styles of failure in late holocene highstand prodelta wedges on the adriatic shelf on the continental shelves of the northern mediterranean basin the late holocene highstand systems tract hst prograded un der the influence of major rivers after the attainment of the present sea level highstand about 5 5 cal kyr bp on the adriatic shelf the thickness distribution of the late holocene hst reflects the location of major deltas on the western side of the basin and the geostrophic cir culation which prevents a more uniform sediment dispersal toward the center of the basin very high sediment accumulation rates 1 to 10 cm year resulted in the construction of a hst depocenter up to 35 m thick this shore parallel depocenter is affected by failure of limited displacement over as much as 40 of its extent gas impregnation is common in the topset region and occurs at very shallow levels a few meters below the sea floor five areas are characterized by a variety of sea floor and subsurface crenulations although locally some of these crenulations have an intriguingly regular geometry sediment failure is the most plausible mechanism for their formation sediment failure better explains the large variety of geometries that characterizes the coastal mud prism of the late holocene hst furthermore we observe that these crenulations occur only where the downlap surface at the base of the hst is disrupted and affected by geometries that are con sistent with fluid escape processes this relationship suggests that the basal surface acts as a weak layer for sediment failure failure occurred in variable water depths from the northern slope of the modern po prodelta 10 20 m water depth to the narrow shelf offshore bari 40 110 m water depth in all these areas the proximal part of the hst prodelta wedge is intensely gas charged the thickness and age of the sediment sections affected by failure are slightly differ ent from place to place but appear everywhere younger than 5 5 cal kyr bp where failure affects the entire hst the detachment occurs on the downlap surface at its base failure geometries characterize the head region whereas compressional features such as pressure ridges and mud diapirs dominate in the toe region ranging in depth between 70 and 110 m where failure is limited to the upper few meters of the hst there is a clear lithologic change decrease in carbonate fraction and grain size across the basal surface this lithological change reflects a switch in sediment supply from local apennine rivers below to po derived mud this change occurred at the onset of the little ice age documenting the indirect control of short term climate change and hu man impact on sediment architecture the deformations affecting the late holocene hst in the various areas show differences in internal geometry but appear everywhere to be characterized by limited downward displacement and can be attri buted to shear dominated retrogressive failure it is suggested that some degree of consolidation occurred immediately after mobilization possibly induced by the escape of fluids nowhere has failure evolved into disintegration and flow likely because the type of cyclic loading that triggered it was not prolonged over a long enough interval short lived radionuclides in the uppermost stratigraphic layers which postdate the failure in the area offshore ortona allowed us to quantify systematic changes in sediment accumulation rates as a func tion of the underlying deformed sea floor in areas of wavy sea floor troughs show sediment accumulation rates of greater than 16 mm yr a figure that is fourfold the rate measured on the flanks of the troughs

a new estimate for present day cocos caribbean plate motion implications for slip along the central american volcanic arc velocities from 153 continuously operatinggps sites on the caribbean north american and pacic plates arecombinedwith61newlyestimatedpacic cocosseafloor spreading rates and additional marine geophysical data to deriveanewestimate of present daycocos caribbean plate motion acomparisonofthepredictedcocos caribbean di rectiontoslipdirectionsofnumerousshallow thrustsubduc tion earthquakes from the middle america trench between costa rica and guatemala shows the slip directions to be deflected 10 clockwise from the plate convergence direc tion supporting thehypothesisthatfrequentdextralstrike slip earthquakes along the central american volcanic arc result from partitioning of oblique cocos caribbean plate convergence linear velocity analysis for forearc locations in nicaragua and guatemala predicts 14 2m m yr 1 of northwestward trench parallel slip of the forearc relative to thecaribbean plate possibly decreasing inmagnitude inel salvador and guatemala where extension east of the vol canic arc complicates the tectonic setting

seafloor undulation pattern on the adriatic shelf and comparison to deep water sediment waves abstract on the adriatic shelf a large field of seafloor and subsurface undulations typically 300 m wide 2 5 m high and several km long parallel to the bathymetric contour affects the progradational clinoforms of the late holocene prodelta wedge above a regional downlap surface that shows evidence of deformation and fluid escape the undulations are associated with mud reliefs that occur farther seaward in elongated swarms perpendicular to the regional slope and to the crests of the undulations a quantitative measurement of key morphobathymetric parameters such as wavelength height asymmetry and wave form indexes was performed on 13 selected seismic reflection profiles perpendicular to the undulations these measurements are determined with respect to water depth or downslope distance from the shallowest undulation the results highlight substantial differences from deep water sediment waves these differences include 1 most undulations show a staircase morphology with sub horizontal upslope limbs of 100 300 m delimited seaward by sharp edges and steep downslope limbs 2 landward or upslope dipping limbs do not develop 3 there is no consistent downslope decrease in wavelength or amplitude as opposed to most cases of sediment waves related to overflowing turbidity currents 4 there is a consistent downslope loss in crest continuity approaching areas where mud reliefs and sediment deformation are evident at the seafloor 5 many of the undulations show differences in angle of climb and in some cases a single undulation at the seafloor results from the burial and merger of more undulations in the underlying section these differences compared to bottom current or turbidity current sediment waves are augmented by the observation that the adriatic shallow water undulations are also typically associated with gas charged sediment fluid escape sediment deformation and localised failure planes it is therefore suggested that seafloor undulations evolved in response to sediment deformation and were successively amplified by differential deposition from bottom currents crossing an irregular seafloor in general we feel that case by case solutions should be found to explain the origin and evolution of seafloor wavy features based on the geologic stratigraphic setting the recognition of possible weak layers and the co existence of a variety of other deformation geometries that may occur within or adjacent to the field of wavy features the adriatic example can reinforce recent suggestions that besides purely depositional bedforms there exist also wave like deformation structures and multi process sediment waves faugeres et al 2002 multi process generated sediment waves on the landes plateau bay of biscay north atlantic marine geology 182 279 302

sediment undulations on the llobregat prodelta signs of early slope instability or sedimentary bedforms a field of sediment undulations has been mapped by means of high resolution multibeam bathymetry and seismic reflection profiles in the llobregat river prodelta off the city of barcelona catalonia spain similar features had previously been recognized in other prodelta environments and interpreted either as downslope sediment deformation or sedimentary structures induced by bottom currents or hyperpycnal flows since the study area is undergoing significant offshore development proper interpretation of such sediment undulations is needed for a correct risk assessment the occurrence of the sedi ment undulations is restricted to the prodelta front on slope gradients between 3 and 0 2o the undulations have developed at the edge and atop an area of gas bearing sediments within the late holocene high stand mud wedge an evaluation is made of the character istics of the sediment undulations in order to determine the most likely process for the origin of these structures amongst these characteristics are the continuity of the reflec tions and lack of diffractions in between different undulations their size distribution large to small both from shallow to deep and with depth in section the asymmetry de creasing from proximal to distal the crest to trough vertical distance on the landward side of the undulations up to 0 5 m and the lack of features that could indicate a pro gressive movement such as growth structures and drag folds these characteristics indi cate that the sediment undulations on the llobregat river prodelta do not result from sediment deformation but rather from the interaction of bottom currents generated by hyperpycnal flows from the llobregat river with regional sea water circulation their identification as sediment waves implies that such features do not pose a major hazard for further offshore development

a newly recognized type of slickenside striation abstract this note summarizes current views on the origin of slickenside striations and points to the existence of a type of striation not readily explained by established genetic ideas such striations have been seen on fault surfaces in naturally deformed shale and in experimentally deformed paraffin wax they are defined by arrays of shallow slip parallel ridges and grooves of millimetric width and below on any given slip surface the ridges are as common as the grooves and display similar dimensions and profile shapes across any pair of slip surfaces in contact at the end of faulting ridges protruding from one surface fit into or nest with grooves on the other surface the origin of these features is not yet understood

the origin and evolution of skarn forming fluids from the phu lon deposit northern loei fold belt thailand evidence from fluid inclusion and sulfur isotope studies abstract the phu lon skarn cu au deposit is located in the northern loei fold belt lfb thailand it is hosted by devonian volcano sedimentary sequences intercalated with limestone and marble units intruded by diorite and quartz monzonite porphyries phu lon is a calcic skarn with both endoskarn and exoskarn facies in both skarn facies andradite and diopside comprise the main prograde skarn minerals whereas epidote chlorite tremolite actinolite and calcite are the principal retrograde skarn minerals four types of fluid inclusions in garnet were distinguished 1 liquid rich inclusions 2 daughter mineral bearing inclusions 3 salt saturated inclusions and 4 vapor rich inclusions epidote contains only one type of fluid inclusion liquid rich inclusions fluid inclusions associated with garnet prograde skarn stage display high homogenization temperatures and moderate salinities 421 6 468 5 c 17 4 23 1 wt nacl equiv by contrast fluid inclusions associated with epidote retrograde skarn stage record lower homogenization temperatures and salinities 350 9 399 8 c 0 5 8 wt nacl equiv these data suggest a possible mixing of saline magmatic fluids with external dilute fluid sources e g meteoric fluids as the system cooled some fluid inclusions in garnet contain hematite daughters suggesting an oxidizing magmatic environment sulfur isotope determinations on sulfide minerals from both the prograde and retrograde stages show a uniform and narrow range of 34 s values 2 6 to 1 1 34 s suggesting that the ore forming fluid contained sulfur of orthomagmatic origin overall the phu lon deposit is interpreted as an oxidized cu au skarn based on the mineralogy and fluid inclusion characteristics

preferential mode of gas invasion in sediments grain scale mechanistic model of coupled multiphase fluid flow and sediment mechanics 1 we present a discrete element model for simulating at the grain scale gas migration in brine saturated deformable media we rigorously account for the presence of two fluids in the pore space by incorporating forces on grains due to pore fluid pressures and surface tension between fluids this model which couples multiphase fluid flow with sediment mechanics permits investigation of the upward migration of gas through a brine filled sediment column we elucidate the ways in which gas migration may take place 1 by capillary invasion in a rigid like medium and 2 by initiation and propagation of a fracture we find that grain size is the main factor controlling the mode of gas transport in the sediment and we show that coarse grain sediments favor capillary invasion whereas fracturing dominates in fine grain media the results have important implications for understanding vent sites and pockmarks in the ocean floor deep subseabed storage of carbon dioxide and gas hydrate accumulations in ocean sediments and permafrost regions our results predict that in fine sediments hydrate will likely form in veins following a fracture network pattern and the hydrate concentration will likely be quite low in coarse sediments the buoyant methane gas is likely to invade the pore space more uniformly in a process akin to invasion percolation and the overall pore occupancy is likely to be much higher than for a fracture dominated regime these implications are consistent with laboratory experiments and field observations of methane hydrates in natural systems

kinematics of the western caribbean collision of the cocos ridge and upper plate deformation subduction of the cocos plate and collision of the cocos ridge have profound effects on the kinematics of the western caribbean including crustal shortening segmentation of the overriding plate and tectonic escape of the central american fore arc cafa tectonic models of the panama region pr have ranged from a rigid block to a deforming plate boundary zone recent expansion of gps networks in panama costa rica and colombia makes it possible to constrain the kinematics of the pr we present an improved kinematic block model for the western caribbean using this improved gps network to test a suite of tectonic models describing the kinematics of this region the best fit model predicts an euler vector for the counterclockwise rotation of the cafa relative to the caribbean plate at 89 10 w 7 74 n 1 193 ma 1 which is expressed as northwest directed relative block rates of 11 3 1 0 16 5 1 1 mm a 1 from northern costa rica to guatemala this model also predicts high coupling along the nicoya and osa segments of the middle american subduction zone our models demonstrate that the pr acts as a single tectonic block the panama block with a predicted euler vector of 107 65 w 26 50 n 0 133 ma 1 this rotation manifests as northeast migration of the panama block at rates of 6 9 4 0 7 8 4 8 mm a 1 from southern costa rica to eastern panama we interpret this motion as tectonic escape from cocos ridge collision redirected by collision with the north andes block which migrates to the northwest at 12 2 1 2 mm a 1

fluid inclusion and h o isotope evidence for immiscibility during mineralization of the yinan au cu fe deposit shandong china abstract the fluid inclusion and h o isotope studies have provided the evidences for the source of ore forming fluids and helped to recognize two types of immiscibility and their relationships with mineralization hydrogen and oxygen isotopic geochemistry shows that the earlier ore forming fluids during the anhydrous skarn stage i and the hydrous skarn magnetite stage ii were mainly derived from magmatic water while the later fluids during the quartz sulfide stage iii and the carbonate stage iv were mainly from magmatic water mixed with small amounts of meteoric water various types of fluid inclusions including abundant vapor or liquid rich two phase aqueous inclusions daughter minerals bearing multiphase inclusions co2 h2o inclusions and less abundant liquid inclusions vapor inclusions and melt inclusions are present in hydrothermal minerals of different stages the liquid vapor fluid inclusions are mainly composed of h2o with significant amounts of co2 and a small amount of ch4 in the opaque bearing fluid inclusions the hematite and fahlore tetrahedrite were identified the homogenization temperature of the aqueous fluid inclusions decreases from stage i 520 410 c through stage ii 430 340 c and iii 250 190 c to stage iv 190 130 c the coexistence of melt inclusions with simultaneously trapped vapor or liquid rich two phase aqueous inclusions and daughter minerals bearing multiphase inclusions in garnet diopside and epidote of stages i and ii suggests an immiscibility between silicate melt and hydrothermal fluid it is an effective mechanism on scavenging and transporting ore forming components from magmas the aqueous fluid inclusions with various vapor liquid ratios from 65 commonly coexist with simultaneously trapped liquid inclusions vapor inclusions daughter minerals bearing multiphase inclusions and co2 h2o inclusions in the quartz of stage iii and the different kinds of the fluid inclusions have similar homogenization temperatures this indicates that the boiling another kind of immiscibility widely took place during stage iii it resulted in the precipitation and enrichment of gold copper and iron

bubble growth and rise in soft sediments the mechanics of uncemented soft sediments during bubble growth are not widely understood and no rheological model has found wide acceptance we offer definitive evidence on the mode of bubble formation in the form of x ray computed tomographic images and comparison with theory natural and injected bubbles in muddy cohesive sediments are shown to be highly eccentric oblate spheroids disks that grow either by fracturing the sediment or by reopening preexisting fractures in contrast bubbles in soft sandy sediment tend to be spherical suggesting that sand acts fluidly or plastically in response to growth stresses we also present bubble rise results from gelatin a mechanically similar but transparent medium that suggest that initial rise is also accomplished by fracture given that muddy sediments are elastic and yield by fracture it becomes much easier to explain physically related phenomena such as seafloor pockmark formation animal burrowing and gas buildup during methane hydrate melting

correlation of shape and size of methane bubbles in fine grained muddy aquatic sediments with sediment fracture toughness abstract gassy sediments contribute to destabilization of aquatic infrastructure air pollution and global warming in the current study a precise shape and size of the buoyant mature methane bubble in fine grained muddy aquatic sediment is defined by numerical and analytical modeling their results are in a good agreement a closed form analytical solution defining the bubble parameters is developed it is found that the buoyant mature bubble is elliptical in its front view and resembles an inverted tear drop in its cross section the size and shape of the mature bubble strongly correlate with sediment fracture toughness bubbles formed in the weaker sediments are smaller and characterized by a larger surface to volume ratio that induces their faster growth and may lead to their faster dissolution below the sediment water interface this may prevent their release to the water column and to the atmosphere shapes of the bubbles in the weaker sediments deviate further from the spherical configuration than those in the stronger sediments modeled bubble characteristics important for the acoustic applications are in a good agreement with field observations and lab experiments

episodic fluid evolution in the formation of the large scale luoyang fe deposit fujian eastern china abstract the luoyang fe skarn deposit is located in the yong an meizhou depression belt in fujian province eastern china skarn alteration and mineralization are concentrated in a zone adjacent to an early yanshanian granite porphyry 146 ma within limestone of the upper carboniferous chuanshan and lower permian qixia formations petrographic observations reveal five paragenetic stages of skarn formation and ore deposition stage 1 early skarn andradite stage 2 diopside magnetite stage 3 late skarn actinolite chlorite tremolite magnetite pyrite stage 4 quartz calcite fluorite pyrite hematite sphalerite galena chalcopyrite and stage 5 calcite quartz we analyzed fluid inclusions in garnet diopside calcite and quartz from stages 1 2 4 and 5 and measured h o isotopic compositions of fluid inclusions in garnet magnetite and quartz from stages 1 2 and 4 observations of fluid compositions and phase assemblages allow three types and two subtypes of fluid inclusions to be distinguished halite bearing type 1a and hematite bearing type 1b vapor rich type 2 and liquid rich aqueous inclusions type 3 in stage 1 garnet contains type 1a 1b and 2 primary fluid inclusions which comprise two immiscible phases that formed through boiling in stage 2 diopside contains type 1a and 2 fluid inclusions that also record boiling which resulted in the precipitation of magnetite in stage 4 quartz contains type 3 primary inclusions that are related to sulfide mineralization in stage 5 calcite and quartz contain type 3 fluid inclusions which represent the post sulfide mineralization fluids microthermometric and h o isotopic data indicate that multiple episodes of fluid flow occurred in the luoyang deposit during the early skarn stage an initial supercritical fluid that exsolved during crystallization of the parent granitic magma ascended and underwent a first boiling event at 488 c 536 c and 380 438 bar lithostatic pressure which produced two fluids with differing salinities represented by type 1a and 2 inclusions this stage of boiling resulted in minor magnetite precipitation and type 1b fluid inclusions associated with this stage contain hematite the magnetite stage was associated with a second episode of fluid ascent as the parent magma cooled to 454 c 498 c which triggered a second boiling event and abundant magnetite precipitation at 336 449 bar lithostatic pressure the sulfide stage is associated to a third period of fluid ascent and occurred at 220 c 261 c at the same pressure conditions as the second boiling event 380 bar this stage included the input of meteoric water which resulted in sulfide precipitation late stage carbonate crystallization involved the influx of further meteoric water at lower temperatures 144 c 193 c and the same pressure 380 bar representing the collapse of the skarn system these observations suggest that the luoyang deposit formed at a shallower depth than the makeng deposit which is located within the same belt variations in skarn alteration and magnetite mineralization are ascribed to the difference in depth between the two skarn systems

formation of the vysoka zlatno cu au skarn porphyry deposit slovakia the central zone of the miocene stiavnica stratovolcano hosts several occurrences of cu au skarn porphyry mineralisation related to granodiorite quartz diorite porphyry dyke clusters and stocks vysoka zlatno is the largest deposit 13 4 mt at 0 52 cu with mineralised mg ca exo and endoskarns developed at the prevolcanic basement level the alteration pattern includes an internal k and na ca silicate zone surrounded by phyllic and argillic zones laterally grading into a propylitic zone fluid inclusions in quartz veinlets in the internal zone contain mostly saline brines with 31 70 wt nacl eq and temperatures of liquid vapour homogenization th of 186 575 c indicating fluid heterogenisation garnet contains inclusions of variable salinity with 1 31 wt nacl eq and th of 320 360 c quartz chalcopyrite veinlets host mostly low salinity fluid inclusions with 0 3 wt nacl eq and th of 323 364 c data from sphalerite from the margin of the system indicate mixing with dilute and cooler fluids the isotopic composition of fluids in equilibrium with k alteration and most skarn minerals both prograde and retrograde indicates predominantly a magmatic origin 18ofluid 2 5 12 3 with a minor meteoric component corresponding low dfluid values are probably related to isotopic fractionation during exsolution of the fluid from crystallising magma in an open system the data suggest the general pattern of a distant source of magmatic fluids that ascended above a zone of hydraulic fracturing below the temperature of ductile brittle transition the magma chamber at 5 6 km depth exsolved single phase fluids whose properties were controlled by changing pt conditions along their fluid paths during early stages ascending fluids display liquid vapour immiscibility followed by physical separation of both phases low salinity liquid associated with ore veinlets probably represents a single phase magmatic fluid magmatic vapour which contracted into liquid upon its ascent

contrasting zircon hf and o isotopes in the two episodes of neoproterozoic granitoids in south china implications for growth and reworking of continental crust abstract the genetic links among rift magmatism crustal growth and water rock interaction are an important issue about mass and heat transfer between mantle and crust during supercontinent breakup a combined study of hf and o isotopes in zircons from neoproterozoic granitoids in south china provides evidence for growth and reworking of juvenile and ancient crusts with different styles of water rock interactions along rift tectonic zones two generations of the granitoids show contrasting features in both zircon hf and o isotope compositions indicating their distinct petrogenesis the 825 ma granitoids exhibit negative ehf t values of 3 4 0 8 to 1 6 0 8 with old model hf ages of 1 81 0 07 to 1 92 0 10 ga and high 18o values of 8 7 to 10 4 these indicate that the source material of granitoid magmas was derived from melting of paleoproterozoic basement that has the hf isotope signature similar to the enriched mantle but experienced chemical weathering process before anatexis reworking of ancient crust is demonstrated to occur at 825 ma in the orogenic collapse zone with overprinting of subsolidus hydrothermal alteration during magma emplacement in contrast the 760 750 ma bimodal intrusives are characterized by positive ehf t values of 3 5 0 8 to 9 9 0 8 with young model hf ages of 0 94 0 06 to 1 18 0 06 ga and both low and high 18o values of 4 2 to 6 2 relative to 5 3 0 3 for the normal mantle zircon prompt reworking of juvenile crust is suggested to occur at 750 ma in the rifted tectonic zone with occurrence of supersolidus hydrothermal alteration and local low 18o magmatism during supercontinent breakup contributions of the depleted mantle to their magma sources are contrasting in the two episodes of magmatism in association with breakup of the supercontinent rodinia while the change in melt source from the crust to the mantle keeps pace with the advance from continental rifting to supercontinent breakup significant transport of both heat and material from the depleted mantle to the continental crust only occurred along the active rifting zone in either case the growth and reworking of continental crust are episodically associated with rift magmatism

generation of normal and adakite like calc alkaline magmas in a non subductional environment an sr o h isotopic study of the apuseni mountains neogene magmatic province romania abstract neogene magmatism in the apuseni mountains of romania was active between 15 and 7 ma with an isolated final eruption at 1 6 ma several groups of magmatic rocks can be distinguished in the province on the basis of ages trace elements and isotopic compositions most are of calc alkaline affinity despite the fact that the region is located 200 km from the postulated carpathian subduction trench however adakite like calc alkaline magmas were also erupted and the youngest eruptions were of alkaline affinity magmatic rocks older than 13 5 ma are characterised by the highest 87sr 86sr 18o and d values in their phenocryst phases this early magmatism is considered to be a result of crustal melting related to the fast rotation of small crustal blocks volcanic rocks younger than 13 5 ma have lower 87sr 86sr and 18o ratios with a narrow range for pyroxene and amphibole mineral separates indicating closed system fractional crystallization a larger scatter of 87sr 86sr and 18o values is found in plagioclase phenocrysts and groundmasses indicating that a small amount of crustal assimilation also occurred the d values for hydrogen bearing phases such as amphibole biotite and groundmass indicate fractional crystallisation in a closed system and a trend of decreasing d in the source with time the magma source of normal calc alkaline adakite like magmas was not related to contemporaneous subduction but was likely due to melting of delaminated eclogitic mafic lower crust in contrast the late stage alkaline magmas were related to asthenospheric upwelling petrological analysis of the complex succession of magmas in the apuseni mountains province demonstrates that normal calc alkaline and adakite like magmatism can be generated in a non subductional environment in this case associated with an unusual extensional setting

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

fluid accumulation along the costa rica subduction thrust and development of the seismogenic zone in 2011 we acquired an 11 55 km 3 d seismic reflection volume across the costa rica margin nw of the osa peninsula to accurately image the subduction thrust in 3 d to examine fault zone properties and to infer the hydrogeology that controls fluid accumulation along the thrust following processing to remove water column multiples noise and acquisition artifacts we constructed a 3 d seismic velocity model for kirchhoff prestack depth migration imaging images of the plate boundary thrust show high reflection amplitudes underneath the middle to lower slope that we attribute to fluid rich poorly drained portions of the subduction thrust at 5 km subseafloor beneath the upper slope the plate interface abruptly becomes weakly reflective which we interpret as a transition to a well drained subduction thrust mineral dehydration during diagenesis may also diminish at 5 km subseafloor to reduce fluid production and contribute to the downdip change from high to low amplitude there is also a layered fabric and systems of both thrust and normal faults within the overriding plate that form a plumbing system faults commonly have fault plane reflections and are presumably fluid charged the faults and layered fabric form three compartmentalized hydrogeologic zones 1 a shallow ne dipping zone beneath the slope 2 a steeply sw dipping zone beneath the shelf slope break and 3 a ne dipping zone beneath the shelf the more direct pathway in the middle zone drains the subduction thrust more efficiently and contributes to reduced fluid pressure elevates effective stress and creates greater potential for unstable coseismic slip

seismogenic zone structure of the southern middle america trench costa rica 1 the shallow seismogenic portion of subduction zones generates damaging large and great earthquakes this study provides structural constraints on the seismogenic zone of the middle america trench offshore central costa rica and insights into the physical and mechanical characteristics controlling seismogenesis we have located 300 events that occurred following the mw 6 9 20 august 1999 quepos costa rica underthrusting earthquake using a three dimensional velocity model and arrival time data recorded by a temporary local network of land and ocean bottom seismometers we use aftershock locations to define the geometry and characteristics of the seismogenic zone in this region these events define a plane dipping at 19 that marks the interface between the cocos plate and the panama block the majority of aftershocks occur below 10 km and above 30 km depth below sea level corresponding to 30 35 km and 95 km from the trench axis respectively relative event relocation produces a seismicity pattern similar to that obtained using absolute locations increasing confidence in the geometry of the seismogenic zone the aftershock locations spatially correlate with the downdip extension of the oceanic quepos plateau and reflect the structure of the main shock rupture asperity this strengthens an earlier argument that the 1999 quepos earthquake ruptured specific bathymetric highs on the downgoing plate we believe that subduction of this highly disrupted seafloor has established a set of conditions which presently limit the seismogenic zone to be between 10 and 35 km below sea level

evidence for magmatic hydrothermal fluids and ore forming processes in epithermal and porphyry deposits of the baguio district philippines the baguio district contains a diverse array of epithermal porphyry and skarn deposits together with a large broadly strata bound advanced argillic lithocap magmatism mineralization and alteration occurred in response to subduction of the south china sea plate and the scarborough ridge beneath northern luzon over the past 3 m y rapid uplift and exhumation resulted in epithermal veins overprinting several porphyry cu au deposits most of the epithermal au ag deposits of the baguio district including antamok and acupan the two largest au deposits are intermediate sulfidation state quartz carbonate adularia illite base metal sulfide veins that contain electrum and minor au ag tellurides in contrast high sulfidation mineralization at kelly includes enargite tennantite electrum and precious metal tellurides and is associated with advanced argillic alteration although the mineralizing fluids that formed the porphyry and epithermal deposits had distinct temperatures and salinities stable and radiogenic data provide evidence for direct magmatic contributions into each deposit type the epithermal mineralizing fluids were dilute generally 600 c hypersaline brines 30 to 70 wt nacl equiv and low density vapor sulfur isotope compositions of sulfides in the porphyry skarn and intermediate sulfidation epithermal veins of the southern and central baguio district are mostly between 1 and 6 per mil consistent with a predominance of h2s in the mineralizing fluids i e reducing conditions in contrast sulfides from the high sulfidation porphyry and intermediate sulfidation deposits located adjacent to the baguio lithocap mostly have negative sulfur isotope values 6 9 to 0 8 consistent with oxidizing so42 predominant mineralizing fluids intermediate sulfidation epithermal veins at acupan have crosscut a well mineralized porphyry cu au stock work at ampucao the two deposits cannot be distinguished on the basis of radiometric age determinations ampucao 0 51 0 26 ma acupan 0 65 0 07 ma and are interpreted to be cogenetic with telescoping of the two environments caused by the rapid uplift and exhumation associated with ridge subduction measured 34ssulfide 1 1 to 6 6 34ssulfate 10 4 to 31 8 values and initial strontium ratios of anhydrite 0 70378 0 70385 are consistent with identical and predominantly magmatic sources of these components for the ampucao porphyry and acupan epithermal veins helium isotopes provide further evidence of mantle derived components in the epithermal veins r ra values of 6 0 and 6 7 oxygen deuterium and carbon isotopes provide evidence for predominantly magmatic water at ampucao and for hybrid magmatic meteoric waters at acupan that precipitated precious metals due to boiling the proportion of magmatic water relative to meteoric water and precious metal grades both decreased with time during epithermal vein formation at acupan the common observation of cross cutting relationships between porphyry and epithermal veins observed throughout the baguio district imply that the evolution of porphyry style to intermediate sulfidation style mineralization was a common phenomenon in this region and contributed significantly to its rich metal endowment

a groove ploughing theory for the production of mega scale glacial lineations and implications for ice stream mechanics mega scale glacial lineations msgls are longitudinally aligned corrugations ridge groove structures 6 100 km long in sediment produced subglacially they are indicators of fast flow and a common signature of ice stream beds we develop a qualitative theory that accounts for their formation and use numerical modelling and observations of ice stream beds to provide supporting evidence ice in contact with a rough scale of 10 10 3 m bedrock surface will mimic the form of the bed because of flow acceleration and convergence in ice stream onset zones the ice base roughness elements experience transverse strain transforming them from irregular bumps into longitudinally aligned keels of ice protruding downwards where such keels slide across a soft sedimentary bed they plough through the sediments carving elongate grooves and deforming material up into intervening ridges this explains msgls and has important implications for ice stream mechanics groove ploughing provides the means to acquire new lubricating sediment and to transport large volumes of it downstream keels may provide basal drag in the force budget of ice streams thereby playing a role in flow regulation and stability we speculate that groove ploughing permits significant ice stream widening thus facilitating high magnitude ice discharge

mobility and h2o loss from fluid inclusions in natural quartz crystals petrographic observations on quartz crystals from the mole granite australia and other localities shed new light on the mechanisms of post entrapment modification of fluid inclusions these modifications include migration away from pseudosecondary trails changes in fluid salinity and density shape distortion and the formation of sweat haloes around strongly deformed inclusions increases in fluid salinity which usually are associated with inclusion migration indicate water losses of up to 50 however la icp ms analysis of unmobilized and mobilized inclusions of the same trail reveals basically unchanged ratios of major and trace element cations with the exception of li which seems to be incorporated into the crystal lattice during migration despite the fact that all these modifications are closely related to deformation processes they occur not only in mechanically deformed quartz but also in free standing crystals in the latter samples stress has been generated internally as a result of brazil twinned growth and compositional zonation these observations and their interpretation leads to a list of practical criteria that should help in differentiating between reliable and suspect fluid inclusions in other samples

diagenetic relationships of methanogenesis nutrients acoustic turbidity pockmarks and freshwater seepages in eckernforde bay abstract high organic loading 4 5 wt and sedimentation rates 1 4 mm yr 1 in eckernforde bay sediments lead to anaerobic conditions within the uppermost 15 cm intense bacterial sulphate reduction 0 011 0 15 mm so 4 red 2 yr 1 exhausts dissolved sulphate around 150 cm sediment depth resulting in methanogenesis at greater sediment depth by carbonate reduction 1 8 8 5 m ch 4 yr 1 extensive regions of eckernforde bay are characterized by acoustically turbid sediments 300 cm sediment depth resulting from deeper sediments supersaturated in methane forming free gas accumulation zones methane migrating upward into the sulphate reduction zone is effectively consumed by sulphate reducing bacteria at rates 3 10 times greater than methanogenesis i e 46 95 m ch 4 ox yr 1 the pathways of methane formation and anaerobic oxidation are confirmed by stable carbon and hydrogen isotope evidence pockmarks i e shallow surface depressions in some eckernforde bay sediments are not associated with gas ebullition rather these physical features result from the expulsion of freshwater these episodic springs or seepages of groundwater from the underlying holocene glacial lags and sands into the basin at pockmark sites have characteristic low chloride and methane concentrations the geochemical evidence indicates that the commercial accumulation of petroleum in the lower cretaceous dogger beta hauptsandstein schwedeneck field in eckernforde bay 1500 mbsf has no surface manifestation and does not influence either the occurrence of acoustic turbidity or pockmarks

genesis and magmatic hydrothermal evolution of the yangla skarn cu deposit southwest china the yangla skarn cu deposit 150 mt at 1 03 cu is located in the central segment of the jinshajiang metallogenic belt within the sanjiang three rivers region southwest china skarn orebodies are mainly developed between different units of devonian carbonate and quartz sandstone rocks with stratiform like shapes or within the contact zone between granitoids and marbles re os dating of molybdenite intergrowth with chalcopyrite yielded a well constrained 187re 187os isochron age of 232 0 1 5 ma with a weighted average age of 231 8 1 3 ma both coeval with the related intrusions 233 1 1 4 and 231 0 1 6 ma at 2 by zircon u pb dating from our previously published work field and textural relationships indicate three hydrothermal stages characterized by assemblages of prograde skarn pre ore stage retrograde skarn and cu fe mo bi sulfides main ore stage and pb zn sulfides associated with calcite and quartz late ore stage as well as one supergene stage marked by secondary cu mineralization malachite and azurite skarns contain garnets with andraditic compositions ad96 gr2 3py0 1 and clinopyroxene two series hd6di94 and hd86di13jo1 with low mn fe ratios 0 1 typical of cu skarn deposits worldwide three stages of fluid evolution were observed by a detailed fluid inclusion study 1 early fluids were trapped under two phase conditions as evidenced by the coexistence of brine homogenization temperatures 560 600 c average salinity 49 4 1 7 wt nacl equiv n 33 and vapor rich inclusions in pre ore stage andradite and diopside trapped at 600 bars or a depth of approximately 2 km assuming lithostatic pressure conditions 2 main ore stage fluid inclusions in quartz were also trapped under two phase conditions boiling as identified by the coexistence of vapor and liquid rich fluid inclusions liquid rich inclusions homogenized between 312 and 389 c average 350 24 7 c n 20 with salinities of 2 4 to 5 6 wt nacl equiv average 4 2 0 9 wt nacl equiv n 13 and a depth of 2 km 200 bars hydrostatic pressure conditions 3 late ore stage fluids are represented by inclusions in calcite characterized by homogenization temperatures ranging from 220 to 290 c average 249 27 c n 14 and salinities between 2 1 and 8 0 wt nacl equiv average 4 6 1 5 wt nacl equiv n 11 sulfur isotope compositions of sulfide minerals pyrite chalcopyrite pyrrhotite and molybdenite from the main and late ore stage have a narrow range of 34s values from 1 9 to 2 6 consistent with a magmatic origin calcite in the late ore stage has 13c values ranging from 3 2 to 5 9 and 18o from 7 2 to 18 0 distinct from the host rock marble compositions 13c 1 2 4 3 18o 10 8 23 9 when corrected for temperature 250 c estimated from fluid inclusion analysis in calcites these calcite data correspond to ore fluid 13cfluid values of 2 0 to 4 6 and 18ofluid values of 0 5 to 11 2 clustering at 10 which are consistent with a magmatic origin lead isotope compositions of sulfides 206pb 204pb 18 273 18 369 207pb 204pb 15 627 15 677 and 208pb 204pb 38 445 39 611 are similar to those of the granitic intrusions and sedimentary wall rocks but distinct from those of basalts 206pb 204pb 18 282 19 133 207pb 204pb 15 564 15 665 and 208pb 204pb 38 367 38 942 in the mining area taken together these geologic geochemical and isotopic data confirm that yangla is a typical cu skarn deposit

fore arc motion and cocos ridge collision in central america 1 we present the first regional surface velocity field for central america showing crustal response to interaction of the cocos and caribbean plates elastic half space models for interseismic strain accumulation on the dipping subduction plate boundary fit the gps data well and show strain accumulation offshore and beneath the nicoya and osa peninsulas in costa rica but not in nicaragua since large subduction zone earthquakes occur in nicaragua we suggest that interseismic locking in nicaragua and some other parts of central america occurs but is mainly shallow 20 km depth too far offshore to be detected by our on land gps measurements our data also show significant trench parallel motion for most of the region generally interpreted as due to oblique convergence and strong mechanical coupling between subducting and overriding plates however trench parallel motion is also observed in central costa rica where plate convergence is normal to the trench and in the nicaraguan fore arc where trench parallel motion is fast up to 9 mm a 1 but mechanical coupling is low a finite element model of collision as opposed to subduction involving the aseismic cocos ridge also fits the gps surface velocity field most significantly reproducing the pattern of trench parallel motion we infer that buoyant thickened cns 2 cocos ridge crust resists normal subduction and instead acts as an indenter to the caribbean plate driving crustal shortening in southern costa rica and contributing to trench parallel fore arc motion in costa rica and perhaps nicaragua as a type of tectonic escape

slickenline orientations as a record of fault rock rheology abstract contact of geometric asperities across rough faults causes perturbations to the shear traction resolved on a fault surface that could potentially deflect the local slip direction slickenlines which record the relative displacement of opposing sides of a fault may therefore be sensitive to fault surface geometry to investigate the relationship between fault geometry shear traction and slip we use ground based lidar to measure the orientations of slickenlines defined by centimeter amplitude corrugations on three fault surfaces slickenline rakes measured in the mean plane of each fault rarely vary by more than a few degrees deviations from the mean rake do not correlate with the fault surface topography at scales up to a few meters but a weak correlation may be present at larger scales slip directions are therefore insensitive to any shear traction perturbations from the contact of geometric asperities at small scales this observation is consistent with scale dependent deformation we show that the roughness of fault surfaces implies that short wavelength asperities fail inelastically because of flattening during fault slip a crossover to elastic deformation occurs at lengths of 10 2 to 10 0 m which defines the minimum dimension of a strength asperity that influences the displacement field the roughness at the crossover length scale corresponds to the typical thickness of fault rocks in the fault core suggesting that fault rock thickness is related to the crossover length scale the data requires that multiple processes combine to produce the fault surface geometry we reconcile the variety of processes with the consistent surface roughness scaling by noting that all of the processes are governed in different ways by the elastic limit of rock

size shape and spatial arrangement of mega scale glacial lineations from a large and diverse dataset mega scale glacial lineations msgls are a characteristic landform on ice stream beds solving the puzzle of their formation is key to understanding how ice interacts with its bed and how this in turn influences the dynamics of ice streams however a comprehensive and detailed characterization of this landform s size shape and spatial arrangement which might serve to test and refine formational theories is largely lacking this paper presents a detailed morphometric analysis and comparison of 4043 msgls from eight palaeo ice stream settings three offshore norway and antarctica four onshore canada and one from under a modern ice stream in west antarctica the length of msgls is lower than previously suggested mode 1000 2000 m median 2892 m and they initiate and terminate at various locations on an ice stream bed their spatial arrangement reveals a pattern that is characterized by an exceptional parallel conformity 80 of all mapped msgls have an azimuth within 5 from the mean values and a fairly constant lateral spacing mode 200 300 m median 330 m which we interpret as an indication that msgls are a spatially self organized phenomenon results show that size shape and spatial arrangement of msgls are consistent both within and also generally between different ice stream beds we suggest this results from a common mechanism of formation which is largely insensitive to local factors although the elongation of msgls mode 6 8 median 12 2 is typically higher than features described as drumlins these values and those of their width mode 100 200 m median 268 m overlap which suggests the two landforms are part of a morphological continuum and may share a similar origin we compare their morphometry with explicit predictions made by the groove ploughing and rilling instability theories of msgl formation although the latter was most compatible neither is fully supported by observations 2014 the authors earth surface processes and landforms published by john wiley sons ltd

interplate seismicity at the crisp drilling site the 2002 mw 6 4 osa earthquake at the southeastern end of the middle america trench we investigate potential relations between variations in seafloor relief and age of the incoming plate and interplate seismicity westward from osa peninsula in costa rica a major change in the character of the incoming cocos plate is displayed by abrupt lateral variations in seafloor depth and thermal structure here a mw 6 4 thrust earthquake was followed by three aftershock clusters in june 2002 initial relocations indicate that the main shock occurred fairly trenchward of most large earthquakes along the middle america trench off central costa rica the earthquake sequence occurred while a temporary network of obh and land stations 80 km to the northwest were deployed by adding readings from permanent local stations we obtain uncommon p wave coverage of a large subduction zone earthquake we relocate this catalog using a nonlinear probabilistic approach within both a 1 d and a 3 d p wave velocity models the main shock occurred 25 km from the trench and probably along the plate interface at 5 10 km depth we analyze teleseismic data to further constrain the rupture process of the main shock the best depth estimates indicate that most of the seismic energy was radiated at shallow depth below the continental slope supporting the nucleation of the osa earthquake at 6 km depth the location and depth coincide with the plate boundary imaged in prestack depth migrated reflection lines shot near the nucleation area aftershocks propagated downdip to the area of a 1999 mw 6 9 sequence and partially overlapped it the results indicate that underthrusting of the young and buoyant cocos ridge has created conditions for interplate seismogenesis shallower and closer to the trench axis than elsewhere along the central costa rica margin

the mineralization age of the makeng fe deposit south china implications from u pb and sm nd geochronology the makeng fe deposit is located in the southwestern fujian district south china the sm nd isochron ages of seven samples of pure garnet and five of pure magnetite separates from the makeng ores yielded an isochron age of 157 15 ma laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb dating of the nearby exposed the dayang juzhou dj porphyritic biotite granite and fine grained syenogranite yielded 206pb 238u ages of 140 2 1 1 and 140 1 1 0 ma respectively these results suggest that the intrusion of the dj granite and the makeng skarn alterations and fe mineralization are contemporaneous the dj granite exhibits geochemical characteristics of a type granites including high values of na2o k2o 8 13 8 92 wt feot mgo 3 4 21 5 and ga al 2 64 3 45 10 4 and low al2o3 10 71 13 29 wt value chondrite normalized rare earth element patterns are characterized by obviously negative eu anomalies eu 0 02 0 28 and primitive mantle normalized spidergrams show the enrichment in high field strength element and depleting in sr ti ba and eu the geochemical characteristics of dj granite suggest that the granite was derived from partial melting of the paleoproterozoic metasedimentary rocks of the cathaysia basement and some underplating of mafic magma in the lower tholeiitic crust and or depleted mantle might be involved and provide the heat source for the partial melting the dj granite also fits the spatiotemporal distribution of the jurassic cretaceous coastward migration of both extensional and arc related magmatism and fills the a type granites gap in the early stage of the early cretaceous 145 125 ma therefore it is suggested that the late jurassic and early cretaceous magmatism in southwestern fujian district were generated in an extensional environment responding to the slab rollback and concomitant retreating arc system of the paleo pacific plate within the south china block and the fe metallogeny in southwestern fujian district is genetically linked with the magmatism during this period

formation of mega scale glacial lineations observed beneath a west antarctic ice stream most discharge from large ice sheets takes place through fast flowing ice streams and their speed is strongly modulated by interactions between the ice and the underlying sediments seismic surveys and investigations through boreholes have revealed a spatial association between fast ice flow and saturated deformable sediments nevertheless our knowledge of the morphology of the interface between ice and sediments is still limited resulting in only rudimentary understanding of the basal boundary conditions beneath ice streams and the generation of subglacial bedforms here we present radar data from the bed of a west antarctic ice stream that reveal the presence of mega scale glacial lineations we combine these data with previously published seismic data and show that these lineations develop in areas of dilatant deforming till and are part of a dynamic sedimentary system that undergoes significant change by erosion and deposition on decadal timescales we find that the mega scale glacial lineations are indistinguishable from those found on beds of palaeo ice streams providing conclusive evidence for the hypothesis that highly elongate bedforms are a characteristic of fast flow regions in ice sheets

composition and evolution of ore fluids in a magmatic hydrothermal skarn deposit the chemistry of brine vapor and low salinity fluid inclusions measured by proton induced x ray emission from the bismark skarn deposit mexico is consistent with an evolving magmatic hydrothermal system with no evidence for external fluid inputs the results support a model that invokes early phase separation of magmatic fluids into brine and vapor two phase field at high temperature and lithostatic pressure followed by the entrapment of a low salinity magmatic fluid one phase field at lower temperature and hydrostatic pressure the early brine and vapor inclusions contain high pb and zn concentrations and low cu however the vapor contains significantly more cu than the brine and was likely transported as a sulfur complex the fluid phase changes observed and behavior of cu are comparable to those of porphyry cu systems the later low salinity fluid at bismark represents a distinct pulse of magmatic fluid with a high k ca ratio in which base metals including cu were transported by chloride complexes paragenetic relationships and variations in the relative concentrations of cu pb and zn suggest that this fluid was primarily responsible for ore deposition the relative cu pb and zn concentrations in fluid inclusions at bismark are consistent with those measured from base metal ores in high temperature carbonate replacement deposits throughout mexico and suggest that the bulk metal budget of these deposits is primarily controlled by magmatic hydrothermal fluids deficient in cu

metallogenic model of the trepca pb zn ag skarn deposit kosovo evidence from fluid inclusions rare earth elements and stable isotope data the trepca pb zn ag skarn deposit 29 mt of ore at 3 45 pb 2 30 zn and 80 g t ag is located in the kopaonik block of the western vardar zone kosovo the mineralization hosted by recrystallized limestone of upper triassic age was structurally and lithologically controlled ore deposition is spatially and temporally related with the postcollisional magmatism of oligocene age 23 26 ma the deposit was formed during two distinct mineralization stages an early prograde closed system and a later retrograde open system stage the prograde mineralization consisting mainly of pyroxenes hd54 100jo0 45di0 45 resulted from the interac tion of magmatic fluids associated with oligocene 23 26 ma postcollisional magmatism whereas there is no direct contact between magmatic rocks and the mineralization the deposit is classified as a distal pb zn ag skarn abundant pyroxene reflects low oxygen fugacity 10 31 bar and anhydrous environment fluid inclu sion data and mineral assemblage limit the prograde stage within a temperature range between 390 and 475 c formation pressure is estimated below 900 bars isotopic composition of aqueous fluid inclusions hosted by hedenbergite d 108 to 130 18o 7 5 8 0 mn enriched mineralogy and high ree content of the host carbonates at the contact with the skarn mineralization suggest that a magmatic fluid was modified during its infiltration through the country rocks the retrograde mineral assemblage comprises ilvaite magnetite arsenopyrite pyrrhotite marcasite pyrite quartz and various carbonates increases in oxygen and sulfur fugacities as well as a hydrous character of min eralization require an open system model the opening of the system is related to phreatomagmatic explosion and formation of the breccia arsenopyrite geothermometer limits the retrograde stage within the temperature range between 350 and 380 c and sulfur fugacity between 10 8 8 and 10 7 2 bars the principal ore minerals galena sphalerite pyrite and minor chalcopyrite were deposited from a mod erately saline ca na chloride fluid at around 350 c according to the isotopic composition of fluid inclusions hosted by sphalerite d 55 to 74 18o 9 6 to 13 6 the fluid responsible for ore deposition was dominantly meteoric in origin the 34s values of the sulfides spanning between 5 5 and 10 point to a magmatic origin of sulfur ore deposition appears to have been largely contemporaneous with the retrograde stage of the skarn development postore stage accompanied the precipitation of significant amount of carbonates including the travertine deposits at the deposit surface mineralogical composition of travertine varies from calcite to siderite and all carbonates contain significant amounts of mn decreased formation temperature and depletion in the ree content point to an influence of ph neutralized cold ground water and dying magmatic system

geochemistry mineralogy and genesis of the ayazmant fe cu skarn deposit in ayvalik balikesir turkey abstract the ayazmant fe cu skarn deposit is located approximately 20 km se of ayvalik or 140 km n of izmir in western turkey the skarn occurs at the contact between metapelites and the metabasites of the early triassic kinik formation and the porphyritic hypabyssal intrusive rocks of the late oligocene kozak intrusive complex the major trace and rare earth element geochemical analysis of the igneous rocks indicate that they are i type subalkaline calc alkaline metaluminous i type products of a high level magma chamber generated in a continental arc setting the 40 ar 39 ar isochron age obtained from biotite of hornfels is 20 3 0 1 ma probably reflecting the age of metamorphic bimetasomatic alteration which commenced shortly after intrusion into impure carbonates three stages of skarn formation and ore development are recognized 1 early skarn stage stage i consisting mainly of garnet with grossular rich gr 75 79 cores and andradite rich gr 36 38 rims diopside di 94 97 scapolite and magnetite 2 sulfide rich skarn stage ii dominated by chalcopyrite with magnetite andraditic garnet ad 84 89 diopside di 65 75 and actinolite and 3 retrograde alteration stage iii dominated by actinolite epidote orthoclase phlogopite and chlorite in which sulfides are the main ore phases 40 ar 39 ar age data indicate that potassic alteration synchronous or postdating magnetite pyroxene amphibole skarn occurred at 20 0 0 1 ma the high pyroxene garnet ratio plus the presence of scapolite in calc silicate and associated ore paragenesis characterized by magnetite hematite chalcopyrite and bornite suggests that the bulk of the ayazmant skarns were formed under oxidized conditions oxygen isotope compositions of pyroxene magnetite and garnet of prograde skarn alteration indicate a magmatic fluid with 18 o values between 5 4 and 9 5 on the basis of oxygen isotope data from mineral pairs the early stage of prograde skarn formation is characterized by pyroxene di 94 97 magnetite assemblage formed at an upper temperature limit of 576 c the lower temperature limit for magnetite precipitation is estimated below 300 c on the basis of magnetite calcite pairs either as fracture fillings or massive ore in recrystallized limestone marble the sulfide assemblage is dominated by chalcopyrite with subordinate molybdenite pyrite cubanite bornite pyrrhotite galena sphalerite and idaite gold copper mineralization formed adjacent to andradite dominated skarn which occurs in close proximity to the intrusion contacts native gold and electrum are most abundant in sulfides as fine grained inclusions grain size with varying from 5 to 20 m sulfur isotope compositions obtained from pyrrhotite pyrite chalcopyrite sphalerite and galena form a narrow range between 4 8 and 1 6 suggesting the sulfur was probably mantle derived or leached from magmatic rocks geochemical data from ayazmant shows that cu is strongly associated with au bi te se cd zn pb ni and co the ayazmant mineralizing system possesses all the ingredients of a skarn system either cogenetic with or formed prior to a porphyry cu au mo system the results of this study indicate that the aegean region of turkey has considerable exploration potential for both porphyry related skarns and porphyry cu and au mineralization

mineral chemistry and h o s pb isotopic compositions of skarn type copper deposits in the jiurui district of the middle lower yangtze river metallogenic belt eastern china abstract the skarn type copper deposits are widespread in the jiurui district in the middle lower yangtze river metallogenic belt this paper reports a detailed study on mineral chemistry and h o s and pb isotopic compositions on skarn silicate and sulfide minerals in the three major skarn dominant deposits wushan dongleiwan and dengjiashan the wushan skarn deposit is characterized with prograde garnet dominated and clinopyroxene limited skarns with average andradite content of 83 and hedenbergite content of 10 whereas the dongleiwan and dengjiashan deposits are featured with retrograde skarn alteration with abundant hydrous minerals such as epidote and chlorite the garnet and clinopyroxene compositions show 59 andradite and 15 hedenbergite for the dongleiwan skarns and 43 and 22 for the dengjiashan skarns respectively the pistacite components ps value defined as fe3 fe3 al and fe3 fe2 value of epidote are 0 12 and 1 63 for the wushan skarns 0 30 and 32 73 for the dongleiwan skarns and 0 17 and 42 85 for the dengjiashan skarns it is suggested that the prograde skarn mineralization in the three deposits was all formed in a relatively oxidizing environment with the wushan showing the highest oxidation potential and the dengjiashan having the least oxidation potential however in the retrograde skarns the dongleiwan and dengjiashan deposits show higher oxidation potential than that of wushan the three deposits show similar sulfur isotopic compositions of 2 9 to 1 4 and similar lead isotopic compositions with 206pb 204pb 207pb 204pb and 208pb 204pb ratios of 17 900 to 18 205 15 538 to 15 649 and 38 170 to 39 025 respectively all the three deposits should have similar magmatic origin for the ore forming materials based on their s and pb isotopes the oxygen isotopic compositions of the prograde and retrograde fluids in the three deposits show some differences with 18ofluid values of 8 13 and 7 81 for the wushan 6 47 and 2 33 for the dongleiwan and 8 27 and 4 43 for the dengjiashan but the hydrogen isotopic compositions are similar for the prograde 65 to 31 and retrograde 64 to 33 fluids therefore the fluid origins and evolution may be different in each deposit the hydrothermal fluids for the prograde skarns in all three deposits were likely derived from magmatic hydrothermal sources but the dongleiwan and dengjiashan show a higher proportion of meteoric water input in the retrograde stage considering the similar average prograde temperatures 574 to 560 c as calculated from coexisting garnet clinopyroxene pairs and similar retrograde temperatures 281 to 246 c as calculated from chlorite chemistry for the three deposits we suggest that the trigger for deposition of sulfide ores in the wushan garnet dominated skarn deposit was mainly caused by system cooling with temperature drop along with magmatic intrusion and crystallization process the dongleiwan and dengjiashan skarn deposits constitute a well developed retrograde skarn system with abundant epidote chlorite quartz and calcite which probably caused by fluid mixing of high temperature saline magmatic hydrothermal fluids with cooler oxidizing and dilute meteoric water

fluid inclusions in skarns carbonate replacement deposits fluid inclusions in ore skarn minerals reflect the physiochemical nature of the solutions present during the skarn forming process because of the dense nature of skarn minerals and the dynamic processes operative during skarn genesis sufficient primary fluid inclusions are usually present ore skarn solutions as opposed to metamorphic skarn or ore vein solutions have much higher cacl2 contents and usually very high formation temperatures 500 c and salinities 40 wt t d s temperatures and salinities generally decrease away from the solution source both in time and space the gradients found at greater distances from the source in distal far from contact skarns tend to be less e g 210 350 c for a particular skarn stage to that in proximal near contact skarns e g 400 650 c this information is useful for delineating the parts of such a hydrothermal system temperatures also tend to decrease with time which is reflected by the superimposition of various overprinting retrograde mineral stages in a few areas e g naica mexico intermittent boiling of ore solutions occurs periodically elevating both temperatures and salinities but commonly boiling only occurs early in skarn genesis just after an early commonly lower temperature phase most fluid inclusions represent a mix of exhaust or reacted solutions with minor unreacted or new pre ore solution components limited data on the distribution of elements present in fluid inclusions that do not normally take part in skarn genesis na k and cl indicate that their proportions reflect the nature of the associated pluton high kc1 contents are found in skarns adjacent to high k granitoids whereas high nacl contents are found in skarns adjacent to calcic granitoids in many examples daughter minerals present in minor proportions in opened fluid inclusion cavities reflect the metal characteristics of the ore solution small rare earth metal tungsten zinc and copper daughter minerals have been identified the temperature and or salinity data for skarns of different metal or geological type is not particularly useful to delineate whether a skarn locality is part of a more complex as yet unexplored system solutions in pb zn skarns tend to be lower temperature 150 400 c and more dilute 30 wt t d s than in other skarn types but exceptions occur

iron transport and deposition mechanisms in the taochong iron rich skarn deposit middle lower yangtze valley eastern china abstract the taochong skarn iron deposit is one of 38 iron prospects in the fanchang iron ore district of the middle lower yangtze river valley one of the most important economic mineral districts in china orebodies are hosted mainly within the middle upper carboniferous huanglong dolomitic limestone in this deposit two types of ore types 1 and 2 are recognized based on the mineral assemblage the type 1 ore is dominant throughout the deposit and consists mainly of hematite magnetite quartz and calcite this ore is characterized by euhedral and skeletal textures and massive brecciated comb like and vein structures the type 2 ore is composed of hematite garnet pyroxene actinolite chlorite quartz and calcite and has a relict metasomatic texture and disseminated structure field evidence and petrographic observations indicate that three stages of hydrothermal activity i e the skarn iron oxide and carbonate stages contributed to the formation of the taochong iron deposit the iron oxide stage can be further divided into early and late oxide stages which saw the formation of the type 2 and type 1 ores respectively fluid inclusion and stable isotope data indicate that the skarn formed at depths of 2 km under lithostatic pressure of 500 bars from high temperature 500 c acidic saline up to 50 wt nacl equiv and iron rich fluids that had chemical and isotopic compositions 18owater 4 5 11 7 similar to those of magmatic fluid replacing a certain amount of the huanglong dolomitic limestone the iron ores formed under hydrostatic conditions after fracturing of the early skarn fluid inclusions within quartz in equilibrium with hematite in the type 2 ores yields homogenization temperatures of 372 390 c and salinities of 31 39 wt nacl equiv whereas fluid inclusions within quartz in equilibrium with hematite in the type 1 ores has lower homogenization temperatures 280 320 c and variable salinities 0 40 wt nacl equiv during the formation of the type 1 ores fluids contained moderate concentrations of ions variable 13c values 5 3 to 5 8 and relatively convergent 18o values 1 7 4 5 the temporal decrease in the concentration of ions and 18o values in the fluid inclusions is matched by marked decreases in fluid salinity and temperature suggesting that the fluids of the oxide stage were mixtures of magmatic brine and meteoric water the coexistence of saline and vapor rich fluid inclusions as internal trails or clusters within individual quartz grains of the late oxide stage with contrasting homogenization characteristics for the liquid and vapor at similar temperatures strongly suggests that fluid boiling occurred during the late oxide stage our estimates of the physico chemical conditions during ore formation together with fluid inclusion data and the results of previous experimental studies indicate that iron in the taochong deposit was transported mainly as fecl4 along with minor amounts of other chloride complexes e g fecl2 and fecl2 h2o 4 the precipitation of hematite followed the breakdown of the iron chloride complexes probably induced by a decrease in temperature and ligand chloride ion activity and an increase in ph based on the results we infer that deposition of the type 2 ore was caused by the replacement of garnet and pyroxene by a retrograde alteration assemblage which was likely induced by fluid rock interaction and the mixing of magmatic brine and meteoric water the type 1 ore was deposited in open spaces probably induced by fluid boiling

dissolution reprecipitation process of magnetite from the chengchao iron deposit insights into ore genesis and implication for in situ chemical analysis of magnetite abstract magnetite formed in different environments commonly has distinct assemblages and concentrations of trace elements that can potentially be used as a genetic indicator of this mineral and associated ore deposits in this paper we present textural and compositional data of magnetite from the chengchao iron deposit daye district china to provide a better understanding in the formation mechanism and genesis of the deposit and shed light on analytical protocols for in situ chemical analysis of hydrothermal magnetite magnetite grains from the ore related granitoid pluton mineralized endoskarn magnetite dominated exoskarn and vein type iron ores hosted in marine carbonate intruded by the pluton were examined using scanning electron microscopy and analyzed for major and trace elements using electron microprobe back scattered electron images reveal that primary magnetite from the mineralized skarns and vein type ores were all partly reequilibrated with late stage hydrothermal fluids forming secondary magnetite domains that are featured by abundant porosity and have sharp contact with the primary magnetite these textures are interpreted as resulting from a dissolution reprecipitation process of magnetite which however are mostly obscure under optically primary magnetite grains from the mineralized endoskarn and vein type ores contain high sio 2 0 92 3 21 wt al 2 o 3 0 51 2 83 wt and low mgo 0 15 0 67 wt whereas varieties from the exoskarn ores have high mgo 2 76 3 07 wt and low sio 2 0 03 0 23 wt and al 2 o 3 0 54 1 05 wt this compositional contrast indicates that trace element geochemical composition of magnetite is largely controlled by the compositions of magmatic fluids and host rocks of the ores that have reacted with the fluids compared to its precursor mineral secondary magnetite is significantly depleted in most trace elements with sio 2 deceasing from 1 87 to 0 47 wt on average and al 2 o 3 from 0 89 to 0 08 wt in mineralized endoskarn and vein type ores and mgo from 2 87 to 0 60 wt in exoskarn ores on the contrary average content of iron is notably increased from 69 2 wt to 71 9 wt in the secondary magnetite grains the results suggest that the dissolution reprecipitation process has been important in significantly removing trace elements from early stage magnetite to form high grade high quality iron ores in hydrothermal environments the textural and compositional data confirm that the chengchao iron deposit is of hydrothermal origin rather than being crystallized from immiscible iron oxide melts as previously suggested this study also highlights the importance of textural characterization using various imaging techniques before in situ chemical analysis of magnetite as is the case for texturally complicated u th bearing accessory minerals that have been widely used for u pb geochronology study

constraints on the mineralization processes of the makeng iron deposit eastern china fluid inclusion h o isotope and magnetite trace element analysis abstract the makeng iron deposit is located in the yong an meizhou depression belt in fujian province eastern china both skarn alteration and iron mineralization are mainly hosted within middle carboniferous lower permian limestone five paragenetic stages of skarn formation and ore deposition have been recognized stage 1 early skarn andradite grossular assemblage stage 2 magnetite mineralization diopside magnetite assemblage stage 3 late skarn amphibole chlorite epidote johannsenite hedenbergite magnetite assemblage stage 4 sulfide mineralization quartz calcite fluorite chlorite pyrite galena sphalerite assemblage and stage 5 carbonate quartz calcite assemblage fluid inclusion studies were carried out on inclusions in diopside from stage 2 and in quartz calcite and fluorite from stage 4 halite bearing type 1 and coexisting two phase vapor rich aqueous type 3 inclusions in the magnetite stage display homogenization temperatures of 448 564 c and 501 594 c respectively salinities range from 26 5 to 48 4 and 2 4 to 6 9 wt nacl equivalent respectively two phase liquid rich aqueous type 2b inclusions in the sulfide stage yield homogenization temperatures and salinities of 182 343 c and 1 9 20 1 wt nacl equivalent these fluid inclusion data indicate that fluid boiling occurred during the magnetite stage and that fluid mixing took place during the sulfide stage the former triggered the precipitation of magnetite and the latter resulted in the deposition of pb zn and fe sulfides the fluids related to magnetite mineralization have 18ofluid vsmow of 6 7 9 6 and d of 96 to 128 which are interpreted to indicate residual magmatic water from magma degassing in contrast the fluids related to the sulfide mineralization show 18ofluid vsmow of 0 85 to 1 04 and d of 110 to 124 indicating that they were generated by the mixing of magmatic water with meteoric water magnetite grains from stage 2 exhibit oscillatory zoning with compositional variations in major elements e g sio2 al2o3 cao mgo and mno from core to rim which is interpreted as a self organizing process rather than a dissolution reprecipitation process magnetite from stage 3 replaces or crosscuts early magnetite suggesting that later hydrothermal fluid overprinted and caused dissolution and reprecipitation of stage 2 magnetite trace element data e g ti v ca al and mn of magnetite from stages 2 and 3 indicate a typical skarn origin

sediment slides and turbidity currents on the laurentian fan sidescan sonar investigations near the epicenter of the 1929 grand banks earthquake the epicenter area of the 1929 grand banks earthquake on the continental slope south of newfoundland has been investigated using sea marc i a deeply towed midrange sidescan sonar with a 4 5 khz subbottom profiler shallow slides pass downslope into debris flows on the muddy continental slope east of the epicenter at the head of the eastern valley of the laurentian fan west of the epicenter arcuate slide scars cut undisturbed upper slope sediment and lead downslope to a lineated erosional seabed at a water depth of about 1600 m this erosional seabed passes into extensive fields of 100 m wavelength gravel waves situated on the broad irregular valley floor the gravel waves become better developed downslope and extend at least to water depths of 3000 m all these morphological features appear fresh on the sidescan sonograms suggesting that they date from the 1929 earthquake event and the distribution of slides corresponds to the area of instantaneous cable breaks in 1929 the upper limit of erosion on valley walls suggests that the 1929 turbidity current was less than 300 m thick timing of cable breaks downfan suggests that flow velocities were sufficient to rework gravel deposits into large bedforms during waning flow stages over elevated areas of the valley floor similar cross bedded coarse sands and gravels are common in ancient channel deposits

reconciling fluid inclusion types fluid processes and fluid sources in skarns an example from the bismark deposit mexico the bismark deposit 8 5 mt at 8 zn 0 5 pb 0 2 cu and 50 g t ag located in northern mexico is an example of a stock contact skarn end member of a continuum of deposit types collectively called high temperature carbonate replacement deposits the deposit is hosted by massive sulfide within altered limestone adjacent to the bismark quartz monzonite stock 42 ma and the bismark fault alteration concurrently developed in both the intrusion and limestone the former contains early potassic alteration comprising k feldspar and biotite which was overprinted by kaolinite rich veins and alteration and later quartz sericite and pyrite with minor sphalerite and chalcopyrite prograde exoskarn alteration in the limestone consists of green andradite and diopside and transitional skarn comprising red brown andradite green hedenbergite and minor vesuvinite calcite fluorite and quartz the main ore stage post dates calc silicate minerals and comprises sphalerite and galena with gangue pyrite pyrrhotite calcite fluorite and quartz the entire hydrothermal system developed synchronously with faulting fluid inclusion studies reveal several distinct temporal compositional and thermal populations in pre syn and post ore quartz fluorite and calcite the earliest primary fluid inclusions are coexisting vapor rich type 2a and halite bearing type 3a type 3b contain sylvite brine inclusions 32 to 60 total wt salts that occur in pre ore fluorite trapping temperatures are estimated to have been in excess of 400 c under lithostatic pressures of 450 bar 1 5 km depth primary fluid inclusions trapped in syn ore quartz display critical to near critical behavior type 1c have moderate salinity 8 4 to 10 9 wt nacl equiv and homogenization temperatures th ranging from 351 to 438 c liquid rich type 1a and 1b calcite bearing inclusions occur as primary to secondary inclusions predominantly in fluorite and show a range in th 104 336 c and salinity 2 7 11 8 wt nacl equiv which at the higher th and salinity ranges overlap with type 1c inclusions oxygen isotope analysis was carried out on garnet quartz and calcite plus carbon isotopes in pre syn post ore and peripheral veins pre ore skarn related garnets have a 18omineral range between 3 9 and 8 4 quartz from the main ore stage range between 13 6 and 16 0 calcite from the main ore stage has 13c values of 2 9 to 5 1 and 18o values of 12 3 to 14 1 which are clearly distinct from post ore veins and peripheral prospects that have much higher 18o 16 6 27 3 and 13c 1 3 3 1 values despite the numerous fluid inclusion types only two fluid sources can be inferred namely a magmatic fluid and an external fluid that equilibrated with limestone furthermore isotopic data does not indicate any significant mixing between the two fluids although fluid inclusion data may be interpreted otherwise thus the various fluid types were likely to have formed from varying pressure temperature conditions through faulting during exsolution of magmatic fluids late stage hydrothermal fluid activity was dominated by the non magmatic fluids and was post ore

a petrological and fluid inclusion study of magnetite scheelite skarn mineralization at kara northwestern tasmania implications for ore genesis abstract the kara magnetite scheelite deposit is located about 40 km south of burnie in northwestern tasmania the deposit consists of a number of orebodies and the total mineable reserves are 1 7 mt of magnetite at 30 fe and 0 3 mt of scheelite at 0 52 wo3 the major orebodies at kara are hosted by the ordovician gordon limestone at the southern end of the devonian housetop granite adjacent to the granite or separated from it by the ordovician moina sandstone at least four paragenetic stages of skarn formation and ore deposition have been recognized stage i clinopyroxene garnet vesuvianite wollastonite quartz scheelite stage ii garnet vesuvianite magnetite scheelite apatite quartz stage iii magnetite amphibole epidote fluorite quartz chlorite garnet vesuvianite scheelite carbonate pyrite clinopyroxene and stage iv hematite fluorite calcite quartz fluid inclusions in clinopyroxene from stage i homogenize at 460 620 c mode 520 c stage ii gave homogenization temperatures of 349 578 c mode 500 c from scheelite and 360 570 c mode 500 c from vesuvianite the stage i clinopyroxene gave a salinity range of 10 0 12 0 equiv wt nacl with only one low value of 2 0 equiv wt nacl the stage ii mineral assemblages also showed moderate salinities of 12 0 and 17 8 equiv wt nacl from scheelite and vesuvianite fluid inclusions in quartz scheelite calcite and fluorite from the main scheelite mineralization phase stage iii homogenize at 230 360 c with a mode at 300 c and salinity varies from 0 2 to 19 8 equiv wt nacl the mineral paragenetic and fluid inclusion studies indicate that magnetite scheelite mineralization at kara was formed as a proximal skarn assemblage in carbonate host the skarn formation and ore deposition occurred in stages starting with prograde anhydrous clinopyroxene garnet metasomatism at relatively high temperatures 500 c this early assemblage was replaced by the subsequent retrograde deposition of hydrous mineral phases e g amphibole epidote and chlorite as temperatures decreased to 300 c or less deposition of scheelite predominantly occurred in association with hydrous minerals e g amphibole in stage iii the high temperature and moderate to high salinity ore fluids in early anhydrous skarn formation stages i and ii are consistent with fluids of magmatic origin in comparison the lower temperature and variable salinity from high 19 8 equiv wt nacl to as low as 0 2 equiv wt nacl in stage iii suggests a possible involvement of low salinity meteoric waters mixing with high salinity fluids originating from the nearby granite in the later hydrous skarn and ore formation

asperities barriers characteristic earthquakes and strong motion prediction recent results from paleoseismology suggest that earthquakes recurrent on a given fault may often have the same characteristic length and amount of slip stable asperities and barriers which survive many earthquakes can explain these results the activity of volcano usu japan since 1977 which produced a dacite dome with a total upheaval of 180 m offered a great opportunity to study the recurrence behavior of a fault seismologists at hokkaido university revealed a family of repeated earthquakes with nearly the same amount of slip generated from the same fault plane on the crater wall along which the dome moved upward this family can be explained by the existence of a stable asperity on the crater wall and is called the asperity type family they found however another type of family of earthquakes which share the same fault plane but show a great range of variation in the amount of slip the behavior of the latter family can be explained by the presence of weak barriers over a fault plane defined by strong stable barriers and this family is referred to as the barrier type family this type of earthquake model has been used successfully in the interpretation of observed strong motion acceleration spectra from california and the results reveal the stability of local stress drop among different earthquakes the agreement found between local stress drops estimated from strong motion data and those inferred from geological observation supports the possibility for predicting earthquake strong motion directly from geological observation of the causative fault

ore genesis and hydrothermal evolution of the baiyinnuo er zinc lead skarn deposit northeast china evidence from isotopes s pb and fluid inclusions the baiyinnuo er zinc lead deposit 32 74 mt at 5 44 zn 2 02 pb and 31 36 g t ag located in the south segment of the great xing an range is the largest zn pb deposit in northern china skarn and orebodies mainly occur between the different units of the huanggangliang formation or within the contact zone between the intrusions and permian marble several phases of igneous rocks exposed within the mining areas and among them the yanshanian plutonic rocks which intruded into limestone of the early permian huanggangliang formation are interpreted to be the source of ore since their pb isotope compositions 206pb 204pb 18 25 18 35 207pb 204pb 15 50 15 56 and 208pb 204pb 38 14 38 32 are highly consistent with the sulfides including sphalerite galena and chalcopyrite 206pb 204pb 18 23 18 37 207pb 204pb 15 47 15 62 and 208pb 204pb 37 93 38 44 sulfur isotope values of the sulfides give a narrow 34s interval of 6 1 to 4 6 mean 5 4 n 15 suggesting the ore forming fluid is of magmatic origin three main paragenetic stages of skarn formation and ore deposition have been recognized based on petrographic observation which are the preore stage garnet clinpyroxene wollastonite magnetite sulfides the synore stage sulfides epidote quartz calcite garnet and the postore stage calcite chlorite quartz fluorite several fluid evolution episodes can be inferred from microthermometric results at the baiyinnuo er zn pb deposit 1 immiscibility preore stage coexistence of halite bearing brine inclusions s1 type 44 wt nacl equiv and vapor rich fluid inclusions v type sharing the same homogenization temperatures 470 c confirms that fluid unmixing occurred under lithostatic pressures of 400 bars 1 5 km and the brine is considered to account for most prograde skarn minerals e g clinopyroxene 2 overpressure trapping preore stage brine inclusions homogenized by halite dissolution s2 type postdated the immiscible assemblages this type of inclusions is characterized by high but variable minimum trapping pressures 150 3 000 bars relative to s1 type inclusions and can be explained as a result of entrapment under overpressuring condition 3 boiling the presence of both vapor and liquid inclusions i e v and l type in the same assemblages within synore stage quartz calcite and sphalerite indicates the occurrence of fluid boiling 350 c at hydrostatic pressures of 150 bars and depth of 1 5 km which resulted in large scale mineralization in the baiyinnuo er zn pb deposit 4 mixing with external fluids fluid inclusions scattered within postore stage calcite or secondary trails in synore stage minerals show low homogenization temperatures 260 c and both decreasing for l type and increasing for cacl2 bearing inclusions i e lc type trends for salinities as homogenization temperatures decrease implying addition of both meteoric water low temperature low salinity and basinal brines low temperature ca rich respectively systematic fluid inclusion studies also indicate that the mineralization related fluid is of magmatic origin prograde minerals formed during the preore stage fluid immiscibility while sulfides deposition occurred during the synore stage fluid boiling mixing with external fluids began as the hydrothermal system cooled to 300 c when the main metal precipitation process had ended

seismic rupture associated with subduction of the cocos ridge the april 3 1983 costa rica earthquake mw 7 4 ms 7 3 occurred where the aseismic cocos ridge has been partially subducting beneath the caribbean plate the epicenter is at the eastern edge of the 70 110 km initial aftershock area which later shows considerable expansion p wave directivity analysis indicates that the rupture front propagated westward 63 km from the epicenter to where the major moment release was truncated the source time history of the 1941 event ms 7 5 which occurred in the same epicentral area appears to be similar to the 1983 event but with more complexity and a slower initiation of moment release the low stress drop of the 1983 event 2 3 bar and low ratio of seismic slip to tectonic slip 0 15 for the 1983 event suggest that the coupling between the descending slab and the overlying plate is weak yet a recurrence time for large events mag 7 0 in this zone of about 40 years is implied by the 1904 1941 and 1983 events suggesting that the cocos ridge causes increased partial coupling compared with that in the adjacent subduction zone the slow source rupture process may reflect the nature of the contact area between the costa rica arc and the subducting plate in the vicinity of the bouyant cocos ridge the normal faulting event of july 1 1979 mb 5 3 is consistent with present day uplift of the burica peninsula which previous studies suggest is related to the subduction of the cocos ridge the burica and osa peninsulas may behave as detached blocks which influence the distribution of partial coupling reflected in the aftershock expansion pattern

effect of gas hydrates melting on seafloor slope instability we present a theoretical study of the thermodynamic chemical equilibrium of gas hydrate in soil by taking into account the influence of temperature pressure pore water chemistry and the mean pore size distribution the model uses a new formulation based on the enthalpy form of the law of conservation of energy the developed model shows that due to a temperature and pressure increase hydrates may dissociate at the top of the hydrate occurrence zone to ensure a chemical equilibrium with the surrounding bulk water this original result confirms what has been already shown through experiments the second part of the paper presents an application of the model through a back analysis of the giant storegga slide on the norwegian margin two of the most important changes during and since the last deglaciation hydrostatic pressure due to the change of the sea level and the increase of the sea water temperature were considered in the calculation simulation results show that melting of gas hydrate due to the change of the gas solubility can be at the origin of a retrogressive failure initiated at the lower part of the storegga slope once again the developed model leads to predictions which are supported by laboratory experiment results but contradictory to previous interpretations and beliefs considering that hydrate dissociation occurs only at the bottom of the gas hydrate stability zone

sedimentary structures offshore ortona adriatic sea deformation or sediment waves the late holocene mud wedge on the adriatic shelf offshore ortona italy shows undulating sub parallel seismic reflector sequences which extend several kilometres along strike and 100 200 m down dip in water depth between 20 and 80 m the amplitude of such undulations is up to 5 m and the undulations continue as stacked sediment packages downwards throughout the 35 m thick mud wedge the undulations are separated by 4 to 5 dipping boundary zones and at first glance these sediment undulations resemble the seafloor sedimentary structures visible in the humboldt feature offshore california there is an ongoing debate whether seafloor undulations are the result of deformation processes or sediment deposition and or reworking due to submarine shelf currents a dense net of recently reprocessed and digitally interpreted high resolution chirp seismic data on the adriatic shelf favours an interpretation that these undulations developed in the upper part of the stratigraphic section through sediment reworking rather than through deformation there are three lines of evidence for this 1 the spatial extent of the undulations coincides with higher seabed reflector amplitudes than found both on the shelf and in the distal part of the shelf if the features were solely caused by slope failure there should be no change of amplitudes 2 the seabed reflector amplitude is generally higher on the gently dipping or flat upslope limbs than on the steeper downslope limbs supporting a current origin that causes preferred deposition of sediments with higher acoustic impedance on the top 3 the boundaries between the undulations are dipping at angles that are much lower than the angle of internal friction of these sediments excluding that a simple model like the mohr coulomb under gravitational loading could describe the undulations as sediment deformation and failures

fluid evolution in a subvolcanic granodiorite pluton related to fe and pb zn mineralization banska stiavnica ore district slovakia the central zone of the miocene stiavnica stratovolcano western carpathians hosts an extensive subvolcanic intrusive complex dominated by a granodiorite pluton 14 5 15 5 ma the granodiorite intrusion has a bell jar form and was emplaced mainly into basement rocks although its central part extends to the base of a subvolcanic and volcanic andesitic complex 1 5 to 3 km below the paleosurface in the more uplifted western part of the complex the margin of the granodiorite includes numerous apophyses with associated magnetite skarns whereas in the central apical part it contains an irregular network of fractures hosting base metal stockwork mineralization that extends to a depth of 250 m the granodiorite intrusion especially in the marginal facies is altered high temperature subsolidus deuteric k feldspar secondary biotite and amphibole and endoskarn pyroxene alteration intimately related to magnetite skarns resulted in depletion in fetotal and increase in cao and mgo in the intrusion low temperature hydrothermal alteration epidote chlorite k feldspar sericite closely related to the stockwork mineralization is characterized by enrichment in k2o pb zn cu and mno and depletion in na2o the overlying andesites are affected by acid leaching fluid inclusions and stable isotopes o h were studied in samples of granodiorite related to the skarn and to the stockwork from the top of the pluton down to 1 230 m in depth magmatic quartz contains hypersaline fluid inclusions up to 71 wt nacl equiv vapor rich saline and low salinity inclusions as well as moderate to low salinity liquid rich aqueous inclusions with homogenization temperatures th ranging from 161 to 600 c brine inclusions from magmatic quartz in marginal phases of the granodiorite show signs of nacl saturation during entrapment with the majority probably having been captured under vapor unsaturated conditions most vapor rich inclusions represent early stages of fluid immiscibility whereas the low salinity liquids are products of dilution by meteoric fluid and or late stage portions of magmatic fluids inclusion bearing minerals in the skarn assemblage contain moderate to low salinity fluid inclusions th 215 371 c with evidence of late stage boiling at low hydrostatic pressure hydrothermal minerals from base metal stockwork and massive silica rich rock contains only low salinity inclusions up to 5 wt nacl equiv th 191 367 c the isotopic composition of magmatic biotite and hornblende from granodiorite indicates open magmatic degassing deuterium depletion during granodiorite crystallization influenced by reequilibration to variable degrees fluids in equilibrium with skarn and stockwork related minerals show a clear progressive mixing trend with isotopically relatively heavy possibly 18o shifted meteoric water magnetite skarns and zones of high temperature subsolidus deuteric alteration are related to ponding of magmatic brines in the roof of the intrusion resulting from fluid immiscibility at relatively low pressures the associated escaping vapor was responsible for acid leaching in andesites above the apical part of the pluton stockwork mineralization and associated low temperature potassic alteration are probably related to the large convective hydrothermal system and upflow of late stage deep exsolved supercritical fluids using the increased permeability fracturing of the central apical part of the intrusion

multi process generated sediment waves on the landes plateau bay of biscay north atlantic detailed analyses of recently collected bathymetric and sparker seismic data support a new interpretation of the landes plateau field of sediment waves located on the aquitaine upper continental slope bay of biscay the wave geometry previously described as the result of a major sediment failure is interpreted as a structure with a complex origin including the interaction of depositional and gravity deformation processes depositional processes are mainly recorded by the upslope migrating pattern of the waves resulting from oblique or sigmoid downlap reflections on the upslope flank of the waves and by toplapping and truncated reflections on the downslope flank hemipelagic and turbiditic sedimentation may be involved in the wave building as well as contouritic processes that could be related to the existing northward polar current and internal waves gravity deformations are syndepositional discontinuous and of low amplitude affecting thick layers which alternate with undeformed layers they seem to correspond to gentle sediment creeping or stretching associated with minor listric or compaction like faults and possible limited back rotation of sediment blocks these multi process generated sediment waves could be rather common on the continental margins as they could have been mistaken with either depositional or deformational structures

fluid evolution in the formation of the fenghuangshan cu fe au deposit tongling anhui china the fenghuangshan cu fe au deposit is located in tongling anhui province in central east china within the middle lower yangtze river polymetallic belt the mineralization is related to late yanshanian magmatic intrusions emplaced in lower triassic limestones and is divided into two episodes the first and more important episode a is related to granodiorite granodiorite porphyry and characterized by massive disseminated veinlet and breccia style mineralization in skarn formed at the contact zone whereas the second episode b is related to a quartz monzodiorite porphyry stock which crosscuts the previous skarn and is characterized by disseminated and veinlet style mineralization within the porphyry based on mineral assemblages and their crosscutting relationships the hydrothermal evolution of episode a is further divided into five substages a1 a5 and that of episode b into four b1 b4 among which a4 a5 and b3 are the main copper mineralization stages this paper focuses on microthermometric studies of fluid inclusions in the various stages with an aim to characterize the thermal and compositional evolution of hydrothermal fluids and to discuss their implications for mineralization in terms of fluid sources and metal deposition mechanisms fluid inclusions were studied in garnet quartz and calcite from stages a1 a4 a5 b1 b2 b3 and b4 four types and 13 subtypes of fluid inclusions were distinguished based on fluid composition and phase assemblages type i fluid inclusions contain one or more salt daughter minerals halite and sylvite and homogenize into the liquid phase whereas type ii inclusions homogenize into the vapor phase both commonly containing an opaque daughter mineral type iii fluid inclusions are aqueous inclusions that do not contain daughter minerals and homogenize into the liquid phase and type iv inclusions are co2 bearing homogenize to the co2 or the aqueous phase and commonly contain an opaque daughter mineral primary fluid inclusions in stage a1 are of type i and ii interpreted to represent two immiscible phases resulting from boiling and those in stages a4 and a5 are of type iii stages b1 and b2 are characterized by type i primary inclusions and stages b3 and b4 by type iii type iv inclusions occur as secondary inclusions in b1 quartz and are interpreted to be related locally to b3 stage mineralization microthermometric data indicate a trend of decreasing temperatures and salinities from early to late stages for both mineralization episodes reflecting a change from a magmatic fluid dominated system to one invaded by fluids from the country rocks and meteoric water the fact that the main stages of mineralization a4 a5 b3 coincided with the development of fluid inclusions without daughter minerals of salt suggests that sulfide precipitation did not take place until the system was diluted by cooler fluids with lower salinities however the observation that the fluid inclusions hosted in minerals before sulfide mineralization i e stages a1 b1 and b2 commonly contain opaque daughter minerals inferred to be sulfides suggests that the ore forming components were likely derived from the higher temperature magmatic fluids and the fluids derived from the country rocks mainly contributed to the precipitation of sulfides through mixing and cooling

geology mineralization and fluid inclusion characteristics of the kensu w mo skarn and mo w cu au alkalic porphyry deposit tien shan kyrgyzstan the kensu deposit is located within a large metallogenic belt of w mo cu mo w au au and pb zn deposits along the late paleozoic active continental margin of tien shan the deposit is related to a small late carboniferous to early permian multiphase gabbro monzonite syenite granite pluton representing an alkaline potassic shoshonitic suite the igneous rocks are related to a deep rooted magmatic source but the pluton emplacement corresponds to shallow porphyry levels the deposit represents an example of a complex w rich alkalic magmatic hydrothermal system that complements the typical mineral deposits related to shoshonitic igneous suites it contains large bodies of w mo skarn of the oxidized type with abundant andradite garnet scapolite k na feldspars and fe oxides magnetite hematite the skarns are overprinted and surrounded by extensive halos of stockwork disseminated porphyry style mo w mo w cu pb zn and au w mineralization with propylitic chlorite amphibole epidote dominated and phyllic quartz sericite carbonate sulfide alteration assemblages consistent with the oxidized nature of the major mineral assemblages the deposit may represent the oxidized lithophile w mo cu au metallogenic type the hydrothermal stages alternate with magmatic phases and fluid inclusion data show the predominance of high temperature 550 450 c high pressure 1 200 700 bars and high salinity 60 45 wt nacl equiv magmatic hydrothermal fluid at prograde and early retrograde skarn stages with its possible direct exsolution from crystallizing magma the general trend of cooling and dilution was complicated by the influx of higher temperature and higher salinity fluid that correlates to the intrusion of quartz monzonite and the initial stages of its degassing and cooling this more advanced phase of magmatic differentiation likely corresponded to the enrichment of residual melt and related magmatic fluids in w and mo intense fluid boiling and phase separation triggered the deposition of molybdoscheelite in skarns that formed at t 625 500 c and p 510 300 bars and continued to a nonboiling fluid at t 420 370 c and p 1 150 750 bars mineralization in propylitic alteration zones was formed by highly to moderately saline nonboiling fluids late quartz sericite carbonate sulfide stage involved both high to low salinity aqueous fluids and co2 rich fluids under decreasing temperature from 400 c to 200 300 c and varying pressure from 1 200 bars to 750 600 bars

formation of anhydrous and hydrous skarn in cu au ore deposits by magmatic fluids most skarn ore deposits are characterized by two distinctly different alteration styles an early prograde stage with anhydrous minerals such as garnet and pyroxene forms from relatively high temperature hypersaline liquid a later retrograde stage with hydrous minerals such as epidote amphibole and chlorite plus sulfide ore minerals forms from lower temperature lower salinity fluids these two alteration stages commonly have been thought to reflect a dominance of magmatic and meteoric water respectively with relevance to the source of ore metals we report data from two different skarn systems one being part of the world s largest cu au resource stable isotope compositions of anhydrous and hydrous alteration minerals from both deposits indicate a magmatic source for both the prograde and retrograde stages 18o averages 5 0 per mil for garnet range 3 4 7 2 6 5 per mil for pyroxene 4 3 8 2 and 7 1 per mil for amphibole 4 3 8 7 the d values of late amphibole are more complex with magmatic values 77 to 78 for one deposit and both magmatic and lighter values for another deposit that could be explained either by magmatic degassing or by limited mixing with meteoric water we conclude that the differences in fluid composition prograde versus retrograde stages resulted from a magmatic fluid that intersected its solvus during the early stage creating vapor and hypersaline liquid whereas in the later stage this magmatic fluid did not intersect its solvus because it followed a different cooling path this late low salinity liquid only boiled once its vapor pressure curve was reached causing sulfide ore to precipitate during the retrograde stage

sediment undulations induced by free gas in muddy marine sediments a modeling approach 1 sediment undulations observed on the continental shelf in muddy prodeltas are often marked by the presence of gas in the upslope location the growth and migration of bubbles within fine grained muddy sediments are associated with sediment fracturing that damages the sediment and changes its effective mechanical properties the presented theoretical investigation demonstrates by modeling that undulations may be induced by creep deformations downslope from the region with gas presence comparison of the dimensions of the modeled undulations with the observed ones suggests that the undulations may be enhanced over time by different processes e g by the different types of the sediment deposition

high resolution 2 7 khz acoustic and geometric characters of submarine creep deposits in the south korea plateau east sea a synthesis of high resolution chirp 2 7 khz seismic profiles in the south korea plateau reveals that large masses of wavy stratified sediment 60 90 m thick cover broad gently sloping 0 5 ridges in water depths of 1000 2000 m the wavy stratified sediment wss is characterized by wavy 0 2 5 km in wavelength and 15 m in relief continuous reflective layers with a basal deformed zone that overlies undeformed strong reflectors the wss exhibits systematic variation in wave dimensions and thickness of internal reflective layers with changes in slope gradient the troughs of the waves are commonly associated with internal growth faults and wave amplitude generally increases with subbottom depth on steep slopes around the ridges the wss masses are bounded downslope by slide and slump deposits including slightly translated or rotated wss blocks the acoustic and geometric characters and association with downslope slides and slumps on the steeper slopes suggest that the wss masses were most probably formed by slow creep movement before slope failure in the absence of significant sediment input to the south korea plateau the deep 1000 2000 m in water depth mass movements were probably triggered by earthquakes that have occurred frequently in this region some slightly displaced intact wss blocks in the associated slides and slumps downslope reflect a progressive evolution from submarine creep into slide and slump

fluid inclusion petrography abstract a procedure of fluid inclusion studies is proposed with emphasis on the criteria of selecting fluid inclusions for detailed microthermometry and spectroscopic analysis an overview of descriptive and genetic classifications of fluid inclusions in single crystals and in massive rocks is given with the intention of further differentiating the commonly used terms primary and secondary fluid inclusions some principles of fluid inclusion modification are explained cathodoluminescence cl studies of quartz with the optical high power cl microscope and the electron microprobe provided with a cl detector are an important help in fluid petrography cl textures are subdivided in primary growth textures and a wide variety of secondary microtextures which are in part induced by fluid inclusions the latter is grouped in textures indicative of local lower crystal order increasing defect structures and microtextures indicative of local quartz healing reduction of the defect structures microtextures showing the genetic relationship between fluid inclusions and the host mineral provide information about the possible post entrapment changes of fluid inclusions and therewith testify their geological relevance

mechanical behaviour of gas charged marine plastic sediments understanding how free gas modifies the mechanical behaviour of marine plastic sediments remains a challenging issue special triaxial tests were carried out on natural sediments recovered from the gulf of guinea special attention was devoted to the laboratory preparation procedure involving saturation of natural marine sediment samples with carbonated water and generation of free gas following undrained unloading experimental data show that soil destructuration and damage generated by gas expansion and exsolution are at the origin of a the increase in the isotropic compressibility and decrease in the preconsolidation pressure and b the decrease in the peak undrained strength and abrupt increase of the pore pressure during undrained shearing the experimental data also show that flooding of gas bubbles and dissolution of free gas do not imply a complete strength recovery of natural sediments

genesis of palaeoproterozoic iron skarns in the misi region northern finland sodic alteration is widespread in palaeoproterozoic greenstone and schist belts of the northern fennoscandian shield in the misi region that forms the easternmost part of the perapohja schist belt several small magnetite deposits show intimate spatial relationships with intensely albitised gabbros raising the possibility that regional sodic alteration released iron which was subsequently accumulated into deposits two of these magnetite deposits raajarvi and puro display a typical paragenesis as follows from oldest to youngest 1 diopside 2 actinolite tremolite magnetite chlorite biotite and 3 serpentine hematite chlorite mass balance calculations suggest that significant amounts of fe ca mg k cu v and ba were lost and na and si gained during the albitisation of the gabbro at near constant al ga ti and zr significant amounts of si ca fe and na were enriched in the formation of skarn related to magnetite deposits fe and v leached from country rocks deposited during the skarn alteration and formed the vanadium rich iron deposits while cu passed through the system without significant precipitation due to low sulphur fugasity variations in na ca mg k and ba contents reflect the composition of the infiltrating fluid during alteration conventional heating freezing measurements and proton induced x ray emission pixe analyses of the fluid inclusions related to actinolite tremolite magnetite stage alteration indicate that the fluids that caused the alteration and the fe mineralisation were complex oxidised highly saline h2o co2 fluids that contained high amounts of na ca k fe and ba as well as elevated concentrations of cu zn and pb the oxygen isotope thermometry suggest that temperature during the fe mineralisation stage was between 390 and 490 c calculated 18ofluid values of 6 1 9 8 smow and 13c values of calcites in the ores and skarns were between 7 7 and 10 9 pdb and most likely reflect admixture of 13c depleted possibly magmatic fluids with the marble wall rocks that show 13ccalcite values of 13 pdb the sims u pb data on the zircons in the albitised gabbro next to the raajarvi and puro deposits suggest that intrusion of the gabbro took place at 2123 7 ma and was accompanied by the formation of diopside skarn the tims data on the metasomatic titanites related to sodic alteration yielded ages of 2062 3 and 2017 3 ma iron was probably stripped from the mafic country rocks by sodic alteration between 2123 and 2017 ma driven by repeated brine influxes subsequently the metal rich brine was focused by a fault system and the iron was precipitated from this fluid by a combination of wall rock reaction fluid mixing and a drop in the temperature

do subducting seamounts generate or stop large earthquakes seamount subduction is a common process in subduction zone tectonics contradicting a widely held expectation that subducting seamounts generate large earthquakes seamounts subduct largely aseismically producing numerous small earthquakes on rare occasions when they do produce relatively large events the ruptures tend to be complex suggesting multiple rupture patches or faults we explain that the seismogenic behavior of these seamounts is controlled by the development and evolution of an adjacent fracture network during subduction and cannot be described using the frictional behavior of a single fault the complex structure and heterogeneous stresses of this network provide a favorable condition for aseismic creep and small earthquakes but an unfavorable condition for the generation and propagation of large ruptures

morphological ripening of fluid inclusions and coupled zone refining in quartz crystals revealed by cathodoluminescence imaging implications for cl petrography fluid inclusion analysis and trace element geothermometry cathodoluminescence cl studies have previously shown that some secondary fluid inclusions in luminescent quartz are surrounded by dark non luminescent patches resulting from fracture sealing by late trace element poor quartz this finding has led to the tacit generalization that all dark cl patches indicate influx of low temperature late stage fluids in this study we have examined natural and synthetic hydrothermal quartz crystals using cl imaging supplemented by in situ elemental analysis the results lead us to propose that all natural liquid water bearing inclusions in quartz whether trapped on former crystal growth surfaces i e of primary origin or in healed fractures i e of pseudosecondary or secondary origin are surrounded by three dimensional non luminescent patches cross cutting relations show that the patches form after entrapment of the fluid inclusions and therefore they are not diagnostic of the timing of fluid entrapment instead the dark patches reveal the mechanism by which fluid inclusions spontaneously approach morphological equilibrium and purify their host quartz over geological time fluid inclusions that contain solvent water perpetually dissolve and reprecipitate their walls gradually adopting low energy euhedral and equant shapes defects in the host quartz constitute solubility gradients that drive physical migration of the inclusions over distances of tens of m commonly up to several mm rarely inclusions thus sequester from their walls any trace elements e g li al na ti present in excess of equilibrium concentrations thereby chemically purifying their host crystals in a process analogous to industrial zone refining non luminescent patches of quartz are left in their wake fluid inclusions that contain no liquid water as solvent e g inclusions of low density h2o vapor or other non aqueous volatiles do not undergo this process and therefore do not migrate do not modify their shapes with time and are not associated with dark cl zone refined patches this new understanding has implications for the interpretation of solids within fluid inclusions e g ti and al minerals and for the elemental analysis of hydrothermal and metamorphic quartz and its fluid inclusions by microbeam methods such as la icpms and sims as ti is a common trace element in quartz its sequestration by fluid inclusions and its depletion in zone refined patches impacts on applications of the ti in quartz geothermometer

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

mechanical behaviour of unsaturated marine sediments experimental and theoretical approaches abstract the costa target areas exhibit different slope failure events which reflect different triggering mechanisms including gas hydrates dissociation gas hydrates stability law depends on temperature pore pressure gas chemistry and pore water salinity any change in the equilibrium parameters may convert the hydrate to gas plus water causing significant weakening of the sediment and generating a rise of pore pressure a significant consequence of the hydrate melting is the gas production which alters significantly the behaviour and mechanical properties of the marine sediments and could be very hazardous when the sediment is unloaded in undrained conditions the behaviour of the unsaturated marine sediment has to be accurately identified in order to quantify the geological risks associated to the hydrate dissociation see for instance sultan n cochonat p foucher j p mienert j this volume effect of gas hydrates melting on seafloor slope instability thus in this work five tests were carried out on synthetic marine sediments in order to identify the gas effect on the hydro mechanical behaviour of unsaturated marine sediments based on the experimental results obtained from this study on previous constitutive models alonso e e gens a josa a 1990 a constitutive model for partially saturated soils geotechnique 40 3 405 430 gens a alonso e e 1992 a framework for the behaviour of unsaturated expansive clays can geotech j 29 1013 1032 and on the relationship of van genuchten van genuchten m th 1980 a closed form equation for predicting the hydraulic conductivity of unsaturated soils soil sci soc am j 44 892 898 a new mathematical formulation was proposed to simulate the behaviour of the unsaturated soil qualitative comparison between experimental results and model predictions shows the capacity of the proposed model to reasonably reproduce the essential features of the hydro mechanical behaviour of marine unsaturated sediment experimental and simulation results show that unloading tidal cycles erosion natural slope instabilities excavation a submarine unsaturated sediment slope in shallow water is much more hazardous than unloading the same submarine slope in deep water

distinguishing sediment waves from slope failure deposits field examples including the humboldt slide and modelling results abstract migrating sediment waves have been reported in a variety of marine settings including submarine levee fan systems floors of fjords and other basin or continental slope environments examination of such wave fields reveals nine diagnostic characteristics when these characteristics are applied to several features previously attributed to submarine landslide deformation they suggest that the features should most likely be reinterpreted as migrating sediment wave fields sites that have been reinterpreted include the humboldt slide on the eel river margin in northern california the continental slope in the gulf of cadiz the continental shelf off the malaspina glacier in the gulf of alaska and the adriatic shelf a reassessment of all four features strongly suggests that numerous turbidity currents separated by intervals of ambient hemipelagic sedimentation deposited the wave fields over thousands of years a numerical model of hyperpycnal discharge from the eel river for example shows that under certain alongshore current conditions such events can produce turbidity currents that flow across the humboldt slide serving as the mechanism for the development of migrating sediment waves numerical experiments also demonstrate that where a series of turbidity currents flows across a rough seafloor i e numerical steps sediment waves can form and migrate upslope hemipelagic sedimentation between turbidity current events further facilitates the upslope migration of the sediment waves physical modelling of turbidity currents also confirms the formation and migration of seafloor bedforms the morphologies of sediment waves generated both numerically and physically in the laboratory bear a strong resemblance to those observed in the field including those that were previously described as submarine landslides

the physics of bubbles in surficial soft cohesive sediments abstract this paper reviews current understanding of the physics of bubbles in soft unlithified cohesive sediments certainly in the top 100 m from the sediment water interface but likely much deeper experimental evidence primarily ct scans and internal pressure records indicate that near surface bubbles grow by elastically compressing and fracturing these sediments which results in thin irregular disks of gas these data do not suggest either plastic or fluid behavior on the part of the bulk sediment in addition there is no hint of capillary invasion of gas into the pores of fine grained sediments the growth rate of an elastic fracturing disk shaped bubble can vastly exceed that of a spherical bubble depending on the eccentricity of the bubble this effect results from the far more favorable surface to volume ratio of flattened bubbles the initial rate of rise of bubbles in cohesive sediments also appears to be governed by a fracture process which is driven by pseudo buoyancy the rate of bubble rise could be controlled by various possible mechanisms but only the predictions from a visco elastic fracture propagation model seem to produce rise velocities that are not ballistic experimental evidence demonstrates that a rising bubble can deviate from its path to the surface if it encounters a zone of sediment with lower lateral fracture toughness such a bubble will begin to move in a lateral direction but stall because pseudo buoyancy is no longer operative subsequent bubbles will do the same and accumulate in the low fracture toughness zone this explains the occurrence of shallow sub seafloor domes of gas and modeling of this process predicts only modest over pressures in such structures

iron skarns of the vegas peladas district mendoza argentina the andean belt southwest of mendoza argentina hosts 23 fe fe cu and cu ag deposits classified variously in the literature as skarn iron oxide copper gold iocg and manto type cu deposits the vegas peladas deposit is one of the best exposed fe skarns with mineral assemblages and hydrothermal features similar to many other calcic fe skarns of the world the plutonic rocks of vegas peladas consist of a series of diorite to granite stocks dikes and sills the major trace and rare earth element geochemistry analyses of these igneous rocks indicate they were derived from subarc mantle sources the vegas peladas deposit formed by the overprinting of two different metamorphic and metasomatic events associated with early diorite and later granite intrusions alteration associated with the early diorite intrusion consists of a metamorphic halo 800 m wide and a zoned calcic skarn with inner garnet ad31 89 py0 2 clinopyroxene magnetite quartz intermediate garnet ad38 51 py1 2 clinopyroxene and distal veins of garnet ad92 100 clinopyroxene hd72 29 jo1 4 the latest alteration consists of widespread albite ab96 98 epidote quartz calcite chlorite pyrite titanite magnetite and hematite are the main iron ore minerals and occur as massive orebodies and veins associated with retrograde epidote and amphibole alteration of the diorite consists of early orthoclase quartz followed by later amphibole quartz magnetite epidote feldspar the granite related skarn overprints the earlier diorite related skarn and consists of garnet clinopyroxene scapolite me28 36 quartz alkali feldspar endoskarn and a zoned exoskarn with proximal garnet clinopyroxene quartz intermediate green garnet ad30 81 py0 1 clinopyroxene di82 93 jo4 2 and distal scapolite me25 36 ferroactinolite pyrite veins based on fluid inclusion stable isotope and ree data the prograde skarn formed at depths of 3 5 km under lithostatic pressure of 1 kbar from high temperature 670 400 c saline and iron rich 50 wt nacl equiv nacl kcl fecl2 magmatic fluids garnet 18oh2o 7 2 8 5 with intermediate oxygen fugacity iron ore and retrograde exoskarn assemblages formed under hydrostatic condition after the fracturing of early skarn fluids in this stage had lower temperature t 550 c and also generated saline 30 3 to 45 3 wt nacl equiv h2o nacl fecl2 vapor fluids by immiscibility that redistributed some of the iron from the previous skarn

ore genesis and hydrothermal evolution of the huanggang skarn iron tin polymetallic deposit southern great xing an range evidence from fluid inclusions and isotope analyses abstract the southern great xing an range is one of the most important metallogenic belts in northern china and contains numerous pb zn ag cu sn fe mo deposits the huanggang iron tin polymetallic skarn deposit is located in the sn polymetallic metallogenic sub belt skarns and iron orebodies occur as lenses along the contact between granite plutons and the lower permian huanggangliang formation marble or dashizhai formation andesite field evidence and petrographic observations indicate that the three stages of hydrothermal activity i e skarn oxide and sulfide stages all contributed to the formation of the huanggang deposit the skarn stage is characterized by the formation of garnet and pyroxene and high temperature hypersaline hydrothermal fluids with isotopic compositions that are similar to those of typical magmatic fluids these fluids most likely were generated by the separation of brine from a silicate melt instead of being a product of aqueous fluid immiscibility the iron oxide stage coincides with the replacement of garnet and pyroxene by amphibole chlorite quartz and magnetite the hydrothermal fluids of this stage are represented by l type fluid inclusions that coexist with v type inclusions with anomalously low d values approximately 100 to 116 the decrease in ore fluid 18oh2o values with time coincides with marked decreases in the fluid salinity and temperature based on the fluid inclusion and stable isotopic data the ore fluid evolved by boiling of the magmatic brine the sulfide stage is characterized by the development of sphalerite chalcopyrite fluorite and calcite veins and these veins cut across the skarns and orebodies the fluids during this stage are represented by inclusions with a variable but continuous sequence of salinities mainly low salinity inclusions these fluids yield the lowest 18oh2o values and moderate d values 1 6 to 2 8 and 101 to 104 respectively the data indicate that the sulfide stage fluids originated from the mixing of residual oxide stage fluids with various amounts of meteoric water boiling occurred during this stage at low temperatures the sulfur isotope 34s values of the sulfides are in a narrow range of 6 70 to 4 50 mean 1 01 and the oxygen isotope 18o values of the magnetite are in a narrow range of 0 1 to 3 4 both of these sets of values suggest that the ore forming fluid is of magmatic origin the lead isotope compositions of the ore 206pb 204pb 18 252 18 345 207pb 204pb 15 511 15 607 and 208pb 204pb 38 071 38 388 are consistent with those of k feldspar granites 206pb 204pb 18 183 18 495 207pb 204pb 15 448 15 602 208pb 204pb 37 877 38 325 but significantly differ from those of permian marble 206pb 204pb 18 367 18 449 207pb 204pb 15 676 15 695 208pb 204pb 38 469 38 465 which also suggests that the ore forming fluid is of magmatic origin

mega scale glacial lineations and cross cutting ice flow landforms landsat images reveal a previously unsuspected large scale pattern of streamlining within drift that is assumed to reflect former phases of ice flow such a glacial grain can be regarded as a landform assemblage comprised of a number of components drumlins and megaflutes form part of the pattern but in addition there are two previously undocumented ice moulded landform elements streamlined lineations of much greater proportions referred to as mega scale glacial lineations and a distinctive cross cutting topology within the grain the ice moulded landform assemblage is described and illustrated with reference to examples from canada possible modes of genesis of such landforms are discussed and their glaciological implications outlined the discovery of this pattern indicates the pervasive nature of subglacial deformation of sediment and demands a radical re interpretation of ice sheet dynamics

stable isotope and fluid inclusion constraints on the source and evolution of ore fluids in the hongniu hongshan cu skarn deposit yunnan province china the hongniu hongshan cu skarn deposit 77 8 mt at 1 8 cu is located in the central part of the zhongdian porphyry and skarn cu belt in southwestern china skarn and orebodies occur mainly between the different units of the upper triassic qugasi formation or within altered limestone adjacent to late cretaceous intrusions 78 76 ma three main paragenetic stages of skarn formation and ore deposition have been recognized on the basis of petrographic observations 1 pre ore stage hornfels with diopside di87 72hd12 7 small scale endoskarn with reddish grossular adr22 57gr78 43 diopside di83 92hd7 15 vesuvianite and abundant exoskarn with red brown andradite adr75 98gr2 22 sahlite di28 41hd58 71 and wollastonite 2 syn ore stage retrograde minerals sulfides pyrite chalcopyrite pyrrhotite molybdenite galena and sphalerite quartz and calcite and 3 post ore stage calcite veins sulfur isotope values of sulfides are relatively high with an average 34s 4 9 n 40 suggesting that the ore forming fluid was magmatic and that the sulfides precipitated from a relatively reducing ore fluid the coexistence of silicate melt and primary fluid inclusions in quartz phenocrysts of the mineralization related quartz monzonite porphyry indicates the simultaneous entrapment of fluid and melt and records the process of the aqueous fluid exsolving from the crystallizing melt the initial single phase fluid has a salinity of 8 8 to 12 7 wt nacl equiv and homogenization temperatures of 566 to 650 c corresponding to pressures of 680 to 940 bar and lithostatic depth of 2 5 to 3 5 km the primary fluid inclusions in the pre ore stage garnet and pyroxene composed of coeval vapor rich v type and halite bearing s i and s ii types containing sylvite inclusions 32 79 total wt salts share similar homogenization temperatures 450 550 c indicative of the occurrence of fluid unmixing under lithostatic pressures of 550 to 780 bar 2 0 km depth primary fluid inclusions trapped in syn ore quartz calcite and epidote show the common development of s type inclusions 37 3 wt nacl equiv with coexisting v type liquid rich l type and co2 bearing c i type inclusions all of which have homogenization temperatures of 300 to 400 c and trapping pressures of 100 to 400 bar 1 5 km depth brine inclusions homogenized by halite dissolution after vapor disappearance in both the pre and syn ore stages are interpreted to have been trapped under overpressured conditions 1 520 bar oxygen isotope analyses were conducted on garnet wollastonite epidote quartz and calcite the pre ore stage garnet and wollastonite have 18ofluid values of 5 6 to 8 1 whereas the syn ore stage epidote quartz and calcite have more variable 18ofluid values in the range of 3 9 to 17 5 the 18ofluid values of the post ore stage vein calcite 15 2 21 3 are much higher than both the pre and syn ore stages the vapor phase of inclusions contains h2s ch4 and c2h6 in the syn ore stages all these observations reveal that 1 the formation of the cu skarn deposit was dominated by a magmatic hydrothermal system 2 multiple fluid pulses contributed to the formation of the pre and syn ore stage skarn minerals and sulfides and 3 the increase in ph due to the neutralization of the acidic fluid could be the main factor controlling the large scale ore deposition in hongniu hongshan

robust estimates of 3d reflector dip and azimuth much of seismic stratigraphy is based on the morphology of seismic textures the identification of reflector terminations and subtle changes in dip and azimuth allows us to infer coherent progradational and transgressive packages as well as more chaotic slumps fans and braided stream complexes infill of karsted terrains gas seeps and of course faults and angular unconformities a major difficulty in estimating reflector dip and azimuth arises at discrete lateral and vertical discontinuities across which reflector dip and azimuth change the smearing across these boundaries produced by traditional dip and azimuth estimations is avoided by using temporally and spatially shifted multiple windows that contain each analysis point this more robust estimation of dip and azimuth leads to increased resolution of well established algorithms such as coherence coherent amplitude gradients and structurally oriented filtering more promising still is the analysis of high resolution dip and azimuth through vol

rupture dynamics and ground motion from 3 d rough fault simulations 1 we perform three dimensional 3 d numerical calculations of dynamic rupture along non planar faults to study the effects of fault roughness on rupture propagation and resultant ground motion the fault roughness model follows a self similar fractal distribution over length scales spanning three orders of magnitude from 102 to 105 m the fault is governed by a strongly rate weakening friction and the bulk material is subject to drucker prager viscoplasticity fault roughness promotes the development of self healing rupture pulses and a heterogeneous distribution of fault slip at the free surface and at depth the inelastic deformation generated by the large dynamic stress near rupture fronts occurs in a narrow volume around the fault with heterogeneous thickness correlated to local roughness slopes inelastic deformation near the free surface however is induced by the stress waves originated from dynamic rupture at depth and spreads to large distances 10 km away from the fault the present simulations model seismic wave excitation up to 10 hz with rupture lengths of 100 km permitting comparisons with empirical studies of ground motion intensity measures of engineering interest characteristics of site averaged synthetic response spectra including the distance and period dependence of the median values absolute level and intra event standard deviation are comparable to appropriate empirical estimates throughout the period range 0 1 3 0 s this class of model may provide a viable representation of the ground motion excitation process over a wide frequency range in a large spatial domain with potential applications to the numerical prediction of source and path specific effects on earthquake ground motion

the geology and genesis of the iron skarns of the turgai belt northwestern kazakhstan abstract the magnetite deposits of the turgai belt kachar sarbai and sokolov in the valerianovskoe zone of the southern urals kazakhstan contain a combined resource of over 3 gt of iron oxide ore the deposits are hosted by carbonate sediments and volcaniclastic rocks of the carboniferous valerianovka supergroup and are spatially related to the gabbroic to granitoid composition intrusive rocks of the sarbai sokolov intrusive series the magnetite deposits are developed dominantly as metasomatic replacement of limestone but also to a lesser extent of volcanic rocks pre mineralisation metamorphism and alteration resulted in the formation of wollastonite and the silicification of limestone magnetite mineralisation is associated with the development of a high temperature skarn assemblage of diopside grossular andradite garnet actinolite epidote and apatite sub economic copper bearing sulphide mineralisation overprints the magnetite mineralisation and is associated with deposition of hydrothermal calcite and the formation of an extensive sodium alteration halo dominated by albite and scapolite chlorite formation accompanies this stage and further later stage hydrothermal overprints the replacement has in places resulted in preservation of primary features of the limestone including fossils and sedimentary structures in magnetite skarn calc silicates and sulphides analysis of re os isotopes in molybdenite indicates formation of the sulphide mineral assemblage at 336 2 1 3 ma whilst u pb analyses of titanite from the skarn alteration assemblage suggests skarn alteration at 326 6 4 5 ma with re equilibration of isotope systematics down to 270 ma analyses of mineral assemblages fluid inclusion microthermometry o and s isotopes suggest initial mineralisation temperatures in excess of 600 c from hypersaline brines 45 50 wt nacl eq with subsequent cooling and dilution of fluids to around 150 c and 20 wt nacl eq by the time of calcite deposition in late stage sulphide bearing veins 18 o in magnetite 1 5 to 3 5 and skarn forming silicates 5 to 9 18 o and 13 c in limestone and skarn calcite 18 o 5 4 to 26 2 13 c 12 1 to 0 9 and 34 s in sulphides 3 3 to 6 6 and sulphates 4 9 to 12 9 are all consistent with the interaction of a magmatic equilibrated fluid with limestone and a dominantly magmatic source for s all these data imply skarn formation and mineralisation in a magmatic hydrothermal system that maintained high salinity to relatively late stages resulting in the formation of the large na alteration halo despite the reported presence of evaporites in the area there is no evidence for evaporitic sulphur in the mineralising system these skarns show similarities to some members of the iron oxide apatite and iron oxide copper gold deposit classes and the model presented here may have implications for their genesis the similarity in age between the turgai deposits and the deposits of the magnitogorsk zone in the western urals suggests that they may be linked to similar magmatism developed during post orogenic collapse and extension following the continent continent collision which has resulted in the assembly of laurussian terranes with the uralide orogen and the kazakh collage of the altaids or central asian orogenic belt this model is preferred to the model of simultaneous formation of very similar deposits in arc settings at either side of an open tract of oceanic crust forming part of the uralian ocean

structure inferred mechanical properties and implications for fluid transport in the decollement zone costa rica convergent margin faults in a variety of tectonic settings can act as both conduits for and barriers to fluid flow sometimes simultaneously documenting the interaction between hydrologic and tectonic processes in active faults in situ is the key to understanding their mechanical behavior and large scale fluid transport properties we present observations of the plate boundary decollement zone at the middle america trench off costa rica showing that it is structurally divisible into an upper brittle fracture dominated domain overlying a lower ductile domain pore water geochemical evidence shows that along fault flow is occurring specifically in the upper brittle domain but is hydrologically isolated from fluids in the underlying footwall sediments we propose a model for the mechanics of these contrasting domains in which differing stress paths coexist in the upper and lower parts of the decollement zone the data suggest a mechanically controlled permeability anisotropy at a scale of several meters to 10 m across the decollement zone this documentation of separate yet simultaneously active mechanical and hydrologic subregimes within a decollement provides a relatively simple explanation for enhanced along fault permeability coexisting with reduced cross fault permeability without requiring matrix scale permeability anisotropy

nonplanar faults mechanics of slip and off fault damage stress interactions and sliding characteristics of faults with random fractal waviness in a purely elastic medium differ both qualitatively and quantitatively from those of faults with planar surfaces with nonplanar fault models solutions for slip diverge as resolution of the fractal features increases and the scaling of fault slip with fault rupture dimension becomes nonlinear we show that the nonlinear scaling of slip and divergence of solutions arise because stresses from geometric interactions at irregularities along nonplanar faults grow with increasing slip and produce backstresses that progressively impede slip however in real materials with finite strength yielding will halt the growth of the interaction stresses which will profoundly affect slip of nonplanar faults we infer that in the brittle seismogenic portion of the earth s crust off fault yielding occurs on pervasive secondary faults predicted rates of stress relaxation with distance from major faults with random fractal roughness follow a power law relationship that is consistent with reported clustering of background seismicity up to 15 kilometers from faults

corrugated megathrust revealed offshore from costa rica exhumed faults are rough often exhibiting topographic corrugations oriented in the direction of slip such features are fundamental to mechanical processes that drive earthquakes and fault evolution however our understanding of corrugation genesis remains limited due to a lack of in situ observations at depth especially at subducting plate boundaries here we present three dimensional seismic reflection data of the costa rica subduction zone that image a shallow megathrust fault characterized by corrugated and chaotic and weakly corrugated topographies the corrugated surfaces extend from near the trench to several kilometres down dip exhibit high reflection amplitudes consistent with high fluid content pressure and trend 11 18 oblique to subduction suggesting 15 to 25 mm yr 1 of trench parallel slip partitioning across the plate boundary the corrugations form along portions of the megathrust with greater cumulative slip and may act as fluid conduits in contrast weakly corrugated areas occur adjacent to active plate bending faults where the megathrust has migrated up section forming a nascent fault surface the variations in megathrust roughness imaged here suggest that abandonment and then reestablishment of the megathrust up section transiently increases fault roughness analogous corrugations may exist along significant portions of subduction megathrusts globally mature parts of the shallow megathrust beneath costa rica are characterized by striking corrugations that may channel fluids according to seismic images nascent sections of the subduction zone plate boundary appear only weakly corrugated