accelerated ice mass depletion revealed by low degree gravity field from satellite laser ranging greenland 1991 2011 1 we detect the acceleration of ice mass depletion in greenland for the period 1991 2011 from the low degree gravity field up to degree and order 4 derived from the satellite laser ranging slr data between 2003 and 2011 during the era when the grace gravity recovery and climate experiment satellite data are available our slr results of gravity changes agree well with grace showing significant negative patterns in greenland prior to that the slr linear trend maps show a near balance in greenland ice mass during 1991 2002 after the glacial isostatic adjustment is accounted for using model values we further confirm the consistency of our slr results with the vertical crustal uplift of the region observed by the global positining system gps which manifests ice mass loading unloading thus the slr data series constitute a continuous benchmark for the time history of the greenland ice mass changes for over two decades

mantle heterogeneity beneath oceanic islands some inferences from isotopes radiogenic isotopes in oceanic basalts are extremely useful as tracers of long lived heterogeneities in the earth9s mantle helium isotopes provide unique information in that high 3 he 4 he ratios are indicative of relatively undegassed mantle reservoirs i e mantle with high time integrated 3 he th u ratios an alternative hypothesis is that high 3 he 4 he ratios may have been produced by ancient melting events if the solid melt partition coefficient k d for he is greater than that for th and u i e yielding relatively high he th u in the residue of melting however the distribution of helium within basaltic phenocrysts and olivine glass helium partitioning within mid ocean ridge basalts suggest that helium behaves as an incompatible element during melting k d olivine glass 3 he 4 he ratios are derived from undegassed mantle reservoirs isotopic measurements of he sr and pb in hawaiian volcanoes lavas demonstrate that the mantle sources have changed on extremely short timescales between 100 and 10 000 years before present the preferred explanation for these variations is that they represent heterogeneities within the hawaiian mantle plume combined with late stage melting in the lithosphere for post shield alkali basalts helium isotopic data from kilauea hualalai and mauna loa suggest that the plume is presently located beneath kilauea and loihi seamount and constrain the melting zone of the hawaiian plume to be less than 40 km in radius

isotopic evolution of mauna loa volcano abstract in an effort to understand the temporal helium isotopic variations in mauna loa volcano we have measured helium strontium and lead isotopes in a suite of mauna loa lavas that span most of the subaerial eruptive history of the volcano the lavas range in age from historical flows to ninole basalt which are thought to be several hundred thousand years old most of the samples younger than 30 ka in age kau basalt are radiocarbon dated flows while the samples older than 30 ka are stratigraphically controlled kahuku and ninole basalt the data reveal a striking change in the geochemistry of the lavas approximately 10 ka before present the lavas older than 10 ka are characterized by high 3 he 4 he 16 20 times atmospheric higher 206 pb 204 pb 18 2 and lower 87 sr 86 sr 0 70365 ratios than the younger kau samples having he pb and sr ratios of approximately 8 5 atmospheric 18 1 and 0 70390 respectively the historical lavas are distinct in having intermediate sr and pb isotopic compositions with 3 he 4 he ratios similar to the other young kau basalt 8 5 atmospheric the isotopic variations are on a shorter time scale 100 to 10 000 years than has previously been observed for hawaiian volcanoes and demonstrate the importance of geochronology and stratigraphy to geochemical studies the data show consistency between all three isotope systems which suggests that the variations are not related to magma chamber degassing processes and that helium is not decoupled from the other isotopes however the complex temporal evolution suggests that three distinct mantle sources are required to explain the isotopic data most of the mauna loa isotopic variations could be explained by mixing between a plume type source similar to loihi and an asthenospheric source with helium isotopic composition close to morb and elevated sr isotopic values an asthenospheric source or variation within the plume source is considered more likely than lithospheric sources due to the elevated 87 sr 86 sr ratios in the recent kau basalts however the distinct isotopic characteristics of the historical lavas are inferred to be related to lithospheric involvement in the latest stages of shield building volcanism

early growth of kohala volcano and formation of long hawaiian rift zones transitional composition pillow basalts from the toe of the hilo ridge collected from outcrop by submersible have yielded the oldest ages known from the island of hawaii 1138 34 to 1159 33 ka hilo ridge has long been interpreted as a submarine rift zone of mauna kea but the new ages validate proposals that it is the distal east rift zone of kohala the oldest subaerial volcano on the island these ages constrain the inception of tholeiitic volcanism at kohala provide the first measured duration of tholeiitic shield building 870 k y for any hawaiian volcano and show that this 125 km long rift zone developed to near total length during early growth of kohala long eastern trending rift zones of hawaiian volcanoes may follow fractures in oceanic crust activated by arching of the hawaiian swell in front of the propagating hotspot

the role of tonalite and diorite in mauna kea volcano hawaii magmatism petrology of summit region leucocratic xenoliths anomaly and poikilitic texture indicate a cumulate origin leucocratic diorite 50 53 wt sio2 1 2 4 wt k2o xenoliths coexist with the tonalite these have intergranular andesine oligoclase 68 85 vol of an50 15 evolved clinopyroxene mg number

gallium germanium indium and other trace and minor elements in sphalerite as a function of deposit type a meta analysis abstract while a significant amount of analytical data on trace and minor element concentrations in sphalerite has been collected over the last six decades no meta analysis of this data has ever been conducted in this study the results of such an analysis are presented while the study focusses on ga ge and in data for six other elements ag cd co cu fe and mn was also included the results show that there are systematic statistically significant differences in the mean concentrations of fe ga ge in and mn in sphalerite from different deposit types while cd and cu concentrations show no such differences and ag and co concentrations are only significantly different for vein type deposits a principal component analysis demonstrates that the differences between deposit types are approximately one dimensional being expressible in terms of a single number this number correlates strongly with the homogenisation temperature of fluid inclusions r 2 0 82 p 16 it may be expressed as follows pc 1 ln c ga 0 22 c ge 0 22 c fe 0 37 c mn 0 20 c in 0 11 with ga ge in and mn concentrations in ppm and fe concentration in wt the relationship is sufficiently strong to be used as a geothermometer ggimfis the empirical relationship between pc 1 and the homogenisation temperature t is t c 54 4 7 3 pc 1 208 10 our results indicate a strong control of sphalerite chemistry by fluid temperature particularly for the concentrations of ga r 2 0 40 ge r 2 0 65 fe r 2 0 30 and mn r 2 0 60 and to a lesser degree in r 2 0 10 the concentrations of ag cd co and cu appear to be independent of temperature as a consequence of the strong temperature control on pc 1 metamorphic overprinting of pb zn deposits even by lower greenschist facies events may lead to significant changes in sphalerite composition namely a relative decrease in ga and ge concentrations and increase in fe mn and to a lesser degree in concentrations the closure temperature of sphalerite in regional metamorphic events appears to be around 310 50 c such that higher grade events will not be reflected in its composition factors other than temperature such as differences in fluid salinity or source rock composition do not appear to be responsible for differences between deposit types but rather appear to cause differences between individual deposits particularly the cu activity in ore forming systems appears to have a strong influence on in concentrations in sphalerite the observed trends in sphalerite compositions provide a useful tool for future studies of different types of pb zn deposits as well as for mineral exploration they should be particularly relevant for the identification of new resources of ga ge and in

geochemical evolution of kohala volcano hawaii kohala volcano the oldest of five shield volcanoes comprising the island of hawaii consists of a basalt shield dominated by tholeiitic basalt pololu volcanics overlain by alkalic lavas hawi volcanics in the upper pololu volcanics the lavas become more enriched in incompatible elements and there is a transition from tholeiitic to alkalic basalt in contrast the hawi volcanics consist of hawaiites mugearites and trachytes 87sr 86sr ratios of 14 pololu basalts and 5 hawi lavas range from 0 70366 to 0 70392 and 0 70350 to 0 70355 respectively this small but distinct difference in sr isotopic composition of different lava types especially the lower 87sr 86sr in the younger lavas with higher rb sr has been found at other hawaiian volcanoes our data do not confirm previous data indicating sr isotopic homogeneity among lavas from kohala volcano also some abundance trends such as mgo p2o5 are not consistent with a simple genetic relationship between pololu and hawi lavas we conclude that all kohala lavas were not produced by equilibrium partial melting of a compositionally homogeneous source

trace element geochemistry and petrogenesis of felsic volcanic rocks associated with volcanogenic massive cu zn pb sulfide deposits volcanogenic massive cu zn pb sulfide vms deposits occur primarily in subaqueous rift related environments e g oceanic fore arc arc back arc continental margin or continental are hosted primarily by bimodal mafic felsic volcanic successions and are typically associated with felsic volcanic rocks with specific geochemical characteristics fi alkalic dacites and rhyodacites despite being abundant in the rock record are typically barren some fii calc alkalic rhyodacites and rhyolites host vms deposits but most are barren fiii tholeiitic and fiv depleted rhyolites and high silica rhyolites are much less abundant in the rock record but commonly host vms deposits regardless of age and fiii rhyolites appear to host the largest deposits most petrogenetic models proposed for the formation of fii and fiii fiv felsic volcanic rocks link felsic magma genesis to fractionation processes in high level magma chambers now represented by associated subvolcanic intrusions where the magma is also interpreted to have supplied the heat and or metals required to generate and sustain the vms forming convective hydrothermal system however the relatively constant compositions of fii and fiii fiv felsic volcanic rocks within individual areas the high eruptive temperatures at or above liquidus of fiii rhyolites and the bimodality of vms hosting volcanic successions indicate that fractional crystallization within subvolcanic intrusions could not have generated or significantly modified the compositions of fii and fiii fiv magmas this coupled with detailed geological geochemical and geochronological studies indicates that many of these subvolcanic intrusions were emplaced in multiple phases and that the later most voluminous phases often cut ore associated hydrothermally altered rocks a reassessment of the physical conditions responsible for producing the geochemistry of ore associated fii and fiii fiv felsic volcanic rocks and a review of the compositions of felsic volcanic rocks associated with vms deposits that range in age from mesoarchean to cenozoic provide important constraints on models for vms associated felsic volcanic rocks and their relationship to mineralization the compositions of felsic volcanic rocks may be explained by low to moderate degrees of partial melting of mafic sources at a range of depths within rift environments where the mineralogy and composition of the source regions modes and degrees of partial melting pressure and temperature of melting and to a lesser extent subsequent fractionation processes account for the compositional variations from fi through fii to fiii fiv long lived enhanced heat flow and structural permeability of rift environments that allows partial melting to form some fii rhyolites at midcrustal levels 10 15 km and fiii fiv rhyolites at shallow crustal levels 10 km both within the zone of brittle fracture permeability are essential to sustain the high temperature convective hydrothermal systems that are required to form large vms deposits and camps rift environments contain long lived thermal magmatic and structural corridors that focus magma ascent heat flow high temperature convective hydrothermal systems and emplacement of subvolcanic intrusions that are favorable environments for the formation of vms deposits and fii and fiii fiv felsic volcanic rocks

geochemistry of tholeiites from lanai hawaii lanai is the third smallest of the fifteen principal subaerial shield volcanoes of the hawaiian hotspot this volcano apparently became extinct during the shield building stage of volcanism as shown by the absence of both alkalic cap and post erosional lavas major and trace element analyses of 22 new samples collected primarily from 3 stratigraphic sections show that lanai tholeiites span a large range in composition some lanai lavas are unique geochemically among hawaiian tholeiites in having the lowest abundances of incompatible trace elements of any hawaiian lavas and well developed positive eu anomalies the geochemical characteristics of these low abundance lanai tholeiites are not the result of alteration differences in mantle source modal mineralogy the presence of residual accessory mantle phases or fractional crystallization of such phases assimilation of depleted morb wall rock or accumulation resorption of phenocrysts or xenocrysts incompatible trace element ratios e g nb la nb th la th la hf ce pb in lanai tholeiites span considerable ranges and form coherent trends with each other and with absolute abundances of these elements large variations in la sm la yb and absolute ree abundances at constant mgo suggest that lanai tholeiites formed by variable amounts of partial melting however large ranges in incompatible element ratios cannot be explained solely by variations in partial melting of a geochemically homogeneous source but must reflect geochemical heterogeneities in the lanai source partial melting modeling indicates that the mixed lanai source is probably lree enriched i e la yb cn 1 one component in the lanai source exemplified by the low abundance tholeiites has markedly lower ree hfse th hfse alkali hfse and ce pb ratios than other lanai or hawaiian tholeiites and may indicate the presence of recycled residual subduction zone materials in the hawaiian plume source the positive eu anomalies that characterize the low abundance lanai tholeiites are not the result of plagioclase accumulation or assimilation but are a feature of this source component progressive temporal geochemical variations in lanai tholeiites from 2 stratigraphic sections indicate that the source composition of these lavas probably evolved over time this change could have resulted from a progressive decrease in the extent of partial melting of the lanai source the compositional variability of lanai tholeiites suggests that geochemical heterogeneities in their source are larger than the scale of partial melting lanai tholeiites could not have formed by smaller degrees of partial melting of plume material than did the larger volume hawaiian shields therefore volume differences between hawaiian shields must be controlled primarily by differences in the volume of supplied plume material rather than by differences in the degree of partial melting the premature cessation of eruptive activity at lanai may be attributed to relatively large degrees of partial melting of a small plume

crystal structure mosaicity and strain analysis of hawaiian olivines using in situ x ray diffraction deformation of olivine in a volcanic context is poorly constrained although deformed olivine is abundant in some volcanic rocks and its presence is important for the definition of the magmatic history of volcanic edifices such as kilauea volcano hawaii deformed olivines at kilauea originate in the lower crust therefore the classic approaches and interpretations applied to mantle derived olivine are not applicable deformed olivine crystals from kilauea lava samples were examined using an in situ xrd technique our results validate and refine optical observations of olivine deformation we also confirm the presence of deformation and quantify it for olivine crystals of any size even for small crystals 0 15 mm there are significant correlations between deformation intensity strain related mosaicity and olivine composition and crystal size although this technique does not allow the simple estimation of the p t conditions of deformation crystal formation or magmatic history some constraints are provided herein in particular we estimate the threshold degree of mosaicity above which we consider that a crystal underwent deformation in situ xrd is shown to be an easy to use fast low cost non destructive technique and is less ambiguous than optical microscopy for crystals optically exhibiting subgrain formation analysis of asterism by in situ xrd has been used to reconstruct the mosaic spread of the original grain and thus its original strain condition prior to subgrain formation

bedded jaspers of the ordovician lokken ophiolite norway seafloor deposition and diagenetic maturation of hydrothermal plume derived silica iron gels sedimentary beds of jasper red hematitic chert in the ordovician lokken ophiolite of norway are closely associated with volcanogenic massive sulphide vms deposits the jaspers occur in the immediate hangingwall and laterally peripheral to the large lokken 25 30 mt and small hoydal 0 1 mt vms deposits and are exposed discontinuously for several kilometres along strike massive or laminated types predominate jasper sulphide debris flow deposits are also abundant near vms deposits the jaspers contain hematite rich laminae showing soft sediment deformation structures and microtextural evidence that record the presence of a colloidal precursor and an origin as gels early textures include 1 straight or curved chains of hematitic filaments 3 10 m in diameter and 20 100 m long 2 branching networks of 15 25 m thick tubular structures surrounded by cryptocrystalline hematite and filled with quartz and euhedral hematite 3 small up to 10 m spherules composed of cryptocrystalline hematite and silica and 4 up to 50 m silica spherules with hematitic cores the small filaments seem to have been deposited in varying proportions in the primary laminae possibly together with hematitic and siliceous microspheroids diagenetic changes are represented by polygonal syneresis cracks and the presence of cryptocrystalline originally opaline silica chalcedony quartz carbonate and cryptocrystalline hematite and or goethite forming botryoidal masses and spheroids 10 m to 5 mm in diameter coarser euhedral grains of quartz carbonate and hematite are integral parts of these textures bleached silica rich jaspers preserve only small relics of fine grained hematite rich domains and locally contain sparse pockets composed of coarse euhedral hematite epidote

oxygen isotope ratios in olivine from the hawaii scientific drilling project oxygen isotope ratios of olivine in 23 tholeiites from the hawaii scientific drilling project hsdp core 15 from mauna kea 8 from mauna loa and three samples of outcropping subaerial or dredged submarine mauna kea lavas have been measured by laser fluorination the 18 o values are 4 6 5 4 confirming previous observations that some hawaiian lavas are derived from sources with 18 o values lower than typical upper mantle 18 oolivine 5 2 0 2 the mauna kea mauna loa transition marks a shift from 18 o values lower than the mantle average in mauna kea olivines 4 8 to more typical mantle values in mauna loa olivines lavas containing olivines with 18 o values similar to the typical upper mantle are associated with more primitive or less depleted radiogenic isotope characteristics i e with higher 3he 4he 13 ra higher 87 sr 86 sr 0 7036 and lower nd 6 5 and with 206 pb 204 pb ratios less than 18 3 these relationships indicate that the 18 o values of the relatively enriched source components of the hawaiian plume sampled by mauna loa lavas are comparable to or greater than the mantle average this conclusion is supported by 18 o values of olivine from other high 3he 4he islands which are also comparable to the upper mantle average the low 18 o values in hawaiian lavas are derived from a source having more morb like or depleted he nd and sr isotope ratios but more radiogenic pb than is seen in the mauna loa lavas assimilation of 18 o depleted lower oceanic crust from the underlying pacific crust by hot mgo rich parental magmas or melting of older recycled oceanic crust entrained in the hawaiian plume are both possible sources of this 18 o depleted morb like component in hawaiian magmas

evolution of mauna kea volcano inferences from lava compositions recovered in the hawaii scientific drilling project the lower 776 m of core recovered during the initial phase of the hawaii scientific drilling project hsdp contains lavas erupted from mauna kea volcano tholeiitic and alkalic basalts including an fe ti rich flow are intercalated in the upper 58 m of mauna kea lavas similar basaltic sections are subaerially exposed on the lower east flank of mauna kea the fe ti rich lavas reflect large amounts of clinopyroxene plagioclase and olivine fractionation within the crust and upper mantle but the range from tholeiitic to alkalic compositions reflects variable extents of melting of a garnet bearing source based on abundances of incompatible elements the extent of melting for a basanitoid was a factor of 2 less than that for nearly coeval tholeiitic lavas all flow units in the lower 718 m of the hsdp core are tholeiitic lavas their variability in major element compositions reflect variable accumulation of olivine incompatible element abundance ratios in these lavas reflect a complex temporal variation in extent of melting within the tholeiitic part of the core lavas from 800 m to 950 m formed by the largest extent of melting whereas tholeiitic lavas from the bottom of the core and from just below the tholeiitic to alkalic transition formed by lower degrees of melting inferred melt compositions at 16 mgo show that the 200 to 400 ka mauna kea lavas from the hsdp core and the 250 ka subaerial exposures define an inverse correlation between sio2 and feo contents based on experimental studies this correlation is caused by differing pressures of melt segregation furthermore abundances of nb and sio2 are also inversely correlated in these calculated melts in general the younger lavas are relatively enriched in feo and incompatible elements but are depleted in sio2 these trends are interpreted to reflect an overall trend of increasing pressure of melt segregation and decreasing extent of melting with decreasing eruption age there are however geochemical variations which indicate short term reversals in this long term trend previously the geochemical trends accompanying the transition from tholeiitic to alkalic volcanism at hawaiian volcanoes have been interpreted as reflecting the effects of increasing distance from the plume axis the long term geochemical trends of tholeiitic lavas in the hsdp core also reflect migration of mauna kea away from the hawaiian plume

geochemical evidence for invasion of kilauea s plumbing system by mauna loa magma from the beginning of the study of hawaiian volcanism there has been controversy over possible relationships between the neighbouring active volcanoes mauna loa and kilauea1 5 seismic activity thought to reflect upward migration of magma reveals that the magmatic plumbing systems apparently converge at depth to form a broad funnel within the mantle6 although on rare occasions they have erupted concurrently the brief historical eruptive record appears to show that when kilauea is most active mauna loa is in repose and vice versa suggesting that they may be competing for the same magma supply5 7 petrological geochemical and isotope data however require a diametrically opposite conclusion distinct differences in major element trace element and isotope compositions of lavas are regarded as compelling evidence that the two volcanoes have separate magmatic plumbing systems supplied by parental magmas from physically and geochemically distinct mantle sources8 13 here we present preliminary geochemical data which show that in the past 2 000 years kilauea has erupted a spectrum of lava compositions resembling historical kilauea lavas at one end and mauna loa lavas at the other we discuss the cause of this diversity and speculate that magma from mauna loa may have invaded kilauea s high level magmatic plumbing system

stratigraphy and alteration of the host rocks united verde massive sulfide deposit jerome arizona the early proterozoic volcanogenic united verde massive sulfide orebody is situated within the cleopatra member of the deception rhyolite the cleopatra member a porphyritic rhyodacite has been subdivided into an upper unit and a lower unit the united verde orebody previously interpreted to lie at the top of the cleopatra member is now recognized as lying within the basal section of the upper unit of the cleopatra member the upper unit and lower unit are differentiated on the basis of alteration mineralogy mineral and rock geochemistry and lithologic peculiarities the contact between the two units is marked by sediments at the base of the upper unit including a distinct green calcitebearing feldspar tuff chert and hematitic chert layers and a quartz porphyry conglomerate the cleopatra member contains six distinct alteration types five alteration types characterize the lower unit and include two types of moderate chloritic and sericitic alteration designated b1 and b2 two spatially distinct types of sericitic and silicic alteration designated s1 and s2 and an area of intense chloritic alteration designated c these five alteration types record the effects of hydrothermal alteration by the massive sulfide ore forming system and of a regional greenschist facies metamorphic event the upper unit contains the least altered rocks of the cleopatra member and the bulk of the sixth alteration type designated h the rocks included within h type alteration have disseminated hematite and or hematitic chert veining whole rock and mineral geochemistry of the lower unit may be used to establish position within the palcohydrothermal system the distal area of moderate alteration b1 contains samples enriched in mgo slightly depleted in alkalies and having ratios of fe 2 o sub 3 sub total fe 2 o sub 3 sub total mgo for whole rocks and fe sub total fe sub total mg for chlorites that are low relative to other cleopatra member samples these attributes are suggestive of the low temperature seawater rock interaction expected in the domain of fluid recharge rocks of alteration type c experienced significant additions of iron and magnesium and losses of cao na 2 o and k 2 o presumed to reflect alteration in the main discharge conduit for the hydrothermal fluid chlorite and whole rock iron to iron plus magnesium ratios decrease within the area of alteration type c toward the sediment water interface this is consistent with mixing of an evolved ore forming fluid with seawater in the upper levels of the area of alteration type c samples from the area of alteration type b2 which is intermediate between the recharge b1 and discharge areas c are greatly depleted in cao and na 2 o and are enriched in iron alteration types s1 and s2 are interpreted to reflect localized sites of fluid discharge where sio 2 and k 2 o have been added and other major elements except for al 2 o 3 have been removed whole rock and mineral chemistry of the alteration types record progressive changes in the hydrothermal fluid from seawater to an ore forming fluid the fluid that was discharging and depositing ore apparently had a log a sub o 2 between 41 7 and 35 5 a log a sub h 2 s between 5 and 2 6 and was saturated with respect to iron sulfides magnesium silicates and ore forming metals

oxygen osmium isotope systematics of west maui lavas a record of shallow level magmatic processes new 18 o and 187 os 188 os data from late shield building stage lavas from west maui volcano hawai i indicate that a range of distinct shallow level processes can affect compositions of plume generated ocean island magmas the relative ages of the samples studied were determined either on the basis of field relationships or from collection depth in a water well the stratigraphically lower lavas have os 61 399 ppt initial 187 os 188 os 0 1311 0 1324 and 18 o olivine 4 53 4 88 the stratigraphically higher lavas have os 20 273 ppt initial 187 os 188 os 0 1323 0 1390 with the exception of one low os sample with 187 os 188 os 0 1517 and 18 o olivine 4 73 5 21 these compositions are generally similar to those of kea type hawaiian lavas from mauna kea and kilauea volcanoes but in detail there are some significant differences between the west maui lavas and other kea type lavas the stratigraphically lower lavas have 187 os 188 os similar to those previously observed for mauna kea and kilauea lavas and define a nearly flat 87 sr 86 sr vs 187 os 188 os trend that is consistent with assimilation by these magmas of small degree melts of pacific oceanic crustal gabbros the stratigraphically higher west maui lavas extend to 187 os 188 os higher than observed at mauna kea or kilauea this probably results from interaction of these magmas with the hydrothermally altered volcanic edifice during the waning phases of the shield building stage this process is likely to affect the isotope systematics of os and o but will have little effect on those of hf nd pb or sr

overlapping volcanoes the origin of hilo ridge hawaii the submarine hilo ridge has been interpreted as a part of mauna kea volcano but is crossed at 1100 m depth by a submerged shoreline terrace composed of basalts that are isotopically distinct from those of mauna kea and similar to those of kohala volcano this terrace evidently is a product of kohala instead of mauna kea almost all of hilo ridge below the terrace therefore must predate the principal growth of mauna kea which has superficially isolated the ridge from its kohala source by overlapping its proximal segment the mauna kea section penetrated by the hawaii scientific drilling project is predicted to be thinner than expected previously owing to the overlap similar overlaps are suspected among other volcanoes and may cause significant changes in the understanding of hawaiian volcanism

the tholeiite to alkalic basalt transition at haleakala volcano maui hawaii previous studies of alkalic lavas erupted during the waning growth stages 0 9 ma to present of haleakala volcano identified systematic temporal changes in isotopic and incompatible element abundance ratios these geochemical trends reflect a mantle mixing process with a systematic change in the proportions of mixing components we studied lavas from a 250 m thick stratigraphic sequence in honomanu gulch that includes the oldest 1 1 ma subaerial basalts exposed at haleakaka the lower 200 m of section is intercalated tholeiitic and alkalic basalt with similar isotopic sr nd pb and incompatible element abundance ratios e g nb la la ce la sr hf sm ti eu these lava compositions are consistent with derivation of alkalic and tholeiitic basalt by partial melting of a compositionally homogeneous clinopyroxene rich garnet lherzolite source the intercalated tholeiitic and alkalic honomanu lavas may reflect a process which tapped melts generated in different portions of a rising plume and we infer that the tholeiitic lavas reflect a melting range of 10 to 15 while the intercalated alkalic lavas reflect a range of 6 5 to 8 melting however within the uppermost 50 m of section 87sr 86sr decreases from 0 70371 to 0 70328 as eruption age decreased from 0 97 ma to 0 78 ma we infer that as lava compositions changed from intercalated tholeiitic and alkalic lavas to only alkalic lavas at 0 93 ma the mixing proportions of source components changed with a morb related mantle component becoming increasingly important as eruption age decreased

low degree spherical harmonic influences on gravity recovery and climate experiment grace water storage estimates we estimate terrestrial water storage variations using time variable gravity changes observed by the gravity recovery and climate experiment grace satellites during the first 2 years of the mission we examine how treatment of low degree gravitational changes and geocenter variations affect grace based estimates of basin scale water storage changes using independently derived low degree harmonics from earth rotation eop and satellite laser ranging slr observations grace based water storage changes are compared with estimates from nasa s global land data assimilation system gldas results from the 22 grace monthly gravity solutions covering the period april 2002 to july 2004 show remarkably good agreement with gldas in the mississippi amazon ganges ob zambezi and victoria basins combining grace observations with eop and slr degree 2 spherical harmonic coefficient changes and slr observed geocenter variations significantly affects and apparently improves the estimates especially in the mississippi ob and victoria basins

geochemistry of diverse basalt types from loihi seamount hawaii petrogenetic implications the wide variety of basalt types tholeiitic to basanite dredged from loihi seamount have minor and trace element abundances that are characteristic of subaerial hawaiian basalts thereby confirming that loihi seamount is a manifestation of the hawaiian hot spot within the loihi sample suite there are well defined positive correlations among abundances of highly incompatible elements p k rb ba nb light ree and ta and moderately incompatible elements sr ti zr and hf and between mgo ni and cr however within the loihi suite abundance ratios of geochemically similar elements zr hf nb ta and la ce vary by factors of 1 2 1 5 and abundance ratios of highly incompatible elements such as p ce p th k rb ba th and la nb vary by factors of 1 2 2 5 these abundance ratios are not readily changed by different degrees of fractionation and melting therefore we conclude that these samples are not genetically related by different degrees of melting of a compositionally homogeneous source on the basis of k p k ti p ce zr nb th p and la sm abundance ratios the twelve samples studied in detail can be divided into six geochemical groups samples within each group are similar in 87sr 86sr 1 and intra group compositional variations may reflect low pressure fractionation and different degrees of melting in addition crossing chondrite normalized ree patterns within the alkalic basalt groups reflect equilibration of the magmas with garnet in ratio ratio plots involving abundance ratios of highly incompatible elements e g la p nb p k p rb p ba p and th p the geochemical groups define linear arrays suggestive of mixing however these data combined with the isotopic data are not consistent with two component mixing

isotopic constraints on the origin of hawaiian lavas from the maui volcanic complex hawaii strontium neodymium and lead isotopic data for samples from five volcanoes of the maui volcanic complex hawaii span nearly the total compositional range previously recognized for the hawaiian islands these data reveal a systematic compositional continuum for hawaiian tholeiites which is interpreted to result from partial melting of a variably mixed two component mantle plume source in contrast post shield building alkalic cap lavas define distinct compositional trends which appear to result from time and volume dependent binary mixing between hawaiian plume melts and a depleted mantle component

lead isotopic compositions of south sandwich island volcanic rocks and their bearing on magmagenesis in intra oceanic island arcs pb isotope ratios have been measured in 12 volcanic rocks from the south sandwich islands the ranges are 206pb204pb 18 51 18 66 207pb204pb 15 55 15 64 208pb204pb 38 42 38 64 in 207pb204pb 206pb204pb and 208pb204pb 206pb204pb correlation diagrams the south sandwich data plot distinctly above the fields for ocean ridge basalts and yield trends showing apparent mixing with a sedimentary end member similar to south atlantic pelagic sediments as reported by chow and patterson 1962 and this study armstrong and cooper 1971 have likewise shown that volcanics from the lesser antilles show mixing trends with north atlantic sediments in pb isotope correlation diagrams the north atlantic sediments have distinctly higher 206pb204pb and 208pb204pb ratios compared to the south atlantic sediments the parallel relationships between sediments and volcanic island arc rocks of the north and south atlantic provide strong evidence for a component of pb from subducted sediments in the lavas of the west atlantic basin in contrast to these data lavas from the mariana arc in the western pacific show little or no component of pb from pelagic sediments the reason for the different behaviors in the two settings is speculative

the 40ar 39ar dating of core recovered by the hawaii scientific drilling project phase 2 hilo hawaii 1 the hawaii scientific drilling project phase 2 hsdp 2 recovered core from a 3 1 km thick section through the eastern flanks of mauna loa and mauna kea volcanoes we report results of 40ar 39ar incremental heating by broad beam infrared laser of 16 basaltic groundmass samples and 1 plagioclase separate mostly from k poor tholeiites the tholeiites generally have mean radiogenic 40ar enrichments of 1 3 and some contain excess 40ar however isochron ages of glass poor samples preserve stratigraphic order in all cases a 246 m thick sequence of mauna loa tholeiitic lavas yields an isochron age of 122 86 kyr all errors 2 at its base beneath the mauna loa overlap sequence lie mauna kea s postshield and shield sequences a postshield alkalic lava yields an age of 236 16 kyr in agreement with an age of 240 14 kyr for a geochemically correlative flow in the nearby hsdp 1 core hole where more complete dating of the postshield sequence shows it to have accumulated at 0 9 0 4 m kyr from about 330 to 200 ka mauna kea s shield consists of subaerial tholeiitic flows to a depth of 1079 m below sea level then shallow submarine flows hyaloclastites pillow lavas and minor intrusions to core bottom at 3098 m most subaerial tholeiitic flows fail to form isochrons however a sample at 984 m yields an age of 370 180 kyr consistent with ages from similar levels in hsdp 1 submarine tholeiites including shallow marine vitrophyres clasts from hyaloclastites and pillow lavas were analyzed however only pillow lava cores from 2243 2614 and 2789 m yield reliable ages of 482 67 560 150 and 683 82 kyr respectively a linear fit to ages for shield samples defines a mean accumulation rate of 8 6 3 1 m kyr and extrapolates to 635 kyr at core bottom alternatively a model relating mauna kea s growth to transport across the hawaiian hot spot that predicts downward accelerating accumulation rates that reach 20 m kyr at core bottom depaolo and stolper 1996 is also consistent with all reliable ages except the deepest

intershield geochemical differences among hawaiian volcanoes implications for source compositions melting process and magma ascent paths as hawaiian volcanoes develop their lavas systematically change in composition and isotopic ratios of sr nd and pb these trends provide important constraints for understanding plume related volcanism as a volcano migrates away from the hotspot there are also geochemical differences between hawaiian shields in particular lavas from adjacent shields such as kilauea and mauna loa on hawaii and koolau and waianae on oahu have significant differences in abundances of some major and incompatible elements and isotopic ratios of sr nd and pb some incompatible element abundance ratios such as zr nb and sr nb are correlated with intershield differences in sr and nd isotope ratios but these isotopic ratios are not correlated with intershield differences in major element composition or even parent daughter abundance ratios such as rb sr and sm nd moreover at kilauea and mauna loa the intershield differences have apparently persisted for a relatively long time perhaps 100 ka these intershield geochemical differences provide important constraints on plume volcanism specifically i each volcano must have distinct magma ascent paths from the region of melt segregation ii the 25 50 km distance between adjacent but geochemically distinct shields requires that the sources vary on a similar scale and that the melt production region is similarly restricted the absence of correlations between lava compositions and radiogenic isotope ratios provides evidence for significant differences in melting process such as each shield forming by a different mean extent of melting with melt segregation at different mean pressures two types of models are consistent with the intershield geochemical differences i a relatively large radius ca 40 km plume conduit with a systematic spatial distribution of geochemical heterogeneities or ii a small radius less than 20 km plume conduit composed of geochemically distinct diapirs because relatively small radius diapirs of limited vertical extent are too small to create the large hawaiian shields a possible alternative is a continuous conduit containing solitary waves which transport geochemically distinct packets of material

submarine lavas from mauna kea volcano hawaii implications for hawaiian shield stage processes the island of hawaii is composed of five voluminous shields but only the youngest active and well exposed shields of mauna loa and kilauea have been studied in detail the shield lavas forming kohala hualalai and mauna kea are largely covered by postshield lavas with geochemical characteristics that differ from the shield lavas in order to determine the geochemical characteristics of the mauna kea shield which is adjacent to the kilauea and mauna loa shields 12 mauna kea shield basalts dredged from the submarine east rift were analyzed for major and trace element contents and isotopic sr nd and pb ratios the lavas are mgo rich 11 to 20 submarine erupted tholeiitic basalts but they are not representative of crystallized mgo rich melts their whole rock and mineral compositions are consistent with mixing of an evolved magma 7 mgo with a magma containing abundant olivine xenocrysts probably disaggregated from a dunitic cumulate at a given mgo content some of the mauna kea whole rocks have lower abundances of cao and higher abundances of incompatible elements the evolved melt component in these lavas reflects significant fractionation of plagioclase and clinopyroxene and in some cases even the late crystallizing phases orthopyroxene and fe ti oxide although these mauna kea lavas are not isotopically homogeneous in general their sr nd and pb isotopic ratios overlap with the fields for lavas from loihi and kilauea volcanoes lavas from these three shields define the low 87sr 86sr high 206pb 204pb and low zr nb ranges for hawaiian shield lavas and they may contain a larger proportion of a component with high 238u 204pb most of these mauna kea shield lavas however are distinguished from kilauea and loihi tholeiitic basalts by having lower la ce and la yb these data provide additional evidence that each hawaiian shield has distinctive geochemical characteristics

deceleration in the earth s oblateness 1 for over three decades satellite laser ranging slr has recorded the global nature of the long wavelength mass change within the earth system analysis of the most recent time series of 30 day slr based estimates of earth s dynamical oblateness characterized by the gravitational degree 2 zonal spherical harmonic j2 indicates that the long term variation of j2 appears to be more quadratic than linear in nature the superposition of a quadratic and an 18 6 year variation leads to the unknown decadal variation reported by cheng and tapley 2004 although the primary trend is expected to be linear due to global isostatic adjustment there is an evident deceleration j 2 18 1 10 13 yr2 in the rate of the decrease in j2 during the last few decades likely due to changes in the rate of the global mass redistribution from melting of the glaciers and ice sheets as well as mass changes in the atmosphere and ocean

geology and volcanic stratigraphy of the canatuan and malusok volcanogenic massive sulfide deposits southwestern mindanao philippines the canatuan and malusok massive sulfide deposits are located near siocon zamboanga del norte in southwestern mindanao philippines the canatuan malusok area is underlain by the jurassic cretaceous tungauan schists which form much of the zamboanga peninsula the volcanic strata at canatuan and malusok can be traced for 7 km along strike and is host to at least three discrete massive sulfide bodies canatuan malusok and se malusok basal basaltic andesite volcanic rocks are generally chemically uniform and show only moderate alteration the massive sulfide deposits occur in overlying rhyolitic to rhyodacitic volcanic rocks that are altered to a schistose assemblage of quartz sericite chlorite and pyrite the alteration is texturally destructive but graded clastic beds are locally observed despite tropical saprolitic weathering four lithogeochemical subunits of the felsic package are identified stratigraphic interleaving however has made correlation of these units over any significant distance difficult the sulfide lenses are overlain by a few metres of felsic schists which locally contain manganese bearing silicates and oxides that serve as a stratigraphic marker hangingwall andesitic volcaniclastic rocks are discontinuously preserved although where present they consist of regularly bedded mafic volcanic sandstones the lateral continuity of a manganese bearing marker and flanking felsic volcaniclastic intervals indicate that locally the volcanic strata form a homoclinal sequence the canatuan au ag cu zn deposit consists of a gossan overlying a massive sulfide lens the sulfides and gossan are flat lying and hosted within felsic volcanic rocks the gossan is gold silver rich and was formed by a combination of oxidation and volume collapse of the original sulfide lens the sulfide minerals present below the current water table are auriferous massive pyrite with base metal sulfides with some supergene chalcocite the transition from gossan to sulfides is very sharp occurring at the water table massive sulfide deposits at malusok are hosted in the same felsic sequence as canatuan and they have similar base and precious metal contents only limited gossan has been found at malusok the bimodal nature of the volcanic rocks at canatuan together with their low hfse contents near flat ree patterns and tholeiitic affinities suggest that they formed in an intra oceanic arc setting above a depleted mantle source mafic and felsic volcanic rocks of similar composition have been recovered from the tonga kermadec and izu bonin marianas island arc systems in the western pacific mafic rocks at canatuan show no evidence for lile enrichment that characterizes melts derived from metasomatized mantle under more mature arcs suggesting that they are the product of a nascent rather than a mature arc there is no evidence from the ree or other incompatible trace elements that continental crust or evolved arc crust was involved in the generation of the canatuan malusok volcanic rocks although it has been proposed that the zamboanga metamorphic complex comprises microcontinental fragments of eurasian affinity our data do not support an evolved crustal setting for the canatuan malusok volcanic rocks which we suggest were derived from an intra oceanic arc and subsequently accreted to the eastern mindanao terrane

magma solidification processes beneath kilauea volcano hawaii a quantitative textural and geochemical study of the 1969 1974 mauna ulu lavas sents a late magma component formed in the summit magma storage region our results are consistent with the hypothesis that the components of the mu magmas followed two different routes the deformed olivine bearing magma moved along the deep basal

geochemical variations in lavas from kahoolawe volcano hawaii evidence for open system evolution of plume derived magmas the kahoolawe shield volcano produced precaldera and caldera filling tholeiites and mildly alkalic post caldera lavas that petrographically and compositionally resemble such lavas from other hawaiian shield volcanoes however kahoolawe tholeiites display wide ranges in incompatible trace element ratios e g nb th 9 24 th ta 0 6 1 3 87sr 86sr 0 70379 0 70440 143nd 144nd 0 51273 0 51298 and 206pb 204pb 17 92 18 37 the isotopic variation exceeds that at any other hawaiian shield volcano and spans about half the range for all hawaiian tholeiites quasi cyclic temporal evolution of kahoolawe tholeiites is consistent with combined fractional crystallization and periodic recharge by primitive magmas ratios of highly incompatible trace elements and sr nd and pb isotopic ratios from coherent sub trends that reflect recurrent interactions between variably evolved magmas and two other mantle components whose compositions are constrained by intersections between these trends the most mgo rich kahoolawe tholeiites are partial melts of a high nb th 23 5 ascending plume possibly comprising ancient subducted oceanic lithosphere slightly evolved tholeiites experienced combined crystal fractionation and assimilation afc of material derived from a distinct reservoir nb th 9 of asthenospheric derivation the most evolved tholeiites display compositional shifts toward a third component having mid ocean ridge basalt like isotopic ratios but enriched oib like trace element ratios representing part of the lithospheric mantle or melts thereof periodic recurrence of all three magma variants suggests that eruptions may have tapped coeval reservoirs distributed over a large depth range kahoolawe provides new evidence concerning the nature of the hawaiian plume the distribution of compositional heterogeneities in the suboeanic mantle and the processes by which hawaiian tholeiites form and evolve

a combined fluid inclusion and s pb isotope study of the neoproterozoic pingshui volcanogenic massive sulfide cu zn deposit southeast china abstract the pingshui cu zn deposit is located in the jiangshan shaoxing fault zone which marks the neoproterozoic suture zone between the yangtze block and cathaysia block in south china it contains 0 45 million tons of proven ore reserves with grades of 1 03 wt cu and 1 83 wt zn this deposit is composed of stratiform massive sulfide ore bodies which contain more than 60 vol sulfide minerals these ore bodies are hosted in altered mafic and felsic rocks spilites and keratophyres of the bimodal volcanic suite that makes up the neoproterozoic pingshui formation metallic minerals include pyrite chalcopyrite sphalerite tennantite tetrahedrite and magnetite with minor galena gangue minerals are quartz sericite chlorite calcite gypsum barite and jasper three distinct mineralogical zones are recognized in these massive sulfide ore bodies a distal zone composed of sphalerite pyrite barite zone i an intermediate zone characterized by a pyrite sphalerite chalcopyrite assemblages zone ii and a proximal zone containing chalcopyrite pyrite magnetite zone iii a thin layer of exhalative jaspilite overlies the sulfide ore bodies except in the proximal zone the volcanic rocks of the pingshui formation are all highly altered spilites and keratophyres but their trace element geochemistry suggests that they were generated by partial melting of the depleted mantle in an island arc setting homogenization temperatures of the primary fluid inclusions in quartz from massive sulfide ores are between 217 and 328 c and their salinities range from 3 2 to 5 7 wt nacl equivalent raman spectroscopy of the fluid inclusions showed that water is the dominant component with no other volatile components fluid inclusion data suggest that the ore forming fluids were derived from circulating seawater the 34 s values of pyrite from the massive sulfide ores range from 3 6 to 3 4 indicating that the sulfur was primarily leached from the arc volcanic rocks of the pingshui formation both pyrite from the massive sulfide ores and plagioclase from the spilites have similar lead isotope compositions implying that the lead was also derived from the pingshui formation the low lead contents of the massive sulfide ores and the geochemistry of their host rocks are similar to many vms cu zn deposits in canada e g noranda and thus can be classified as belonging to the bimodal mafic subtype the presence of magnetite and the absence of jaspilite and barite at the 505 m level in the pingshui deposit suggest that this level is most likely the central zone of the original lateral massive sulfide ore bodies if this interpretation is correct the deep part of the pingshui cu zn deposit may have significant exploration potential

formation of submarine flat topped volcanic cones in hawai i high resolution bathymetric mapping has shown that submarine flat topped volcanic cones morphologically similar to ones on the deep sea floor and near mid ocean ridges are common on or near submarine rift zones of kilauea kohala or mauna kea mahukona and haleakala volcanoes four flat topped cones on kohala were explored and sampled with the pisces v submersible in october 1998 samples show that flat topped cones on rift zones are constructed of tholeiitic basalt erupted during the shield stage similarly shaped flat topped cones on the northwest submarine flank of ni ihau are apparently formed of alkalic basalt erupted during the rejuvenated stage submarine postshield stage eruptions on hilo ridge mahukona hana ridge and offshore ni ihau form pointed cones of alkalic basalt and hawaiite the shield stage flat topped cones have steep 25 sides remarkably flat horizontal tops basal diameters of 1 3 km and heights 300 m the flat tops commonly have either a low mound or a deep crater in the center the rejuvenated stage flat topped cones have the same shape with steep sides and flat horizontal tops but are much larger with basal diameters up to 5 5 km and heights commonly greater than 200 m the flat tops have a central low mound shallow crater or levees that surrounded lava ponds as large as 1 km across most of the rejuvenated stage flat topped cones formed on slopes 10 and formed adjacent semicircular steps down the flank of ni ihau rather than circular structures all the flat topped cones appear to be monogenetic and formed during steady effusive eruptions lasting years to decades these and other submarine volcanic cones of similar size and shape apparently form as continuously overflowing submarine lava ponds a lava pond surrounded by a levee forms above a sea floor vent as lava continues to flow into the pond the lava flow surface rises and overflows the lowest point on the levee forming elongate pillow lava flows that simultaneously build the rim outward and upward but also dam and fill in the low point on the rim the process repeats at the new lowest point forming a circular structure with a flat horizontal top and steep pillowed margins there is a delicate balance between lava heat supply to the pond and cooling and thickening of the floating crust factors that facilitate construction of such landforms include effusive eruption of lava with low volatile contents moderate to high confining pressure at moderate to great ocean depth long lived steady eruption years to decades moderate effusion rates probably ca 0 1 km3 year and low but not necessarily flat slopes with higher effusion rates sheet flows flood the slope with lower effusion rates pillow mounds form hawaiian shield stage eruptions begin as fissure eruptions if the eruption is too brief it will not consolidate activity at a point and fissure fed flows will form a pond with irregular levees the pond will solidify between eruptive pulses if the eruption is not steady lava that is too volatile rich or that is erupted in too shallow water will produce fragmental and highly vesicular lava that will accumulate to form steep pointed cones as occurs during the post shield stage the steady effusion of lava on land constructs lava shields which are probably the subaerial analogs to submarine flat topped cones but formed under different cooling conditions

geochemical constraints on the role of oceanic lithosphere in intra volcano heterogeneity at west maui hawaii 87 sr 86 sr 206 pb 204 pb variation in the stratigraphically lowest lavas is orthogonal to the all hawaii variation indicating that it is not the result of mixing between components normally sampled by hawaiian shield stage magmas we compare our west maui data with observed compositions of pacific oceanic basaltic and gabbroic crust and predicted compositions for 2ga basaltic and gabbroic oceanic crust the observed fine scale compositional variability in the stratigraphically lowest west maui lavas is consistent with 10 15 mixing of small degree 2 partial melts of the pacific gabbroic oceanic crust with plume derived kea type magmas mass balance considerations indicate that this geochemical signal can be present in no more than 5 of the total volume of lavas erupted at west maui

the isotope systematics of a juvenile intraplate volcano pb nd and sr isotope ratios of basalts from loihi seamount hawaii abstract sr nd and pb isotope ratios for a representative suite of 15 basanites alkali basalts transitional basalts and tholeiites from loihi seamount hawaii display unusually large variations for a single volcano but lie within known ranges for hawaiian basalts nd isotope ratios in alkali basalts show the largest relative variation 0 51291 0 51305 and include the nearly constant tholeiite value 0 51297 pb isotope ratios show similarly large ranges for tholeiites and alkali basalts and continue tatsumoto s 31 loa trend towards higher 206pb 204pb ratios resulting in a substantial overlap with the kea trend 206pb 204pb ratios for loihi and other volcanoes along the loa and kea trends 31 are observed to correlate with the age of the underlying lithosphere suggesting lithosphere involvement in the formation of hawaiian tholeiites loihi lavas display no correlation of nd sr or pb isotope ratios with major element compositions or eruptive age in contrast with observations of some other hawaiian volcanoes 38 isotope data for loihi as well as average values for hawaiian volcanoes are not adequately explained by previously proposed two end member models new models for the origin and the development of hawaiian volcanoes must include mixing of at least three geochemically distinct source regions and allow for the involvement of heterogeneous oceanic lithosphere

mineralogy and geochemistry of the masa valverde blind massive sulphide deposit iberian pyrite belt spain abstract masa valverde is a blind volcanic hosted massive sulphide deposit recently discovered in the spanish sector of the iberian pyrite belt ipb the deposit is more than 1 km long and is located at depths between 400 and 850 m in direct spatial association with a residual gravimetric anomaly the ore body is concealed beneath culm sedimentary rocks which cover the western extension of a hercynian age anticline a few kilometers west of an area where older massive sulphide workings existed the masa valverde deposit consists of two main ore bodies composed dominantly of massive and banded pyrite which are hosted by a volcano sedimentary sequence made up of felsic tuffs interlayered with shale siliceous exhalite and radiolarian chert the abundance of sedimentary host rocks to the deposit is a feature shared by other large massive sulphide deposits in the eastern sector of the ipb and is interpreted as significant with respect to the origin of the deposit a break in volcanic activity the thickness of the upper massive sulphide orebody varies between a few meters and 70 m and it consists of lenses and blankets of massive sulphides with interbedded tuff and shale and occasionally stockwork zones the lower orebody is smaller and thinner than the upper one but this may be due to incomplete drilling two types of stockwork occur beneath the massive sulphide bodies the more common type consists of irregular and anastomosing sulphide veinlets and irregular blebs formed by replacement stockwork with cross cutting generally straight sided sulphide veins is by contrast suggestive of formation by hydraulic fracturing the mineralogy and alteration processes of the ore and host rocks at masa valverde are analogous to those of other ipb massive sulphides the average temperature of formation of the components of the ore zones estimated on the basis of chlorite thermometry are as follows siliceous exhalites 290 c massive sulphides 325 c and stockworks 305 c rare earth element measurements indicate that the lowest metal concentrations occur in chloritites which occasionally host cu rich stockwork and are characterised by a strongly negative eu anomaly by contrast rocks hosting the sulphide lenses where silicification sericitization and carbonatization are more intense are enriched in lree two main stages of hydrothermal activity are suggested for the masa valverde deposit during an early stage ore fluids would have discharged onto the sea floor resulting in the deposition of pyrite with sphalerite and galena later on with continued input of high temperature fluids 290 to 315 c chalcopirite precipitated especially in the stockworks and at the base of the sulphide lenses at masa valverde this late cu rich hydrothermal event would have produced an ascending cu front which overpassed the stockwork zone and reached a higher temperature 325 c at the base of the massive sulphide lenses the combination of geological mineralogical and geochemical features of the masa valverde deposit provide guidelines for exploration for new blind orebodies in this part of the ipb where tuffs and sedimentary rocks are the dominant host lithologies the masa valverde deposit can be considered as a vhms subtype transitional to shms

high magnesium primary magmas from haleakala volcano east maui hawaii petrography nickel and major element constraints abstract for any given volcanic field the compositions of primary melts provide important constraints on models of magmatic processes and volcanic eruptions in this paper based on petrography olivine and bulk rock compositions two tholeiitic picrites samples c122 and c123 from haleakala volcano east maui are evaluated as possible primary melts sample c122 bulk rock mgo 16 6 has a high apparent mg fe exchange coefficient kd between olivine phenocrysts and bulk rock 0 6 however major elements and ni mass balance calculations show that the olivines in c122 are in equilibrium with the residual melt matrix after closed system equilibrium fractionation of 25 wt olivine therefore the mg fe ratio ca content and ni content of c122 are consistent with the hypothesis that the bulk composition of c122 is close to a primary melt formed by partial melting of a mantle containing olivine with composition around fo89 to fo91 the uniform composition and small size mostly 0 2 0 3 mm of the olivine and the glass patches in the matrix suggest fast ascent and rapid cooling at shallow depth for c122 on the contrary sample c123 which has an apparent kd between the most mafic olivine megacrysts and the bulk rock close to the equilibrium value 0 27 the multiple planar subgrain boundaries in most of the olivine crystals indicate that it may not be a primary melt unless the deformed olivines are generated at magmatic condition as phenocrysts if the deformed subgrain boundary texture in olivine could indeed be generated at magmatic condition then the wide compositional range of olivine crystals in c123 fo74 to fo91 suggests multi stage crystallization over a wide range of cooling temperatures the compositions of the two picrites and a differentiated basalt which does not contain xenocrysts suggest that the haleakala tholeiites are derived from primary melts with at least 16 17 wt mgo lavas with such high mgo content are rare in haleakala and other hawaiian volcanoes therefore most hawaiian tholeiites must have undergone extensive fractionation histories

models of hawaiian volcano growth and plume structure implications of results from the hawaii scientific drilling project the shapes of typical hawaiian volcanoes are simply parameterized and a relationship is derived for the dependence of lava accumulation rates on volcano volume and volumetric growth rate the dependence of lava accumulation rate on time is derived by estimating the eruption rate of a volcano as it traverses the hawaiian plume with the eruption rate determined from a specified radial dependence of magma generation in the plume and assuming that a volcano captures melt from a circular area centered on the volcano summit the timescale of volcano growth is t 2 r plate where r is the radius of the melting zone of the circular plume and plate is the velocity of the pacific plate the growth progress of a volcano can be described by a dimensionless time t t plate 2r where t 0 is chosen to be the start of volcano growth and t 1 approximates the end of shield growth using a melt generation rate for the whole plume of 0 2 km 3 yr a plume diameter of 50 km and a plate velocity of 10 cm yr we calculate that the lifetime of a typical volcano is 1000 kyr for a volcano that traverses the axis of the plume the standard dimensions are a volume of 57 000 km 3 a summit thickness of 18 km a summit elevation of 3 6 km and a basal radius of 60 km the volcano first breaches the sea surface at t 0 22 when it has attained only 5 of its eventual volume 80 of the volume accumulates between t 0 3 and t 0 7 typical lava accumulation rates start out over 50 m kyr in the earliest stages of growth from the seafloor and level out at 35 m kyr from t 0 05 until t 0 4 from t 0 4 to t 0 9 the submarine lava accumulation rates decrease almost linearly from 35 m kyr to 0 subaerial accumulation rates are about 30 lower the lava accumulation rate is a good indicator of volcano age a volcano that passes over the plume at a distance 0 4r off to the side of the plume axis is predicted to have a volume of about 60 of the standard volcano a lifetime about 8 shorter and lava accumulation rates about 15 20 smaller the depth age data for mauna kea lavas cored by the hawaii scientific drilling project are a good fit to the model parameters used given that mauna kea appears to have crossed the plume about 15 20 km off axis the lifetime of mauna kea is estimated to be 920 kyr mauna loa is predicted to be at a stage corresponding to t 0 8 kilauea is at t 0 6 and loihi is at t 0 16 the model also allows the subsurface structure of the volcanoes the interfaces between lavas from different volcanoes to be modeled radial geochemical structure in the plume may be blurred in the lavas because the volcanoes capture magma from a sizeable cross sectional area of the plume this inference is qualitatively born out by available isotopic data the model predicts that new hawaiian volcanoes are typically initiated on the seafloor near the base of the next older volcano but generally off the older volcano s flank

recent changes in the earth s oblateness driven by greenland and antarctic ice mass loss 1 we use temporal gravity variations from grace to investigate changes in a 34 year time series of earth s oblateness j2 observed by satellite laser ranging slr we use 2002 2010 grace data to compute the effects of greenland and antarctic ice mass variations on j2 2 0 and 1 7 10 11 year respectively their combined effect on the j2 trend during the grace mission is 3 7 10 11 year which agrees well with the gia corrected slr j2 trend over the same time period the results suggest that at least since 2002 ice loss from greenland and antarctica has been the dominant contributor to the current gia corrected j2 trend which apparently began sometime in the 1990s