a comparison of bistatic scattering from two geologically distinct mid ocean ridges a comparison is made of bistatic scattering from two distinct deep ocean ridges the ridges are located along a segment valley on the western flank of the mid atlantic ridge mar the acoustic data sets were acquired during the main acoustics experiment of the acoustic reverberation special research program detailed analysis of bistatic scattering from one of these ridges named b has been previously presented by some of the authors the purpose of this paper is to present a similar analysis for the second ridge c for comparative purposes this comparison is important because the ridges span the two geologically distinct classes found in the mar there is a possibility therefore that their scattering characteristics may be extrapolated to ridges throughout the mar for example b is an outside corner and therefore is composed of highly lineated scarps and terraces while c is an inside corner that is characteristically amorphous with irregular large throw normal faults while major scarps on these ridges can be easily resolved by the towed array system smaller scale anomalies such as gullies and trellises are often underresolved by nearly an order of magnitude these anomalies are found to introduce large variances in the bistatic scattering characteristics of a given scarp

geochronology of the tumpangpitu porphyry au cu mo and high sulfidation epithermal au ag cu deposit evidence for pre and postmineralization diatremes in the tujuh bukit district southeast java indonesia the tumpangpitu porphyry and high intermediate sulfidation epithermal deposit is the largest deposit in the tujuh bukit district southeast java indonesia the porphyry resource contains 1 9 billion tonnes 0 45 cu and 0 45 g t au for 28 1 moz au and 19 billion lbs of cu there are an additional 2 1 moz au and 72 9 moz of ag in oxidized high sulfidation epithermal mineralization tumpangpitu is located along a nw striking structural corridor covering an area of 12 5 km that hosts several cu au mo mineralized tonalitic porphyries each with varying degrees of metal enrichment at least eight discrete intrusions spanning the alteration mineralization sequence have been identified at tumpangpitu what is unusual however is the presence of both a premineralization relatively dry volcanic breccia pipe tanjung jahe and a late mineralization diatreme complex associated with a significant large magmatic hydrothermal system tumpangpitu in the same district magmatism mineralization and alteration at tumpangpitu occurred in response to north directed subduction of the indo australian plate beneath the asian continental plate margin the tujuh bukit district is floored by early to late miocene sedimentary and andesitic volcanic rocks volcanic hydrothermal activity at tujuh bukit began with the formation of the weakly altered tanjung jahe diatreme complex u pbzircon ages of 8 78 0 22 8 52 0 21 ma mineralization at tumpangpitu was preceded by the intrusion of a large equigranular dioritic batholith 5 81 0 20 5 18 0 27 ma hydrothermal activity associated with mineralization has been constrained by u pb age determinations from syn to late mineralization porphyries that were emplaced in the early pliocene from 5 40 0 46 to 3 94 0 69 ma high and intermediate sulfidation au ag cu mineralization and associated advanced argillic alteration part of a district scale lithocap has overprinted and significantly upgraded the top of the porphyry orebody ar ar dating of alunite 4 385 0 049 ma and re os dating of molybdenite 4 303 0 018 ma have defined a short time period between the high sulfidation epithermal and porphyry mineralization events this suggests extreme rates of uplift exhumation and erosion in the vicinity of the sunda banda magmatic arc volcanic hydrothermal activity associated with the tumpangpitu diatreme occurred during epithermal mineralization breccia matrix zircon age of 2 7 1 0 ma with systematic errors clasts of high sulfidation state mineralized rocks are a minor but significant component of the diatreme and late stage epithermal veins cutting the diatreme demonstrate an intermineralization timing with respect to epithermal activity in the district implying that epithermal mineralization continued intermittently for 1 to 1 5 m y after porphyry mineralization ceased at tumpangpitu

the colima volcanic complex mexico part ii late quaternary cinder cones since the late pleistocene eleven cinder and lava cones have erupted on the floor of the southern colima graben ne and nw of the large active andesitic volcano colima scoria and lava samples from nine of the cones form a completely transitional basic alkalic series including basanites 9 leucite basanites 3 and minettes 15 the commonest variety of mica lamprophyre these samples represent primitive high temperature magmas with 47 6 50 3 sio2 7 4 15 3 mgo 2 5 4 4 k2o and 2 2 9 9 normative nepheline all members of this basic alkalic suite contain mg olivine fo75 94 chromite augite and late plagioclase and titanomagnetite the petrographic transition from basanite to minette is marked by the appearance of sanidine and the volatile bearing phases phlogopite apatite and analcime during late stages of crystallization as these phases increase in abundance presumably reflecting a rise in magmatic volatile content there are corresponding increases in the whole rock concentrations of 16 incompatible elements although these incompatible elements are relatively abundant even in the basanites many are highly concentrated in the minettes ba 4 200 ppm sr 3 100 ppm zr 550 ppm ce 190 ppm hf 18 ppm among the incompatible elements the degrees of enrichment in the minettes relative to the basanites decrease in the order h th ce la nd zr hf u ba sm eu pb p nb sr ti these enrichments may reflect the increasing importance of minor incompatible element rich mantle phases during partial melting the concentrations of alkali metals k na rb and cs do not correlate with these other elemental enrichments the leucite basanties have similar incompatible element contents to many minettes differing from them only in the presence of leucite rather than analcime and ti f rich groundmass phlogopite rather than hydrous phlogopite phenocrysts thus the leucite basanites represent relatively dry equivalents of minettes two of the eleven cinder cones are calc alkaline in nature and do not belong to the basanite minette group the easternmost cone is constructed of high al basalt and the northernmost of basaltic andesite the high al basalt 49 5 sio2 9 3 mgo 221 ppm ni closely approximates a parental magma to the post caldera andesitic suite of v colima 56 5 61 6 sio2 the basaltic andesite is relatively enriched in incompatible elements compared to the high al basalt v colima trend the ne normative basanite minette samples are highly enriched in incompatible elements while the contemporaneous hy qz normative calc alkaline suite encompassing the high al basalt and v colima s andesites is characterized by relatively low abundances of these elements no likely mineral assemblage can relate the alkaline and calc alkaline suites through crystal fractionation they probably represent fundamentally different melting events during the quaternary the main focus of andesitic volcanism in the southern colima graben has migrated southward with time volcan colima marks its present position 5 km south of the pleistocene volcano nevado de colima and another 15 km from the still older volcan cantaro the eruptions of basic alkalic magma probably occurred during the late stages of nevado s life and through the life of v colima they generally migrated from west to east with time towards v cantaro the most recent cone v apaxtepec is the only one east of the andesitic colima cantaro axis the oldest and the two youngest cones produced basanites while minettes dominated at cones of intermediate ages the cinder cone eruptions may have coincided with a phase of lamprophyre dike injection into plutons solidifying beneath the extinct volcanoes north of v colima the southern end of the colima graben can be viewed then as the volcanic analog of many classical post plutonic hypabyssal lamprophyre localities

crustal accretion at high temperature spreading centres rheological control of crustal thickness abstract new determinations of lateral crustal thickness variations at anomalous oceanic spreading centres such as iceland have shown that the crust may be thinner at the ridge axis above the plume thickening towards the sides bjarnason and schmeling 2009 to understand this behaviour crustal accretion models have been carried out solving the conservation equations of mass momentum and energy with melting melt extraction and feedback of extracted material as newly formed crust for an extending lithosphere system underlain by a hot mantle plume the dynamics of rifting are thermally and rheologically controlled by the feedback due to accreted new crust four accretional modes with characteristic crustal thickness variations are identified depending on the width of the volcanic emplacement zone the accretional heating rate which can be associated with the thickness of the surface layer in which magmatic emplacement takes place and the spreading rate mode 1 zero crustal thickness at the spreading axis develops for cool accretion and a wide emplacement zone mode 2 strongly or moderately crustal thickening away from the axis develops in case of warm deep reaching accretion and wide emplacement zones mode 3 nearly constant crustal thickness develops in case of warm deep reaching accretion but narrow emplacement zones dynamic topography of mode 3 shows only a weak or no regional minimum at all near the axis modes 2 or 3 may be identified with the situation in iceland mode 4 a stagnating central crustal block evolves for cool accretion and narrow emplacement this mode disappears for increasing spreading rates no accretional mode with maximum crustal thickness above the plume at the rift axis has been found the absence of mode 1 accretion with zero crust at ridge axis on earth may be an indication that in general crustal accretion is not cold and shallow the model is also applied to other hotspot ridge settings azores galapagos and suggests modes 2 3 accretion

low grazing angle monostatic acoustic reverberation from rough and heterogeneous seafloors numerical wavefield modeling based on time domain finite difference solutions to the full elastic wave equation is used to quantitatively predict the sensitivity of monostatic backscatter to variations in geological properties of the seabed this article addresses the hypothesis that observed backscatter signals from the seafloor are produced by a combination of seafloor interface and subseafloor volume scattering from structures having variations at scale lengths comparable to the wavelength of the insonifying acoustic field wavelength scale seafloor roughness and subseafloor volume heterogeneity parameters are defined using stochastic spatial probability functions having gaussian autocorrelations the range of the variations in these parameters is constrained to realistic values based on estimates derived from seafloor bathymetry and other geologic data modeling results show that backscattering from rough basaltic hard bottoms in the absence of large scale seafloor slope is dominated by rough surface scattering with little contribution from volume scattering contrary to this sediment soft bottoms with subseafloor volume heterogeneity with or without seafloor roughness produce significant backscattering signals compared to a homogeneous sediment bottom

new petrological and geochemical data on mid paleozoic island arc volcanics of northern sierra nevada california evidence for a continent based island arc the mid paleozoic volcanics of northern sierra nevada consist of the sierra buttes rhyolites the taylor basalts and andesites and the keddie ridge basalt latite rhyolite suite the sierra buttes calc alkaline rhyolites display strong light rare earth element enrichment and negative end values the taylor basalts and andesites in the northern hough and genesee blocks exhibit calc alkaline affinities ree rare earth element patterns highly enriched in lree whereas in the southern hough block they are tholeiitic flat rare earth element patterns the abundance of silicic lavas the low end values of both the sierra buttes and taylor volcanics and the 18o values of the sierra buttes rhyolite and bowman lake trondjhemite provide evidence that the northern sierra nevada island arc was continent based the keddie ridge differentiated volcanics characterized by high zr y nb k and light rare earth elements are geochemically similar to a shoshonite suite their eruption at the end of the mid paleozoic v

age of the camaguey gold silver district cuba tectonic evolution and preservation of epithermal mineralization in volcanic arcs epithermal precious metal deposits commonly form in middle to late cenozoic volcanic arcs several kilometers above the level at which batholiths are emplaced this relationship has led to the guideline that epithermal deposits should not be sought in volcanic arcs where batholiths are widely exposed the camaguey district in central cuba violates this tenet and provides important insights into arc forming processes that create and expose epithermal deposits the camaguey district hosts the jacinto and florencia low sulfidation vein deposits and the deseada and golden hill high sulfidation prospects all of which are within a few kilometers of the large camaguey batholith some of the deposits such as jacinto lie immediately below a local paleosurface that exposes the batholith and probably formed when rhyolite domes were emplaced onto this surface a second group of deposits such as the deseada high sulfidation system is hosted by volcanic rocks that overlie the camaguey batholith and stand above the paleosurface new ar ar age measurements indicate that jacinto type deposits and prospects cooled through ar ar closure temperatures for adularia and muscovite at about 71 ma and are slightly younger than the widespread granodiorite facies of the camaguey batholith in contrast deseada type deposits and mineralized zones cooled through roughly similar closure temperatures for sericite illite and alunite at about 80 ma which is older than the age of the immediately underlying camaguey batholith these ages are best explained if the camaguey batholith and surrounding volcanic rocks underwent rapid uplift probably by tectonic unroofing to form the paleosurface below which jacinto type deposits formed and if the older deseada type deposits were thrust into place over this surface this tectonic unroofing probably took place in an extensional regime generated during oblique convergence of cuba with yucatan as the greater antilles arc moved north into the caribbean region during late cretaceous time thrusting probably accompanied late stages of this convergence and or later collision with the bahamas bank in eocene time all of the epithermal deposits were covered by late cretaceous eocene sedimentary rocks that have been removed only recently by erosion thus accounting for the preservation of these unusually old epithermal deposits extensional events causing tectonic unroofing are probably common in arcs that undergo oblique convergence and could be an important agent for formation of epithermal deposits in other parts of the world preservation of these deposits might be aided by deposition and later erosion of sedimentary cover related to later collisions

the bi azimuthal scattering distribution of an abyssal hill high resolution bistatic images of a typical abyssal hill on the western flank of the mid atlantic ridge are made with a low frequency towed array system operating remotely at 1 2 convergence zone 33 3 km stand off comparison with modeled images generated from high resolution supporting bathymetry sampled at 5 m intervals roughly the wavelength scale reveals that steep scarps return the strongest echoes because they project the largest area along the acoustic path from the source to receiver prominent returns deterministically image scarp morphology when the cross range axis of the system s resolution footprint runs along the scarp axis statistical fluctuations inherent in the scattered field prevent the system from distinguishing smaller scale anomalies on the scarps such as canyons and gullies 100 200 m scale that would otherwise be resolvable in range in certain bistatic geometries the mean bi azimuthal scattering distributions of the two major scarps on the abyssal hill are identical a

tectonics and geology of porphyry cu au deposits along the eastern sunda magmatic arc indonesia the discovery of the world class cu au deposit at tumpangpitu east java 1 9 gt 0 45 cu 0 45 g t au has reinforced the eastern sunda arc as a significant metallogenic belt that is highly promising for the discovery of major porphyry deposits the arc hosts three premier porphyry cu au deposits at batu hijau elang and tumpangpitu 300 t au and 5 mt cu these giant porphyry deposits are confined to the eastern segment of the eastern sunda arc eastern java to sumbawa constructed on island arc crust where the roo rise is being subducted by contrast major epithermal low sulfidation dominant deposits associated with poorly endowed porphyry prospects occur along the western segment of the arc western java developed on thick continental crust on the southern margin of sundaland associated with subduction of typically thin indian oceanic crust porphyry cu au deposits of the eastern sunda arc are spatially associated with small nested dioritic to tonalitic intrusive complexes with low k calc alkaline to weakly alkaline signatures hypogene alteration and mineralization developed during three main temporally and spatially overlapping events termed early transitional and late the hypogene cu au mineralized zone of the giant deposits forms a bell shaped body of 0 3 cu shell greater than 1 km in both diameter and vertical extent that is centered on multiphase elongate pencil like tonalite intrusions 200 to 1 200 m in diameter and 2 km vertical extent large 20 km 2 lithocaps associated with high sulfidation epithermal systems and postporphyry mineralization diatreme breccias characterize productive porphyry districts at batu hijau elang and tumpangpitu the known porphyry deposits with metal content exceeding 300 t au and 5 mt cu all formed later than 5 ma suggesting an important change in the metallogeny of the arc at this time these giant porphyry deposits formed relatively rapidly typically over a period of 30 to 860 k y during the pliocene pleistocene between 5 and 2 5 ma porphyry deposits along the eastern sunda arc display characteristic geologic features similar to porphyry deposits elsewhere significant differences include low k systems dominance of hydrothermal biotite over k feldspar early intense actinolite alteration associated with ore widespread shreddy chlorite after secondary biotite narrow quartz sericite pyrite alteration zones lack of development of chalcopyrite veins large overlying lithocaps and abundant chalcocite bornite covellite veinlets associated with late overprinting epithermal systems hydrothermal oligoclase is also more abundant than k feldspar in the central biotite magnetite zones

crystallization paths of leucite bearing lavas examples from italy the salic phases found in leucite basanites trachytes and phonolites may be used to portray crystallization in the system naalsio 4 kalsio 4 caal 2si 2o 8 sio 2 the phonolite pentahedron only two lavas have been found that contain the assemblage leucite nepheline plagioclase sanidine and liquid a natural pseudo invariant assemblage at 900 c 100 equivalent to the isobaric invariant point of the four component system the diversity of phases in this group of lavas illustrates the role of halogens in controlling their crystallization paths thus the presence of f in the leucite basanites has stabilized magnesian biotite and suppressed sanidine as has been found in other basanitic lavas brown and carmichael 1969 the presence of cl in these same lavas has induced the crystallization of sodalite which takes the place of nepheline in the groundmass however in the leucite trachytes biotite has suppressed olivine and coexists with sanidine and leucite the presence of s may produce hauyne at the expense of nepheline and in general sulphate minerals which include apatite have the role in lavas of low silica activity that pyrrhotite plays in liquids of high silica activity both pyroxenes and titaniferous magnetites in this suite of lavas are very aluminous groundmass crystals of pyroxene may have one fifth of si replaced by al other phases which occur occasionally are melanite garnet and a potassium rich hastingsite but neither ilmenite nor a sulphide mineral has been found phenocryst equilibration temperatures derived from olivine and sr rich plagioclase are generally in the range from 1 050 c to 1 150 c the high content of incompatible elements e g k ba rb f sr p in these lavas suggests that they represent a small liquid fraction from a mantle source which possibly contains phlogopite

geology and geochemistry of gunung subang gold deposit tanggeung cianjur west java indonesia abstract the gunung subang gold deposit is located in the sunda arc volcanic belt in west java indonesia the ore bodies are associated with volcanic rocks from the miocene koleberes and bentang formation to constrain the significance of the ore genesis and mineralization this study was carried out with the aim of examining the deposit using methods such as detailed field observation petrography petrochemistry zircon u pb dating hf isotope fluid inclusion analysis and sulfur and in situ pb isotope analyses the results suggest the following 1 the volcanic rocks in gunung subang belong to the basalt andesite group with 48 66 79 17 average 61 04 sio2 the trace element patterns of the volcanic rocks exhibit relatively low hree content flat hree patterns and weak negative or positive eu anomalies which are similar to those of typical arc magmatic rocks 2 most zircons selected from the volcanic rocks are magmatic and only a few are inherited the magmatic zircons have a weighted mean u pb age of 17 0 0 4 ma and the inherited zircons are from the precambrian dated at 887 2379 ma the magmatic zircons have ehf t values ranging from 1 24 to 13 59 indicating that the magmatism may be contaminated predominantly with juvenile crust but also with a small percentage of ancient crust 3 the sulfur isotopic compositions are fairly uniform and the 34s values of pyrite galena and sphalerite range from 0 53 to 2 97 suggesting a magmatic origin 4 the pb isotopic compositions of pyrite and galena are clustered and some include relatively high amounts of radiogenic lead the mean ratios of 206pb 204pb 207pb 204pb and 208pb 204pb are 18 59 0 007 15 65 0 007 and 38 89 0 017 respectively indicating that the ore forming material is highly related to miocene to pliocene volcanic rocks 5 fluid inclusions in the quartz from the ores are liquid and vapor liquid phases with components of the nacl h2o system with homogenization temperatures of 240 320 c and salinities of 0 2 6 2 wt nacl the coexistence of vapor and liquid rich fluid inclusions suggests that boiling occurred throughout the deposition of the ore 6 the results of electron probe microanalysis epma indicate that pyrite is the major au bearing mineral combined with the observation of scanning electron microscope sem gold is primarily present as au ag telluride minerals and there may also be native gold au0 finally we consider the gunung subang is an epithermal gold deposit related to the mid miocene magmatism

low sulfidation epithermal gold deposits in java indonesia characteristics and linkage to the volcano tectonic setting abstract java island a part of the eastern sunda magmatic arc is becoming an emerging part of the region for gold and copper endowment a total of 15 4 of 1044 tons of java gold endowment is originated from low sulfidation ls epithermal deposit type as a matter of fact the mineralization type that has given a significant credit to the gold endowment of java is intriguing to be geologically evaluated this paper is aimed to document some data information and summarizing the characteristics of selected 10 ls epithermal gold deposits in java including cibaliung kerta cisoka cikidang pongkor gunung peti cihar cijaringao petungkriyono and dalang turu as well as discussing their relationship with the volcano tectonic setting the formation of 10 ls epithermal deposits took place in the time span between early miocene and pleistocene which is coincident with the mio pliocene magmatic arc activities and even probably continue on to pleistocene all deposits show typical ls epithermal characteristics i e quartz veins with crustiform colloform textures relatively high au ag au ratio the cibaliung veins seem to have genetic linkage with the dioritic intrusion and diatreme phreatomagmatic breccias as well as with rhyolitic domes in kerta the veins exhibit close relationship with the rhyolitic rhyodacitic plugs the pongkor and cisoka veins are genetically related to rhyodacite dome plugs within caldera setting which is controlled by extensional structures cikidang and gunung peti may be related with the andesitic sub volcanic plugs cihar and cijaringao might be related to andesite dykes petungkriyono is linked with andesite and dacite plugs as well as diatreme breccia formed in an extensional basin with few calderas developed the dalang turu has been considered having a close linkage with andesite plug at extensional structures in relation to the volcano tectonic setting six deposits cibaliung kerta pongkor cisoka cikidang and gunung peti are obviously emplaced in bogor trough a back arc rift basin related to the mio pliocene arc the presence of rhyolitic to dacitic magmatism that could be related with caldera systems e g in kerta pongkor cisoka and the common association with subvolcanic plugs e g kerta are evidences of their linkage to the back arc rift basin setting the basaltic rocks in close proximity with the rhyolite rhyodacite as identified in cibaliung and kerta suggest the bimodal volcanism which is commonly occurred in the back arc rifting environment exploration for ls epithermal prospects therefore should be targeted along the back arc rifting basins e g bogor trough preferably over the areas with bimodal magmatism the bogor trough is reported extending to east java as kendeng trough basin which is also reasonably targeted for exploration

on the orientation of tensile dikes in a ridge centered plume abstract we present three dimensional numerical models of the ascent of a plume under a spreading ridge and the concomitant melt generation and crust formation using a mantle viscosity which depends on pressure temperature melt content and optionally water content from the velocity field of these convection models we compute the viscous stress tensor in the mantle assuming that melt rich channels or melt filled dikes are oriented parallel to the maximum compressional stress we calculate the orientation of such dikes in the partially molten zone of the plume head and beneath the ridge for the central part of the plume we find dike orientations parallel to the ridge in shallow parts of the plume head while they are ridge perpendicular at greater depth the boundary between these two regimes is shifted downwards for a water rich plume which dehydrates upon melting the two regimes of different dike or melt channel orientations seem to be in good agreement with seismic observations on depth dependent seismic anisotropy indicating a preference of our wet model we find a modest focusing of melt towards the spreading center beneath normal ridge in both models but also in the fully dehydrated parts of the plume head in the model where water was included those are regions where upwelling is essentially passive in contrast the plume in the water free model and the only partly dehydrated parts of the plume in the water bearing model tend to develop a dike orientation which moves melt away from the spreading center these regions are characterized by active upwelling the defocusing of melt in actively upwelling plume mantle has radial symmetry about the plume axis i e an outward orientation of the dikes is not only visible in planes perpendicular to the ridge but also along the ridge

seafloor acoustic backscattering from different geological provinces in the atlantic natural laboratory the characteristics of acoustic signals backscattered from inside corner oceanic crust and outside corner crust are investigated using acoustic reverberation data from the 1993 arsrp acoustics cruise specifically the seafloor dip distribution is compared between areas of each crustal type and correlations are sought between true grazing angle and backscattered signal strength beamformed and match filtered acoustic data from the monostatic wideband lfm experiment at site a are used to find the scattering strength corresponding to specific areas of the seafloor scattering strength determined from intersecting beams of different segments are summed to reduce left right ambiguity at the scale of analysis high scattering strengths are found to correspond to steep flanks of seafloor features and can be used to map their shape and orientation some of these features are characteristic of specific crustal regions scattering strength is found to increase with increasing effective grazing angle at a rate o

epithermal gold veins in a caldera setting banska hodrusa slovakia the central zone of the large miocene stiavnica stratovolcano in the western carpathians hosts epithermal au mineralization of intermediate sulfidation type located at deep levels of the historic rozalia base metal mine at banska hodrusa the au mineralization occurs as subhorizontal veins at the base of pre caldera andesites close to the roof of a subvolcanic granodiorite intrusion the veins are dismembered by a set of quartz diorite porphyry sills and displaced by the younger steeply dipping rozalia base metal vein and parallel structures the base metal vein structures are related to resurgent horst uplift in the caldera center the au mineralization formed during two stages based on fluid inclusion evidence both stages formed from fluids of low salinity 0 3 wt nacl eq which underwent extensive boiling at moderate temperatures 280 330 c variable pressure conditions 39 95 bars neglecting the effect of co2 indicate continual opening of the system and a transition from suprahydrostatic towards hydrodynamic conditions at shallow depths 550 m the fluid inclusions of the rozalia base metal vein show homogenization temperature peaks at 285 and 187 c and salinities between 1 and 4 wt nacl eq precipitation of au is considered to be the result of prolonged boiling of fluids and associated decrease in au solubility oxygen and hydrogen isotope data for quartz and carbonate from the au veins show a relatively homogeneous fluid composition 2 7 to 1 1 18o 78 to 62 d the combined 18ofluid and dfluid values suggest a mixed character of fluids falling between the fields of typical magmatic and meteoric water influenced by 18ofluid shift due to fluid rock isotopic exchange end stages of open system boiling and fractionation could have been reached at least locally significantly lower isotopic composition of meteoric fluids associated with au mineralization compared to those associated with the intrusion related mineralizations could have resulted from changing paleoclimate and or analytical problems of extraction of water from fluid inclusions the proposed genetic model for the au deposit at rozalia mine highlights the importance of hydrothermal activity during the early stage of caldera collapse caldera subsidence established new convective fluid flow paths along marginal caldera faults which acted as infiltration zones major metal precipitation occurred within subhorizontal structures that formed as the result of a collapse related stress field a shallow differentiated magma chamber at the base of the volcano was the likely source of heat and magmatic components for the mineralizing fluids

evidence for deep melting of hydrous metasomatized mantle pliocene high potassium magmas from the sierra nevadas 1 phase equilibrium experiments have been conducted on a primitive pliocene olivine leucitite wc 1 from the central sierra nevada california the near liquidus phase relations were determined from 1 2 to 3 4 gpa and at temperatures from 1350 to 1460 c in a piston cylinder apparatus the composition with 2 h 2 o is multiply saturated with olivine and clinopyroxene at approximately 3 1 gpa and 1460 c and with 6 water in the coexisting melt phlogopite is stable these results indicate that the magma was derived from a hydrous source at greater than 100 km depth xenoliths carried by other young pliocene lavas in the vicinity of wc 1 have yielded temperatures of equilibrium from 700 to 900 c with one outlier at 1060 c these xenoliths are consistent with the hypothesis that the lower lithosphere under the sierra nevada delaminated just prior to the pliocene and fluid metasomatized mantle melted to produce the high potassium pliocene lavas we suggest that subduction derived fluids drive a reaction that consumes garnet orthopyroxene to create clinopyroxene phlogopite and that the high potassium sierran magmas are created by melting phlogopite clinopyroxene metasomatized peridotite

using a coherent hydrophone array for observing sperm whale range classification and shallow water dive profiles sperm whales in the new england continental shelf and slope were passively localized in both range and bearing and classified using a single low frequency 2500 hz densely sampled towed horizontal coherent hydrophone array system whale bearings were estimated using time domain beamforming that provided high coherent array gain in sperm whale click signal to noise ratio whale ranges from the receiver array center were estimated using the moving array triangulation technique from a sequence of whale bearing measurements multiple concurrently vocalizing sperm whales in the far field of the horizontal receiver array were distinguished and classified based on their horizontal spatial locations and the inter pulse intervals of their vocalized click signals the dive profile was estimated for a sperm whale in the shallow waters of the gulf of maine with 160 m water column depth located close to the array s near field where depth estimation was feasible by employing time difference of arrival of the direct and multiply reflected click signals received on the horizontal array by accounting for transmission loss modeled using an ocean waveguide acoustic propagation model the sperm whale detection range was found to exceed 60 km in low to moderate sea state conditions after coherent array processing

petrology and geochemistry of the lamongan volcanic field east java indonesia primitive sunda arc magmas in an extensional tectonic setting new geochemical data are presented from prehistoric and historical multifarious process involving possible inputs from the subducted oceanic lithosphere subducted oceanic sedieruptive products of the lamongan volcanic field lvf east java a region of the sunda arc covering 260 km and containing ments and fluids the asthenospheric and lithospheric portions of the mantle wedge above the subduction zone 90 eruptive vents plus the historically active lamongan volcano lvf lavas include medium k basalts and basaltic andesites from and the arc crust e g tatsumi eggins 1995 following melt generation processes such as crystal fractionation historical eruptions of lamongan and prehistoric eruptions in the eastern lvf along with a high k suite represented by prehistoric accumulation and crustal assimilation during transit to the surface may obscure the true nature of the magma deposits in the western lvf although lacking some of the characteristics of truly primary basalts the least evolved lavas identified source region the effects of these processes on the compositions of erupted lavas must therefore be removed in the lvf have some of the lowest sio2 contents 43 wt sio2 yet reported in sunda arc volcanic rocks mass balance before models of arc magma genesis can be tested for this reason it is desirable to sample magmas that considerations indicate that two chemically distinct lvf magmas may be parental to suites currently being erupted from the neighbouring have suffered minimal modification since segregation from their source region the compositions of the primary volcanoes semeru and bromo lamongan s historical lavas can be related to the medium k andesitic products of semeru by fractional or primitive magmas from different arcs provide a window on the diverse mechanisms of and the components crystallization despite the former s location at the same distance from the trench as bromo a high k volcano extensional tectonics involved in melt production at convergent margins and as such are essential to our understanding of the possibly related to arc segmentation in the region of the lvf creating subduction zone environment conditions that promote the rapid ascent of parental magmas is many studies have highlighted the correlation between probably responsible for this and several other features of the complex extensional tectonics in volcanic arcs and the eruption of lavas with primitive chemical characteristics e g luhr carmichael 1981 knittel oles 1995 bacon et al

seismic evidence for hotspot induced buoyant flow beneath the reykjanes ridge volcanic hotspots and mid ocean ridge spreading centers are the surface expressions of upwelling in earth s mantle convection system and their interaction provides unique information on upwelling dynamics i investigated the influence of the iceland hotspot on the adjacent mid atlantic spreading center using phase delay times of seismic surface waves which show anomalous polarization anisotropy a delay time discrepancy between waves with different polarizations this anisotropy implies that the hotspot induces buoyancy driven upwelling in the mantle beneath the ridge

potassium rich volcanic rocks of the muriah complex java indonesia products of multiple magma sources abstract the extinct pleistocene volcano muriah situated behind the main pleistocene recent sunda magmatic arc in north central java has erupted at least two contrasted groups of lavas one group forms a well defined compositional series anhydrous series from leucite basanite to tephritic phonolite with olivine and tschermakitic clinopyroxene the main phenocrysts the other group the hydrous series includes compositionally variable tephrites and high k andesites with common plagioclase biotite and amphibole lavas of the anhydrous series are much richer in lil trace elements than the most potassic lavas of neighbouring active volcanoes but relative hfs element enrichment is less pronounced ree patterns have almost constant slopes from la 250 600 times chondrites to yb 5 10 times chondrites while those of lavas of active centres are less light enriched and show flattening in the heavy ree anhydrous series initial 87sr 86sr ratios 0 7043 0 7046 are lower than those of active centres 0 7047 0 7053 hydrous series lavas are intermediate in all these geochemical characteristics the most mafic a series leucite basanite with mg mg fe 2 0 69 140 ppm ni and 620 ppm cr was probably derived from the primary magma for the series by fractionation of only 5 wt olivine its ree pattern suggests derivation from a garnet bearing source experiments on this basanite with up to 10 olivine and 20 orthopyroxene added and in the presence of h2o and h2o co2 mixtures have shown that for all but very high magma water contents the olivine and garnet liquidus fields are widely separated by fields of phlogopite and clinopyroxene there is no liquidus field of orthopyroxene hence if magma production involved an equilibrium melting process alone the most probable sources are of garnet bearing phlogopite clinopyroxenite type alternatively this magma may represent the end product of interaction between a low k basanite magma from a garnet lherzolite source in the asthenosphere and a phlogopite bearing lherzolite zone in the lower lithosphere its production was probably related to crustal doming and extension superimposed on the dominant subduction regime hydrous series magmas may have resulted from mixing between anhydrous series magmas and high k calc alkaline basaltic to andesitic magmas more directly related to subduction processes

deterministic reverberation from ocean ridges the deterministic relationship between low frequency reverberation and detailed geomorphology is documented for wide area insonifications of the western mid atlantic ridge charted reverberation registers precisely with extended ridges and has a high correlation with negative transmission loss confirming previous analysis with lower resolution data j acoust soc am 95 1865 1881 1993 for a given ridge prominent returns come from steep escarpments and cliffs that face the bistatic source and receiving arrays this was hypothesized in the above reference but could not be proven without the higher resolution waveforms and more sophisticated charting procedures of the present analysis monostatic and bistatic returns from the same lineated ridge at 1 2 11 2 and 21 2 convergence zone ranges are used to thoroughly document the registration with steep scarps a decrease in resolution of the scattering site is also documented for increasing measurement range ambiguity from the horizontal receiving array is resolved by two independent methods that show close agreement for prominent returns the first is an environmental symmetry breaking esb technique that requires detailed knowledge of bathymetry to be incorporated into a range dependent propagation model the second is a global inversion of reverberation charts obtained from differing receiving array locations and orientations the global inversion requires no a priori environmental information and has not been previously applied to field data

thermal and petrological consequences of melt migration within mantle plumes the high temperatures and high degrees of melting expected in the core of mantle plumes have virtually no expression in the eruption temperatures of hotspot lavas nor in the composition of their glasses which is restricted in the basaltic field a solution to this paradox is looked for in the melt migration processes within the melting region of mantle plumes three dimensional convective calculations at rayleigh number of 10 6 allow estimates of the possible temperature melt fraction and stress fields within a plume two regions with different melt migration patterns can be distinguished a lower zone ranging in depth from the base of the melting region 150 km to around 80 100 km where the first melt fraction is redistributed in a sub horizontal vein network and convects in response to the steep horizontal temperature gradient this process is able to homogenize the temperature within the melting region very efficiently the high 300 c temperature contrast between the centre of the plume and the surrounding mantle can be reduced to a few tens of degrees at the top of this zone fractional crystallization of high pressure phases will strongly modify the composition of the melt as it circulates toward the periphery of the melting region a second upper zone where the sub vertical vein orientation will make possible rapid melt migration toward the surface extends to the base of the lithosphere due to the buffering of the plume temperature around a value close to the mean upper mantle temperature the degree of adiabatic melting within this upper zone will not greatly exceed that beneath normal spreading centres even in the case of on ridge hotspots the lavas erupted at hotspots are likely to result from the mixing in various proportions of these low pressure melts basalts with the highly evolved liquids possibly with kimberlitic to alkalic affinities resulting from fractional crystallization of the high pressure melt fractions produced at the base of the melting region this scenario could account for the low eruption temperatures and mg contents of hotspot lavas in spite of a complex high pressure and thus high temperature history evidenced by some geochemical trends

miocene shoshonite volcanism in sardinia implications for magma sources and geodynamic evolution of the central western mediterranean in this paper we document the existence of a miocene shoshonite sho volcanism in northern sardinia anglona this occurrence completes the spectrum of orogenic magmas related to the subduction process which developed from the eocene along the palaeo european continental margin in concert with the opening of the ligurian balearic back arc basin and southeastward drift rotation of the sardinia corsica continental block k ar ages show that the oldest volcanics of the area are calcalkaline ca basalts and andesites 21 ma overlain by 19 7 18 4 ma old more potassic products such as high potassium calcalkaline hk ca and sho lavas ca hk ca and sho suites include basalts and differentiated lavas of andesite and latite composition respectively that according to the pele software modelling represent 40 45 residual liquid fraction after shallow fractional crystallization application of the arc magma simulator software suggests that the generation of primary melts of the distinct suites may occur at similar degrees of partial melting 5 8 and melting pressures 2 2 2 gpa 60 70 km depth in the mantle wedge by contrast the potassic character of parental melts of ca hk ca and sho suites is controlled by 1 the amount of subducted continental components possibly terrigenous sediments and 2 the pressure depth at which these metasomatic agents are released from the slab results suggest that the slab depth beneath the volcanic district increased from 80 100 to 100 120 km for ca and sho magmas respectively accordingly the evolution from ca to sho magmatism in the same plumbing system could be related to slab deepening and increase of the subduction angle of 5 10 in the time span of 2 3 ma this tectono magmatic scenario conforms to the major anticlockwise rotation 30 event of the sardinia block between 20 5 and 18 ma this geodynamic evolution preludes the development of the volcanism in the apennine tyrrhenian domains where the final collisional post collisional stages of subduction were characterized by accentuated slab retreat and roll back inter arc extension and eruption of highly potassic magmas in the frontal arc roman and aeolian provinces

genetic links between ash flow calderas and associated ore deposits as revealed by large scale thermo mechanical modeling abstract in addition to a number of epithermal ore deposits some porphyry type ore deposits are also hosted by ash flow calderas spatial correlation between ash flow calderas and these deposits is observed in several parts of the world but temporal correlation between the mineralization and the episode of caldera formation remains unclear especially because geochronological data indicate that the mineralization may date to several million years before or after caldera formation because caldera collapse represents only a very short event in a long time scale evolution between a silicic magma chamber and its host rocks we have developed a thermo mechanical model of upper crustal and magmatic system behavior during the pre and post caldera formation stages major petrophysical properties of ash flow caldera related rocks are incorporated into the model which accounts for brittle elasto ductile rheology and heat transfer and reproduces fault initiation and various caldera collapse scenarios large scale mechanisms of initiation of thermal and structural traps for epithermal ore deposits are described in particular we found that the outer sides of caldera border faults are associated with both anomalous heat transfer and a high fracture density the finite size of the insulating intracaldera units forces the accumulated heat excess to be laterally transferred across the border faults in most cases the model predicts y shaped fault geometry which is surprisingly similar to that of mineralized faults in the field variations in lithostatic pressure on the magma chamber roof and in the vicinity of the border faults can reach 10 to 20 mpa with deep overpressured zones close to the inner edge of the chamber corners despite the fact that hydrothermal convection and fluid geochemistry are not included in the model these thermal and mechanical results are believed to constrain the conditions for mineralization processes our results show that in the presence of regional extension the development of caldera border faults may be suppressed to the advantage of deep seated fractures clustered above the central part of the magma chamber thus favoring conditions for the formation of porphyry type ore deposits finally we demonstrate that well before the eruption the gradual emplacement of a hot and large silicic magma chamber may create significant extensional stress in the brittle upper crust resulting in breakup and pre eruptive normal faulting and thus allowing for conditions of pre caldera mineralization

natural examples of olivine lattice preferred orientation patterns with a flow normal a axis maximum tectonic plate motion is thought to cause solid state plastic flow within the underlying upper mantle and accordingly lead to the development of a lattice preferred orientation of the constituent olivine crystals the mechanical anisotropy that results from such preferred orientation typically produces a direction of maximum seismic wave velocity parallel to the plate motion direction this has been explained by the existence of an olivine preferred orientation with an a axis maximum parallel to the induced mantle flow direction in subduction zones however the olivine a axes have been inferred to be arranged roughly perpendicular to plate motion which has usually been ascribed to localized complex mantle flow patterns recent experimental work suggests an alternative explanation under conditions of high water activity a b type olivine preferred orientation may form with the a axis maximum perpendicular to the flow direction natural examples of such b type preferred orientation are however almost entirely unknown here we document widespread b type olivine preferred orientation patterns from a subduction type metamorphic belt in southwest japan and show that these patterns developed in the presence of water our discovery implies that mantle flow above subduction zones may be much simpler than has generally been thought

efemcukuru b rich epithermal gold deposit izmir turkey efemcukuru located in the aegean region turkey is an example of vein type epithermal gold deposit with related stockwork and replacement mineralisation the veins are hosted by late cretaceous paleogene flysch facies rocks of the izmir ankara zone which were intruded by rhyolites from of neogene volcanism gold mineralisation is associated with late pulses of magmatic hydrothermal activity and is present in zones of hydraulic brecciation adjacent to veins or stockwork zones around a dome shaped small intrusion the intrusion and later epithermal mineralisation are both controlled by nw setrending faults and mineral deposits occur along strike with dips 60j to 80j to the northeast individual quartz veins associated with sulphide minerals and mineralised hornblende facies hornfels are other important ore bearing formations the alteration associated with mineralisation is represented mainly by rhodonite rhodochrosite axinite quartz calcite and adularia in veins and stockwork zone and chlorite sericite illite and kaolinite in the wall rock homogenisation temperatures of 200 300 jc reflect emplacement of ore distant from inferred magmatic heat in epithermal environment due to wide range in salinity of the fluids 0 9 eq wt nacl sulphide diversity in the deposit is rather rich than the low sulphidation epithermal systems the fluid inclusion data indicate that a complicated geothermal system existed both the gas data and the microthermometry data indicate that there was fluid mixing each type of mineralisation has been studied with the aim of clarifying the paragenetic relationships among the different minerals arsenopyrite pyrite marcasite sphalerite galena and chalcopyrite are the main minerals with pyrrhotite fahlore group sphene rutile and gold occurring as accessories pyrolusite limonite goethite lepidocrocite covellite chalcocite malachite and azurite are of secondary origin d 2003 elsevier science b v all rights reserved

the trinity pattern of au deposits with porphyry quartz sulfide vein and structurally controlled alteration rocks in ciemas west java indonesia the ciemas gold mining area is located in the sunda arc volcanic rock belt west java indonesia ore bodies are associated with miocene andesite dacite and quartz diorite porphyrite to constrain ore genesis and mineralization significance a detailed study was recently conducted examining these deposits which included detailed field observation petrographic study petrochemistry sulfur isotope analyses zircon u pb dating and fluid inclusion analysis the results include the following findings 1 ore types have been identified as porphyry a quartz sulfide vein and structure controlled alteration rocks 2 in host rocks zircon la icp ms u pb dating of quartz diorite porphyrite amphibole tuff breccia and andesite yield ages of 17 1 0 4 ma 17 1 0 4 ma and 17 5 0 3 ma respectively 3 fluid inclusions in the quartz from ore are given priority to liquid and gas liquid phases and their components are of the nacl h2o system with homogenization temperatures of 240 320 c salinities of 14 17 densities of 0 85 0 95 g cm3 and fluid pressure values between 4 1 and 46 8 mpa corresponding to metallogenic depths from 150 to 1730 m fluid characteristics are identified as similar to those of high sulfur epithermal deposits 4 the sulfur isotopic compositions are notably uniform the 34s values of wall rocks range from 3 71 to 3 85 and the 34s values of ores vary from 4 90 to 6 55 the sulfur isotopic composition of ores is similar to that of the wall rocks indicating a mixed origin of mantle with a sedimentary basement 5 the trace element patterns of different ore types are similar which indicates that they originate from the same source au deposits primarily occurred during the late magmatic activity finally we have set up the regional metallogenic model confirming that this gold deposit in the sunda arc volcanic rock belt belongs to a metallogenic system from porphyry to epithermal type

the influence of large scale seafloor slope and average bottom sound speed on low grazing angle monostatic acoustic scattering variations in large scale seafloor slope and average seabed sound speed account for a significant portion of the variations in scattering intensity observed in low grazing angle monostatic reverberation numerical modeling using a finite difference solution to the elastic wave equation is used to quantify the effect of these large scale parameters in interpretations of reverberation data for hard rough seafloor e g basalt the results of the modeling suggest that the monostatic backscattering strength increases with increasing large scale seafloor slope up to a slope of about 15 dipping toward the incident direction once the grazing angle of the incident wavefield exceeds the critical grazing angle for the flat reference seafloor the backscattering intensity increases only slowly with increasing grazing angle similarly average subseafloor sound speed has a significant effect seafloor with low sound speeds characteristic of soft bottoms e g sediment generate significantly weaker backscatter signals than seafloor with sound speeds characteristic of hard bottoms e g basalt the difference is that the shear waves can always be passed into soft bottoms because even for a flat seafloor there is no shear wave critical grazing angle

reverberation at the mid atlantic ridge during the 1993 arsrp experiment seen by r v alliance from 200 1400 hz and some modeling inferences in july 1993 saclantcen participated in an experiment for the acoustic reverberation special research program arsrp the primary objective was to take high resolution measurements to shed light on the detailed physical processes dominating the low frequency scattering from rough topographic features and from deep sediment pond areas a very detailed set of monostatic and bistatic scattering experiments were conducted just west of the mid atlantic ridge near 26 degrees n 47 degrees w results from saclantcen s r v alliance are presented which show monostatic and bistatic scattering from selected bathymetric features using pulsed sources from 200 1400 hz and sus charges area water depths ranged from 3300 to greater than 5200 m the receivers were a horizontal array of 128 elements spaced at 0 5 1 and 2 m source depths varied from 120 to 1200 m and receiver depths ranged from 400 to 500 m received reverberation levels are presented as functions of the estimated scatterer position on area bathymetry maps results show the same high scattering areas from one seamount were observed in three distinct frequency bands centered at 227 350 and 700 hz even at 1350 hz the correlation of scattering highlights with nearby bathymetric features is quite good comparisons of measured reverberation and modeled reverberation are presented which suggest that the dominant longer range scattering from the large features is driven by the steep slopes present above the critical depth but that small scale roughness is also essential for strong backscatter

influence of melt on the creep behavior of olivine basalt aggregates under hydrous conditions the influence of melt on the creep behavior of olivine basalt aggregates under hydrous conditions has been investigated by performing a series of high temperature triaxial compression experiments samples with melt fractions of 0 02 0 12 were deformed under water saturated conditions at temperatures between 1373 and 1473 k and a confining pressure of 300 mpa in a gas medium apparatus at constant differential stress and temperature the rate of deformation increased rapidly but systematically with increasing melt fraction in the diffusion creep regime at a given differential stress samples with melt fractions of 0 02 and 0 12 deformed a factor of 2 and 20 respectively faster than a melt free sample in the dislocation creep regime a sample with a melt fraction of 0 12 deformed a factor of 40 faster than a melt free sample for partially molten olivine basalt aggregates deformed under hydrous conditions the dependence of creep rate on melt fraction can be expressed in the form 0 exp where 26 for diffusion creep and 31 for dislocation creep the results of this study combined with reasonable estimates for the spatial variation in the concentrations of water and melt as well as for the geotherm and the activation volume for creep provide constraints on the viscosity structure of earth s upper mantle as an example we present a viscosity profile for the mantle wedge above a subducting plate demonstrating that the viscosity in that region can vary by 3 orders of magnitude over a depth of 60 km due to the combined effects of water and melt weakening

the geochemistry and petrogenesis of k rich alkaline volcanics from the batu tara volcano eastern sunda arc mineralogical major and trace element and isotopic data are presented for leucite basanite and leucite tephrite eruptives and dykes from the batu tara volcano eastern sunda arc in general the eruptives are markedly porphyritic with phenocrysts of clinopyroxene olivine leucite plagioclase biotite set in similar groundmass assemblages these k rich alkaline volcanics have high concentrations of large ion lithophile lil light rare earth lre and most incompatible trace elements and are characterized by high 87sr 86sr 0 70571 0 70706 and low 143nd 144nd 0 512609 0 512450 compared with less alkaline volcanics from the sunda arc they also display the relative depletion of ti and nb in chondrite normalized plots which is a feature of subalkaline volcanics from the eastern sunda arc and arc volcanics in general chemical and mineralogical data for the batu tara k rich rocks indicate that they were formed by the accumulation of variable amounts of phenocrysts in several melts with different major and trace element compositions the compositions of one of these melts estimated from glass inclusions in phenocrysts is relatively fe rich 100 mg mg fe2 48 51 and is inferred to have been derived from a more primitive magma by low pressure crystal fractionation involving olivine clinopyroxene and spinel mg rich mg 90 and cr rich up to 1 7 wt cr2o3 zones in complex oscillatory zoned clinopyroxene phenocrysts probably also crystallized from such a magma the marked oscillatory zoning in the clinopyroxene phenocrysts is considered to be the result of limited mixing of relatively evolved with more primitive magmas together with their phenocrysts along interfaces between discrete convecting magma bodies

effects of volcano loading on dike propagation in an elastic half space we use laboratory experiments and numerical models to examine the effects of volcano loading on the propagation of buoyant dikes in a two dimensional elastic half space in laboratory experiments we simulate the propagation of buoyant dikes in an isotropic regional stress field by injecting air into tanks of solidified gelatin a weight resting on the surface of the gelatin represents a volcanic load a numerical model is used to simulate these experiments both experiments and numerical simulations show that as a dike ascends it begins to curve toward the load in response to the local stress field imposed by the load the lateral distance over which dikes curve to the load increases with the ratio of average pressure at the base of the load to the dike driving pressure for realistic volcano and dike dimensions this pressure ratio is going to be large suggesting that dikes can converge to a volcano over lateral distances several times the load width numerical calculations involving an anisotropic regional stress field however predict that the lateral extent of dike attraction shrinks as the regional horizontal compressive stress decreases relative to the vertical compressive stress dike focusing will be substantial if the regional differential stresses are less than the average pressure at the base of the load if this is the case then our models predict a positive feedback between the size of volcanoes and the area of dike attraction this feedback may promote the development of large discrete volcanoes and also predicts a positive correlation between the spacing and sizes of adjacent volcanoes to test this prediction we examine nearest neighbor pairs of the 21 largest volcanoes in the cascade range the 14 pairs examined show a large range in volcano spacing 6 115 km and a statistically significant correlation between spacing and average volcano height this result is consistent with our model results and suggests that the local compressive stress induced by these volcanoes may be an important factor in controlling magma transport in the lithosphere

the continental crust contributes to magmatic hydrothermal gold deposit in ciemas west java indonesia constraints from hf isotopes of zircons and in situ pb isotopes of sulfides abstract multiple periods of arc magmatism induced by the subduction of the indian australian plate northward developed on java island and multistage porphyry epithermal metallogenic systems occurred within the late eocene early miocene and the late miocene early pleistocene magmatic belts these porphyry epithermal metallogenic systems have obvious spatial variations in west java there are large populations of low sulfidation type epithermal deposits while east java and its east are characterized by the occurrences of porphyry deposits however the newly discovered ciemas deposit in west java a middle miocene 17 ma porphyry epithermal au deposit provides an opportunity for further understanding the porphyry epithermal mineralization in java to elucidate the controlling factors of porphyry epithermal mineralization in west java we analyzed the hf isotopies of zircons from the igneous rocks and in situ pb isotopes of sulfides galena pyrite arsenopyrite in the ciemas deposit the results show that the zircons ehf t of igneous rocks are uniform with an average value of 11 5 0 39 and the peak value of tdm2 is 1500 1650 ma suggesting the middle miocene arc magmatism in ciemas suffered intense crustal contamination the pb isotopic compositions of sulfides are very uniform and have high amounts of radiogenic lead the mean ratios of 206pb 204pb 207pb 204pb and 208pb 204pb are 39 343 0 059 15 73 0 015 and 18 854 0 025 respectively indicating that the mineralization materials of the ciemas gold deposit mainly originated from ancient continental crust the multistage arc magmatism induced by the subduction of the indian australian plate northward beneath java island control the porphyry and epithermal mineralization in java the middle miocene arc magmatism in ciemas contaminated intensely by the sundaland and the ancient continental crust provides the main metal source for the ciemas deposit in west java

contribution of remote sensing techniques to the identification and characterization of miocene calderas lesvos island aegean sea hellas remote sensing techniques were combined with field investigations in order to locate and accurately characterize volcanic structures in the 17 my volcanic field of lesvos island which are difficult to recognize due to erosion and faulting landsat thematic mapper landsat tm and satellite pour observer la terre panchromatic spot pan satellite images as well as the digital elevation model dem of the study areas were digitally processed in order to reveal specific geological characteristics related with caldera structures such as topographic caldera rims and floors ring faults areas of hydrothermal alteration drainage networks and lava domes both internal and external to caldera structures six caldera structures have been recognized of which four have been identified for the first time and are reported here sigri mesotopos agra and skalohori calderas the calderas of stipsi and vatoussa have been previously reported in the literature but their revised geometry and dimensions are reported here

imaging fluid related subduction processes beneath central java indonesia using seismic attenuation tomography abstract we use local earthquake data observed by the amphibious temporary seismic meramex array to derive spatial variations of seismic attenuation qp in the crust and upper mantle beneath central java the path averaged attenuation values t of a high quality subset of 84 local earthquakes were calculated by a spectral inversion technique these 1929 t values inverted by a least squares tomographic inversion yield the 3d distribution of the specific attenuation qp analysis of the model resolution matrix and synthetic recovery tests were used to investigate the confidence of the qp model we notice a prominent zone of increased attenuation beneath and north of the modern volcanic arc at depths down to 15 km most of this anomaly seems to be related to the eocene miocene kendeng basin mainly in the eastern part of the study area enhanced attenuation is also found in the upper crust in the direct vicinity of recent volcanoes pointing towards zones of partial melts presence of fluids and increased temperatures in the middle to upper crust the middle and lower crust seems not to be associated with strong heating and the presence of melts throughout the arc enhanced attenuation above the subducting slab beneath the marine forearc seems to be due to the presence of fluids

fish population and behavior revealed by instantaneous continental shelf scale imaging until now continental shelf environments have been monitored with highly localized line transect methods from slow moving research vessels these methods significantly undersample fish populations in time and space leaving an incomplete and ambiguous record of abundance and behavior we show that fish populations in continental shelf environments can be instantaneously imaged over thousands of square kilometers and continuously monitored by a remote sensing technique in which the ocean acts as an acoustic waveguide the technique has revealed the instantaneous horizontal structural characteristics and volatile short term behavior of very large fish shoals containing tens of millions of fish and stretching for many kilometers

adularia in epithermal veins queensland morphology structural state and origin four types of adularia i e sub rhombic rhombic tabular and pseudo acicular are recognised from examination of samples from ten epithermal vein deposits and prospects in queensland based on morphology of the individual crystals further investigation of the structural state of adularia reveals that each group has some specific features in terms of the degree of al si disordering which can be related to various crystallisation conditions and the thermal history sub rhombic adularia is commonly 2 4 mm in size and subhedral with more or less rhombic outlines and has a relatively ordered al si distribution 2t1 0 84 reflecting slow crystallisation conditions adularia of this type in association with coarse grained quartz is predominant at deep levels of epithermal systems where boiling is initiated in an environment of low permeability and the fluid is slightly supersaturated with respect to adularia and quartz tabular adularia characterised by its lath shape and disordered structure 2t1 values ranging from 0 64 to 0 74 is likely to have formed when the fluid moves up to a more permeable environment and starts boiling violently relatively high temperatures and rapidly changing conditions account for its special morphology and disordered structure rhombic adularia showing very small crystal size 0 2 mm with euhedral rhombic form has an intermediate degree of al si ordering pseudo acicular adularia is interpreted as pseudomorphs after carbonate and its high al si ordered structure is attributed to the presence of a carbonate precursor these two types of adularia commonly occur within crustiform and colloform bands in association with high grade ore and chalcedony or fine grained quartz which often displays various recrystallisation textures it is most likely that adularias of these two types are formed when extensive boiling is protracted microprobe analyses indicate the composition of all adularia types close to pure kalsi3o8 sericite and or carbonate altered adularias consistently display more ordered structures suggesting that the post crystallisation thermal regime affects the structural state of altered adularia even at temperatures as low as in epithermal environments

azimuthal anisotropy and phase velocity beneath iceland implication for plume ridge interaction abstract we have determined the pattern of azimuthal anisotropy beneath iceland from shear wave splitting and rayleigh wave tomography using seismic data recorded during the icemelt and hotspot experiments the fast directions of shear wave splitting are roughly n s in western iceland and nnw sse in eastern iceland in western iceland azimuthal variations in rayleigh wave phase velocity show that fast directions are close to the plate spreading direction at short periods of 25 40 s and roughly parallel to the mid atlantic ridge at longer periods of 50 67 s beneath the rift zones in central iceland we find a ridge parallel fast direction at periods of 25 40 s and significantly weaker azimuthal anisotropy at periods of 50 67 s the 2 d variation of isotropic phase velocity at periods of 33 67 s indicates that the lowest velocities are beneath the rift zones in central iceland rather than above the plume conduit in southeast iceland while ridge parallel alignment of melt films might contribute to anisotropy above 50 km depth beneath the rift zones the overall observations are consistent with a model in which plume influenced hot buoyant mantle rises beneath the mid atlantic ridge at depths greater than 50 km and is preferentially channeled along the ridge axis at the base of the lithosphere beneath iceland the shear wave splitting results are attributed primarily to a n s mantle flow at depths greater than 100 km

geothermal systems on the island of java indonesia abstract this paper presents an overview of the geothermal systems on the island of bali indonesia physicochemical data of hot springs and shallow geothermal wells were collected from four geothermal locations penebel batur banjar and banyuwedang the concentrations for the three main anions varied significantly indicating a different geothermal history the values for cl ranged from 0 1 to 1000 mg l for hco3 from 20 to 2200 mg l and for so42 from 0 1 to 500 mg l although the island of bali is underlain by carbonate rocks a carbonate host rock for the geothermal reservoirs could not be confirmed because the ca2 mg2 hco3 molar ratios were approximately 0 4 well below 1 0 and the k mg ratios were approaching those of a calc alkaline rock reservoir the hco3 of the thermal waters correlated with ca2 mg2 sr2 and k indicating water rock interaction in the presence of carbonic acid phase separation was inferred for the bedugul and banjar geothermal systems because of relatively high b cl ratios boron isotopes were determined for selected samples with values ranging from 11b of 1 3 to 22 5 nbs 951 the heavy 11b of 22 5 together with a low b cl ratio indicated seawater input in the banyuwedang geothermal system the hydrogen and oxygen isotopic composition of the thermal water plotted along the global meteoric water line gmwl and close to the mean annual value for precipitation in jakarta indicating a meteoric origin of the geothermal water comparison of the si na k na k ca and na li geothermometers with actual reservoir temperature measurements and physicochemical considerations led to the conclusion that the na li thermometer provided most reliable results for the determination of geothermal reservoir temperatures on bali using this thermometer the following reservoir temperatures were calculated 1 penebel bedugul from 235 to 254 c 2 batur 240 c and 3 banjar 255 c due to seawater input this thermometer could not be applied to the banyuwedang geothermal system there application of a sio2 thermometer indicated a reservoir temperature below 100 c

exploration tools for linked porphyry and epithermal deposits example from the mankayan intrusion centered cu au district luzon philippines the mankayan mineral district of northern luzon philippines hosts several significant ore deposits and prospects of various types within an area of similar to 25 km 2 including the far southeast porphyry cu au deposit the lepanto high sulfidation epithermal cu au deposit the victoria intermediate sulfidation epithermal au ag vein deposit the teresa epithermal au ag vein deposit the guinaoang porphyry cu au deposit and the buaki old palidan porphyry cu au prospects all having formed in a period of about 2 m y from similar to 3 ma the geologic units include 1 a basement composed of late cretaceous to middle miocene metavolcanic rocks volcaniclastic rocks 2 the miocene 12 to 13 ma tonalitic bagon intrusive complex 3 the pliocene similar to 2 2 to 1 8 ma imbanguila dacite porphyry and pyroclastic rocks and 4 postmineralization cover rocks including die similar to 1 2 to 1 0 ma bato dacite porphyry and pyroclastic rocks and the similar to 0 02 ma lapangan tuff extensive advanced argillic alteration crops out for similar to 7 kin along the inconformity between the basement rocks and the imbanguila dacite formation consists of quartz alunite pyrophyllite or diaspore with local zones of silicic alteration and a halo of dickite kaolinite the alteration and its subhorizontal geometry indicate that it is a lithocap or coalesced lithocaps the northwest striking portion is similar to 4 km long and hosts the lepanto enargite au ore deposit also controlled by the lepanto fault the lepanto epithermal deposit is related to the underlying far southeast porphyry the quartz alunite alteration halo of lepanto is contemporaneous with the similar to 1 4 ma potassic alteration of the porphyry there are also silicic advanced argillic alteration patches similar to 600 m above the far southeast orebody at the present surface these are interpreted to be perched alteration there is no systematic mineralogical or textural zoning in the lepanto lithocap that indicates direction to the intrusive source most surface samples of the lithocap contain less than 50 ppb au despite many being less than a few hundred meters from underground cu au ore this study found that several characteristics of the lepanto lithocap change systematically with distance from the causative intrusion the alunite absorption peak at similar to 1 480 nm in the short wavelength infrared swir spectrum shifts to higher wavelengths where the sample is closer to the intrusive center due to higher na and lower k content in the alunite published experimental studies indicate that high na na k is related to higher formation temperature high ca alunite including huangite also occurs at locations proximal to the intrusive center alunite mineral composition analyzed by laser ablation inductively coupled plasma mass spectrometry la icp ms indicates that the pb content decreases toward the intrusive center whereas sr la sr ph and la pb increase markedly whole rock compositions using only nonmineralized taken as cu similar to 350 m above the upper extent of the veins an airborne geophysics survey indicates that the far southeast orebody is associated with a wide zone of demagnetization due to extensive magnetite destructive phyllic alteration such low magnetic anomalies on the margin of a large lithocap elsewhere may deserve attention the directional indicators and mineralization signatures found in this study have the potential to indicate direction to the intrusive center during exploration of similar porphyry epithermal districts

supergene alteration of primary ore assemblages from low sulfidation au ag epithermal deposits at pongkor indonesia and nazareno peru the textures and mineralogical assemblages of high grade ore samples from the low sulfidation au ag epithermal deposits of pongkor 2 ma west java indonesia and nazareno 10 ma cordillera shila southern peru were studied to investigate processes related to post depositional alteration of primary mineral parageneses both deposits are characterized by a late primary high grade base and precious metal stage composed of chalcopyrite sphalerite galena pyrite polybasite pearceite tennantite tetrahedrite electrum minerals of the polybasite pearceite series the main ag carriers were found to be transformed into acanthite acanthite was also found locally in association with native silver as a replacement product of base metal sulfides as veinlets alternating rhythmically with supergene iron oxyhydroxides replacing pyrite as well as associated with barite iron oxyhydroxides and covellite as boxwork fillings primary electrum grains with a composition of about au0 6ag0 4 are partially replaced by au ag sulfide locally identified as uytenbogaardtite ag3aus2 and or by acanthite with both of the replacing minerals commonly associated with vermicular electrum of a greater fineness up to au0 8ag0 2 the occurrence of the replacement textures near the present day surface and the associated secondary minerals strongly suggests a supergene origin for the au and ag sulfide phases the comparison of pongkor and nazareno also suggests that supergene remobilization of au and ag is geochemically significant and can occur in widely differing morphological and climatic contexts

a comparison of bistatic scattering from two geologically distinct abyssal hills the bistatic scattering characteristics of two geologically distinct abyssal hills located on the western flank of the mid atlantic ridge known as b and c are experimentally compared using data acquired with low frequency towed array systems at 12 convergence zone 33 km stand off the comparison is significant because the abyssal hills span the two classes of elevated seafloor crust that cover the mid atlantic ridge the highly lineated b feature is representative of abyssal hills composed of outside corner crust the most commonly occurring category whereas the domed c promontory is representative of the rougher low aspect ratio abyssal hills composed of inside corner crust the latter are less common and usually restricted to segment valley margins the mean biazimuthal scattering distributions of the two abyssal hills each exhibit lambertian behavior with comparable albedos suggesting that the distinction between abyssal hills composed of differing crust is not significant in modeling long

migration of backscatter data from the mid atlantic ridge in studies of low frequency reverberation within the marine environment a central concern is the relationship between reverberation events and morphological features of the seafloor a time domain migration algorithm for the reverberation intensity field is developed that produces scattering coefficient maps coregistered with a bathymetry database the algorithm is tailored to broadband transient sources with good range resolution and was developed to analyze an extensive set of reverberation records from a 200 255 hz source collected on the flanks of the mid atlantic ridge the precise sample by sample tracking of wavefronts across elements of the bathymetry database that forms the foundation of the algorithms implementation results in reverberation maps that show a clear and detailed correlation between scattering and morphology with narrow scarp slopes consistently highlighted environmentally induced asymmetries in transmission loss and incidence angle are exploited to break the inherent left righ

neodymium isotopic composition of quaternary island arc lavas from indonesia abstract 143 nd 144 nd ratios measured in quaternary lavas from java and the banda arc of indonesia range from 0 51242 to 0 51280 and exhibit an inverse correlation with 87 sr 86 sr isotopically the indonesian samples resemble andean rather than island arc lavas the samples from java plot either within or adjacent to the mantle array towards higher 87 sr 86 sr ratios samples from the banda arc and the anomalous calc alkaline volcano papandajan are characterized by relatively low 143 nd 144 nd and high 87 sr 86 sr ratios these characteristics are consistent with the interpretation that subducted terrigenous material was involved in the genesis of these lavas furthermore the banda arc samples appear to lie on a mixing line between isotopic compositions characteristic of the mantle and upper continental crust a high k trachyte from the alkaline volcano muriah java has isotopic characteristics of the mantle 143 nd 144 nd 0 51270 87 sr 86 sr 0 70424 which implies that the extreme enrichment in large ion lithophile elements in its source must have occurred only shortly before its formation the inferred 143 nd 144 nd ratio of the unmodified mantle beneath java and the banda arc is lower than that observed in mid ocean ridge basalt which may have important implications for a better understanding of the geochemical structure of the mantle

temperature and melting of a ridge centred plume with application to iceland part ii predictions for electromagnetic and seismic observables summary the dynamic and melting processes of a ridge centred plume have been investigated in a companion paper by ruedas et al hereafter referred to as paper i in a set of 3 d numerical fluid dynamic models with varying plume excess temperatures and melt extraction thresholds in paper i the modelled thickness of the generated crust has been compared to observations of the icelandic crust using the results of those plume models magnetotelluric mt transfer functions and seismic velocity anomalies are predicted in this paper together with paper i a dynamically consistent set of geophysical observables of a ridge centred plume is presented and applied to iceland temperature partial melting and the connectivity of the melt phase influence the electrical conductivity of crust and mantle rocks the temperature and melt fraction of our plume models are used to calculate 3 d conductivity models for mt modelling for the melt geometry ellipsoidal inclusions with appropriate aspect ratios were assumed to control melt connectivity the resulting transfer functions are compared to each other and to models not including a plume to separate signals from the ridge and the plume they may be applied to observed mt measurements if the plume head contains only 1 per cent of melt the plume signal cannot be distinguished from the ridge signal at least 3 per cent melt is needed for such distinction the other predicted observables calculated from the different numerical models are seismic velocity anomalies the temperature induced vp and vs anomalies were estimated including anharmonic and anelastic effects as well as the water induced increase of dislocation mobility that lowers seismic velocities realistic melt geometries as observed in laboratory experiments were used to calculate the effect of partial melts on the seismic velocities vs anomaly distributions are synthesized from the different plume models and compared to seismic observations to reconcile seismic anomalies of the plume head and plume stem a wet plume stem overlain by a partially molten dehydrated plume head is favoured the combined interpretation of available observations crustal thicknesses paper i and seismic results with our dynamic plume models paper i leads to a favoured plume model with 135 k excess temperature and a vertical velocity of approximately 13 cm yr 1 at 200 km depth with 1 per cent melt extraction threshold and a melting zone of approximately 500 km width and 100 km depth extent

range dependent waveguide scattering model calibrated for bottom reverberation in a continental shelf environment an analytic model is developed for scattering from random inhomogeneities in range dependent ocean waveguides using the rayleigh born approximation to green s theorem the expected scattered intensity depends on statistical moments of fractional changes in compressibility and density which scatter as monopoles and dipoles respectively and the coherence volume of the inhomogeneities the model is calibrated for ocean bottom scattering using data acquired by instantaneous wide area ocean acoustic waveguide remote sensing oawrs and geophysical surveys of the onr geoclutter program the scattering strength of the seafloor on the new jersey shelf a typical continental shelf environment is found to depend on wave number k medium coherence volume vc and seabed depth penetration factor fp following a 10log10 fpvck4 dependence a computationally efficient numerical approach is developed to rapidly compute bottom reverberation over wide areas using the parabolic equation by exploiting correlation between

mafic potassic lavas of the quaternary west eifel volcanic field major and trace element analyses for 103 volcanoes of the quaternary west eifel volcanic field show the lavas to be dominantly primitive mgo 7 wt and potassic na2o k2o 1 the rocks are divided into 1 a foidite f suite volumetrically dominant and consisting of four types leucitites and nephelinites melilite bearing foidites olivine free foidites sodalite bearing melilite free foidites and 2 a younger olivine nephelinite and basanite onb suite concentrated in the southeastern part of the field dominantly cpx phyric f suite magmas differ from the dominantly ol phyric onb suite mainly in higher k2o na2o and cao al2o3 ratios higher rb cu h2o co2 and lree concentrations and slightly lower sr ni and y contents most magmas have fractionated small amounts of olivine clinopyroxene and minor phlogopite systematic compositional variations within volcanoes or volcano groups are rare five more differentiated volcanoes 2 tephrites 3 phonolites occur in the center of the field their magmas are interpreted to have formed by fractionation within crustal magma chambers

petrogenesis and tectonic setting of the roman volcanic province italy abstract the volcanism in the roman province of italy can be modelled by the partial melting of heterogeneously enriched mantle sources the heterogeneity was created by materials derived from a subducted slab which can still be traced geophysically beneath the central apennines new petrographical and chemical data are presented for the high k calc alkaline and the shoshonitic volcanics of the campania region primary magmas are present only locally the existence of spatial zonation in the volcanism of campania is documented for the first time the shoshonitic leucite basanitic and leucititic volcanics of the phlegraean fields procida ischia and the somma vesuvius areas are at similar degrees of evolution about two times richer in nb and ba than those of northwestern campania and the latium part of the roman province accordingly distinct north western and south eastern subprovinces can be defined the evaluation of enrichment factors that is the abundance ratio between the average contents of each element in the relatively primitive lavas of the low k and the high k suites shows that the mantle sources prior to k metasomatism were different in the two sub provinces of the roman province in the north western one they resembled the sources of ocean island tholeiites and moderately enriched mor basalts in the south east they were similar to those of ocean island alkaline lavas and enriched morb s modelling based on k p ce sr rb ba th sm eu gd y nb and 87 sr 86 sr was carried out it indicates that the range of mantle sources of the volcanics in northwestern campania and latium can be modelled by the addition of 3 to 20 of materials derived by partial melting of carbonaceous pelites to a sr enriched mantle wedge comparable to the honolulu mantle source least enriched in nb the production of sr enriched mantle wedge requires either the action of fluids produced by dehydration of subducted oceanic crust or a small amount of metasomatism caused by the presence of carbonatite melts the near absence of ti ta nb yb and the highly fractionated ree in the metasomatizing component requires the presence of residual garnet and accessory ti rich minerals during the partial melting of the subducted sediments the writers propose that the mantle wedge overlying the subducted slab was hybridized by melts produced by partial fusion of subducted material derived from the continental crust probably sediments this process played a dominant role in the generation of the mantle sources from which the high k calc alkaline shoshonitic leucite basanitic and leucititic magmas of the roman province were derived

deformation and regional carbonate metasomatism of turbidite hosted cretaceous alkaline lamprophyres northwestern papua new guinea abstract a suite of variably metasomatised camptonite dykes and rare stocks named the fu intrusives has been recognised within thrust plates of mesozoic slates in a 3000 km2 portion of the new guinea thrust belt the intrusions were emplaced prior to oligo miocene fold deformation and low grade regional metamorphism of their host and consequently have foliated margins and are cross cut by metamorphic quartz veins samples from the less altered stocks display primary cumulophyric aggregates of kaersutite titansalite titanbiotite set in a matrix of albite salite apatite olivine quartz calcite ocelli are occasionally present ree patterns la cn lu cn 10 la 100 chondrite and initial sr ratios 0 7042 are typical of alkaline lamprophyres kaersutite and titanbiotite separates from such samples have yielded concordant k ar ages of 75 ma campanian which we accept as the age of intrusion however the dykes have suffered heavy texture destructive carbonate sericite alteration though relict cumulophyric texture and globular structures are sometimes observed composition volume calculations suggest that metasomatism was accompanied by loss of na ti and p and systematic addition of ca fe and co2 as well as progressive lree depletion and fe reduction alteration carbonates exhibit a narrow range of 18o values 13 8 to 14 9 indicating uniform conditions of metasomatism throughout the terrain the calculated fluid 18o at a model temperature of 300 50 c is 8 2 which corresponds with that deduced from the 18o value 12 3 of the cleanest sericite separate the four analysed sericite separates have a mean d of 64 12 implying an hydrogen isotopic composition for the alteration fluid of 58 30 at 300 50 c the calculated fluid composition therefore overlaps the normal range of metamorphic and magmatic waters however c and sr isotopic ratios of the alteration carbonates 13c 7 3 to 0 4 87 sr 86 sr 0 7076 0 7126 strongly support a crustal source for the metasomatic fluids this is corroborated by field evidence that country rock slates adjacent to the dykes are unaffected by carbonate metasomatism and hence were in equilibrium with the alteration fluid we therefore conclude that regional carbonate metasomatism of the fu intrusive suite occurred as a result of metamorphic dewatering of their host rocks during slaty cleavage development

prospectivity mapping for high sulfidation epithermal porphyry deposits using an integrated compositional and topographic remote sensing dataset abstract the targeting and discovery of epithermal porphyry mineral deposits can be enhanced using a structured quantitative methodology to analyse the distribution of ore deposits and model their spatial association with exploration evidence providing improved understanding on the controls of ore deposition a novel exploration tool integrating field and aster swir and tir satellite imagery has been developed which provides an enhanced means of resolving surface expressions of the residual silica core of the lithocap the alteration zones were clearly resolved by the remote sensing data and an intimate spatial relationship between high grade altered rocks and topographic highs was identified at a number of locations a mineral prospectivity modelling mpm approach parameterized by the results of the remote sensing study using a gis based weighted linear combination implementation of a multi criteria evaluation approach and utilising a fuzzy analytical hierarchy process to elucidate expert knowledge has been implemented to target high sulfidation epithermal porphyry deposits on the island of lesvos greece the results from this integrated altitudinal compositional modelling approach closely matched the hydrothermal alteration mapped in the field supporting the accuracy of this mpm approach

melt dynamics of a layered mantle plume source the supply rates of basaltic magma to volcanoes restrict the flow rates within their mantle sources layered source regions consisting of alternating layers of melt and residuum have permeabilities that are orders of magnitude larger than percolative sources relevant supply rates for hawaiian volcanoes are obtained for source permeabilities within the range 10 4 10 2 cm2 the results are within the range for layered sources suggesting that a layered source is a physically viable model for hawaiian plume sources

world class base and precious metal deposits a quantitative analysis over 62 percent of the 193 000 metric tons of gold discovered to date is located in four countries and more than 68 percent occurs in four types of mineral deposits about 55 percent of the 1 740 000 metric tons of silver found is in four countries and 45 percent is in four types of deposits fifty six percent of the 1 52 billion metric tons of discovered copper is from four countries and four types of deposits contain 88 percent of the total over 50 percent of both the 713 000 000 metric tons of zinc and 349 000 000 metric tons of lead discovered to date come from four countries and 70 percent of both metals occur in four types of deposits all discovered gold would fit in a cube with a height of 22 m silver in a 55 m cube copper in a 550 m cube zinc in a 460 m cube and lead in a 310 m cube at least 74 percent of gold silver zinc and lead is in deposits having average grades above the respective median grades and 44 percent of copper is in deposits with average grades above the median grade of all deposits lower grade deposits contain less total metal than higher grade deposits tonnage of mineralized rock is an even better predictor of contained metal with over 96 percent of each metal s total residing in deposits having greater than median size and between 47 and 79 percent of metal contained in the largest 10 percent of deposits world class deposits defined as the upper 10 percent of deposits in terms of contained metal account for over 86 percent of all gold 79 percent of silver 84 percent of copper 71 percent of zinc and 73 percent of lead these giant deposits contain at least 100 metric tons 3 2 moz gold 2 400 metric tons 77 moz silver 2 million metric tons copper 1 7 million metric tons zinc or 1 million metric tons lead mineral deposits occur rarely in the earth s crust and large ones are especially uncommon this analysis shows that only the unusually large deposits can significantly affect supply

pongkor west java indonesia a pliocene supergene enriched epithermal au ag mn deposit the pongkor gold silver epithermal deposit with reserves of at least 98 tonnes of gold and 1026 tonnes of silver average grades 16 4 g t au and 171 2 g t ag is one of the most recent and largest gold and silver discoveries in indonesia proven within a short period 1988 1991 40ar 39ar dating on adularia samples give an age of 2 05 0 05 ma the deposit is of the low sulfidation epithermal type and consists of four main mineralized quartz veins located close to the internal rim of a volcano tectonic depression caldera this resulted from an explosive ignimbritic eruption that produced pyroclastic flows and accretionary lapilli with rare intercalations of epiclastic rocks this volcanic unit unconformably overlies miocene subaqueous volcanic andesitic rocks with interbedded epiclastic rocks the mineralized bodies are thick average 4 2 m steeply dipping quartz carbonate adularia veins with a very low sulfide content 0 5 wt their genesis is related to an extensional episode within a tectonic corridor showing nw se and nne ssw conjugate strike slip faults the major vein being located on the inner rim of the caldera the vein fill reveals four successive stages of deposition marked by a specific facies 1 carbonate quartz breccia with dominant quartz and calcite and minor kutnahorite rhodochrosite and rhodonite cq facies 2 a network of banded quartz and former carbonate transformed into manganese oxides through supergene alteration moq facies 3 banded opaline milky quartz boq facies and 4 grey locally banded sulfide rich quartz breccia cutting all the other types gsq facies adularia was deposited at the same time as the quartz the mineralogy and internal structures of the veins crustiform banding vugs collapse breccia clearly indicate a dilational context which is common in low sulfidation epithermal systems gold and silver grades as well as sulfide mineral abundances increase steadily through stages 1 to 4 locally reaching 1 kg t in the gsq facies the sulfides are dominated by pyrite accompanied by common acanthite aguilarite polybasite pearceite and electrum in which the gold content ranges from 48 to 74 wt sphalerite galena chalcopyrite and hessite are fairly rare although present within the cq facies the fluid inclusions of the four facies show homogenization temperatures ranging from 150 to 382 c indicating boiling of a hydrothermal fluid with an initial temperature of around 205 c no marked difference is seen in the gsq facies which has the highest gold content salinities are low generally below 1 wt eq nacl lead isotope compositions of the associated volcanic rocks and the mineralization are very similar 206pb 204pb between 18 706 and 18 814 and between 18 744 and 18 801 respectively demonstrating a genetic link between the pliocene volcanism and the auriferous hydrothermal activity the isotopic signature suggests that the source of the mineralization and associated volcanic rocks is an underlying ancient continental crust that melted and remobilized during the pliocene volcanic and hydrothermal events these conclusions seem applicable to the entire bayah dome the existence of both a tectonic corridor and a caldera favoured channelling of the hydrothermal fluids and the deposition of primary ore in the veins late intense weathering of the ore deposit to depths of 250 m below the surface has given rise to manganese oxide layers limonite zones and silver micronuggets within the veins as well as to gold enrichment

monostatic and bistatic reverberation statistics west of the mid atlantic ridge monostatic and bistatic reverberation of highly resolved signals from very rough bottoms at one site is statistically analyzed scattering at a mean frequency of about 230 hz from a large number of bottom footprints is considered the reverberation envelope is found to be non rayleigh with the degree of departure from rayleigh dependent upon the bottom grazing angle for two cases considered g 5 and 40 and upon the bistatic angle in the entire range 0 to 180 these rough bottom observations can be explained by adopting a continuous scattering model having a rayleigh envelope added to a discrete scattering model arising from a small number of individual features within the sonar footprint having a distinctly non rayleigh envelope these models plus a heuristic mechanism of self selection within the discrete scattering model arguably explain the observed angle dependence of the reverberation statistics

40ar 39ar geochronology of the pongkor low sulfidation epithermal gold mineralisation west java indonesia abstract the pongkor gold deposit located approximately 90 km southwest of jakarta is well known as the typical low sulfidation ls epithermal gold deposit and the largest gold vein deposit in indonesia the pongkor gold mineralisation has been the subject of several geological studies determination of the duration of gold mineralisation events however is less well understood the mineralisation events are important for understanding the genesis of ore deposits this study presents 40ar 39ar age results for four adularia samples from ciguha gold bearing quartz vein yielding plateau ages of 1 80 0 03 ma 2 33 0 32 ma and 1 88 0 02 ma plus one weighted mean age of 1 95 0 04 ma adularia from the kubang cicau gold bearing quartz veins yielded a 40ar 39ar plateau age of 2 02 0 03 ma the period of adularia growth in the ciguha vein may have extended from ca 2 07 to 1 77 ma that includes the ages of 1 95 0 04 ma and 1 88 0 02 ma the time interval indicates multiple generations of the adularia the data suggest that mineralisation of ciguha may have continued episodically or continuously the age of adularia from the kubang cicau gold bearing quartz vein 2 02 0 03 ma is within the error of the ciguha vein age and the adularia growth of kubang cicau vein reveals at the beginning of ciguha s adularia growth the data suggest that gold mineralisation in the pongkor deposit for kubang cicau and ciguha veins was initiated at the relatively similar time the 40ar 39ar adularia ages of this study are within error of the previously reported 40ar 39ar results milesi et al 1999 but significantly younger than the previously reported k ar adularia dating result kageyama 1999 in rosana and matsueda 2002

a unified model for reverberation and submerged object scattering in a stratified ocean waveguide a unified model for reverberation and submerged target scattering in a stratified medium is developed from wave theory the advantage of the unified approach is that it enables quantitative predictions to be made of the target echo to reverberation ratio in an ocean waveguide analytic expressions are derived for both deterministic and stochastic scattering from the seafloor and subseafloor asymptotic techniques are used to derive expressions for the scattering of broadband waveforms from distant objects or surfaces expressions are then obtained for the scattered field after beamforming with a horizontal line array the model is applied to problems of active detection in shallow water sample calculations for narrow band signals indicate that the detection of submerged target echoes above diffuse seafloor reverberation is highly dependent upon water column and sediment stratification as well as array aperture source receiver and target locations in addition to the scattering properties of the target and seafloor the model is also applied to determine the conditions necessary for echo returns from discrete geomorphologic features of the seafloor and subseafloor to stand prominently above diffuse seafloor reverberation this has great relevance to the geologic clutter problem encountered by active sonar systems operating in shallow water as well as to the remote sensing of underwater geomorphology

shear wave splitting across the iceland hot spot results from the icemelt experiment 1 we report on observations of upper mantle anisotropy from the splitting of teleseismic shear waves sks skks and pks recorded by the icemelt broadband seismometer network in iceland in a ridge centered hot spot locale mantle anisotropy may be generated by flow induced lattice preferred orientation of olivine grains or the anisotropic distribution of magma splitting measurements of teleseismic shear waves may thus provide diagnostic information on upper mantle flow and or the distribution of retained melt associated with the iceland mantle plume in eastern iceland fast polarization directions lie between n10 w and n45 w and average n24 w delay times between the fast and slow shear waves are generally 0 7 1 35 s in western iceland in contrast the fast polarization directions while less well constrained yield an average value of n23 e and delay times are smaller 0 2 0 95 s we propose that splitting in eastern iceland is caused by a 100 to 200 km thick anisotropic layer in the upper mantle the observed fast directions in eastern iceland however do not correspond either to the plate spreading direction or to a pattern of radial mantle flow from the center of the iceland hot spot we suggest that the relatively uniform direction and magnitude of splitting in eastern iceland situated on the eurasian plate may therefore reflect the large scale flow field of the north atlantic upper mantle we hypothesize that the different pattern of anisotropy beneath western iceland part of the north american plate is due to the different absolute motions of the two plates by this view splitting in eastern and western iceland is the consequence of shear by north american and eurasian plate motion relative to the background mantle flow from absolute plate motion models in which the eurasian plate is approximately stationary and the north american plate is moving approximately westward the splitting observations in both eastern and western iceland can be satisfied by a background upper mantle flow in the direction n34 w and a velocity of 3 cm yr in a hot spot reference frame this inference can be used to test mantle flow models in particular it is inconsistent with kinematic flow models which predict southward flow or models where flow is dominated by subduction related sources of mantle buoyancy which predict westward flow our observations are more compatible with the flow field predicted from global seismic tomography models which in particular include the influence of the large scale lower mantle upwelling beneath southern africa while the hypothesized association between our observations and this upwelling is presently speculative it makes a very specific and testable prediction about the flow field and hence anisotropy beneath the rest of the atlantic basin index terms 7218 seismology lithosphere and upper mantle 8120 tectonophysics dynamics of lithosphere and mantle general 8155 tectonophysics plate motions general keywords iceland anisotropy hot spot plate motion shear wave splitting mantle flow

volcanic and seismic hazards at a proposed nuclear power site in central java abstract a nuclear power plant site has been proposed near the base of mount muria a long dormant volcano in indonesia over a period of eight years the volcanic and seismic hazards were investigated first by the contractor and later by a joint team of indonesian geologists and consultants to the international atomic energy agency in order to assess the risk posed by a large volcano for which there is no record of historical eruptions it was necessary to determine the age of the last activity by geological and geochronological means and to deduce from this whether the volcano posed a credible risk similarly because there was no adequate record of seismic activity the seismic hazards were investigated mainly by geological geomorphological and geophysical methods that identified and characterized potential seismogenic sources related to the volcano or tectonic movements i e active capable faults muria volcano has not erupted since about two thousand years ago but the last activity was sufficiently recent to rule out any assumption that the volcano is extinct detailed studies indicated that the proposed site may be vulnerable to the effects of air borne tephra pyroclastic flows and surges debris flows lahars and opening of new vents a more serious factor however was the poor geotechnical properties of the foundation material that required a careful analysis of the seismic hazards although the project was suspended the study proved useful because it provided an opportunity to develop procedures and techniques that could be applied in similar studies elsewhere

geochemistry of a transitional ne trachybasalt q trachyte lava series from patmos dodecanesos greece further evidence for fractionation mixing and assimilation trace element and preliminary sr and o isotopic data are reported for a transitional alkaline sub alkaline lava series mvs from patmos greece the lava types belonging to this series are ne trachybasalt hy trachybasalt hy trachyandesite and q trachyte rb sr and ba contents as well as k rb ratios of the ne trachybasalts differ from those of alkali basalts of oceanic islands and those of k rich alkaline lavas of continental regions and are consistent with the occurrence of these volcanics in a destructive plate margin environment qualitatively the variations shown by many trace elements throughout the mvs are explicable in terms of magma evolution via fractional crystallization involving removal of the observed phenocryst phases cross cutting ree patterns can be explained by removal of small amounts of apatite however certain features of the data cannot be reconciled with the operation of fractional crystallization alone these are a the compatible behavior of ba throughout the mvs b the moderately as opposed to highly incompatible behavior of zr rb and nb relative to th and c the significant decrease of k th rb th zr th zr nb nb th yb th ta th u th and zr ta ratios especially but not exclusively in the mafic part of the series quantitative modeling indicates that the hy trachybasalts are anomalously enriched in both highly incompatible and highly compatible elements and these lavas are shown to be hybrids formed by mixing of ne trachybasalt and hy trachyandesite mixing proportions of the end members calculated from incompatible element abundances 19 ne trachybasalt differ from those calculated from compatible element abundances 62 ne trachybasalt and are inconsistent with proportions calculated from published mineral chemical data in addition mixing cannot account for the observed variations in incompatible element ratios and this is taken as evidence for the simultaneous operation of assimilation isotopic variations 87sr 86sr from 0 7049 to 0 7076 and 18o 16o from 4 7 to 8 6 and the positive correlation of isotope ratios with sio2 and th contents provide conclusive proof that assimilation occurred calculations show that the isotopic characteristics and the concentrations of many trace elements in the q trachytes can be explained by fractional crystallization of ne trachybasalt combined with assimilation of average continental crust 87sr 86sr 0 710 and that large amounts of assimilation are not necessary ma mc 0 55 ree data are not well explained by this model and suggest a crustal end member enriched in lree relative to the average crust zr and hf data are also not well explained and indicate that the assimilant was depleted in hfse relative to average crust or that hfse are held back in relatively insoluble phases such as zircon in the restite during assimilation nevertheless the results of the modeling demonstrate that ba concentrations may decrease during afc processes and that high sr contents 1500 ppm in the mvs ne trachybasalts do not render mafic parental magmas immune to the effects of assimilation in terms of their 87sr 86sr ratios the results of this study confirm conclusions based upon major oxide and mineral chemical data for the mvs lavas but more importantly show that careful analysis of trace element data allows the various processes involved in magma evolution to be identified and quantified even in the absence of major oxide and isotopic data finally it is reiterated that magma mixing and assimilation may be coupled processes in the magma chambers beneath many volcanic centers and recognition of this fact has profound implications for studies of magmas erupted at continental margins and through continental crust