log y 3log ff 2log 4lni 4log xgi 1l 650 t examples of applications are given for three peraluminous granitic rocks and three pelitic schists the calculated oxygen fugacity values corrected for mineral compositions generally agree with published estimated values based on the compositions of coexisting iron and titanium oxide phases

interpreting modern and fossil pollen data along a steep environmental gradient in northern patagonia vegetation reconstructions rest on modern vegetation pollen rain relationships and deductive reasoning establishing this relationship is a nontrivial task because differences among pollen assembla

a 14kyr record of the tropical andes the lago chungara sequence 18 s northern chilean altiplano abstract high resolution geochemical analyses obtained using an x ray fluorescence xrf core scanner as well as mineralogical data from the lago chungara sedimentary sequence in the northern andean chilean altiplano 18 s provided a detailed reconstruction of the lacustrine sedimentary evolution during the last 14 000 cal yr bp the high resolution analyses attained in this study allowed to distinguish abrupt periods identify the complex structures of the early and mid holocene arid intervals and to compare their timing with titicaca lake and sajama ice records three main components in the lake sediments have been identified a biogenic component mainly from diatoms b volcanics ash layers from the nearby parinacota volcano and c endogenic carbonates the correlation between volcanic input in lago chungara and the total particles deposited in the nevado sajama ice core suggests the parinacota volcano as the common source the geochemical record of lago chungara indicates an increase in siliceous productivity during the early holocene lagging behind the rise in temperatures inferred from the nevado sajama ice core the regional mid holocene aridity crisis can be characterized as a number of short events with calcite and aragonite precipitation in the offshore lake zones

climatic controls of holocene fire patterns in southern south america holocene fire climate vegetation linkages are mostly understood at individual sites by comparing charcoal and pollen records with other paleoenvironmental proxy and model simulations this scale of reconstruction often obscures detection of large scale patterns in past fire activity that are related to changes in regional climate and vegetation a network of 31 charcoal records from southern south america was examined to assess fire history along a transect from subtropic to subantarctic biomes the charcoal data indicate that fire activity was greater than present at ca 12 000 cal yr bp and increased further and was widespread at 9500 cal yr bp fire activity decreased and became more spatially variable by 6000 cal yr bp and this trend continued to present atmospheric circulation anomalies during recent high fire years show a southward shift in westerlies and paleoclimate model simulations and data syntheses suggest that such conditions may have prevailed for millennia in the early holocene when the pole to equator temperature gradients were weaker and annual temperatures were higher than present in response to orbital time scale insolation changes

climatic and disturbance influences on the temperate rainforests of northwestern patagonia 40 s since 14 500 cal yr bp abstract we present a detailed record from lago pichilafquen to unravel the vegetation climate and disturbance history of the lowlands of northwestern patagonia 40 s since 14 500 cal yr bp the presence of 30 tephras throughout the record attest for the proximity of the site to active volcanic centres and allows assessment of the role of volcanic disturbance on past vegetation and fire regime shifts we interpret alternations in dominance between north patagonian and valdivian rainforests driven by changes in temperature and precipitation of westerly origin at multi millennial and millennial timescales these trends were punctuated by centennial scale changes most of which were coeval with or immediately followed the deposition of tephras and or paleofires we identify departures of the local vegetation from the regional trend between 2400 and 7100 cal yr bp which we interpret as a response of rainforest vegetation and local fire regimes to the disturbance effect of tephra deposition near lago pichilafquen we also find that volcanic disturbance promoted consistent increases in eucryphia caldcluvia within 30 years and paleofires between 60 and 120 years following tephra deposition comparisons with palynological records having similar span time resolution and age control suggest that regional climate has played a central role on the establishment composition and maintenance of temperate rainforests this influence is overprinted by disturbance regimes at the local and landscape level driving divergences and heterogeneity especially at times of relatively weak climatic forcing

a 7000 year high resolution lake sediment record from coastal central chile lago vichuquen 34 s implications for past sea level and environmental variability we present a 7 ka environmental reconstruction based on sedimentological and geochemical data from lago vichuquen a coastal eutrophic lake in central chile 34 48 s 72 03 w 4 m a s l a relatively shallow and restricted marine environment with low productivity high detrital input and dominant anoxic conditions in the vichuquen basin occurred from 7 0 to 6 5 cal ka bp rapid onset of a holocene marine transgression at 6 5 cal ka bp favoured deeper and more biologically productive environments that existed until 2 8 cal ka bp bioproductivity changes during the mid holocene 6 5 4 2 cal ka bp were related to upwelling dynamics controlled by the intensity of the south east pacific anticyclone spa periods with lower organic productivity and dominant anoxic conditions reflect an increased intensity of spa increased upwelling and decreased precipitation a shift at 4 0 cal ka bp reflects the onset of modern southern westerly winds and el nino southern oscillation patterns tectonic uplifting and geormorphological activity dune advancement are possible reasons behind the vichuquen basin closure at 1 2 cal ka bp leading to a low bioproductivity lacustrine environment which has developed until the present

mid latitude trans pacific reconstructions and comparisons of coupled glacial interglacial climate cycles based on soil stratigraphy of cover beds abstract south westland new zealand and southern chile are two narrow continental corridors effectively confined between the pacific ocean in the west and high mountain ranges in the east which impart significant influence over regional climate vegetation and soils in both these southern mid latitude regions evidence for extensive and repeated glaciations during cold phases of the quaternary is manifested by arrays of successively older glacial drift deposits with corresponding outwash plain remnants in south westland these variably aged glacial landforms are mantled by layered multisequal soils characterised by slow loess accretion and pedogenesis in an extreme leaching and weathering environment these cover bed successions have undergone repeated coupled phases of topdown and upbuilding soil formation that have been related to fluctuating cycles of interglacial warm and glacial cold climate during the quaternary in this study we recognise multisequal soils overlying glacial landforms in southern continental chile but unlike the spodic podzolic soil sequences of south westland these are of dominantly volcanigenic andic provenance and are very similar to multisequal soils of andic provenance that predominate in and adjacent to areas of rhyolitic to andesitic volcanism in north island new zealand here we develop a soil stratigraphic model to explain the observed occurrence of multisequal soils mantling dominantly glacial landforms of southern continental chile based on proxy data from southern chile we propose that persistent vegetation cover and high precipitation on the western side of the andes during colder than present episodes tended to suppress the widespread production of glacially derived loessial materials despite the pervasive occurrence of glacial and glacio fluvial deposits that have frequently inundated large tracts of this landscape during the quaternary given the lack of loess cover beds that have traditionally assisted in the relative dating of glacial episodes prior to the late quaternary surface exposure dating techniques could provide another chronological alternative to address this issue however there have been two main obstacles to successfully apply this dating technique in patagonia first minimum exposure ages may be obtained on moraines older than the last glacial cycle due to erosion although dating outwash plains is more robust second on the wet western side adjacent to the andes persistent vegetation cover during both glacial and post glacial times as well as widespread inundation by volcanic mass flows appear preventive we make a case that soil genesis within this region appears to be dominated by a constant flux of intermittently erupted andean sourced tephra which has continued to upbuild soils at the ground surface separated by intervals where topdown weathering processes are intensified as already demonstrated by new zealand studies multisequal soil successions have a clear implied connection to coupled glacial and interglacial climate cycles of the quaternary on this basis similar sequences in northwest patagonia provide a relatively untapped archive to enable quaternary glacial and environmental changes in this pervasively glaciated volcanic region to be constructed

the accretionary svecofennian orogen insight from the babel profiles abstract the babel profiles b c 1 7 form a 1200 km long nearly continuous cross section through the svecofennides the near vertical marine reflection profiles display a wide range of crustal structures that can be associated with both the accretionary svecofennian orogeny 1 96 1 75 ga and the following subjotnian and jotnian rift stages 1 65 1 11 ga the svecofennian accretionary orogeny took place when a number of micro plates with island arc affinities and surface expression of a large archipelago accreted to the continental karelian plate some of the accreting terranes seem to have had older cores that have acted as crustal indentors during the collision babel profiles 3 and 4 image a series of collisional terrane boundaries between karelian continental margin savo arc sa and central finland arc cfa in the north the karelian margin has been both over and underthrust by the savo arc cfa comprises a folded thrust package on top of a continental nucleus and the savo arc the associated subduction zone and accretionary prism are interpreted to lie to the south underneath the bothnian basin area where prominent ne dipping lower to middle crustal reflections are found along babel profiles 1 and 4 an oblique collision of the central finland arc and the continent resulted in the development of the strike slip fault on the young hot savo arc babel profiles 1 6 7 and c image the internal architecture of the southern and central finland arcs the unusually thick crust 55 60 km hosts unreflective high density mafic intrusions acting as a crustal indentor a highly reflective antiform structure developed on the southern side of it southern finland arc complex sfa is an imbrication structure comprising stacked slices of arc related crust on an older continental nucleus bergslagen nucleus prior to the collision the sfa suffered from gravitational collapse during which the crust was thinned profile b images the architecture of the central and southern swedish svecofennides the sormland terrane sob is interpreted as the accretionary prism of the southern finland arc squeezed between the svecofennian collage in the north and the advancing continent to the south the southern continent island arc is characterised by ne dipping crustal reflections and moho offsets as well as step wise increasing thickness of the crust after the final collision large volumes of mantle derived material intruded the crust as large mushroom shaped plutons they are interpreted as the heat source for the tib magmatism in southern and western scandinavia

archean proterozoic collision boundary in central fennoscandia revisited abstract archean proterozoic ap collision boundary in central fennoscandia is a complex collage of archean basement rocks its paleoproterozoic supracrustal cover rocks and svecofennian 1 93 1 78 ga supracrustal and plutonic rocks the apparent steep nature and complexity of the ap boundary has led to contradictory tectonic models varying from arc continent collision via back arc closure to accretion of arc terranes along a strike slip shear zone we present new geochronology data from detrital zircons combined with whole rock geochemical and sm nd isotopic data on paleoproterozoic sedimentary and volcanic rocks across the boundary to revise its nature the 2 06 ga siilinjarvi volcanic complex and associated turbidites with an inferred deposition age at 2 1 2 06 ga are part of the cover sequence the siilinjarvi volcanic rocks derive from both plume oib and sub continental lithospheric mantle sclm magma sources and are often contaminated by the archean crust the sahara suite sedimentary cover rocks are derived from local 1 95 1 92 ga bimodal volcano plutonic source which source also explains the common age population found in younger sedimentary rocks the nalantojarvi suite psammites with maximum depositional ages of 1 97 1 93 ga are continental slope to deep water sediments deposited at the continental margin contemporaneous mafic magmatism seen as lavas and dykes show a change from sclm dominated present east to asthenospheric depleted mantle dm dominated present west melts the interpretation of the nalantojarvi suite as cover rocks of the lower plate indicates that the archean crust continues at least 50 km more to the west than thought earlier parautochthonous sedimentary rocks from salahmi eastern kansanneva and loutemaki with maximum depositional ages at 1 92 1 91 ga are inferred as collision related foredeep deposits from local sources both the lampaanjarvi suite and pyhajarvi suite sedimentary rocks have deposited at 1 89 1 88 ga or later whereas the lampaanjarvi suite rocks are dominated by a local source and the pyhajarvi suite rocks derive from a mixture of older sediments and 1 89 1 88 ga granitoids at least two tectono metamorphic stages separated with a major unconformity can be differentiated in the study area the early deformation and metamorphic stage in the nalantojarvi suite has occurred before the intrusion of the late to post collisional pyroxene granitoids at 1 88 ga the pyhajarvi suite sedimentary rocks have been deposited after the intrusion of these granitoids between 1880 and 1875 ma and then subsequently deformed and metamorphosed at 1875 ma we propose a tectonic model where the continental breakup occurred at 2 1 2 06 ga followed by a new spreading within the pre existing passive margin at 1 98 1 93 ga during initial continent arc collision the subducted slab steepened strongly at high angle subduction ceased rapidly and finally detached and shallow slab breakoff occurred at 1 92 1 91 ga followed subsequently by ophiolite obduction and a formation of a foreland fold and thrust belt mantle crust decoupling of the archean lithosphere occurred and a crocodile jaw formed where the arc rocks are partly buried beneath the bounding archean continent similar features have been recorded in other ap collision zones which could indicate that the buoyant nature of the archean lithosphere combined with denser paleoproterozoic lithosphere may be a general cause for decoupling of archean crust and mantle during arc continent collision in paleoproterozoic

a continuous record of vegetation fire regime and climatic changes in northwestern patagonia spanning the last 25 000 years abstract we present a high resolution precisely dated terrestrial paleovegetation paleoclimate record from lago pichilaguna northwestern patagonia 40 44 s which spans continuously from the last glacial maximum lgm to the present we find abundant and continuous presence of arboreal pollen chiefly nothofagus during the lgm accompanied by other trees shrubs and alpine herbs these results suggest subantarctic parkland and or scattered woodlands under a cold and hyperhumid climate during the lgm 25 000 17 800 cal yr bp with expansion of nothofagus under relatively warm interstadial conditions between 25 000 and 19 200 cal yr bp this was followed by cooling and a precipitation increase between 19 200 and 17 800 cal yr bp which was contemporaneous with the youngest lgm advance of andean glaciers in the region and maximum influence of the southern westerly wind sww the last glacial termination t1 started at 17 800 cal yr bp and featured the spread of thermophilous trees and ferns characteristic of north patagonian rainforests along with lake level lowering these results suggest a warm pulse and southward shift of the sww concurrent with a rapid collapse of andean glacier lobes subsequent changes led to the establishment of closed canopy rainforests under peak interstadial warmth between 16 000 and 15 000 cal yr bp we detect a shift to cold wet conditions during the antarctic cold reversal 14 800 12 700 cal yr bp and a precipitation decline during younger dryas time followed by maximum temperature relatively lower lake level and minimum sww influence between 11 300 and 7700 cal yr bp precipitation then rose punctuated by centennial scale variations since 6200 cal yr bp chilean european deforestation and spread of invasive exotic species started at 350 cal yr bp aided by fire we conclude that temperate rainforests have persisted with little interruption since t1 with major changes in floristic composition driven by climate change and fires rainforest composition and heterogeneity declined in response to chilean european disturbance during the 1600s and intensified since the 1800s these events constitute the fastest largest magnitude vegetation changes of the last 25 000 years

the deglaciation of the americas during the last glacial termination this paper reviews current understanding of deglaciation in north central and south america from the last glacial maximum to the beginning of the holocene together with paleoclimatic and paleoceanographic data we compare and contrast the pace of deglaciation and the response of glaciers to major climate events during the global last glacial maximum glgm 26 5 19 ka average temperatures decreased 4 to 8 c in the americas but precipitation varied strongly throughout this large region many glaciers in north and central america achieved their maximum extent during the glgm whereas others advanced even farther during the subsequent heinrich stadial 1 hs 1 glaciers in the andes also expanded during the glgm but that advance was not the largest except on tierra del fuego hs 1 17 5 14 6 ka was a time of general glacier thickening and advance throughout most of north and central america and in the tropical andes however glaciers in the temperate and subpolar andes thinned and retreated during this period during the bolling allerod interstadial b a 14 6 12 9 ka glaciers retreated throughout north and central america and in some cases completely disappeared many glaciers advanced during the antarctic cold reversal acr 14 6 12 9 ka in the tropical andes and patagonia there were small advances of glaciers in north america central america and in northern

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

metamorphic and structural evolution of the early proterozoic puolankajarvi formation finland i structural and textural relations the amphibolite facies puolankajarvi formation pjf occupies the western margin of the early proterozoic kainuu schist belt ksb of northern finland the lower and middle parts of the pjf consist of turbiditic psammites and pelites and tempestitic semipelites this report concentrates on the pelitic lithologies which include quartz two mica plagioclase schists with variable amounts of garnet staurolite andalusite and biotite porphyroblasts as well as sillimanite and cordierite segregations the ksb forms a major north south trending synclinorium between two archaean blocks it contains both autochthonous and allochthonous units and is cut by faults and shear zones the pjf lies on the western side of the ksb and is probably allochthonous the formation has undergone six major deformation phases d1 d2 d3a d3b d4 and d5 during d3a d5 the maximum principal stress 1 changed in a clockwise direction from south west to north east between d2 and d3 the intermediate principal stress 2 changed from horizontal to vertical and the interval between d2 and d3 marks a transition from thrust to strike slip tectonics relict structures in the porphyroblasts indicate the following mineral growth deformation evolution in the pjf 1 throughout the pjf there was a successive crystallization of garnet syn d1 poryphyroblastic biotite inter d3 4 and staurolite inter d3 4 during the pre d4 stage 2 a syn d4 inter d4 5 crystallization of kyanite sillimanite fibrolite porphyroblastic tourmaline magnetite rutile cordierite and muscovite biotite plagioclase pseudomorphs after staurolite was most localized at and near d4 shear zones 3 a syn to post d5 generation of andalusite ilmenohematite and sheet silicates after staurolite and after cordierite occurred near d5 faults the evolution outlined here permits the relative dating of the pjf parageneses which is used in the second part of the study tuisku laajoki 1990 and together with the knowledge of the pressure temperature conditions during various growth events makes it possible to compile pressure temperature deformation paths for the pjf

geochemical characteristics of granulite facies rocks in the archean varpaisjarvi area central fennoscandian shield abstract archean lower crustal granulites are exposed as fault bounded blocks in the varpaisjarvi area central finland the prevailing rock types in these blocks are igneous enderbites tonalitic trondhjemitic granodioritic migmatites and mafic granulites although metamorphosed at moderate pressures 8 10 kbar the varpaisjarvi granulites are not in a geochemical sense good representatives of depleted restitic lower crust having invariably negative or negligible eu anomalies only the enderbites have k rb ratios showing depleted granulite trends the enderbites are orthopyroxene bearing igneous rocks ranging in composition from diorite to tonalite they have distinctive flat lree patterns with la sm from 2 03 2 86 which may be due to the removal of a lree rich phase during fractionation if not the result of infiltration by a co 2 rich fluid mafic granulites occur as intercalations within the tonalitic trondhjemitic granodioritic gneisses and while all are tholeiitic in composition they fall into two groups on the basis of major and trace element abundances the group 1 tholeiites are mostly basaltic with steeply increasing alkali contents over a short range in sio 2 ti zr ratios are close to the chondritic value of 110 the group 2 tholeiites vary from picrobasaltic to andesitic in composition with the latter being dominant ti zr ratios lie below the chondritic value the group 1 rocks have higher ni and cr and lower zr y ratios than their group 2 counterparts the varpaisjarvi area represents at least two accreted blocks or terranes that exhibit marked lithological and geochemical differences with the jonsa block being the most distinctive the main differences are the two contrasting groups of tholeiitic mafic granulites the jonsa block having only the group 2 metatholeiites and the presence of quartz cordierite and cordierite orthoamphibole orthopyroxene rocks only in the jonsa block where they are found as interlayers amongst the group 2 tholeiites the ti zr and zr y ratios of these latter lithologies are closely comparable with those of the group 2 tholeiites the jonsa block cordierite orthoamphibole orthopyroxene rocks have high mgo mgo feo tot ratios compared to most cordierite orthoamphibole rocks produced by seawater basalt interaction their major and trace element geochemistry nevertheless indicates that they were derived from a mafic igneous precursor

trans pacific glacial response to the antarctic cold reversal in the southern mid latitudes abstract elucidating the timing and regional extent of abrupt climate events during the last glacial interglacial transition 18 11 5 ka is critical for identifying spatial patterns and mechanisms responsible for large magnitude climate events the record of climate change in the southern hemisphere during this time period however remains scarce and unevenly distributed we present new geomorphic chronological and equilibrium line altitude ela data from a climatically sensitive mountain glacier at monte san lorenzo 47 s central patagonia twenty four new cosmogenic 10be exposure ages from moraines provide a comprehensive glacial record in the mid latitudes of south america which constrain the timing spatial extent and magnitude of glacial fluctuations during the antarctic cold reversal acr 14 5 12 9 ka rio tranquilo glacier advanced and reached a maximum extent at 13 9 0 7 ka three additional inboard moraines afford statistically similar ages indicating repeated glacier expansions or marginal fluctuations over the acr our record represents the northernmost robust evidence of glacial fluctuations during the acr in southern south america documenting not only the timing of the acr maximum but also the sequence of glacier changes within this climate event based on ela reconstructions we estimate a cooling of 1 6 1 8 c at the peak of the acr the rio tranquilo record along with existing glacial reconstructions from new zealand 43 s and paleovegetation records from northwestern 41 s and central west 45 s patagonia suggest an uniform trans pacific glacier climate response to an acr trigger across the southern mid latitudes we posit that the equatorial migration of the southern westerly winds provides an adequate mechanism to propagate a common acr signal across the southern hemisphere

the precambrian supracrustal rocks of finland and their tectono exogenic evolution abstract the precambrian supracrustal rocks of finland were produced during four main evolutionary stages 1 late archaean pre svecokarelidic greenstone schist evolution on an unknown basement 2 at least four cycles of early proterozoic karelian continental epi pericontinental sedimentation and volcanism on or next to the cratonized late archaean basement 3 early proterozoic svecofennian eugeosynclinal evolution west of or in part on the late archaean basement and its cratonic cover and 4 middle to late proterozoic jotnia continental sedimentation on the stabilized early proterozoic post svecokarelidic basement

contact zone interaction of metabasites with metapelites amphibolite facies mineral assemblages chemical profiles and their origin the puolankajarvi formation finland abstract the amphibolite facies iron rich metapelites garnet staurolite mica schists of the early proterozoic puolankajarvi formation are intercalated with metamorphosed basic rocks which vary from iron rich amphibolites to magnesium rich layered sills and serpentinites garnet cummingtonite hornblende assemblages are abundant at the contacts of the metapelites with amphibolites while garnet chlorite garnet gedrite chlorite garnet gedrite cummingtonite chlorite and chlorite cummingtonite hornblende assemblages occur at their contacts with the layered magnesium rich sill the bulk composition profiles of these contacts normalised with respect to chromium and or aluminium show conspicuous enrichment in fe s ga and co and depletion in si k ba and rb some elements e g mg mn ni p zr and hf are depleted or enriched in only small amounts while others e g ca na sr and the rare earth elements may show both enrichment and depletion in the course of a profile although early infiltration during the hydration of metabasites and tectonic reworking may have produced some interaction of the basites with the pelites the major metasomatic event is considered to have bile elements the composition of the metapelites for example approached that of magnesium rich ultramafites through potassium depletion while the ultramafites became markedly enriched in iron to conserve the volume silica was depleted from the contact which underwent iron enrichment

chilean and southeast pacific paleoclimate variations during the last glacial cycle directly correlated pollen and δ18o records from odp site 1234 abstract joint pollen and oxygen isotope data from ocean drilling program site 1234 in the southeast pacific provide the first continuous record of temperate south american vegetation and climate from the last 140 ka located at 36 s 65 km offshore of concepcion chile site 1234 monitors the climatic transition zone between northern semi arid summer dry winter wet climate and southern year round rainy cool temperate climate dominance of onshore winds suggests that pollen preserved here reflects transport to the ocean via rivers that drain the region and integrate conditions from the coastal mountains to the andean foothills down hole changes in diagnostic pollen assemblages from xeric lowland deciduous forest characterized by grasses herbs ferns and trees such as deciduous beech nothofagus obliqua mesic valdivian evergreen forest including conifers such as the endangered prumnopitys andina and subantarctic evergreen rainforest comprised primarily of southern beech n dombeyi reveal large rapid shifts that likely reflect latitudinal movements in atmospheric circulation and storm tracks associated with the southern westerly winds during glacial intervals mis 2 4 and 6 rainforests and parkland dominated by nothofagus moved northward into the region at the mis 6 5e transition coeval with the rapid shift to lower isotopic values rainforest vegetation was rapidly replaced by xeric plant communities associated with mediterranean type climate an increased prominence of halophytic vegetation suggests that mis 5e was more arid and possibly warmer than mis 1 although rainforest pollen rises again at the end of mis 5e lowland deciduous forest pollen persists through mis 5d and 5c into mis 5b substantial millennial scale variations occur in both interglacial and glacial regimes attesting to the sensitivity of the southern westerly belt to climate change comparison of the cool mesic n dombeyi rainforest assemblage from site 1234 with 18 o in the byrd ice core shows that on time scales longer than 10 ka cool moist conditions in central chile were coherent with and occurred in phase with antarctic cooling this is also likely at millennial scales although rainforest pollen lags antarctic cooling with exponential response times of about 1000 years which plausibly reflects the ecological response time to regional climate change

the last glacial termination a major puzzle of paleoclimatology is why after a long interval of cooling climate each late quaternary ice age ended with a relatively short warming leg called a termination we here offer a comprehensive hypothesis of how earth emerged from the last global ice age a prerequisite was the growth of very large northern hemisphere ice sheets whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation the southern hemisphere westerlies shifted poleward during each northern stadial producing pulses of ocean upwelling and warming that together accounted for much of the termination in the southern ocean and antarctica rising atmospheric co2 during southern upwelling pulses augmented warming during the last termination in both polar hemispheres

major palaeoproterozoic shear zones of the central fennoscandian shield abstract employing two recently studied crustal scale shear zones as type examples this paper summarizes the major palaeoproterozoic svecokarelian shear tectonics of the central fennoscandian shield and demonstrates that this part of the shield was not as stable during the svecokarelian orogeny as commonly assumed the collision of the svecofennian island arc with the karelian continent first created numerous nw se trending folds and thrusts of stages d1 and d2 which were then modified by successive shearing during stages d3 and d4 stage d3 built up a system of n s trending shear zones here named the savolappishearsystem the type example of which is the hirvaskoski shear zone this is a dextral strike slip shear zone at least 150 km long and 10 30 km wide characterized by blastomylonitic fault rocks and various structures such as hook folds z folds and sheath folds associated with the principal displacement zone synthetic riedel shears and pinnate shears the traces of the axial planes of f3 en echelon folds deviate 15 30 anticlockwise from the plane of the principal displacement zone other members of the savolappi shear system are the pajala shear zone in northern sweden and the russian north karelia shear zone in the east stage d4 created a conjugate shear system called the finlandia shear system the type example of which is the oulujarvi shear zone this is a ne sw trending sinistral strike slip shear zone more than 250 km long and 20 30 km wide across its southwestern end it is composed of a ne sw trending principal displacement zone synthetic riedel shears and pinnate shears with antithetic riedel shears in a nw se direction typical fault rocks within these shears are s c mylonites the axial plane traces of f4 folds of all scales diverge by 20 40 clockwise from the plane of the principal displacement zone the kuopio shear zone is a conjugate nw se trending counterpart of the oulujarvi shear zone as a whole the finlandia shear system forms a conjugate network of nw se and ne sw trending shear zones which occupies most of the northern and central fennoscandian shield

deglacial and postglacial climate history in east central isla grande de chiloe southern chile 43 s abstract palynologic and stratigraphic data from laguna tahui 42 50 s 73 30 w indicate cool temperate and humid conditions there between 14 000 and 10 000 14c yr b p followed by warmer and drier than present conditions between 10 000 and 7000 14c yr b p and subsequent cooling and rise in precipitation over the last 5800 14c yr the thermophilous valdivian trees eucryphia cordifolia and caldcluvia paniculata reached their maximum abundance during the early holocene warm dry phase 10 000 7000 14c yr b p followed by a rise in lake levels and reexpansion of north patagonian conifers starting at 7000 and 5800 14c yr b p respectively variations in the stratigraphic and geographic distribution of temperate rainforests in southern chile suggest multimillennial trends in temperature and westerly activity which are spatially and temporally coherent with paleoclimate records from neighboring regions climate variability at millennial and submillennial time scales may account for the establishment and persistence of fine scale mosaics of valdivian and north patagonian rainforest species in low to mid elevation communities since 5800 14c yr b p

changes in fire regimes since the last glacial maximum an assessment based on a global synthesis and analysis of charcoal data fire activity has varied globally and continuously since the last glacial maximum lgm in response to long term changes in global climate and shorter term regional changes in climate vegetation and human land use we have synthesized sedimentary charcoal records of biomass burning since the lgm and present global maps showing changes in fire activity for time slices during the past 21 000 years as differences in charcoal accumulation values compared to pre industrial there is strong broad scale coherence in fire activity after the lgm but spatial heterogeneity in the signals increases thereafter in north america europe and southern south america charcoal records indicate less than present fire activity during the deglacial period from 21 000 to 11 000 cal yr bp in contrast the tropical latitudes of south america and africa show greater than present fire activity from 19 000 to 17 000 cal yr bp and most sites from indochina and australia show greater than present fire activity from 16 000 to 13 000 cal yr bp many sites indicate greater than present or near present activity during the holocene with the exception of eastern north america and eastern asia from 8 000 to 3 000 cal yr bp indonesia and australia from 11 000 to 4 000 cal yr bp and southern south america from 6 000 to 3 000 cal yr bp where fire activity was less than present regional coherence in the patterns of change in fire activity was evident throughout the post glacial period these complex patterns can largely be explained in terms of large scale climate controls modulated by local changes in vegetation and fuel load

an early proterozoic ophiolite the jormua mafic ultramafic complex northeastern finland abstract the 1 96 ga old jormua complex comprises a fault bounded unit 2 5 20 km in the centre of the kainuu schist belt at the eastern margin of the early proterozoic svecokarelides the complex was dismembered and metamorphosed to lower amphibolite facies during the svecokarelian orogeny in the intact complex the basal unit was formed by serpentinites the middle unit of mafic dykes and the uppermost extrusive unit of basaltic pillow lavas gabbroic rocks are present as intrusive bodies in the serpentinites and narrow interdyke screens within the dyke unit trondhjemitic rocks occur as minor segregations in the gabbroic rocks or as cross cutting narrow dykes in the mafic dyke unit the dyke unit is locally composed exclusively of subparallel metabasalt and metadolerite dykes in places interdyke metagabbro and serpentinite screens are abundant well preserved chilled margins are common and many dykes are split and intruded by younger dykes the chemical composition of the serpentinites indicates derivation from harzburgitic dunitic mantle peridotites the gabbroic rocks which represent obvious tholeiitic cumulates show extreme differentiation similar to gabbros of the high ti ophiolites and gabbros dredged from present midocean ridges in chemistry the trondhjemitic rocks are close to granitic rocks from mid ocean ridges and high ti ophiolites the similar chemical composition of the dykes and lavas of the complex indicates that they are cogenetic both being tholeiitic metabasalts with chondrite normalized ree patterns ranging from slightly lree depleted to slightly lree enriched ones compared with modern rocks the jormua metabasalts most closely resemble transitional midocean ridge basalts it is suggested that the jormua complex and related mafic ultramafic bodies in eastern finland originated as divergent margin ophiolites concomitantly with the break up of the archaean craton in the extensional stage of the svecokarelian orogeny which culminated in the opening of a major ocean after 1 97 ga the tectonic emplacement of these ophiolites into their present locations occurred in connection with thrusting during the compressional stage of the orogeny about 1 9 ga ago

evaluation of biotite garnet geothermometers application to the english river subprovince ontario in recent years there have been numerous calibrations of the biotite garnet fe mg exchange geothermometer the eastern lac seul region of the english river subprovince ontario provides an excellent field area in which to compare these calibrations

the metamorphic behaviour and petrogenetic significance of zinc in amphibolite facies staurolite bearing mica schists puolankajarvi formation central finland abstract whole rock analyses and mineral analyses were performed on 24 samples of mica schists from the early proterozoic puolankajarvi formation pjf the whole rock zn content 36 127 ppm mean 77 ppm was at the normal level for pelitic and crustal rocks staurolite being the only mineral phase to contain zinc in measurable amounts 0 0 1 33 wt zno mean 0 28 wt when staurolite was present it contained nearly all of the zinc of the rock the zn content does not vary between the rocks in which staurolite has never been generated those in which staurolite is present and those from which staurolite has been destroyed this suggests that despite the fact that staurolite is a very strong acceptor of zn the generation of staurolite under reducing conditions log f o 2 22 5 t 545 c p 3 7 kbar did not increase the content of zn in the whole rock neither did the destruction of staurolite under more oxidizing conditions log f o 2 22 2 21 0 t 500 520 c p 2 1 3 5 kbar reduce it because there is evidence of considerable fluid flow through the rock during certain stages of the metamorphism of the pjf it is concluded that zn is an immobile element in amphibolite facies metamorphism in petites zinc should be treated as an additional component in metamorphic reactions of staurolite which increases the degrees of freedom of these reactions because of the immobility of zn and the increase in degrees of freedom these reactions will become dependent upon the concentration of zn in the rock

timing and structure of vegetation fire and climate changes on the pacific slope of northwestern patagonia since the last glacial termination abstract by virtue of its location in the southern mid latitudes northwestern patagonia 40 44 s offers the opportunity to unravel the mechanisms involved in the initiation and propagation of paleoclimate signals of hemispheric and global significance of particular importance is deciphering the evolution of the southern westerly winds sww considering their influence at continental zonal hemispheric and global scale here i present a multi decadal record from lago proschle a small closed basin lake located on the pacific slope of northwestern patagonia to examine the timing and structure of vegetation fire and climate change along a continuum since the onset of the last glacial termination t1 the record shows rapid glacier recession during t1 reaching the western andean foothills in 400 years or less nothofagus dominated forests established between 17 4 17 ka followed by closed canopy north patagonian rain forests nprf with shade tolerant thermophilous trees between 16 3 15 4 ka these changes suggest an abrupt warming trend and an increase in precipitation at 16 3 ka associated with a northward shift of the sww subsequent increases in cold tolerant hygrophilous trees between 15 4 12 8 ka imply a shift to cold more humid conditions during the antarctic cold reversal suggesting stronger sww influence this was followed by stand replacing fires brought by a sudden decline in summer precipitation at 12 8 ka associated with a millennial scale southward shift of the sww which was contemporaneous with the onset of the younger dryas dominance of thermophilous summer drought tolerant valdivian rainforest trees and high fire activity ensued between 10 3 7 8 ka suggesting peak warmth and overall decline in annual precipitation associated with weakening of the sww during the early holocene a multi millennial cooling and wetting trend started at 7 8 ka brought by stronger sww influence followed by recurrent centennial scale variations in temperature and precipitation starting at 6 4 ka deforestation fire and spread of non native herbs by chilean european settlers began during the late 18th century abrupt vegetation changes in the lago proschle record were driven by rapid climate changes over the last 17 400 years amplified in some instances by fire disturbance

garnet chloritoid equilibria in eclogitic pelitic rocks from the sesia zone western alps their bearing on phase relations in high pressure metapelites abstract a detailed study of garnet chloritoid micaschists fom the sesia zone western alps is used to constrain phase relations in high pressure hp metapelitic rocks in addition to quartz phengite paragonite and rutile the micaschists display two distinct parageneses namely garnet chloritoid chlorite and garnet chloritoid kyanite talc has never been observed garnet and chloritoid are more magnesian when chlorite is present instead of kyanite the distinction of the two equilibria results from different bulk rock chemistries not from p t conditions or redox state estimated p t conditions for the eclogitic metamorphism are 550 600 c 15 18 kbar the presence of primary chlorite in association with garnet and chloritoid leads us to construct two possible afm topologies for the sesia metapelites the paper describes a kfmash multisystem for hp pelitic rocks which extends the grid of harte hudson 1979 towards higher pressures and adds the phase talc observed parageneses in hp metapelites are consistent with predicted phase relations critical associations are gt ctd chl and gt ctd ky at relatively low temperatures and gl chl ky and gt tc ky at relatively high temperatures

onset of deglacial warming in west antarctica driven by local orbital forcing an annually resolved ice core record from west antarctica indicates that warming driven by local insolation resulting from sea ice decline began in that region about 2 000 years before warming in east antarctica reconciling two alternative explanations for deglacial warming in the southern hemisphere

a petrogenetic grid for pelitic schists in the system sio 2 al 2 o 3 feo mgo k 2 o h 2 o a quantitative petrogenetic grid for pelitic schists in the system kfmash that includes the phases garnet chlorite biotite chloritoid cordierite staurolite talc kyanite andalusite sillimanite and pyrophyllite with quartz h2o and muscovite or k feldspar in excess is presented the grid is based on thermodynamic data of berman et al 1985 and berman 1988 for endmember kfash and kmash equilibria and natural fe mg partitioning for the kfmash system calculation of p t slopes and the change in fe fe mg along reactions in the kfmash system were made using the gibbs method in addition the effect on the grid of mno and cao is evaluated quantitatively the resulting grid is consistent with typical buchan and barrovian parageneses at medium to high grades at low grades the grid predicts an extensive stability field for the paragenesis chloritoid biotite which arises because of the unusual facing of the reaction chloritoid biotite quartz h2o garnet chlorite muscovite which proceeds to the right with increasing t in the kfmash system however the reaction proceeds to the left with increasing t in the mnkfash system so the assemblage chloritoid biotite is restricted to bulk compositions with high fe fe mg mn typical metapelites will therefore contain garnet chlorite at low grades rather than chloritoid biotite

vegetation fire and climate change in central east isla grande de chiloe 43 s since the last glacial maximum northwestern patagonia abstract we present a detailed record from lago lepue to examine vegetation climate and fire regime changes since the last glacial maximum lgm in central east isla grande de chiloe 43 s northwestern patagonia precipitation in this region correlates with the intensity of the southern westerly winds sww allowing reconstruction of past sww behavior through precipitation sensitive sensors recession from the lgm glacier margins exposed the central east sector of isla grande de chiloe by 17 800 cal yr bp followed by the immediate colonization of pioneer cold resistant herbs shrubs and rapid establishment of closed canopy nothofagus forests by 17 000 cal yr bp broad leaved temperate rainforests have persisted since then with compositional changes driven by changes in temperature hydrologic balance and disturbance regimes we detect low lake levels and enhanced fire activity between 800 2000 4000 4300 8000 11 000 and 16 100 17 800 cal yr bp implying southward shifts and or weaker sww flow that alternated with cold humid phases with muted fire activity covariation in paleoclimate trends revealed by the lago lepue record with tropical and antarctic records since the lgm suggests that the sww have been a highly dynamic component of the climate system capable of linking climate changes from low and high southern latitudes during the last glacial termination and the current interglacial

centennial and millennial scale hydroclimate changes in northwestern patagonia since 16 000 yr bp abstract we examine hydroclimate changes at centennial millennial timescales since 16 000 yr bp in northwestern patagonia based on the pollen and charcoal record from lago el salto a small closed basin lake located in the chilean lake district 41 38 48 02 s 73 5 48 42 w we observe cold wet conditions between 14 500 16 000 yr bp followed by further cooling with increased precipitation until 13 000 yr bp enhanced precipitation seasonality and or variability between 11 600 13 000 yr bp and an extended warm and dry interval between 7600 and 11 300 yr bp with peak paleofire activity colder and wetter than present conditions and muted paleofire activity prevail between 5300 and 7600 yr bp followed by alternating cold wet and centennial scale warm dry phases starting at 5300 yr bp with three conspicuous megadroughts since 2500 yr bp the most recent megadrought occurred during the medieval climate anomaly we identify a cold reversal that spans the antarctic cold reversal acr and the younger dryas yd chrons with stronger than present westerly influence during the former and enhanced variability during the latter these results extend the northern limit of strong cooling and increase in precipitation during the acr and the southern limit of influence of strong hydrologic variations during the yd in terrestrial environments suggesting an overlap in the spheres of influence of processes originating from southern and northern polar latitudes an extended warm southern westerly wind sww minimum interval is evident between 7600 and 11 300 yr bp followed by a rapid shift to cool moist conditions between 5300 and 7600 yr bp brought by a mid holocene sww maximum since then we observe centennial scale hydroclimate variability which has driven biodiversity and fire regime shifts of evergreen temperate rainforests

multiply deformed paleoproterozoic foreland fold and thrust belt in northern fennoscandia the peripheral kuusamo belt as a key example abstract the central lapland belt clb perapohja belt pb and kuusamo belt kb form an important part of northern fennoscandia and record ca 700 ma 2 5 1 8 ga of precambrian tectonic processes the 2 5 2 1 ga sedimentary volcanic successions in these belts form a basin wide surfaces with a wide lateral continuum tidal influenced shallow epeiric sea setting dominated at 2 4 2 1 ga followed by a continental breakup and subsequent formation of a passive margin at 2 1 ga the collisional evolution 1 93 1 76 ga started with an e w locally nw se and ne sw compressional phase d1 1 93 1 90 ga that resulted in at least 600 km long and in part over 300 km wide e vergent lapland foreland fold and thrust belt ftb the kb is the best preserved example of this ftb and shows e vergent imbricated structures in the east and e vergent out of sequence thrusting in the west the southern part of the kb has been affected by n s shortening d2 seen as upright to slightly inclined open to tight f2 folds and as oval shaped dome and basin structures the d3 overprinting causes folding with nw se trending spaced foliation in less competent rocks and parallel folds and faults in orthoquartzites the d4 ne sw trending overprinting deformation is characteristic for the high grade areas of the kb and is seen in outcrop to map scale tight folding in general the easternmost peripheral part of the e vergent lapland foreland ftb formed upon non stretched archean basement is only moderately affected by the later deformation events in the stretched part of the archean basement the earlier rift structures have facilitated the n s shortening and the d2 structures dominate the map pattern the d3 due to a sw ne shortening shows strong strain partitioning and localized deformation after prolonged heating the archean basement started to act ductile and long wavelength crustal scale ne sw trending d4 folds formed the metamorphic zonation in the kb from greenschist facies in the south to medium pressure amphibolite facies in the north is explained by a major d4 anticlinorium wavelength 70 100 km

moderate overthickening of thinned sialic crust and the origin of granitic magmatism and regional metamorphism in low p high t terranes formation of low pressure p high temperature t metamorphic terranes by homogeneous shortening and thickening of tectonically thinned sialic crust and overlying sedimentary basins at geologically reasonable strain rates avoids the shortcomings of hypotheses linking the characteristically high geothermal gradients to doubling of normal thickness crust crustal extension alone intrusion of granitoids or extensive basic magmatism on the basis of geological and p t constraints from the archean slave province the p t histories of three points in a hypothetical block of crust are presented in p t p distance and p time diagrams the relations between the rock that ends up at the surface base of the basin base of the crust isotherms and depth determine the type of metamorphism and the degree of partial melting required to produce abundant granitoids this simple qualitative framework can account for the characteristic features of low p high t metamorphic terranes and reconcile those who believe granites are the cause of the metamorphism with those who favor the contrary

stratigraphy age and correlation of lepue tephra a widespread c 11 000 cal a bp marker horizon sourced from the chaiten sector of southern chile we describe the stratigraphy age and correlation of a prominent tephra marker named lepue tephra extensively distributed in north western patagonia lepue tephra is well dated at c 11 000 cal a bp from numerous lake and soil cover bed sequences and its recognition is useful for assessing the rate and timing of deglaciation as well as associated environmental changes in this region during the last glacial termination and early holocene lepue tephra has attributes typical of a complex and compositionally zoned phreatomagmatic eruptive while the initial rhyolitic phase can be readily distinguished from multiple eruptive products sourced from the adjacent volcan chaiten the main erupted end member is of basaltic andesitic bulk composition similar to younger tephras sourced from holocene monogenetic cones adjacent to the volcan michimahuida massif tmim lepue tephra can be correlated to an equivalent aged pyroclastic flow deposit amarillo ignimbrite prominently distributed in the south eastern sector of tmim the source vent for these co eruptive events is obscured by an extensive ice field and is currently unknown the widespread radially symmetrical distribution of lepue tephra centred on tmim cannot be attributed solely to volcanological considerations reduced southern hemisphere westerly wind influence interpreted from climate proxies at the time of eruption are also implicated

the deuterium excess records of epica dome c and dronning maud land ice cores east antarctica new high resolution deuterium excess d data from the two epica ice cores drilled in dronning maud land edml and dome c edc are presented here the main moisture sources for precipitation at edc and edml are located in the indian ocean and atlantic ocean respectively the more southward moisture origin for edml is reflected in a lower present day d value compared to edc the edml and edc isotopic records 18o and d show the main climate features common to the east antarctic plateau and similar millennial scale climate variability during the last glacial period however quite large 18o and d differences are observed during mis5 5 and the glacial inception with a long term behaviour a possibility for this long term difference could be related to uncertainties in past accumulation rate which are used in the glaciological models regional climate anomalies between the two sites during mis5 5 could also be consistent with the observed edml edc 18o and d gradient anomalies simulations performed with the general circulation model echam4 for different time slices provide a temporal temperature isotope slope for the edml region in fair agreement to the modern spatial slope tsite and tsource records are extracted from both ice cores using a modelling approach after corrections for past 18o seawater and elevation changes a limited impact of d on antarctic temperature reconstruction at both edml and edc has been found with a higher impact only at glacial inception the aim antarctic isotope maximum events in both ice cores are visible also after the source correction suggesting that these are real climate features of the glacial period the different shape of the aim events between edc and edml as well as some climate features in the early holocene points to a slightly different climate evolution at regional scale a comparison of our temperature reconstruction profiles with the aerosol fluxes show a strong coupling of the nssca fluxes with antarctic temperatures during glacial period and a tighter coupling of 18o and tsite with ssna flux at edml compared to edc during the glacial period and mis5 5

temperate rainforest response to climate change and disturbance agents in northwestern patagonia 41 s over the last 2600 years abstract we present detailed pollen and charcoal records from lago pichilafquen 41 s to decipher the effects of climate change and varying disturbance regimes on the composition and structure of the vegetation on the andean foothills of northwestern patagonia during the last 2600 yr here temperate rainforests have dominated the landscape since 2600 cal yr bp with variations ranging from cool temperate and wet north patagonian rainforests to relatively warm and summer drought resistant valdivian rainforests we interpret relatively warm dry conditions between 1900 2600 690 750 and 320 430 cal yr bp alternating with cold wet conditions between 1500 1900 750 1100 and 430 690 cal yr bp rapid deforestation and spread of plants introduced by europeans occurred at 320 and 140 cal yr bp the record includes five tephras with ages of 2130 1460 1310 1210 and 340 cal yr bp all of which precede local fire events and increases in trees favored by disturbance by less than 100 yr we conclude that centennial scale changes in the southern westerlies were the primary driver of vegetation shifts in northwestern patagonia over the last 2600 yr within this interval local disturbance regimes altered the structure composition and dynamics of the lowland rainforest vegetation during several discrete short lived episodes

understanding the sam influence on the south pacific enso teleconnection the relationship between the el nino southern oscillation enso and the southern hemisphere annular mode sam is examined with the goal of understanding how various strong sam events modulate the enso teleconnection to the south pacific 45 70 s 150 70 w the focus is on multi month multi event variations during the last 50 years a significant p 0 10 relationship is observed most marked during the austral summer and in the 1970s and 1990s in most cases the significant relationship is brought about by la nina el nino events occurring with positive negative phases of the sam more often than expected by chance the south pacific teleconnection magnitude is found to be strongly dependent on the sam phase only when enso events occur with a weak sam or when a la nina el nino occurs with a positive negative sam phase are significant south pacific teleconnections found this modulation in the south pacific enso teleconnection is directly tied to the interaction of the anomalous enso and sam transient eddy momentum fluxes during la nina sam and el nino sam combinations the anomalous transient momentum fluxes in the pacific act to reinforce the circulation anomalies in the midlatitudes altering the circulation in such a way to maintain the enso teleconnections in la nina sam and el nino sam cases the anomalous transient eddies oppose each other in the midlatitudes overall acting to reduce the magnitude of the high latitude enso teleconnection

crustal conductors along the sveka profile in the fennoscandian baltic shield finland summary electrical properties of the crust in the central fennoscandian baltic shield are examined along the 435 km magnetotelluric profile sveka a 2 d geoelectric model shows large variations in the crustal resistivity with the model resistivities ranging from 0 1 to 35 000 m the main geoelectrical features of the crust and upper mantle are 1 a resistive archaean lower crust conductance 30 s 2 a conductive palaeoproterozoic lower crust beneath the central finland granitoid complex 170 900s free h2o rich fluids trapped into the lower crust seem less plausible causes for enhanced conductivity as long retention times are required and no possible sources seem to be available to produce fluids into the dry lower crust most likely causes for permanent enhancement of lower crustal conductivity include the conductive fill of ductile shear zones conductive graphite bearing lamellae conduction in mafic rocks perhaps via conduction in magnetite or conductive solid remnants of an ancient shear zone between two crustal blocks thin graphitic grain boundary films precipitated from co2 rich fluids also seem less plausible 3 a very resistive 10 000 35 000 m upper crust of the palaeoproterozoic central finland granitoid complex and the archaean domain 4 narrow and elongated conductors 0 1 100 m beneath the palaeoproterozoic kainuu ksb and tampere tsb schist belts are caused by graphite bearing metasedimentary rocks buried deep into the crust in the collisions of crustal terranes during the formation of the palaeoproterozoic svecofennian crust the 500 km long tsb conductor represents an internal svecofennian terrane boundary whereas the ksb conductor is a part of a discontinuous archaean proterozoic boundary conductor 5 resistive upper mantle there are no indications of an upper mantle conducting layer within the uppermost 300 km in the central part of the fennoscandian shield

influence of deformation on pressure temperature paths of metamorphism pressure temperature p t paths in structural terranes dominated by folds and thrust faults can be complex and can vary widely within a single metamorphic belt the complexity and variability of p t paths result from the advection of heat by folding and thrusting conductive heat transfer during and after deformation and the relatively short times for thermal relaxation within folds and thrusts in fold terranes contrasting p t paths are observed between anticlines and adjacent synclines cooling paths are observed within anticlines whereas heating paths are observed within synclines these different p t paths result from the folding of isotherms during deformation and the subsequent relaxation of isotherms after deformation in polydeformed fold terranes noncoaxial folding results in complex p t paths over small distances less than 15 km within a metamorphic belt because of the repetition of the process of folding and relaxation of isotherms during each folding event in structural terranes dominated by thrust faults p t paths differ between major thrust sheets because heat is transferred from the hotter overriding sheet to the cooler lower plate during deformation heat transfer during thrusting causes the upper plate to cool and the lower plate to heat in terranes with multiple thrust sheets p t paths can be complex and will depend upon the relative timing of thrust development and the rate at which heat can be transferred from one thrust sheet to the next the p t paths observed in both the fold and thrust terranes discussed here record relatively short time intervals of 10 5 or 10 6 yr because the mineral equilibria respond to small scale thermal perturbations there may be a wide variability in p t paths over a small distance in a metamorphic belt therefore before p t paths are used to reconstruct tectonic histories both structural and petrologic investigations must be carried out

metamorphic and structural evolution of the early proterozoic puolankajrvi formation finland ii the pressure temperature deformation composition path the paragenetic relationships between sillimanite andalusite kyanite chlorite cordierite biotite garnet and staurolite in the early proterozoic puolankajarvi formation pjf together with mineral compositions are used to construct a partial petrogenetic grid for metapelites with significant mn content mno 0 1 0 5 by adding a six phase invariant point over the garnet absent invariant point for mn free amf phases the grid and textural relations of the pjf are used to construct part of the p t deformation path for the pjf relatively short deformation pulses and associated flow of oxidizing fluid along shear zones were responsible for the paragenetic and compositional changes during cooling and decompression at 600 500 c and 6 0 2 5 kbar oxidation led to decreased fe2 and further stressed the importance of mn increased mn divalent cations a tectonothermal evolution of the kainuu schist belt is presented which includes crustal thinning and steepening of a previously established thermal gradient this was followed by thrusting and folding of the isotherms into a thermal antiform on the western side of the belt

tracing bottom water oxygenation with sedimentary mn fe ratios in lake zurich switzerland abstract redox dynamics of manganese mn were studied in the sediment of lake zurich using precise sediment core age models monthly long term oxygen o 2 monitoring data of the water column 1936 2010 and high resolution xrf core scanning the age models were based on bi annual lamination and calcite precipitation cycles if present mn exhibits distinct maxima which coincide with the annual maximum deep water o 2 concentrations in spring according to the monitoring data in contrast the iron fe signal is mainly the result of calcite dilution as indicated by a strong negative correlation between fe and calcium ca xrf data the mn fe ratio in the core from the maximum lake depth zh10 15 137 m revealed a moderate correlation with o 2 measurements in the lake bottom water confirming the successful application of the mn fe ratio to semi quantitatively reconstruct bottom water oxygenation in the lake mostly low ratios were observed between 1895 and the mid 1960s as a result of eutrophication however geochemical focusing and sedimentological factors can reduce the applicability of the mn fe ratio in reconstructing o 2 concentrations in the bottom water of lakes

have the southern westerlies changed in a zonally symmetric manner over the last 14 000 years a hemisphere wide take on a controversial problem the prevailing view in the palaeoclimate literature of the last 20 years is that the southern westerly winds sww were intensified over southern australia and tasmania during the warmer than present early holocene 11e8 ka at similar latitudes on the opposite side of the southern mid latitudes palaeoclimate studies have suggested a poleward shift of the northern edge of the westerlies and focusing at 49 s in southern south america this zonal asymmetry contrasts with the modern day zonal symmetry displayed by the sww and poses a formidable challenge to an understanding of the modes of climatic variability of the southern extra tropics this paper presents an updated synthesis of continuous radiocarbon dated palaeoenvironmental data from the westerlies zone of influence in all southern hemisphere continents synchronous multi millennial trends in moisture vegetation fire and hydrologic balance are remarkably consistent with the way the sww changes impact upon the climate in southern hemisphere landmasses in the modern climate considering the modern relationships between local precipitation and zonal wind speeds it is suggested that the sww changed in a zonally symmetric manner at multi millennial scale between 14 and 5 ka regional asymmetry develops after 5 ka across the southern hemisphere with a pattern of precipitation anomalies akin to the modern functioning of el nino e southern oscillation which started w6200 years ago

radiocarbon chronology of the last glacial maximum and its termination in northwestern patagonia abstract we examine the timing and magnitude of the last glacial maximum lgm and the last glacial termination lgt in northwestern patagonia situated in the middle latitudes of south america our data indicate that the main phase of the lgt began with abrupt warm pulses at 17 800 and 17 100 cal yrs bp accompanied by rapid establishment of evergreen temperate rainforests and extensive deglaciation of the andes within 1000 years this response shows that south american middle latitude temperatures had approached average interglacial values by 16 800 cal yrs bp the temperature rise in northwestern patagonia coincides with the beginning of major warming and glacier recession in the southern alps of new zealand at southern mid latitudes on the opposite side of the pacific ocean from this correspondence the warming that began at 17 800 cal yrs bp appears to have been widespread in middle latitudes of the southern hemisphere accounting for at least 75 of the total temperature recovery from the lgm to the holocene moreover this warming pulse is coeval with the first half of the heinrich stadial 1 hs1 in the north atlantic region hs1 featured a decline of north atlantic meridional overturning circulation a southward shift of the westerly wind belt in both hemispheres and of the intertropical convergence zone as well as a weakening of the asian monsoon along with the initiating trigger identifying the mechanisms whereby these opposing climate signals in the two polar hemispheres interacted whether through an oceanic or an atmospheric bipolar seesaw or both lies at the heart of understanding the lgt

slicing up the san francisco bay area block kinematics and fault slip rates from gps derived surface velocities received 26 october 2004 revised 11 february 2005 accepted 10 march 2005 published 16 june 2005 i observations of surface deformation allow us to determine the kinematics of faults in the san francisco bay area we present the bay area velocity unification bavu bay view a compilation of over 200 horizontal surface velocities computed from campaign style and continuous global positioning system gps observations from 1993 to 2003 we interpret this interseismic velocity field using a three dimensional block model to determine the relative contributions of block motion elastic strain accumulation and shallow aseismic creep the total relative motion between the pacific plate and the rigid sierra nevada great valley sngv microplate is 37 9 0 6 mm yr 1 directed toward n30 4 w 0 8 at san francisco 2 fault slip rates from our preferred model are typically within the error bounds of geologic estimates but provide a better fit to geodetic data notable right lateral slip rates in mm yr 1 san gregorio fault 2 4 1 0 west napa fault 4 0 3 0 zone of faulting along the eastern margin of the coast range 5 4 1 0 and mount diablo thrust 3 9 1 0 of reverse slip and 4 0 0 2 of right lateral strike slip slip on the northern calaveras is partitioned between both the west napa and concord green valley fault systems the total convergence across the bay area is negligible poles of rotation for bay area blocks progress systematically from the north america pacific to north america sngv poles the resulting present day relative motion cannot explain the strike of most bay area faults but fault strike does loosely correlate with inferred plate motions at the time each fault initiated