inferences on the mesozoic evolution of the north aegean from the isotopic record of the chalkidiki block the chalkidiki block is a major domain in the north aegean that contrary to other domains in the region largely escaped thermal perturbations during tertiary extension as a result the chalkidiki block is an ideal candidate to glean information related to the timing of mesozoic thermal events using appropriate geochronological techniques we have undertaken a laser ablation inductively coupled plasma mass spectrometry la icp ms study u th pb on monazites and u pb on zircons coupled with 40ar 39ar dating on nine samples from various structural levels within the thrust system of the chalkidiki block the eastern and structurally lower part of the system revealed a complete isotopic reset of carboniferous early triassic monazites coeval with partial monazite destruction ree mobilisation and formation of apatite allanite epidote coronas at 132 ma a reaction that is commonly observed in amphibolite facies rocks these coronas formed after crystallisation of garnet i e at t 580 c and in all probability either close to the peak temperature conditions 620 c on a prograde path or during retrogression between the peak temperature and the low temperature boundary of the amphibolite facies cooling of these rocks and arrival at mid crustal levels occurred at 95 100 ma by contrast the western and structurally uppermost part of the system went through the same event by 120 125 ma further structural considerations with respect to medium temperature geochronology data imply that syn metamorphic thrusting must have ceased by early late cretaceous we emphasize that with the sole exception of the chalkidiki block no pre 45 ma medium temperature geochronology data are preserved in other north aegean domains a feature that is clearly related to the extension induced thermal perturbation of the region during the tertiary

cyclic stacking pattern architecture and facies of the turbidite lobes in the macigno sandstones formation chattian aquitanian northern apennines italy abstract this study presents a detailed facies analysis of an 800 m thick stratigraphic succession in the basinal turbidites of the macigno sandstones formation msf recording the first foredeep in the northern apennines italy this stratigraphic succession shows an evident stacking pattern that besides the basal part 200 m thick dominated by fine grained and thin beds is characterized by seven magnificently exposed sandstone lobes from 90 to 19 m thick separated by well developed fine grained interlobe deposits thanks to the detailed facies analysis not only a well defined architectural hierarchy has been identified but a facies scheme has also been proposed whereby cyclic recurring of three facies associations has in turn been identified each facies association records a well determined evolutionary stage of lobe development where an early depositional stage of the lobe building phase is followed by a flow impact and bypass stage recording flow decelerations and hydraulic jumps induced by the morphology created by the underlying depositional lobe the latter phase promotes a switching and channel feeder avulsion that heralds the third phase of abandonment with the deposition of fine grained interlobes the facies stacking pattern and the evolutionary model of the msf also supported by other similar field and experimental works are intended as a contribution to the understanding of intrinsic autogenic mechanisms at the basis of sand rich depositional lobe development

gravity anomalies flexure and the elastic thickness structure of the india eurasia collisional system wehaveusedbouguergravityanomalyandtopographydatatodeterminetheequivalentelasticthicknessofthelithosphere te in the region of the india eurasia collisional system comparison of observed and modelled gravity anomalies along 1dimensional profiles suggest there are significant variations in te along strike of the himalaya foreland estimates decrease from a high of 70 km in the central region to 30 50 km in the east and west we have verified these inferences of spatial variations using a 2 dimensional non spectral interative flexure and gravity anomaly modelling technique the himalaya foreland forms a high te 40bteb100 km rigid block with a well defined edge as shown by the localisation of faulting and deformation along its northern margin other highteblocks occur to the north beneath the qaidam and sichuan basins the tibetan plateau forms a low te 0bteb20 km weak region that extends from the central part of the plateau into south western china tectonic styles in the india eurasia collisional system therefore involve both drigidt and dnon rigidt blocks where high te rigid blocks are present the stylesdominatedbyunderthrustingofthemorerigidblock wherethecollisionalzoneisnotconstrainedbyrigidblocks however the style appears to be dominated by lower crustal flow and a more continuous style of deformation d 2005 elsevier b v all rights reserved

geochronology geochemistry and isotope tracing of the oligocene magmatism of the buchim damjan borov dol ore district implications for timing duration and source of the magmatism abstract timing source and magmatic evolution of the intrusions in the buchim damjan borov dol ore district of the former yugoslav republic of macedonia f y r o m have been studied they intrude the circum rhodope unit close to the contact with the vardar zone and are a part of the late eocene oligocene macedonian rhodope north aegean belt the magmatism at buchim damjan borov dol occurred between 24 04 0 77 and 24 51 0 89 ma as indicated by chemical annealing ca la icp ms zircon dating major element trace and rare earth element analyses have been performed on the various intrusive rocks all ore bearing magmas were classified as trachyandesitic except the youngest intrusion which is not associated with mineralization the black hill locality 24 04 0 77 ma shows a trachytic composition the distribution of the trace elements enrichment of large ion lithophile elements lile and depletion in high field strength elements hfse indicates subduction related magmatism most of the magmas follow a calc alkaline fractionation trend with shoshonitic affinities additionally sr y 10 to 90 and la yb values show some similarities to adakite like magmas sr and nd isotope ratios sr i 0 70658 to 0 70740 and nd i 0 512425 0 512497 show that the magmatic products were slightly contaminated by continental crust material e g the variscan cadomian basement in the late eocene oligocene belt the magmatism between 29 and 35 ma is dominated by crustal melting with an increase in the mantle contribution between 20 and 27 ma we suggest the following scenario for the magmatic history of the buchim damjan borov dol ore district a slab rollback of an oceanic slab located further to the sw which led to extensional and compressional features in upper levels of the continental crust in the middle to upper crust three consecutive crystallization stages occurred at variable depths as indicated by amphibole zonation mixing of newly formed crust with mantle like affinities and continental crust material in variable degrees during the ascent of the magma can explain all geochemical characteristics the magma crystallized as dykes or stocks near the earth s surface 1 km after its final emplacement and contemporaneous hydrothermal activity led to different mineralization styles depending on the lithology of the host rocks

deposition of sheet like turbidite packets and migration of channel overbank systems on a sandy submarine fan an example from the late miocene early pliocene forearc basin boso peninsula japan abstract sheet like turbidite packets and channel overbank systems are interpreted to be major components of submarine fans spatial and temporal relationships between the two major components however are not yet clearly understood in particular for sand dominated submarine fans in active margin basins three dimensional outcrop analysis of an ancient sandy submarine fan succession in a late miocene early pliocene forearc basin on the boso peninsula japan together with mapping of chronostratigraphic markers defined by volcanic ash beds indicates that deposition of sheet like turbidite packets was intimately associated with the lateral migration of depocenters of channel overbank systems and distinct entrenchment of fan channels in response to upfan avulsion deposition of a sheet like turbidite packet is not restricted in a single interchannel low but rather is spread out over most of the channel overbank area possibly reflecting the high width to depth ratio of channel overbank systems on sandy submarine fans largely contemporaneous deposition of sheet like turbidite packets and channel overbank systems further indicates that the basin floor fan and slope fan of the sequence stratigraphic model do not necessarily characterize different parts of a relative sea level lowstand or temporally different types of depositional systems

sedimentary facies of the nova scotian upper and middle continental slope offshore eastern canada a detailed survey of the upper and middle nova scotian continental slope at 42 50 n and 63 30 w indicates a complex morphology dominated by mass movements on various scales and an immature turbidity current channel the range of sediment facies is diverse including hemipelagic and turbidite muds turbidite sands and gravelly sandy muds of debris flow origin deformed units interpreted as slump deposits are also observed several facies associations related to discrete morphological environments are recognized thick turbidite sand units with minor intervening mud beds are characteristic of the high relief uppermost slope and channel margin thinner turbidite sands deformed slump beds and various mud facies are associated with small scale hummocky mid slope topography sand beds are more abundant in the depressions than on intervening hummocks indicating the preferred transport paths of small turbidity currents at the lower end of the main turbidity current channel frequent turbidite sand beds with relatively minor mud beds are deposited on a depositional lobe in areas unaffected by mass movements alternating bioturbated mud and sandy muds make up the core sequences a local model of sedimentation is proposed for this area and illustrates that simple models of continental slope sedimentation only apply to a limited range of settings

3d subduction dynamics a first order parameter of the transition from copper to gold rich deposits in the eastern mediterranean region the natural variability of geometry and dynamics of subduction zones leads to a variety of mantle and crustal processes that may influence the genesis of ore deposits in the overriding plate these complex interactions cannot be fully represented by two dimensional 2d models but require that the spatial and temporal evolution of ore deposits be examined in a detailed 3d tectonic framework we compare and discuss the geodynamic and metallogenic evolution of the eastern mediterranean subduction zone since the late cretaceous by integrating a newly compiled metallogenic database with a recent kinematic reconstruction model the resulting paleotec tonic maps identify 1 a late cretaceous cu rich metallogenic period with large deposits formed above a linear and stable subduction zone that produced large amounts of potentially fertile magmas in a narrow magmatic arc and 2 a late eocene miocene pb zn followed by au rich metallogenic period with generally smaller deposits spread over a wide back arc basin that was opened due to subduction retreat and lateral slab tearing supported by high resolution numerical modeling the proposed dynamic arc and back arc metallogenic models emphasize 1 the influence of 3d slab dynamics and associated asthenospheric flow on ore distribution in space and time and 2 the importance of exhuming metamorphic domes in extensional back arc setting to focus metal bearing fluid circulations these models differ from collision and post collision models and may be valid on the western and eastern terminations of the whole tethyan orogenic belt i e mediterranean and southeast asia where fast 3d subduction dynamics has influenced the geodynamic and metallogenic evolution of the overriding plate

stable isotope study of the mineralization and alteration in the madjarovo pb zn district south east bulgaria the madjarovo ore district is centred on the exposed section of a lower oligocene volcano and consists of radially disposed pb zn precious metal veins and attendant intermediate sulfidation wallrock alteration earlier high sulfidation and potassic porphyry style alterations are found in the centre of the district spatially associated with monzonitic intrusions the total duration of all mineralization and alteration was ca 300 ka stable isotope analyses s o h have been carried out on a suite of sulfides sulfates and silicates from the mineralization high and intermediate sulfidation alterations and a suite of basement rocks these data range between the following limits delta 34 s sulfides 1 2 operatorname to 6 8 text delta 34 s sulfates 21 4 text to 24 9 delta 18 o sulfates 5 8 operatorname to 11 6 delta d sulfates 35 1 operatorname to 67 1 delta 18 o silicates 5 2 text to 13 5 delta d operatorname silicates 36 3 to 77 0 we also analysed d of fluid inclusions in quartz and barite for which we obtained respectively the ranges of 43 6 to 78 6 and 58 4 to 67 1 the data show that high sulfidation alteration was dominated by magmatic fluids with minor meteoric water whereas the fluids responsible for the intermediate sulfidation alteration were essentially magmatic the fluids responsible for the intermediate sulfidation pb zn mineralization were mixed magmatic meteoric and certainly contained a significant meteoric component sulphur is likely derived from basement and or igneous sources the evolution of alteration and mineralization styles from potassic porphyry copper style to high sulfidation to intermediate sulfidation can be understood in terms of changing ore fluid composition resulting from an increasing permeability of the system and an increasingly remote source of magmatic fluid with time these changes link directly to the geological evolution of this volcanic centre

volcanism and erosion during the past 930 k y at the tatara san pedro complex chilean andes geologic mapping together with 73 new k ar and 40ar 39ar age determinations of 45 samples from 17 different volcanic units plus paleomagnetic orientations geochemical compositions and terrestrial photogrammetry are used to define the chronostratigraphy of the tatara san pedro complex an eruptive center at 36 s on the volcanic front of the andean southern volcanic zone the tatara san pedro complex preserves 55 km3 of lavas that erupted from at least three central vent regions remnant unconformity bound sequences of lavas are separated by lacunae that include significant periods of erosion quaternary volcanism commenced ca 930 ka with eruption of voluminous dacitic magma followed 100 k y later by the only major rhyolitic eruption from 780 ka onward more than 80 of the preserved volume is basaltic andesite 52 57 sio2 but petrographically and geochemically diverse dacitic magmas 63 69 sio2 erupted sporadically throughout this younger dominantly mafic phase of activity a few basaltic lavas 49 52 sio2 are present mainly in portions of the complex older than 230 ka the number of vents the petrologic and geochemical diversity and the temporal distribution of mafic and silicic lavas are consistent with emplacement of many separate batches of mafic magma into the shallow crust beneath the tatara san pedro complex over the past million years nearly two thirds of the preserved volume of the tatara san pedro complex comprises the two youngest volcanoes which were active between ca 188 83 ka and 90 19 ka repeated advances of mountain glaciers punctuated growth of the complex with major erosional episodes that removed much of the pre 200 ka volcanic record particularly on the south flank of the complex dating the inception of a glaciation on the basis of preserved material is difficult but the age of the oldest lava above a lacuna may be used to estimate the timing of deglaciation on this basis the argon ages of basal lavas of multiple sequences indicate minimum upper limits of lacunae at ca 830 790 610 400 330 230 110 and 17 ka these are broadly consistent with global ice volume peaks predicted by the oxygen isotope based astronomical time scale and with age brackets on north american glacial advances estimated growth rates for the two young volcanoes are 0 2 to 0 3 km3 k y these are three to five times greater than a growth rate estimated from all preserved lavas in the complex 0 06 km3 k y removal of up to 50 95 of the material erupted between 930 and 200 ka by repeated glacial advances largely explains this discrepancy and it raises the possibility that episodic erosion of mid latitude frontal arc complexes may be extensive and common

sand rich turbidite system of the late oligocene northern apennines foredeep physical stratigraphy and architecture of the macigno costiero coastal tuscany italy

sedimentation in the northern apennines corsica tectonic knot northern tyrrhenian sea central mediterranean offshore drilling data from the elba pianosa ridge the northern tyrrhenian sea is located on the collisional zone between the alpine corsica and the northern apennines and is a key area for gaining a better understanding of the complex relationships between these two systems the knowledge of the wide offshore part of this zone located between corsica france and mainland italy is based primarily on the analysis of several seismic profiles tied to the outcropping geology and unpublished preliminary reports of few offshore wells the here presented study of two offshore wells provides a revision of the sedimentology biostratigraphy and petrography of the thick mainly siliciclastic tertiary successions about 3 600 m composing the elba pianosa ridge epr a structural morphological high separating the tuscan shelf to the east from the corsica basin to the west a comparison with similar deposits cropping out in the surrounding onshore areas northern apennines corsica tuscan archipelago piedmont tertiary basin provides additional constraints for refinement of the complex geodynamic and regional setting in which the epr evolved

coarse grained and fine grained turbidite systems as end member models applicability and dangers abstract submarine fan turbidite systems can have any net to gross percentage prior to developing a model that best represents the deposits under investigation the earth scientist should have an adequate understanding of the major external parameters that influence the transport and deposition of sediment tectonics influence the sediment source area and its overall distance to the shoreline shelf width and basin morphology the sand clay ratio and size range dictate how far sediment can be transported climate influences erosion transport and diagenesis relative sea level fluctuations impact the transport from coast to basin using those parameters and two end members coarse grained and fine grained an applicable model can be developed that best characterizes the fan under consideration

the importance of earthquake induced landslides to long term slope erosion and slope failure hazards in seismically active regions abstract this paper describes a general method for determining the amount of earthquake induced landsliding that occurs in a seismically active region over time this determination can be used as a quantitative measure of the long term hazard from seismically triggered landslides as well as a measure of the importance of this process to regional slope erosion rates and landscape evolution the method uses data from historical earthquakes to relate total volume of landslide material dislodged by an earthquake to the magnitude m and seismic moment m0 of the earthquake from worldwide data a linear regression relation between landslide volume v and m0 is determined as v m0 1018 9 0 13 where v is measured in m3 and m0 is in dyn cm to determine the amount of earthquake generated landsliding over time this relation is combined with data on seismic moment release for a particular region which may be derived from either earthquake history or fault slip data the form of the m0 v relation allows the rate of production of earthquake induced landslides over time to be determined from total rate of seismic moment release without regard to the distribution of individual events thus simplifying and generalizing the determination application of the method to twelve seismically active regions with areas ranging from 13 275 to 2 308 000 km2 shows that erosion rates from earthquake induced landslides vary significantly from region to region of the regions studied the highest rates were determined for the island of hawaii new zealand western new guinea and the san francisco bay region of california significantly lower rates were determined for iran tibet the sierra nevada great basin region of california and central japan for the time period from 715 ad to the present intermediate rates were determined for peru southern california onshore california turkey and central japan for the time period from 1586 ad to the present to determine the relative long term importance of seismically triggered landslides these erosion rates are compared to erosion rates calculated for other slope processes and to rates calculated from fluvial sediment discharge comparisons with other slope processes indicate that earthquake induced landslides are the predominant agents of slope erosion on the island of hawaii in the san francisco bay region and in western new guinea for hawaii the san francisco bay region and sierra nevada great basin region of california the erosion rates calculated for earthquake induced landslides also exceed the regional erosion rates calculated from fluvial sediment discharge

contemporaneous formation of adjacent porphyry and epithermal cu au deposits over 300 ka in northern luzon philippines there is commonly a close spatial relation between porphyry cu au and high sulfidation epithermal cu au deposits throughout the world although a genetic association has not been proven nowhere is this spatial association better seen than in northern luzon philippines where the lepanto epithermal cu au deposit overlies the far southeast fse porphyry cu au deposit both world class orebodies fresh rock and hydrothermal mineral separates yield k ar ages indicating that premineralization and postmineralization volcanism occurred at 2 2 1 8 ma and 1 2 0 9 ma respectively and that the hydrothermal system was active from 1 5 to 1 2 ma k ar ages of alunite from lepanto have the same range as those of hydrothermal biotite and illite from the fse deposit indicating that both epithermal and porphyry mineralization formed from an evolving magmatic hydrothermal system that was active for about 300 ka this temporal relation strengthens the argument for a genetic link between these two styles of ore deposit and has implications for exploration where one style of mineralization is found there is potential for the other nearby

predicting orogenic wedge styles as a function of analogue erosion law and material softening 1 the evolution of a compressive frictional wedge on a weak frictional and planar decollement subjected to frontal accretion is predicted with a two step method called sequential limit analysis the first step consists in finding with the kinematic approach of limit analysis the length of the active decollement and the dips of the emerging ramp and of the conjugate shear plane composing the emerging thrust fold the second step leads to a modification of the geometry first because of the thrust fold development due to compression and second because of erosion erosion consists in removing periodically any material above a fictitious line at a selected slope as done in analogue experiments this application of sequential limit analysis generalizes the critical coulomb wedge theory since it follows the internal deformation development with constant frictional properties the deformation is mostly diffuse a succession of thrust folds being activated so that the topographic slope reaches exactly the theoretical critical value frictional weakening on the ramps results in a deformation style composed of thrust sheets and horses applying an erosion slope at the critical topographic value leads to exhumation in the frontal central or rear region of the wedge depending on the erosion period and the weakening erosion at slopes slightly above or below the critical value results in exhumation toward the foreland or the hinterland respectively regardless of the erosion period exhumation is associated with duplexes imbricate fans antiformal stacks and major backthrusting comparisons with sandbox experiments confirm that the thickness dips vergence and exhumation of thrust sheets can be reproduced with friction and erosion parameters within realistic ranges of values

evolution and geodynamic significance of the tertiary orogenic volcanism in northeastern greece the tertiary volcanism of eastern macedonia and western thrace greece developed in association with the sedimentary basin which formed from eocene to oligocene along the southern margin of the rhodope massif the volcanic products ranging in composition from basaltic andesites to rhyolites show an overall calc alkaline orogenic affinity while chemical characteristics identify different groups of rocks probably reflecting minor differences among parent magmas the observed evolution within any group of rocks is compatible with fractional crystallization processes acting on relatively shallow magma bodies the sr isotopic composition of rhyolitic member shows an initial87sr 86sr ratio comparable with that of basaltic andesites reinforcing the hypothesis of a crystal liquid line of descent geochemical and petrographic evidence on the whole suggests that the investigated orogenic association developed on an active continental margin characterized by a relatively thick crust acting as a density filter for the basic magmas and facilitating their storage and fractionation within the crust itself minor contamination by interaction with host materials may also have occurred stratigraphic and k ar geochronological data indicate that the volcanic activity started in upper eocene and reached its maximum development in upper oligocene from lower miocene the volcanism shifted southward in the central aegean area and in part of western anatolia coming to an end by middle miocene the southward migration of the volcanic front has been interpreted as a consequence of the increase in the dipping of the benioff zone due to the decrease of penetrative strength after the main phase of continental collision

40ar 39ar geochronology of magmatism and hydrothermal activity of the madjarovo base precious metal ore district eastern rhodopes bulgaria the madjarovo volcanic complex and ore district comprise alteration styles from potassium silicate advanced argillic and sericite alteration to adularia sericite alteration mineralization with a close and unambiguous spatial relationship to specific magmatic events new 4 ar 39ar laser fusion and incremental heating experiments on nine sanidine biotite adularia k feldspar and alunite samples constrain the ages and time span of lavas and tepluas comprising the complex and their relationship to the hydrothennal activity these results demonstrate that high k calc alkaline to shoshonitic volcanic activity began c 32 7 ma and terminated c 500 ka later with the extrusion of quartz latite lavas at 32 2 ma the final stage of volcanism was accompanied by intrusion of cornpositionally similar monzonite stocks and trachytic dykes c 32 2 32 1 ma and associated barren advanced argillic and sericite alteration lithocap and adularia sericite base precious metal vein mineralization a probable thermal event at c 12 13ma disturbed the ages of alunite and sericite bearing alteration at low stratigraphic levels however field relations combined with a plateau age of 32 1 0 2 ma from adularia in low sulphidation veins that cross cut lithocap indicate that hydrothermal activity including baseand precious metal vein deposition was coeval with the youngest magmatic activity although most recent models of epithermal systems emphasize close spatial association among volcanic and plutonic events alteration and deposition of ore hedenquist lowenstern 1994 sillitoe 1993 1995 only rare combinations of geological events provide examples where relationships between igneous rocks porphyry and epithermal systems both high and low sulphidation are exposed this is mainly because young epithermal systems are poorly exposed whereas older deposits are eroded or deformed hedenquist arribas 1999 cooke simmons 2000 most economic epithermal ore deposits are tertiary and conventional k a r dating cannot precisely constrain the timing of magmatism alteration and mineralization at the 95 confidence level the precision of 4 ar 39ar age determinations of krich minerals is typically better than i0 5 thus for the oligocene materials of this investigation differences in age of about 200 ka may be distinguished e g marsh et al 1997 singer march

the timing of adularia sericite type mineralization and alunite kaolinite type alteration mount skukum epithermal gold deposit yukon territory canada 40 ar 39 ar and u pb geochronology the lower eocene mount skukum epithermal au deposit southwestern yukon territory 60 degrees 13 n 135 degrees 28 w exhibits both hypogene alteration and mineralization facies characteristic of the adularia sericite deposit type and barren advanced argillic alteration of the alunite kaolinite type the two being separated by only 750 m on the present erosional surface the advanced argillic alteration forms a crudely cylindrical possibly downward tapering body with an alunite quartz core and surrounding pyrophyllite or kaolinitc zones and is centered on a small or 150 m diam rhyolitic stock the delta d and delta 34 s values of the alunite which average 175 or 0 5 1sigma per mil and 2 93 or 0 43 1sigma per mil respectively suggest that this alteration conforms to the hypogene type formed by magmatic so 2 mixing with meteoric water an inference that is consistent with mineral associations and textures that imply fairly high temperatures pyrophyllite stable the 40 ar 39 ar age spectra for alunite generated by furnace heating exhibit good multi step plateaus and show that during slow heating with small increment steps alunite releases virtually all of its argon through volume diffusion at temperatures below 540 degrees c the preferred age for the alunitic alteration is 55 69 or 0 24 2sigma ma the error weighted average of four plateau dates that range from 55 00 or 0 55 to 56 12 or 0 45 ma calculated closure temperatures for alunite average 280 degrees or 20 degrees c 2sigma at a cooling rate of 50 degrees c m y gold bearing quartz calcite adularia veins are hosted by andesitic volcanic strata of the eocene skukum group and by rhyolitic dikes the mineralized veins conform entirely to the adularia sericite class and were controlled by strike slip faults and fracture zones a wide rhyolite dike cut by the most important ore zone was emplaced at 56 3 or 0 4 2sigma ma earliest eocene as defined by u pb zircon dating step heating 40 ar 39 ar dating of vein adularia with orthoclase structure yields plateaus which suggest that no significant ar loss occurred the error weighted average of two plateau dates for the lake zone and the lowest age steps in two slightly saddle shaped plateaus for the cirque zone 54 05 or 0 31 ma is taken as the age of adularia sericite type mineralization which is slightly but significantly younger than the alunite kaolinite type alteration a swarm of intermediate dikes some of which cut ore veins was intruded over an interval that embraced the time of mineralization one of these dikes which cuts the wide rhyolite dike yielded a u pb zircon age of 55 7 or 0 3 ma but this does not further constrain the age of the mineralization the ages of alunite and adularia from mount skulmm indicate a succession from the barren alunite kaolinite type hydrothermal system to the gold bearing adularia sericite type system both of which formed during ongoing magmatism in the mount skukmn volcanic complex

small scale variations of 87 sr 86 sr isotope composition of barite in the madjarovo low sulphidation epithermal system se bulgaria implications for sources of sr fluid fluxes and pathways of the ore forming fluids the madjarovo ore district is located in the volcanic rocks of the oligocene madjarovo shield volcano and underlying precambrian and palaeozoic high grade metamorphic rocks of the rhodope massif bulgaria it is situated in the eastern part of a large tertiary magmatic metallogenic belt which resulted from the cretaceous collision of serbo macedonian and rhodope massifs with the pelagonian microplate the low sulphidation base and precious metal mineralisation at madjarovo 32 1 ma formed shortly after the cessation of the shoshonitic and high k calc alkaline volcanic and intrusive activity 32 6 32 2 ma and is spatially and temporally related to late monzonite trachyte intrusions the strontium isotope composition of five barite samples hosted in the volcanic sequence is used to characterise the source s of sr in associated base and precious metal mineralisation and to infer fluid fluxes and pathways of the ore forming fluids the 87sr 86sr compositions for barite samples from ore veins fall in the range 0 70854 0 70955 with the lowest and highest values found in the smaller brecciated veins barite from a thin vein in the basal latite lava flow has the most radiogenic 87sr 86sr isotope composition likely reflecting the involvement of more radiogenic metamorphic basement rocks the least radiogenic composition was determined for barite from a similar vein high in the volcanic pile 500 600 m above the metamorphic basement barites from large veins taken from different stratigraphic positions in the host lavas have almost identical isotopic compositions in the range 0 70883 0 70899 the 87sr 86sr values for barite within the deposit are higher than those for host magmatic rocks 0 70775 0 70863 but lower than those of the metamorphic basement 0 7110 0 7278 it is concluded that strontium in the fluids is a mixture of predominantly magmatic strontium and a variable amount of more radiogenic sr from the metamorphic basement rocks the ore bearing fluid may have been derived from a shallow 1 4 km silicic pluton with an initial 87sr 86sr value 0 7080 because of the short distance to the site of deposition the fault focused ore fluids maintained homogeneous strontium predominantly magmatic strontium isotope ratios with slight contribution s of more radiogenic strontium from the metamorphic basement rocks larger variations in the small brecciated veins can be explained by more extensive fluid rock interaction with local host metamorphic or volcanic rocks

interaction of gravity flows with a rugged mid ocean ridge seafloor an outcrop example from macquarie island rugged bathymetry along slow spreading mid ocean ridges has the potential to impinge a strong control on gravity flows derived from oceanic fault scarps sedimentary lithofacies from the macquarie island ophiolite supports this hypothesis by displaying systematic variations that correspond with volcanic substrate differences and proximity to rift related faults pillow basalt terranes are associated with tightly confined bedrock corridors that funnel gravity flows into one direction vertical lithofacies variations formed from high density to low density turbidity currents record successive fill stages of the corridor axis during initial stages tight confinement in the axis suppressed flow dilution and fluid turbulence with continued corridor axis filling more dilute gravity flows predominated and formed lateral gradations from axial coarse grained turbidites into thinly interbedded overbank lithofacies along corridor margins these gravity flow lithofacies converge into very thin muddy condensed intervals along inter corridor highs where significant bottom current reworking occurred conversely partly confined tabular basalt floored basins promoted lateral expansion and dilution of gravity flows throughout the duration of basin filling variable paleocurrent indicator directions record multiple reflections of single gravity flow events off basin bounding fault barriers coarsening upward trends in these partly confined basins from thinly interbedded pelagic chert and ripple bedded sandstones up into stacked turbidites preserves the ponding of sediment starved submarine fans in general these ponded basins preserve the fine grained distal ends of a gravity flow continuum from coarse grained fault proximal en masse failures and cohesionless debris flows into medial high density turbidity flows and distal dilute turbidity flows

evaluation of factors controlling earthquake induced landslides caused by chi chi earthquake and comparison with the northridge and loma prieta events over 10 000 landslides were triggered by the september 21 1999 chi chi earthquake a large number of these landslides have been mapped from spot images and a smaller number were described in a detailed field investigation geographic information systems gis was used to conduct a spatial characterization of the slope failures including distribution of type size slope angle bedrock geology ground motion and distance from earthquake source the most abundant landslides were shallow disaggregated rock and soil slides landslides occurred primarily in tertiary sedimentary rocks which are well known for their susceptibility to landsliding in many parts of the world landslide concentration values diminish beyond epicentral distances of 40 and 70 km from the epicenter and the surface projection of the fault plane respectively ground motion was found to be the most significant factor in triggering the shallow landslides in the chi chi earthquake overall 74 of all slope failures occurred in regions with vertical ground motions greater than 0 2g and 81 of all slope failures occurred in the region with mean horizontal peak ground accelerations pga greater than 0 15g these factors were used to compare landslides generated by the chi chi earthquake to the landslides triggered by the 1989 loma prieta earthquake and the 1994 northridge earthquake the major difference in distribution of landslides between the chi chi earthquake and the two california earthquakes was the distribution of slope angles in the chi chi earthquake 90 of the failures occurred on slopes steeper than 45 while more than 80 of failures occurred on slopes less than 50 in california apparently reflecting much steeper and tectonically more active geologic setting in taiwan

geochronology of the sleeper deposit humboldt county nevada epithermal gold silver mineralization following emplacement of a silicic flow dome complex the high grade gold silver deposits at the sleeper mine are low sulfidation quartz adularia type epithermal deposits formed during the final stages of igneous hydrothermal activity of a small middle miocene silicic flow dome complex in north central nevada potassiumargon and 40 ar 39 ar ages of alkali feldspar indicate that the rhyolitic flow dome complex was emplaced before about 16 5 ma hydrothermal alteration and mineralization followed lasting from about 16 2 to 14 ma based on ages of adularia associated with electrum there were multiple pulses of alteration and mineralization but all occurred within a period of less than 2 m y later supergene alteration formed opal and alunite about 5 4 ma but produced no au or ag mineralization other than some remobilization to produce locally rich pockets of secondary au and ag enrichment and is unrelated to the older magmatic hydrothermal system the sleeper deposit in the northern part of the great basin is genetically related to bimodal volcanism that followed a long period of arc related andesitic volcanism in the same general region

magmatism and associated hydrothermal activity during the evolution of the tavua caldera 40 ar 39 ar dating of the volcanic intrusive and hydrothermal events the tavua caldera in viti levu fiji occurs in the upper part of the shoshonitic tavua volcano precaldera rocks forming the edifice of the volcano are predominantly mafic absarokite in composition whereas intracaldera rocks are intermediate shoshonite and banakite in composition the caldera hosts subeconomic porphyry style copper gold mineralization and minor weakly auriferous acid sulfate epithermal alteration both associated with monzonite intrusions in the center of the caldera and adularia sericite epithermal mineralization the emperor gold deposit on the caldera margin ten tavua samples ranging from hydrothermally altered or mineralized to relatively fresh material were dated by the 40 ar 39 ar incremental heating technique these dates establish that caldera collapse occurred between 4 6 and 4 5 ma precaldera absarokites have an age greater than 4 6 ma and probably as much as 4 7 ma while intracaldera shoshonites and banakites have a maximum age of 4 51 ma so there was a gap of at least 0 1 m y between mafic and major intermediate volcanism in this area monzonite intrusion and concurrent porphyry style alteration in the center of the caldera occurred between 4 51 and 4 44 ma essentially synchronous with intracaldera volcanism the last magmatic event within the caldera a banakite vent phase pyroclastic unit occurred at 4 14 or 0 08 ma adularia deposited during epithermal mineralization at emperor was formed at 3 71 or 0 13 ma this history which is clearly indicated by 40 ar 39 ar data would not have been possible to deduce by conventional k ar dating the results are similar to those obtained in other porphyry and epithermal systems where porphyry style magmatic hydrothermal activity is deemed to be synchronous with magmatism but a measurable interval occurs between magmatism and epithermal mineralization tavua is unusual in that samples of both types of mineralization are available are amenable to dating techniques and can be tied to the history of the caldera

thermochronology of economic mineral deposits dating the stages of mineralization at panasqueira portugal by high precision 40 39 ar age spectrum techniques on muscovite 40 ar 39 ar age spectrum dates for 13 muscovites have been used to reconstruct the thermal history thermochronology of the panasqueira portugal tin tungsten deposit a deposit spatially associated with a belt of hercynian plutons muscovite samples with an age difference as small as 2 2 m y 0 7 of the age are statistically distinct statistics are even better for comparison of multiple samples from separate events that is a difference of 0 9 m y 0 3 can be resolved in this approximately 300 m y old deposit the major tin and tungsten ore forming stages which are the oxide silicate stage the main sulfide stage and greisenization occurred between 296 3 or 0 8 1 sigma and 291 6 or 0 8 m y 1 sigma the first substage of the oxide silicate stage was a short lived thermal pulse at 296 3 or 0 6 m y the fluids responsible may have emanated from the known granite cupola the main sulfide stage was active at 294 5 or 0 9 m y as a slightly longer lived pulse with oldest evidence for this stage 295 8 or 0 6 m y coming from areas farthest away from the known cupola and youngest evidence 293 5 or 0 8 m y closest to the cupola a second substage of the oxide silicate stage occurred as a short lived thermal pulse at 292 9 or 0 7 m y synchronous with greisenization of the cupola and alteration of the silica cap at 292 1 or 0 4 m y the duration of activity of the oxide silicate stage the main sulfide stage greisenization and alteration of the silica cap based on the ages of all 13 muscovites was greater than 4 2 or 0 5 m y 1 sigma minor argon loss from all dated muscovites occurred during later reheating probably during the longer lived pyrrhotite alteration stage a single center the known cupola had a prolonged role and was the source for main sulfide stage oxide silicate stage ii greisenization and alteration of the silica cap and possibly oxide silicate stage i and the pyrrhotite alteration stage however a separate source for these latter two stages cannot be ruled out this study is an example of a new and powerful application of 40 ar 39 ar age spectrum dating of muscovite because of the high precision demonstrated in this study it is now possible to establish time constraints necessary for solving some of the long standing problems in economic geology beyond this the unique geologic situation of panasqueira has allowed us to quantify the thermal characteristics of muscovite published fluid inclusion data have been used to estimate a muscovite argon closure temperature of approximately 325 degrees c during rapid cooling or short reheating and a temperature of approximately 270 degrees c during slow cooling or extended reheating argon loss patterns displayed by all dated muscovites resulted from reheating after original closure the mechanism for this argon loss appears to have been argon transport by volume diffusion thus 40 ar 39 ar age spectrum dating of muscovite can be used to evaluate thermal conditions controlling argon diffusion as well as age duration and number of episodes of mineralization

seismically induced mass movements and volumetric fluxes resulting from the 2010 mw 7 2 earthquake in the sierra cucapah mexico the observation that sediment flux from mountain ranges struck by high magnitude earthquakes can be strongly influenced by coseismic mass movements brings into question the nature of coseismic deformation as a net contributor to mountain building to better constrain the role of high magnitude earthquakes in orogenesis high resolution data of earthquake induced mass wasting is required for areas of differing tectonic morphological and climatic settings here we compare the erosional flux to the tectonic flux associated with the 2010 mw 7 2 sierra el mayor earthquake in mexico and examine the landslide patterning of coseismic mass movements associated with this event the ruptured fault system has a significant strike slip component with subsidence along the eastern flank and uplift on the western flank of the range peak ground acceleration was highest along the steepest sections of the range such that the frequency of landslide occurrence was strongly correlated to slope gradient both vertical and horizontal coseismic displacement demonstrated a strong control over landslide initiation this result suggests that strike slip systems experience very different landslide patterning to thrust faults during earthquakes based on interferometric analysis of synthetic aperture radar images the earthquake resulted in a total uplifted volume of 41 6 106 m3 and a loss of 95 2 106 m3 due to subsidence this suggests a net tectonic volumetric flux of 53 6 106 m3 sediment mobilisation by coseismic landslides is estimated at 2 7 106 m3 derived from a manually mapped inventory using spot 5 multispectral imagery thus the net volume loss through coseismic subsidence of the mountain range generated a strongly negative mass flux which was only marginally enhanced by mass wasting

thresholds of intrabed flow and other interactions of turbidity currents with soft muddy substrates controlled laboratory experiments reveal that the lower part of turbidity currents has the ability to enter fluid mud substrates if the bed shear stress is higher than the yield stress of the fluid mud and the density of the turbidity current is higher than the density of the substrate upon entering the substrate the turbidity current either induces mixing between flow derived sediment and substrate sediment or it forms a stable horizontal flow front inside the fluid mud such intrabed flow is surrounded by plastically deformed mud otherwise it resembles the front of a bottom hugging turbidity current the suprabed portion of the turbidity current i e the upper part of the flow that does not enter the substrate is typically separated from the intrabed flow by a long horizontal layer of mud which originates from the mud that is swept over the top of the intrabed flow and then incorporated into the flow the intrabed flow and the mixing mechanism are specific types of interaction between turbidity currents and muddy substrates that are part of a larger group of interactions which also include bypass deposition erosion and soft sediment deformation a classification scheme for these types of interactions is proposed based on an excess bed shear stress parameter which includes the difference in the bed shear stress imposed by the flow and the yield stress of the substrate and an excess density parameter which relies on the density difference between the flow and the substrate based on this classification scheme as well as on the sedimentological properties of the laboratory deposits an existing facies model for intrabed turbidites is extended to the other types of interaction involving soft muddy substrates the physical threshold of flow substrate mixing versus stable intrabed flow is defined using the gradient richardson number and this method is successfully validated with the laboratory data the gradient richardson number is also used to verify that stable intrabed flow is possible in natural turbidity currents and to determine under which conditions intrabed flow is likely to be unstable it appears that intrabed flow is likely only in natural turbidity currents with flow velocities well below c 3 5 m s 1 despite the fact that a wider range of flows is capable of entering fluid muds below this threshold velocity intrabed flow is stable only at high density gradients and low velocity gradients across the upper boundary of the turbidity current finally the gradient richardson number is used as a scaling parameter to set the flow velocity limits of a natural turbidity current that formed an inferred intrabed turbidite in the deep marine aberystwyth grits group west wales united kingdom this article is protected by copyright all rights reserved

tertiary extensional tectonics in tuscany northern apennines italy abstract two extensional events have been recognized in the tertiary evolution of tuscany the first event occurred in the period between the late oligocene and late tortonian and caused a stretching of 120 or greater the second event occurred between the late tortonian and quaternary periods and caused a stretching not greater than 10 the first event is characterized by the exhumation of middle crust rocks and therefore by the development of core complexes the most significant structures of the first event are low angle normal faults which characterize the upper plate of the core complexes and ductile shear zones which characterize the lower plate the low angle normal faults tend to die out in the late triassic evaporite level which constitutes the main detachment of the core complexes the main structures of the second extensional event are high angle normal faults which dissect all the previous tectonic features these faults border tectonic depressions which were the site of clastic sedimentation from late tortonian to quaternary time these normal faults may tend to flatten in a seismic lozenge shaped band explained as an active extensional shear zone which is located at the brittle ductile boundary a similar explanation is given for the detachment located in the late triassic evaporite level during the first extensional event while the first extensional event is in the framework of the northern apennine post collisional evolution the second extensional event because it affects an already stretched crust could be attributed to the southern tyrrhenian opening which began during late tortonian

how long can a hydrothermal system be sustained by a single intrusive event published numerical calculations show that the convective systems which produce near surface geothermal systems or ore deposits are likely to cool their intrusion heat source in at most a few tens of thousands of years even if the intrusion is large generally hydrothermal circulation near surface geothermal activity and magmatic intrusion should be closely tied in time and space long lived approximately 1 m y hydrothermal activity normally suggests multiple pulses of intrusion with associated pulses of hydrothermal circulation however if the permeability of the intruded environment is just above that which allows convection and the volume of the intrusion is very large calculations presented here show that a single episode of intrusion can sustain hydrothermal circulation and near surface geothermal activity for approximately 800 000 yr for a deep sill heat source these unusually long lived hydrothermal systems can vent through a few very widely separated discharge sites and have the potential to produce isolated massive sulfide deposits of unusually large size

brief duration of hydrothermal activity at round mountain nevada determined from ar 40 ar 39 geochronology the round mountain gold silver deposit is one of the world s largest volcanic hosted precious metal deposits reserves plus production total at least 16 million oz 500 000 kg au the deposit occurs in ash flow tuff that is ponded within its source caldera along and overlying the caldera ring fracture host rocks have undergone propylitic potassic and high level silicic and intermediate argillic alteration these are interpreted either as a temporal sequence from early propylitic to late silicic and argillic or as a spatial progression from a potassic core outward to a propylitic halo 40 ar 39 ar ages determined by single crystal fusion of sanidine from host tuff and incremental heating of adularia indicate a most likely duration of hydrothermal activity of approximately 0 1 m y possibly no more than 0 05 m y and a maximum of 0 5 m y eruption of host ash flow tuff and caldera collapse occurred at 26 5 ma a late or postalteration tuff that rests upon mineralized rock is 26 0 ma hydrothermal circulation is unlikely to have been established immediately after caldera collapse so duration was probably considerably less than 0 5 m y eight adularia samples give ages between 25 94 or 0 09 and 26 09 or 0 05 ma and one is 26 20 or 0 05 ma the mean of all nine is 26 03 or 0 08 ma the maximum and minimum values and their uncertainties allows a duration of as much as 0 4 m y but for the following reasons the longevity is probably much less the absolute ages of seven samples that can be placed in the possible temporal alteration sequence do not correlate with that sequence this does not disprove the temporal sequence but does indicate that alteration occurred in a time span which is not resolvable even with precise 40 ar 39 ar dating furthermore all samples show flat age spectra which themselves argue against a long continuously active system kinetic studies of two adularia reveal diffusion domains with ar closure temperatures between approximately 230 degrees and approximately 390 degrees c adularia that crystallized and remained at temperatures of 275 degrees c the maximum temperature inferred from fluid inclusion data would yield age spectra with age gradients spanning the lifetime of the system no spectra are consistent with a thermal history that incorporates sustained 0 1 m y temperatures at or above 275 degrees c episodic activity to account for the one older adularia date cannot be precluded but is inconsistent with most data therefore the hydrothermal system probably was active for less than the uncertainty in the ages of individual samples possibly as little as 50 000 years we conclude that hydrothermal activity at round mountain was a brief event at approximately 26 0 ma and was closely linked to caldera structure and magmatism this activity followed initial ash flow eruption by 0 5 m y and may have been driven by a ring fracture intrusion

turbidites in foreland and on thrust basins of the northern apennines abstract turbiditic sediments are associated with all stages of development of the apennines orogen not only the classical flysch of oligo miocene age macigno cervarola marnoso arenacea but also the coeval smaller bodies based on thrust sheets loiano of ranzano sequence and the younger molasse of the plio pleistocene foredeep except for more recent ones quaternary turbidite units are affected to some degree by thrusting and later block faulting the equivalent marginal deposits were also deformed uplifted and eroded to a great extent however identification and correlation of sequences and paleoenvironments across the orogenic belt can be helped by a deposits with rather strong eustatic imprint high stands and b preservation of marginal sediments by early remobilization cannibalism into deeper depocentres the following categories of basins can be recognized main foreland basin or foredeep in front of thrust sheets based on undeformed or previously rifted continental crust thrust top basins meso autochthonous auct in absence of a well defined major foredeep satellite basins thrust based but inwardly associated with a foredeep and of much smaller size linear dimensions in the order of kilometers and ten of kilometers volume of fill in the order of tens to hundreds cubic kilometers the foredeep persisted for the whole orogenic cycle but changed its character and was more or less segmented two main stages can be recognized conventionally labelled as the flysch stage up to the late miocene appenines mostly submerged and the molasse stage late miocene to recent present relief already in existence satellite basins floating on the ligurian sheet epi ligurian persisted up to the mid pliocene but received turbidites only in the oligocene and miocene others were created later on thrusts of different style involving the foreland sedimentary cover piggyback basins of ori and friend 1984 turbidite lithosomes of the flysch group are the largest ones volumes up to 30 000 km 3 with maximum size and lateral continuity of individual beds megaturbidites they are not seen as overlapping units filling coexisting and adjacent basins but as distinct superposed isochronous units within which only time transgressive sedimentation could occur macigno thus stands for all oligocene turbidites of the northern apennines foredeep cervarola for early miocene ones and marnoso arenacea for mid late miocene ones it is assumed that these units reflect sedimentary cycles of some order correlatable with global charts and splittable into depositional sequences sensu vail and collaborators

an outer ramp to basin plain transect interacting pelagic and calciturbidite deposition in the eocene oligocene of the tuscan domain adria microplate italy abstract the interaction of ramps basin plains and turbidite systems on the scale of tens of km has been rarely observed in fossil examples deep marine eocene oligocene beds are exposed in the axial zone of the chianti mountains italy and compose a regionally continue stratigraphic succession known as the scaglia toscana formation the formation was deposited in the tuscan domain of the adria microplate this research aims at depicting its depositional architecture and evolution in the type area stratigraphic and sedimentologic analyses were performed on a ca 25 km long transect that includes depositional systems sectioned both in the down and along dip directions shaly carbonate deposits compose a complex of interacting ramps basin plains and turbidite floor fan systems ramp deposits accumulated above the lysocline and in oxic conditions basin plain beds were deposited below the lysocline and were subject to episodes of oxygen depletion turbidity flows fed elongate fan lobes characterized by poor channelisation the basin palaeogeography hampered the development of slope apron turbidite systems the eocene oligocene geodynamic setting of the tuscan domain was characterized by the evolution of a peripheral bulge and by the early structuring of a foredeep basin syn sedimentary tectonism acted a primary role in the basin scale arrangement however other mechanisms also contributed to the local facies distribution including the disposition of sediment source areas and intrabasinal confinement morphologies as well as relative oscillations of the depositional surface with respect to the lysocline and oxycline

submarine mass wasting deposits as an indicator of the onset of foreland thrust loading late permian bowen basin queensland australia in the eastern part of the permo triassic bowen basin of queensland australia a transition from passive thermal subsidence to flexural foreland basin subsidence is recorded within the upper permian stratigraphy two coarse grained intervals containing deposits of mass wasting processes occur within an otherwise siltstone dominated succession over 1500 m thick the moah creek beds and equivalents these intervals can be traced over at least 350 km north south along the structural eastern margin of the basin the lower of the coarse grained intervals is spectacularly exposed in the banks of the fitzroy river west of rockhampton here interbedded sandstones and siltstones of marine shelf origin are abruptly truncated by a mudrock succession containing evidence of slumping and contemporaneous magmatic activity this unit passes up section into packages of mass flow conglomerates and diamictites interpreted to have formed on an unstable submarine slope the character of the mass flow deposits their stratigraphic position and lateral extent are interpreted in terms of destabilization of a sloping marine surface by pulsed subsurface thrust propagation

temporal evolution of arc magmatism and hydrothermal activity including epithermal gold veins borovitsa caldera southern bulgaria plutonic volcanic and hydrothermal activity in magmatic arcs is commonly focused spatially leaving behind complex records of multiple ore forming processes that can be appreciated in detail only if the timing of igneous and hydrothermal systems is ascertained the spahievo ore district bulgaria is adjacent to the oligocene borovitsa caldera one of the largest in europe juxtaposition of porphyry mineralization barren advanced argillic alteration and low sulfidation epithermal alteration and mineralization zones along the caldera margin provides an uncommon opportunity to examine the temporal development of an evolved magmatic hydrothermal system 40 ar 39 ar ages determined using a co 2 laser to fuse or incrementally heat minerals from fresh igneous and altered rocks indicate a rapid succession of 1 pre caldera intermediate magmatism including monzonitic intrusion and coeval porphyry style mineralization and advanced argillic alteration between 32 9 and 32 3 ma 2 rhyolitic ash flow tuffs dikes and domes with adularia sericite alteration accompanied by epithermal precious metal mineralization at 32 1 ma and 3 nearly synchronous collapse of a nested caldera and intrusion of a ring fault rhyolite dome and intracaldera dikes at 31 8 ma these ages link monzonitic intrusion cu mo mineralization and advanced argillic alteration and indicate that rhyolitic magmatism and adularia sericite alteration with associated base metal plus au mineralization is slightly younger about 100 to 500 k y deposition of au ore ca 300 k y prior to caldera collapse distinguishes this ore district from many well known deposits in which ore formation accompanied andesitic or rhyolitic intrusions along ring fractures that postdate the collapse

the growth of geological structures by repeated earthquakes 1 conceptual framework in many places earthquakes with similar characteristics have been shown to recur if this is common then relatively small deformations associated with individual earthquake cycles should accumulate over time to create geological structures following this paradigm we show that existing models developed to describe leveling line changes associated with the seismic cycle can be adapted to explain geological features associated with a fault in these models an elastic layer containing the fault overlies a viscous half space with a different density fault motion associated with an earthquake results in immediate deformation followed by a long period of readjustment as stresses relax in the viscous layer and isostatic equilibrium is restored deformation is also caused as a result of the loading and unloading due to sediment deposition and erosion in this paper the parameters that control the growth of dip slip structures are identified we find that the flexural rigidity of the crust or the apparent elastic thickness provides the main control of the width of a structure the loading due to erosion and deposition of sediment determines the ratio of uplift to subsidence between the two sides of the fault the flexure due to sediment load is much more important in this respect than whether the fault is normal or reverse in character we find that in general real structures are associated with apparent elastic thicknesses of 4 km or less and thus with very low flexural rigidities

small scale spatial variability in turbidity current flow controlled by roughness resulting from substrate erosion field evidence for a feedback mechanism abstract analysis of turbidity flow processes from turbidite outcrops remains difficult in this paper the distribution of orientations of paleoflow indicators around scours a few centimeters to a few decimeters deep is analyzed two examples are presented one from the gres de champsaur formation in southeastern france and one from the macigno formation in northern italy the orientations of paleoflow data sets on either side of the scours are analyzed and differ 10 15 over horizontal distances of only a few meters this mismatch is argued to represent a rotation of the flow whilst it flowed over the scour the reconstructed rotation is a new example of a feedback mechanism involving interaction between the current and its substrate paleoflow indicators only record flow direction at the base of the flow however the flow substrate interaction can be expected to affect the complete turbulent velocity structure of the flow so that erosion by frontal parts of the current influences the suspended sediment transport processes of hindward regions of the current

prolonged seismically induced erosion and the mass balance of a large earthquake large earthquakes deform the earth s surface and drive topographic growth in the frontal zones of mountain belts they also induce widespread mass wasting reducing relief the sum of these two opposing effects is unknown using a time series of landslide maps and suspended sediment transport data we show that the mw7 6 chi chi earthquake in taiwan was followed by a period of enhanced mass wasting and fluvial sediment evacuation peaking at more than five times the background rate and returning progressively to pre earthquake levels in about six years therefore it is now possible to calculate the mass balance and topographic effect of the earthquake the choshui river has removed sediment representing more than 30 of the added rock mass from the epicentral area this has resulted in a reduction of surface uplift by up to 0 25 m or 35 of local elevation change and a reduction of the area where the chi chi earthquake has built topography for other large earthquakes erosion may evolve in similar predictable ways reducing the efficiency of mountain building in fold and thrust belts and the topographic expression of seismogenic faults prolonging the risk of triggered processes and impeding economic regeneration of epicentral areas

the mass balance of earthquakes and earthquake sequences large compressional earthquakes cause surface uplift as well as widespread mass wasting knowledge of their trade off is fragmentary combining a seismologically consistent model of earthquake triggered landsliding and an analytical solution of coseismic surface displacement we assess how the mass balance of single earthquakes and earthquake sequences depends on fault size and other geophysical parameters we find that intermediate size earthquakes mw 6 7 3 may cause more erosion than uplift controlled primarily by seismic source depth and landscape steepness and less so by fault dip and rake such earthquakes can limit topographic growth but our model indicates that both smaller and larger earthquakes mw 7 3 systematically cause mountain building earthquake sequences with a gutenberg richter distribution have a greater tendency to lead to predominant erosion than repeating earthquakes of the same magnitude unless a fault can produce earthquakes with mw 8 or more

the effect of early alpine thrusting in late stage extensional tectonics evidence from the kulidzhik nappe and the pelevun extensional allochthon in the rhodope massif bulgaria abstract in the northeastern rhodope massif the kulidzhik nappe exposes a unique juxtaposition of a high grade basement allochthon onto a low grade mesozoic unit and the counterpart pelevun extensional allochthon belonging to the same unit the kulidzhik nappe tectonostratigraphy comprises structurally upward i a lower unit consisting of high grade basement orthogneisses ii a low grade greenschist phyllite unit consisting of jurassic extrusive rocks and metasedimentary rocks iii the nappe allochthon built by the lower high grade basement unit orthogneisses and iv eocene sedimentary rocks and oligocene volcanic cover rocks the pelevun extensional allochthon is heterogeneous and consists of mesozoic low grade unit marbles and greenschists and the upper high grade basement unit we have combined structure and kinematics with lithological information and 40 r 39 r geochronology to constrain the tectonic evolution and regional significance of the kulidzhik nappe and the pelevun extensional allochthon mineral chemistry reveals igneous phases of the granitic protolith of the allochthonous orthogneisses with textures related to ductile deformation and metamorphism higher than 500 c their trace element patterns are indistinguishable from the high grade basement orthogneisses in the eastern rhodope mineral chemistry of the metamorphic assemblage in the underlying greenschists is consistent with medium grade greenschist facies metamorphism at temperatures well below 450 c whose geochemistry defines transitional morb to iat affinities with a strong arc imprint the greenschist s composition is extremely similar to the composition of a supra subduction zone jurassic arc extrusive suite that occurs in the low grade unit of the eastern rhodope the structural elements in all of the tectono metamorphic units and the nappe surface indicate top to the nne tectonic transport deformation evolved from ductile to brittle conditions coevally with a progressive decrease from lower amphibolite to weak greenschist facies metamorphism towards the structural top two klippen gave plateau 40 r 39 r mica ages of 154 23 0 66 ma and 156 70 0 81 ma respectively which reflect cooling following the greenschist facies event below 350 c during shallow crustal level thrust emplacement and exhumation of the kulidzhik allochthon the hanging wall pelevun extensional allochthon preserves an internal nne directed ductile tectonic transport trend but is underlain by a ssw directed ductile brittle extensional detachment and has experienced ne sw brittle extension on high angle normal faults an amphibole 40 r 39 r inverse isochron age of 156 58 0 60 ma constrains a late jurassic upper greenschist facies tectono metamorphic event whereas a white mica plateau age of 39 66 0 47 ma provides evidence for middle eocene cooling and exhumation of the pelevun extensional allochthon in the hanging wall of the detachment we relate the kulidzhik nappe to late jurassic crustal deformation during arc continental margin collision that involved nne directed nappe staking and metamorphism of continental margin basement and island arc units the nappe shares a tectono metamorphic history with the nappes of the adjacent strandzha massif implying a region wide early alpine orogenic system our results reveal a record of early alpine thrust tectonics and show the significance of crustal accretion related assembly for the tectonic evolution of the rhodope massif both the late jurassic thrusting event and the subsequent cretaceous thrusting event thickened the rhodope crust creating crustal instability which influenced tertiary crustal extension

deep sea fan deposits in the macigno formation middle upper oligocene of the gordana valley northern apennines italy abstract facies characteristics are described for a 2300 m thick turbidite succession of the macigno formation middle upper oligocene which crops out as a continuously exposed section in the gordana valley northern apennines in the study area the macigno formation consists of two sandy members separated by a shaly member the sandy members contain lithic associations characteristic of submarine fan deposits and form distinct fan complexes the middle shaly member represents a period of basin starvation three main facies associations are recognized in the macigno fan deposits fan fringe outer fan lobe and braided midfan facies associations the fan fringe deposits consist of monotonous or small scale cyclically arranged thin bedded turbidites the outer fan lobe deposits are composed of medium to very thick bedded classical turbidites internally organized in thickening upward cycles with minor intercalations of thin bedded sandstone beds two distinct types of outer fan lobe deposits distal and proximal are recognized on the basis of rock type internal organization and vertical facies relationships the midfan deposits consist of amalgamated massive sandstone and pebbly sandstone which display repeated thinning upward cycles the three main facies associations are superposed t define major thickening and coarsening upward cycles reflecting distinct episodes of fan progradation the relationships between the facies associations of the macigno deposits and the existing models of submarine fan sedimentation are discussed after the deposition of the fan complexes fan sedimentation in this part of the basin was replaced by movements of allochthonous units heralded by large olistostromes

regional patterns of earthquake triggered landslides and their relation to ground motion 1 we have documented patterns of landsliding associated with large earthquakes on three thrust faults the northridge earthquake in california chi chi earthquake in taiwan and two earthquakes on the ramu markham fault bounding the finisterre mountains of papua new guinea in each case landslide densities are shown to be greatest in the area of strongest ground acceleration and to decay with distance from the epicenter in california and taiwan the density of co seismic landslides is linearly and highly correlated with both the vertical and horizontal components of measured peak ground acceleration based on this observation we derive an expression for the spatial variation of landslide density analogous with regional seismic attenuation laws in its general form this expression applies to our three examples and we determine best fit values for individual cases our findings open a window on the construction of shake maps from geomorphic observations for earthquakes in non instrumented regions

from geodetic imaging of seismic and aseismic fault slip to dynamic modeling of the seismic cycle understanding the partitioning of seismic and aseismic fault slip is central to seismotectonics as it ultimately determines the seismic potential of faults thanks to advances in tectonic geodesy it is now possible to develop kinematic models of the spatiotemporal evolution of slip over the seismic cycle and to determine the budget of seismic and aseismic slip studies of subduction zones and continental faults have shown that aseismic creep is common and sometimes prevalent within the seismogenic depth range interseismic coupling is generally observed to be spatially heterogeneous defining locked patches of stress accumulation to be released in future earthquakes or aseismic transients surrounded by creeping areas clay rich tectonites high temperature and elevated pore fluid pressure seem to be key factors promoting aseismic creep the generally logarithmic time evolution of afterslip is a distinctive feature of creeping faults that suggests a logarithmic dependency of fault friction on slip rate

the corsica sardinia massif as source area for the early northern apennines foredeep system evidence from debris flows in the macigno costiero late oligocene italy large isolated gravity flows debrites are widely present in the stratigraphic record of the northern apennines foreland basin system these strata may be useful for provenance signals and dispersal pathways during foreland evolution this paper examines a cohesive debris flow bed interbedded with turbidite strata of the macigno formation late oligocene tuscany italy in order to obtain new data on the provenance of the clastic material clasts in the debris flow are predominantly plutonic granodiorite tonalite and s granite and subordinately metamorphic gneiss and schist and sedimentary calcareous clasts the composition of the clasts within the debris flow is similar to the clastic composition of the interbedded turbidite sandstones of the macigno costiero the depositional features of the debris flow suggest that it traveled for a short distance within the basin before it was deposited not far from the slope the absence of a high pressure low temperature hp lt paragenesis in the plutonic and metamorphic clasts of the debris flow indicates a provenance from a crystalline basement not involved in the high pressure phases of the alpine orogenesis previous studies have indicated the central western alps as potential source areas for the macigno formation sediments the lack of hp lt metamorphic signatures in our studied samples excludes the pennidic and austroalpine nappes of the western alps as possible sources for the debris flows of the macigno costiero these new data sedimentological petrographical and microstructural suggest that the corsica sardinia hercynian basement lacking a hp lt paragenesis is the more accredited source area of the debris flow and of the related turbidite sandstones of the macigno costiero succession these foredeep feeding sediments were probably before deposited within an episutural basin developed close to the northern apennines orogenic wedge

a coarse grained turbidite system with morphotectonic control middle albian ondarroa northern iberia the middle albian ondarroa turbidite system is a coarse grained deep water unit which outcrops in the north eastern part of the basque cantabrian region west of the pyrenees it is about 18 km long and 7 km wide and shows an unusual l shape resulting from both a direct morphotectonic confinement and the presence of nearby shallow water carbonate buildups eight main facies have been distinguished within this turbidite system 1 clast supported conglomerates 2 mud supported conglomerates 3 slump deposits 4 normally graded pebbly sandstones 5 cross stratified sandstones 6 interbedded graded sandstones and mudstones 7 interbedded non graded sandstones and mudstones and 8 mudstones inner system middle system outer system and basin plain divisions have been distinguished the inner turbidite system is characterized by stacked channel fill conglomerates and lesser sandy turbidites and mudstones the middle system consists of sandy and conglomeratic fining upwards sequences normally several metres thick the outer system has alternating non channellized sandstones and mudstones without any predictable vertical arrangement the basin plain is characterized by mudstone siltstone laminations and lesser randomly occurring thin bedded sandy turbidites three main channel fills make up the inner turbidite system although all of them can be compared with the valley channel fills of the modern mississippi fan and thus their bases can be interpreted as sequence boundaries only the lowermost and the uppermost channel bases are documented as allocyclic boundaries the ondarroa turbidite system was deposited in an immature passive margin subjected to transtensional movements it filled a composite pull apart depression with coarse clastics derived from a narrow platform to the north of the present outcrops which was invaded by fan deltas a major pattern of sinistral strike slip faulting linked to the opening of the bay of biscay is invoked to explain the ondarroa turbidite system appearance and its tectonic confinement

fluid mineral relations in the comstock lode the comstock lode a world class precious metal vein deposit in the comstock district 15 mi 24 km southeast of reno nevada formed 13 7 ma in miocene eruptive rocks of the alta and kate peak formations and in pre tertiary metavolcanic and intrusive rocks production of 8 25 million oz 311 850 kg in gold and 192 million oz 7 26 million kg in silver came largely from bonanzas or vein segments containing hundreds of thousands to millions of tons and grading or 0 4 oz ton approximately 14 g ton gold and or 10 oz ton approximately 340 g ton silver within the 8 mi 12 9 km long comstock fault bonanza ores are distributed 3 mi 4 8 km along strike and persist from the present surface to 3 300 ft 1 007 m below the surface during the middle miocene andesitic to rhyodacitic alta and kate peak rocks formed a stratovolcano that exceeded 7 000 ft 2 134 m in elevation bonanza ores were deposited within this volcano from a 200 degrees c hydrothermal system that affected more than 37 mi 3 150 km 3 of rock at least one cretaceous and several miocene hydrothermal events were imposed on comstock district rocks the comstock lode vein assemblage which resulted from the youngest and only economically important event consists of quartz electrum silver minerals mainly acanthite pyrite base metal sulfides and minor amounts of calcite sericite chlorite k feldspar and albite andesite adjacent to veins is altered to quartz sericite and pyrite at vein contacts and quartz sericite montmorillonite chlorite and pyrite distally kaolinite is present in wall rocks adjacent to vein segments in which boiling occurred addition of the external components water co 2 and sulfur gases sufficed to produce all comstock vein alteration assemblages based on paragenetic and fluid inclusion studies multiple generations of hydrothermal fluid formed comstock district veins but the earliest and highest temperature fluid deposited ore minerals it ranged in temperature from 300 degrees c at the north end of the lode cedar hill to 6 wt percent nacl and was composed of both meteoric and magmatic water according to fluid isotopic analyses younger cospatial fluid s contained up to 2 1 wt percent co 2 the thermal center of the comstock lode hydrothermal system cedar hill is also the site of the highest measured ore fluid salinities ore fluid isotherms and to an extent salinity isopleths display reversals and convolutions that are spatially related to bonanzas these sharp temperature gradients coupled with mixing of ore fluid and at least one other high temperature fluid indicated by enthalpy salinity relationships and deuterium enrichment most likely caused precipitation of ore minerals sphalerite and electrum compositions indicate that bonanzas were deposited over a narrow range of f sub s 2 13 5 to 15 2 while sphalerites from low grade and barren vein segments indicate more widely variable f sub s 2 gold silver ratios both in electrum and bulk ore appear to be temperature controlled as higher temperatures generally correlate with high au ag ratios local boiling of 250 degrees to 285 degrees c fluid provides a paleosurface datum but vein temperatures 300 degrees c require up to 3 800 ft 1 152 m of cover over the tops of bonanzas during mineralization the distribution of both ore stage and late vein calcite partially reflects hydrothermal fluid circulation patterns in veins at district margins the abundance of late calcite marks the demise of hot water circulation and the influx of large amounts of cold miocene ground water into vein interstices kate peak intrusions between cedar hill and mount davidson share a common structural control with vein segments that comprise the comstock lode and their ages span vein ages the coeval kate peak magmas that provided heat for hydrothermal circulation formed the core of and uplifted the miocene stratovolcano which was centered over cedar hill partial symmetry of thermal compositional and kinetic gradients about cedar hill suggests that additional bonanzas await discovery along unexplored comstock fault segments within declining palcothermal gradients to the north

provenance changes for arenaceous formations of the northern apennines italy a complex pattern of provenances is displayed by 15 formations in the northern apennines composed chiefly of turbidites that were deposited during the alpine orogenesis q f l and qp lv ls values can be used to characterize specific source areas that existed in the apennine region from cretaceous through miocene time whereas sandstone mineralogy can be used to infer plate tectonic setting such an approach must make allowances for both the size of the area studied and the tectonic framework that existed prior to sandstone deposition in an early stage of the compressive phase of the tethys late cretaceous both arkose and litharenite were derived from cratonic blocks whereas volcanic sandstone was derived from uplifted oceanic sediments and lavas sediments recording the main oligo miocene collisional tectonic phases accumulated in two principal tectonic settings 1 intermontane successor basins and 2 foreland basins in the first case individual formations exhibit a wide provenance variability arkosic lithic sandstone recycled orogen volcanic sandstone magmatic arc and arkose were deposited simultaneously in the second case basins filled with thick turbidite sequences composed of arkose and lithic arkose which were supplied by basement rocks uplifted along the edge of the european craton and or by the nascent orogenic belt

constraints on magma degassing beneath the far southeast porphyry cu au deposit philippines k silicate alteration in the far southeast fse porphyry cu au introduction deposit formed at 1 4 ma concentric to dikes of quartz diorite magmas become saturated with volatile components as porphyry at 2 km paleodepth the hydrothermal system consisted they ascend in the crust and either erupt or crystallize of magmatic hypersaline liquid and vapor at 550 c and 50 at depth saturated magmas that remain at depth exsolve mpa lithostatic pressure advanced argillic alteration formed at an aqueous fluid that forms a hydrothermal system on the same time over the deposit at 1 km paleodepth from acidic separation from the magma chamber burnham 1979 condensates of the vapor at 1 3 ma k silicate alteration was although part of the exsolved fluid a low density vapor overprinted by 350 c magmatic liquid 5 wt nacl equiv may discharge to the surface from passively degassing at hydrostatic pressure sericite alteration and much of the cu au volcanoes hedenquist 1995 part will remain at depth mineralization formed at this later stage evolution of the magmatic and this dense residual magmatic liquid may be asfluid composition was simulated with a magma chamber cryssociated with hydrothermal mineralization in the portallization model homogeneous crystallization during early stage phyry ore environment hedenquist lowenstern convection is assumed whereas at 50 vol crystals the chamber 1994 becomes stagnant and crystallizes from rim to core over a narrow in this paper we use evidence from a porphyry ore crystallization interval the model calculation based on a magma deposit in the philippines to determine the composition chamber with 2 km thickness at 6 km depth 150 mpa and of the fluid that exsolved from the deeper parent magma 800 c saturated melt composition at 30 vol crystals 5 the evolving composition of the magmatic fluid at the wt h2o 0 2 wt cl and dd of 40 can reproduce the depth of the ore body can then be used to place constraints chemical and isotopic compositions of the early and late magmatic on the nature of the evolved magma chamber far below fluids the most critical factor controlling the compositional evolution the porphyry ore body this approach differs from that of the model hydrothermal system is the transition from convective of other studies where a portion of the parent magma to stagnant magma chamber crystallization there is also a sharp chamber is available to study directly e g at yerington decrease in the rate of fluid exsolution associated with this transition nevada dilles 1987 which can account for the thermal collapse of the fse porphyry the far southeast fse porphyry cu au deposit system from k silicate to sericite alteration and overlying lepanto epithermal cu au ore body are

mass wasting triggered by the 2008 wenchuan earthquake is greater than orogenic growth shallow earthquakes lead to the uplift of mountain ranges but also trigger landslides that remove mass an analysis of the 2008 wenshuan earthquake suggests that more material was removed from the orogen by widespread landslides than was added by coseismic uplift

structure and u pb zircon geochronology of an alpine nappe stack telescoped by extensional detachment faulting kulidzhik area eastern rhodopes bulgaria the rhodope metamorphic complex is a stack of allochthons assembled during obduction subduction and collision processes from jurassic to paleogene and overprinted by extensional detachment faults since middle eocene in the study area the following nappes occur in superposition from base to top an orthogneiss dominated unit unit i garnet bearing schist with amphibolite and serpentinite lenses unit ii greenschist phyllite and calcschist with reported jurassic microfossils unit iii and muscovite rich orthogneiss unit iv u pb dating of zircons from a k feldspar augengneiss unit i yielded a protolith age of ca 300 ma garnet bearing metasediment from unit ii yielded an age spectrum with distinct populations between 310 and 250 ma detrital ca 150 ma and ca 69 ma the last two of high grade metamorphic origin an orthogneiss from unit iv yielded a wide spectrum of ages the youngest population gives a concordia age of 581 5 ma interpreted as the age of the granitic protolith unit i represents the lower allochthon byala reka kechros dome unit ii the upper allochthon krumovitsa kimi unit unit iii the uppermost allochthon circum rhodope belt and unit iv a still higher far travelled unit of unknown provenance telescoping of the entire rhodope nappe stack to a thickness of only a few 100 m is due to late eocene north directed extensional shearing along the newly defined kulidzhik detachment which is part of a major detachment system along the northern border of the rhodopes older top to the south mylonites in unit i indicate that tertiary extension evolved from asymmetric top to the south to symmetric top to the south and top to the north bivergent unroofing

estimating the return times of great himalayan earthquakes in eastern nepal evidence from the patu and bardibas strands of the main frontal thrust the return times of large himalayan earthquakes are poorly constrained despite historical devastation of cities along the mountain range definitive links between events and specific segments of the main frontal thrust mft are not established and paleoseismological records have not documented the occurrence of several similar events at the same location in east central nepal however recently discovered primary surface ruptures of that megathrust in the a d 1255 and 1934 earthquakes are associated with flights of tectonically uplifted terraces we present here a refined longer slip history of the mft s two overlapping strands patu and bardibas thrusts in that region based on updated geomorphic neotectonic mapping of active faulting two 1 3 km long shallow seismic profiles and logging of two river cut cliffs three paleoseismological trenches and several pits with constraints from 74 detrital charcoals and 14 cosmogenic nuclide ages the amount of hanging wall uplift on the patu thrust since 3650 450 years requires three more events than the two aforementioned the uplift rate 8 5 1 5mm yr thrust dip 25 5 n and apparent characteristic behavior imply 12 17 5m of slip per event on the bardibas thrust discrete pulses of colluvial deposition resulting from the coseismic growth of a flexural fold scarp suggest the occurrence of six or seven paleo earthquakes in the last 4500 50 years the coeval rupture of both strands during great himalayan earthquakes implies that in eastern nepal the late holocene return times of such earthquakes probably ranged between 750 140 and 870 350 years

landslide patterns reveal the sources of large earthquakes the distribution of fault slip in an earthquake controls seismic surface deformation and ground shaking and is the most direct record of fault response to tectonic stress detailed information about slip patterns in large earthquakes is only available where a dense local network of seismometers is in place elsewhere the evaluation of earthquake source and mechanism relies on observation of proxies such as surface change or damage intensity in upland areas the density of seismically induced landslides is strongly influenced by the intensity and duration of strong ground motion and therefore contains information about the earthquake source mechanism here we show that density patterns of co seismic landslides closely track the distribution of fault slip in two large thrust earthquakes in japan when adjusted for site effects landslide distributions readily obtained from remote sensed images can supplement or replace instrumental records of earthquakes opening historical and remote events for close geophysical investigation

lower edge of locked main himalayan thrust unzipped by the 2015 gorkha earthquake faults are unlocked by earthquakes analysis of seismic data from the 2015 nepal earthquake shows that only part of the main himalayan thrust fault was unzipped by the quake leaving much of the fault locked and ready to slip in a future event

amalgamation surfaces bed thicknesses and dish structures in sand rich submarine fans numeric differences in channelized and unchannelized deposits and their diagnostic value abstract hydraulic differences between channelized and unchannelized flows in sand rich submarine fans result in different distributions of amalgamation surfaces bed thicknesses and dish structures in successions of these two different environments distribution trends of these fabrics were quantified for the sand rich fans of the reiselsberger sandstein cenomanian turonian these trends can be used as criteria to distinguish channelized from unchannelized paleoenvironments of sand rich submarine fans amalgamation surfaces in the studied fans channelized regions are considerably more abundant than in the unchannelized fan areas in unchannelized deposits tabular amalgamation surfaces outnumber nontabular ones whereas the opposite occurs in channelized successions these results indicate a higher degree of erosive power of gravity driven sediment flows in channels as a result of a greater flow thickness higher flow velocity and turbulence the average turbidite layer thickness in channelized successions is markedly greater than in unchannelized deposits layer as defined herein this is mainly attributed to the combined effects of differences in sediment fall out rate and the inefficiency of sand rich suspensions to transport sand in the proximal and channelized fan areas more sediment is deposited from a flow in the form of a layer than in distal unchannelized fan regions despite a higher degree of erosion in channels the greater average bed thickness in channel fills is a function of layer thickness and more frequent amalgamations bed as defined herein dish structures seem to be considerably more common in midfan than in outer fan successions this may indicate a higher sedimentation rate from individual suspension currents in midfan areas

proximal to distal sedimentological variation in a linear turbidite trough implications for the fan model determination of geographically dependent sedimentological variation proximality in ancient flysch deposits formed an important part of early turbidite studies attempts to quantify this variation highlighted anomalies which were neatly resolved by application of vertical sequence analysis and the use of fan models however there are many turbidite formations such as the lower cretaceous cumberland bay formation cbf of south georgia which cannot be described in terms of existing fan models but show strong proximal to distal sedimentological changes the cbf is a thick sequence of volcaniclastic sandstone turbidites deposited in a linear back arc basin principally by currents flowing wnw parallel to the basin margin four lithofacies associations are recognized on the basis of sandstone shale ratio the two finergrained associations are constant in character across the cbf outcrop in the coarse grained associations there is a change in character wnw down the palaeocurrent direction this is brought out by decreasing sandstone bed thickness and percentage amalgamation but these changes are not always marked or consistent in contrast the internal character of the sandstone beds changes strongly with a marked proportional increase in tb and tc divisions within the bed downcurrent the evidence suggests that the system was aggradational rather than progradational tectonic control of the basin margins prevented major migration of the depositional system and most areas remained in the same position relative to source through time comparison of the cbf with other turbidite formations suggests two end member states which will produce radically different vertical sequences progradational systems will produce strong vertical facies changes where beds deposited in distal environments are overlain by beds deposited in environments progressively nearer source however there will be no lateral change in the character of any particular facies type in contrast in aggradational systems the major sedimentological variation will be lateral rather than vertical

density distribution of landslides triggered by the 2008 wenchuan earthquake and their relationships to peak ground acceleration the distribution of landslides induced by the 2008 m w 7 9 wenchuan earthquake was investigated following the method of meunier et al 2007 to examine the relationships to peak ground acceleration pga results suggest that landslide densities are quantifiably related to pga thresholds of pgacr for landslide failure are graphic 1 for average horizontal pga and graphic 2 for average vertical pga as with other earthquakes the distribution of the wenchuan earthquake triggered landslides can be described by two equations based on area and source densities respectively the similar damping factors of 20 in these two equations suggest that both density distribution patterns of landslides reflect the dissipation of seismic energy landslide derived pga equations were then produced for the hanging wall region of the earthquake affected area the results indicate that it should be possible to produce an earthquake shake map from the distribution of earthquake triggered landslides in an area where there are few or no seismic instruments but many landslides 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif

the north tyrrhenian northern apennines post collisional system constraints for a geodynamic model the north tyrrhenian northern apennines post collisional system ntas has been analysed on the basis of marine reflection profiles and bibliographic sources with the aim of providing an up to date geotectonic and evolutive framework consistent with structural data the continental rifting began to affect the most internal western side of the system in the middle upper miocene while the most external eastern zones were touched by rifting only in pleistocene times the birth and development of extensive asymmetric basins took place with a progressive speeding up of rifting towards the external sectors a diachronous regionally extended and eastward rejuvenating unconformity recognizable within the neogene quaternary basins marks the passage from the syn rift to the post rift tectonic regime while the first is everywhere dominated by extension the second one produces vertical movements reflection terminations related to this unconformity are interpreted in terms of vertical tectonic component three zones that experienced different post rift vertical movements are thus recognized in the ntas subsidence in the north tyrrhenian deep water region tectonic stability or alternation of moderate subsidence and uplift in the continental shelf and western tuscany strong uplift in eastern tuscany the updated structural data demonstrate that the ntas upper crust is crosscut by both tyrrhenian dipping and apennine dipping low angle detachment planes above which the upper crustal blocks rotated and experienced extensional transport along two opposite directions to the west and to the east respectively the coexistence of opposite dipping crustal surfaces bears two fundamental implications for the ntas geodynamics first it stresses the importance of the anti apennine transfer faults since they separate crustal blocks of opposite extension polarity secondly it testifies that the extension tectonics not only re utilized former crustal thrust planes but also gave origin to new significant e and ne dipping detachment planes plan and crossview geometries of faults together with considerations on the role of the metamorphic core complexes point to an interpretation of the ntas structure that is more consistent with the anastomosing shear model rather than the simple shear or the delamination ones

fluid disturbed hornblende k ar ages from the dalradian rocks of connemara western ireland the results of k ar age determinations and hydrogen and oxygen stable isotope measurements on hornblendes from the poly metamorphic dalradian schists of connemara western ireland indicate that the hornblende k ar systems have been significantly disturbed by low temperature fluid reaction correlations between k ar ages d values structural water contents and the occupancy of the hornblende structural a sites suggest that excess water as h 3 o occupies vacant a site positions during stable isotope exchange and displaces ar causing lowering of the k ar ages this process occurs below the normally accepted closure temperature for ar in hornblende and is not detectable by optical or x ray investigation of the mineral this process may not be unique to connemara hornblendes and so is of potential importance to geochronology in other metamorphic terranes

2 hydrothermal ore deposits related to post orogenic extensional magmatism and core complex formation the rhodope massif of bulgaria and greece abstract the rhodope massif in southern bulgaria and northern greece hosts a range of pb zn ag cu mo and au ag deposits in high grade metamorphic continental sedimentary and igneous rocks following a protracted thrusting history as part of the alpine himalayan collision major late orogenic extension led to the formation of metamorphic core complexes block faulting sedimentary basin formation acid to basic magmatism and hydrothermal activity within a relatively short period of time during the early tertiary large vein and carbonate replacement pb zn deposits hosted by high grade metamorphic rocks in the central rhodopean dome e g the madan ore field are spatially associated with low angle detachment faults as well as local silicic dyke swarms and or ignimbrites ore formation is essentially synchronous with post extensional dome uplift and magmatism which has a dominant crustal magma component according to pb and sr isotope data intermediate and high sulphidation pb zn ag au deposits and minor porphyry cu mo mineralization in the eastern rhodopes are predominantly hosted by veins in shoshonitic to high k calc alkaline volcanic rocks of closely similar age base metal poor high grade gold deposits of low sulphidation character occurring in continental sedimentary rocks of synextensional basins e g ada tepe show a close spatial and temporal relation to detachment faulting prior and during metamorphic core complex formation their formation predates local magmatism but may involve fluids from deep mantle magmas the change in geochemical signatures of palaeogene magmatic rocks from predominantly silicic types in the central rhodopes to strongly fractionated shoshonitic bulgaria to calc alkaline and high k calc alkaline greece magmas in the eastern rhodopes coincides with the enrichment in cu and au relative to pb and zn of the associated ore deposits this trend also correlates with a decrease in the radiogenic pb and sr isotope components of the magmatic rocks from west to east reflecting a reduced crustal contamination of mantle magmas which in turn correlates with a decreasing crustal thickness that can be observed today hydrogen and oxygen isotopic compositions of the related hydrothermal systems show a concomitant increase of magmatic relative to meteoric fluids from the pb zn ag deposits of the central rhodopes to the magmatic rock hosted polymetallic gold deposits of the eastern rhodopes

evolution of a thrust sheet top basin the tertiary barreme basin alpes de haute provence france in the french sector of the tertiary alpine mountain belt of southern europe the early stages of compression established an initial thrust front a long distance into the foreland 30 40 km rearward of the terminal thrust front an extensive region of thrust sheet top basins was established behind this initial thrust front particularly after a regional marine transgression in late eocene time priabonian these basins were initially connected but became increasingly compartmentalized as the thrust belt evolved the basins are now preserved as a series of structurally isolated synclinal remnants in the external zones of the alpine thrust belt one of these remnants known as the barreme basin has a preserved fill that is 900 m thick spans 18 m y and is exposed over 50 km 2 the tertiary basin fill comprises initial nonmarine deposits overlain by a marine succession and subsequent continental strata and includes evidence of submarine gravity slides growth structures and abrupt changes in sediment transport directions and provenance evolution of the basin fill was influenced by both far field and more localized near field deformation events the latter being dominated by the progressive growth of a steep thrust related anticline that defined the eastern margin of the basin this basin fill records several key steps in the evolution of the alpine mountain belt such as the first incursion of clasts derived from the emplacement of major thrust structures in the inner parts of the mountain belt ca 32 30 ma synsedimentary volcanic activity and the growth of an important out of sequence anticline that progressively separated the barreme basin from the gres d9annot basin to the east in addition the basin preserves the progression from an early underfilled flysch basin to a subsequent overfilled molasse basin in early oligocene time rupelian between ca 33 and 30 ma records of these events are not available from the fill of the younger foreland basin preserved beyond the final thrust front and this remnant of the thrust sheet top basin province therefore provides a unique record of the early structural and stratigraphic evolution of the alpine mountain belt

turbidite channel overbank deposition in a lower devonian orogenic shale basin fortin group of gaspe peninsula northern appalachians canada abstract the lower devonian fortin group one of the major stratigraphic units in connecticut valley gaspe synclinorium of the gaspe peninsula and its stratigraphic equivalent the temiscouata formation in northwestern new brunswick and southeastern quebec are interpreted as a base of slope to deep basin turbidite succession sandwiched between shallow marine to nonmarine siluro devonian sediments the deep water interpretation is based on a comparison with modern deep sea turbidite depositional environments and the lower slope to deep basinal settings established by previous investigators for equivalent rocks in new england the monotonous sequences of largely unfossiliferous well bedded dark slate phyllite and siltstone with intercalated sandstone packets of the fortin group and temiscou ta formation in the matapedia and madawaska st john valley regions respectively are interpreted as submarine overbank and channel fill facies associations seven lithofacies have been distinguished 1 associations of massive sandstone beds up to 13 m thick and 2 associations of sandstone beds of intermediate 0 5 2 0 m thickness forming isolated sandstone packets encased in slate and siltstone are the equivalent of modern deep channel fill deposits 3 5 laterally continuous largely nonbioturbated thin siltstone layers with climbing ripple lamination turbidite c division and parallel lamination turbidite d division followed by slate turbidite e division and hemipelagite are analogous to muddy spill over turbidites with interbedded hemipelagites on modern natural levees th t accompany deep channels among the fine grained sediments a proximal to distal facies succession with respect to presumed lateral distance from channels consists of 3 siltstone slate 4 banded slate and 5 laminated slate if found in lateral succession the same succession may reflect spill over from progressively deeper channels the channel levee interpretation is supported by field observations of i a partly exposed channel wall ii truncation of siltstone and slate layers at sandstone contacts iii lag material at the base of massive sandstone layers and iv the chevron pattern of nearly opposing paleocurrent directions in the spill over facies 6 syndepositionally deformed and diamictite facies comprise fine grained rocks of facies 3 5 7 volumetrically subor inate conglomerates are the coarsest of the redeposited sediments siegenian praguian emsian turbidite deposition occurred in a deep basin of the connecticut valley gaspe trough that developed in response either to wrench tectonics or back arc spreading related to a volcanic island arc piscataquis volcanic belt deep sea trench system merrimack fredericton trough