the stabilization of self organised leucogranite networks implications for melt segregation and far field melt transfer in the continental crust abstract net structured leucocratic vein systems are ubiquitous in high grade and migmatite terrains and are interpreted to represent interconnected former magma bearing structures that accommodated the migration of granitic magmas out of their anatectic source regions net structured leucogranite vein systems in high grade gneisses from the damara belt in namibia describe a size based hierarchy and spatial distribution that indicates self organisation of the magma transfer system the internal geometry and connectivity of the net structured leucogranites are controlled by variations in melt pressure whereas regional strains control the orientation of the leucogranites foliation parallel stromatic and shear band hosted granite veins accommodate transport at relatively low melt volumes and account for the metre scale segregation of melt close to the anatectic source during times of higher melt supply the formation of extensional fractures that cross cut stromatic and shear band hosted melt sheets at high angles is promoted extensional fracturing and associated dilatancy create gradients in magmastatic head that cause melt to be drained from pervasive stromatic and shear band hosted vein networks into spaced dilatant fractures this has the potential to initiate buoyancy driven far field melt transfer along suitably orientated extensional fractures as vertical dykes or self propagating hydrofractures our results suggest that melt transfer systems are able to adjust to variations in melt supply by forming conduits that accommodate varying melt volumes and will tend to develop towards a state of self organisation

granite ascent and emplacement during contractional deformation in convergent orogens based on a case study in the central maine belt of west central maine u s a it is proposed that crustal scale shear zone systems provide an eaective focussing mechanism for transfer of granite melt through the crust in convergent orogens during contractional deformation flow of melt in crustal materials at depths below the brittle plastic transition is coupled with plastic deformation of these materials the flow is driven by pressure gradients generated by buoyancy forces and tectonic stresses within the oblique reverse central maine belt shear zone system stromatic migmatite and concordant to weakly discordant irregular granite sheets occur in zones of higher strain which suggests percolative flow of melt to form the migmatite leuco somes and viscous flow of melt channelized in sheet like bodies possibly along fractures cyclic fluctuations of melt pressure may cause instantaneous changes in the eaective permeability of the flow network if self propa gating melt filled tensile and or dilatant shear fractures are produced due to melt enhanced embrittlement in homogeneous migmatite and schlieric granite occur in zones of lower strain which suggests migration of partially molten material through these zones en masse by granular flow and channelized flow of melt carrying entrained residue founded on the central maine belt case study we develop a model of melt extraction and ascent using the driving forces stress conditions and crustal rheologies in convergent especially transpressive orogens ascent of melt becomes inhibited with decreasing depth as the solidus is approached for intermedi ate a h2o muscovite dehydration melting the water saturated solidus occurs between 400 and 200 mpa near the brittle plastic transition during high t low p metamorphism where the balance of forces favors sub horizontal fracture propagation emplacement of melt may be accommodated by ductile flow and or stoping of wall rock and inflation may be accommodated by lifting of the roof at shallower crustal levels and or sink ing of the pluton floor the resultant plutons have sub horizontal tabular geometries with floors that slope down to the ascent conduits although these plutons may have locally discordant relations with country rock structures when viewed at the crustal scale granite ascent and emplacement in convergent orogens are syn tec tonic processes 1998 elsevier science ltd all rights reserved

alpine crustal shear zones and pre alpine basement terranes in the romanian carpathians and apuseni mountains the carpathian orocline formed by complex suturing of small continental fragments to the east european and moesian plate remnants of continental fragments belong to three pre alpine lithotectonic assemblages a greenstone granite association and two gneissic assem blages during alpine collision pieces of crust were repeatedly fragmented and welded to accommodate heterogeneous strain along the irregular east european plate boundary shallow structural levels of alpine tectonic discontinuities in which the locus of most intense strain migrated over time are now exposed as wide retrograde greenschist grade belts repeated mainly transpressive deformation resulted in early ductile fabrics being overprinted by local brittle shear strain igneous intrusion accompanied different phases of tectonic activity the age of shearing initiation is probably late paleozoic and the configuration of the zones and their alpine internal structures are consistent with the geometry of the carpathian arc

syntectonic anatexis and magmatism in a mid crustal transpressional shear zone an example from the hercynian rocks of the eastern pyrenees abstract hercynian metamorphism and magmatism in the cap de creus peninsula eastern pyrenees occurred contemporaneously with non coaxial deformation in a transpressive regime an example of this has been taken from a migmatite complex in the northern coast the studied area is formed by partially melted sillimanite schists together with two different suites of igneous rocks a calc alkaline magmatic sequence consisting of small granitoid bodies and later peraluminous leucogranites and pegmatites all these rocks occur within a ne sw to e w trending sub vertical high strain zone where a first schistosity is tightly folded and transposed the relations between folds and crenulation cleavage in the metasediments and deformational fabrics in the granitoids and migmatites provide good evidence for the penecontemporaneity of deformational processes magmatism and migmatization furthermore the analysis of cross cutting relationships between different granitoids as well as the observation of their different degrees of deformation verifies that magmatism in this area took place as synkinematic consecutive intrusions from the more basic magmas to the peraluminous acid dykes

tertiary tectonic evolution of the external south carpathians and the adjacent moesian platform romania depth interpreted seismic sections of the getic depression foredeep paleostress indicator data and analysis of outcrop to regional scale structures are integrated to derive the tectonic evolution of the south carpathians moesian platform area following late cretaceous and older orogenic phases the south carpathians moesian platform area underwent strike slip deformation with ne sw oriented compression and nw se tension in paleogene to early burdigalian times tensional deformation is recorded which led to the opening of wsw ene to e w trending extensional basins in the late burdigalian ne sw oriented contraction took over causing the oblique inversion of preexisting extensional structures during sarmatian times nw se and slightly younger n s trending compression caused the activation of mainly nw se dextral strike slip faults and in the frontal areas south directed thrusting the nw se direction of extension determined for paleogene to early burdigalian times is hardly compatible with presently accepted models of substantially continuous dextral wrenching between the intra carpathians units to the north of the south carpathians and the moesian platform to the south in contrast we have demonstrated dextral transpressive to transtensional movements within an e w trending corridor from the late burdigalian to late sarmatian which are compatible with available models

variscan vs alpine tectonothermal evolution of the southern carpathian orogen constraints from 40ar 39ar ages abstract 40 ar 39 ar hornblende and muscovite ages indicate that basement units exposed within all major alpine nappes of the southern carpathian orogen were penetratively deformed and metamorphosed during late variscan carboniferous tectonothermal events subsequent exhumation resulted in cooling from ca 500 c hornblende k ar retention temperature to ca 375 c muscovite k ar retention temperature between ca 320 and 295 ma late variscan exhumation of middle crustal levels is interpreted to have resulted from intracontinental contraction and regional uplift subsequent to variscan continental collision between gondwana derived tectonic elements e g africa and laurussia muscovite ages within mylonite zones suggest that late variscan shear zones were probably associated with a regional shear system that developed along the southern margins of laurussia alpine metamorphic effects within the southern carpathians are generally nonpenetrative and are only significant within narrow zones of retrogression that are interpreted to have formed during initial attenuation of variscan crust associated with formation of the jurassic severin rift

sea level topographical and sediment supply controls on holocene sediment composition in the humber estuary uk to increase our understanding of the relative control of antecedent topography sediment supply and sea level change on grain size and organic content in the humber estuary the composition of its holocene fill over space and time has been evaluated a model based upon bed by bed description of over 3500 boreholes was sub horizontally sliced to analyse the composition of sediments in different parts of the estuary across the entire fill as well as solely within estuary marginal sequences results demonstrate that different physiographic parts of the estuary are characterized by distinctive vertical sediment profiles that reflect the relative control of antecedent topography as well as sea level upon them the results raise questions about the processes controlling sand and gravel abundance in marginal sequences where the estuary is physiographically most constrained this semi quantitative evaluation the first of its kind on an estuarine fill provides a technique for interpreting the relative importance of controls on an estuarine system but highlights the need for improved modelling of estuarine channel form and dynamics over centurial to millennial time scales

the anatomy of a gondwanan terrane the neoproterozoic ordovician basement of the pre alpine sebes lotru composite terrane south carpathians romania abstract the sebes lotru terrane in the south carpathians mountain range comprises a lower neoproterozoic metamorphic unit lotru and an upper ordovician metamorphic unit cump na that were juxtaposed during the variscan orogeny two orthogneisses from the lotru metamorphic unit yield u pb la icp ms zircon crystallization ages of 549 3 3 8 ma and 587 5 3 ma respectively two orthogneisses from the cump na metamorphic unit yield zircon crystallization ages of 458 9 3 5 ma and 466 0 4 2 ma respectively high u zircons from two other orthogneisses from the cump na metamorphic unit have ages ranging from 400 ma to 320 ma which are interpreted to reflect protracted zircon recrystallization during the regionally significant variscan collisional event detrital zircons from a metasedimentary gneiss in the cump na metamorphic unit have ages ranging from 0 5 ga to 2 8 ga the 0 5 ga age constrains the maximum sediment deposition age to be late cambrian the source most compatible with the range of precambrian detrital ages in the sebes lotru terrane is northeastern gondwana the sebes lotru terrane was part of a continental subduction collision system as a lower plate after about 400 ma and reached peak metamorphic conditions between 350 and 320 ma e g medaris et al 2003 a cross cutting granite vein has a zircon u pb crystallization age of 321 5 3 1 ma which constrains minimum age of ductile deformation during the variscan collision in this region the trace of the rheic suture within the south carpathians is located between the ordovician upper part of the sebes lotru terrane and the dr gsan pre alpine terrane of the danubian domain

timing of rotational motion of apuseni mountains romania paleomagnetic data from tertiary magmatic rocks paleomagnetic results are reported from 8 sites in eocene to oligocene magmatic rocks and 27 sites in middle miocene to upper miocene volcanic rocks of the apuseni mountains following af demagnetization 29 sites were selected for tectonic interpretation these results together with previously published data imply a northward displacement of the area studied between the late cretaceous and oligocene followed by a large clockwise rotation prior to the middle miocene after which no significant movement has occurred these results agree with other data from the carpatho pannonian domain showing a period of great mobility during the early miocene

influence of paleotopography base level and sedimentation rate on estuarine system response to the holocene sea level rise the example of the marais vernier seine estuary france the response of coastal systems to allogenic forcing factors is of interest to diverse research communities including those interested in global change sequence stratigraphy and modelling quaternary systems are of particular interest because they provide analogues for ancient rock records to understand the processes responsible for the sedimentary evolution of estuarine systems it is necessary to study as many fluvial systems as possible the objective of this review of the sedimentary evolution of a coastal marsh is to describe the influence of glacial paleotopography on the record of climatic and sea level changes the marais vernier located at the interface between the marine and fluvial parts of the estuary is a part of the lower seine valley wetland network which formed after the last glacial maximum previous studies have described the holocene filling which is composed of peat and detrital material deposited following climatic and sea level changes to understand the sedimentary evolution a paleotopographical based on drillings and electromagnetic surveys and a chronological framework based on radiocarbon dates for the southern peat marsh were defined the peat marsh paleotopography has three erosional surfaces the s1 surface is the oldest and also the highest topographically the s2 surface is younger wider and incised below the s1 surface the s3 surface the youngest of the three is narrow and deeply incised radiometric ages were considered on the basis of their geographical position in relation to the s3 surface prior to 7 5 ka cal bp sediments accumulated only above the narrow area described by the s3 surface at a rate of 5 5 mm yr 1 after 7 5 ka cal bp shortly after the flooding of the seine estuary sediments accumulated as peat deposits over the entire peat marsh at a rate of 3 mm yr 1 in response to the sea level rise the paleotopography delimits the area of deposition during the holocene and thus plays a critical role in determining the vertical accretion rate expressed as a thickness prior to 7 5 ka cal bp the vertical accretion rate 5 5 mm yr 1 was less than that observed for the seine estuary 6 8 mm yr 1 however rate of sea level rise and sediment supply which also affects sediment accumulation rates vary in northwestern europe during the holocene therefore although the marais vernier is a good illustration of paleotopographic influence the effects of autocompaction sea level and sediment supply complicate efforts to quantify the degree to which it controls sediment accumulation

evolution of the rheic ocean the rheic ocean which separated laurussia from gondwana following the closure of iapetus is arguably the most important ocean of the palaeozoic its suture extends from mexico to turkey and its closure produced the climactic variscan alleghanian ouachita orogeny that assembled the supercontinent pangaea following protracted cambrian rifting that represented a continuum from neoproterozoic orogenic processes the rheic ocean opened in the early ordovician with the separation of several neoproterozoic arc terranes from the continental margin of northern gondwana separation occurred along the line of a former neoproterozoic suture following the onset of subduction in the outboard iapetus ocean the timing of rift drift transition and drive for subsequent spreading was likely governed by slab pull accounting for the rapid rate 8 10 cm yr at which the rheic ocean widened during the ordovician the ocean broadened at the expense of iapetus and attained its greatest width 4000 km in the silurian by which time baltica had sutured to laurentia and the neoproterozoic arc terranes had accreted to laurussia closing iapetus in the process closure of the rheic ocean began in the devonian and was facilitated by northward subduction beneath southern baltica and southward subduction beneath northwest gondwana closure was largely complete by the mississippian as gondwana and laurussia sutured to build pangaea north africa colliding with southern europe to create the variscan orogen in the devonian carboniferous and west africa and south america suturing to north america to form the alleghanian and ouachita orogens respectively during the carboniferous permian the rheic ocean consequently plays a dominant role in the basement geology of southern europe in the appalachian ouachita orogeny of north america and in the palaeozoic sedimentary structural and tectonothermal record from middle america to the middle east with its closure the ocean brought about the assembly of pangaea and brought the palaeozoic era to an end

lower cretaceous provenance and sedimentary deposition in the eastern carpathians inferences for the evolution of the subducted oceanic domain and its european passive continental margin

evolution of the sibisel shear zone south carpathians a study of its type locality near răsinari romania and tectonic implications romanian executive agency for higher education research development and innovation pn ii id pce 2011 3 0217 pn ii id pce 2011 3 0030

late glacial to holocene depositional architecture of the ombrone palaeovalley system southern tuscany italy sea level climate and local control in valley fill variability the ombrone palaeovalley was incised during the last glacial sea level fall and was infilled during the subsequent late glacial to holocene transgression a detailed sedimentological and stratigraphic study of two cores along the palaeovalley axis led to reconstruction of the post last glacial maximum valley fill history stratigraphic correlations show remarkable similarity in the late glacial to early holocene succession but discrepancy in the holocene portion of the valley fill above the palaeovalley floor about 60 m below sea level late glacial sedimentation is recorded by an unusually thick alluvial succession dated back to ca 18 cal kyr bp the holocene onset was followed by the retrogradational shift from alluvial to coastal facies in seaward core om1 the transition from inner to outer estuarine environments marks the maximum deepening of the system by comparison in landward core om2 the emplacement of estuarine conditions was interrupted by renewed continental sedimentation swamp to lacustrine facies stratigraphically equivalent to the fully estuarine facies of core om1 represent the proximal expression of the maximum flooding zone this succession reflects location in a confined segment of the valley just landward of the confluence with a tributary valley it is likely that sudden sediment input from the tributary produced a topographic threshold damming the main valley course and isolating its landward segment from the sea the seaward portion of the ombrone palaeovalley presents the typical estuarine backfilling succession of allogenically controlled incised valleys in contrast in the landward portion of the system local dynamics completely overwhelmed the sea level signal following marine ingression this study highlights the complexity of palaeovalley systems where local morphologies changes in catchment areas drainage systems and tributary valleys may produce facies patterns significantly different from the general stratigraphic organization depicted by traditional sequence stratigraphic models

strengthening the link between geochronology textures and petrology time must be integrated with other geologic parameters such as pressure temperature p t composition or structural textural information in order to quantify the dynamics of geologic processes like mountain building faulting metamorphism or magmatism in the past this connection was weak due to large sample sizes required in geochronology however recent developments open up exciting new possibilities texturally controlled in situ dating of minerals utilizing uv laser ablation 40ar 39ar or rb sr microsampling facilitates the crucial link between ages and textures at high spatial resolution in situ u pb ages of accessory minerals can now be linked to the corresponding p t evolution via their characteristic trace elemental signatures indicative of mineral reactions in rocks garnet dating by sm nd and more recently lu hf can greatly benefit from both laser ablation inductively coupled plasma mass spectrometry icpms screening and improved leaching strategies improving the link between time and p t such integrated approaches can yield the duration and rates of deformation in shear zones the rates of burial and exhumation of subducted rocks or the duration of entire metamorphic loops to name a few potential for further development is identified in diverse areas dating of carbonate minerals related to brittle faulting using u pb could provide previously unavailable constraints on rates and duration of brittle deformation in the earth s upper crust in situ rb sr dating applicable to micas could become available using either laser ablation dynamic reaction cell icpms or microbeam accelerator mass spectrometry other future developments and trends and their limitations are discussed briefly

crustal lineament control on magmatism and mineralization in northwestern argentina geological geophysical and remote sensing evidence abstract the relationship between long lived deep crustal lineaments and the locations of magmatic centers and associated mineral deposits has been investigated in the puna region of northwestern argentina through the analysis of regional aeromagnetic surveys landsat images and geological information the good exposure and excellent preservation of basement and supracrustal geology in this region makes it particularly suitable for such a study at a regional scale several contrasting magnetic domains are recognized which correlate with crustal geology two basement domains are separated by a nne trending boundary which is believed to correlate with a paleozoic suture zone between the pampia to the southeast and arequipa antofalla terranes to the northwest locally overlying these basement terranes is the cenozoic magmatic domain which is best developed in the n s trending volcanic arc at the western edge of the puna the cordillera occidental in addition four southeast trending volcanic zones extend for several hundred kilometers across the puna many important mineral deposits and areas of hydrothermal alteration are associated with these volcanic breakouts and we have selected three such areas for more detailed study bajo de la alumbrera argentina s largest porphyry copper deposit cerro galan the largest ignimbrite caldera in argentina with associated hydrothermal alteration zones and el queva a historic polymetallic district located within a major volcanic range a comparison of lineament maps generated from aeromagnetic and landsat tm images reveals broad correlation between these different remote sensing techniques which respectively highlight subsurface magnetic and surface geological features in addition the locations of magmatic and hydrothermal centers can be related to the interpreted structural framework and are seen to occur near the intersections of major lineament zones it is suggested that in three dimensions such intersection zones form trans lithospheric columns of low strength and high permeability during transpressional or transtensional tectonic strain and may thereby serve as conduits for magma ascent to the shallow crust pooling of large volumes of deeply derived magma in shallow crustal magma chambers may then result in voluminous devolatilization and the formation of hydrothermal mineral deposits it is important to note that in this model structural intersections serve as facilitators for magma ascent and volatile exsolution but do not in themselves cause this process other factors such as magma supply rate and tectonic stress are essential primary ingredients and local magmatic and volcanic processes affect the ultimate potential for ore formation nevertheless we suggest that lineament analysis provides a valuable framework for guiding the early stages of mineral exploration other regional and local geological considerations must then be applied to identify priority targets within this framework

tertiary palaeomagnetic data for the carpatho pannonian region in the light of miocene rotation kinematics abstract the tectonic interpretation of the palaeomagnetic data for the neogene history of the carpatho pannonian region has usually been based on the palaeomagnetic data for the pre cenozoic complexes here a review of the tertiary palaeomagnetic data is given for the sites with two or more sets of data new site mean directions are calculated for most areas new area mean directions are given with a uniform criterion for the limitation of the normally distributed sub populations based on radiometric data some neogene volcanic sequences are subdivided into two complexes with separate area mean directions the possible influence of the areal tilts on the area mean palaeomagnetic directions is analysed and conclusions on the horizontal rotations are drawn the palaeomagnetic rotations are interpreted in the light of the author s kinematic model for the neogene history of the carpatho pannonian region the rotation of both the southeastern unit by about 100 clockwise and the northwestern unit by about 35 anti clockwise are supported by palaeomagnetic data in addition some rotations predicted by the model are documented by palaeomagnetic data as follows 1 the anti clockwise rotation of the flanks of the darno line gemer bukk area with sinistral displacements in the early miocene 2 the anti clockwise rotations along the southeastern margin of the northwestern unit with sinistral displacements before 10 ma 3 the anti clockwise rotation of the ukrainian carpathians before 12 ma some palaeomagnetic rotations have not been predicted by the kinematic model but occur in the regions where deformations are quite probable these unexpected palaeomagnetic rotations throw a new light on some details of the kinematics 1 the advance of the outer west carpathian nappes later than 14 ma is documented by the increased palaeomagnetic inclination of the pieniny andesites 2 the movement of the central and inner west carpathians later than 12 ma is recorded in the palaeomagnetic rotations of the central and east slovakian volcanites this movement seems to reflect a bay of thin crust within the underthrust european plate margin or more precisely the reaction of the eastern contour of the bay on the drag of the northwestern unit towards the northeast by the still rotating southeastern unit the rotation and deformation of the northwestern unit in the miocene have to be taken into account in the reconstructions of the pre neogene situations since they intensely influenced the arrangement of all older palaeotectonic and palaeogeographic zones the southeastern unit also suffered intense rotation and deformation in the miocene unfortunately there are almost no palaeomagnetic data available for its tertiary complexes

tectonic setting of the sandia pluton an orogenic 1 4 ga granite in new mexico structural studies of the circa 1 42 ga sandia pluton and its aureole document significant deformation synchronous with pluton emplacement and call into question the anorogenic label associated with this and other 1 4 ga granites in the southwestern united states the se margin of the pluton is a 1 to 2 km wide nw dipping ductile shear zone field and microstructural observations melt filled shear bands high temperature dynamic recrystallization of k feldspar megacrysts and crosscutting pegmatite dikes indicate that top to the nw normal movement in the shear zone took place in the presence of melt subparallel magmatic fabrics north of and structurally above the shear zone contain kinematic indicators consistent with top to the nw shear sense suggesting that over large regions of the pluton magmatic flow mimicked solid state strain in the northern aureole contact metamorphic aluminosilicate porphyroblasts grew during the formation of a ne striking crenulation cleavage s3 and related folds of late stage pegmatite dikes these features document the synchroneity of magma emplacement shortening and metamorphism and indicate that the sandia pluton is syntectonic not anorogenic we interpret the kinematic consistency of structural elements from the base of the pluton the interior of the pluton and the northern aureole to reflect a regional larger than the pluton strain field and suggest that the orogeny recorded in and around the sandia pluton involved a three dimensional strain field with subhorizontal extension n s and contraction e w directions n s extension is documented by the orientation of mineral lineations and movement directions in the basal shear zone and in high strain zones in the northern aureole and by the orientations of tabular pegmatite and aplite dikes in the pluton and aureole east to se shortening is documented in the northern aureole by orientations of folded pegmatite dikes and associated s3 crenulation cleavage and east to se shortening or least extension directions in the pluton proper are documented by the intersections of orthogonal dikes thus emplacement of the sandia pluton is interpreted to record a snapshot of regional strains inboard of an active plate margin rather than local strains generated by emplacement

synconvergent ductile flow in variable strength continental crust numerical models with application to the western grenville orogen 1 we present results from numerical models for a convergent orogen with laterally variable lower crustal strength representing a simplified orogenic system in which a strong craton flanked by progressively weaker terranes collides with another continent with progressive convergence crustal thickening and thermal relaxation lower crust becomes decoupled from upper and middle crust forming a ductile orogenic infrastructure beneath a stronger superstructure collision with strong external crust results in uplift and expulsion of ductile nappes from the orogenic core creating allochthonous terranes overlying a lower crustal indentor the extent of transport and exhumation of lower crustal nappes over the indentor reflects the amount of convergence and the erosion rate the western grenville orogen displays across strike variations in age tectonic history and protolith association suggesting a systematic variation in precollision crustal strength the laurentian craton margin and accreted terranes were variably reworked at synorogenic depths of 25 35 km during the ottawan orogeny deformation propagated from younger monocyclic rocks in the southeast into older polycyclic rocks flanking the craton on the northwest a comparison between numerical model results and crustal scale cross sections from the georgian bay and montreal val d or transects shows close correspondence between crustal structure and model geometry this indicates that the models produce geologically realistic results and provides a context for interpreting the tectonic evolution of the western grenville orogen contrasts between the results of homogeneous channel flow models and the present ductile nappe models suggest that the effects of different styles of ductile flow can be distinguished in the geologic record

thermal constraints on the emplacement rate of a large intrusive complex the manaslu leucogranite nepal himalaya the emplacement of the manaslu leucogranite body nepal himalaya has been modelled as the accretion of successive sills the leucogranite is characterized by isotopic heterogeneities suggesting limited magma convection and by a thin 100 m upper thermal aureole these characteristics were used to constrain the maximum magma emplacement rate models were tested with sills injected regularly over the whole duration of emplacement and with two emplacement sequences separated by a repose period additionally the hypothesis of a tectonic top contact with unroofing limiting heat transfer during magma emplacement was evaluated in this latter case the upper limit for the emplacement rate was estimated at 3 4 mm year or 1 5 myr for 5 km of granite geological and thermobarometric data however argue against a major role of fault activity in magma cooling during the leucogranite emplacement the best model in agreement with available geochronological data suggests an emplacement rate of 1 mm year for a relatively shallow level of emplacement granite top at 10 km uninterrupted by a long repose period the thermal aureole temperature and thickness and the isotopic heterogeneities within the leucogranite can be explained by the accretion of 20 60 m thick sills intruded every 20 000 60 000 years over a period of 5 myr under such conditions the thermal effects of granite intrusion on the underlying rocks appear limited and cannot be invoked as a cause for the formation of migmatites

cretaceous to miocene thrusting and wrenching along the central south carpathians due to a corner effect during collision and orocline formation field studies in the romanian south carpathians longitude 22 5 to 24 2 e and latitude 45 2 to 45 6 n demonstrate 1 cretaceous top to ne shearing parallel to the present strike of the thrust system connected with coaxial flattening within the generally northwest dipping foliation 2 paleogene ductile brittle dextral wrenching e w compression 1 87 15 and basin formation petrosani basin along the cerna jiu fault system 3 large scale miocene dextral wrenching along the northern margin of moesia 1 143 16 and 4 probably pliocene early pleistocene n s compression 1 205 25 we discuss the tectonics of the south carpathians stressing the corner effect of the moesian foreland promontory during convergence and formation of the carpathian orocline up to the late early cretaceous subduction of oceanic crust was active between europe moesia on one side and east carpathia rhodopia on the other side collision and intracontinental deformation occurred during the late early and late cretaceous the pinning of the thrust front at the western tip of moesia and the foreland recess north of it caused superposition of thrusting and wrenching during collision and lateral translation tangential stretching during orocline formation and spreading into the recess further convergence during the early tertiary resulted in dislocation of the previously welded east carpathian rhodopian and moesian fragments along the cerna jiu fault system and the further northeast translation of the western segment the intramontane petrosani basin opened as a northeasterly propagating transient pull apart structure along the cerna jiu fault system which acquired a curved northwesterly convex transtensional trace due to the shape of the moesian promontory tightening of the carpathian orocline and or rearrangement of the microplate geometry during the formation of the pannonian basin system led to large scale dextral wrenching along the northern margin of moesia pliocene n s compression reflects final shortening in the carpathian system before ongoing convergence between europe and africa was transferred to the mediterranean rotation of material lines around the moesian corner is corroborated by paleomagnetic studies

pre mesozoic alpine basements their place in the european paleozoic framework prior to their alpine overprinting most of the pre mesozoic basement areas in alpine orogenic structures shared a complex evolution starting with neoproterozoic sediments that are thought to have received detrital input from both west and east gondwanan cratonic sources a subsequent neoproterozoic cambrian active margin setting at the gondwana margin was followed by a cambrian ordovician rifting period including an ordovician cordillera like active margin setting during the late ordovician and silurian periods the future alpine domains recorded crustal extension along the gondwana margin announcing the future opening of the paleotethys oceanic domain most areas then underwent variscan orogenic events including continental subduction and collisions with avalonian type basement areas along laurussia and the juxtaposition and the duplication of terrane assemblages during strike slip accompanied by contemporaneous crustal shortening and the subduction of paleotethys under laurussia thereafter the final pangea assemblage underwent triassic and jurassic extension followed by tertiary shortening and leading to the buildup of the alpine mountain chain recent plate tectonic reconstructions place the alpine domains in their supposed initial cambrian ordovician positions in the eastern part of the gondwana margin where a stronger interference with the chinese blocks is proposed at least from the ordovician onward for the visean time of the variscan continental collision the distinction of the former tectonic lower plate situation is traceable but becomes blurred through the subsequent oblique subduction of paleotethys under laurussia accompanied by large scale strike slip since the pennsylvanian this global collisional scenario has been replaced by subsequent and ongoing shortening and strike slip under rising geothermal conditions and all of this occurred before all these puzzle elements underwent the complex alpine reorganization

regional implications of geochemistry and style of emplacement of miocene i type diorite and granite delos cyclades greece abstract the miocene plutons of the cyclades were emplaced in a subduction setting during regional back arc extension of continental crust that led to flat lying mid crustal detachment faulting mapping of the island of delos shows that quartz diorite and tonalite were emplaced as dykes in country rock of schist and marble within shear zones parallel to the extension direction mafic magmas were followed by numerous small batches of felsic magma with magmatic and ductile deformation synchronous with magma emplacement late granite dykes occupy brittle fractures in the more deformed rocks mafic and intermediate rocks show a bimodal distribution of incompatible trace elements with one group of broadly tholeiitic character and the other with substantial enrichment in sr nb and hfse but low th and ba these differences appear to be inherited from two distinct mafic sources that are different from the mafic source for the plutons of the eastern cyclades voluminous granodiorite results from these mafic magmas fractionating and or mixing with felsic crustal material some of which was derived by anatexis of a sedimentary protolith indicated by high b and mn some late granites appear derived from partial melting of hercynian paragneiss regionally the shear zones appear to be feeders to more extensive granitic plutons located at space produced at ramps in detachment fault zones the shear zones parallel the mid cycladic lineament a broad zone of displacement between two crustal blocks rotating in opposing directions as rollback took place at the hellenic subduction zone distinctive geochemical features in miocene igneous rocks suggests that these two blocks had quite different geological histories the localisation of plutonism and core complexes near the mid cycladic lineament suggests that this crustal scale shear played a role in bringing subduction derived magmas to mid crustal levels the heat supplied by the mafic magmas promoted ductile deformation high in the crust where extension was concentrated leading to the formation of core complexes the regional extension resulted in progressive shallowing of the position of the granite solidus within the crust leading to welding of the mid cycladic lineament which is no longer seismically active

shear fractures in anisotropic ductile materials an experimental approach abstract analogue models have been used to investigate the influence of planar mechanical anisotropy on the orientation of shear fractures in an elastoviscous brittle material multilayered models consisting of a mixture of plasticine vaseline and preferentially oriented paper flakes have been coaxially deformed for this purpose the evolution of the orientation length and connectivity of fracture sets has been systematically analysed with progressive coaxial deformation the experimental results show that the orientation of fractures with respect to the deformation axes depends on the orientation of transverse anisotropy two symmetrical sets of shear fractures are formed in models with layering parallel to the extension axis x while the fracture network is asymmetrical with respect to the deformation axes for cases with oblique anisotropy the average dihedral angles between fracture sets are higher than 100 with the obtuse bisector between the two sets oriented perpendicular to layers the stress fields calculated from fracture data differ from the boundary conditions applied by the deformation apparatus this misorientation is related to the degree of anisotropy in models with high oblique anisotropy both fracture arrays rotate in a dextral sense together with layers towards the x axis indicating that the presence of a strong anisotropy controls their evolution with progressive deformation

the competition between rates of deformation and solidification in syn kinematic granitic intrusions resolving the pegmatite paradox abstract while fully crystallized granites rich in feldspar generally serve to strengthen the continental crust their precursor melts are assumed to be important agents of crustal weakening many syn tectonic granitic pegmatites are deformed within shear zones but ubiquitously preserve undeformed primary magmatic textures implying that they were largely molten during shearing yet the shapes of pegmatite bodies indicate that they deformed with a greater competence than their surroundings this co located pair of material behaviours is paradoxical we interpret field relationships in a typical pegmatite shear zone association torrisdale nw scotland and propose a mechanism by which syn tectonic granitic melts may in effect act as competent bodies while not yet fully crystallized competence was rapidly increased by preferential crystallization on intrusion margins that served to encapsulate residual melt inside stiff rinds further crystallization may have been pulsed as the concentrations of crystallization inhibitors fluxes increased in residual fluids postulating the existence of initial stiff rinds also consistent with modern estimates for rates of feldspar crystallization cms yr from undercooled hydrous silicic magma to form pegmatites these greatly outpace strain rate estimates for shear zones thus fully liquid granitic melts may only be present fleetingly and have little opportunity to weaken deforming crust before crystallization begins

deformation and kinematics in a melt bearing shear zone from the western betic cordilleras southern spain abstract this work deals with the structural evolution and kinematics of the basal dynamothermal aureole of the ronda peridotites located in the sierra bermeja massif of the western betic cordilleras in southern spain this aureole is characterized by 1 a marked strain gradient towards the contact with the overlying peridotites 2 the great angular dispersion 90 of stretching lineations and 3 the intrusion of thin syn kinematic granite sheets these features are consistent with the aureole being a low viscosity shear zone formed at temperatures high enough 725 c to promote the partial melting of crustal metamorphic rocks the high temperature deformation is demonstrated by the activation of c slip in quartz we consider that the heat source came from the thrusting of the hot subcontinental mantle over metamorphic crustal rocks the interaction of alternating events of melt enhanced deformation and melt enhanced embrittlement explains the heterogeneity of this ductile shear zone and the strong narrowing to only 30 meters of the deformed domain the small thickness of this shear zone is in contradiction with classical conceptual models of shear zones suggesting a broadening of ductile shear zones with increasing depths and temperatures

transect across the northwestern grenville orogen georgian bay ontario polystage convergence and extension in the lower orogenic crust the grenville orogenic cycle between 1190 and 980 ma involved accretion of magmatic arcs and or continental terranes to the laurentian craton a transect across the western central gneiss belt georgian bay ontario which crosses the boundary between parautochthonous and allochthonous units at an inferred orogenic depth of 20 30 km offers some insights on the thermal and mechanical behavior of the lower crust during the development of the grenville orogen prior to grenvillian metamorphism this part of laurentia consisted largely of meso proterozoic 1450 ma granitoid orthogneisses granulites and subordinate mafic and supracrustal rocks grenvillian convergence along the transect began with transport of the previously deformed and metamorphosed 1160 ma parry sound domain over the craton sometime between 1120 ma and 1080 ma this stage of transport was followed by out of sequence thrusting and further convergence along successively deeper foreland propagating ductile thrust zones a major episode of extension at 1020 ma resulted in southeast directed transport of allochthonous rocks along the midcrustal shawanaga shear zone the final stage of convergence involved deformation and metamorphism in the grenville front tectonic zone at 1000 980 ma peak metamorphism along most of the transect at 1065 1045 ma followed initial transport of allochthonous rocks over the craton by 15 35 m y regional cooling which postdated peak metamorphism by 70 m y was probably delayed by the combined effects of late stage extension and convergence transport of allochthons at least 100 km over the craton was accomplished along a weak migmatitic decollement further propagation of the orogen into the craton followed partial melting and weakening of parautochthonous rocks below this decollement extensional deformation was associated with distributed ductile flow the formation of regional transverse folds with axes parallel to the stretching direction and reactivation of the allochthon parautochthon thrust boundary as an extensional decollement the extensional lower crustal flow was likely the primary cause of the subhorizontal attitude of many structures and seismic reflectors in this part of the central gneiss belt

evidence for a cadomian ophiolite and magmatic arc complex in sw bulgaria abstract new geochronological and geochemical data from the magmatic rocks of the kraishte area sw bulgaria reveal the existence of cadomian arc magmatism intruding an ophiolitic complex similar geochemical signatures and crystallization ages of the basic to acidic rocks of the struma unit and the osogovo lisets complex suggest that these rocks were derived from one calc alkaline magma source they were parts of a magmatic arc associated during ediacaran early cambrian 560 540 ma times with subduction of the proterozoic prototethys ocean the geochemical analysis of the coeval calc alkaline granitic magmatism 577 551 ma in the morava nappe reveals a trend from a within plate towards volcanic arc affinity

the recognition of reactivation during continental deformation reactivation involves the accommodation of geologically separable displacement events intervals 1 ma along pre existing structures the definition of a significant period of quiescence is central to this phenomenological definition and the duration of the interval chosen represents the resolution limit of reactivation criteria found in most ancient settings in neotectonic environments reactivation can be further defined as the accommodation of displacements along structures that formed prior to the onset of the current tectonic regime this mechanistic definition cannot always be applied to ancient settings due to the uncertainties in constraining relative plate motion vectors four sets of criteria may be used to recognize reactivation in the geological record stratigraphic structural geochronological and neotectonic some structural criteria may not be reliable if used in isolation to identify reactivated structures much of the previously published evidence cited to invoke structural inheritance is equivocal as it uses similarities in trend dip or three dimensional shape of structures numerous fault and shear zone processes can cause significant weakening both synchronously with deformation and in the long term and may be invoked to explain reactivation the collage of fault bounded blocks forming most continents therefore carries a long term architecture of inheritance which can explain much of the observed complexity of continental deformation zones

role of melt in the formation of a deep crustal compressive shear zone the maclaren glacier metamorphic belt south central alaska the maclaren glacier metamorphic belt is an exhumed portion of a deep crustal shear zone where hot upper amphibolite facies rocks were emplaced over cooler lower grade rocks it is located in south central alaska within the collision zone between terranes previously accreted to north america and the wrangellia superterrane crosscutting relationships and orientations of thin granitoid sills within the hanging wall show that melt was repeatedly intruded into the shear zone during overall compression in addition a 1 km thick tonalite sill the valdez creek tonalite was emplaced into the shear zone while it was active this conclusion is based on the presence of a well developed foliation within the sill which is concordant to the fabric of the shear zone the alignment and tiling of plagioclase laths the presence of highly strained mafic enclaves within a matrix which shows no evidence of any subsolidus deformation and the preservation of a delicate magmatic texture which indicates that a magmatic fluid was still present after deformation in the sill had ceased a one dimensional thermal model for sill shaped plutons of varying thicknesses which are emplaced into country rocks at different initial temperatures indicates that melt can be present for long periods of time in the deep crust 1 m y an important factor controlling the length of time that a sill remains molten is the temperature of the surrounding rocks which in the lower crust can be as high as the solidus temperature of granitoid melts if the amount of time for melt to crystallize is sufficiently long potentially large amounts of strain will be accommodated by zones containing melt due to the low strength of melt compared to rock in the maclaren glacier metamorphic belt the amount of time needed for the valdez creek tonalite to fully crystallize is calculated to be about 90 000 years this is a minimum value since the original thickness of the sill is not known nevertheless using the 90 000 year value and assuming that the bulk of convergence between north america and wrangellia was concentrated within the valdez creek tonalite a displacement of at least 10 km could have been accommodated across the sill while melt was present

deformation and metamorphism at the south margin of the alps east of bellinzona switzerland deformation and metamorphism of rock series at the south margin of the alps e of bellinzona are studied magmatic relics and metamorphic minerals and rock types of the tonalite and of the augengneiss of melirolo are examined these bodies are regarded as of magmatic origin zoning of plagioclase is ascribed to rise of melts and cooling under loss of volatiles subvolcanic dykes branch off the augengneiss into the tonale series the magmatics are late alpine and intruded into the southerly cover plate on top of the subduction zone the cover plate was still cold and unaffected by alpine deformation during this intrusion later deformation and heating of cover plate and magmatics is late alpine the tonalite deformation was quantified by a study of xenolith deformation the tonalite was flattened to 1 20 of its original width we extrapolate this flattening to the southerly steep zone now 5 km broad we conclude that this zone was 100 km wide befor late alpine flattening this deformation occurred during the higher t part of lepontine heat rise a maximum t of ca 580 c and ph20 5 6 kbar is reached after the main deformation considerable stretching upward buried the niveau of intrusion formerly shallow under 15 20 km of rocks the tonale series suffered 3 fold rotational refolding under subsiding t after the main deformation an early alpine subduction eclogite was found imbricated into the tonale series it still contains parts of the subduction paragenesis preserved or pseudomorphosed and relics of subduction preferred orientation under late alpine deformation it is changed into amphibolite this proves continuation of subduction from val sesia to our area and further e the magmatics are interpreted as subduction magmatites they cannot be derived as partial melts from the subducted slice which underlies the tonale series from which the eclogite was imbricated into the tonale series during late alpine movements voll has found a more northerly subduction zone adula nappe misox zone this may have reached our area in sufficient depth to produce partial melts before late alpine flattening of the marginal zone last movements at the insubric line formed blastomylonites at 300 c indicating vertical movements in our area lepontine garnet staurolite kyanite schists abut directly against the insubric line and the seealpen lower t areas towards the s are cut off by the insubric line

holocene sea level change and coastal evolution in the humber estuary eastern england an assessment of rapid coastal change new stratigraphic data collected from six sites in the humber estuary establish a record of holocene relative sea level rsl change and enable testing of four possible causes of rapid coastal change sea level rise changes in sedimentation storm surge history and human impact mean high water of spring tides mhwst in the humber rose from c 9 m od at 7500 cal yrs bp to 0 m od by 4000 cal yrs bp at an average long term rate of c 3 9 mm yr 1 after this the rate of rise gradually decreased to c 1 mm yr discrete episodes of rapid rsl rise are not identified although their absence may reflect limited data availability however we do observe two episodes of rapid coastal change in the humber estuary the first occurs between c 3200 and 1900 cal yrs bp as marine conditions expand to their holocene maximum and then contract this pattern of coastal development differs from that in the east anglian fenlands suggesting local processes control sedimentation at one or both of these sites the sec

a review of the trends observed in british isles mean sea level data measured by tide gauges summary this report presents an up to date review of the british isles bi mean sea level msl data set obtained from tide gauges and of the long term secular trends in bi msl the data are of mixed quality and not as copious as one would like for scientific analysis given the complexity of long term sea and land level changes around bi coasts nevertheless the small number of very long records can be studied evectively and indicate that twentieth century secular trends in bi msl are consistent with those obtained from nw europe as a whole and with the bottom range of estimates for global average msl change during the past 100 years century timescale low frequency accelerations in msl of the order of 0 4 0 8 mm yr 1 century 1 are obtained from the three longest records which are also similar to estimates from mainland europe sea level indices for the bi are constructed which can provide responsible agencies with a guide to the average state of bi sea level combined ocean tide and storm surge tide surge numerical modelling is demonstrated to be a valuable tool in understanding part of the variability of msl around the bi although modelling of long term changes is limited at present by the lack of adequate meteorological data sets from before 1955 nevertheless it is shown that even if a complete meteorological modelling data set were available it would not be able to account for all of the msl variability finally recommendations are made for the development of tide gauge and global positioning system gps recording in the bi for the purpose of long term msl monitoring in the next century

emplacement and deformation features of syntectonic leucocratic veins from rainy lake zone western superior province canada abstract networks of leucocratic veins are widespread in the rice bay redgut bay domain of the rainy lake zone at the wabigoon quetico subprovince boundary archean superior province canada vein geometries and their cross cutting relationships with host rocks are indicative of syntectonic emplacement within a regional late archean transpressional deformation event kenoran orogeny the relative folding and boudinage of the veins compared to their host rocks indicate that they were emplaced syntectonically with the d2 deformation semi quantitative strain and vorticity analyses confirm the syn d2 timing of the veins the observed structural features are interpreted as being formed during magma emplacement along dilatant fractures and subsequent solid state deformation under overall ductile deformation conditions the structures related to emplacement are better preserved in domains of low post emplacement strain and veins intruded into competent host rocks whereas the folds and boudins related to post emplacement deformation are well developed in veins intruded into relatively incompetent host rocks in domains of high strain the primary intrusive structures are modified or even locally obliterated due to increasing deformation it is envisaged that regional kinematics and the rheological state of host rocks are the main controls on the style of vein emplacement and deformation the variety of observed structures is considered the result of deformation and lithological heterogeneity rather than several distinct magmatic events

significance of a hiatus in down temperature fabric development within syn tectonic quartz diorite complexes channel islands uk detailed fabric development histories have been deduced for neoproterozoic foliated quartz diorite complexes of the channel islands uk the plutons were emplaced during regional d2 deformation magmatic fabrics formed at low crystal contents pre rheologically critical melt percent are only locally preserved due to overprinting by solid state deformation which occurred at moderate temperatures 400 550 c this is demonstrated by brittle microcracking of plagioclase and amphibole with only local ductile bending and dynamic recrystallization marginal recrystallization and myrmekite development on alkali feldspar ductile deformation of quartz to form types 2 3 ribbons quartz recrystallization by sub grain rotation associated with a slip but not c slip biotite recrystallization within micro shears and variable amphibole recrystallization the deformation histories display a distinct division between magmatic state and moderate temperature solid state deformation features with little evidence for intervening high temperature solid state fabrics this contrasts with criteria widely considered diagnostic of syn tectonic plutons which envisage development of a continuum of magmatic through high temperature solid state deformation fabrics however we consider the plutons syn tectonic and attribute the hiatus to contrasting strain and pluton cooling rates length and nature of deformation events and host rock ambient temperatures intermediate magmas emplaced at moderate to shallow levels in the crust may be more prone to develop such apparently punctuated deformation histories than sio 2 richer granitoids

a tectonic model for the emplacement of the main donegal granite nw ireland the main donegal granite is shown to lie in a major late stage ne sw trending transcurrent sinistral shear zone in the caledonides of nw ireland the zone which is bent both laterally and upwards around the pluton has displacements which diminish sw along its length from a maximum of approximately 20 km at the ne end of the pluton the granite has also been deformed by this sinistral shear but it has a strain component of its own the nature and development of which indicate that the pluton was accommodated rather than forcefully emplaced in the shear zone strain variations between granite and wall rock and an early plagioclase fabric associated with the petrographic banding of the granite suggest that intrusion and deformation were more or less synchronous at around 400 ma it is suggested that unconsolidated granite in the shear zone locally created high strain rates and instability which caused the zone to bend split lengthwise and progressively create an internal low pressure zone into which the main granite was emplaced the wide variety of emplacement styles of the other radiometrically synchronous plutons of the batholith can be attributed to the progressive development of the shear zone thorr and fanad in tension between the zone and a complimentary structure to the n ardara and toories in local compression at the shear zone termination rosses in tension on the outer arc of the bending zone and trawenagh bay as displaced main granite magma in a similar tensional setting during the final stages of deformation

role of melt during deformation in the deep crust deformation in the deep crust is strongly influenced by the presence of melt injected melt or magma weakens the crust because strain will tend to localize where melt is present the amount of strain a pluton may accommodate is dependent on the length of time it takes for a pluton to crystallize and the strain rate for plutons that intrude into rocks which are near the solidus temperature of the melt crystallization times can be quite long 1myr partial melting of deep crustal rocks can lead to melt enhanced embrittlement this occurs because the volume change for most melting reactions is positive therefore when the rate of melt production outpaces the rate at which melt can leave the system the melt pressure increases eventually the melt pressure may become sufficiently high that the melting rocks behave in a brittle fashion and fracture conjugate sets of dilatant shear fractures filled with melt occur in migmatite from the central gneiss belt canada this suggests that melt enhanced embrittlement occurred in these rocks an expression which relates the magnitude of differential stress to the angle between conjugate dilatant shear fractures is derived assuming that migmatite has a small tensile strength differential stresses are 20 mpa in migmatitic rocks at the time melt enhanced embrittlement occurs the occurrence of melt enhanced embrittlement shows that a switch in deformation mechanism from plastic flow to cataclasis is possible in the deep crust during melting furthermore repeated episodes of melt enhanced embrittlement in migmatitic rocks may be an efficient mechanism for extracting melt from partially melted terrains

neogene tectonic evolution of the southern and eastern carpathians constrained by paleomagnetism the neogene geodynamic evolution of the southeastern carpatho pannonian system is constrained by the timing and magnitude of vertical axis tectonic rotations derived from paleomagnetic analysis we report results from 13 paleomagnetic localities 139 sites 993 samples of middle miocene to pliocene sediments of the eastern carpathians region the southern carpathians region and the actively deforming bbend areaq between these two regions absolute age control of the sampled sediments is provided by previous magnetostratigraphic analysis our results indicate 1 systematic 308 clockwise rotations occurred in the southern carpathians after 13 ma 2 tectonic rotation had ceased in the investigated eastern and southern carpathians regions after 9 ma except in the bend area where recent clockwise rotations took place after 5 ma this pattern of rotations implies a concentration of tectonic activity during the middle to late miocene collision of the carpathian arc with the european platform followed by relative tectonic quiescence through the pliocene except in the bend area subject to late stage slab pull d 2005 elsevier b v all rights reserved

constraints on geological strain rates arguments from finite strain states of naturally deformed rocks a summary of known finite strain states is presented longitudinal strains 1 e as measured in many rocks often range from 1 to 40 and 1 to 0 025 the time span available to produce such measureable strains in young orogenic zones seems to be less than 10 m y possibly less than 1 m y which constrains conventional strain rates into the range of 10 sup 13 s sup 1 to 10 sup 15 s sup 1 for both pure and simple shear the most efficient way and much less efficient way to accumulate incremental strains respectively the ellipticity of the finite strain ellipse increases in a nonlinear manner finite strain variations in adjacent layers which give rise to features such as cleavage refraction arise with only slight differences in the strain rates within these layers

late quaternary multiple incised valley systems an unusually well preserved stratigraphic record of two interglacial valley fill successions from the arno plain northern tuscany italy

origin abundance and storage of organic carbon and sulphur in the holocene humber estuary emphasizing human impact on storage changes an organic carbon corg and sulphur s storage inventory for holocene sediments in the humber estuary is established sources of organic matter and their variation over time are identified and with chronological control the importance of estuarine sediments as corg and s stores is demonstrated humber holocene sediments are grouped into seven widespread environmental facies with statistically significant geochemical data sets 1 oak hazel fenwood ohf 2 alder carr ac appearing as peats in core 3 river channel muds or sands rcm s 4 high saltmarsh hsm 5 low saltmarsh lsm 6 intertidal mudflat itmf and 7 a sandy facies s carbon nitrogen and sulphur cns abundances show that these facies have diagnostic geochemical signatures and 13c values for bulk organic matter exhibit a range of average values 28 terrestrial peats 27 hsm and 24 5 itmf reflecting the up core transition from terrestrial peats through saltmarshes to more open marine mudflat environments as regional sea level rose chronology and average sedimentation rates are partly constrained by radiocarbon dates palaeomagnetic techniques helped define discrete sediment packages and discontinuities time gaps although the humber holocene sediment record is not continuous long term sedimentation rates about 1 mm a 1 show that sediment accretion kept pace with regional sea level rise between 6 and 2 cal ka bp this sedimentation rate combined with core evidence to allow a geographic reconstruction of the palaeo humber 3 2cal ka bp is used to calculate storage values for corg and s in the various environments of the palaeo humber comparison of the corg and s sedimentation and storage terms for the palaeo humber with modern values highlights the impacts of reclamation and commercial urban development in the estuary in the last 300 years ohf and ac peats which were the largest corg and s stores in the palaeo estuary are now absent reclaimed while saltmarshes are no longer widespread conservative calculations show a net decrease in corg deposition from about 3 2 105 tonne in the palaeo estuary to no more than 2 5 103 tonne today a 99 reduction in potential corg storage capacity the total modern yearly s deposition is approximately 2 of its value 2ka ago removal of saltmarsh and associated brackish freshwater wetland suggests that suspended sediment and associated corg and s are currently bypassing former holocene storage areas and may be impacting north sea biogeochemical cycling

melt enhanced deformation a major tectonic process convergent tectonics between continental crustal blocks result in deep burial and anatexis of supracrustal rocks anatectic and or mantle derived melts combine to form a melt weakened zone in the thickened lower crust the accumulation of melt eventually leads to crustal failure along melt lubricated shear zones rapid 1 mm yr vertical component movements of large crustal blocks result we refer to these crustal displacements as tectonic surges the melt lubricated shears are characterized by the close association of sheared country rocks with foliated or massive igneous sills and plutons rocks that formed at different crustal levels are juxtaposed across these shear zones one result of surges with large lateral component of movement is metamorphic inversion with high pressure and high temperature metamorphic rocks structurally over lower pressure and temperature assemblages large and rapid vertical surges may displace crust containing abundant melt and may result in high t p including granulite facies metamorphism and preservation of metamorphic textures caused by rapid decompression

magmatic belts in accretionary margins a key for tectonic evolution the tonalite belt of north victoria land east antarctica occurring in the early palaeozoic palaeomargin of the east antarctica craton the tonalite belt of north victoria land is a narrow linear magmatic belt up to 200 km long made up of strongly foliated tonalitic and granodioritic intrusions they were synkinematically emplaced into the lanterman murchison shear zone a major tectonic structure across which different tectono metamorphic terranes were accreted during the late cambrian ross orogeny the deformational and kinematic features of the intrusions indicate that strain and displacement during terrane accretion were partitioned into oblique thrust high angle thrust and strike slip shear zones from this it is deduced that a transpressional regime prevailed during early palaeozoic deformation and terrane accretion this and other magmatic belts which exploited major tectonic structures in collisional margins such as the coast plutonic complex of nw america are basic keys for understanding deformational processes and kinematic regimes during terrane accretion moreover the occurrence of such types of magmatic belts might be regarded as a reliable indication of large scale strike slip motion between accreting terranes in an oblique convergent setting

response of continental magmatic arcs to regional tectonic changes recorded by synorogenic plutons in the middle crust an example from the coast mountains of british columbia abstract the coast mountains of british columbia record an increase in magmatic activity acceleration in exhumation rate and a change from transpression to extension between 60 and 52 ma structural analysis of fabrics in three mid crustal plutons and country rocks leads to conclusions about pluton emplacement mechanisms and strain partitioning during changing tectonic conditions the quottoon and kitlope plutons 60 ma have steep foliations and lineations consistent with partitioned transpressional deformation the chief matthew s pluton 57 55 ma intruded during the formation of a sub horizontal transposition foliation and has radially distributed lineations consistent with sub vertical flattening during extension the change in orientation of the foliation represents an almost orthogonal rotation of the shortening direction from sub horizontal to sub vertical the chief mathew s pluton is interpreted to intrude initially into gently dipping fractures perpendicular to the steeply dipping foliation these melt filled fractures acted as conduits for melt triggering horizontal flow and eventually formed kilometer scale sills the steeply dipping fabrics of the coast shear zone provided pathways for melt to ascended from lower to middle crustal depths partitioning deformation into three dimensional domains of flattening simple shear and constrictional strain created the space for plutons this pattern of deformation reflects the interaction of regional deformation with magma emplacement

geological impacts on coastal wetland landscapes some general effects of sediment autocompaction in the holocene of northwest europe a simulation model is described providing general insights into autocompaction effects in stratigraphic sequences formed on coastal mudflats and marshes over uneven basements lithological units and buried landscapes are progressively displaced and distorted the synthetic sequences resembling bedding geometries described from the northwest european holocene autocompaction also promotes local deposition rates that may greatly exceed the rates at which accommodation space is created transgressive silts are associated with especially large deposition rates because of the high compressibility of underlying peats the experimental relationships between apparent rates of sea level rise and bed thickness resemble empirical trends for the holocene the latter are however reinforced by an intrinsic lithology related effect not included in the model

diffusion in mineral geochronometers present and absent abstract in solid state physics and materials science fick s law diffusion is a well established process in earth sciences laboratory experiments on garnet olivine and other anhydrous minerals do document the intra grain element concentration gradients that follow the functional form required by fick s law natural gradients in minerals have rarely been analyzed with the necessary spatial resolution reports of actual observations of diffusion profiles of element concentrations are rare in the literature and diffusion profiles of isotope ratios in minerals used for geochronology are absent an in depth re examination of recent and older literature suggests that isotope transport in minerals is instead often dominated by fluid mediated retrogression reactions imaging microtextures by cathodoluminescence or back scattered electron maps provides ubiquitous evidence of patchy or dendritic replacement structures which correspond to multiple growth stages in zircon monazite muscovite biotite k feldspar etc the u pb k ar and rb sr systems in these partly retrogressed minerals show isotopic inheritance that survived the retrograde reactions at least in part in close correspondence with the petrologic relicts depending on the relative rates of the petrological processes relevant for isotope transport geochronometers can be grouped in two classes class i thermochronometers are those for which the diffusivity of a given radiogenic isotope is faster than the rate of dissolution and or reprecipitation and class ii hygrochronometers are those for which aqueous dissolution reprecipitation is the faster process all of the abovementioned geochronometers for which patchy dendritic textures formed by diachronous mineral generations and isotopic inheritance were observed must be assigned to class ii class ii samples in petrologic equilibrium can but need not record purely thermal diffusion of daughter isotopes the isotope record of class ii minerals in petrologic disequilibrium being controlled by inheritance and retrogression reactions depends chiefly on the reaction promoting factors water activity and strain the dependence of class ii mineral ages on thermal diffusion is subordinate and never unique

finite element modelling of shear zone development in viscoelastic materials and its implications for localisation of partial melting the development of shear zones initiating on random weaker initial perturbations is modelled numerically for low deborah number viscoelastic materials considering the influence of effective viscosity contrast power law rheology strain softening and different imposed bulk deformation geometries ranging from pure to simple shear conjugate shear zones initiate at 90 to one another and rotate with increasing bulk deformation the basic pattern not being markedly influenced by the vorticity of imposed deformation the rate of propagation of individual conjugate shear zones is little affected by increased effective viscosity contrast between matrix and inclusion but is promoted by power law rheology however the most marked effect is observed for strain softening behaviour where rapid propagation produces straighter and narrower shear zones the localisation of strain is reflected in a correspondingly heterogeneous stress distribution in particular mean stress or pressure is higher in the extending near planar weaker zones of localised shear melting of gneissic or pelitic compositions is pressure dependent with free water present increased pressure promotes melting whereas the opposite is true for water absent melting for water present conditions a positive feedback could develop between localised shearing increased pressure and partial melting this is potentially more effective in concentrating melt in shear zones than shear heating where melt related softening has a negative feedback effect

anatexis and metamorphism in tectonically thickened continental crust exemplified by the sevier hinterland western north america the generation of granitoid magmas by partial melting of crustal rocks during continental thickening events is well documented in many geological provinces throughout the world including the late mesozoic sevier belt of western north america we present a thermal and petrologic model of anatexis and metamorphism in regions of crustal thickening where the only mantle contribution is the normal conductive supply of heat through the base of the lithosphere i e advection of mass and energy are excluded we distinguish between formation of migmatites and generation of mobile granitoid magmas and examine the temporal and spatial relationships between these two distinct anatectic processes between anatexis and regional deformation and between anatexis and metamorphism a fundamental conclusion is that if protoliths rich in hydrous minerals are present regional anatexis is the end product of classical barrovian metamorphism in thickened continental crust even in the absence of a free water rich fluid phase barrovian metamorphic facies series are predicted with thickening ratios maximum crustal thickness attained initial crustal thickness as low as 1 3 but mobile granitoid magmas are not formed if this ratio is less than approximately 1 5 above these lower bounds barrovian metamorphism and anatectic granitoid magmatism occur independently of the magnitude of thickening and of the way in which thickening is accomplished both processes are sensitive to a diminished heat supply lowering either moho heat flow or crustal radioactive heat production results in blueschist eclogite metamorphism and inhibits the formation of mobile granitoid magmas we model anatexis under fluid absent conditions and show that with such a constraint migmatization is always a syn kinematic process relative to the crustal thickening event whereas generation of mobile granitoid magmas is in most cases post kinematic relative to crustal thickening but can be syn kinematic if thickening takes more than approximately 50 myr the typical time intervals for melting are consistent with geological observations mobile granitoid magmas are predicted by most of our models within approximately 10 myr of the end of the crustal thickening event this incubation period results primarily from the temperature increase required for the dehydration melting reactions capable of producing large melt fractions to occur the energetic requirements of anatexis are relatively minor compared to conductive crustal thermal budgets as shown by the fact that once the necessary p t conditions are attained melting reactions are completed within time intervals on the order of 1 myr i e 1 2 orders of magnitude smaller than the characteristic time scales of the tectonic processes involved in crustal thickening

himalayan metamorphic sequence as an orogenic channel insight from bhutan the bhutan himalayas differ from the rest of the himalayas in two major ways i low grade sedimentary rocks lie above the greater himalayan sequence as klippen i e erosional remains of the south tibetan detachment and ii an out of sequence thrust the kakhtang thrust lies structurally above the klippen and it doubles the exposed thickness of the greater himalayan sequence our field observations and geochronological data constrain the main kinematic events in the bhutan himalayas crystallisation ages of leucogranite dykes deformed by the main central thrust and the south tibetan detachment indicate that these two structures operated together between 16 and 22 ma the out of sequence kakhtang thrust was active at 10 14 ma and was concurrent with reactivation of the south tibetan detachment restoration of the bhutan himalayas prior to the out of sequence thrusting shows that the greater himalayan sequence was the core of a long low viscosity crustal channel extending under the tibetan plateau we propose that the gravity driven southward extrusion of the channel material from underneath the tibetan plateau caused the inverted metamorphic sequence in the lesser himalayan sequence and in the greater himalayan sequence this process also led to occurrences of present day surface rocks that were derived from variable distances down dip but from similar crustal depths such an exhumation pattern can explain the similar peak pressures for the greater himalayan sequence along the length of the himalayas

modelling geomorphic response to environmental change in an upland catchment in the uk s upland catchments river terraces and alluvial features indicate a history of periodic aggradation and degradation linked to holocene changes in land use primarily deforestation and climate change altering flood frequency and magnitude although both factors are important calculating their individual effects is complicated by the likelihood of their concurrent alteration to investigate the relative impacts of land use and climate change a cellular model is applied to the upland catchments of cam gill beck above starbotton north yorkshire this is divided into 1 million 2 m by 2 m grid cells to which a range of process laws are applied these include approximate expressions for mass movement rates soil creep the influence of vegetation and hillslope hydrology as well as fluvial erosion and deposition in ten grain size fractions this provides a good representation of valley floor geometry while retaining a fully dynamic interaction with the surrounding valley sides previous applications of this model have shown the detailed formation of bars and berms as well as examples of braiding avulsion and channel range running on a silicon graphics origin 2000 computer an ensemble of simulations were completed bracketing a wide range of environmental scenarios involving changes in flood frequency magnitude and vegetation cover over time scales ranging from 10 to 100 years these showed that decreasing tree cover and increasing rainfall magnitude individually produced similar 25 to 100 increases in sediment discharge whereas in combination they generated a 1300 rise furthermore channels formed by the model in response to increased rainfall magnitudes are located where relic channels are found in cam gill beck implying that these are the products of previous periods of high rainfall magnitudes copyright 2000 john wiley sons ltd

from nappe stacking to out of sequence postcollisional deformations cretaceous to quaternary exhumation history of the se carpathians assessed by low temperature thermochronology 1 apatite fission track aft and u th he ahe thermochronology have been combined to constrain the exhumation history of the se carpathians cooling ages generally decrease from cretaceous for the internal basement nappes aft ages to miocene quaternary aft and ahe respectively for the external sedimentary wedge the aft and ahe data show a paleogene age cluster which confirms a suspected but never demonstrated tectonic event the new data furthermore suggest that the se carpathians have been affected by a middle miocene exhumation phase related to continental collision which occurred at rates of 0 8 mm yr similar to the one previously inferred for the east carpathians the se carpathian tectonic evolution however is overprinted by two younger exhumation events in the pliocene pleistocene the first exhumation phase latest miocene early pliocene occurred at high exhumation rates 1 7 mm yr and is interpreted as a tectonic event and or associated with a sea level drop in the paratethys basins during the messinian low stand the youngest recorded tectonic phase suggests rapid pleistocene exhumation 1 6 mm yr and is interpreted to represent crustal scale shortening different in mechanics from collisional processes the data suggest that the se carpathians did not develop as a typical double vergent orogenic wedge instead exhumation was related to a foreland vergent sequence of nappe stacking during collision and was subsequently followed by a large out of sequence shortening event truncating the already locked collisional boundary

alpine polyphase tectono metamorphic evolution of the south carpathians a new overview abstract the main terrains involved in the cretaceous tertiary tectonism in the south carpathians segment of the european alpine orogen are the getic supragetic and danubian continental crust fragments separated by the severin oceanic crust floored basin during the early middle cretaceous times the danubian microplate acted initially as a foreland unit strongly involved in the south carpathians nappe stacking multistage folding thrusting events uplift erosion and extensional stages and the development of associated sedimentary basins characterize the south carpathians during cretaceous to tertiary convergence and collision events the main cretaceous tectogenetic events responsible for contraction and crustal thickening processes in the south carpathians are mid cretaceous austrian phase and latest cretaceous laramide or getic phase in age the architecture of the south carpathians suggests polyphase tectonic evolution and mountain building and includes from top to bottom the getic supragetic basement cover nappes the severin and arjana cover nappes and danubian basement cover nappes all tectonically overriding the moesian platform the severin nappe complex including obarsia and severin nappes with late jurassic early cretaceous ophiolites and turbidites is squeezed between the danubian and getic supragetic basement nappes as a result of successive thrusting of dismembered units during the inferred mid to late cretaceous subduction collision followed by tectonic inversion processes early cretaceous thick skinned tectonics was replaced by thin skinned tectonics in late cretaceous thus the former middle cretaceous austrian nappe stack and its albian lower senonian cover got incorporated in the intra senonian laramide getic stacking of the getic supragetic severin arjana nappes onto the danubian nappe duplex the two contraction events are separated by an extensional tectonic phase in the upper plate recorded by the intrusion of the banatitic magmas 84 73 ma the overthrusting of the entire south carpathian cretaceous nappe stack onto the fold thrust foredeep units and to the moesian platform took place in the late miocene intra sarmatian times and was followed by extensional events and sedimentary basin formation

calibration of shear wave splitting in the subcontinental upper mantle beneath active orogenic belts using ultramafic xenoliths from the canadian cordillera and alaska abstract despite the abundance of measurements of shear wave splitting around the world some fundamental questions about its geological interpretation have not yet been answered in order to constrain 1 i the orientation and magnitude of s wave anisotropy 2 ii the thickness of the anisotropic layer and 3 iii the possible variation of the anisotropy with depth in the subcontinental upper mantle beneath active orogenic belts we have carried out a systematic investigation on shear wave properties of mantle xenoliths from recent alkaline basalts of the canadian cordillera and alaska it is found that the polarization direction of the fast s wave as well as the time delay t between the two arrivals are strongly dependent on the propagation direction with respect to the structural frame at a single station the variations of measured and t values for sks phases from different events can result from this dependence because the average grain size of olivine in upper mantle samples is commonly larger than 0 5 mm dislocation creep prevails over a thickness of at least 250 km and results in olivine lpo and hence anisotropy and shear wave splitting a single thick anisotropic layer in mountain parallel subvertical shear zones may cause high values of tgd while multiple subhorizontal layers will produce multiple splitting making the measurement and interpretation of s wave splitting difficult our results also suggest that the s wave splitting observed in cold old stable cratons such as the canadian shield is likely dominated by fossil anisotropy whereas that observed in hot active orogenic regions such as the northwest american cordillera and the tibetan plateau may be dominated by modern tectonic deformation in the lithosphere and flow in the asthenosphere

emplacement of polygeneration pegmatites in relation to sveco norwegian contractional tectonics examples from southern norway abstract recent studies have demonstrated that there is a strong link between sites of concentrated magmatism and crustal deformation zones magmatism is often described as being syn kinematic where one or more increments of intrusion punctuate deformation with successive generations of injections being progressively deformed pegmatite formation in the mesoproterozoic of south norway has been considered as post kinematic in nature relative to sveconorwegian grenvillian deformation 1 13 ga to 0 85 ga during accretion of the sw margin of baltica this paper presents structural observations from mapping of some pegmatites in the bamble terrane of south norway demonstrating that the pegmatites are structurally related to sveconorwegian fold geometries associated with peak metamorphism at approximately 1 14 ga and are kinematically related to overthrust geometries associated with the initial overthrusting phase of the porsgrunn kristiansand fault when the bamble terrane docked with the underlying telemark terrane local fold geometries suggest a strain regime where the maximum contractional axis is sub horizontal and oriented nw se consistent with the regional kinematics the pegmatites display a systematic deformation pattern consistent with deformation in the isoclinal fold limbs pegmatites are also deformed into asymmetric antiformal folds above reverse shear structures and are also cut by these structures thus showing a thrust geometry the undeformed pegmatites are emplaced in sub horizontal fractures and suggests sub horizontal contractional axis related to overthrusting which is identical to the strain regime of the folding the evidence suggests that the pegmatites are syn tectonic and were injected into reverse shear related fractures deformation was progressive and incremental with longer periods of ductile deformation at low strain rate punctuated by shorter periods of fracturing and pegmatite injection at high strain rate this work therefore implies an intimate spatial and temporal relationship between deformation and magmatism during crustal accretion on the western margin of fennoscandia

sm nd dating of spatially controlled domains of garnet single crystals a new method of high temperature thermochronology ganguly and tirone meteorit planet sci 36 2001 167 175 recently presented a method of determining the cooling rates of rocks from the difference between the core and bulk ages of a crystal as determined by a single decay system here we present the first application of the method using the core and bulk ages of garnet single crystals according to the sm nd decay system in two rock samples with contrasting cooling rates which can be constrained independently the samples belong to the metamorphic core complex valhalla british columbia and the mid crustal magmatic arc exposure of the salinian terrane california we have micro sampled the garnet crystals over specific radial dimensions and measured the nd isotopes of these small sample masses as ndo via solid source mass spectrometry to determine the sm nd age difference between the core and bulk crystals using a peak metamorphic p t condition of 8 1 kbar 820 30 c spear and parrish j petrol 37 1996 733 765 the core 67 3 2 3 ma and bulk 60 9 2 1 ma ages of the british columbian garnet sample yield a cooling rate of 2 13 c myr which is in very good agreement with the cooling rates that we have derived by modeling the retrograde fe mg zoning in the same garnet and assuming the same peak metamorphic p t condition considering earlier cooling rate data derived from closure temperature vs age relation of multiple geochronological systems spear and parrish j petrol 37 1996 733 765 a cooling rate of v15 20 c myr seems most reasonable for the valhalla complex diffusion kinetic analysis shows that the sm nd core age of the selected garnet crystal could not have been disturbed during cooling consequently the core age of the garnet crystal 67 3 2 3 ma corresponds to the peak metamorphic age of the valhalla complex the salinian sample on the other hand yields indistinguishable core 78 2 2 7 ma and bulk 77 9 2 9 ma ages as expected from its fast cooling history which can be constrained by the results of earlier studies the sm nd decay system in garnet has relatively high closure temperature usually s 650 c therefore the technique developed in this paper fills an important gap in thermochronology since the commonly used thermochronometers are applicable only at lower temperatures simultaneous modeling of the retrograde fe mg zoning in garnet spatially resolved sm nd ages of garnet single crystals and resetting of the bulk garnet sm nd age

generation of tonalitic and dioritic magmas by coupled partial melting of gabbroic and metasedimentary rocks within the deep crust of the famatinian magmatic arc argentina the source regions of dioritic and tonalitic magmas have been identified in a deep crustal section of the famatinian arc sierras pampeanas of western argentina the source zones of intermediate igneous rocks are located at the transition between a gabbro dominated mafic unit and a tonalite dominated intermediate unit in the upper levels of the mafic unit mafic magmas intruded into metasedimentary wall rocks crystallized mainly as amphibole gabbronorite and caused the partial melting of the surrounding metasediments in turn the leucogranitic melts sourced from the metasedimentary rocks intruded into the newly crystallized but still hot mafic layers and catalysed the process of partial melting of the gabbroic plutonic rocks the gabbroic rocks became mafic migmatites comprising amphibole rich pyroxene bearing mesosomes and leucotonalitic veins significantly most of the mafic migmatites have isotopic compositions sr sr t 50 7063 and end t 1 4 0 94 to 2 24 similar to those of the gabbroic rocks and distinct from those of their complementary leucotonalitic veins sr sr t 1 4 0 7075 0 7126 and end t 5 2 65 providing evidence for the idea that melting of the mafic rocks was triggered by the intrusion of leucogranitic anatectic melts sr sr t 1 4 0 715 and end t 1 4 6 21 mass balance calculations show that the model reaction plagioclase amphibole leucogranitic melt leucotonalitic melt clinopyroxene orthopyroxene can better explain the partial melting of the gabbroic rocks based on field observations we argue that the coalescence of leucotonalitic veins in the mafic migmatites led to breakdown of the solid matrix to form melt dominated leucotonalitic pools however the leucotonalitic veins that crystallized before leaving behind the mafic migmatitic rock are chemically elemental and isotopic more evolved than the dioritic and tonalitic rocks we envisage that once detached from their source region the leucotonalitic magmas were able to react commingle and mix with entrained fragments of both mafic and metasedimentary rocks this process gave rise to melts that became tonalitic and dioritic magmas this study concludes that the generation of intermediate magmas is a multistage process with three critical steps 1 influx and emplacement of hydrous mafic magmas into a deep crust containing metasedimentary country rocks 2 physically and chemically coupled melting of mafic and metasedimentary rocks leading to the formation of a leucotonalitic vein and dyke system that coalesces to form leucotonalitic or tonalitic magma bodies 3 retrogression of the leucotonalitic magmas by partially assimilating entrained fragments of their mafic and metasedimentary precursors the dimensions of the

the role of subgrain boundaries in partial melting abstract evidence for partial melting along subgrain boundaries in quartz and plagioclase is documented for rocks from the lost creek gneiss of the llano uplift central texas the wet mountains of central colorado and the albany fraser orogen southwestern australia domains of quartz or plagioclase crystals along subgrain boundaries are preferentially involved in partial melting over unstrained domains of these minerals material along subgrain boundaries in quartz and plagioclase has the same morphology as melt pseudomorphs present along grain boundaries and is commonly laterally continuous with this former grain boundary melt indicating the material along subgrain boundaries can also be categorized as a melt pseudomorph subgrain boundaries consist of arrays of dislocations within a crystal lattice and unlike fractures would not act as conduits for melt migration instead the presence of former melt along subgrain boundaries requires that partial melting occurred in these locations because it is kinetically more favorable for melting reactions to occur there preferential melting in high strain locations may be attributed to strain energy which provides a minor energetic contribution to the reaction and leads to preferential melting in locations with weakened bonds and or the presence of small quantities of water associated with dislocations which may enhance diffusion rates or locally lower the temperature needed for partial melting

influence of lithological heterogeneity mechanical anisotropy and magmatism on the rheology of an arc north cascades washington abstract many aspects of crustal dynamics are dependent on changes in rheology and strength with depth in the lithosphere several of the controlling factors for rheology are difficult to study experimentally particularly lithological heterogeneity mechanical anisotropy and magmatism and we focus on these in a study of the deformation patterns in a thick crustal section 5 to 40 km paleodepth through the cretaceous cascades core of the nw cordillera this magmatic arc consists of metamorphosed oceanic and arc terranes intruded by magmatic bodies ranging from heterogeneous brittle deformation marked by serpentinite melange characterizes the shallowest part of the crustal section and the remainder of the section is characterized by heterogeneous fold dominated ductile deformation early tight to isoclinal recumbent folds and associated axial planar fabrics are refolded by one or more cycles of nearly coaxial open to isoclinal upright to overturned folds layering played a mechanically active role during folding at all levels as indicated by cleavage refraction boudinaged layers and kinematic indicators that record fold related shear ductile deformation intensifies in the narrow structural aureoles of plutons and sw directed reverse shear was partitioned into some of the aureoles the poor strain memory of these magmatic bodies makes it difficult to determine if deformation was focused in the pluton magma chambers before they reached the solidus as commonly predicted all of the plutons have magmatic foliations that at least in part reflect regional strains and these foliations are strong in the deeper plutons the thinner sheets acted as competent bodies during folding and boudinage after they reached the solidus but generally did not cause marked strain gradients in their hosts a relative strength profile constructed for the cascades crustal section shows an overall decrease in strength with depth for the ductile part of the arc that fits idealized strength profiles however in more detail relative strengths are markedly variable units were able to accumulate large ductile strains but even small variations in the physical properties of interlayered rock types exerted a strong influence on deformation patterns throughout the mid to deep crustal part of the profile this profile thus emphasizes the complex vertical rheological stratification of arcs at the crustal to thin section scale and should be applicable to many other magmatic arcs

1 57 ga magmatism in the south carpathians implications for the pre alpine basement and evolution of the mantle under the european continent abstract chemical and isotopic analyses of amphibolites and gneisses from the oldest lithostratigraphic group in the south carpathians produce new insights regarding the chronology and evolution of the mobile proterozoic crust in central eastern europe these results date an episode of magmatism related to oceanic crust consumption reveal a period of continental stabilization and put constraints on the underlying mantle composition amphibolites from the cump na group have their origin in basalts chemically similar to island arc tholeiites a whole rock isochron age of documentclass aastex usepackage amsbsy usepackage amsfonts usepackage amssymb usepackage bm usepackage mathrsfs usepackage pifont usepackage stmaryrd usepackage textcomp usepackage portland xspace usepackage amsmath amsxtra usepackage ot2 ot1 fontenc newcommand cyr renewcommand rmdefault wncyr renewcommand sfdefault wncyss renewcommand encodingdefault ot2 normalfont selectfont declaretextfontcommand

cation diffusion in feldspars feldspars are among the most common minerals in the earth s crust and are found in a variety of rock types diffusion in feldspars has been studied for well over half a century with rosenqvist s 1949 measurements of ra and pb diffusion among the earliest published works major efforts in measuring diffusion in feldspars primarily of the alkali elements were undertaken in the early 1970s with the work of bailey 1971 lin and yund 1972 petrovic 1972 foland 1974 giletti et al 1974 and kasper 1975 many of these early studies used bulk exchange techniques rather than direct depth profiling or employed methods of limited depth resolution such as serial sectioning these methods while state of the art for their time impose several limitations including a range of measurement restricted to relatively fast diffusivities and the difficulty of distinguishing the effects on measured chemical or isotopic compositions that may be a result of diffusional fast paths surface reaction and or other artifacts from those contributions due solely to volume diffusion development of high resolution depth profiling techniques such as sims and rbs have permitted measurement of much smaller diffusivities for a broader range of elements and reduced some of the uncertainties characteristic of bulk exchange methods feldspar diffusion data have been previously summarized in yund 1983 and smith and brown 1988 and were included in brady s 1995 compilation of diffusion data for silicate minerals since the publication of these works there have been numerous diffusion studies of feldspars encompassing a range of compositions in alkali feldspars and across the plagioclase series these have included measurements of diffusion of major elements na k ca ba oxygen and silicon as well as na k and caal nasi interdiffusion diffusion of noble gases and diffusion of minor and trace elements including fe mg sr

influence of inherited topography on the holocene sedimentary evolution of coastal systems an example from arno coastal plain tuscany italy abstract understanding the relative control exerted by autogenic factors such as changes in sediment supply local subsidence and inherited topography is of crucial interest for a thorough comprehension of the sedimentary evolution of late quaternary coastal systems through an example from the arno coastal plain in tuscany we show to what extent sedimentation of the holocene succession even after the time of maximum marine ingression was influenced by the presence of a buried 5 7 km wide incised valley system generated by the arno river during the late pleistocene in response to the last glacial sea level fall a prominent stratigraphic marker locally known as pancone ca 5 15 m thick made up of extremely soft and homogeneous organic rich clays is reported from the upper 20 30 m of the mid holocene succession buried beneath the arno coastal plain high resolution stratigraphy integrated with microfossil investigations enables detailed facies characterization and mapping of this marker horizon at proximal most locations pancone consists of thin lagoonal deposits sandwiched between backswamp clays around the city of pisa and at more distal locations this stratigraphic marker is made up almost entirely of lagoonal clays with lateral transition to backswamp deposits the development of pancone was triggered by an abrupt transgressive pulse that led to the ultimate flooding of the arno paleovalley this transgressive event occurred shortly after a widespread episode of sub aerial exposure and climate deterioration related to the 8200 yr bp cold event confinement of the mid holocene pancone lagoon into an area formerly occupied by the post glacial arno incised valley system along with transition to backswamp facies in coincidence of the former interfluves is interpreted to reflect the higher compaction of the less indurated valley fill relative to the adjacent stiff pleistocene substratum the local increase in land subsidence contributed to the prolonged persistence of a 6 km wide lagoonal system encompassing the peak of holocene transgression and the early phases of decelerated sea level rise up to ca 6000 cal yr bp the arno coastal plain thus offers a good illustration of how inherited topography due to the presence of formerly active incised valleys may influence the holocene evolution of coastal plains favoring local development and preservation of topographic lows

pluton emplacement along an active ductile thrust zone piute mountains southeastern california interaction between deformational and solidification processes plutons that are emplaced synchronously with regional deformation offer the opportunity to understand the partitioning of deformation and metamorphism in time and space during orogeny the 85 ma east piute pluton of the eastern mojave desert is an unusually clear example of a syntectonic pluton it was emplaced during thrusting in the southern cordillera combined petrologic and structutal studies lead to empirical models for the dynamic interaction of magmatic and deformational processes during granitoid emplacement and final crystallization trace and major element and isotopic data suggest that closed system differentiation of a single magma batch was responsible for compositional variation granodiorite to leucocratic granite correlation between degree of chemical evolution of compositional units and intrusive sequence suggests that discrete melt segregation events punctuated fractional crystallization modeling of trace element data suggests segregation of monzogranite melts after 50 70 crystallization of the magma and segregation of leucocratic granite after about 80 crystallization deformation promoted segregation of melt fractions at discrete times during crystallization during final ascent and after the magma had crystallized sufficiently 50 70 to attain shear strength monzogranite liquid was incompletely segregated along the active thrust zone at the southern margin of the pluton at essentially the present crustal level and after about 80 crystallization the remaining leucocratic granite melts were more effectively segregated and migrated into thrust related extensional openings including tension gashes undeformed pegmatite and aplite dike arrays indicate that final crystallization coincided with final increments of shear zone movement solid state deformational fabrics and brittle synthetic thrusts that offset the pluton margin record sharp temperature decline during and after crystallization because plutons crystallize rapidly they can be used to estimate strain rates during orogeny thermal modeling suggests that the transition from rheological liquid to solid in the east piute pluton occurred during an interval of about 10 4 yr as final increments of ductile deformation coincided with final crystallization of evolved compositional units total strain recorded by fabric in the pluton apparently accumulated during this interval shear strains estimated from the s c fabric in the granodiorite unit and rotation of pegmatite filled vein arrays are on the order of 1 thus strain rates in the shear zone were on the order of 10 12 sec during crystallization of the pluton this corresponds to displacements of tens of centimeters per year these high strain rates suggest punctuated melt enhanced movement episodes during contractional orogeny

modelling deformation of partially melted rock using a poroviscoelastic rheology with dynamic power law viscosity abstract a poroviscoelastic constitutive model is developed and used to study coupled rock deformation and fluid flow the model allows the relaxation of both shear and symmetric components of the effective stress experimental results are usually interpreted in terms of the power law viscous material however in this work the effect of strain damage on viscosity is considered by treating the viscosity as a dynamic time dependent parameter that varies proportionally to the second invariant of the strain rate healing is also taken into account so that the dynamic power law viscosity has a constant asymptotic at a given strain rate the theoretical model is implemented in a finite element fe formulation that couples fluid flow and mechanical equilibrium equations the fe method is applied to numerically study the triaxial compression of partially melted rocks at elevated pt conditions it is found that the numerically calculated stress strain curves demonstrate maxima similar to those observed in laboratory experiments also the computed pattern of melt redistribution and strain localization at the contact between the rock sample and a stiff spacer is qualitatively similar to the experimental observations the results also indicate that the matrix sensitivity to damage affects the scale of strain localization and melt redistribution

strain rate influence on fracture development in experimental ductile multilayers abstract the far field strain rate is a crucial parameter that controls the transition between brittle and ductile deformation we have used analogue experiments to study the strain rate influence on the development of brittle fractures in a ductile composite material plasticine multilayer models were deformed under coaxial boundary conditions at three different strain rates to analyse the transition from non localised deformation to the development of a brittle fracture network that accommodates part of the deformation the results show that tension cracks and voids are the first macroscopic structures that nucleate after an early stage of ductile deformation coalescence and collapse of these structures lead to the development of brittle shear fractures the evolution of fracture orientations lengths and displacements was systematically analysed the ratio of the accumulated fracture displacement vs fracture length dmax l depends not only on the total deformation but also on the strain rate at which the system is deformed the accumulated displacement with respect to fracture length increases with strain rate

late cambrian ordovician northeastern gondwanan terranes in the basement of the apuseni mountains romania abstract the pre alpine basement of the apuseni mountains romanian carpathians comprises three terranes somes baia de aries and biharia metaigneous rocks within these terranes record late cambrian ordovician u pb zircon crystallization ages two samples from an orthogneiss layer in the somes terrane yielded an age of 459 8 2 7 ma in the baia de aries terrane an augen gneiss yielded an age of 470 8 3 8 ma a porphyroid yielded an age of 467 8 3 8 ma and two metagranites yielded ages of 467 8 4 7 ma and 467 1 3 9 ma respectively three samples from a metagranitoid outcrop located in the lower part of the biharia terrane yielded an age of 495 0 2 1 ma three other samples from a metabasite layer situated lithostratigraphically several hundred metres above the metagranitoid yielded an age of 477 8 3 2 ma detrital u pb zircon ages from a paragneiss interlayered within the baia de aries terrane scatter between 548 and 3518 ma detrital zircon ages together with the inherited ages recorded by magmatic zircon populations suggest a northeastern gondwanan provenance for the somes baia de aries and biharia terranes adjacent to the arabian nubian shield lead loss in some zircons is interpreted to have taken place during the variscan orogeny supplementary material coordinates for samples from the apuseni mountains palaeozoic palaeogeographical models of gondwana laurentia and baltica to the formation of pangaea sample preparation and analytical procedures sample description and age measurements of zircon grains are available at http www geolsoc org uk sup18425

experimental deformation of partially melted granitic aggregates abstract the effects of varying amounts of partial melt on the deformation of granitic aggregates have been tested experimentally at conditions 900 c 1500 mpa 10 4 to 10 6 s where melt free samples deform by dislocation creep with microstructures approximately equivalent to those of upper greenschist facies experiments were performed on samples of various grain sizes including an aplite 150 m and sintered aggregates of quartz albitemicrocline 10 50 and 2 10 m water was added to the samples to obtain various amounts of melt 1 15 in the aplite 1 5 in the sintered aggregates optical and tem observations of the melt distribution in hydrostatically annealed samples show that the melt in the sintered aggregates is homogeneously distributed along an interconnected network of triple junction channels while the melt in the aplites is inhomogeneously distributed the effect of partial melt on deformation depends an melt amount and distribution grain size and strain rate for samples deformed with 1 melt all grain sizes exhibit microstructures indicative of dislocation creep for samples deformed with 3 5 melt the 150 m and 10 50 m grain size samples also exhibit dislocation creep microstructures but the 2 10 m grain size samples exhibit abundant tem scale evidence of dissolution precipitation and little evidence of dislocation activity suggesting a switch in deformation mechanism to predominantly melt enhanced diffusion creep at natural strain rates melt enhanced diffusion creep would predominate at larger grain sizes although probably not for most coarse grained granites the effects of melt percentage and strain rate have been studied for the 150 m aplites for samples with 5 and 10 melt deformation at 10 6 s squeezes excess melt out of the central compressed region allowing predominantly dislocation creep conversely deformation at 10 5 s produces considerable cataclasis presumably because the excess melt cannot flow laterally fast enough and a high pore fluid pressure results for samples with 15 melt deformation at both strain rates produces cataclasis presumably because the inhomogeneous melt distribution resulted in regions of decoupled grains which would produce high stress concentrations at point contacts at natural strain rates there should be little or no cataclasis if an equilibrium melt texture exists and if the melt can flow as fast as the imposed strain rate however if the melt is confined and cannot migrate a high pore fluid pressure should promote brittle deformation