calculated mineral equilibria for eclogites in cao na2o feo mgo al2o3 sio2 h2o application to the pouebo terrane pam peninsula new caledonia the high p medium t pouebo terrane of the pam peninsula northern new caledonia includes barroisite and glaucophane bearing eclogite and variably rehydrated equivalents the metamorphic evolution of the pouebo terrane is inferred from calculated p t and p t xh2o pseudosections for bulk compositions appropriate to these rocks in the model system cao na2o feo mgo al2o3 sio2 h2o the eclogites experienced a clockwise p t path that reached p 19 kbar and t 600 c the eclogitic mineral assemblages are preserved because reaction consequent upon decompression consumed the rocks fluid extensive reaction occurred only in rocks with fluid influx during decompression of the pouebo terrane

airborne gravity reveals interior of antarctic volcano abstract understanding antarctic volcanoes is important as they provide a window on magmatic and tectonic processes of the antarctic plate and contain datable records of ice sheet changes we present the results from the first detailed airborne radar and gravity surveys across james ross island northern antarctic peninsula which is dominated by mt haddington an ice covered miocene recent alkaline stratovolcano the surveys provide new insights into the subsurface structure of the volcano and hence its development which are unavailable from the surface geology alone we show that mt haddington is associated with a significant negative bouguer gravity anomaly 26 mgal which suggests that there has not been significant pooling and solidification of a dense shallow level mafic magma chamber during the growth of the volcano over at least the past 6 m y which is consistent with independent geochemical evidence simple flexural isostatic models cannot explain the localised negative bouguer anomaly 3d modelling techniques show that the negative anomaly is best explained by a shallow low density intra crustal body with its top close to or at the surface although comparable gravity anomalies are commonly associated with large 20 km ash filled calderas as seen at yellowstone or toba there is no geological evidence on james ross island for a similar structure we therefore propose that the james ross island volcanic edifice subsided into the thick underlying pile of relatively soft jurassic and cretaceous sediments which were displaced by low density hyaloclastite breccia the type of deformation envisaged is similar to that associated with concepciou or iwaki volcanoes in south america although mt haddington is much larger

thick sections of layered ultramafic cumulates in the oman ophiolite revealed by an airborne hyperspectral survey petrogenesis and relationship to mantle diapirism abstract using the hymap instrument we have acquired visible and near infrared hyperspectral data over the maqsad area of the oman ophiolite 15 60 km this survey allowed us to identify and map the distribution of clinopyroxene rich cumulates inter layered clinopyroxenites and wehrlites whose occurrence was previously undocumented in this area the cumulates reach several hundred meters in thickness and crop out at distances exceeding 15 km on both sides of the maqsad former spreading centre they occur either in mantle harzburgites as km sized layered intrusions surrounded by fields of pegmatitic dykes consisting of orthopyroxene rich pyroxenite and gabbronorites or at the base of the crustal section where they are conformably overlain by cumulate gabbros these ultramafic cumulates crystallized from silica and mg rich melts derived from a refractory mantle source e g high cr low al 2 o 3 low tio 2 these melts are close to high ca boninites although strictly speaking not perfect equivalents of present day supra subduction zone boninites chemical stratigraphy reveals cycles of replenishment mixing and fractional crystallization from primitive high mg melts typical of open magma chambers and migration of inter cumulus melts the tio 2 content of clinopyroxene is always low 0 2 wt but quite variable compared to the associated pegmatites that are all derived from a source ultra depleted in high field strength elements hfse this variability is not caused by fractional crystallization alone and is best explained by hybridization between the ultra depleted melts parent melts of the pegmatites and the less depleted mid ocean ridge basalts morb parent of the dunitic troctolitic gabbroic cumulates making up the crustal section above the maqsad diapir we propose that following a period of magma starved spreading the maqsad mantle diapir impregnated with tholeiitic melts of morb affinity reached shallow depths beneath the ocean ridge this diapir induced melting of the formerly accreted and hydrothermally altered lithosphere at this stage these boninitic like lithospheric melts crystallized as pegmatitic dykes as the diapir continued to rise the amount of morb reaching shallow depths increased together with the surrounding temperature leading to the formation of magma chambers where the crystallization of layered cumulates became possible these cumulates remained rich in pyroxene and devoid of plagioclase as long as the contribution of morb derived melts was moderate relative to the lithospheric derived melts as the contribution of morb to the refilling of the magma chamber increased gabbroic cumulates started to crystallize

high temperature emplacement of the cerro galan and toconquis group ignimbrites puna plateau nw argentina determined by trm analyses estimates of pyroclastic flow emplacement temperatures in the cerro galan ignimbrite and toconquis group ignimbrites were determined using thermal remanent magnetization of lithic clasts embedded within the deposits these ignimbrites belong to the cerro galan volcanic system one of the largest calderas in the world in the puna plateau nw argentina temperature estimates for the 2 08 ma cerro galan ignimbrite are retrieved from 40 sites in 14 localities 176 measured clasts distributed at different distances from the caldera and different stratigraphic heights additionally temperature estimates were obtained from 27 sample sites 125 measured clasts from seven ignimbrite units forming the older toconquis group 5 60 4 51 ma mainly outcropping along a type section at rio las pitas vega real grande the paleomagnetic data obtained by progressive thermal demagnetization show that the clasts of the cerro galan ignimbrite have one single magnetic component oriented close to the expected geomagnetic field at the time of emplacement results show therefore that most of the clasts acquired a new magnetization oriented parallel to the magnetic field at the moment of the ignimbrite deposition suggesting that the clasts were heated up to or above the highest blocking temperature tb of the magnetic minerals tb 580 c for magnetite tb 600 630 c for hematite we obtained similar emplacement temperature estimations for six out of the seven volcanic units belonging to the toconquis group with the exception of one unit lower merihuaca where we found two distinct magnetic components the estimation of emplacement temperatures in this latter case is constrained at 580 610 c which are lower than the other ignimbrites these estimations are also in agreement with the lowest pre eruptive magma temperatures calculated for the same unit i e 790 c hornblende plagioclase thermometer folkes et al 2011b we conclude that the cerro galan ignimbrite and toconquis group ignimbrites were emplaced at temperatures equal to or higher than 620 c except for lower merihuaca unit emplaced at lower temperatures the homogeneity of high temperatures from proximal to distal facies in the cerro galan ignimbrite provides constraints for the emplacement model marked by a relatively low eruption column low levels of turbulence air entrainment surface water interaction and a high level of topographic confinement all ensuring minimal heat loss

spectral and dynamical hints on the time scale of preparation of the 5 april 2003 explosion at stromboli volcano stromboli volcano is well known for its continuous strombolian activity moreover the volcano occasionally shows effusive phases the latest in 1985 1986 on 28 december 2002 stromboli entered a new effusive phase accompanied by different paroxysmal events that led to considerable hazards for inhabitants and tourists on the island of stromboli on 30 december 2002 a major sector collapse affected the sciara del fuoco slope and initiated a tsunami on 5 april 2003 a powerful explosion which can be compared in size with the most recent explosion in 1930 covered a large part of the normally tourist accessible summit area with bombs as this explosion was not forecasted although the island was by then effectively monitored by a dense deployment of instruments in this paper we tackle the problem of highlighting the time scale of preparation of this event and conduct a search for possible precursors for this purpose we analyze the seismic data preceding the paroxysm with spectral and dynamical methods

the volcanic and magmatic evolution of volcan ollague a high k late quaternary stratovolcano in the andean central volcanic zone abstract volcan ollague is a high k calc alkaline composite volcano constructed upon extremely thick crust in the andean central volcanic zone volcanic activity commenced with the construction of an andesitic to dacitic composite cone composed of numerous lava flows and pyroclastic deposits of the vinta loma series and an overlying coalescing dome and coulee sequence of the chasca orkho series following cone construction the upper western flank of ollague collapsed toward the west leaving a collapse amphitheater about 3 5 km in diameter and a debris avalanche deposit on the lower western flank of the volcano the deposit is similar to the debris avalanche deposit produced during the may 18 1980 eruption of mount st helens u s a and was probably formed in a similar manner it presently covers an area of 100 km2 and extends 16 km from the summit subsequent to the collapse event the upper western flank was reformed via eruption of several small andesitic lava flows from vents located near the western summit and growth of an andesitic dome within the collapse amphitheater additional post collapse activity included construction of a dacitic dome and coulee of the la celosa series on the northwest flank field relations indicate that vents for the vinta loma and post collapse series were located at or near the summit of the cone the vinta loma series is characterized by an anhydrous two pyroxene assemblage vents for the la celosa and chasca orkho series are located on the flanks and strike n55 w radial to the volcano the pattern of flank eruptions coincides with the distribution in the abundance of amphibole and biotite as the main mafic phenocryst phases in the rocks a possible explanation for this coincidence is that an unexposed fracture or fault beneath the volcano served as a conduit for both magma ascent and groundwater circulation in addition to the lava flows at ollague magmas are also present as blobs of vesiculated basaltic andesite and mafic andesite that occur as inclusions in nearly all of the lavas all eruptive activity at ollague predates the last glacial episode 11 000 a b p because post collapse lava flows are overlain by moraine and are incised by glacial valleys present activity is restricted to emission of a persistent 100 m high fumarolic steam plume from a vent located within the summit andesite dome sr and nd isotope ratios for the basaltic andesite and mafic andesite inclusions and lavas suggest that they have assimilated large amounts of crust during crystal fractionation in contrast narrow ranges in 143nd 144nd and 87sr 86sr in the andesitic and dacitic lavas are enigmatic with respect to crustal contamination

field evidence for flank instability basal spreading and volcano tectonic interactions at mt cameroon west africa the mt cameroon volcano is the highest and most active volcano of the cameroon volcanic line little geological information is available for improving the understanding of the structure of this large volcanic system and its relationship to regional tectonics after reviewing the tectonic evolution of the region the analysis of a digital elevation model and results from a field campaign dedicated to mapping geological structures in the summit area and at the se base of mt cameroon are presented mt cameroon is a lava dominated volcano with long steep over 30 flanks it is elongate parallel to its well defined rift zone the summit plateau is bordered by 10 m high cliffs formed by summit subsidence along normal faults geological profiles were measured along rivers cutting through a topographic step at the se base of mt cameroon this step is associated with deformed miocene sediments from the douala basin that are overlain by volcanic products weak sediments of this area are deformed by 050 060 and 020 030 trending asymmetrical folds verging toward the se and thrusts faults related to the spreading of the volcano over its mechanically weak substratum combined remote sensing and field observations suggest that spreading is accommodated by summit subsidence and flanks sliding both slow spreading movements and catastrophic collapses of the steep flanks are interpreted to result from complex interactions between the growing edifice repeated dyke intrusions the weak sedimentary substratum and tectonic structures

alteration and geochemical patterns in the 3 7 3 8 ga isua greenstone belt west greenland abstract volcanic rocks of the 3 7 3 8 ga isua greenstone belt have undergone heterogeneous poly phase post magmatic alteration resulting in mobilisation of many elements including lree and th in contrast nb ta ti zr y and hree were relatively immobile during alteration processes the degree of element mobility appears to have been controlled by chemical composition primary volcanic structures carbonate and silica enrichment and proximity to ultramafic units and shear zones on the basis of the geochemical characteristics of the least altered samples two distinct associations have been recognised in structurally separated lithotectonic sequences these magmatic associations are a low hfse association tio2 0 20 0 40 wt zr 12 30 ppm nb 0 13 0 80 ppm y 6 14 ppm in the central arc sequence resembling tertiary boninites and a high hfse association tio2 0 50 1 14 wt zr 34 77 ppm nb 1 2 2 7 ppm y 11 28 ppm in the outer and inner arc sequences comparable to phanerozoic island arc basaltic to picritic volcanic rocks these two geochemically distinct sequences were likely to have been juxtaposed as a consequence of phanerozoic style plate tectonic processes operating in the early earth the isua volcanic rocks are characterised by sub chondritic nb ta 10 16 ratios post magmatic alteration can be ruled out as the cause of these low ratios rather these ratios reflect a compositional characteristic of the paleoarchean mantle source s the sub chondritic nb ta ratios may have resulted from either preferential sink of nb into the core as a weakly siderophile element or preferential retention of nb in the subducted oceanic crust during subduction zone petrogenetic processes alternatively the building blocks of the earth were not composed of ci like chondritic material

recent dyke induced large scale block movement at mount etna and potential slope failure here we report the results of a geodetic survey undertaken on mount etna between 1981 and 1988 observed horizontal ground movements in the vicinity of the valle del bove caldera demonstrate that dyke emplacement during 1983 and 1985 resulted in the 2 8 m eastward displacement of a block of western caldera rim a history of past instability and collapse along the rim is indicated by the presence of large back rotated blocks of prehistoric volcanics1 furthermore the unusually linear form of the present western rim indicates past slope failure along north south aligned surfaces and therefore that dyke induced collapse may have been an important agent in caldera enlargement we suggest a self sustaining mechanism whereby the stress regime generated as a consequence of the caldera s existence results in the repeated injection of north south orientated dykes adjacent to the western rim2 3 dilation associated with magma intrusion leads in turn to periodic phases of slope instability and failure of the cliff wall causing a progressive westward migration of the western rim

new evidence about the structure and growth of ocean island volcanoes from aeromagnetic data the case of tenerife canary islands 1 we present 3 d magnetic models of tenerife based on a high resolution aeromagnetic survey carried out in 2006 two different inverse modeling techniques have been applied 1 a linear method aimed at imaging lateral magnetization contacts and 2 a nonlinear method aimed at obtaining a 3 d description of deep intrusive bodies in which a constant magnetization value characterizes the main sources magnetic models show that deep intrusive structures are located beneath the northern part of the island and aligned along the e w direction this arrangement of intrusive bodies does not support the hypothesis of a three armed rift system that has been present since the early formation of the island the shallow portion of the intrusive structures shows a round geometry that agrees with the previously proposed location of some of the landslide headwalls suggesting that collapse scars have acted as preferential sites for magma upwelling our magnetic model probably provides the first geophysical evidence of the location of the headwall of the icod landslide beneath the teide pico viejo complex thus supporting the vertical collapse hypothesis for the origin of the canadas caldera the largest intrusive complex is located to the northwest of teide and pico viejo revealing the presence of a very high dike density in this area this complex probably resulted from the intrusion of magma over the span of millions of years beginning with the early phases of basaltic shield volcanism in central tenerife and lasting until the building of teide and pico viejo stratovolcanoes

geological and isotopic geochemical constraints on the evolution of the fuping complex north china craton abstract the neoarchean to paleoproterozoic fuping complex together with the adjacent hengshan and wutaishan complexes form the middle part of the central zone that separates the north china craton into the eastern and western archean continental blocks the fuping complex comprises three major lithological assemblages the 2 50 ga fuping trondhjemite tonalite granodiorite ttg gneisses the wanzi paragneisses and the 2 08 and 2 02 ga nanying granitic gneisses the ttg gneisses contain abundant enclaves of highly metamorphosed supracrustal rocks including 2 70 ga mafic granulites and amphibolites with endt of 3 29 to 3 96 and tdm of 2 72 2 82 ga and are characterized by tdm of 2 76 3 04 ga and a linear correlation between endt 1 64 to 0 96 and 1 nd indicative of mixing of melts derived from the 2 70 ga metabasic rocks and 3 0 ga crustal materials mafic dikes along the chengnanzhuang shear zone were most likely emplaced at 2 31 ga and have endt of 2 24 to 4 78 and tdm of 2 34 2 59 ga the nanying granitic gneisses with endt of 4 04 to 5 24 were most likely related to partial melting of the 2 70 ga supracrustal rocks and or the 2 50 ga ttg gneisses these geological relationships and isotopic data suggest that the fuping complex probably formed from the following five major tectonomagmatic events 1 mafic magmatism and early crustal growth at 2 7 ga with the possible existence of older 3 0 ga crust s 2 collision related crustal thickening underplating of basaltic magma high grade metamorphism crustal anatexis and ttg magmatism at 2 5 ga 3 extensional deformation and emplacement of the mafic dikes and the nanying granitic plutons along the chengnanzhuang shear zone 2 5 to 2 0 ga 4 s type granitic magmatism and associated amphibolite facies metamorphism 2 0 to 1 80 ga and 5 emplacement of granitic pegmatite dikes at 1 80 ga

what controls sheet intrusion in volcanoes structure and petrology of the stromboli sheet complex italy abstract a multidisciplinary study has been conducted on 109 intrusive sheets of stromboli the relation between sheet injection conditions with the magmatic and structural variations of the volcano and the parameters governing the preferential intrusion geometry inside the volcano in a time perspective have been determined during its subaerial activity the last 100 ka stromboli experienced periods of extrusive growth and sheet intrusions alternated to caldera and lateral collapses of the nw sciara del fuoco flank the sheet intrusions similar to the extrusive rocks span a large compositional range from calc alkaline to potassic through high k calc alkaline and shoshonitic series the most evolved compositions of the effusive rocks however have not been found as intrusions whereas some mafic and basic magmas of sheets were never erupted the repeated time change of location of the intrusions from strombolicchio to the ne sw trend passing trough the inferred paleostromboli summit cone and the southern flank could represent the expression of the shift of the magma chamber towards the southeast and the subsequent onset of a clear ne sw elongated magma chamber located along the main stromboli weakness zone the stromboli evolution in the last 100 ka has been characterized by the persistent n 10 55 e intrusion direction which reflects the influence of the edifice s state of stress on the magma feeding paths after 13 ka ago sheets mainly intruded along to the sector collapse scarps in a circum amphitheatre geometry which has been demonstrated to be influenced by the new cone morphostructure and not by different magma rheological characters

estimates of stress directions by inversion of earthquake fault plane solutions in sicily summary the tectonic stress orientation is estimated in the lithosphere of northern sicily the southern tyrrhenian sea and southern calabria and in the wadati benioff zone below the tyrrhenian by inversion of fault plane solutions of earthquakes covering a magnitude range from 2 5 to 7 1 focal mechanisms of 97 earthquakes are taken from the literature after a critical evaluation of their data quality an average misfit of f 13 indicates that the set of all shallow 50 km earthquakes is generated by a heterogeneous stress field for three subsets based on regional and magnitude separation f was small enough 2 8 lfs5 9 to support the assumption of a homogeneous stress direction for an additional subset with f 7 4 such a condition is close to being fulfilled even though some heterogeneity appears to be present the number of earthquakes in these subsets ranged from nine to 22 and the uncertainties of the principal stress directions were generally of the order of 20 at the 90 per cent confidence level the earthquakes with a425 define a regional stress field with the greatest principal stress ul dipping at a shallow angle to the south in north eastern sicily and south western calabria the stress field estimated by earthquakes is extensional with o3 in a direction of wnw and a near vertical ol in agreement with the graben tectonics mapped geologically in this area in western sicily the c1 direction is oriented wnw but this result is judged less reliable than the others based on the broader confidence limits of the solution and the average misfit of 7 4 the earthquakes in the wadati benioff zone define ol dipping at about 70 to the nw subparallel to the zone with o2 horizontal and striking parallel to the zone

characterization of hyperalkaline fluids produced by low temperature serpentinization of mantle peridotites in the oman and ligurian ophiolites a regional survey of alkaline springs in oman and ligurian ophiolites shows that the alkaline water compositions significantly vary from one ophiolite to the other and within the same ophiolite the first order correlation between the na and k and cl concentrations points to fluid compositions only partly due to evaporation the scatter around the evaporation line implies that na and cl may not be conservative during the alteration of the ultramafic rocks mg is almost entirely depleted at ph 10 5 as a result of serpentine formation within the ultramafic body and of brucite and minor hydrotalcite precipitation at the springs ca accumulates in the high ph fluids and is consumed by ca carbonate formation at the springs by mixing with river waters or by the co2 supply from the atmosphere thermodynamic calculations show that brucite saturation is reached at ph values around 10 5 which triggers major changes in the water composition the waters evolve from a quartz saturated low ph continental environment to a brucite dominated high ph serpentinizing system at low temperature the highest water salinities are found in springs located along the basal thrust plane of the ophiolite the highest al concentrations are found in some springs located on the crustal side of the mantle crust boundary this poses the question of the hydrologic pathways and of the role of the mineralogical composition of the altered formations key points new temperature and composition of the alkaline waters brucite formation at ph 10 5 triggers major chemical and mineralogical changes relationship between the water compositions and the hydrologic pathways

aster mapping of limestone formations and study of caves springs and depressions in parts of sultanate of oman caves springs and large depressions of limestone karst formations are becoming more attractive tourist places and have potential importance on socio economic development the present study is a multi scale point of view on limestone karst from the space images to microscopic fabric here the karst features consist of limestone formations of cretaceous albian cenomanian age of tanuf valley and tertiary late paleocene middle eocene age of sur region of parts of sultanate of oman which are mapped in the visible near infrared and shortwave infrared spectral bands of advanced spaceborne thermal emission and reflection radiometer aster using decorrelated stretch image processing technique and the occurrences of caves springs and depressions of the formations in the field were studied the decorrelated rgb images of aster spectral bands 8 3 and 1 discriminated well the limestone formations and associated lithology the limestone formations of tanuf valley natih formations of hajar unit are thick bedded massive shallow marine limestone and clayey limestone which have caves and springs large depressions are studied as collapsed structures at the boundary between abat formations they consist of gray to white marly or micritic limestone with chert nodules and seeb formation of bioclastic limestone calcarenite marl and sandstone of sur region interpretations of limestone formations their occurrences and distributions of caves springs and depressions of these regions are verified and confirmed in the field and studied in the laboratory occurrences of more springs and depressions in the limestone formations of the study sites are interpreted and located on the google earth image the study proved the capability of aster sensor in mapping of limestone formations and recommends the technique to other geographical regions where similar geological questions need to be resolved

late neoarchean or late paleoproterozoic high pressure granulite facies metamorphism from the east hebei terrane north china craton abstract it is debated whether there are neoarchean high pressure hp granulites in the east hebei terrane north china craton three mafic granulite samples from the saheqiao belt are investigated here for their petrography p t evolution and zircon dating all the samples contain the typical hp granulite assemblages involving garnet clinopyroxene plagioclase and amphibole these assemblages commonly overprint on an early phase assemblage dominated by coarse grained clinopyroxene these hp granulites share clockwise p t paths with the peak conditions constrained to be 900 c 12 5 kbar and 880 c 12 8 kbar for two samples using the isopleths of the maximum ti content from amphibole and the minimum anorthite from plagioclase in p t psueudosections the post peak p t paths are inferred to be dominant of decompression with cooling based on the core rim zoning with increasing anorthite in plagioclase plagioclase coronas around garnet and decreasing ti from core to rim in amphibole zircon dating yields one metamorphic age of 2 48 ga for sample j1850 and two metamorphic ages of 2 47 and 1 81 ga for sample yc223 the older zircons show enriched hree patterns indicating no garnet involved whereas the younger zircons have flat hree patterns reflecting the presence of garnet moreover the older ages are consistent with the late neoarchean granulites that have anticlockwise p t paths and the younger ages correspond to the hp granulites from both metabasic dykes and supracrustal rocks constrained already thus the studied hp granulites are considered to be formed in the late paleoproterozoic related to a crust thickening orogenic event

high precision photogrammetry for monitoring the evolution of the nw flank of stromboli volcano during and after the 2002 2003 eruption high precision aerial photogrammetry has been used in addition to other geophysical techniques such as bathymetric surveys geodetic measurements microseismicity recording etc for monitoring slope deformations and the volcanic activity of stromboli island aeolian arc italy during the last effusive eruption which started on december 28 2002 and soon after the major landslide tsunami event of december 30 qualitative and quantitative description of topographic and morphological changes of the sciara del fuoco were possible thanks to a recent pre eruption photogrammetric survey performed in 2001 the comparisons of 12 multi temporal digital terrain models carried out during the period january june 2003 were used to evaluate the displaced mass by the landslide the lava accumulation and the erosion processes of the sciara del fuoco after the end of the eruption four additional photogrammetric surveys were performed between july 2003 and october 2005 to monitor the evolution of the slope and detect potential instability phenomena the slope appeared significantly modified and continued to evolve showing marked erosion both on the lower part and toward the craters terrace over the same period the new lava flows showed progressive contraction of the thicker part of the lava pile caused by its cooling and compaction and the possible sliding along the shear surface of the december 2002 deep seated movement the present morphology seems to be far from equilibrium and the deformation processes are still ongoing justifying a continuous monitoring activity to understand the evolution of these instability phenomena

development and recent activity of the san andres landslide on el hierro canary islands spain abstract extremely voluminous landslides with a long run out also known as megalandslides on oceanic volcanic islands are infrequent denudational processes on such islands at the same time they represent a major geological hazard that must be looked into to avoid negative consequences for the inhabitants of these islands their occurrence can be related to periods of intense seismo volcanic activity similar to that which occurred on el hierro island over 2011 2012 landslides on volcanic islands are studied using onshore and offshore geological geophysical and geomorphological records considering their unique triggering conditions e g lava intrusions eruptive vents magma chamber collapses previous work has pointed out similarities between specific cases of landslides on volcanic islands and deep seated gravitational slope deformations dsgsds which are typical in high mountain settings nevertheless the methodological approaches and concepts used to investigate dsgsds are not commonly applied on volcanic islands studies even though their use may provide new information about the development stage recent movements and future hazards therefore this approach for studying the san andres landslide sal on el hierro canary islands has been developed applying a detailed morphological field mapping an interpretation of digital elevation models structural measurements kinematic testing and a precise movement monitoring system the acquired information revealed a strong structural influence on the landslide morphology and the presence of sets of weakened planes acting as the sliding surfaces of the sal or secondary landslides within its body the presence of secondary landslides deep erosive gullies coastal cliffs and high on shore relative relief also suggests a high susceptibility to future landslide movement direct monitoring on the landslide scarps and the slip plane performed between february 2013 and july 2014 using an automated optical mechanical crack gauge with a precision of up to 10 2 mm detected creep movement in the order of 1 mm yr 1 with a persistent sinistral component as well as episodic horizontal and a subtle vertical movement this monitoring will continue in the future in order to verify the initial observations which instead of long term movement patterns could represent a landslide response to the period of an intense seismo volcanic activity during 2011 12

the transformation of amphibolite facies gneiss to charnockite in southern karnataka and northern tamil nadu india amphibolite facies metamorphic grade gives way southward to the granulite grade in southern karnataka as acid gneisses develop charnockite patches and streaks and basic enclaves develop pyroxenes petrologic investigations in the transitional zone south of mysore have established the following points 1 the transition is prograde amphibole bearing gneisses intimately associated with charnockite at kabbal and several similar localities are not retrogressive after charnockite as proved by patchy obliteration of their foliation by transgressive very coarse grained charnockite high fluorine content of biotite and amphibole in gneisses and high large ion lithophile element contents in gneisses and charnockites these features are in contrast to very low fluorine in retrogressive amphiboles and biotites very low large ion lithophile element contents and zonal bleaching of charnockite in clearly retrogressive areas as at bhavani sagar tamil nadu 2 metamorphic temperatures in the transitional areas were 700 800 c pressures were 5 7 kbar and h2o pressures were 0 1 0 3 times total pressures based on thermodynamic calculations using mineral analyses dense co2 rich fluid inclusions in the kabbal rocks confirm the low h2o pressures at the first appearance of orthopyroxene farther to the south in the nilgiri hills and adjacent granulite massif areas peak metamorphic temperatures were 800 900 c pressures were 7 9 kbar and water pressures were very low so that primary biotites and amphiboles those with high f contents are rare 3 the incipient granulite grade metamorphism of the transitional areas was introduced by a wave of anatexis and k metasomatism this process was arrested by drying out under heavy co2 influx charnockites so formed are hybrids of anatectic granite and metabasite of metabasite and immediately adjacent gneiss or are virtually isochemical with pre existing gneiss despite gross recrystallization to granulite mineralogy these features show that partial melting and metasomatism are attendant rather than causative in charnockite development copious co2 from a deep crustal or mantle source pushed ahead of it a wave of more aqueous solutions which promoted anatexis granulite metamorphism of both neosome and paleosome followed the process is very similar to that deduced for the madras granulites by weaver 1980 the massif charnockites for the most part extremely depleted in lithophile minor elements show many evidences of having gone through the same process

zircon u pb geochronology and hf isotopes of major lithologies from the jiaodong terrane implications for the crustal evolution of the eastern block of the north china craton abstract as an important component of the western shandong complex in the eastern block of the north china craton the yishui terrane consists of neoarchean high grade supracrustal rocks granitoid gneisses and charnockites la icp ms zircon u pb dating and hf isotopic analyses on these lithologies have been carried out and the results provide new insights into the neoarchean crustal evolution of the eastern block of the north china craton new zircon dating results reveal that the magmatic precursors of the supracrustal metapelites and granitoid gneisses were generated at 2 54 2 53 ga and 2 57 2 55 ga respectively and the charnockites were emplaced contemporaneously around 2 56 2 53 ga single metamorphic zircon grains and overgrowth rims from these rocks document consistent metamorphic ages at 2 50 ga suggesting that the yishui terrane experienced a high grade metamorphic event at the end of the neoarchean detrital zircons from pelitic gneisses yield 207pb 206pb ages of 2 89 2 65 ga with a major age peak at 2 53 ga and a subordinate age peak at 2 70 ga implying that the sedimentary protoliths of the pelitic gneisses may have been sourced from 2 53 ga rocks in the yishui terrane and 2 70 ga rocks in the adjacent luxi granite greenstone terrane hf isotopic compositions show that the neoarchean magmatic zircons have positive ehf t values ranging from 1 4 to 7 8 and depleted mantle model ages of 2 92 2 60 ga with a prominent peak at 2 8 2 7 ga suggesting that the neoarchean crust was derived mainly from juvenile sources and partly from the recycling of old continental crust in the yishui area combined with previous data from the adjacent luxi granite greenstone terrane and other complexes in the eastern block it is concluded that the neoarchean was an important period of crust accretion in the eastern block of the north china craton

petrogenesis of taxitic dioritic tonalitic gneisses and neoarchean crustal growth in eastern hebei north china craton abstract the taxitic dioritic tonalitic gneisses in the zunhua qinglong microblock of eastern hebei north china craton are composed of dioritic quartz dioritic tonalitic and trondhjemitic gneisses they show taxitic or banded structures and were subjected to amphibolite to local granulite facies metamorphism based on their whole rock geochemistry the dioritic and quartz dioritic gneisses dq group can be classified into a high ni subgroup hndq subgroup and a low ni subgroup lndq subgroup and the tonalitic and trondhjemitic gneisses tt group into a low fractionated subgroup lftt subgroup and a high fractionated subgroup hftt subgroup la icp ms zircon u pb isotopic dating reveals that the magmatic precursors of the hndq lndq and lftt subgroups were emplaced from 2522 13 to 2533 14 ma whereas those of the hftt subgroup emplaced at 2499 4 ma studies in petrogenesis revealed that the magmatic precursors of the hndq subgroup were derived from partial melting of mantle peridotites metasomatized chiefly by slab melts while those of the lftt subgroup were formed by fractional crystallization of the magmas of the hndq subgroup with clinopyroxene magnetite plagioclase and apatite as the major fractionated phases magmatic precursors of the lndq subgroup were derived from partial melting of mantle peridotites metasomatized in a dominant manner by slab derived fluids with melts experiencing fractionation of hornblende magnetite plagioclase and apatite during the magmatic evolution further magmatic precursors of the hftt subgroup were derived from partial melting of volcanic sedimentary rocks formed in the fore arc to trench belt which were subducted along with oceanic slabs with the melts contaminated by mantle peridotites during their ascent through the mantle wedge these new data combined with previous investigations on metavolcanic rocks and granitoid orthogneisses suggest that the magmatic precursors of these taxitic dioritic tonalitic gneisses were formed in an arc to back arc tectonic setting from north to south furthermore lu hf isotopic data from the late neoarchean metavolcanic rocks and granitoid gneisses in the zunhua qinglong microblock reveal that the zunhua qinglong microblock experienced three major periods of juvenile crustal growth during neoarchean at 2 72 2 70 ga 2 64 2 56 ga and 2 53 2 50 ga respectively with the latter two periods coupled with reworking of old crustal materials

subaerial submarine evidence of structures feeding magma to stromboli volcano italy and relations with edifice flank failure and creep abstract structural field data including parameters of 109 sheets strike mostly n10 55 e average dip angle mostly 70 90 average thickness two peaks at 1 2 m and 4 2 m and of 14 eruptive fissures and vents as well as bathymetric and numerical data suggest that stromboli experienced the development of a volcanic rift zone across the cone summit with a tendency to widen towards the lower submarine flanks during the last 100 ka inside this rift zone intrusive sheets mostly strike ne and become more abundant more steeply dipping and thicker on approaching the rift axis this rift persistence reflects the edifice s state of stress with a nw se horizontal least principal stress on the magma intrusion paths after 13 ka ago sheets mainly intruded with a horseshoe shaped geometry in plan view along the boundaries of the northwestern unstable volcano flank where four main lateral collapses occurred during the last 13 ka they also intruded with a ne strike across the volcano summit and the northeastern volcano flank the horseshoe shaped geometry is influenced by the lateral creep of the volcano flank which provides space for intrusion along the transtensional boundaries of the unstable sector where thinner sheets were emplaced when the collapse depression was filled up by new deposits ne striking thicker dykes emplaced across the northwestern volcano flank indicating a rapid re establishment of regional tectonic forces across the cone unbuttressing due to the present sciara del fuoco depression and ongoing flank creeping can account for intrusions also inside the sciara del fuoco the latter in 2007

deformation of stromboli volcano italy during the 2007 eruption revealed by radar interferometry numerical modelling and structural geological field data abstract the activity of stromboli volcano is characterized by very low energy explosions occurring every 10 15 min throwing out lava above the crater rim during 2007 the volcano showed an anomalous activity in which new effusive vents developed 27 february and 9 march and a major explosion took place on 15 march this paper presents an integrated study based on a structural geological field survey interferometric radar monitoring and numerical modelling on the deformations of the upper nw flank of the volcano sciara del fuoco sdf the field survey carried out during the 2007 events shows the development of mainly ne striking fissures and fractures on the northern part of the upper sdf in january 2007 the ground based synthetic aperture radar gb insar installed on the flank of the sdf showed a progressive acceleration of movement on the ne crater preceding the eruption of 27 february 2007 by the first half of february the acceleration also involved the upper portion of the sdf and on 27 february the eruption started with the opening of new vents and deformation rates higher than the measurement capability of the radar device on 8 9 march 2007 the gb insar highlighted the formation of a bulge on the nw sector of the sdf preceding the opening of an additional vent to understand the deformation pattern recorded during the eruption a numerical simulation was carried out by using the flac 3d code based on the integration of all the data the deformations observed in the pre effusive phase before 27 february seem to be related to the intrusion of a sw ne striking dyke the bulging recorded before the 9 march vent opening is instead to be associated with the intrusion of a sub horizontal sill

geological evidence for recurrent collapse driven phreatomagmatic pyroclastic density currents in the holocene activity of stromboli volcano italy abstract we present a multidisciplinary geological study of lithified to unconsolidated ash rich lapilli tuff deposits bearing accretionary lapilli that crop out in scattered sites along the lower slopes of the stromboli volcano southern italy these deposits are related to three pyroclastic successions called semaforo nuovo secche di lazzaro and semaforo labronzo with distinctive lithologic and volcanologic features and different stratigraphic position within the neostromboli volcano stratigraphy holocene their juvenile clasts have slightly different major and trace element compositions whole rock and glass isotopic ratios and mineralogical characteristics although they are all within the most evolved high k shoshonites typical of neostromboli the three successions are independently recognized in distinct sectors of the volcano displaying an asymmetric areal distribution that is interpreted as the result of directed pyroclastic density currents and minor fallout generated from summit eruptive vents lithological characteristics and morphoscopic features of ash particles indicate phreatomagmatic fragmentation combined with mechanisms of volatile exsolution or decompression which is atypical with respect to the dominant strombolian effusive eruptive behaviour of stromboli during the holocene we suggest that the three phreatomagmatic eruptions are linked to different major lateral collapses associated to flank fissure eruptions that occurred along the nw dipping sciara del fuoco collapsed flank it is argued that the collapses have unloaded the magmatic and hydrothermal system enabling magma water interaction and explosive decompression of a shallow magma reservoir the recurrent collapse eruption link with generation of directed pdcs able to reach the lower slopes of the volcano highlights a previously underestimated source of volcanic hazard at stromboli

the evolution of volcanic systems following sector collapse abstract sector collapses affect volcanic edifices across all tectonic settings and involve a rapid redistribution of mass comparable in scale to the largest magmatic eruptions the eruptive behaviour of a volcano following sector collapse provides a test of theoretical relationships between surface loading and magma storage which imply that collapse driven unloading may lead to changes in eruption rate and erupted magma compositions large sector collapses are infrequent events globally with all historical examples being relatively small in comparison to many of the events documented in the geological record as a result exploration of the impacts of sector collapse on eruptive behaviour requires detailed investigation of prehistoric collapses but this is often hindered by poorly resolved stratigraphic relationships and dating uncertainties nevertheless observations from a number of volcanoes indicate sharp changes in activity following sector collapse here a global synthesis of studies from individual volcanoes in both arc and intraplate settings is used to demonstrate a number of common processes in post collapse volcanism multiple examples from large 5 km3 sector collapses in arc settings show that collapse may be followed by compositionally anomalous large volume and often effusive eruptions interpreted to originate via disruption of a previously stable upper crustal reservoir these anomalous eruptions highlight that magma compositions erupted during periods of typical i e unperturbed by sector collapse volcanism may not be representative of the range of compositions stored within a vertically extensive crustal reservoir if eruptible magma is not present upper crustal reservoirs may rapidly solidify following collapse without further eruption allowing more mafic compositions to ascend to the surface with only limited upper crustal modification resulting in edifice regrowth at temporarily elevated eruption rates subsequent re establishment of an upper crustal reservoir further supports a relationship between surface loading and crustal storage but long term chemical and mineralogical differences between pre and post collapse evolved magmas imply that a newly developed reservoir can overprint the influence of a preceding reservoir forming a spatially and compositionally distinct plumbing system these broad patterns are replicated in intraplate settings despite differences in scale and melting processes current evidence suggests that post collapse evolution of intraplate volcanoes can be explained by unloading induced destabilisation of the magma plumbing system rather than increased melt production what emerges from an apparently diverse set of observations is a systematic behaviour that strongly supports a coupling between edifice growth and magma ascent storage and pressurisation eruption rates erupted compositions and the style of volcanism at any particular system may thus be modulated from the surface and long term shifts in surface behaviour may occur without any changes in the deep parts of magmatic systems observations of sharp post collapse changes in erupted compositions including the ascent of primitive mafic magmas also require a crystal dominated mid to upper crustal reservoir consistent with recent models of crustal magmatic systems

deformation at stromboli volcano italy revealed by rock mechanics and structural geology abstract we approach the reconstruction of the recent structural evolution of stromboli volcano italy and the analysis of the interplay between tectonics gravity and volcanic deformation by tying together structural lithostratigraphic and rock mechanics data we establish that since 100 ka bp the edifice has faulted and jointed mainly along ne striking planes faults mostly dip to the nw with normal displacement taking also into account the presence of a nw trending regional least principal stress and of tectonic earthquake hypocenters inside the cone we suggest that this fracturing can be related to the transmission of tectonic forces from the basement to the cone dyking concentrated along a main ne trending weakness zone nez across the volcano summit resembling a volcanic rift whose geometry is governed by the tectonic field in the past 13 ka stromboli experienced a reorganisation of the strain field which was linked with the development of four sector collapses affecting the nw flank alternating with growth phases the tectonic strain field interplayed with dyking and fracturing related to unbuttressing along the collapse shoulders we propose that tectonics control the geometry of dykes inside the cone and that these in turn contribute to destabilise the cone flanks

signature of coseismic decarbonation in dolomitic fault rocks of the naukluft thrust namibia unequivocal geological signatures of seismic slip are rare exceptionally so in carbonate hosted faults where carbonate minerals dissociate at temperatures lower than those required for producing a friction melt this thermal dissociation leads to significant fault weakening by increased fluid pressure and or nanoparticle lubrication preventing further heating of the fault surface pseudotachylyte is therefore unlikely to form in carbonate hosted faults and other evidence for seismic slip must be identified we studied the lower cambrian naukluft thrust which crops out in central namibia it contains a cataclastic dolomite fault rock referred to as gritty dolomite which we interpret as a signature of coseismic carbonate dissociation and subsequent fluid rock interactions the fault was active at ambient temperatures below 2001c gritty dolomite contains rounded low aspect ratio dolomite clasts with a uniform fe rich dolomite coating euhedral to subhedral magnetite quartz and k feldspar in a fine grained massive to laminated carbonate matrix of particulate dolomite and crystalline calcite cement the fault rock texture combined with evidence of injectites of gritty dolomite into the wallrock indicates the cataclasite deformed as a fluidized granular flow at seismic slip velocities frictional heating caused dissociation of dolomite to co 2 and ca fe and mg oxides this release of co2 decreased the ph of the pore fluid in the fault causing dissolution and rounding of dolomite clasts within an inertial grain flow and precipitation of carbonate coatings and euhedral silicates and oxides during subsequent cooling and co2 escape examples of similar rocks having some if not all of these characteristics have been described from other carbonate hosted faults the geological setting of the naukluft thrust is unique in spatial extent and quality of exposure allowing us to eliminate alternative hypotheses for sources of co2 to drive fluidization

formation age and tectonic setting of the shirengou neoarchean banded iron deposit in eastern hebei province constraints from geochemistry and sims zircon u pb dating abstract the shirengou iron deposit a typical bif deposit located in eastern hebei province in the north china craton is hosted in neoarchean metamorphic rocks the metamorphic rocks include hornblende plagiogneiss plagioclase amphibolite and magnetite quartzite we use contents and ratios of major elements for protolith reconstruction showing that protoliths of the hornblende plagiogneiss and plagioclase amphibolite should be dacite and basaltic andesite respectively based on geology and geochemistry of the hosting rocks we infer that the shirengou bif is an algoma type deposit formed in an arc related basin in the neoarchean constrains from sims u pb dating and oxygen isotopic analysis of zircon from wall rocks and interlayer of the shirengou iron bodies can be summarized as follow 1 igneous zircons from two samples of amphibolite and gneiss yield u pb ages of 2541 21 ma and 2553 31 ma respectively providing the age of the neoarchean protolith because the shirengou bif is an algoma type deposit determined u pb age 2541 2553 ma for zircons from hosting volcanic rocks can constrain the bif forming time 2 metamorphic overgrowth zircons from amphibolite and gneiss give two u pb ages of 2512 13 ma and 2510 21 ma respectively corresponding to the neoarchean matemorphism 3 the zircons with 18o values of 5 9 7 6 also indicate magmatic origin the zircons have 18o values of 6 8 9 9 suggesting that exotic high 18o fluids were involved during metamorphism based on the geology and geochemistry of bif and combing with zircon age and oxygen isotopic systematics we suggest that the shirengou iron deposit was formed in a submarine volcanic setting related to subduction of an oceanic slab

ultrahigh temperature mafic granulite in the huai an complex north china craton evidence from phase equilibria modelling and amphibole thermometers abstract the huai an complex in the north western trans north china orogen north china craton is recognized to have undergone high pressure metamorphism with controversial ages two mafic granulite samples 17ht13 and 16ht22 from huangtuyao of the huai an complex are documented for metamorphism based on petrography mineral chemistry phase equilibria modelling and zircon dating the rocks comprise garnet clinopyroxene orthopyroxene amphibole plagioclase and ilmenite they show clockwise p t paths involving the pre tmax decompressional heating the tmax and the post tmax cooling stages the pre tmax decompressional heating is revealed by the core rim mantle anorthite ascending zoning in coarse grained plagioclase the tmax stage is constrained to 8 5 10 5 kbar 980 1010 c 17ht13 and 7 5 9 5 kbar 1000 1030 c 16ht22 by the high ti content of amphibole and the anorthite content of coarse grained plagioclase rims mantles and fine grained plagioclase cores these temperatures are slightly higher than the results of amphibole thermometers 940 980 c the post tmax cooling is defined by the later growth of amphibole and some conventional geothermobarometers because it is dominated by temperature with ilmenite present the ti content of amphibole is proposed as a reliable thermometer and the ti rich amphibole with ti 0 28 p f u or tio2 2 4 2 6 wt is indicative of ultrahigh temperature 900 c uht conditions the anorthite content of plagioclase is also significant in confining peak temperatures for uht granulite but requires defining proper water content zircon dating for 17ht13 yields an upper intercept age of 1910 35 ma representing the cooling of uht granulite we conclude that the huai an complex may have at least locally undergone uht metamorphism at 1 92 1 91 ga after high pressure granulite metamorphism at 1 95 ga similar to the jining complex therefore the huai an and jining complexes share the same tectonic evolution involving 1 95 ga crustal thickening 1 92 1 91 ga extension with regional or local uht metamorphism and subsequent cooling and uplifting

the structure of composite volcanoes unravelled by analogue modelling a review abstract volcanic edifices are unstable accumulations of eruptive and intrusive products with complex internal structures a documentation of these structures facilitates the assessing of the various hazards associated with volcanoes e g flanks instabilities and eruptive events however structures are not easily assessed in the field as volcanoes are regularly covered by eruptive products and are rapidly eroded in the case of recent and active volcanoes internal structures are generally extrapolated from the external morphology of the edifice which can be documented using digital elevation models dem and geodetic data interpretation of such data greatly benefits from analogue models which are idealised representations of reality used to test the impact that various processes may have on the shape of a volcanic edifice this short review focuses on the contribution of analogue models to our comprehension of the internal structure of composite volcanic cones the other volcanic morphologies e g caldera are excluded from this review as they have distinct structure and evolution that have already been thoroughly reviewed the reviewed models were used to investigate the impact that regional faults magma injections and ductile substratum among other processes have on the internal structure and surface morphology of many volcanic edifices these models were also used to locate unstable flanks and eruption sites

imaging spectroscopy earth and planetary remote sensing with the usgs tetracorder and expert systems 1 imaging spectroscopy is a tool that can be used to spectrally identify and spatially map materials based on their specific chemical bonds spectroscopic analysis requires significantly more sophistication than has been employed in conventional broadband remote sensing analysis we describe a new system that is effective at material identification and mapping a set of algorithms within an expert system decision making framework that we call tetracorder the expertise in the system has been derived from scientific knowledge of spectral identification the expert system rules are implemented in a decision tree where multiple algorithms are applied to spectral analysis additional expert rules and algorithms can be applied based on initial results and more decisions are made until spectral analysis is complete because certain spectral features are indicative of specific chemical bonds in materials the system can accurately identify and map those materials in this paper we describe the framework of the decision making process used for spectral identification describe specific spectral feature analysis algorithms and give examples of what analyses and types of maps are possible with imaging spectroscopy data we also present the expert system rules that describe which diagnostic spectral features are used in the decision making process for a set of spectra of minerals and other common materials we demonstrate the applications of tetracorder to identify and map surface minerals to detect sources of acid rock drainage and to map vegetation species ice melting snow water and water pollution all with one set of expert system rules mineral mapping can aid in geologic mapping and fault detection and can provide a better understanding of weathering mineralization hydrothermal alteration and other geologic processes environmental site assessment such as mapping source areas of acid mine drainage has resulted in the acceleration of site cleanup saving millions of dollars and years in cleanup time imaging spectroscopy data and tetracorder analysis can be used to study both terrestrial and planetary science problems imaging spectroscopy can be used to probe planetary systems including their atmospheres oceans and land surfaces

hornblende dehydration melting in mafic rocks and the link between massif type charnockite and associated granulites eastern ghats granulite belt india a massif type intrusive charnockite body in the eastern ghats granulite belt india is associated with hornblende bearing mafic granulite two pyroxene granulite and enderbitic granulite the charnockite is characterised by pervasive gneissic foliation s1 this is axial planar to the folded layers of hornblende bearing mafic granulite f1 folds indicating that the granulite protoliths were present before the development of s1 two pyroxene granulite and enderbitic granulite occur as lenticular patches disposed along the foliation and hence could be syngenetic to s1 the tonalitic to granodioritic metaluminous to weakly peraluminous compositions and relatively high sr rb of the charnockite are consistent with its derivation by partial melting of a mafic protolith strong y depletion lack of sr depletion and strongly fractionated ree patterns with high la yb n ratio but relatively lower hree gd lu fractionation with marked positive eu anomalies suggest major residual hornblende as well as garnet but not plagioclase consistent with the hornblende dehydration melting in the source rocks such a residual mineralogy is broadly similar to those of some of the hornblende bearing mafic granulite inclusions which have compositional features indicative of a restitic nature quantitative modelling supports an origin for the charnockite melts by partial melting of a hornblende rich mafic granulite source although source heterogeneity is very likely given the rather variable trace element contents of the charnockite the whole rock and mineral compositions of the two pyroxene granulites and enderbitic granulites are consistent with them representing peritectic phase segregations of hornblende dehydration melting a clockwise p t path implies that melting could have occurred in thickened continental crust undergoing decompression

geochemistry zircon u pb geochronology and lu hf isotopes of metavolcanics from eastern hebei reveal neoarchean subduction tectonics in the north china craton abstract the neoarchean metavolcanic rocks of saheqiao occur within the central domain of the precambrian terrane in eastern hebei within the north china craton these rocks consist mainly of garnet two pyroxene granulites garnet clinopyroxene amphibolites amphibole plagioclase gneisses and biotite plagioclase gneisses these metavolcanic rocks are exposed as several kilometers scale of massive blocks or several tens of centimeters scale of enclaves within precambrian granitoid gneisses based on whole rock geochemistry we classify these intermediate mafic volcanic rocks into four groups group 1 exhibits low sio2 yb and nb ta ratios and high ni and cr and shows n morb like normal mid ocean ridge basalts geochemical features suggesting that the magmatic precursors of these rocks were derived through partial melting of depleted mantle compared to group 1 group 2 shows slightly right declined ree and nearly flat multi element patterns with variable negative nb anomalies matching with primitive arc basaltic rocks formed by partial melting of the mantle wedge group 3 exhibits chemical compositions of basaltic and andesitic rocks and is characterized by pronounced lree enrichment but hree depletion and shows distinctly negative nb and ta anomalies and weakly negative zr and hf anomalies these rocks may compare with island arc volcanic rocks and were probably generated by partial melting of the mantle wedge modified by dehydration of subducted oceanic slab the magmatic precursors of the andesites were derived from the crystallization differentiation of the basaltic magma group 4 is characterized by clearly right declined ree patterns and slightly positive or no nb ti anomalies which are analogous to nb enriched basalts neb and originated from melting of hfse enriched mantle sources la icp ms u pb dating of magmatic zircons from five samples from the three groups reveals that group 1 n morb like rocks formed at 2525 7 ma group 2 primitive arc basaltic rocks at 2518 15 ma and group 3 typical arc volcanic rocks at 2523 6 ma to 2614 18 ma zircons from all the dated samples also preserve signatures of 2450 2370 ma metamorphisms or thermal events the zircon lu hf data from the three dated samples in group 3 show ehf t values ranging from 1 4 to 9 0 and tdm values of 2627 ma to 2965 ma suggesting a significant episode of 2 6 2 9 ga crustal growth in this region the 2525 ma n morb like basaltic rocks are younger than the arc related rocks 2614 2518 ma suggesting that the morb like basaltic rocks were generated in a back arc environment on the basis of the rock association of back arc morb basalts group 1 arc related andesites basalts groups 2 and 3 and neb like rocks group 4 we suggest that the neoarchean volcanic rocks of the eastern hebei region formed in a subduction related setting within a convergent plate margin

relationships of soil grass and bedrock over the kaweah serpentinite melange through spectral mixture analysis of aviris data abstract a linear mixing model is used to model the spectral variability of an airborne visible infrared imaging spectrometer aviris scene from the western foothills of the sierra nevada and calibrate these radiance data to reflectance five spectral endmembers from the aviris data plus an ideal shade endmember were required to model the continuum reflectance of each pixel in the image three of the endmembers were interpreted to model the surface constituents green vegetation dry grass and illumination these are the main transient surface constituents that are expected to change with shifts in land use or climatic influences and viewing conditions shade only the spectral distinction between the other three endmembers is very small yet the spatial distributions are coherent and interpretable these distributions cross anthropogenic and vegetation boundaries and are best interpreted as different soil types comparison of the fraction images to the bedrock geology maps indicates that substrate composition must be a factor contributing to the spectral properties of these endmembers detailed examination of the reflectance spectra of the three soil endmembers reveals that differences in the amount of ferric and ferrous iron and or organic constituents in the soils is largely responsible for the differences in spectral properties of these endmembers

neoarchean subduction a case study of arc volcanic rocks in qinglong zhuzhangzi area of the eastern hebei province north china craton abstract we report on volcanic rocks of the qinglong zhuzhangzi area in northeastern eastern hebei province north china craton the supracrustal rock associations in the study area consist of amphibole biotite plagioclase gneiss mica plagioclase gneiss schist biotite k feldspar gneiss pyroxene plagioclase amphibolite and amphibolite twenty five new mafic intermediate to felsic samples can be geochemically classified into four groups group 1 is similar to fore arc low ti tholeiite and is characterized by low sio 2 49 7 wt and tio 2 0 43 wt slightly depleted lree and mree pattern with la yb n ratio of 0 74 gd yb n ratio of 0 82 it most likely derived from depleted mantle in a subduction initiation environment group 2 is akin to primitive arc tholeiites with low sio 2 49 7 51 8 wt slight enrichments of lree la sm n 1 06 1 53 and negative nb anomalies nb la pm 0 50 0 76 group 3 resembles evolved arc tholeiites and displays pronounced enrichments of lree la yb n of 2 38 11 3 la sm n of 1 70 2 86 and negative nb ta anomalies nb la pm 0 14 0 34 except sample 11jd28 4 with that ratio of 1 00 group 2 and 3 formed by partial melting of sub arc depleted mantle wedge modified by differing quantities of slab flux addition group 4 comprises k rich andesite dacites which are distinguished by the highest sio 2 54 0 71 8 wt k contents up to 5 03 wt strong enrichments of lree la yb n ratios of 4 83 19 and negative nb ta anomalies analogous to shoshonitic rocks marking late stage of subduction la icpms zircon u pb and lu hf analyses of evolved arc basalts and k rich andesite dacites display crystallization ages of 2511 2604 ma and single stage hf model ages of 2534 2927 ma most focus on 2650 2800 ma in contrast to 2510 2560 ma arc associations 2604 ma shoshonitic dacites most plausibly represent an older orogenic event collectively supracrustal rocks in the qinglong zhuzhangzi area constitute a series of volcanic arc associations that correspond to an entire subduction cycle ranging from orogen to primitive arc evolved arc and back to an orogenic setting which further demonstrate that by the late archean plate tectonic and subduction processes already closely resembled modern counterparts

new insights into the origin of kabbaldurga charnockites karnataka south india abstract a detailed study of the structure and petrology of the rocks bordering the kabbaldurga type charnockites provides important constraints on the origin of these charnockites the structural elements register three phases of deformation and show a uniform pattern in the larger area a pattern consistent with the regional structure of the precambrian of southern karnataka in the kabbaldurga area however some of the earlier structures are poorly preserved yet there are vestiges of early folds described by banded layered charnockites as in the neighbouring kodamballi area and a consistent development of dilatant structures which can be related to the kinematics of deformation in the larger terrain at kabbaldurga the pegmatitic charnockites occur as veins of diverse orientation but they rarely follow the shear generated structures the metamorphic reactions invoked by previous workers to explain in situ transformation of gneiss to charnockite were based on chemical similarity of some close pairs but the petrographic and chemical variations in the pegmatitic charnockites and the peninsular gneisses at kabbaldurga quarry are compelling features which cannot be explained by the hypothesis of in situ transformation we have argued on the basis of rock and mineral chemistry that derivation of the pegmatitic charnockites by dehydration melting in metabasites offers a better explanation pressure temperature values at least 850 to 900 c 7 kbar obtained by us for the granulites of this area viewed against the results of experimental dehydration melting in basic rocks with hornblende and or biotite provide strong support for this model in the field leucosomes within the basic granulites of kabbaldurga are not uncommon the compositions of the pegmatitic charnockites tonalitic and granitic match those of the melts produced in experiments further the pattern of variation in the composition of hornblende and plagioclase in the basic granulites of the kabbaldurga area is compatible with extraction of melts this alternative model for the origin of the kabbaldurga charnockites is petrologically feasible and does not require either in situ transformation or structurally controlled growth which incidentally are not ubiquitous at kabbaldurga

role of large flank collapse events on magma evolution of volcanoes insights from the lesser antilles arc flank collapse events are now recognized as common processes of destruction of volcanoes they may occur several times on a volcanic edifice pulling out varying volumes of material from km3 to thousands of km3 in the lesser antilles arc a large number of flank collapse events were identified here we show that some of the largest events are correlated to significant variations in erupted magma compositions and eruptive styles on montagne pelee martinique magma production rate has been sustained during several thousand years following a 32 ka old flank collapse event basic and dense magmas were emitted through open vent eruptions that generated abundant scoria flows while significantly more acidic magmas were produced before the flank collapse the rapid building of a new cone increased the load on magma bodies at depth and the density threshold magma production rate decreased and composition of the erupted products changed to more acidic compared to the preceding period of activity these low density magma generated plinian and dome forming eruptions up to the present in contrast at soufriere volcanic centre of st lucia and at pitons du carbet in martinique the flank collapses have an opposite effect in both cases the acidic magmas erupted immediately after the flank collapses these magmas are highly porphyritic up to 60 phenocrysts and much more viscous than the magmas erupted before the flank collapses they have been generally emplaced as voluminous and uptight lava domes called the pitons such magmas could not ascent without a significant decrease of the threshold effect produced by the volcanic edifice loading before the flank collapse

volcanic structure and composition of old shiveluch volcano kamchatka this paper reports results of a new comprehensive geological mapping of the late pleistocene old shiveluch volcano the mapping results and geochemical data on major and trace element composition of the volcanic rocks are used to characterize spatial distribution eruptive sequence and volumetric relationships between different rock types of the volcano old shiveluch volcano had been constructed during two main stages initial explosive and subsequent effusive ones pyroclastic deposits of the initial stage are represented by agglomerate and psephytic tuffs with very few lava flows and form at least 60 of volume of the old shiveluch edifice the deposits of the second stage are dominantly lava flows erupted from four vents central western baidarny and southern reconstructed from the field relationships of their lava flows about 75 of the old shiveluch edifice both pyroclastic deposits and lava are composed of magnesian andesites sio2 57 3 63 8 wt mg 0 53 0 57 the most abundant andesitic lavas were coevally erupted from the central and western vents in the central part of the edifice less voluminous high al basaltic andesites sio2 53 5 55 7 wt mg 0 52 0 56 were produced by the western baidarny and southern vents situated in the south western sector small volume high mg basaltic andesites sio2 53 9 55 0 wt mg 0 59 0 64 occur in the upper part of the pyroclastic deposits andesites of old and young shiveluch volcanoes have similar compositions whereas old shiveluch basaltic andesites are compositionally distinctive from those of the young shiveluch by having lower mg sio2 cr and ni and higher al2o3 feot cao tio2 and v contents at given mgo geochemical modeling suggests that the compositions of the intermediate old shiveluch magmas can be reasonably explained by simple fractional crystallization of olivine clinopyroxene plagioclase and magnetite hornblende from water bearing 3 wt h2o high mg basaltic parental magma at intermediate to shallow crustal depths 60 wt mg 0 65 played a relatively minor role in creating the compositional diversity of the old shiveluch magmas compared to the young shiveluch ones the pronounced change in the shiveluch magma compositions could have been related to adjustments of the magma plumbing system beneath old shiveluch following the large scale sector collapse in the late pleistocene that enabled a common mixing of evolved and primitive magmas on the later holocene stage of the volcano evolution

on the fidelity of shell derived δ18oseawater estimates article i nfo 18 oseawater a robustproxyforsurfacesalinity we assessthe fidelity of shell derived 18 oseawater estimates for the surface dwelling foraminifer globigerinoides ruber white using an atlantic meridional coretop transect spanning basin scale temperature and salinity gradients shell derived and observed 18 oseawater values are well correlated r 2 0 77 but a large systematic bias is observed shell mg ca ratios are significantly elevated above values expected from observed and isotopic calcification temperatures in the saline subtropical gyres of both hemispheres this temperature independent shell mg ca ratio variability termed excess mg ca i s highly correlated with surface salinity r 2 0 77 and the observed salinity dependence 27 4 is much higher than indicated by culture studies 6 2 our coretop data are used to develop new atlantic basin temperature and salinity calibration equations that are accurate 1 1 c and 0 20 respectively precise r 2 0 82 and 0 81 respectively and verifiable using previously published data these results are valid for the relatively high salinities of the subtropical atlantic 35 5 37 3 we discover that inclusion of other published data from lower salinity regions b35 indicates little or no excess mg ca taken together these results point to a strongly non linear positive salinity effect on shell mg ca ratios that significantly affects the accuracy of sst and 18

zircon u pb hf isotopes and geochemistry of neoarchean dioritic trondhjemitic gneisses eastern hebei north china craton constraints on petrogenesis and tectonic implications abstract dioritic trondhjemitic gneisses of neoarchean age are widely distributed throughout the gualanyu shangying area in eastern hebei north china craton these orthogneisses consist of dioritic trondhjemitic and quartz rich trondhjemitic gneisses which were subjected to amphibolite to granulite facies metamorphism la icp ms zircon u pb isotopic dating reveals that the magmatic precursors of these rocks were contemporaneously emplaced from 2535 23 to 2513 8 ma reflecting an important neoarchean dioritic trondhjemitic magmatic event followed by sequential proterozoic tectonothermal events between 2472 60 and 2307 50 ma dioritic and trondhjemitic gneisses exhibit similar zircon hf t values of 1 5 to 5 2 and 2 9 to 5 3 respectively indicating their depleted mantle affinity geochemical analysis reveals that the dioritic gneisses have low sio2 contents 55 4 63 0 various mgo contents 2 07 4 78 and mg 36 07 63 56 and high la yb n ratios 5 45 15 19 in contrast the trondhjemitic gneisses exhibit higher sio2 contents 67 4 73 8 and la yb n ratios 12 86 76 73 and lower mgo contents 0 66 2 67 although their mg 36 29 61 41 are similar to those of dioritic gneisses these geochemical and zircon lu hf isotopic features together with geochemical modeling suggest that the dioritic magmas were derived mainly from the partial melting of a depleted mantle wedge that was metasomatized by slab derived melts or fluids and that the trondhjemitic magmas were formed by fractional crystallization of the dioritic magmas quartz rich trondhjemitic gneisses exhibit extremely high sio2 contents 77 4 84 6 with zircon hf t values ranging from 3 4 to 4 1 suggesting that their precursors formed after the partial melting of a mixed magmatic source it is suggested that the precursors comprised a mafic member derived from a mantle wedge altered by oceanic slab melts or fluids and a felsic member derived from the partial melting of ancient crustal material these new data combined with previous studies of contemporaneous metavolcanic rocks in gualanyu shangying area and surrounding areas suggest that the magmatic precursors of these neoarchean dioritic trondhjemitic gneisses formed in a subduction related tectonic environment at an e w strike convergent plate margin furthermore the eastern block of the north china craton had a major lateral accretion of crustal growth in the north margin in the neoarchean whereas vertical crustal growth and recycling under plume tectonic backgrounds occurred in the interior of the eastern block

mapping of neoproterozoic source rocks of the huqf supergroup in the sultanate of oman using remote sensing abstract in recent years the neoproterozoic huqf supergroup formations of the oman salt basins have been the target for oil exploration the present study maps the surficial exposure of the huqf supergroup in and around khufai dome of the huqf area in the sultanate of oman using low cost multi spectral remotely sensed satellite data and image processing methods such as decorrelation stretching principal component analysis pca and spectral angle mapper sam as alternative to expensive and time consuming tools which have the capability and potential to be used by geoscientists for oil exploration in this research the study of advanced spaceborne thermal emission and reflection radiometer aster spectral bands 8 3 and 1 by decorrelation stretching well discriminated the masirah bay the khufai the shuram and the buah formations of the nafun group the source rocks of huqf supergroup with the quaternary deposits the analysis of visible and near infrared shortwave infrared spectral bands of aster by pca clearly showed the occurrence and spatial distribution of such formations in the rgb principal component images r pc1 g pc2 b pc3 the spatial distributions of such formations are assessed by confusion matrix after using maximum likelihood ml spectral angle mapper sam and spectral information divergence sid algorithms the matrix of ml algorithm has provided the best overall accuracy of 92 93 and kappa coefficient of 0 92 the minerals of the formations were detected by sam further the detection of such mineral groups was confirmed through the aster thermal infrared tir spectral indices image developed using the carbonate index ci quartz index qi and mafic index mi all results of image analyses are evaluated in the field and laboratory studies the study also evaluates the satellite data and image processing methods for the formations of jabal akhdar the equivalent formations of the khufai dome to show the sensor capability and the use of the image processing methods to study the source rocks the results of the study provided similar discriminations comparable to the khufai dome therefore the data and the techniques are recommended to the exploration geologists for use in similar regions of the world

multiple sector collapses at stromboli volcano italy how they work this paper demonstrates that four large sector collapses have affected the nw flank of the stromboli volcano in the past 13 ka alternating with growth phases in order to contribute to the evaluation of the critical conditions which trigger lateral collapses a reconstruction of the geometry of each collapse of the volcano edifice in the four stages that preceded the relative collapse events is also presented and a computation of the landslide volume this reconstruction is based on new field data plotted in three dimensions prior to the initial 13 ka collapse the volcano was 1125 100 m high above sea level the collapse had a volume of 2 23 0 87 km3 whereas the pre collapse volcano volume was 218 8 7 7 km3 the next edifice that failed was 900 70 m high a s l the collapse volume was 1 0 54 km3 with a precollapse volcano volume of 201 4 5 4 km3 the edifice then grew to 1000 60 m a s l the third collapse had a volume of 1 08 0 39 km3 and occurred within a volcano with a volume of 209 1 4 6 km3 this was followed by a new growth phase followed by the last collapse with a volume of 0 73 0 22 km3 the volcano volume was about the same as the present one the present active crater zone is at 780 m a s l in the first three collapses sliding surfaces cut the main magma conduit in the last collapse the upper scarp coincided with the conduit location dyking along a main ne trending weakness zone across the volcano summit exerted a lateral force for collapse inception the decrease of the landslide volumes with the age and the concentric scarps of the four collapses suggest that the younger sliding planes tended to become more superficial and to decrease the areal extent this is interpreted as due to a successively weaker eruptive products from dominantly lavas to dominantly pyroclastics and b the feedback effects between collapses and dykes that injected along the lateral segments of the first collapse slide plane

mineralogical assemblages forming at hyperalkaline warm springs hosted on ultramafic rocks a case study of oman and ligurian ophiolites 1 we report on the mineralogical assemblages found in the hyperalkaline springs hosted on liguria and oman ophiolites based on exhaustive x ray diffraction and scanning electron microprobe analyses in liguria hyperalkaline springs produce a thin brownish calcite precipitate that covers the bedrock due to the concomitant atmospheric co2 uptake and neutralization of the hyperalkaline waters no brucite and portlandite minerals are observed the discharge of alkaline waters in oman ophiolite forms white orange precipitates calcium carbonate minerals calcite and or aragonite are the most abundant and ubiquitous precipitates and are produced by the same mechanism as in liguria this process is observed as a thin surface crust made of rhombohedral calcite morphological features of aragonite vary from needle bouquet dumbbell spheroidal like habitus according to the origin of carbon temperature and ionic composition of the hyperalkaline springs and the biochemical and organic compounds brucite is observed both at hyperalkaline springs located at the thrust plane and at the paleo moho the varying mixing proportions between the surface runoff waters and the hyperalkaline ones control brucite precipitation the layered double hydroxide minerals occur solely in the vicinity of hyperalkaline springs emerging within the bedded gabbros finally the dominant mineralogical associations we found in oman ca bearing carbonates and brucite in a serpentinizing environment driven by the meteoric waters are surprisingly the same as those observed at the lost city hydrothermal site in a totally marine environment

a systematic mapping procedure based on the modified gaussian model to characterize magmatic units from olivine pyroxenes mixtures application to the syrtis major volcanic shield on mars clenet et al 2011 have developed an adapted version of the modified gaussian model mgm the improvements allow the characterization of spectra of olivine pyroxene s mixtures addressing both modal composition and individual minerals chemical composition this version of mgm is fully automated and operational with large amounts of hyperspectral imaging data two natural cases are considered the first one is the sumail massif in the oman ophiolite earth based on our approach applied to hymap data two contrasted lithologic units are mapped the mantle which is harzburgite dominated and the crust made of gabbros and clinopyroxene rich cumulates with spectral variations interpreted in terms of pyroxenes chemical compositions once this new mgm mapping approach has been validated on a controlled natural situation we map the distribution of mafic assemblages across the syrtis major volcano on mars using a visible and near infrared vnir short wave infrared swir observatoire pour la mineralogie l eau les glaces et l activite omega mars express mex mosaic our results are in agreement with previous work but olivine appears to be more abundant than previously estimated in the central part of the volcanic edifice especially in ternary mafic assemblages augite olivine enstatite based on these results we propose a possible scenario for the igneous and thus thermal evolution of the syrtis major region surrounding terrains have formed first and local heterogeneity can be observed between northern and southern areas of the noachian crust we also observe variations in the mineral assemblages within syrtis major lavas which can be interpreted in terms of differentiation from a common parent melt and or of a progressive evolution of the mantle source composition and temperature key points mgm systematic mapping on syrtis major to characterize mafic minerals mixtures olivine and pyroxenes mixture is detected in the central lavas of the volcano pyroxenes have chemical compositions spanning the enstatite augite range

mapping in the oman ophiolite using enhanced landsat thematic mapper images abstract the large areal extent and complex nature of the terrain has meant that previous largely field based mapping programmes in the oman ophiolite have produced maps of internally inconsistent quality recognition of subtle changes and minor outcrops across the area of a 1 1 map sheet is possible in the field only by unrealistically exhaustive mapping by using parts of the short wavelength infrared spectrum landsat thematic mapper data have the capacity to capitalize on distinctions in the spectral reflectances of different rock types and their weathering products and to allow consistent mapping across the whole ophiolite decorrelation stretching of these data produces images in which it is possible to recognize variations in gabbro composition to identify small acidic gabbroic and ultramafic intrusions to discriminate the uppermost mantle from the deeper mantle to locate the moho precisely and to delineate gossans and areas subject to chloritic epidotic alteration off axis plutonism is more widespread and dispersed than previously appreciated the significance of certain faults is reassessed in the light of new insights provided by the imagery such data could be a valuable mapping tool in similarly exposed terrains in arid and semi arid regions even where already mapped at the 1 100 000 scale

active tectonic features and structural dynamics of the summit area of mt etna italy revealed by soil co2 and soil temperature surveying project cgl2005 07509 cli ministry of education and science of spain dpc ingv project flank istituto nazionale di geofisica e vulcanologia osservatorio etneo sezione di catania

major changes in volcano behaviour after a sector collapse insights from stromboli italy in recent years increasing numbers of volcanoes are being recognized as having undergone large sector collapses how far such events can change the succeeding behaviour of the volcano is poorly known despite the importance for natural hazards and economic applications by analysing the last 100 kyr geological history of stromboli italy which has involved multiple collapses this paper illuminates the feedback effect between sector collapse and magma upwelling and emplacement the collapsed zone of stromboli is episodically unbuttressed draining magma preferentially with formation of eruptive centres in the collapse amphitheatre and dyking along the collapse shoulders after a collapse there were no further linear eruptions across the cone on opposing middle lower slopes but these occurred again after rebuilding of the cone the time averaged eruption rate increased immediately before the first collapse and remained higher during the succeeding period of frequent collapses

mapping of moho and moho transition zone mtz in samail ophiolites of sultanate of oman using remote sensing technique abstract moho and moho transition zone mtz of the samail ophiolite of sultanate of oman are characteristic to potential occurrences of chromite deposit hydrothermal mineralization and serpentinization mapping of moho and mtz and discriminating them in between the mafic and ultramafic rocks in ophiolite sequence are more significant and important the present study describes the remote sensing spectral characters of minerals and rocks of the moho and mtz and discriminates the moho of wadi al abyad of nakhl massif and wadi nidab and wadi abda regions of sumail massif in the visible and near infrared vnir and short wavelength infrared swir spectral regions using low cost multispectral satellite data of the advanced spaceborne thermal emission and reflection radiometer aster results of this study show that the red green blue rgb color composite images of aster spectral bands 8 3 and 1 and 8 7 and 4 are able to delineate the moho and mtz of the regions the rgb images of aster band ratios 4 8 4 1 3 2 4 3 and 1 3 2 4 6 5 7 9 8 are capable to discriminate the mantle material ultramafic harzburgites and crustal rocks mafic gabbros the occurrence of such rock types is demonstrated by detection of their minerals using spectral angle mapper sam image processing method the presence of moho and mtz and associated lithologies are verified in field at wadi al abyad wadi nidab wadi abda wadi tayin wadi fizh and several locations of nakhl regions of samail ophiolites the laboratory study shows the occurrence of typical minerals namely olivine orthopyroxene and clinopyroxene in the harzburgite and the minerals such as plagioclase clinopyroxene hornblende orthopyroxene and olivine in the layered gabbro the spectral properties of the rocks are studied using portable infrared mineral analyzer pima spectrometer and the occurrences of minerals are confirmed by x ray diffraction xrd analyses this study demonstrates the sensor capability of aster to map moho and mtz and thus it is recommended to the geoscientists and geophysicists working on moho and mtz the satellite image interpretations of moho and mtz and the associated rocks and minerals are consistent with the field research studies carried out in these regions our images have potential to map the chromites mineralized zone and dunites refractory materials bearing mtz

how can satellite imagery be used for mineral exploration in thick vegetation areas the hokuroku district northern japan is globally recognized for rich ore deposits kuroko and vein types which have been thoroughly explored under thick vegetation cover this situation is ideal to evaluate the effects of ore deposits on vegetation anomalies through geobotanical remote sensing here we present novel methods to detect vegetation anomalies caused by ore deposits and verify their usefulness by comparing the anomalies with a deposit potential map produced from multiple geological data we use the reflectance spectra of landsat etm images acquired in summer and autumn to calculate a vegetation index for plant physiological activity a key variable to detect the anomalies is a variation of vegetation index with time at each pixel difference in variation is enlarged by a sequence of image enhancement methods for the detection we find that the vegetation anomalies defined by the large ratios correspond well to the high potential zones of ore deposits and known major deposits consequently our methods can extend the applicability of remote sensing based mineral exploration to the areas covered by thick vegetation in addition to traditional arid and semi arid areas this article is protected by copyright all rights reserved

morphology of pyroclastic cones and tectonics the relationships between morphology and spatial distribution of 1315 quaternary pyroclastic cones and coeval faulting of the volcanic substrate are analyzed in the following regions with different structural settings tepic rift mexico ethiopian rift mexican volcanic belt canary archipelago and mount etna field data and analog experiments of tephra cone emplacement and collapse enable the definition of a number of parameters which can be used to infer the geometry of the fracture feeding the magma to a pyroclastic cone the strike of the feeding plane is directly related to 1 the elongation of cone base and crater 2 the location of depressions on the crater rim and 3 the alignment of pyroclastic cones in relation to a given vent spacing in addition the strike and dip of faults affect the direction of cone breaching these relationships are valid for volcanic substrate topographic surfaces with an inclination of less than 9 and are especially sensitive to fault escarpment and cone height lava and cone density and fault orientation with respect to the dip of the volcanic substrate topography relations 1 and 2 become more pronounced for regions undergoing extensional tectonics where edifices also have a larger dimension whereas breaching in the direction of the fault dip is more widespread in regions under extension breaching along the fault strike as well as the coincidence between fault strike and vent alignment are more frequent in regions with transcurrent or transtensional tectonics

timing and mechanism for intratest mg ca variability in a living planktic foraminifer abstract geochemical observations indicate that planktic foraminifer test mg ca is heterogeneous in many species thereby challenging its use as a paleotemperature proxy for paleoceanographic reconstructions we present mg ca and ba ca data collected by laser ablation icp ms from the shells of orbulina universa cultured in controlled laboratory experiments test calcite was labeled with ba spiked seawater for 12 h day or night calcification periods to quantify the timing of intratest mg banding across multiple diurnal cycles results demonstrate that high mg bands are precipitated during the night whereas low mg bands are precipitated during the day data obtained from specimens growing at 20 c and 25 c show that mg ca ratios in both high and low mg bands increase with temperature and average test mg ca ratios are in excellent agreement with previously published empirical calibrations based on bulk solution icp ms analyses in general mg band concentrations decrease with increasing ph and or co2 3 but this effect decreases as experimental temperatures increase from 20 c to 25 c we suggest that mitochondrial uptake of mg2 from the thin calcifying fluid beneath streaming rhizopodial filaments may provide the primary locus for mg2 removal during test calcification and that diurnal variations in either mitochondrial density or activity produce mg banding these results demonstrate that mg banding is an inherent component of test biomineralization in o universa and show that the mg ca paleothermometer remains a fundamental tool for reconstructing past ocean temperatures from fossil foraminifers

extensional tectonics and volcano lateral collapses insights from ollague volcano chile bolivia and analogue modelling understanding the process of volcanic lateral collapse which may be governed by numerous possible factors can be significantly improved by identifying the role of each factor here we test the perturbation induced in a volcano by tectonic normal faulting in the basement magma inflation and multiple flank deformation based on fieldwork and analogue experiments ollague volcano chile bolivia provides a good example of a sector collapse with exposed substrate extensional tectonics and our experiments have been done with conditions consistent with field data results show that none of the possible tectonic conditions led to complete lateral failure in agreement also with the field data sector collapse of the model cone occurred only when a shallow magmatic intrusion within the volcano was reproduced we also found out that volcano flank deformation is enhanced if a previous flank destabilization occurred interleaved by new cone growth terra nova 18 282 289 2006

lateral collapses and active sedimentary processes on the northwestern flank of stromboli volcano italy abstract the marine volcaniclastic system extending to 3 km water depth on the northwest flank of stromboli volcano has been surveyed using seismo acoustic profiling multibeam bathymetry deep towed long range side scan sonar imaging and box core sampling deposits and sea floor topography record repeated flank collapses that have occurred during the last 13 ka and created the present sciara del fuoco scar an extensive 170 km2 debris avalanche deposit characterized by subdued hummocks megablocks is buried by turbidites formed from gravity currents that originated in sciara del fuoco the currents were mainly deflected along the margin of the avalanche deposit but also spilt over onto it the turbidites reflect topographic flow stripping and their thinning towards slightly steeper slopes indicates that some material that settled there drained further downslope as secondary higher concentration flows the estimated volume of the entire fan shaped bulge amounts to 12 2 5 km3 about 3 5 km3 of which is attributed to the post collapse sedimentation the remaining 8 5 2 5 km3 is in the order of the volume computed for the material removed by the multiple sector collapses that affected the nw stromboli flank two units are identified in the distal part of the bulge through the recognition of their fronts and these indicate a layered structure for successive debris avalanche deposits granulometric and particle type characterization of seabed samples shows clast population evolution with sedimentary transport distance from the main entrance point of debris in sciara del fuoco to the confluence with the stromboli canyon and into the marsili basin some 45 km from the island changes in particle populations are due to selective sedimentation and also mixing with a wide range of terrigenous detritus brought by currents that descended the main stromboli canyon from the continental shelf abundant fine sand and silt is produced at the volcano and occurrence of mainly coarse grained material along the channel to the marsili basin indicates that a considerable volume of volcaniclastic material from stromboli lies in the sedimentary succession accumulating on the distal basin floor where a deep sea fan is growing

empirical calibration of the silica ca tschermak s anorthite scan geobarometer the pressure sensitive equilibrium among anorthite quartz and the ca tschermak component in clinopyroxene caal2sio6 cats caal2siocpx6 sioqtz2 caal2si2opl8 scan can be used as a geobarometer in granulites with the proper assemblage and has been calibrated using mineral composition data from partial melting experiments of natural assemblages and from phase equilibrium experiments on the end member cmas system the experimental data cover the p t range 4 32 kbar and 900 1400 c linear least squares regression analysis of the experimental data resulted in the following empirical expressions for pressure in terms of composition and temperature p 5 066 0 760 1300 800 t lnk276 16 t 2 5 kbar orp 6 330 0 116 lnk301 9 t 1 0 kbar where k aplan acpxcats the first equation incorporates an enthalpy term but is less accurate than the second equation in which the enthalpy of reaction is ignored application of these expressions to natural and experimental equilibrium mineral assemblages demonstrates that the empirical barometers are applicable over a wide range of pressures 4 kbar temperatures 700 c and bulk compositions mg 32 5

volcanic and geochemical evolution of the teno massif tenerife canary islands some repercussions of giant landslides on ocean island magmatism large scale catastrophic mass wasting is a major process contributing to the dismantling of oceanic intraplate volcanoes recent studies however have highlighted a possible feedback relationship between flank collapse or incipient instability and subsequent episodes of structural rearrangement and or renewed volcano growth the teno massif located in northwestern tenerife canary islands is a deeply eroded miocene shield volcano that was built in four major eruptive phases punctuated by two lateral collapses each removing 20 25 km3 of the volcano s north flank in this paper we use detailed field observations and petrological and geochemical data to evaluate possible links between large scale landslides and subsequent volcanism magmatism during teno s evolution inspection of key stratigraphic sequences reveals that steep angular unconformities relics of paleolandslide scars are marked by polymict breccias near their base these deposits typically include abundant juvenile pyroclastic material otherwise scarce in the region while some of teno s most evolved low density magmas were produced just before flank collapses early postlandslide lava sequences are characterized by anomalously high proportions of dense ankaramite flows extremely rich in clinopyroxene and olivine crystals a detailed sampling profile shows transitions from low mg lavas relatively rich in sio2 to lavas with low silica content and comparatively high mg after both landslides long term variations in zr nb normative nepheline and la lu are coupled but do not show a systematic correlation with stratigraphic boundaries we propose that whereas loading of the growing precollapse volcano promoted magma stagnation and differentiation the successive giant landslides modified the shallow volcano tectonic stress field at teno resulting in widespread pyroclastic eruptions and shallow magma reservoir drainage this rapid unloading of several tens of km3 of near surface rocks appears to have upset magma differentiation processes while facilitating the remobilization and tapping of denser ankaramite magmas that were stored in the uppermost mantle degrees of mantle melting coincidently reached a maximum in the short time interval between the two landslides and declined shortly after probably reflecting intrinsic plume processes rather than a collapse induced influence on mantle melting our study of teno volcano bears implications for other oceanic volcanoes where short term compositional variations may also directly relate to major flank collapse events

shrimp u pb and cameca 1280 oxygen isotope results from ancient detrital zircons in the caozhuang quartzite eastern hebei north china craton evidence for crustal reworking 3 8 ga ago the caozhuang quartzite located in eastern hebei province in the eastern part of the north china craton has long been known to contain the oldest detrital zircon population in china a suite of 30 zircons with preliminary ages 3 7 ga were selected for detailed shrimp u pb and cameca 1280 oxygen isotope analyses shrimp u pb dating reveals that ages range from 3860 to 3135 ma the former being the oldest 207 pb 206 pb zircon age so far obtained from the north china craton values of 18 o range from 5 4 to 7 5 permil similar to archean igneous zircons worldwide but the average value for the 30 zircons is 6 6 permil which is 0 3 permil higher than suite averages for detrital zircons from the jack hills and beartooth mountains and nearly 1 permil higher than magmatic zircons from igneous rocks of the superior province and barberton these elevated values of 18 o suggest reworking of a significant amount of juvenile crust older than 3 8 ga that underwent a low temperature supracrustal history and was distributed throughout the source region in northeast china

rifting recurrent landsliding and miocene structural reorganization on nw tenerife canary islands we studied mechanisms of structural destabilization of ocean island flanks by considering the linkage between volcano construction and volcano destruction exemplified by the composite teno shield volcano on tenerife canary islands during growth tenerife episodically experienced giant landslides genetically associated with rifting and preferentially located between two arms of a three armed rift system the deeply eroded late miocene teno massif allows insights into the rifting processes the failure mechanisms and related structures the semicircular geometry of palaeo scarps and fracture systems breccia deposits and the local dike swarm reconfigurations delineate two clear landslide scarp regions following an earlier collapse of the older los gigantes formation to the north the rocks around the scarp became fractured and intruded by dikes substantial lava infill and enduring dike emplacement increased the load on the weak scarp and forced the flank to creep again finally resulting in the collapse of the younger carrizales formation once more the changing stress field caused deformation of the nearby rocks a fracture belt formed around the scarp and dikes intruded into new concentric directions the outline size and direction of the second failed flank of teno very much resembles the first collapse we suggest structural clues concerning mechanisms of recurrent volcano flank failure verifying the concept that volcano flanks that have failed are prone to collapse again with similar dimensions

zircon u pb hf isotopes and geochemistry of two contrasting neoarchean charnockitic rock series in eastern hebei north china craton implications for petrogenesis and tectonic setting abstract the zunhua qinglong microblock in eastern hebei north china craton exposes two contrasting charnockitic rock series in the yuhuzhai taipingzhai and cuizhangzi areas charnockitic plagioclase gneiss series with chemical compositions of dioritic and tonalitic rocks and charnockite series showing tonalitic and granodioritic components petrographic observation reveals that two types of orthopyroxenes are preserved in these rocks medium fine grained anhedral orthopyroxenes are preserved in both series and coarse grained subhedral orthopyroxenes are preserved only in the charnockite series in situ trace element analyses reveal that the coarse grained subhedral orthopyroxenes exhibit typical chemical features of magmatic orthopyroxene whereas the medium fine grained anhedral orthopyroxenes display lower medium to heavy rare earth elements ree and no obvious eu anomalies resulting in left inclined ree patterns combined with petrographic features these new data indicate that the medium fine grained anhedral orthopyroxenes were formed by granulite facies metamorphism caused by dehydration reactions whereas the coarse grained subhedral orthopyroxenes were directly crystallized from their magmatic precursors laser ablation inductively coupled plasma mass spectrometry la icp ms zircon u pb isotopic dating reveals that the magmatic precursors of the charnockitic plagioclase gneiss series were emplaced between 2530 17 and 2523 12 ma and those of the charnockite series were emplaced between 2527 28 and 2515 22 ma we conclude that these magmatic precursors are contemporaneous emplacements of two neoarchean granitoid magmatic events which were followed by regional granulite facies metamorphism at 2 45 ga the charnockitic plagioclase gneiss series and charnockite series exhibit similar hf t values of 2 4 to 5 3 and 3 2 to 5 5 indicating either depleted mantle or juvenile crust affinity and involvement of ancient crustal components the charnockitic plagioclase gneiss series exhibit relatively low sio2 contents 54 1 65 2 with various mgo contents 1 93 5 36 mg 0 36 0 55 and la yb n values 3 49 56 00 the charnockite series exhibit higher sio2 contents 60 1 69 2 with similar la yb n values 14 61 42 69 mgo contents 2 10 3 99 and mg 0 29 0 52 these geochemical and zircon lu hf isotopic features together with chemical modeling suggest that the magmatic precursors of the charnockitic plagioclase gneiss series may have been primarily derived from the partial melting of a depleted mantle that was metasomatized by slab derived melts fluids and experienced fractional crystallization processes with hornblende and plagioclase as primary fractionated phases the aforementioned features further suggest that the charnockite series originated from a partial melting of the subducted slab and it was strongly contaminated by mantle peridotites these new data combined with the previous studies of neoarchean basement rocks in the zunhua qinglong microblock in eastern hebei suggest that the magmatic precursors of these two contrasting charnockitic rock series were formed in a back arc related tectonic environment at a convergent plate margin

discrimination and origin of the sanukitoid series geochemical constraints from the neoarchean western karelian province finland abstract neoarchean late to post tectonic sanukitoid intrusions are found in the western part of the karelian province in finland variable sized even grained to k feldspar porphyritic intrusions form a series of diorites tonalites and granodiorites that are calc alkaline to alkali calcic magnesian and mostly peraluminous the major and trace element geochemistry of the intrusions show typical sanukitoid affinities a mantle signature high content of mg ni cr and high mg and enrichment in lile especially k ba and sr the intrusions form a distinctive series that can be distinguished from the ttg series of the karelian province by their high ba sr signature low na 2 o k 2 o ratio and uniform hree pattern the sanukitoid series can be compositionally constrained as follows sio 2 55 70 wt na 2 o k 2 o 0 5 3 mgo 1 5 9 wt mg 45 65 k 2 o 1 5 5 0 wt ba sr 1400 ppm and gd er n 2 6 the probable source was enriched subcontinental lithosphere mantle with high lile concentrations in phlogopite and or sanidine the accumulation of k ba and sr in the mantle source may have occurred as a consequence of two separate metasomatic events 1 by subduction related fluids melts and 2 by metasomatism related to asthenospheric mantle upwelling caused by slab breakoff the slab breakoff at the end stage of subduction is also a viable trigger for the sanukitoid magmatism

a past giant lateral collapse and present day flank instability of fogo cape verde islands fogo island is a large and extremely steepsided oceanic island volcano in the cape verde archipelago it has a large ca 9 km across east facing summit collapse structure the monte amarelo collapse with a probable volume of at least 150 200 km3 for most of its history the monte amarelo volcano had a small but productive central vent complex and radial rift zones fed by laterally propagating dykes shortly before the collapse the latter were replaced by north south trending arrays of en echelon vertically propagating dykes since the monte amarelo collapse the scar has partly filled with a new volcano the cha das caldeiras volcano the summit cone of this volcano the pico do fogo is a very young feature but has been abandoned in the most recent phase of activity from the 18th century onwards the same period has also seen the abandonment of earlier radial rift zones with laterally propagating dykes and their replacement with en echelon arrays of vents fed by vertically propagating dykes these form an n s trending array within the older collapse structure and are associated with seaward displacement of the eastern flank of the volcano within the old collapse structure the most recent eruptions those of 1951 and 1995 appear to be associated with episodes of flank instability manifested in n s surface fissuring and east facing normal faults these recent structural changes in the volcano parallel those which took place in the monte amarelo volcano prior to its collapse

plagioclase wehrlites and peridotites on the east pacific rise hess deep and the mid atlantic ridge dsdp site 334 evidence for magma percolation in the oceanic upper mantle abstract textural and petrological data are presented that record the formation of plagioclase bearing wehrlites and peridotites at slow spreading and fast spreading ridges that are comparable to the wehrlites and peridotites formed in ophiolitic complexes evidence is provided for locally pervasive magma percolation in the oceanic residual upper mantle the samples studied come from the east pacific rise epr hess deep and the mid atlantic ridge mar dsdp site 334 at both sites parts of the peridotites display poikilitic textures with oikocrysts of clinopyroxene and interstitial plagioclase that include xenocrysts of strained and partly annealed olivine and subidiomorphic spinel crystals petrofabric data for olivine suggest a magmatic origin for the hess deep wehrlite its phase chemistry is comparable to intrusive plagioclase wehrlites and lherzolite from ophiolites that are thought to have crystallized from a crystal mush it differs drastically from the associated hess deep diopside bearing harzburgites and dunites which are quite similar to oceanic and ophiolitic residual peridotites the epr wehrlite is therefore considered as an intrusive rock the leg 37 plagioclase peridotites display a weak lattice fabric of olivive which may have resulted from high temperature plastic flow these rocks have a phase chemistry that is typical of ophiolitic and oceanic residual rocks these rocks are hence interpreted as residual dunite or harzburgite which has been pervasively impregnated by a melt from which the clinopyroxene and plagioclase crystallized these peridotites could have an intrusive origin or may have formed in situ at the crust mantle transition in association with intrusions of large gabbro bodies

archean crustal evolution in china u pb geochronology of the qianxi complex abstract the qianxi complex formerly the qianxi group in eastern hebei province is a key terrain for studying the archean crustal evolution of the sino korean craton in china the evolution of the complex involved several stages of supracrustal deposition and magmatic intrusion except for a few post tectonic intrusives all rock assemblages have been metamorphosed to high grade granulite and amphibolite facies the evolution of the complex has spanned more than 1 ga since about 3 5 ga ago in the present work two areas in the qianan region qianan county have been investigated for u pb age study 1 the caozhuang area in the south and 2 the shuichang yangyashan area in the north important tectonothermal events and magmatic episodes of the qianxi complex were identified by the u pb isotopic analyses of zircons extracted from various rock types the results of age determination and the most likely interpretation in terms of temporal evolution of the complex are summarized schematically the oldest zircons 3 65 3 67 ga of china have been found in a fuchsite bearing quartzite in association with the 3 5 ga sm nd isochron age amphibolites in the caozhuang area this emphasizes the existence of early archean sialic crust in the qianxi complex however no ages older than 2 9 ga have been revealed for grey gneisses enclosing the ca 3 5 ga amphibolite enclaves in the caozhuang area but a leptynite sample of dacitic composition gave a minimum 207pb 206pb age of 3 3 ga obtained by a single zircon stepwise evaporation analysis this age and the 3 5 ga sm nd isochron age for amphibolites suggest that the earliest deposition of supracrustal rocks took place about 3 5 3 3 ga ago the deposition of fuchsite quartzite could have taken place contemporaneously or in an earlier period up to 3 6 ga but its precise stratigraphic positions remains to be determined nevertheless the presence of very ancient zircons clearly advocate for the existence of sialic crust at least 3 6 ga in china in the shuichang yangyashan area a supracrustal sequence containing abundant banded iron formations was intruded by a granitic gneiss dated at 2 96 ga by the conventional multigrain zircon method sm nd model ages of about 3 3 ga were obtained for two amphibolite enclaves in a charnockitic gneiss it appears that supracrustal deposition of the qianxi complex might have migrated to the north and took place in the period of 3 3 3 0 ga in addition to supracrustal rocks the qianxi complex is characterized by polyphase granitoid intrusions except for the contaminated grey gneisses sm nd tdm 3 2 3 3 ga in the caozhuang area and the ca 3 ga granitic gneiss in the yangyashan area most granitoid intrusions are of late archean ages the period of 2 7 2 5 ga has undoubtedly recorded the most important tectonothermal events in the evolution of the sino korean craton the present zircon age study and available age data in the literature demonstrate that the archean crustal development in china culminated towards the end of the archean

mapping of an ophiolite complex by high resolution visible infrared spectrometry the sumail massif of the oman peridotite has been surveyed by the high spectral resolution imager hymap the field measurements have been taken simultaneously to the hymap campaign with a ger 3700 spectrometer to compare the two data sets further calibration and atmospheric correction are made through empirical line corrections a continuum removal by a modified gaussian model on reflectance is then performed for each pixel to minimize atmospheric scattering and shadowing effects classification from spectral distance is established using field observations and comparisons at full spectral resolution to identify peridotite subunits harzburgites and dunites and to distinguish plagioclase wehrlites from gabbros detections of hydrothermal transformations of olivine in serpentines and their alteration in carbonates along fracture networks characterized by narrow spectral signatures validate the classification this demonstrates the utility of the high spectral resolution and the development of appropriate processing methods for geological identifications

towards reconstructing ancient seawater mg ca by combining porcelaneous and hyaline foraminiferal mg ca temperature calibrations the temperature of the deep ocean plays a vital role in the earth s climate system paleo reconstructions of deep sea temperatures have traditionally been based on the oxygen isotope composition of deep sea benthic foraminiferal calcite shells although this parameter depends upon polar ice volume as well as temperature more recent reconstructions use mg ca in these shells with temperature calibrations based on empirical relationships observed in present day oceans incorporation of mg dmg into foraminiferal calcite is however not solely dependent on temperature but also on seawater mg ca due to its long oceanic residence time mg concentrations remained relatively constant over time scales of a few hundred thousand years but varied significantly over longer geological time scales accurate reconstruction of past temperatures using foraminiferal mg ca therefore hinges on our understanding of mg ca seawater changes on geological timescales we explore a novel independent approach to reconstructing past seawater mg ca using the temperature dependent offset in dmg between porcelaneous secreting intermediate or high mg calcite abbreviated as imc or hmc respectively and hyaline producing low mg calcite abbreviated as lmc benthic foraminifera we calibrated the mg ca temperature dependence for pyrgo spp one of the few common large sized porcelaneous taxa present in the deep sea since the middle miocene and combined this with an existing calibration of hyaline cibicidoides spp to mathematically solve for changes in mg ca seawater through time we show that changes in mg ca seawater can be reconstructed using the offset between porcelaneous and hyaline foraminifera but absolute values are highly dependent on the species specific offset between mg ca seawater and mg partition coefficients

growth and reworking of the early precambrian continental crust in the north china craton constraints from zircon hf isotopes abstract we synthesize more than 2600 hf isotope data on the archean paleoproterozoic zircons from the north china craton ncc recalculation of the data based on single stage and two stage hf model ages of the eastern block of the ncc shows peak ages of 3902 13 ma and 3978 18 ma respectively and also small peaks at 3 5 4 0 ga the majority of zircon ehf t values are positive suggesting the possibility of the crust and the mantle differentiation at ca 3 9 4 0 ga in the eastern block of the ncc most magmatic zircons from the whole of ncc have their hf model age range of 2 4 2 9 ga and the single stage model ages is cluster at 2698 4 ma whereas the two stage model ages concentrate at 2714 5 ma implying that the protoliths were juvenile crustal rocks the most prominent peak at 2 7 ga indicates that this period marks the most important stage of the crust mantle differentiation and crust formation of the ncc the widespread 2 5 ga rocks in the ncc and the absence of the 2 5 ga peaks in hf model ages are consistent with the partial melting and reworking of the juvenile rocks at 2 5 ga furthermore the 2 5 1 7 ga zircon hf isotope features are also related to the reworking of the crustal rocks our results from the integration of a large database suggest that the eastern block and the trans north china orogen have undergone similar crust mantle differentiation and magmatism leading to the conclusion that the essential cratonization of the north china took place at the end of neoarchean

aster capability in mapping of mineral resources of arid region a review on mapping of mineral resources of the sultanate of oman abstract advanced space borne thermal emission and reflection radiometer aster has exclusive capability to map minerals and ore deposits and able to discriminate rock types useful for geological applications especially the improved spectral and spatial resolutions of spectral bands of the sensor are well utilized by the exploration geologists working on arid region where the surface deposits are directly exposed to the sensor without disturbances of the vegetation several fruitful research studies have been carried out to map mineral resources in arid region with inaccessible rugged mountains and deserts area where it is difficult to do conventional geological mapping these were demonstrated and documented in the scientific publications using the aster spectral bands and image processing methods this study reviews scientific literatures published on mapping of the economic mineral resources of the sultanate of oman using aster and simples image processing methods

high grade metamorphism during archean paleoproterozoic transition associated with microblock amalgamation in the north china craton mineral phase equilibria and zircon geochronology abstract metamorphic regimes in archean terranes provide important keys to the plate tectonic processes in early earth the north china craton ncc is one of the ancient continental nuclei in asia and recent models propose that the cratonic architecture was built through the assembly of several archean microcontinental blocks into larger crustal blocks here we investigate garnet and pyroxene bearing granulite facies rocks along the periphery of the jiaoliao microcontinental block in the ncc the garnet bearing granulites contain peak mineral assemblage of garnet clinopyroxene orthopyroxene magnetite plagioclase quartz biotite ilmenite mineral phase equilibria computations using pseudosection and geothermobarometry suggest peak p t condition of 800 830 c and 7 8 kbar for metamorphism isopleths using xmg of orthopyroxene and xca of garnet in another sample containing the peak mineral assemblage of garnet orthopyroxene quartz magnetite fluid yield peak p t conditions of 860 920 c and 11 14 kbar geochemical data show tonalitic to granodioritic composition and arc related tectonic setting for the magmatic protoliths of these rocks zircon la icp ms analyses yield well defined discordia with upper intercept ages of 2562 20 ma mswd 0 94 and 2539 21 ma mswd 0 59 which is correlated with the timing of emplacement of the magmatic protolith a younger group of zircons with upper intercept ages of 2449 41 ma mswd 0 83 n 6 as 2449 41 ma mswd 0 83 n 6 and 2480 44 ma mswd 1 2 n 9 constrains the timing of metamorphism zircon lu hf data show dominantly positive ehf t values up to 8 5 and yield crustal residence ages tdmc in the range of 2529 to 2884 ma suggesting magma sources from meso neoarchean juvenile components the high temperature and medium to high pressure metamorphism is considered to have resulted from the subduction collision tectonics associated with microblock amalgamation in the ncc at the end of archean together with the evidence for high pressure metamorphism from an adjacent locality our results correlate with models that predict paired metamorphism at the archean proterozoic transition with the onset of modern style plate tectonics

structural features of the 2007 stromboli eruption abstract on 27 february 2007 two ne sw and nnw sse dike fed effusive vents opened to the north at 650 and 400 m above sea level asl of the summit craters at stromboli forming a fissure parallel to the inner walls of the sciara del fuoco sdf sector collapse depression the formation of these vents was soon followed by rapid subsidence of the summit crater area this partly obstructed the central conduit temporarily choking the fissure and increasing the deformation of the upper part of sdf the reactivation of the nnw sse vent and the opening of a new vent located at 500 m asl fed by a second dike released the internal pressure and surface deformation ceased the eruption then continued again from the 400 m vent after a summit explosion on 15 march until ending in early april after a progressive decrease of magma output repeated ne sw dike intrusions have occurred in recent years close to the upper se limit of the sdf in that zone named bastimento the eruptive fractures traced the discontinuities that borders the sdf increasing the risk of triggering new sector collapse whereas the ne sw trending structures lie along the regional volcano structural trend of the aeolian arc through stromboli the nnw sse vents are oblique to this trend and may be controlled by the anomalous stress field within the unstable flank of the sdf another fundamental aspect of the 2007 eruption is the collapse of the central conduit due to the rapid and deep magma drainage linked to the opening of the 400 m vent the intrusion of dikes and development of flank vents during the 2007 eruption could possibly have triggered catastrophic landslides and related tsunami or eruptive paroxysms but the opening of new effusive vents released the internal pressures diminishing the hazard

regional stress field in the area of stromboli italy insights into structural data and crustal tectonic earthquakes abstract crustal tectonic seismicity on stromboli is here discussed along with the regional tectonic and geodynamic context of the aeolian archipelago italy the aim of this paper is to contribute to the reduction of the crucial gap in information concerning the tectonic activity originating at the volcano stromboli in the last decade it is indeed well known that strombolian eruptions related to the persistent state of activity on this volcano allow a fast collection of seismic data which are mainly represented by explosion quakes and tremor however only some sporadic information concerns tectonic earthquakes due to their low occurrence rate a catalog of 150 crustal tectonic earthquakes recorded at stromboli from 1985 to 1996 is presented here the analyses of the seismograms were carried out on the basis of the records of the station str located in the southwestern part of the island the magnitude considered ranged from 1 5 to 3 7 hypocentral location indicates foci at less than 12 km although for the majority of the earthquakes which are not recorded at the seismic stations deployed on the other islands of the aeolian archipelago a shallower within a few kilometers depth can be hypothesized the strain release associated with the 150 tectonic earthquakes of our catalog was also evaluated the low levels of occurrence and seismic energy release reached throughout the ca twelve years analyzed here confirm the minor role played by processes of brittle failure of rocks this aspect of seismic activity is nevertheless important as it can provide a contribution to the knowledge of the dynamics of this volcano the focal mechanisms available integrated with data from the literature show the t axes oriented about ne sw and nw se these findings are consistent with the deformative and tectonic characteristics of this volcanic edifice and of the aeolian archipelago which shows the same two directions of extension this is in agreement with subduction which is very old or which passively evolves towards the final stages and is controlled by the transform activity of the aeolian tindari giardini fault system

geomorphic development of white island volcano based on slope stability modelling abstract white island shows many geomorphic features associated with stratovolcanoes that have undergone major sector collapse most notably the flat floored amphitheatre comprising the present crater arcgis is used to develop a reconstructed pre failure cone and 2d limiting equilibrium stability analysis is undertaken of the reconstructed cone water table ranges from 0 dry to 100 saturated are assumed and earthquake accelerations of 0 0 5 g bracket the likely range of accelerations expected in a volcanic setting geotechnical data from moon et al moon v bradshaw j smith r and de lange w 2005 geotechnical characterization of stratocone crater wall sequences white island volcano new zealand engineering geology 81 146 178 are used the models suggest that flank failure is a feasible explanation for the present day geomorphology and indicate that there were at least two retrogressive failures the best model sees a core of hydrothermally altered material overlying relatively unaltered andesite lavas and breccias where accelerations of 0 17 g saturated slope to 0 45 g dry slope are required to initiate failure f 1 0 the failure modelled was relatively small volume of 0 21 km3 and would have mostly involved hydrothermally altered materials with some fresh rock mass two toreva blocks are recognised occupying the seaward margin of the amphitheatre with a lobe of debris offshore suggested as the debris avalanche deposits modification of both the outer slopes of the island and the inner crater walls has occurred since the failure event especially on the southwestern margin of the crater modelling suggests that further failure of the inner walls is likely and poses a significant hazard to tourists visiting the island further outer slope failures are unlikely

petrogenesis and geodynamics of late archean magmatism in eastern hebei eastern north china craton geochronological geochemical and nd hf isotopic evidence abstract the eastern part of the north china craton contains large volumes of late archean hornblenditic tonalitic dioritic granodioritic and granitic rocks la icpms zircon u pb dating of three plutons from eastern hebei eastern north china craton record emplacement ages of 2526 2515 ma and metamorphic ages of 2500 2490 ma for the diorite granodiorite and monzogranite and 2440 ma for the k feldspar granite hornblendites have high mgo 8 6 10 6 wt cr 674 1126 ppm ni 125 159 ppm and v 224 315 ppm at low basic silica contents sio2 45 7 49 0 wt they are enriched in light rare earth elements lrees and large ion lithophile elements liles and depleted in high field strength elements hfses with positive nd t values 1 2 to 2 0 indicating they were derived from an enriched mantle source the monzogranites have high sr and ba contents and sr y and la yb ratios low y and hrees abundances and positive nd t and zircon hf t values with nd and hf model ages less than 3 0 ga reflecting that they were derived from partial melting of a juvenile lower crust at high pressure however the k feldspar granites with low sr and ba concentrations and high hree and y contents are considered to have originated from partial melting of juvenile crustal materials at shallow crustal levels the diorites and granodiorites have variable major and trace element concentrations magmatic zircons from these rocks have heterogeneous hf t values but record uniform homogeneous u pb ages indicating they resulted from mixing of mafic and felsic magmas coupled with fractional crystallization because of the widespread distribution of late archean magmatism and evidence for magma mixing possibly related to mafic magma underplating it appears likely that this event in the eastern north china craton may relfect mantle plume activity that resulted in significant growth of continental crust during the late archean

two phases of granulite facies metamorphism during the neoarchean and paleoproterozoic in the east hebei north china craton records from mafic granulites abstract archean cratons are commonly reworked during the late paleoproterozoic orogeny which may result in multi phase granulite facies metamorphism in many domains the east hebei terrane of the north china craton is developed with two phases of granulite facies metamorphism in the neoarchean and paleoproterozoic the neoarchean granulite facies metamorphism is recognized mainly in the rafts or slivers of supracrustal rocks from the taipingzhai ovate structural domain characteristic of anticlockwise p t paths the mafic granulites at this domain contain two pyroxene granulite assemblages which are commonly overprinted by a late phase of granulite facies marked by tiny grained vermicular orthopyroxene bearing assemblages they only record the neoarchean metamorphic ages at 2 53 2 52 ga and 2 51 2 48 ga as indicated by zircon u pb data para simultaneously with the emplacement of ttg rocks in contrast the paleoproterozoic granulite facies metamorphism can be well recognized in the saheqiao linear structural belt which is characterized by high pressure granulite assemblages in mafic rocks with clockwise p t paths in this belt the archean two pyroxene granulite assemblages are locally preserved showing red eye socket overprinting textures consisting of garnet coronas or fine grained garnet and clinopyroxene bearing assemblages surrounding the early stage pyroxenes zircon u pb data indicate that mafic granulites from the saheqiao belt record not only the neoarchean metamorphic ages of 2 50 ga but also some paleoproterozoic ages of 1 97 1 83 ga the first application of lu hf garnet whole rock isochron method to garnet bearing mafic granulites from the saheqiao belt yields ages of 1766 6 7 0 and 1787 22 ma confirming that the overprinting of garnet bearing assemblages occurred in the late paleoproterozoic thus the saheqiao linear structural belt may represent a strongly reworked domain during the paleoproterozoic orogeny rather than an archean high grade greenstone belt as previously considered

remote sensing based approach for mapping of co2 sequestered regions in samail ophiolite massifs of the sultanate of oman abstract documentation of chemical weathering and co 2 sequestration in the samail ophiolite massifs of the sultanate of oman represents an important case study for geological carbon capture and storage system gccss the present research study demonstrates the capability of remote sensing technique for mapping of weathered zones and potential co 2 sequestration area abundances at different scales within peridotites in the northern mountain region of the samail ophiolite massifs the carbonate mineral index ci applied with other mineral indices to the tir wavelength region of advanced spaceborne thermal emission and reflection radiometer aster tir spectral bands 13 and 14 mapped co 2 sequestered minerals along the structural and wadi controlled co 2 flowing regions peridotites the source rocks of co 2 sequestration in the study area were mapped using an aster 8 3 and 1 band combinations the decorrelated landsat tm image discriminated the rock types associated with peridotites of ophiolite sequences and delineated the region of weathered and altered serpentinized peridotites in the zone of co 2 sequestration co 2 sequestration mapping was carried out using landsat tm satellite data that span 20 years 1986 1998 2000 2003 and 2006 to assess the present status of co 2 sequestration in this region the image interpretations are verified with existing geological maps and through field and laboratory studies the spectral measurements of carbonate minerals at 1300 to 2500 nm with the spectral resolution of 7 nm using a pima sp infrared spectrometer in the field and laboratory show the presence of hydroxyl bearing minerals and carbonates that have spectral absorption features around 1 4 m 1 9 m and 2 35 m the strong absorptions around 2 35 m are mainly due to c o bonds in carbonate minerals such as calcite caco 3 dolomite camg co 3 2 magnesite mgco 3 aragonite caco 3 and siderite feco 3 which form 15 to 57 12 to 53 9 to 38 11 to 21 and 3 to 8 respectively in the samples the absorptions around 1 4 m and 1 9 m are caused by hydration effects of hydroxyl minerals including antigorite and montmorillonite present at 10 to 21 and 37 to 81 respectively in the samples the alterations of serpentinite are evidenced by the presence of antigorite and lizardite minerals x ray powder diffraction analyses further confirms the occurrence of co 2 sequestered major carbonate minerals such as aragonite calcite and dolomite in the samples the study demonstrates that the aster and landsat tm satellite multispectral sensors are useful to detect the carbonate minerals to delineate the peridotites and to discriminate the areal abundance of potential co 2 sequestration this technique is a useful tool to map and monitor the region of co 2 sequestration in well exposed arid and semi arid regions and to analyze and understand this aspect of the world geological carbon capture and storage system

the effects of environmental parameters on diffuse degassing at stromboli volcano insights from joint monitoring of soil co2 flux and radon activity abstract soil co 2 flux and 222 rn activity measurements may positively contribute to the geochemical monitoring of active volcanoes the influence of several environmental parameters on the gas signals has been substantially demonstrated therefore the implementation of tools capable of removing or minimising the contribution of the atmospheric effects from the acquired time series is a challenge in volcano surveillance here we present 4 years long continuous monitoring from april 2007 to september 2011 of radon activity and soil co 2 flux collected on the ne flank of stromboli volcano both gases record higher emissions during fall winter up to 2700 bq m 3 for radon and 750 g m 2 day 1 for co 2 than during spring summer seasons short time variations on 222 rn activity are modulated by changes in soil humidity rainfall and changes in soil co 2 flux that may be ascribed to variations in wind speed and direction the spectral analyses reveal diurnal and semi diurnal cycles on both gases outlining that atmospheric variations are capable to modify the gas release rate from the soil the long term soil co 2 flux shows a slow decreasing trend not visible in 222 rn activity suggesting a possible difference in the source depth of the of the gases co 2 being deeper and likely related to degassing at depth of the magma batch involved in the february april 2007 effusive eruption to minimise the effect of the environmental parameters on the 222 rn concentrations and soil co 2 fluxes two different statistical treatments were applied the multiple linear regression mlr and the principal component regression pcr these approaches allow to quantify the weight of each environmental factor on the two gas species and show a strong influence of some parameters on the gas transfer processes through soils the residual values of radon and co 2 flux i e the values obtained after correction for the environmental influence were then compared with the eruptive episodes that occurred at stromboli during the analysed time span 2007 2011 but no clear correlations emerge between soil gas release and volcanic activity this is probably due to i the distal location of the monitoring stations with respect to the active craters and to ii the fact that during the investigated period no major eruptive phenomena paroxysmal explosion flank eruption occurred comparison of mlr and pcr methods in time series analysis indicates that mlr can be more easily applied to real time data processing in monitoring of open conduit active volcanoes like stromboli where the transition to an eruptive phase may occur in relatively short times

paleozoic accretion and cenozoic redeformation of the chinese tien shan range central asia the tien shan range in central asia contains two late paleozoic sutures the older southern suture marks the collision of a passive margin at the north of the tarim block and an active continental margin subduction under the latter was to the north the younger northern suture separates a northern carboniferous island arc from an active continental margin developed over a south dipping subduction zone the subduction direction under the island arc is unknown mesozoic elastics were deposited over the doubly sutured orogen rate and energy of sedimentation waned until deposition of oligocene conglomerates above a regional unconformity interpreted as marking the onset of deformation induced by the india asia collision molasse deposition accelerated in pliocene and quaternary time and deposition continues today as active thrusts generate relief paleozoic structures control the gross divergence of cenozoic thrusts across the orogen