silent heralds of megathrust earthquakes d uring an earthquake rupture propagates along the fault plane within a few tens of seconds much slower rupture lasting for weeks or months has recently been observed in slip transients or slow earthquakes 1 1 2 2 these events are also dubbed silent earthquakes because

petrology and geochemistry of potassic and ultrapotassic volcanism in central italy petrogenesis and inferences on the evolution of the mantle sources major trace element sr isotopic and mineral chemical data are reported for mafic volcanic rocks mg value 65 from the northern central sector of the potassic volcanic belt of central italy the rocks investigated range from potassic series ks and high k series hks to lamproitic lmp and kamafugitic kam through a transitional series trans thus covering the entire compositional spectrum of potassic and ultrapotassic magmas kam rocks are strongly silica undersaturated and compared with the other rock series have low sio2 al2o3 na2o sc and v and high cao k na na k al ks and hks have high al2o3 cao and variable enrichment in k2o and incompatible elements lmp rocks are saturated in silica and have high sio2 k2o k2o na2 mgo ni and cr and low al2o3 cao na2o sc and v trans rocks display intermediate compositional characteristics between lmp and ks all the rocks under study have fractionated hygromagmaphile element patterns with high lil hfs element values and negative anomalies of ti ta nb and ba negative sr anomalies are observed in the lmp and trans rocks lil elements show overall positive correlations with k2o whereas different trends of sr and hfse vs k2o are defined by lmp trans and ks hks kam 87sr 86sr range from about 0 710 to 0 716 ks hks and kam rocks have similar 87sr 86sr values clustering around 0 710 lmp and trans rocks have the highest 87sr 86sr values geochemical and isotopic data reported for the most primitive italian potassic and ultrapotassic rocks support the hypothesis that the interaction between crustal and mantle reservoirs was a main process in the genesis of italian potassic magmatism simple mass balance calculations exclude however an important role of crustal assimilation during ascent of subcrustal magmas to the surface and indicate that the sources of central italy volcanics underwent contamination with fluids and or melts released by upper crustal material previously brought into the mantle by subduction processes different trends of incompatible elements vs k2o observed in the studied rocks suggest distinct metasomatic processes for the sources of the investigated magmas liquids derived by bulk melting of pelitic sediments are believed to be the most likely contaminants of the source of lmp rocks fluids or melts rich in ca sr and with high lile hfse value and sr isotopic composition around 0 710 are the most likely contaminant of the source region of ks hks and kam volcanics variations in cao na2o and ferromagnesian element abundances and ratios suggest that in some zones the mantle source of potassic magmas experienced partial melting with extraction of basaltic liquids prior to metasomatism

resolving volatile sources along the western sunda arc indonesia we present the chemical and isotope hecn characterization of active fumaroles and hydrothermal gases and waters from the summits and flanks of 19 volcanic centers along the western sunda arc indonesia samples were collected over two field expeditions 1991 and 2010 and cover 13 volcanic centers in sumatra 5 in java and one in bali in addition we present data from three geothermal sites in sumatra associated with active fault systems in between volcanic centers ibvc the overall aim is to resolve volatiles associated with the sub arc mantle subducting slab and mantle wedge from inputs derived from the over riding arc crust the western sunda arc is a prime locality to assess controls on volatile provenance at subduction zones due to changes in composition and thickness of over riding crust and variations in sediment input rates along the strike of the arc the dry gas chemistry of the majority of volcanic samples is dominated by co2 with inert gas variations hearn2 typical of subduction zone gases however there is a strong crustal control on the heco2 isotope and relative abundance systematics on a number of volcanic centers this effect is most clearly observed at flank localities and in water phase samples filtering the entire database for modifications due to air contamination degassing induced fractionation c isotopes and co2 3he ratios and crustal contamination associated with volatile transport within shallow level hydrothermal systems allows recognition of the magmatic volatile signature of individual volcanoes along the arc helium isotopes at all but two volcanic centers talang and dempo on sumatra range from 5 3 ra to 8 1 ra ra air 3he 4he pointing to the mantle wedge as the principal source of he but with a small input of crustal radiogenic he at some localities samples from java and bali span an even more limited range 6 6 to 7 9 ra implying a relatively smaller input of crustal he carbon isotope and co2 3he ratios vary from 1 4 to 6 4 and 4 38 to 150 109 respectively with higher and more variable values to the north of sumatra this latitudinal effect is not apparent in air corrected n isotope values 15nc 3 91 to 5 92 or various elemental ratios such as n2 ar and n2 he the three ibvc sites all located in sumatra have significantly lower 3he 4he ratios 3 6 ra with co2 3he values both higher and lower than volcanic centers their 13c 15nc and gas ratios overlap with the volcanic centers the elemental and isotopic characteristics of carbon and helium have been modified at ibvc sites due to crustal processes however based upon relationships between ch4 and 3he as well as co variations between hecn isotopes the over riding crust and associated sediments add minimal volatiles to volcanic centers throughout the western sunda arc in turn subducted sediment particularly the nicobar fan which supplies himalayan derived sediment to the slab off sumatra exerts a strong control on the magmatic co2 characteristics although it is less influential for n2 in spite of large sections of incoming sedimentary material being off scraped during subduction our data suggest that a significant fraction must enter the trench enhancing fluid melt production in the mantle wedge we propose that subduction related source contamination plays the dominant role over thick old crustal basement in supplying the major volatile output budget of the western sunda arc

along arc segmentation and interaction of subducting ridges with the lesser antilles subduction forearc crust revealed by mcs imaging highlights we image the deep structure of the lesser antilles subduction zone by mcs profiles the complex deformation of the outer forearc crust is induced by subducting ridges we discuss also the effect of the subducting compressive nam sam plate boundary along strike variations of the seaward edge of the outer forearc crust are discovered the updip limit proxy of the seismogenic part reaches 20 km trenchwards than believed abstract we present the results from a new grid of deep penetration multichannel seismic mcs profiles over the 280 km long north central segment of the lesser antilles subduction zone the 14 dip lines and 7 strike lines image the topographical variations of i the subduction interplate decollement ii the top of the arcward subducting atlantic oceanic crust toc under the huge accretionary wedge up to 7 km thick and iii the trenchward dipping basement of the deeply buried forearc backstop of the caribbean upper plate the four northernmost long dip lines of this new mcs grid reveal several kilometre high topographic variations of the toc beneath the accretionary wedge offshore guadeloupe and antigua islands they are located in the prolongation of those mapped on the atlantic seafloor entering subduction such as the barracuda ridge this mcs grid also provides evidences on unexpected huge along strike topographical variation of the backstop basement and of the deformation style affecting the outer forearc crust and sediments their mapping clearly indicates two principal areas of active deformation in the prolongation of the major barracuda and tiburon ridges and also other forearc basement highs that correspond to the prolongation of smaller oceanic basement highs recently mapped on the atlantic seafloor although different in detail the two main deforming forearc domains share similarities in style the imaged deformation of the sedimentary stratification reveals a time and space dependent faulting by successive warping and unwarping which deformation can be readily attributed to the forearc backstop sweeping over the two obliquely oriented elongated and localized topographical ridges the induced faulting producing vertical scarps in this transport does not require a regional arc parallel extensional regime as proposed for the inner forearc domain and may support a partitioned tectonic deformation such as in the case of an outer forearc sliver a contrasted reflectivity of the sedimentary layering at the transition between the outer forearc and accretionary domains was resolved and used to define the seaward edge of the outer forearc basement interpreted as being possibly a proxy to the updip limit of the interplate seismogenic zone its mapping documents along arc variations of some tens of kilometres of the subduction backstop with respect to the negative gravity anomaly commonly taken as marking the subduction trench with the exception of the southernmost part the newly mapped updip limit reaches 25 km closer to the trench thus indicating a possible wider seismogenic zone over almost the whole length of the study area

structure of the lesser antilles subduction forearc and backstop from 3d seismic refraction tomography in 2007 the sismantilles ii experiment was conducted to constrain structure and seismicity in the central lesser antilles subduction zone the seismic refraction data recorded by a network of 27 obss over an area of 65 km 95 km provide new insights on the crustal structure of the forearc offshore martinique and dominica islands the tomographic inversion of first arrival travel times provides a 3d p wave velocity model down to 15 km basement velocity gradients depict that the forearc is made up of two distinct units a high velocity gradient domain named the inner forearc in comparison to a lower velocity gradient domain located further trenchward named the outer forearc whereas the inner forearc appears as a rigid block uplifted and possibly tilted as a whole to the south short wavelength deformations of the outer forearc basement are observed beneath a 3 to 6 km thick sedimentary pile in relation with the subduction of the tiburon ridge and associated seafloor reliefs north offshore dominica island the outer forearc is 70 km wide it extends as far as 180 km to the east of the volcanic front where it acts as a backstop on which the accretionary wedge developed its width decreases strongly to the south to terminate offshore martinique where the inner forearc acts as the backstop the inner forearc is likely the extension at depth of themesozoicmagmatic crust outcropping to the north in la desirade island and along the scarp of the karukera spur the outer forearc could be either the eastern prolongation of the inner forearc but the crust was thinned and fractured during the past tectonic history of the area or by recent subduction processes or an oceanic terrane more recently accreted to the island arc

isotope evidence for the involvement of recycled sediments in diamond formation diamonds as chemically robust containers of material from the mantle have provided important information regarding the evolution of the earth s interior1 yet despite much effort2 9 the origins of diamonds themselves have remained controversial10 13 sulphur isotope ratios measured in most mantle or meteoritic samples exhibit minimal deviation from the meteoritic standard whereas the ratios in crustal materials deviate by as much as 70 ref 14 for this reason isotopic studies of sulphide mineral inclusions in diamonds and mantle material are an attractive means of investigating the possible role of crust mantle interaction in the formation of diamonds15 recent ion microprobe studies have found departures from mantle values in the sulphur isotope compositions of individual diamond inclusions16 and some mantle rocks17 which would be consistent with subduction of altered ocean crust into the region of diamond growth here we present new sulphur and lead isotope data from diamond sulphide inclusions which suggest that sedimentary material might also be subducted into the mantle and that the crustal recycling process has been operative for at least 1 000 million years

pyroclastic deposits within the east greenland tertiary flood basalts stratigraphic geochemical and mineralogical characterization of pyroclastic deposits on the gronau west nunatak of east greenland indicates that both alkaline and basaltic tephras occurred during the eruption of flood basalts associated with the opening of the north atlantic ocean in the early tertiary within the exposed section of gronau west nunatak c 1 km thick representing c 1 6 ma 17 of the horizons are phreatomagmatic basaltic tephras near the top of the section an alkaline tuff was dated at 53 8 0 3 ma by 40 ar 39 ar method this tuff contains a distinctive mineralogy sanidine mg katophorite aegirine and geochemistry melt inclusion compositions and trace and rare earth element abundances that indicate it was erupted from the gardiner melanephelinite carbonatite volcanic complex located 175 km to the se which was active from c 55 to 52 ma the alkaline tuff can be correlated to age equivalent compositionally similar alkaline pyroclastic horizons reported in north atlantic sediment cores and in outcrops in northern europe making it an important regional time stratigraphic marker this study indicates that north atlantic explosive volcanic events were prevalent regionally widespread and originated in east greenland during continental rifting suggesting the need for reappraisal of the impact of north atlantic volcanism on climate change during the early tertiary

searching for unconventional seismic signals on a subduction zone with a submerged forearc obs offshore the lesser antilles abstract detecting unconventional seismic signals related to subduction zone processes at depth in continuous ocean bottom seismometer obs records requires the analysis and identification of noise due to instrumental problems deployment sites or sea state conditions the temporary obs deployment at the lesser antilles subduction zone provides new insights into the feasibility of detecting unconventional signals such as non volcanic tremor nvt long period lp or ultra long period ulp events analysis of noise at an array comprising several sites and types of instruments and comparison with recordings on land shows transients in the noise episodes can be identified considering the diversity of sites and instrument types and comparing the seismic signals with meteorological and oceanographic data in order to reliably detect nvt 1 10 hz originating from inside the solid earth one must first characterize noise induced by the activity of the atmosphere and hydrosphere at the sea bottom as well as on land the semidiurnal modulation of noise amplitude can be shown here not to be due to that of the nvt from a seismic source at depth which is related to the subduction interplate and whose activity is modulated by the tidal stresses as inferred for other megathrusts on emerged forearcs here the semidiurnal modulation is rather due to the effect of the tides themselves such as tidal currents since they do not affect all types and all components of the unique multi station array of obs that could be deployed on this submerged forearc the short period cut off of the strong noise due to ocean surface infragravity waves increases to longer periods with obs depth thereby increasing the observational window with low noise to lower frequencies and deep obs sites may be advantageous for detecting lp events

search for the origin of exotic helium in deep sea sediments merrihue1 first observed helium with a very high 3he 4he isotope ratio 10 4 here termed exotic helium in a magnetic separate of a deep ocean sediment and attributed it to input of extraterrestrial material krylov et al 2 subsequently reported the existence of exotic he in several deep sea sediments while tilles3 measured argon isotope ratios in magnetic separates of two ocean sediments observing that the 3he 4he ratio is inversely correlated with the sedimentation rate ozima et al 4 concluded that the exotic he is carried by interplanetary dust particles idps we have now examined other deep sea sediments to characterize the exotic he and to identify its carrier and have confirmed that the exotic he resides mainly in a strongly magnetic fraction stepwise degassing experiments suggest that the exotic he consists of a single component the carrier of the he is likely to be chondritic idps the higher level of exotic he in magnetic fractions of sediments can be explained by secondarily produced magnetite in idps as a result of thermal shock during atmospheric entry

high resolution records of the late paleocene thermal maximum and circum caribbean volcanism is there a causal link two recently drilled caribbean sites contain expanded sedimentary records of the late paleocene thermal maximum a dramatic global warming event that occurred at ca 55 ma the records document significant environmental changes including deep water oxygen deficiency and a mass extinction of deep sea fauna intertwined with evidence for a major episode of explosive volcanism we postulate that this volcanism initiated a reordering of ocean circulation that resulted in rapid global warming and dramatic changes in the earth s environment

constraining sediment transport to deep marine basins through submarine channels the levant margin in the late cenozoic abstract the recent world class gas discoveries in early miocene sand units offshore israel raises the question of their origin apparently the simplest explanation is to relate them to a fluvial system that arrived from arabia at that time this system predated the modern pliocene nile river supply and existed until captured by the dead sea valley interestingly however very little sedimentation occurred along the levant continental margin before the pliocene in spite of its stepped structure that provided much space for accommodation the only way that sediments could have bypassed the continental margin and arrive at the deep basin without being trapped in the middle is through submarine channels that crossed the continental margin here we explore this possibility using 3 d stratigraphic modeling techniques that quantify the sediment load and the water discharge required to fill the basin by pushing enough sediment through submarine channels we show that such a scenario requires a fluvial system in the order of the largest rivers that exist today on earth in terms of drainage area and water discharge alternatively it requires extreme hydraulic conditions in terms of diffusion coefficients and an elevated drainage basin that could not have existed in the study area we therefore challenge the traditional view of arabia as the main source for oligo miocene deposits in the levant basin and suggest that the basin was mainly fed by a proto nile system that transported clastic material to the north african margin and then farther east by ocean currents in a wider view we demonstrate how numerical modeling can constrain sediment transport through submarine channels as a function of basin geometry and hydraulic conditions and how paleogeographic knowledge can be combined with current data on world rivers to evaluate if modeling results are plausible

volatile fluxes from volcanoes volatile fluxes from mid ocean ridge mor and subaerial volcanism have been estimated or re evaluated using several natural tracers 3he 210po so2 and chemical ratios of volatile species in lavas and volcanic gases these estimates confirm the net predominance of anthropogenic fluxes over volcanic fluxes for co2 so2 and trace metals they also suggest that while most of the volatiles transferred during mor volcanism come from the mantle volatiles stored at the surface of the earth supply an appreciable fraction of subaerial fluxes and can be the dominant source for some of them the surface inventory of volatile species cannot result from steady state degassing with constant rate and needs much greater fluxes in the past or other volatile supply processes this inventory is the result of several of the following processes capture of the solar nebula and its subsequent partial escape impact degassing of accreting bodies and from archean to present mantle degasssing through volcanism and associated phenomena with recycling into the mantle through subduction

steep microbial boundstone dominated plaform margins abstract seaward progradation of several kilometers has been documented mostly for leeward margin low angle carbonate slope systems with a dominant platform top sediment source however steep and high relief margins fronting deep basins can also prograde and as such are somewhat perplexing characteristics of two prograding carboniferous examples provide a model which may apply elsewhere 1 outcrops in asturias northern spain serve as important analogs for 2 hydrocarbon reservoirs in steep sided isolated platforms of the north caspian basin kazakhstan such as tengiz seismic and well data from tengiz corroborate outcrop patterns for slope development showing progradation of up to 5 and more than 10 km respectively despite the high relief up to 600 m and steep 20 35 nature of these margins the two examples share a highly productive microbial boundstone factory extending from the platform break down the slope to nearly 300 m or more depth and a lower slope dominated by mega breccias and grain flow deposits derived from the margin and slope itself the broad depth range of microbial boundstone increases the potential for production during both lowstands and high stands of sea level and thereby facilitates progradation independent from platform top derived sediment rapid in situ lithification of the boundstone provides stability to the steep slopes but also leads to readjustment through shearing and avalanching what controls the microbial cement boundstone formation remains a debate but its presence is a key factor controlling the progradational geometry of these and possibly other margins this new model of slope shedding has implications for slope readjustment processes and resulting architecture sequence stratigraphic interpretation reservoir characterization and reservoir modeling especially the isotropic character of microbial boundstone will reduce the potential for coherent seismic reflections to develop and possibly invoke under certain stress regimes shattering and fracturing thereby generating significant non matrix permeability key considerations are the contrasts with the bahamian high stand shedding depositional model slope progradation rates that range from 450 to 1500 m my and net growth rates of in situ boundstone of 1000 m my comparable to or higher than accretion rates for metazoan skeletal reef growth

seismic stratigraphy of the antarctic peninsula pacific margin a record of pliocene pleistocene ice volume and paleoclimate multichannel seismic profiles across the pacific margin of the antarctic peninsula show a series of oblique progradational sequences these sequences exhibit a variety of unusual characteristics that suggest they were produced by the action of ice sheets grounded out to the shelf edge at times of glacial maximum reflection events from deeper stratigraphic levels followed down the continental slope and onto the rise overlie ocean crust of known age showing that at least eight such glacial sequences have been deposited within the past 6 m y similar groundings have probably occurred on most antarctic margins but the depositional record is particularly well preserved at this margin because of pliocene pleistocene thermal subsidence neogene global sea level fluctuations have been attributed to changes in volume of continental ice sheets the depositional sequences on the pacific margin of the antarctic peninsula are thought to record west antarctic ice sheet fluctuations directly further investigation of these sequences would assess the relation between fluctuations in ice volume and the low latitude record of global sea level change

petrology and geochemistry of ultrapotassic rocks from the montefiascone volcanic complex central italy magmatic evolution and petrogenesis abstract the montefiascone volcanic complex belongs to the roman magmatic province of central italy the volcanic activity took place in an extensional post collisional setting during late pleistocene giving rise to lava flows and pyroclastic deposits the extrusive products consist of moderately to strongly undersaturated k rich lavas ranging in composition from trachybasalts through leucite basanites and leucititic tephrites to tephritic leucitites they show the typical geochemical and isotopic characters of the roman potassic magmas i e low tio2 low k2o al2o3 strong enrichment in lile high lile hfse ratios highly radiogenic 87 sr 86 sr ratios 0 71005 0 71112 and unradiogenic 143 nd 144 nd 0 51209 0 51229 corresponding to end 10 7 to 6 8 large chemical variations have been recognized within the montefiascone volcanics resulting both from the occurrence of different primary magmas and shallow level fractionation processes the differentiation mainly took place by means of closed system fractional crystallisation with local influence of crustal assimilation the leucite basanites represent primary mantle magmas which did not yield derivative products whereas the leucititic tephrites tephritic leucitites and trachybasalts comprise highly differentiated rocks strongly depleted in compatible elements and enriched in lile fractional crystallisation dominated respectively by clinopyroxene leucite and clinopyroxene plagioclase yielded the most evolved tephritic leucitites and trachybasalts in contrast assimilation of metamorphic basement rocks characterized by highly radiogenic 87 sr 86 sr is needed to explain the moderate increase of the 87 sr 86 sr ratio within the leucititic tephrites the geochemical and isotopic signatures shown by the montefiascone primary magmas require a clinopyroxene and phlogopite rich mantle source in particular partial melting of a veined lithospheric mantle can account for the occurrence of different primary magmas characterized by relatively constant sr and nd isotopic compositions depleted mantle nd model ages 1 1 1 5 ga suggest that the mantle enrichment may be a very old event unrelated to the subduction that preceded the roman magmatism this hypothesis is further supported by the strong similarity in age and isotopic composition between the montefiascone volcanics and the kamafugitic and carbonatitic rocks of the adjoining ultra alkaline umbria latium district

helium and carbon geochemistry of hydrothermal fluids from the mid okinawa trough back arc basin southwest of japan abstract hydrothermal systems located in the okinawa trough back arc basin are considered to be related to rifting activities in the continental margin hydrothermal fluids sampled from two sites jade and clam are significantly enriched in gas species compared to those from mid oceanic ridges a high temperature fluid 320 c from the jade site shows a co 2 concentration of 200 mmol kg 1 which is more than one order of magnitude higher than that of sediment starved ridge crest hydrothermal systems both helium r r a 6 1 6 5 and carbon 13 c co2 5 0 to 4 7 pdb isotopic compositions are typical of island arc magmatic gases also the abundance ratio of co 2 3 he 3 10 10 is within the range of values found in island arcs chemical and isotopic composition of the jade fluid are considered to indicate that both co 2 and helium are derived from a magmatic source beneath the hydrothermal system without significant contamination contrary to these species ch 4 is attributed to a thermogenic origin based on its isotopic composition 13 c ch 4 41 to 36 pdb and high concentration 7 1 mmol kg 1 which values are similar to those observed in sediment hosted hydrothermal systems the clam fluids show gas geochemistry much more affected by fluid sediment interaction lower 3 he 4 he ratios r r a 3 7 3 8 and higher co 2 3 he ratios 10 11 may reflect involvement of gas species introduced during secondary fluid circulation within the sedimentary pile magmatic activity is the main contributor of gas species to the hydrothermal fluids in both the jade and clam sites although fluid sediment interaction modifies their composition the relatively high abundance of co 2 in the mid okinawa trough hydrothermal systems reflects the geochemical nature of island arc magma

seismic investigations in the weddell sea embayment abstract seismic multi channel data collected during norwegian antarctic research expeditions in 1976 1977 and 1978 1979 outline aspects of the cenozoic depositional environment in the weddell sea embayment acoustic basement probably representing the east antarctic craton is exposed in a 50 100 km wide swath along the ice barrier between 78 s 75 5 s on the eastern side of the crary trough the shelf prograded westward and northward from the craton into a subsiding basin colinear with the transantarctic mountain range measured sediment thicknesses exceed 5 km during middle and late tertiary times a submarine fan complex the crary fan developed on the southeastern margin of the weddell sea embayment the glacially eroded crary trough is located at the contact between the craton and a sedimentary basin to the west the entire sedimentary section is undisturbed by faulting or folding which indicates that any movements related to cenozoic uplift of the trans antarctic mountains and or relative motion of east antarctica had little effect in the area north of the filchner ice shelf east of 41 w

sediment subduction and the source of potassium in orogenic leucitites leucitites from the italian volcanic province show a marked enrichment of the large ion lithophile elements lile over the high field strength elements hfse indicative of a subduction related origin despite sr and nd isotope ratios similar to those in lamproites trace element variations do not suggest the latter as a source for the k enrichment instead potassium and the other lile and rare earth elements ree are derived from subducted sediments in a multicomponent mixing process that involves both dehydration and partial melting of the subducted material the slightly elevated 18 o and high 87 sr 86 sr values of the primitive italian lavas are shown to be consistent with a three component mixing model which can also explain other unusual geochemical features of the italian lavas stabilization of phlogopite in hybridized mantle above the subduction zone is regarded as an essential aspect of the petrogenesis of the orogenic leucitites

from platform to basin the evolution of a paleocene carbonate margin eastern desert egypt in this study progradation and the subsequent retrogradation of a late paleocene isolated carbonate platform galala mountains eastern desert egypt is demonstrated by variations of distinct facies associations from the platform margin in the north to the hemipelagic basin in the south a combination of a sea level drop and tectonic uplift at around 59 ma calcareous nannofossil biozone np5 favored the initiation of the carbonate platform from this time onwards the facies distribution along the platform basin transect can be subdivided into five facies belts comprising nine different facies associations their internal relationships and specific depositional settings are strongly coupled with the maastrichtian paleocene seafloor topography which resulted from local tectonic movements patch reefs and reef debris were deposited at the platform margin and the horizontally bedded limestones on the upper slope slumps and debris flows were stored on the lower slope in the subhorizontal toe of slope facies belt mass flow deposits pass into calciturbidites further southwards in the basin only hemipelagic marls were deposited between 59 and 56 2 ma np5 np8 the overall carbonate platform system prograded in several pulses distinct changes in facies associations from 56 2 to 55 5 ma np9 resulted from rotational block movements they led to increased subsidence at the platform margin and a coeval uplift in the toe of slope areas this resulted in the retrogradation of the carbonate platform furthermore the patch reef and reef debris facies associations were substituted by the larger foraminifera shoal association the retrogradation is also documented by a significant decrease in slump and debris flow deposits on the slope and calciturbidites at the toe of slope

seismic activity offshore martinique and dominica islands central lesser antilles subduction zone from temporary onshore and offshore seismic networks this work focuses on the analysis of a unique set of seismological data recorded by two temporary networks of seismometers deployed onshore and offshore in the central lesser antilles island arc from martinique to guadeloupe islands during the whole recording period extending from january to the end of august 2007 more than 1300 local seismic events were detected in this area a subset of 769 earthquakes was located precisely by using hypoellipse we also computed focal mechanisms using p wave polarities of the best azimuthally constrained earthquakes we detected earthquakes beneath the caribbean forearc and in the atlantic oceanic plate as well at depth seismicity delineates the wadati benioff zone down to 170 km depth the main seismic activity is concentrated in the lower crust and in the mantle wedge close to the island arc beneath an inner forearc domain in comparison to an outer forearc domain where little seismicity is observed we propose that the difference of the seismicity beneath the inner and the outer forearc is related to a difference of crustal structure between the inner forearc interpreted as a dense thick and rigid crustal block and the lighter and more flexible outer forearc seismicity is enhanced beneath the inner forearc because it likely increases the vertical stress applied to the subducting plate

earth s free oscillations recorded by free fall obs ocean bottom seismometers at the lesser antilles subduction zone three unburied ocean bottom seismometers obs equipped with trillium 240 s broad band seismometers recorded spheroidal free oscillations of the earth out to periods over 1000 s period for the m 8 1 april 1 2007 solomon islands earthquake in contrast to broadband observatories of the global network that operate in quiet continental locations these instruments were dropped on the several km thick layer of sediments of the forearc and accretionary wedge of the lesser antilles subduction zone furthermore a high ambient noise level due to the ocean surface infragravity waves is expected to cover the frequency band of earth s normal modes band when recorded at these sites in spite of these hostile environmental conditions the frequency of clearly defined peaks of the earth s normal modes were measured after the earthquake this suggests that the recording of normal modes and long period waves can be extended to parts of the hitherto inaccessible ocean with currently available obs technology

geochemical polarity of the early cretaceous gambier group southern coast belt british columbia the gambier group of the southern coast belt was developed on the eastern edge of the wrangellia terrane in early cretaceous time a u pb zircon age determination from rhyolite produced a date of 112 0 0 3 ma consistent with albian fauna in sedimentary units major element geochemistry of volcanic rocks from separate east northeast and southwest volcanic centres displays both tholeiitic and calc alkalic affinities across the axis of the coast belt however assemblages in the east northeast have higher feot mgo ratios highlighting a more pronounced tholeiitic trend and are characterized by high al basalts volcanic rocks in the southwest are enriched in k trace element variations feature a southwesterly increase in ba rb and zr ti towards more alkalic values and a decrease in sr when compared with across arc geochemical trends from numerous other arcs the data may be interpreted to suggest that the gambier arc was east facing above a west to southwest dipping subduction zone such an interpret

submarine deltaic geometries linked to steep mountainous drainage basins in the northern shelf of the alboran sea filling the gaps in the spectrum of deltaic deposition abstract a comprehensive analysis of small deltaic environments linked to short mountainous and seasonal fluvial systems in the northern shelf of the alboran sea was undertaken in order to define the controlling parameters of the geomorphological variability the database includes multibeam and backscatter imagery surficial sediment samples and high resolution seismic profiles additionally geomorphological and hydrodynamic modeling and statistical analysis principal component and cluster analysis of hydrological and physiographic variables were performed most of the studied deltaic systems have high gradient coarse grained deposits with preferential development of the submarine portions to the detriment of the deltaic plains the geomorphological analysis identified three basic types of plan view distributions according to the length to width ratios elongate linguoid and lobate cross slope profiles evidence dominant concave upward geometries fewer occurrences of planar geometries and no sigmoid profiles sediment depocenters are extremely thick in proximal locations but thin out rapidly seawards the geometric distribution patterns of the deltaic systems are characterized by a predictable pattern in plan view according to the type of fluvial system ranging from a relatively large river to ephemeral creeks prevailing concave and secondary planar profiles support strong sediment progradation in the submarine realm and low sediment retention in the emerged deltaic environment two different types of systems are distinguished 1 larger rivers where deltaic deposition is largely controlled by basin dimensions ultimately dictating the magnitude of water and sediment discharges and 2 smaller rivers and creeks where deltaic geometries are related to the basin slopes the influence of hydrodynamic variables on defining the submarine deltaic geometry has been observed in the case of concave upward geometries where geomorphological boundaries are defined by medium and high energy wave conditions

the structure and origin of prydz bay and macrobertson shelf east antarctica abstract a marine geophysical survey in early 1982 conducted by the australian bureau of mineral resources indicated that much of prydz bay is underlain by a sedimentary basin severe seismic multiples preclude an accurate estimate of total sediment thickness but interpretation of the seismic and magnetic data suggest that it is probably at least 5 km the trends of the southeast basin margin and of mild faulting and folding in the southwest indicate an overall nne trend roughly orthogonal to the continental margin in the south of prydz bay two series of seismic sequences are evident separated by a mildly erosional unconformity the lower series ranges from poorly to well stratified has minor folding and faulting and probably derives from continental and perhaps shallow marine pre breakup sediments the upper series is generally well stratified and prograded near the shelf edge it probably represents shallow marine post breakup sediments the seabed is distinctly unconformable with the underlying sediments implying both that much of the upper series sediments and some of the lower series sediments have been bulldozed off by advances of the amery ice shelf and that present sedimentation rates are very low possible thin moraines or tillites in the northeast part of the prydz bay are also attributed to these glacial advances the continental slope and rise sedimentary section ranges from at least 3 km thick off prydz bay to thin off the macrobertson shelf to the west reflecting the more prolific sediment source in prydz bay the deep water section includes several seismic sequences the most distinctive being interpreted as sheet volcanics and turbidite fans the deepest visible unconformity is locally strongly faulted and may separate the pre breakup and post breakup sediments indo antarctic breakup has been tentatively dated as early neocomian 130 ma and the e w orientation of the resultant antarctic coast invites interpretation of the lambert glacier prydz bay structure as a possible failed rift arm of a triple junction direct information on the age and nature of the sediments under prydz bay is lacking but permian continental sediments cropping out at beaver lake to the south may correspond to the lower pre breakup series this interpretation gains some support from analogies with fault bounded intracratonic basins in india which contain permian to triassic continental strata and which may have been juxtaposed prior to breakup the upper series probably consists of upper cretaceous and cainozoic sands and shales with moraines or tillites at the top of the section

an adaptive sampling strategy developed for studies of diffuse volcanic soil gas emissions abstract the spatial distribution of diffuse soil degassing from a volcanic source and quantifying of the amount of gas release are key aspects for understanding the gas release pattern the measurement of the entirety of a particular area of interest cannot be possible due to obvious logistical and economic restrictions to reduce the logistic and economic impacts spatial interpolation techniques are generally used with limited observation which is always associated with a high level of uncertainty in the quantification of diffuse soil degassing here we are developing an adaptive sampling strategy and robust analytical tool that can be used to guide measurement strategies by optimizing the sampling locations and reducing the uncertainty for gas emission estimation our adaptive sampling strategy hybridized two well known algorithms kriging interpolation and genetic algorithm optimizer to optimize the locations of future sampling we have validated our tool using a synthetic data set and then applied it to two volcanic soil degassing data sets pacaya volcano and yellowstone volcano both the synthetic data results and case study applications demonstrated that the developed adaptive sampling tool significantly outperforms random and pseudo random approaches to reduce the uncertainty of gas quantification

carbonate platform flanks slope angle and sediment fabric more than 20 examples of fossil carbonate platform systems were compared for slope angle and sediment fabric plots of slope angle versus sediment fabric show that grainy non cohesive mud free sediments build steeper slopes than muddy cohesive sediments examples near the end members of grainy and muddy carbonate platform flanks are found in the triassic of the dolomites in northern italy and in the bahamas respectively they document the flank geometry and the processes readjusting the slope profile once the limiting slope angle is exceeded the grainy flank sediments in the dolomites modified by shearing and avalanching produce straight slope profiles with declivities up to 35 whereas the muddy bahamian flank sediments modified by large scale creep and rotational to translational sliding and slumping produce a concave upwards slope profile inclined at less than 4 the comparison between slope angle and sediment fabric indicates that the physical behaviour of sediments in the gravity field angle of shearing and mode of readjustment processes is linked to the composition of the slope sediment among the variables such as sea level subsidence climate plate motion and oceanographic setting windward leeward sediment fabric is suggested to be a major if not the major control on slope angle and slope curvature of carbonate platform flanks besides the recently documented tendency of carbonate sediments to build steeper slopes than siliciclastics this proposed relation sheds new light on the analysis and quantification of the variables influencing the geometry and depositional evolution of carbonate systems furthermore it provides an opportunity to deduce sediment composition from seismic lines and predict lithology prior to drilling

he ar o sr and nd isotope constraints on the origin and evolution of mount etna magmatism abstract the 0 5 ma history of the origin and evolution of mount etna sicily has been investigated by analysing the isotopic composition of he ar o sr and nd in 21 selected lava samples the near constancy of the isotopic compositions of oxygen 18 o 5 4 0 3 and of helium trapped in olivine phenocrysts 6 7 0 4 ra is interpreted as evidence of a single mantle source despite drastic petrological changes during the volcano s history he analyses performed by crushing cogenetic pyroxene and olivine phenocrysts show a tendency to lower 3 he 4 he ratios in pyroxenes this is best explained by crystallization of pyroxenes at a depth shallower than that of olivines and or by exchange of helium trapped in pyroxenes with atmospheric or radiogenic he before eruption 87 sr 86 sr ratios of recent lavas tend to increase with time and to correlate with rb th ratios and for historical lavas these variations are tentatively attributed to shallow selective contamination from underlying sediments based on the similarity of the 3 he 4 he ratios at etna to those of european mantle xenoliths 1 we propose that the baseline geochemical signature of isotopic tracers at etna reflects the composition of the subcontinental mantle comparison to other southern italian active volcanoes etna vulcano ischia campi flegrei vesuvius shows gradual dilution of the predominantly mantle etnean end member by more radiogenic sr and he and material with higher 18o and c 3 he which is reasonably explained by the progressively important influence of subducted continental crust

geochemical and tectonic relationships in the east indonesian arc continent collision region implications for the subduction of the australian passive margin abstract van bergen m j vroon p z and hoogewerff j a 1993 geochemical and tectonic relationships in the east indonesian arc continent collision region implications for the subduction of the australian passive margin in m j r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 97 116 variations in the isotopic signatures of volcanics along the east sunda banda arc reflect changes in the nature and amount of sedimentary material supplied by the northeast indian ocean floor and the adjacent australian passive continental margin which form the two major domains of the indian ocean plate that approach the arc system a compilation of isotopic data for 200 500 km long arc sectors shows that the trend in magmatic signatures follows distinct subduction collision stages reached by the corresponding oceanic and continental margin sections entering the trench system maximum amounts of magma source contamination are inferred for volcanics near an extinct sector north of timor where the australian continent started to collide with the arc first pb nd isotopic source mixing models point to contamination by sediments with variations in composition similar to observed along arc changes in sediments entering the trench the results indicate an increasing contribution of subducted continental material in the direction of the collision region mass balance calculations considering the magmatic output and minimum input of subducted continental material required to generate the composition of the volcanic arc in the collision region are difficult to reconcile with subduction of ocean floor sediments alone thicknesses of sediments presently covering oceanic crust near the margin are close to calculated thicknesses of the sediments fluxed into the trench and magmatically returned to the arc crust but cannot account for the additional volumes of material accreted on the overriding plate in the same period of time it is inferred that leading portions of the australian continental margin have reached magma generation zones in the easternmost sunda arc and western banda arc which implies subduction to depths greater than 100 km

categorizing the morphologic variability of siliciclastic passive continental margins the basic morphology of the continental shelf slope and rise on passive continental margins has many variations in the modern ocean environment through using a satellite derived bathymetric data set of the global ocean we have developed a classification for the shape of modern siliciclastic dominated passive margins the classification subdivides 50 margins into five distinct shape categories based on each margin s pattern of sea floor slopes as a function of depth by comparing these shape categories with the underlying stratal architecture sediment input and present degree of canyon incision of the margins we find apparent correlations between these factors and basic margin shape in general gently sloped margins tend to occur in regions with high sediment input few modern canyons and unstable substrates higher gradient margins tend to have lower sediment input more modern canyons and a variety of subsurface architectures these results suggest two important conclusions 1 morphology differences among modern siliciclastic passive margins can be objectively and systematically categorized and 2 these shape differences seem to be related to aspects of the modern sedimentary environment despite the fact that the margins have evolved over geologic time

chemical and isotopic compositions of volcanic gases from the east sunda and banda arcs indonesia the easternmost sunda arc and the banda arc represent a continent arc collision zone where magma genesis is influenced by subducted continent derived material chemical and isotopic studies of volcanic gas samples from this environment provide information on the sources of volatiles in arc magmas these volcanic gases some of which last equilibrated at magmatic temperatures are characterized by anomalous low sup 3 he sup 4 he values but by common arc values of c s approx 2 4 delta sup 13 c approx minus 3 per thousand and delta sup 34 s sub tot approx 5 per thousand abundant helium and high he ar ratios are consistent with the subduction of terrigenous components in local sediments or slivers of continental crust although individual concentration and isotope ratios of volatile components may be explicable by complex fractionation in the recycling process the combined data are in agreement with an important role of subducted sedimentary source components comparison of the authors results with volcanic gas data from other arcs indicates that the carbon and sulfur signals in arc gases are relatively insensitive to the amount and nature of sediment on the subsiding plate hence a contribution to arc volcanic gases from subducted altered oceanic crust cannot be excluded

convective hydrothermal c02 emission from high heat flow regions abstract in addition to volatiles released from volcanoes the flux of co2 to the atmosphere from other sources e g metamorphism and subsurface magmatism represents an important aspect of the global carbon cycle we have obtained a direct estimate of the present day atmospheric co2 flux from convective hydrothermal systems within subaerial seismically active high heat flow regions geothermal systems of the salton trough california u s a and the taupo volcanic zone new zealand provide benchmarks for quantifying convective hydrothermal co2 fluxes from such regions co2 fluxes from the salton trough 109 mol yr 1 and the taupo volcanic zone 8 109 mol yr 1 were computed using data on convective heat flow and the temperatures and co2 concentrations of reservoir fluids the similarity in specific co2 flux 106 mol km 2 yr 1 from these two disparate geologic tectonic settings implies that this flux may be used as a baseline to compute convective hydrothermal co2 emission from other areas of high heat flow if this specific flux is integrated over high heat flow areas of the circum pacific and tethyan belts the total global co2 flux could equal or exceed 1012 mol yr 1 adding this flux to a present day volcanic co2 flux of 4 1012 mol yr 1 the total present day earth degassing flux could balance the amount of co2 consumed by chemical weathering 7 1012 mol yr 1

northern cascadia episodic tremor and slip a decade of tremor observations from 1997 to 2007 1 we analyze continuous seismic and gps records collected in the last decade 1997 2007 to establish the most comprehensive observational basis for northern cascadia episodic tremor and slip ets events a simple ets scale system using a combination of a letter and a digit is proposed to quantitatively characterize the spatial and temporal dimensions of ets events clear correlation between gps and tremor signals is observed for all a b class episodes but the gps signature is less obvious for minor ones regular ets recurrence can be established only for a b class episodes in southern vancouver island halting and jumping are very common in ets migration patterns and along strike migration can happen in both directions a prominent tremor gap is observed in midisland around 49 5 n this gap coincides with the epicenters of the only two large earthquakes beneath vancouver island ets tremors also tend to occur in places where the local seismicity is relatively sparse the tremor depth distribution shows a peak in the 25 35 km range where strong seismic reflectors i e the e layer are documented detailed waveform analysis confirms the existence of shallow tremors above the currently interpreted plate interface our results suggest that a significant portion of the tremor activity and perhaps associated shearing are taking place along well developed structures such as the e layer while fewer tremor bursts are generated elsewhere in response to the induced stress variation throughout the source volume

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

nloadf a program for computing ocean tide loading the loading of the earth by the ocean tides produces several kinds of signals which can be measured by geodetic technique in order to compute these most accurately a combination of global and local models of the ocean tides may be needed the program nloadf convolves the green functions for loading with ocean tide models using a station centered grid with fixed dimensions making it easy to combine different ocean models without overlap in the convolution the program computes all the quantities of interest gravity displacement tilt and strain and includes the case where measurements are made beneath the surface of the ocean

environmental impact of volcanic margin formation late rift stage uplift and subsequent massive transient volcanism during breakup of rifted volcanic continental margins constrain paleoenvironments by modifying basin geometry and the composition of the atmosphere hydrosphere and thus biosphere on regional and global scales the early tertiary north atlantic breakup history shows that lava emplacement was accompanied by regional ashfalls and that extrusive complexes influenced paleogene oceanic and continental margin circulation and sedimentation temporal correspondence with the terminal paleocene deep sea extinction event and the earliest eocene greenhouse suggests a global impact possibly by enhanced atmospheric co 2 levels leading to polar warming and thereby changing patterns of deep water formation in this context transient subaerial volcanism at continental margins should be considered with the much discussed continental flood basalt provinces and oceanic plateaus

a criticism of the holm munksgaard oxygen and strontium isotope study of the vulsinian district central italy discussion sur l article de holm p m munksgaard n c paru dans earth planet sci letters nld 1982 60 376 388

erosional and depositional processes on the submarine flanks of ontong java and nukumanu atolls western equatorial pacific ocean abstract ontong java and nukumanu atolls sit atop earth s largest oceanic plateau the ontong java plateau in the western equatorial pacific ocean in 2014 scientists aboard the schmidt ocean institute s rv falkor mapped the seafloor surrounding ontong java atoll solomon islands and nukumanu atoll papua new guinea for the first time using multibeam acoustic systems these and pre existing data help reveal the evolution of the atolls which has involved volcanism erosion deposition and carbonate growth we use the new multibeam bathymetry and backscatter data together with legacy seismic reflection data to i qualitatively characterise the submarine flanks of the atolls ii identify broad and fine scale geomorphological features and classify the seafloor environment iii investigate how submarine processes have influenced the morphological evolution of the atolls over geological timescales and iv provide evidence that these atolls have fed sediment downslope to kroenke canyon that incises the ne flank of the ontong java plateau submarine erosion is widespread on both atolls and submarine landslides control at least in part the dynamic geomorphology and hence development of both atolls channels and gullies are abundant on the flanks of both atolls scarps are common on the upper flanks of both atolls whereas undulating bedforms and crescent shaped bedforms are more common at the foot of the atolls slopes the ontong java atoll coastline has widespread bights that appear to be linked to submarine debris deposits downslope the overall shape of ontong java atoll could result from one or more extensive edifice failure s or multiple smaller cones amalgamating to form one island active erosion of nukumanu atoll is manifested by crescent shaped bedforms although compared to ontong java nukumanu has a much less sinuous coastline and more subdued mass wasting we estimate 1500 km3 of volcaniclastic sediment has been eroded and transported from ontong java and nukumanu atolls some of which has likely fed kroenke canyon downslope

helium and argon from an atlantic morb glass concentration distribution and isotopic composition data are reported for detailed he and ar measurements on a single morb glass from the atlantic ch 98 dr 11 30 41 n 41 49 w depth 3500 m grain size fractions prepared under ambient conditions are strongly affected by diffusive loss of he from grains and by adsorption of atmospheric argon on grain surfaces both effects could be controlled by crushing gram sized chunks of glass under vacuum and analyzing the powder without any further handling in particular without its exposure to the atmosphere gases from vesicles released upon crushing are characterized by a4he 40ar ratio of6 1 and a40ar 36ar ratio of up to 22 600 in dissolved gases the4he 40ar ratio was found to be 7 2 1 6 times higher and the40ar 36ar ratio to be about ten times lower than in vesicles the difference of theelemental ratio he ar is as anticipated from the ratio of the solubilities ca nine in the investigated basalt of he and ar thus whileelemental abundance ratios are compatible with equilibrium between vesicles and basalt the grossly different argonisotopic ratios are not it is proposed that two basalts chemically very similar but with different40ar 36ar ratios were mixed shortly before eruption the overall4he 40ar ratio in the vesiculated basalt is12 2 so that for the ratio in the primary magma we find6 4he 40ar 12 which is considerably higher than the radiogenic production ratio in all conceivable sources of morb preferential removal from a melt of argon via vesicles is suggested to be the most likely explanation whereas any metasomatic transfer seems unrealistic

isotopic constraints on the role of subducted sialic material in indonesian island arc magmatism the island arcs of indonesia exhibit a range of subduction related tectonic environments and consequently are of particular interest in studying the relationship between the nature of the subducted plate and volcanism the sunda arc in java manifests the underthrusting of oceanic lithosphere beneath the newly accreted margin of asia in the banda arc continental material appears to be subducting beneath a volcanic arc that is underlain by oceanic crust 87sr 86sr ratios 0 7040 to 0 7059 in holocene andesitic lavas from java are higher than those from other volcanic arcs except those arcs where sialic contamination has been inferred a group of anomalous calc alkaline lavas characterized by high 87sr 86sr ratios 0 7054 to 0 7059 and relatively high abundances of k and related elements appear to be the result of sialic contamination of a mantle derived melt high 87sr 86sr ratios as large as 0 7095 together with values of 18o as large as 9 2 smow in lavas from the banda arc imply mixing of mantle derived and sialic components because of the tectonic peculiarities of the region the most likely source of contamination is from subduction of terrigenous material derived from the northwest continental shelf of australia lead isotopic ratios in lavas from java are generally transitional to the trends defined by other arc lavas and are characterized by higher 207pb 206pb ratios than oceanic basalts the anomalous calc alkaline lavas in particular are characterized by relatively high 207pb 206pb ratios interpreted to result from subduction and melting of sediments derived from the precambrian shields of australia and india during the opening of the indian ocean neodymium isotope ratios lie within the range defined from other volcanic arcs in terms of 143nd 144nd and 87sr 86sr the banda arc samples lie on a mixing line between compositions typical of the mantle and the upper continental crust that subducted sediments appear as a component in at least some of the holocene indonesian lavas implies melting at the top of the subducted lithospheric slab and provides constraints on the thermal structure of the descending plate

a neogene back arc origin for the banda sea basins geochemical and geochronological constraints from the banda ridges east indonesia abstract dredgings conducted during the french indonesian cruises banda sea ii and iii collected volcanic rocks from several ridges of the banda sea area tukang besi ridge site 218 lucipara ridge sites 214 and 305 nieuwerkerk emperor of china sites 219 and 220 with the exception of one 46 ma old n morb type basalt thought to belong to an ophiolitic complex k ar and ar ar datings indicate that all the dredged volcanics are neogene they range in age from ca 10 ma tukang besi back arc basalts to 8 7 ma nieuwerkerk emperor of china calc alkaline andesites and to 7 3 ma lucipara oib type transitional basalts and cordierite bearing andesites radiogenic isotopic signatures of andesites are consistent with an afc assimilation coupled with fractional crystallization process involving assimilation of continental crust 8 3 ma old calc alkaline volcanic activity is also recorded on the wetar segment an inactive part of the east sunda arc and corresponding isotopic compositions are also consistent with an afc process involving continental crust these features suggest that lucipara nieuwerkerk emperor of china ridges and the wetar segment were representing a single volcanic arc 8 7 ma ago the corresponding calc alkaline activity was related to the subduction of the indian oceanic lithosphere beneath continental blocks of australian origin back arc opening processes occurred from 6 to 3 ma as a multi rift opening for the wetar basin and as a single rift opening for the damar basin while subduction related magmatism was still active in the wetar segment volcanic activity stopped at 7 ma in the nieuwerkerk emperor of china ridge on lucipara ridge 6 3 ma volcanic activity emplaced concomitantly transitional basalts and cordierite bearing andesites the mineralogical and chemical features of the latter are consistent with an afc process involving assimilation of continental crust by mantle derived basaltic magmas the end of magmatic activity on both volcanic segments at 3 ma is thought to result from the collision of timor with the wetar segment of the sunda arc

formation and evolution of the changbaishan volcanic geothermal system in a convergent plate boundary back arc region constrained by boron isotope and gas data abstract the goal of this study is to analyze fluid geochemistry boron isotope and gas data to reassess the formation and evolution processes of the changbaishan volcanic geothermal system jilin china due to the presence of hot fumaroles with temperatures of higher than 100 c and sinters we believe that phase separation is occurring underground which is also indicated by the characteristics of the b and gas data based on their hydrochemical data and b cl ratios the thermal water samples in this area can be divided into three groups 1 group 1 is steam heated condensate water group 1 1 jj jlq group 1 2 sbdg xrq 2 group 2 is karst water cr3 and lsd and 3 group 3 is residual water cr1 and cr2 the preliminary discrimination of samples using b and gas data implies that group 1 1 around the crater is controlled by a second phase separation process which is induced by the input of hot magmatic material group 1 2 in the basin area is controlled by the transformation of clay minerals and the xrq water sample shows contamination by sewage group 2 represents karst water that has leached metamorphic rock and been directly heated by the input of hot magmatic volatiles and group 3 is the result of one seawater phase separation process the mixing and fluid rock interaction models based on the mass balance of boron concentration and isotope imply that the phase separation and input of magmatic volatiles are more important than fluid rock interactions in the formation of the changbaishan geothermal system and the first phase separation process in the deep carbonate reservoir occurred in a late stage with approximately 75 87 5 of water becoming vapor additionally the rayleigh distillation of b isotope implies that new magma is being generated below this area with the low b concentrations and high boron isotopic values of its gases implying that the mixed component may be derived from the subducted pacific plate e g marine sediment the addition of excess heat due to the continued subduction of the pacific plate has further encouraged the phase separation process and the subduction process has also accelerated the transition of the hydrothermal system into a non hydrothermal system

submarine slopes with an exponential curvature abstract the curvature of submarine slopes is a little used source of information on transport processes and sediment composition in a survey of modern submarine slopes selected from all over the world about 15 are characterized by very regular profiles with sharp shelfbreaks and concave upward curvature an exponential function describes this morphology very well these exponential profiles are from three very different depositional settings a continental margin close to a young mountain belt with very high rates of sedimentation high latitude continental margins with evidence of ice cover during quaternary glacial intervals and a carbonate platform margin we propose that the curvature is controlled by the exponential decay of transport capacity with increasing distance from the shelf edge while exponential decrease of transport may be a general property of most slopes the development of a regular exponential profile is commonly disturbed by other factors in particular by the interplay with wave dominated transport at the upper boundary during sea level fluctuations and with turbidite dominated sedimentation at the lower boundary the good exponential fit of the profiles described here results from the fact that vertical shifts of the shelfbreak are very small compared to the horizontal progradation the three depositional settings mentioned above prevent the shelf edge from fluctuations in the vertical high rates of sedimentation and therefore rapid progradation result in minimal movements of the shelfbreak ice covered margins are limited by the grounding level of the ice and margins built by reef organisms are stationary because the hard limestone is relatively resistant to erosion during lowstands of sea level the numerical value of the exponent is distinctly different for sandy and muddy slopes indicating the possibility of using the curvature to deduce sediment composition of submarine slopes

oxygen isotope systematics of the banda arc low delta o 18 despite involvement of subducted continental material in magma genesis abstract this study reports new laser fluorination oxygen isotope data for 60 volcanic rocks and 15 sediments distributed over the whole length of the banda arc eastern indonesia the melt oxygen isotope values 18omelt were calculated from phenocryst 18o data using theoretical and empirical mineral melt fractionation factors the 18omelt of individual volcanic centers within the arc varies between 5 57 and 6 54 except for serua 18omelt 6 13 7 48 and ambon 18omelt 8 12 8 38 these 18omelt values are up to 2 lower than new and previously published oxygen isotope data obtained on whole rock powders by conventional methods we attribute this discrepancy to post emplacement low temperature alteration and or to a systematic deviation of the bulk analysis sediment 18owr calculated from the 18o carbonate and silica fractions both measured conventionally range between 12 9 and 24 2 the low 18omelt values excluding serua and ambon overlap with the mantle range and are in agreement with simple two component source mixing models that predict 1 5 addition of subducted continental material to a depleted morb type source in the sub arc mantle this percentage is consistent with previous models based on sr nd pb th he hf isotope data however correlations between incompatible trace element ratios and oxygen isotope systematics requires involvement of partial melts derived from subducted continental material as the major slab component rather than bulk addition the contribution of hydrous fluids from both subducted altered oceanic crust and continental material is probably of minor importance magma mantle wedge interaction models could account for the observed low 18o signatures but predicted effects are difficult to distinguish from models without mantle wedge interaction assimilation of arc crust material is thought to be important for the high 18omelt values of serua and ambon afc modelling suggests up to 20 and 80 assimilation at serua and ambon respectively inclusions of meta sedimentary material and whole rock sr nd isotopes point to assimilation processes at nila but this probably had little effect on the 18o of phenocrysts which record original source values according to radiogenic isotope data magma sources in the banda arc are the most heavily influenced by fluxes of subducted continental material among currently active oceanic island arcs hence the results of this study suggest that high 18o 6 5 in arc lavas are difficult to reconcile with addition of subducted components to magma sources but must reflect assimilation of arc crustal material

the sirung volcanic boiling spring an extreme chloride rich acid brine on pantar lesser sunda islands indonesia abstract the sirung volcano with a history of phreatomagmatic outbreaks has its present active center within a 1000 m wide subsidence crater the sirung crater lake scl has 15 g l 1 cl and 19 g l 1 so4 ph 0 75 temperature 40 c a highly saline brine sirung boiling spring sbs boils to the surface beside the lake it contains 116 g l 1 cl ph 1 4 chemical geothermometers indicate a reservoir temperature of 240 c the maximum depth of this reservoir is estimated to be 400 m the stable isotope composition is d 12 and 18o 5 0 to 6 0 tritium in the sbs is 0 0 tu in the scl 4 6 tu evidence against invading seawater as a source is the negative d value in addition to the six times higher cl concentration of the sbs evaporites are rejected as a source of the cl because of the geologic setting the average cl h 2 o ratio in sirung volcanic glasses as estimated by microprobe is very close to the cl h 2 o ratio of 0 047 for the sbs the zero tritium level in the sbs its high cl concentration and the acid character are other evidences for magmatic water as source for the sbs the acid sbs is poor in sulphur which may have been precipitated at depth as sulphides theories on porphyry cu formation in volcanic arc environments invoke highly saline brines as the transporting agent the acid saline brines from the sirung and white island new zealand craters and cl rich crater lakes associated with andesitic volcanism in subduction zones indicate that such fluids occur more frequently at the surface than has been possibly realized hitherto

slow earthquakes coincident with episodic tremors and slow slip events we report on the very low frequency earthquakes occurring in the transition zone of the subducting plate interface along the nankai subduction zone in southwest japan seismic waves generated by very low frequency earthquakes with seismic moment magnitudes of 3 1 to 3 5 predominantly show a long period of about 20 seconds the seismicity of very low frequency earthquakes accompanies and migrates with the activity of deep low frequency tremors and slow slip events the coincidence of these three phenomena improves the detection and characterization of slow earthquakes which are thought to increase the stress on updip megathrust earthquake rupture zones

postcollision extension in arc continent collision zones eastern indonesia postcollisional extension superimposed on arc continent collision complexes is a common feature in the orogenic belts of eastern indonesia in the southern banda arc the arc continent collision event is essentially a pliocene and younger feature but already an element of extension is being superimposed on the compressional structures of the collision complex it is thus likely that the extension commences within a very short period 5 m y after the initiation of collision related compressional deformation a similar history of fold belt development immediately followed by extension can be inferred for the lengguru fold belt and the adjacent wandamen wondiwoi terranes of irian jaya and for the gulf of bone in sulawesi it is suggested that the extension results from decoupling of the subducting oceanic lithosphere from the unsubductable continental lithosphere and that the superimposition of extension is a virtually unavoidable consequence of the arc continent collision

bridging the gap between seismically and geodetically detected slow earthquakes 1 recently observed unusual seismic events deep low frequency earthquakes and tremor very low frequency earthquakes and slow slip events form a family of slow earthquakes that are governed by a scaling law different from ordinary earthquakes guided by this scaling law we have observed previously unknown events with source duration of 20 200 s and moment magnitude of 3 4 under the kii peninsula in western japan these events radiate seismic energy in the 2 8 hz band in direct proportion to their seismic moment rate though the constant of proportionality is 4 5 orders of magnitude smaller than for ordinary earthquakes slow earthquakes in this region may be comprised of numerous shear slip events which in aggregate are manifest seismically as tremor or isolated longer events up to 200 s and geodetically as slow slip events

the effects of volatile recycling degassing and crustal contamination on the helium and carbon geochemistry of hydrothermal fluids from the southern volcanic zone of chile abstract we report new helium and carbon isotope 3he 4he 13c and relative abundance co2 3he characteristics of a suite of hydrothermal gases and fluids fumaroles hot springs geothermal wells from 18 localities in the central southern volcanic zone csvz of chile the csvz is characterized by a wide range of 3he 4he ratios from 1 50 to 6 47 ra where ra air 3he 4he 13c co2 values from 2 9 to 17 7 vs pdb and co2 3he ratios which vary over 5 orders of magnitude 3 1 105 to 2 3 1011 one hydrothermal locality aguas calientes has combined he co2 characteristics remarkably similar to other arc related systems worldwide implying that the underlying subduction zone complex and mantle wedge supplies volatiles to the volcanic front with little or no modification en route to the surface the mechanism controlling helium isotope ratios of other hydrothermal systems appears to be mixing between mantle derived helium and a radiogenic component derived from 4he rich country rock the variable he co2 elemental relationships and 13c co2 values at these localities are consistent with gas separation gas samples or temperature dependent calcite precipitation water samples in shallow level hydrothermal systems both processes result in co2 loss which exacerbates the effects of contamination by crustal gases whereas the aguas calientes locality is useful for understanding the role of the underlying mantle wedge and subducting slab in supplying volatiles to the andean volcanic front the value of the majority of hydrothermal samples in the present study lies with discerning the potentially complicating effects of degassing and or crustal contamination on the resulting he co2 record

landslides and the evolution of el hierro in the canary islands seismic and sonar data have been used to evaluate the extent and characteristics of giant landslides on the flanks of el hierro in the canary islands as the youngest and most southwesterly of the canary islands el hierro has experienced rapid growth and destructive events in its 1 12 million year history at least four giant landslides el golfo el julan san andres and las playas have modified 450 km3 of el hierro during the last 200 300 thousand years with each landslide event removing around 3 of the total edifice volume the extent of landsliding indicates that it is the main process of decay we characterise flank morphology around el hierro and distinguish between rugged unfailed flank failed flank and steep gullied ridge flanks affected by landsliding have downslope long profiles with distinctive b coefficients and exponential forms the el golfo landslide is the most recent 15 ka best described and clearly defined landslide in the canary islands the el julan landslide sw flank has an estimated volume of 130 km3 an age of 200 ka and is characterised by gravitational slumping on the se flank two new landslide events are reported the younger landslide las playas occurred 145 176 ka has a narrow steep sided embayment and a corresponding blocky debris avalanche deposit the older landslide san andres is recognised on the basis of a highly chaotic seismic facies offshore and reduced upper flank gradients its lack of an upper flank embayment and offshore blocky debris avalanche lead us to interpret that the landslide involved gravitational slumping possibly a series of events which reduced upper flank gradients but did not catastrophically collapse to produce a debris avalanche

a model for atmospheric co 2 over phanerozoic time a new model has been constructed for calculating the level of atmospheric co sub 2 over phanerozoic time which is much simpler mathematically than the blag model but more complex geologically and biologically results suggest that there has been a notable pattern of varying atmospheric co sub 2 level over the past 570 my with high levels during the mesozoic and early paleozoic and low levels during the permo carboniferous and late cenozoic sensitivity analysis shows that within reasonable limits of the principal governing parameters this qualitative trend of varying co sub 2 is relatively insensitive to the actual values chosen for these parameters causes of the co sub 2 variation are multiple and no single geological or biological process can be called upon to explain all co sub 2 variation for all time the calculated trend of co sub 2 over time agrees well with independent estimations of paleoclimates thus the greenhouse theory of paleoclimate on a long geological time scale is supported by the results of the present study

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

is there a distinct continental slope fauna in the antarctic abstract the antarctic continental slope spans the depths from the shelf break usually between 500 and 1000 m to 3000 m is very steep overlain by warm 2 2 5 c circumpolar deep water cdw and life there is poorly studied this study investigates whether life on antarctica s continental slope is essentially an extension of the shelf or the abyssal fauna a transition zone between these or clearly distinct in its own right using data from several cruises to the weddell sea and scotia sea including the andeep antarctic benthic deep sea biodiversity colonisation history and recent community patterns i iii biopearl biodiversity phylogeny evolution and adaptive radiation of life in antarctica 1 and easiz ecology of the antarctic sea ice zone ii cruises as well as current databases sombase scar marbin four different taxa were selected i e cheilostome bryozoans isopod and ostracod crustaceans and echinoid echinoderms and two areas the weddell sea and the scotia sea to examine faunal composition richness and affinities the answer has important ramifications to the link between physical oceanography and ecology and the potential of the slope to act as a refuge and resupply zone to the shelf during glaciations benthic samples were collected using agassiz trawl epibenthic sledge and rauschert sled by bathymetric definition these data suggest that despite eurybathy in some of the groups examined and apparent similarity of physical conditions in the antarctic the shelf slope and abyssal faunas were clearly separated in the weddell sea however no such separation of faunas was apparent in the scotia sea except in echinoids using a geomorphological definition of the slope shelf slope abyss similarity only changed significantly in the bryozoans our results did not support the presence of a homogenous and unique antarctic slope fauna despite a high number of species being restricted to the slope however it remains the case that there may be a unique antarctic slope fauna but the paucity of our samples could not demonstrate this in the scotia sea it is very likely that various ecological and evolutionary factors such as topography water mass and sediment characteristics input of particulate organic carbon poc and glaciological history drive slope distinctness isopods showed greatest species richness at slope depths whereas bryozoans and ostracods were more speciose at shelf depths however significance varied across weddell sea and scotia sea and depending on bathymetric vs geomorphological definitions whilst the slope may harbour some source populations for localised shelf recolonisation the absence of many shelf species genera and even families in a poorly dispersing taxon from the continental slope indicate that it was not a universal refuge for antarctic shelf fauna

shelf architectures of an isolated late cretaceous carbonate platform margin galala mountains eastern desert egypt abstract an asymmetrical carbonate platform margin to basin transect has been investigated in the upper campanian maastrichtian succession of the galala mountains northern egypt identification of systems tracts and their lateral correlation was possible in slope sections only whereas the monotonous chalk marl alternations of the basinal sections could not be subdivided with respect to sequence stratigraphic terminology the platform asymmetry is expressed by varying large scale depositional architectures exhibiting a rimmed platform with a sigmoidal slope curvature in south easterly dip sections and a ramp with a linear slope curvature in south westerly dip sections the rimmed platform is subdivided into a gentle upper slope and a steep lower slope the platform formed as a result of the initial topography that was controlled by the tectonic uplift of the northern galala wadi araba syrian arc structure the calculated angles of the steep lower slope of the rimmed part range from 5 to 8 whereas the ramp part has an angle of less than 0 1

ancient subcontinental mantle a source for k rich orogenic volcanics active island arc volcanoes west of the arc continent collision between the sunda arc and northwest australia are erupting mafic volcanics that range from calc alkaline basalts through shoshonitic trachybasalts to leucitites these mafic arc volcanics display a threefold enrichment in k rb sr ba la and nb contents along the arc from bali to flores increasing toward the collision zone the enrichment is very well correlated with increasing 87sr 86sr and decreasing 143nd 144nd values the geochemical and isotopic data imply that the arc volcanics are being generated from two source materials one yielding material poor in k group elements with relatively low 87sr 86sr 0 707 values and low 143nd 144nd values the k rich material appearing in the arc volcanoes is being derived from ancient subcontinental mantle involved in the collision zone eastern sunda k rich mafic volcanism first appeared after the collision began before the collision ancient northwest australian mantle erupted k rich diamond bearing ultramafics with high 87sr 86sr values and low 143nd 144nd values these form part of a typical ultrapotassic continental volcanic association yet they have ba la and ba nb values characteristic of arc volcanism showing their parent mantle to be geochemically and isotopically capable of supplying the k rich material appearing in the eastern sunda arc volcanoes terranes possibly underlain by similar gondwanaland mantles surround the collision zone which is the site of large scale mixing between oceanic and continental lithospheres other petrogenetic theories seem incapable of accounting for the regional variations in eastern sunda arc geochemistry striking geochemical and isotopic resemblances between eastern sunda leucitites and k rich orogenic volcanics elsewhere in the world such as those of the roman region imply similar origins involving k rich subcontinental mantle material where a k h correlation occurs it might only be a signal that subduction of a lithospheric slab beneath a continental margin is inducing melting in old mantle deep in the continental lithosphere

model for the sigmoidal curvature of submarine slopes sigmoidal slope profiles are common on the margins of continents and intracratonic basins we propose that these profiles consist of two genetically different segments the lower concave part reflects the exponential decrease of the sedimentation rate with increasing distance from the source at the shelf edge the upper convex part represents the gradational boundary between the shelf domain where sediment is moved by waves and wave induced currents and the slope domain where sediment is moved by gravity the boundary is narrow and the shelf edge is sharp if sedimentary base level remains stationary during progradation the boundary becomes gradational and the shelf edge becomes rounded if storms and sea level cycles induce significant fluctuations of base level this model is supported by observations on holocene sedimentary systems as well as numerical simulations with the program strata based on the diffusion equation for sediment dispersal

mapping magma sources in the east sunda banda arcs indonesia constraints from helium isotopes abstract we report new helium isotope analyses of olivine and clinopyroxene separates from recent lavas for eleven volcanoes from flores in the east sunda arc through the inactive segment between the arcs to banda island at the extreme of the contiguous banda arc in the east sunda arc 3 he 4 he ratios r vary between 4 5 ra r a air 3 he 4 he for the leucitic batu tara volcano to a remarkable low of pure radiogenic helium 0 0075 ra for werung at the southern tip of lomblen island lavas from the inactive zone which represents the locus of collision of the australian continent with the arc have a narrower range in r r a from 3 9 for kisu in the straits of pantar to 1 0 for romang island our one locality banda island in the banda arc gives the highest r r a ratio 3 1 observed along this arc to date the results are consistent with the involvement of crustal material in magma genesis throughout the east sunda banda arcs as far west as iya in central flores we combine these helium isotope results with published and on going strontium isotope studies and show that the source of the helium in the crustal component is unlikely to be terrigenous sediments derived from the australian continent rather degassing of australian continental crust appears to be the dominant process controlling the helium budget the he sr isotope systematics also provide a framework to account for the areal pattern of 3 he 4 he in this part of the arcs the radiogenic crustal component is diluted with mantle helium both in a down dip direction and with increasing lateral distance from the collision zone these factors result in an excellent first order relationship between the 3 he 4 he ratio degree of he sr enrichment relative to the postulated mantle endmember and alkalinity of the erupted lavas such a relationship has a direct bearing on models of the tectonic evolution of the collision zone and on the observation that helium isotopes are decoupled from strontium and other geochemical signatures along the banda arc

low frequency continuous tremor around the moho discontinuity away from volcanoes in the southwest japan 1 recent enhancement of seismic networks in the japan islands revealed occurrence of low frequency continuous tremors of a beltlike distribution in the southwest japan where the subducting philippine sea plate reaches depths of 30 40 km source depth of the tremor is estimated by selecting tremor segments with relatively clear p wave onsets the source region of the tremor is assumed to correspond to lowermost parts of crust close to a triple boundary of the crust mantle wedge and the subducting slab the long duration of the phenomenon indicates existence of fluid relating to the generation of the tremor the most probable fluid is considered to be water produced by dehydration process of chlorite and amphibole in the slab on the basis of data from high pressure and temperature experiments the northern border of the beltlike distribution is possibly rimmed by the edge of the mantle wedge because serpentine formation absorbs fluid water

wave spectral energy variability in the northeast pacific 1 the dominant characteristics of wave energy variability in the eastern north pacific are described from noaa national data buoy center ndbc buoy data collected from 1981 to 2003 ten buoys at distributed locations were selected for comparison based on record duration and data continuity long period lp t 12 s intermediate period 6 t 12 s and short period t 6 s wave spectral energy components are considered separately empirical orthogonal function eof analyses of monthly wave energy anomalies reveal that all three wave energy components exhibit similar patterns of spatial variability the dominant mode represents coherent heightened or diminished wave energy along the west coast from alaska to southern california as indicated by composites of the 700 hpa height field the second eof mode reveals a distinct el nino southern oscillation enso associated spatial distribution of wave energy which occurs when the north pacific storm track is extended unusually far south or has receded to the north monthly means and principal components pcs of wave energy levels indicate that the 1997 1998 el nino winter had the highest basin wide wave energy within this record substantially higher than the 1982 1983 el nino an increasing trend in the dominant pc of lp wave energy suggests that storminess has increased in the northeast pacific since 1980 this trend is emphasized at central eastern north pacific locations patterns of storminess variability are consistent with increasing activity in the central north pacific as well as the tendency for more extreme waves in the south during el nino episodes and in the north during la nina

peculiar features of suiyo seamount hydrothermal fluids izu bonin arc differences from subaerial volcanism abstract this is the first report of the dissolved gas composition of a deep sea venting hydrothermal system originating from arc volcanism the origin of dissolved gases in hydrothermal fluids from the suiyo seamount in the southern izu bonin ogasawara arc is discussed on the basis of chemical and isotopic compositions twelve high temperature up to 310 c fluid samples were collected from three vents of the hydrothermal system using the submersible shinkai 2000 the average 3 he 4 he ratio of the dissolved he is 8 1 r r atm which is within the range of values reported for n morb the co 2 3 he ratio is 12 109 which is within the range of arc volcanic gas values the 13c values of co2 and ch4 are 1 and 8 5 respectively which is quite high compared with other subaerial arc volcanic gases and those from mid ocean ridges these results which do not accord with those from subaerial volcanism are unlikely to result from fractionation or addition of carbon sources during the fluid circulation but are regarded as characteristic of the magma source of suiyo seamount a simple mixing of 97 morb mantle with 3 subducting slab explains well the composition of the helium and carbon in the parent magma

role of autochthonous versus detrital micrite in depositional geometries of middle triassic carbonate platform systems middle triassic platforms formazione di contrin upper anisian in the italian dolomites southern alps record large changes in carbonate production and depositional geometry the changes include variation in the abundance of detrital micrite i e allochthonous calcareous mud relative to the autochthonous micrite which formed in situ and was syndepositionally lithified carbonate factory dynamics controlled the geometry of the clinostratified slope units and were probably associated with changes in oxygenation early anisian low relief platforms were followed by late anisian high relief buildups associated with basinal dysoxic anoxic environments the geometric evolution of the platform slopes records a progressive increase in the dip angle of clinostratifications matched by a deepening evolution of the basinal environments at the same time the slope sediments record a gradual change from loose detrital micrite characterizing the lower portion to autochthonous micrite dominating the upper part and recording massive syndepositional lithification the development of the autochthonous micrite was associated with the preservation of significant amounts of organic matter this sharp increase in automicrite formation was probably induced by a rapid change from oxic to suboxic conditions in the carbonate slope and margin environments while anoxic conditions developed in the adjacent organic rich basin moena formation the low oxygen level promoted the preservation of organic matter and the activity of sulfate reducing bacteria which in turn induced in situ deposition of autochthonous micrite through biomediated processes this pervasive early cementation and lithification induced the development of steep platform slopes the conceptual model distilled from this middle triassic case can support the interpretation of analogous buildups where the skeletal framework is subordinate to the micrite component

identifying and removing tilt noise from low frequency 0 1 hz seafloor vertical seismic data low frequency 0 1 hz vertical component seismic noise can be reduced by 25 db or more at seafloor seismic stations by subtracting the coherent signals derived from 1 horizontal seismic observations associated with tilt noise and 2 pressure measurements related to infragravity waves the reduction in effective noise levels is largest for the poorest stations sites with soft sediments high currents shallow water or a poorly leveled seismometer the importance of precise leveling is evident in our measurements low frequency background vertical seismic spectra measured on a seafloor seismometer leveled to within 1 10 4 radians 0 006 degrees are up to 20 db quieter than on a nearby seismometer leveled to within 3 10 3 radians 0 2 degrees the noise on the less precisely leveled sensor increases with decreasing frequency and is correlated with ocean tides indicating that it is caused by tilting due to seafloor currents flowing across the instrument at low frequencies this tilting generates a seismic signal by changing the gravitational attraction on the geophones as they rotate with respect to the earth s gravitational field the effect is much stronger on the horizontal components than on the vertical allowing significant reduction in vertical component noise by subtracting the coherent horizontal component noise this technique reduces the low frequency vertical noise on the less precisely leveled seismometer to below the noise level on the precisely leveled seismometer the same technique can also be used to remove background noise due to the seafloor pressure field up to 25 db noise reduction near 0 02 hz and possibly due to other parameters such as temperature variations

carbon sources in arc volcanism with implications for the carbon cycle new co2 3 he data from the east sunda arc indonesia confirm earlier observations that arc volcanic gases have higher co2 3 he ratios than mor environments on average 80 of arc volcanic co2 is recycled exogene carbon addition of a few percent of carbonate bearing sediments to the mantle wedge explains much of the carbon abundance andcarbon isotopic data of arc gases but can not explain the he isotope observations the co2 3he in arc volcanoes is not strongly dependent on the composition of modem trough sediments e g deep sea clays vs carbonate rich sequences and calcite veins in the hydrothermally altered subducted slab may provide a contribution to the recycled carbon flux of arcs the sum of globally deep subducted sediment and slab carbon exceeds the estimated arc co2 flux and approximately 3 5 teramole of carbon may return annually to the mantle in convergent zones the modem combined processes of mor volcanism slab alteration and subduction volcanism do not produce a substantial carbon flux into the exosphere and rate changes in ocean floor spreading are unlikely to cause major changes in atmospheric co2 as a result of changes in the volcanic co2 fluxes intense pulses of flood basalt volcanism however may alter the co2 contents of the atmosphere over the course of a millenium or so and influence global climate

modeling the carbon and sulfur isotope compositions of marine sediments climate evolution during the devonian abstract a model of global biogeochemical cycles coupled to an energy balance climatic model modified after the combine model godderis y joachimski m m 2004 global change in the late devonian modeling the frasnian famennian short term carbon isotope excursions palaeogeogr palaeoclimatol palaeoecol 202 309 329 is used to calculate the short term evolution of atmospheric p co 2 during the devonian the geochemical cycles for carbon alkalinity phosphorus sulfur and oxygen are included in this model with also 13 c and 34 s cycles high resolution records of 13 c of marine carbonates and 34 s of marine sulfates are used as forcing parameters of the geochemical cycles in an inverse modeling atmospheric p co 2 and p o 2 at the end of the silurian are calculated to have been 3000 ppmv and 0 165 bar 0 75 pal respectively a long term decrease in p co 2 is modeled for almost the entire devonian short term lowering of p co 2 to concentrations around 2000 ppmv is calculated for the silurian devonian transition and the pragian contents around 900 ppmv are modeled for the eifelian givetian givetian frasnian and frasnian famennian boundaries as a consequence of enhanced organic carbon burial during deposition of lochkovian eifelian and frasnian grey and black shales organic carbon burial is enhanced by the increase of phosphorus delivery to the ocean triggered by short term sea level falls the corresponding short term global climatic cooling at the silurian devonian boundary at the end of the pragian and the givetian frasnian as well as frasnian famennian boundaries reached 2 c at the equator the rapid colonization of continental surface by land plants during the middle and late devonian increasing chemical alteration of the continents and co 2 consumption by silicate weathering is assumed to have caused cooling of surface seawater as suggested by the 18 o values of biogenic apatites

the origin of the potassic rock suite from batu tara volcano east sunda arc indonesia abstract atu tara is an active potassic volcano in the eastern sunda arc its leucite bearing rock suite can be subdivided into two groups one less evolved with th 20 ppm 87sr 86sr 18o and trace element systematics in the less evolved group suggests that existence of parental magmas with different mantle origins the mantle below batu tara is most likely heterogeneous and several source components are involved in magma genesis trace element and isotopic compositions of batu tara and adjacent volcanoes are consistent with the involvement of a subducted sedimentary crustal component as well as morb and oib mantle the latter with geochemical characteristics comparable to the mantle underlying muriah java melt extraction from this complex mixture is envisioned as a two stage process partial melts of the crust contaminated morb mantle mix in the mantle wedge with partial melts of oib domains different mixtures of these two melts provide the parental magmas that enter the volcanic plumbing system where crystallization hybridization and refilling processes occur the calcalkaline volcanoes in the arc segment show stronger signatures for a subducted crustal component than batu tara which displays a greater influence from the oib mantle source the potassium enrichment can therefore be attributed to contributions both from the enriched mantle and from subducted crustal material mantle type 18o values of the batu tara magmas indicate that the mantle wedge below potassic orogenic volcanoes is not necessarily strongly enriched in 18o

estimation of the paleoflux of terrestrial derived solids across ancient basin margins using the stratigraphic record a simple inversion scheme for estimating sediment flux from ancient shelf margin successions is presented here by treating shelf margin clinothems as the product of deposition associated with migration of a shelf edge clinoform with constant shape at a rate equal to the shelf margin progradation rate assuming sediment conservation deposition can be broken into components of 1 response to subsidence and sea level changes and 2 basinward migration of the clinoform profile sediment flux can therefore be estimated with knowledge of progradation rate subsidence sea level change rate and clinoform dimensions an advantage of this methodology is that it requires only two dimensional data i e dip oriented cross sections rather than three dimensional volumes making it ideal for use with sparse data sets as well as with outcrops this methodology is also useful for analyzing areally limited data sets because it can predict the flux of sediment transported beyond the area of data coverage the approach is able to accurately reproduce the sediment flux estimates of previous workers from several margins the fox hills lewis zambezi new jersey and north slope margins using both volumetric and forward modeling methods not only are the predicted distributions for sediment flux across ancient shelf margins similar to distributions predicted by more data intensive theoretical models the estimated magnitudes for paleofluxes favorably compare with measured loads from modern rivers growth of continents is achieved in part by accretion of sediment on shelf margins the rates and patterns of continental expansion are therefore partially dependent on the magnitude and distribution of mass transfer from eroding hinterlands to continental margins fluxes which also play a critical role in global biogeochemical cycles flux estimates cast into a mass balance framework suggest that approximately two thirds of continental margin sediments are exported past the shelf edge into deeper water at long term geologic time scales this finding implies that two thirds of the terrestrial derived particulate organic carbon poc delivered from rivers to the ocean can be stored in deep water over geologic time scales the observations presented here indicate that repetitive delivery of sediment to margins by shelf edge deltas is fundamental to the long term process of margin accretion

fluid immiscibility in volcanic environments volatile components enter the atmosphere oceans and other surface waters through pre syn and post eruptive volcanic processes that involve a variety of fluids aluminosilicate poor fluids include aqueous or carbonic to sulfide sulfate chloride fluoride carbonate and phosphate rich compositions in volcanic environments but other more complex combinations of these constituents may be involved giggenbach 1977 roedder 1984 1992 lowenstern 1995 other rare gases and dissolved constituents e g h2 n2 he ar h3bo3 hg ch4 and other hydrocarbon compounds metals and metalloids are also present but in general they are not sufficiently concentrated to form their own phases or control bulk fluid composition and volcanic processes as a result of their diverse compositions volcanic fluids ranging from vapor to liquid exhibit widely different densities and show strong distinctions in heat capacity dielectric behavior viscosity and other chemical and physical characteristics geiger et al 2006a the density of a saline liquid in the system nacl h2o at 50 mpa and 800 c for example is more than 7 times that of the coexisting aqueous vapor e g 0 2 gm cm3 henley and mcnabb 1978 multiple fluids move mix and or unmix in magma chambers and volcanic conduits in the root zone of fumaroles and in the convective hydrothermal systems that are ubiquitous to volcanic environments hydrothermal systems are typically centered on magmatic intrusions and may include crater lakes at the top of eruptive conduits hydrothermal processes involving two or more fluid phases operate through a variety of geologically relevant shallow crustal pressure temperature composition conditions volcanic fluids occur at supersolidus to subsolidus conditions meaning that the dense aluminosilicate melt that is common to volcanism may or may not be present this chapter addresses the evidence for and occurrence of two or more low density aluminosilicate poor fluids

subduction and seismic hazard in the northern lesser antilles revision of the historical seismicity an important set of french and british archives on the historical seismicity of the northern lesser antilles is analyzed we present the most significant data which help to constrain the 8 february 1843 the 16 may 1851 and the 29 april 1897 earthquakes the 1843 event is the largest reported historical earthquake of the lesser antilles subduction arc and produced intensity ix on a segment about 100 km long between antigua and grande terre guadeloupe which contradicts the 300 km long proposed by other authors who mainly rely on robson s catalog 1964 this suggests a magnitude 7 5 to 8 0 the absence of tsunami and noticeable vertical deformation of the coasts in the source area makes very unlikely a normal fault mechanism but does not rule out the possibility of a subduction event because of the low dip angle of the interplate plane the dominance of moderate instrumental thrust earthquakes in the source area suggests a subduction mechanism for the 1843 event the northern and southern limits of the 1843 source area roughly coincide with the barracuda ridge and the tiburon ridge respectively which may have acted as barriers during the rupture process the northwestern portion of the tiburon ridge is associated with a lack of instrumental seismicity near grande terre which could indicate a possible magnitude 7 5 to 8 0 event in the next future moreover its mechanism could be normal which would provide the additional risk of a damaging tsunami the evaluation of seismic hazard must also take into account possible shallow moderate earthquakes as the 1851 and the 1897 events which produced intensities vii to viii in guadeloupe and may be related to observed major plioquaternary faults in this island

paleoatmospheric consequences of co2 released during early cenozoic regional metamorphism in the tethyan orogen the eocene was the warmest epoch of the cenozoic with published estimates of eocene atmospheric co2 content ranging from two to six times the current value calculations of co2 consumption by silicate weathering show that co2 fluxes to the atmosphere of ca 1018 myr could account for inferred paleocene eocene atmospheric co2 contents and the resulting greenhouse effect would have contributed to eocene warmth extensive portions of the tethyan orogen underwent regional metamorphism culminating in the eocene prograde metamorphism may have been contemporaneous with the late paleocene global warming we calculated the amount of metamorphic co2 produced at depth in the himalayan orogen with data on the timing of the india asia collison duration of prograde regional metamorphism and proportions and bulk compositions of metamorphic co2 source rocks if co2 was generated at a constant rate over a 10 myr period of prograde metamorphism in the himalayan orogen we estimate that ca 1018 1019 moles myr of metamorphic co2 were produced at depth significant expulsion of metamorphic co2 to the atmosphere may have occurred by focused fluid flow along shear zones such as the extensive main central thrust in the himalayan orogen an additional ca 1018 myr could have been contributed by eocene regional metamorphism in the mediterranean tethys i e from the alps to turkey the extensive metamorphism associated with the india asia collision and the closing of tethys may have contributed to co2 greenhouse warming in the early to mid cenozoic

tidal modulation of nonvolcanic tremor episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of japan and cascadia in cascadia such episodes typically last a few weeks and differ from normal earthquakes in their source location and moment duration scaling the three most recent episodes in the puget sound southern vancouver island portion of the cascadia subduction zone were exceptionally well recorded in each episode we saw clear pulsing of tremor activity with periods of 12 4 and 24 to 25 hours the same as the principal lunar and lunisolar tides this indicates that the small stresses associated with the solid earth and ocean tides influence the genesis of tremor much more effectively than they do the genesis of normal earthquakes because the lithostatic stresses are 10 5 times larger than those associated with the tides we argue that tremor occurs on very weak faults

morphology and curvature of delta slopes in swiss lakes lessons for the interpretation of clinoforms in seismic data seismic surveys were conducted and bathymetric data obtained from four alpine lakes in switzerland the curvature of the delta slopes was analysed with mathematical equations linear or exponential profiles are observed representing planar or concave morphologies respectively planar profiles are interpreted to represent sediment that rests at the angle of repose the slope angle of these profiles shows a correlation with sediment calibre exponential profiles do not show a clear correlation between sediment calibre and slope angle they do not rest at the angle of repose and different kinds of sediment can rest at the same slope angle at the transition from lower slope to toeof slope the exponential equation fails to predict the present day morphology the toe of slope lies above the predicted trend this is attributed to a drastic increase in turbidite deposition that provides additional sediment and raises the basin floor profile above the predicted trend the breaks between delta plain and slope are sharp reflecting an abrupt change from transport by river flow and waves to gravity driven transport in these lakes the base level fluctuations relative to supply are small and insufficient to alter this sharp topographic break the absence of sigmoidal profiles on the swiss deltas is attributed to the high rate of progradation coupled with small fluctuations in base level