dating young zircon a case study from southeast asian megacrysts abstract u pb geochronology of quaternary zircon crystals is challenging due to their low levels of radiogenic pb the importance of accurate common pb correction and the potential need for secular disequilibrium correction u th he dating offers an independent benchmark for the quality of u pb data and their reduction including the various corrections as the closure temperature of the he system in zircon is 900 c hence u pb ages must predate u th he ages or at least be equal to them in the case of rapid cooling analyses of southeast asian mantle derived zircon megacrysts from tram poung tr tok phrom to bang kacha ba and pailin pa provide new information about their pre eruptive and eruptive history sims u pb zircon ages of 6 7 3 4 ma tr 2 45 0 23 ma to 1 44 0 13 ma ba and 0 97 0 41 ma pa correspond to u th he ages of 5 30 0 52 ma tr 2 42 0 10 ma to 1 05 0 05 ma ba and 0 91 0 02 ma pa respectively the youngest of these u pb ages pa is corroborated by la icpms mapping of a grain that yields an age of 1 017 0 067 ma the grain mapping reveals no evidence for pb diffusion and the calculated pb diffusion temperatures for these megacrysts of 1110 1250 c are significantly greater than ti in zircon apparent temperatures of 659 c these observations may imply that the u pb ages reflect magmatic crystallization and hence the close similarity of the u pb and u th he dates observed in all samples documents high zircon megacryst growth rates of 1 10 12 to to 2 10 14 cm s tr

tropical glaciers recorders and indicators of climate change are disappearing globally in this paper we review the interaction of el nino southern oscillation enso variability and warming trends recorded in ice core records from high altitude tropical glaciers discuss the implications of the warming trends for the glaciers and consider the societal implications of glacier retreat enso has strong impacts on meteorological phenomena that directly or indirectly affect most regions on the planet and their populations many tropical ice fields have provided continuous annually resolved proxy records of climatic and environmental variability preserved in measurable parameters especially oxygen and hydrogen isotopic ratios d 18 o dd and the net mass balance accumulation these records present an opportunity to examine the nature of tropical climate variability in greater detail and to extract new information on linkages between rising temperatures on tropical glaciers and equatorial pacific sea surface temperatures in critical enso indicator regions the long term climate records from a collection of high altitude tropical ice cores provide the longer term context essential for assessing the significance of the magnitude and rate of current climate changes that are in large measure driving glacier retreat the well documented ice loss on quelccaya in the peruvian andes naimona nyi in the himalaya kilimanjaro in eastern africa and the ice fields near puncak jaya in papua indonesia presents a grim future for low latitude glaciers the ongoing melting of these ice fields response is consistent with model predictions for a vertical amplification of temperature in the tropics driver and has serious implications for the people who live in these areas

volcanism and faulting of the campania margin eastern tyrrhenian sea italy a three dimensional visualization of a new volcanic field off campi flegrei by means of information technology 3d digital geologic models are increasingly the best methods of constraining interpretations of geology at depth visualization in three dimensions has allowed us to develop solutions that explain the stratigraphic and structural complexity of the campania margin of the eastern tyrrhenian sea especially the lateral relationships among volcanoes and underlying normal faults using seismic and sequence stratigraphy and structural geology approaches in a dedicated gis environment we interpreted a seismic grid and investigated a subsurface volcanic field in gaeta bay off campi flegrei located within the campania margin the gaeta bay basin fill is characterized by several volcanic units that were analyzed using 2d structure contour maps and isochron maps these volcanoes are comparable in size to the edifices of campi flegrei vesuvius and the submerged volcanoes of the bay of naples their age spans from the lower pleistocene for the isolated v0 volcano sited in central gaeta bay to 0 4 0 1 ma for the volcanic field of southern gaeta bay the study of the interplay between volcanic units and faults allowed us to distinguish 1 the oldest fault buried by the lower pleistocene v0 volcano in central gaeta bay 2 a normal fault swarm ne sw that in the middle pleistocene gave rise to a half graben filled by the v1 v5 volcanic field in southern gaeta bay and 3 post 0 4 ma normal faults that downthrow the v1 and v3 volcanoes we correlated the 1 500 m thick late quaternary volcanoes of southern gaeta bay to the buried lava volcanoes interlayered with volcanoclastic deposits drilled at campi flegrei geothermal wells

retreat of glaciers on puncak jaya irian jaya determined from 2000 and 2002 ikonos satellite images puncak jaya irian jaya indonesia contains the only remaining tropical glaciers in east asia the extent of the ice masses on puncak jaya has been mapped from high resolution ikonos satellite images acquired on 8 june 2000 and 11 june 2002 exclusive of southwall hanging glacier the ice extent on puncak jaya was 2 326km 2 and 2 152km 2 in 2000 and 2002 respectively from 2000 to 2002 the puncak jaya glaciers lost a surface area of 0 174km 2 or 7 48 of their 2000 ice extent comparison of the ikonos based glacier extents with previous glacier extents demonstrates a continuing reduction of ice area on puncak jaya by 2000 ice extent on puncak jaya had reduced by 88 of its maximum neoglacial extent between 1992 and 2000 meren glacier disappeared entirely all remaining ice masses on puncak jaya continue their retreat from their neoglacial maxima comparison of 2000 2002 ice extents with previous extents suggests that these glaciers have not experienced accelerating rates of retreat during the last half of the 20th century if the recession rates observed from 2000 to 2002 continue the remaining ice masses on puncak jaya will melt within 50 years

predictions of changes of glacier mass balance in the nepal himalaya and tibetan plateau a case study of air temperature increase for three glaciers

geochemistry and geochronology of late cenozoic basalts of southeast asia summary geological maps of southeast asia asia 1971 vietnam 1971 thailand 1969 show numerous occurrences of basalt which are considered to be late cenozoic in age occurrences in thailand and western kampuchea are generally small and scattered those in eastern kampuchea southern laos and vietnam are larger and more extensive fig 1 basalt bodies of similar age also occur in malaysia and southern china fig 1 these basalts form a late cenozoic continental volcanic province comparable to those in eastern australia irving and green 1976 and the western united states christiansen and lipman 1972 leeman and rogers 1970 basalts in southeast asia are especially intriguing as they are a major source of gem quality ruby sapphire and zircon fontaine and workman 1978 berrange and jobbins 1976 the purpose of this paper is to describe the distribution geochemistry and age of basalts in southeast asia available geochemical and age data are compiled and combined with new data from previously unstudied areas this is the first known regional synthesis that has been attempted for this large but relatively undocumented basaltic province

oil shale sedimentology and geochemistry in cenozoic mae sot basin thailand the intermontane mae sot basin thailand contains carbonate rich oil shales in which oil yield mineralogy and major and trace element geochemistry are related to the rock type higher grade oil shale is significantly enriched in silicate minerals quartz feldspars clays and analcite relative to carbonates and in dolomite relative to calcite couplets of organic rich and mineral rich laminae increase in mean thickness from 0 080 mm to 0 670 mm from high to low grade oil shale the organic material consists mainly of lamalginite and yields up to 341 l of oil mt 81 8 gal ton on retorting fish and vascular plant fragments are the main megafossils mappable oil shale sequences 10 m 33 ft thick are interstratified with marlstone sandstone sequences 70 m 230 ft thick markov chain analysis applied to stratigraphic sequences indicates that low grade oil shale passes gradually into high grade oil shale and vice versa the strata are interpreted as the deposits of extensive fresh to brackish lakes with oil shale sequences formed in perennial stratified lakes and marlstone sandstone sequences formed in shallow perennial lakes and subaerially exposed flats dolomite in the oil shales was authigenic the systematic changes in mineralogy and geochemistry between rock types probably reflect a gradient in redox potential from the center to the margins of the lake sandstone and siltstone beds and some carbonate laminae are interpret d as density flow deposits and form a significant proportion of the sequences the episodic deposition of oil shales reflects changes in lake level within the enclosed basin probably due to climatic fluctuations on a 24 000 to 46 000 year scale

broad synchrony of a late glacial glacier advance and the highstand of palaeolake tauca in the bolivian altiplano the morphology and sedimentology of glacially influenced fan deltas on massifs at the margin of the southern altiplano bolivia suggest a broadly synchronous expansion of glaciers and palaeolake tauca during the late glacial interval this is shown by sedimentary successions of glacigenic glacifluvial and glacideltaic facies linking palaeoglaciers with palaeolake tauca on the flanks of cerro azanaques and cerro tunupa at altitudes of 3770 3720 m radiocarbon dates from peat overlain by glacial diamict and glacifluvial outwash indicate that glaciers in this area reached their last glacial maximum extent after ca 13 300 14 c yr bp glacifluvial fan deltas contiguous with the moraines confirm that the advance coincided with a highstand of palaeolake tauca radiocarbon dated to the interval ca 13 500 11 500 yr bp modeling of climatic controls on this glacier advance suggests the primary forcing was increased summer wet season moisture possibly amounting to 600 mm above the modern values of 200 400 mm greater cloud cover probably depressed local temperatures and reduced the evaporation rate the consequent rise in effective annual moisture p e comfortably accommodates a palaeolake 48 50 10 3 km 2 in area and up to 100 m deep in the southern altiplano because the palaeoglacier equilibrium line altitudes rose toward the south and west like the gradient of modern precipitation totals we conclude that the increased late glacial moisture was brought by weather systems similar to those of the present but that atmospheric conditions were cloudier and cooler 1997 john wiley sons ltd

basin superposition on the northern margin of the south china sea abstract basin superposition on the northern margin of the south china sea is a product of pulsed basin development with geometries which changed through space and time of changing strain fields and of tectonically inherited pre existing zones of crustal weakness this region of the south china sea was welded together or assembled prior to the cretaceous three distinct episodes of continental disassembly and accompanying basin evolution ensued each episode commencing with rifting and the formation of grabens or half grabens and each terminating with a gentle subsidence phase the major trends of the faults and basins varied from predominantly ne for the first episode through ne ew for the second to ew nw for the third the first episode occurred during the late cretaceous to paleocene as a back arc extensional domain induced by the dip steepening of a subducted oceanic slab the second basin episode of the late eocene to early oligocene was initiated by the collision of the indian plate with the eurasian plate the continued penetration of the former into the latter led to the tectonic escape and subsequent clockwise rotation of the indochina block creating regional transtension and left lateral motion along the red river fault the third episode of basin development occurred during the middle miocene as a reactivated product of this collision owing to the clockwise rotation of indochina the approximately e w trend of the simple shear principal displacement zone changed to northwest by the pliocene the eastward extrusion of south china had exceeded that of indochina reversing the sense of red river fault displacement to right lateral a clockwise rotation of the red river geosuture together with considerations of the influence of zones of inherited crustal weakness provides a model for the observed episodic changes in regional strain such a model best explains the post cretaceous evolution of superimposed basins on the northern margin of the south china sea

the arcuate shape of the umbria marche sabina apennines central italy abstract the umbria marche belt constitutes the most southern and external portion of the northern apennine arc typically convex to the northeast within this the central part the umbria marche sabina apennines is the most elevated and is characterized by a locally more pronounced curvature the umbria marche belt is a thrust belt built mainly by thrust faults affecting a multilayer sedimentary series characterized by levels with markedly different competence the main thrust the m sibillini thrust produced the tectonic superposition of the umbria marche sabina apennines over the most external units represented by the lazio abruzzi platform to the south and the marche abruzzi domain to the north farther north it joins the thrusts buried under the po plain the most important of the more internal thrusts is that of the valnerina the pronounced local curvature of the umbria marche sabina apennines may be due to accentuation of an original arcuate shape this accentuation is probably caused by differential displacement along the two main thrusts during the initial stage of the evolution of the belt late messinian early pliocene at that time this displacement was more important in the northern part where the thrust fronts show a nw se trend than in the southern portion where they are n s trending on account of the lazio abruzzi carbonate platform which perhaps represented a local obstacle to thrusting as for the initial curvature we think that this is determined by older discontinuities which controlled thrust development the final arcuate shape was not substantially changed during the subsequent compressional history of the belt early pliocene middle pliocene

multiple opening and closing of the eastern mediterranean and south china basins the eastern mediterranean east of crete and the south china basin are small ocean basins surrounded by continental masses and are currently undergoing closure they were both formed by the rifting of continental fragments away from large continents a comparison of the geological evolution of the two basins indicates a remarkable similarity in the sequence of evolutionary stages that took place in both basins although the age of these stages is probably different for each of the two the formation of the two basins is a consequence of a much larger process in which large lithospheric plates south and north of the basins move toward each other africa including sinai and arabia toward eurasia and india australia toward eurasia and the pacific each basin went through several stages of evolution during which oceanic crust was created and destroyed during each stage the area of the newly formed oceanic crust was smaller than the area formed in the previous stage it appears as if similar evolutionary patterns also occurred in other marginal and small ocean basins formed by continental rifting

late cenozoic basalt and gabbro in the subsurface in the phetchabun basin thailand implications for the southeast asian volcanic province abstract fragments of basaltic and gabbroic rocks were obtained in cuttings from 15 exploration wells in the na sanun area of the wichian buri sub basin of the phetchabun basin in central thailand the samples represent flows and sills in lacustrine and fluvial sedimentary rocks of the lower to mid miocene wichian buri group mafic igneous units were identified in the sections based on their typically high amplitude seismic reflections confirmed by the examination of several hundred well cuttings and magnetic susceptibility measurements cross sections of the sub basin were constructed on the basis of previously published subsurface interpretations seismic and well data and petrological observations basaltic flows a b e and f have ages of ca 2 ma 16 ma 24 ma and 18 ma based on inferred stratigraphic position gabbroic sill c and dioritic sill g are inferred to be correlative at ca 11 6 ma and differ petrologically from ca 12 8 ma gabbroic sill d major minerals in both basaltic and gabbroic samples are plagioclase ca an50 anorthoclase and augite with pervasive alteration to na and ca zeolite minerals and analcime leucodioritic sill g also contains amphibole and high ti phlogopite overall the rocks show within plate tholeiitic to alkalic characteristics and show similarities to basaltic surface outcrops of similar ages in the wichian buri lop buri area no evidence was seen in the subsurface for the andesitic to rhyolitic rocks of similar ages that occur at surface but their presence cannot be precluded based on our limited data

geometry and kinematics of the north monagas thrust belt venezuela abstract the complex geometry and structural evolution of the north monagas thrust belt were investigated and new exploration trends in this part of eastern venezuela considered the pirital thrust and related structures of the maturin basin are used to discuss the sequence of thrusting and to illustrate the constant balance between erosion and thrust reactivation in a recent fold and thrust belt a careful analysis of the chronostratigraphy and the internal geometry of the foredeep and piggy back syntectonic deposits has been used to constrain balanced cross sections and to establish the kinematics of each individual structure basement involvement is postulated for the pirital thrust which remobilizes previously emplaced cover structures such as the el furrial or orocual structural units it thus probably relates to the pinch out of a shallow decollement level coal measures of the barranquin formation older late jurassic to lower cretaceous evaporites or other mesozoic plastic horizons and to the reactivation of a deeper basement fault the westward emergence of the pirital and el furrial thrusts in a complex transfer area the urica fault is also analysed according to transverse profiles the surficial urica fault does not connect directly to a basement fault but instead acts as a lateral ramp for the el furrial cover unit and as a tear fault for the pirital thrust reactivation of ancient thrust faults also occurs at the rear of the pirital thrust in the west in areas where the topographic profile of the eastern venezuelan ranges has recently been modified by the pirital thrust emplacement these out of sequence thrusts resulting from fault reactivation in the inner parts of the prism are discussed in terms of the preservation of the critical taper they effectively relate directly to erosional processes which significantly decrease the load applied on this portion of the wedge the influence of the sequence of thrusting on the potential plays is considered

cross section balancing in the central apennines an application of locace locace logiciel de construction assistee de coupes equilibrees a recently developed computer program for balancing geological cross sections has been used here on the geology of the central apennines although initially conceived to help explorationists improve seismic interpretations involving no more than two or three fault bounded tectonic units or modules locace is also expected to address regional problems involving complete geologic sections with numerous and complex structures our study area is a cross section across the complex thrust belt and foreland basin of the central apennines because surface mapping and subsurface data conventional seismic profiles with well control do not provide adequate deep constraints on the amount of basement involvement and details of basement fault configuration we present two alternative balanced cross sections in contrast to previous interpretations with only thin skinned deformation both of our hypotheses involve basement thrusting one involves a piggyback thrusting sequence the other involves later emplacement of an out of sequence basement thrust our study demonstrates the ability of locace to restore structurally complex cross sections it also demonstrates that more than one distinct balanced solution can be derived from the same observed near surface geometry and that additional investigations such as deep seismic profiling are required to help resolve the problems at depth

characterization of recent glacier decline in the cordillera real by landsat alos and aster data the changing sizes of glaciers in the cordillera real 16 2 s 68 2 w bolivian andes between 1987 and 2010 were determined by a band ratio method using cloud free landsat tm and alos avnir 2 data from 1987 to 2010 glacier covered areas in the cordillera real were found to have diminished by more than 30 the rate of glacierized area shrinkage within this andean region and particularly of its glaciers has significantly increased in the past 5 years to characterize the change in glacierized area a changing factor k was introduced to capture the effects of topographic factors including elevation slope angle and aspect as identified using aster 30 m global dem data on the huayna potosi mururata charquini illimani and serkhe khollu glaciers this study also further analyzed the huayna potosi glacier and discussed the inhomogeneity of changes in its area with elevation slope aspect and the distribution of solar radiation

cenozoic volcanic and petrochemical provinces of mainland asia abstract mainland asia has been subdivided into 14 distinct volcanic petrochemical provinces alkaline rocks form about 88 of the extrusive materials potassic basalts form 62 of the basaltic clan andesitic rocks are relatively uncommon except near the seaboard and in tibet peralkaline rocks are found in korea and neighboring parts of china the majority of the potassic basalt appear to be derived by variable degrees of partial melting of a mantle with lateral compositional heterogeneity the peak of volcanic activity was during the miocene and corresponded to the collision of the indian continent and the development of back arc basins

the impact of glaciers on the runoff and the reconstruction of mass balance history from hydrological data in the tropical cordillera blanca peru a 41 years series of runoff and precipitation data from the peruvian cordillera blanca demonstrates the high hygric seasonality in this tropical high mountain range in this area glaciers have a crucial impact on runoff which is of essential importance for the highly populated and cultivated valley of the callejon de huaylas particularly during the dry season whereas the mid latitudes glacier runoff amplifies the seasonal variation of runoff the effect of glaciers in the low latitudes is a smoothing one it decreases clearly with the decreasing degree of glaciation in addition particular circumstances of this tropical environment allow the reconstruction of a glacier mass balance history from the hydrological data for the second half of the 20th century it shows a high synchronicity with the global trend of periods with glacier mass loss and gain comparison with length variations of three individual glaciers indicate a rather fast reaction of these glaciers to changes in mass balance although the mass balance variations show some differences among the individual catchment basins the over all trend is uniform a general positive correlation of mass balance variations with soi is obvious but not regular

paleomagnetism of peninsular malaysia abstract paleomagnetic results from upper jurassic to paleocene rocks in peninsular malaysia show counter clockwise ccw rotations while clockwise rotations cw are predominantly found in older rocks continental redbeds of the upper jurassic to lower cretaceous tembeling group have a post folding remagnetization giving a vgp at n54 e29 corresponding to approximately 40 of ccw rotation relative to eurasia and 60 ccw relative to the indochina block khorat plateau samples from cretaceous to paleocene mafic volcanics of the kuantan dike swarm and the segamat basalts give vgps at n59 e47 and n34 e36 respectively these malayasian data are indistinguishable from the late eocene and oligocene vgps reported for borneo and the celebes sea and are similar to the eocene vgps reported for southwest sulawesi and southwest palawan the occurrence of ccw deflected data over this large region suggests that much of malaysia borneo sulawesi and the celebes sea rotated approximately 30 to 40 ccw relative to the geocentric axial dipole gad between the late eocene and the late miocene although not necessarily synchronously nor as a single rigid plate these regional ccw rotations are not consistent with simple extrusion based tectonic models cw declinations have been measured in late triassic granites permian to triassic volcanics and remagnetized paleozoic carbonates the age of this magnetization is poorly understood and may be as old as late triassic or as young as middle or late cretaceous the plate or block rotations giving rise to these directions are correspondingly weakly constrained

tectonic setting of the permo triassic chiang khong volcanic rocks northern thailand based on petrochemical characteristics abstract the inferred permo triassic chiang khong volcanic belt is composed of felsic to mafic volcanic rocks and their pyroclastic equivalents almost all the least altered mafic volcanic rocks are lava flows a few might have occurred as dykes these mafic volcanic rocks are non foliated to weakly foliated and mostly have porphyritic textures the phenocrysts microphenocrysts in porphyritic samples are commonly plagioclase and may include clinopyroxene olivine fe ti oxide apatite and amphibole the matrix of lava flows ranges texturally from felty to trachytic but a few samples show felty to ophitic subophitic and glassy textures whereas that of possible dyke samples is holocrystalline the primary matrix constituents are largely plagioclase and variable proportions of clinopyroxene fe ti oxide amphibole olivine apatite quartz alkali feldspar and or glass all the studied samples have been subjected to greenschist facies regional metamorphism chemically the samples show narrow ranges of least mobile incompatible element ratios and range compositionally from dacite to basalt of tholeiitic series these samples are chemically analogous to those of the tertiary andesite from sardinian rift sardinia italy particularly in terms of least mobile incompatible element ratios accordingly the studied mafic volcanic rocks are interpreted to have formed in a continental volcanic arc however the problem related to the geometry of plate convergence giving rise to the continental volcanic arc still exists

hydrological characteristics of slope deposits in high tropical mountains cordillera real bolivia abstract the hydrological processes within slope deposits are not well known particularly for high tropical mountains with climatic conditions giving seasonal contrasts in the hydrological cycle measurements have been taken in a high andean valley of the cordillera real bolivia with the aim to determine the role of the slope deposits in the framework of a hydraulic modelling different transfer time measurements combined with morphometrical and sedimentological analysis were carried out on three talus slopes and two moraines during the rainy season after injection of salt the electrical conductivity of the water in slope deposits springs is monitored to estimate transfer velocities the hydrological behaviour of these slope deposits depends on the season in the dry season all the water infiltrates and there is no visible outlet during the wet season one part soaks in and gives springs down slope the lag times estimated by the measurement of tracer velocity demonstrate that these slope deposits delayed the flow depending on the type of deposit the delay is at least 24 h in the case of the talus slopes and more than 48 h in the case of lateral moraines

contamination of surface waters by mining wastes in the milluni valley cordillera real bolivia mineralogical and hydrological influences this study is one of very few dealing with mining waste contamination in high altitude tropical latitude areas exploited during the last century geochemical mineralogical and hydrological characterizations of potentially harmful elements phes in surface waters and sediments were performed in the milluni valley main reservoir of water supply of la paz bolivia 4000 m a s l throughout different seasons during 2002 2004 to identify contamination sources and sinks and contamination control parameters phe concentrations greatly exceeded the world health organization water guidelines for human consumption the very acidic conditions which resulted from the oxidation of sulfide minerals in mining waste favoured the enrichment of dissolved phes cd zn as cu ni pb sn in surface waters downstream from the mine stream and lake sediments mining waste and bedrock showed the highest phe content in the mining area with the exception of fe the phes were derived from specific minerals fe pyrite zn cd sphalerite as fe arsenopyrite cu fe chalcopyrite pb galena sn cassiterite but the mining was responsible for phes availability most of the phes were extremely mobile as fe pb cd zn cu sn in the mining wastes and the sediments downstream from the mine ph and oxyhydroxides mainly explained the contrasted availability of zn mostly in labile fractions and as associated with fe oxyhydroxides unexpectedly pb zn as and fe were significantly attenuated by organic matter in acidic lake sediments hydrological conditions highly influenced the behaviours of major elements and phes during wet seasons major elements were diluted by meteoric waters whereas phes increased due to the dissolution of sulfides and unstable tertiary minerals that formed during dry seasons this is particularly obvious at the beginning of the wet season and contributes to flushes of element transport downstream the high altitude of the study area compensates for the tropical latitude rendering the geochemical behaviour of contaminants similar to that of temperate and cold regions these results might be representative of geochemical processes in ore deposits located in the high andes plateau and of their influence on phe concentrations within the upper amazon basin although mining activities in this region stopped 10 years ago the impact of mining waste on water quality remains a serious environmental problem

seismotectonics of the calabrian arc abstract relocation of intermediate and deep earthquakes of tyrrhenian sea area through joint hypocenter determination for the period 1962 1979 has allowed a more detailed definition of the geometry of this peculiar benioff zone earthquakes dip along a quasi vertical plane to 250 km depth there is a 50 dip in the 250 340 km depth range and a low dip angle to 480 km depth the structure sketched from the hypocenters is almost continuous but most energy has been released in the 230 340 km depth interval an evaluation of fault plane solutions of intermediate earthquakes in this area indicates predominance of down dip compressions in the central part of the slab at the border strike slip motion occurs independent of depth some earthquakes that occurred at intermediate depth less than 100 km along the ionian margin of calabria show predominance of reverse faulting with the p axis oriented se nw however shallow earthquakes in the calabria sicily region indicate a more complex motion with predominance of normal faulting a possible interpretation of these features according to the available geological history which involves subduction of continental lithosphere is discussed

deflection gravity anomalies and tectonics of doubly subducted continental lithosphere adriatic and ionian seas three profiles across the southern adriatic and northern ionian seas span an intermediate foreland area that is or has recently been subducted both westward under the apennine calabrian thrust belt and eastward under the hellenide belt gravity and deflection data from the base of the pliocene along the three profiles are qualitatively similar to those predicted for a thin elastic sheet subject to end loads at both plate ends more detailed analysis of the profiles shows very good agreement between observations and predictions if the intermediate foreland lithosphere is treated as a thin elastic sheet with an effective elastic thickness between about 15 and 20 km equivalent to a flexural rigidity between 2 1022 and 6 1022 nm these results coupled with seismicity data suggest that active convergence within the hellenides extends as far north as southwestern yugoslavia analysis of the northernmost profile across the southern adriatic sea shows a well constrained elastic plate thickness of 14 km and an initial water depth prior to loading of about 1 km the distance between the two subduction systems on this profile is estimated at about 275 km analysis of the two more southerly profiles yields a minimum effective elastic plate thickness of about 15 km but no maximum value could be determined the initial water depths for these two profiles are well constrained at 1 3 and 1 6 km prior to loading and the distance between the two subduction systems is estimated at about 175 km on both profiles along the northwest trend of the two opposing subduction systems the change in distance between the two systems occurs abruptly and the hellenic subduction system appears to be segmented into a series of northwest trending roughly linear subduction segments the calculated deflection profiles also show pronounced asymmetry on the northernmost profile and an opposite sense of asymmety on the southernmost profile

small glaciers disappearing in the tropical andes a case study in bolivia glaciar chacaltaya 16 o s glaciar chacaltaya is an easily accessible glacier located close to la paz bolivia since 1991 information has been collected about the evolution of this glacier since the little ice age with a focus on the last six decades the data considered in this study are monthly mass balance measurements yearly mappings of the surface topography and a map of the glacier bed given by ground penetrating radar survey a drastic shrinkage of ice has been observed since the early 1980s with a mean deficit about 1 m a 1 w e from 1992 to 1998 the glacier lost 40 of its average thickness and two thirds of its total volume and the surface area was reduced by 40 with a mean estimated equilibrium line altitude lying above its upper reach the glacier has been continuously exposed to a dominant ablation on the whole surface area if the recent climatic conditions continue a complete extinction of this glacier in the next 15 years can be expected glaciar chacaltaya is representative of the glaciers of the bolivian eastern cordilleras 80 of which are small glaciers 0 5 km2 a probable extinction of these glaciers in the near future could seriously affect the hydrological regime and the water resources of the high elevation basins

late quaternary glaciation in the tropics future research directions abstract glacier snowline depressions in the tropics of 800 1000 m indicate an atmospheric cooling of 5 7 c during the late pleistocene such a temperature depression and the presence of large glaciers in the tropics in the past suggests that on glacial interglacial time scales the tropics have undergone substantial climatic and hydrologic change however uncertainties in the chronology of glaciation the response of glacial mass balance in the tropics to a variety of climate forcings and the relation of proxy records in alpine regions to synoptic tropical paleoclimate limit the full utility of the snowline proxy future research in these three areas will provide information on the phasing of climate change in the tropics in comparison to higher latitude regions and the correspondence of tropical glaciation to large scale changes in precipitation temperature and solar radiation

can the snowline be used as an indicator of the equilibrium line and mass balance for glaciers in the outer tropics because the glacier snowline is easy to identify on optical satellite images and because in certain conditions it can be used as an indicator of the equilibrium line it may be a relevant parameter for the study of the relationships between climate and glaciers although several studies have shown that the snowline altitude sla at the end of the hydrological year is a good indicator of the equilibrium line altitude ela for mid latitude glaciers such a relationship remains conjectural for tropical glaciers indeed unlike in mid latitudes tropical climate conditions result in a distinct seasonality of accumulation ablation processes we examine this relationship using direct field ela and mass balance measurements made on glaciar zongo bolivia 168 s and glaciar artesonraju peru 98 s and the sla retrieved from satellite images acquired in the past two decades we show that on glaciers in the outer tropics 1 ablation is reduced during the dry season in austral winter may august the sla does not change much and satellite images acquired between may and august could be used to compute the sla and 2 the highest sla detected on a number of satellite images acquired during the dry season provides a good estimate of the annual ela however as snowfall events can occur during the dry season the sla detected on satellite images tends to underestimate the ela thus we recommend validating the sla computed from satellite images with field data collected on a benchmark glacier before measuring the sla on other glaciers in the same mountain range for which no field data are available this study is a major step towards extending the measurement of glacier parameters ela and mass balance at the scale of a whole mountain range in the outer tropics to better document the relationships between climate and glaciers

tectonic controls on the late miocene holocene volcanic eruptions of the tengchong volcanic field along the southeastern margin of the tibetan plateau abstract the tengchong volcanic field located along the southeastern margin of the tibetan plateau experienced multiple eruption stages since the late miocene including time intervals of 5 5 4 0 ma 3 9 0 9 ma 0 8 0 01 ma and younger than 0 01 ma these eruption stages produced different volcanic rocks principally basaltic and basaltic andesite series at the same time or prior to volcanic eruptions in the tengchong volcanic field ne nne trending rift basins and ns striking normal faults formed during the late miocene pliocene in addition rapid exhumation of the neighboring mountains occurred at 6 5 ma constrained by apatite fission track dating and its thermochronological modeling at present the state of stress in the tengchong volcanic field and its surroundings is nne ne compression and wnw nw extension based on seismic foci mechanisms petrologic and geochemical data indicate that the source of the tengchong volcanic rocks belongs to an intracontinental tectonic setting but not a subduction or collision zone between indian and eurasian plates since the late miocene the dextral strike slip motion of the sagaing fault induced e w extension the sagaing dextral strike slip motion might disturb the lower crust upper mantle of the tengchong block resulting in the partial melting of the upper mantle which in turn induced volcanic eruptions characterized by mature island arc features

floodplain deposits channel changes and riverbank stratigraphy of the mekong river area at the 14th century city of chiang saen northern thailand abstract riverbank stratigraphy and paleochannel patterns of the mekong river at chiang saen provide a geoarchaeological framework to explore for evidence of neolithic bronze age ad 5th century yonok and ad 14 16th century lan na cultures typical bank stratigraphy charted on the thailand side is imbricate cobble gravel overlain by 5 10 m of reddish brown sandy silt the silt section is composed chiefly of 1 2 to 2 m thick layers of massive silt without paleosols interpreted as near channel floodplain and gently inclined levee deposits laid down by episodic infrequent large floods the surface soil is dark brown clay loam 20 m since lan na time and has exposed a silt filled moat a radiocarbon age of 1475 cal yr ad was obtained from charcoal at the bottom of the moat beneath 5 6 m of silt lag material from erosion of the silt banks contains neolithic and bronze age artifacts out of stratigraphic context as well as ceramics and bricks of lan na age these artifacts as well neolithic artifacts obtained from a 1972 excavation near the mouth of the kham river indicate long human habitation of this riverbank area in northern thailand the mekong is mostly in a bedrock canyon but shifting topography along the active strike slip mae chan fault has formed the upstream 2 5 km wide floodplain at chiang saen and downstream has diverted the river into a broad s shaped loop in the otherwise straight course of the river a 1 7 ma basalt within the bedrock channel 45 km downstream of chiang saen indicates little vertical incision by the river satellite images show former channels in the chiang saen area meander point bar scrolls radii of curvature 1 2 km and floodplain edges as arcuate cuts of similar curvature into the saprolite mantled bedrock hills these features indicate channel avulsion occurred by meander loop cutoff in the past brick buddhist monuments of the 14th 16th century were built upon the floodplain with meander features on the thai and laos side of the river indicating that these meandering channel features and the broader floodplain are mostly older than 600 years

contribution of glacier runoff to water resources of la paz city bolivia 16 s the supply of glacier water to la paz city bolivia between 1963 and 2006 was assessed at annual and seasonal timescales based on the mass balance quantification of 70 glaciers located within the drainage basins of la paz glaciers contributed 15 of water resources at an annual scale 14 in the wet season 27 in the dry season uncertainties in our estimation are related to the assumed constant precipitation 0 5 for ice free areas and up to 6 5 for glaciated areas the constant runoff coefficient 1 the surface areas of the glaciers and catchments 5 and the mean mass balance uncertainty of the 21 glaciers used to obtain the mass balance of the 70 glaciers 12 of the total discharge despite the loss of 50 of the glacierized area during the study period runoff at la paz did not change significantly showing that increase in ice melt rates compensated for reduction in the surface area of the glaciers in the future assuming complete disappearance of the glaciers and no change in precipitation runoff should diminish by 12 at an annual scale 9 during the wet season and 24 during the dry season

tropical climate and glacier hydrology a case study in bolivia runoff from intertropical glaciers is highly variable indicating that they are greatly affected by climatic changes peculiar to tropical climates the 3 km2 basin presented in this case study lies in the cordillera real of bolivia and is 77 covered by glacier ice ranging in elevation from 6000 to 4830 m a s l a comparison of 2 years of study demonstrates the peculiar feature of intertropical glaciers that accumulation and melting periods coincide during the rainy season during the first hydrological year 1991 1992 runoff was 1793 mm for an average precipitation on the glacier of approximately 916 mm during the second year 1992 1993 runoff was 1080 mm for a precipitation of 1060 mm solar radiation and daily mean duration with positive temperature on the ablation zone are the parameters best explaining variation in monthly runoff gauge readings taken downstream enable discharge from the glacier to be established over a period of nearly 20 years the most prominent events coincide with significantly negative values of the southern oscillation index often linked to el nino southern oscillation enso phenomena in conclusion results show that these intertropical glaciers are receding rapidly as precipitation does not compensate for loss from melting

el nino southern oscillation events recorded in the stratigraphy of the tropical quelccaya ice cap peru snow accumulation measured during 1982 1983 on the quelccaya ice cap peru was 70 percent of the average from 1975 through 1983 inspection of 19 years 1964 through 1983 of accumulation measured near the summit of quelccaya reveals a substantial decrease 30 percent in association with the last five el nino southern oscillation enso occurrences in the equatorial pacific the enso phenomenon is now recognized as a global event arising from large scale interactions between the ocean and the atmosphere understanding this extreme event with the goal of prediction requires a record of past occurrences the quelccaya ice cap which contains 1500 years of annually accumulated ice layers may provide a long and detailed record of the most extreme enso events

structural styles chronology rates of deformation and time space relationships in the umbria marche thrust system central apennines italy structural interpretation of geological and geophysical data available for the central apennines italy allowed us to draw balance and restore three geological profiles across the external zones of the umbria marche thrust system and to evaluate the timing and rates of deformation in a roughly 4 ma time window from late messinian to late pleistocene time from this data set we established a general correlation between spacing l and thickness d of the thrust sheets which was used as a depth correction factor for deriving local versus regional depths to the sole thrust and a time space relationship between the closing time of activity of each thrust and the distance x from a reference point within the system

the role of salt in fold and thrust belts davis d m and engelder t 1985 the role of salt in fold and thrust belts in n l carter and s uycda editors collision tectonics deformation of continental lithosphere tectonophysics 119 67 88 the style of deformation in thin skinned fold and thrust belts is critically dependent upon the resistance to sliding along the detachment between the mass of deforming sediments and the underlying rocks evaporites can provide an extremely weak horizon within which a basal detachment can form and along which only a relatively small shear traction can be supported fold and thrust belts that form atop a salt layer such as the appalachian plateau the franklin mountains in northwestern canada and the jura of the alps among others share several readily observable characteristics as predicted by a simple mechanical model for fold and thrust belts a detachment in salt permits a thrust belt to have an extremely narrow cross sectional taper in addition predicted orientations of the principal stress axes over a salt dtcollement are consistent with the commonly observed lack of a consistently dominant vergence direction of structures within the thrust belt other common attributes of salt basal thin skinned deformation include the presence of several widely but regularly spaced folds and abrupt changes in deformational style at the edge of the salt basin

building the 3 d jigsaw puzzle applications of sequence stratigraphy to 3 d reservoir characterization permian basin reservoir characterization involves the quantification integration reduction and analysis of geological petrophysical seismic and engineering data this is no small task a principal goal of reservoir characterization is to derive a spatial understanding of interwell heterogeneity traditionally geologic attempts to characterize interwell heterogeneity have been done using hand drawn or computer generated two dimensional 2 d maps and cross sections results can be improved dramatically using three dimensional 3 d interpretation and analysis techniques three dimensional reservoir characterization requires the same input data used in 2 d approaches and the cost is equal to and commonly lower than traditional 2 d methods the product of 3 d reservoir characterization is a 3 d reservoir model the language used to communicate the results of a 3 d reservoir model is visualization i e visual images of numerical data all of the available log and core data in a model area are incorporated in a 3 d model but the data are depicted as colored cells rather than as log traces the integrity of the 3 d reservoir model is largely a function of the stratigraphic framework interpreting the correct stratigraphic framework for a subsurface reservoir is the most difficult and creative part of the 3 d modeling process sequence and seismic str tigraphic interpretation provide the best stratigraphic framework for 3 d reservoir modeling the purpose of this paper is to discuss the process of 3 d deterministic reservoir modeling and to illustrate the advantages of using a sequence stratigraphic framework in 3 d modeling mixed carbonate and siliciclastic sediment outcrop and subsurface examples from the permian basin of west texas and new mexico will be used as examples but the concepts and techniques can be applied to reservoirs of any age three dimensional reservoir modeling results in an improved geologic interpretation provides a means of integrating geological petrophysical geophysical and engineering data and allows for immediate model updates as new data are acquired as a result of 3 d reservoir characterization reservoir management decisions data quality control volumetric calculations numerical sim lation input and communication between disciplines are improved

glacier decline between 1963 and 2006 in the cordillera real bolivia 1 the volume changes of 21 glaciers in the cordillera real have been determined between 1963 and 2006 using photogrammetric measurements these data form the longest series of mass balances obtained with such accuracy in the tropical andes our analysis reveals that temporal mass balance fluctuations are similar revealing a common response to climate over the entire studied region the mass of these glaciers has clearly been decreasing since 1975 without any significant acceleration of this trend over recent years we have found a clear relationship between the average mass balance of these glaciers as a function of exposure and altitude from this relationship the ice volume loss of 376 glaciers has been assessed in this region the results show that these glaciers lost 43 of their volume between 1963 and 2006 essentially over the 1975 2006 period and 48 of their surface area between 1975 and 2006

3d geometrical modelling of post foliation deformations in metamorphic terrains syros cyclades greece superposed to ductile syn metamorphic deformations post foliation deformations affect metamorphic units during their exhumation understanding the role of such deformations in the structuration of metamorphic units is key for understanding the tectonic evolution of convergence zones we characterize post foliations deformations using 3d modelling which is a first order tool to describe complex geological structures but a challenging task where based only on surface data we propose a modelling procedure that combines fast draft models interpolation of orientation data with more complex ones where the structural context is better understood implicit modelling allowing us to build a 3d geometrical model of syros island blueschists cyclades based on field data with our approach the 3d model is able to capture the complex present day geometry of the island mainly controlled by the su perposition of three types of post metamorphic deformations affecting the original metamorphic pile i a top to south ramp flat extensional system that dominates the overall island structure ii large scale folding of the metamorphic units associated with ramp flat extensional system and iii steeply dipping normal faults trending dominantly nnw sse and ew the 3d surfaces produced by this method match outcrop data are geologically consistent and provide reasonable estimates of geological structures in poorly constrained areas

holocene hydrological reconstructions from stable isotopes and paleolimnology cordillera real bolivia multiproxy analyses of sediment cores from lago taypi chaka kkota ltck cordillera real bolivia provide a record of drier conditions following late pleistocene deglaciation culminating in pronounced aridity between 6 2 and 2 3 ka b p today ltck is a glacial fed lake that is relatively insensitive to changes in p e because it is largely bu ered from dry season draw down through the year round supply of glacial meltwater this was not the case during the middle to late holocene when glaciers were absent from the watershed lake water d18o values inferred from d18o analysis of sediment cellulose range from 12 9 to 5 3 and average 8 7 between 6 2 and 2 3 ka b p modern lake water d18o from ltck averages 14 8 which is compatible with the d18o 8 value of 14 3 for the surface sediment cellulose analyses of d18o from modern surface waters in 23 lakes that span the range from glacial fed to closed basin vary from 16 6 to 2 5 this approximates the magnitude of the down core shift in d18o 8 values in ltck during the middle to late holocene from 12 9 to 5 3 strong paleohydrologic change during the middle holocene is also evident in diatom assemblages that consist of shallow water non glacial periphytic taxa and bulk organic d13c and d15n that show increases likely resulting from degradation of lacustrine organic matter periodically exposed to subaerial conditions neoglaciation began after 2 3 ka b p as indicated by changes in the composition of the sediments lower d18o values and a return to diatom assemblages characteristic of the glacial sediments that formed during the late pleistocene collectively these data indicate that the past 2 3 ka b p have been the wettest interval during the holocene millennial scale shifts in the paleohydrologic record of ltck during the early to middle holocene conform to other regional paleoclimatic time series including lake titicaca and nevado sajama and may be driven by insolation and resultant changes in atmospheric circulation and moisture supply in contrast an apparent 1200 year lag in the onset of wetter conditions at ltck 2 3 ka b p compared to lake titicaca 3 5 ka b p provides evidence for variable sub regional hydrologic response to climate change during the middle to late holocene 2000 elsevier science ltd all rights reserved

the calabrian arc and the ionian sea in the dynamic evolution of the central mediterranean in the central mediterranean area it is possible to recognize three main realms the tyrrhenian sea the pelagian block and the ionian block these domains are limited by important fracture zones that are easily recognizable on land and offshore these fracture zones can be grouped into four main trends 1 the nw se trend which is characterized by dextral horizontal movements 2 the ne sw trend which is generally characterized by sinistral lateral horizontal movements 3 the e w trend which also shows dextral shear movements and 4 the n s trend which is characterized by normal faults only the tyrrhenian sea realm is characterized by a thinned crust of oceanic type and is connected to the apenninic chain by means of listric faults from a geophysical point of view the area shows a high heat flow which follows the main structural trends and positive gravimetric anomalies which are compatible with seismic refraction data and can be explained by the proposed model the pelagian block shows a continental crust about 20 km thick which progressively increases beneath the sicilian chain here an abrupt interruption with the tyrrhenian block takes place in the pelagian realm rifting processes developed according to the nw se and n s trend the n s trend characterizes the westernmost zone of the realm where volcanic processes and a relatively high heat flow can also be observed the ionian block is characterized by the following a thinned crust 17 20 km which increases 40 km towards the southern calabrian chain a thick sedimentary sequence high positive bouguer anomalies 300 mgal and very low heat flow 50 mw m 2 geophysical and structural analyses allowed us to evaluate the post tortonian evolution of the whole area under consideration this evolution resulted in continental crust formation according to a rigid plastic deformation model according to our model the ionian block can be considered as a domain characterized by a thinned continental crust and affected by intrusive material derived from the upper mantle furthermore this domain of probably jurassic age can be considered as a pelagic basin bordered by the pelagian block to the west and by the apulian block to the east northeast this basin according to its position with respect to the apenninic and sicilian chains has not been affected by tectogenesis and still represents a site of continuous sedimentation from a kinematic point of view the ionian realm can be linked with the pelagian block shifting towards the east northeast whereas it is limited towards the north by an e w fracture zone which regulates the opening of the tyrrhenian sea and the counterclockwise rotation of the apenninic chain according to the proposed model the opening of the tyrrhenian sea can be considered as a megaextension fracture which developed parallel to the maximum principal stress direction and evolved as a triangular shaped structural feature in preparing the model the authors have taken into account a large set of data collected both on land and offshore

origin of zircon megacrysts from cenozoic basalts in northeastern cambodia evidence from u pb age hf o isotopes and inclusions abstractzircon megacrysts found in basalts may provide a window into metasomatic processes and element transport in the upper mantle however little is known about the formation conditions of these zircons here we report u pb ages hf o isotope compositions trace element data and mineral inclusion analyses for six large fragments of zircon megacrysts from the gem village in northeastern cambodia the zircons have low contents of u th y p and rare earth elements rees 130 288 ppm the normalized ree pattern is characterized by a steeply rising slope from light rees to heavy rees and positive ce anomalies secondary ion mass spectrometer isotopic analyses on the zircon megacrysts yield a mean u pb age of 0 98 0 04 ma 2 and homogeneous oxygen isotopic composition with a mean 18o value of 5 0 0 18 2 identical to the 18o mantle value the 176hf 177hf values range from 0 282970 0 000024 2 to 0 283040 0 000016 2 with ehf 0 98 ma values of 6 6 9 0 obtained by the laser ablati

upper plate deformation as marker for the northern step fault of the ionian slab tyrrhenian sea central mediterranean abstract the eastern tyrrhenian margin etm the active boundary of the tyrrhenian sea backarc basin is the key for understanding the geodynamics of the central mediterranean numerous seismic tomography studies have been carried out in this region proposing different reconstructions of the lower subducting plate and cause of the slab break off existing beneath the southern apennines however the area and mode of the recent deformation of the tyrrhenian sea are still not fully defined and understood in this study we combine the analysis of a recent seismic tomography model and geological data in order to understand the relationship between the subducting lower plate and the tectonic evolution of the sedimentary basins formed on the upper plate with this aim we interpreted a large data set of seismic reflection profiles and several well logs the results consist in 2d and 3d geological models of the basins sedimentary infill and fault networks taking into account the geological data of the etm and those of the adjacent inner flank of the apennines we observe i a system of linked sedimentary basins developed on a narrow deformation belt bounded by transform fault zones ii a polyphase rifting within the upper plate iii an abrupt change of the direction of extension 90 from ne oriented in the lower pleistocene to se oriented in the middle pleistocene since these etm features are not the typical expressions of the current backarc extensional models we propose a link between the evolution of upper plate and the onset and development of a step subduction transform edge propagator fault along the northern margin of the ionian slab

development of cenozoic basins in thailand abstract there are over 60 cenozoic basins distributed in various parts of thailand both onshore and offshore these basins are mainly n s trending half grabens or grabens and most were initiated in the late oligocene the structural framework of the basins is generally governed by n s trending extensional faults which are spatially related to the movement of the nw se and ne sw trending strike slip faults that have been active since the oligocene the nw se faults are the principal dextral strike slip faults whereas the ne sw faults are the conjugate sinistral strike slip faults the collision of the india craton with southern asia since 40 50 ma caused clockwise rotation of southeast asia and movements on the strike slip faults with the associated development of cenozoic basins in this region four major cenozoic basins mergui pattani malay and phitsanulok contain up to 8000 m of sediments generally the cenozoic fills are continental sediments except in the mergui basin in the andaman sea where the sedimentary fill is mainly marine sediments fluviatile with occasional lacustrine deposits were prominent in the gulf of thailand and onshore basins during the oligocene to early miocene from early to middle miocene widespread perennial lake conditions were well developed in the onshore basins and in the western graben area of the gulf of thailand a change in tectonic and or climatic conditions took place in the middle to late miocene times resulting in the cessation of perennial lake conditions and development of a regional unconformity

monthly balance and water discharge of an inter tropical glacier zongo glacier cordillera real bolivia 16 s measurements of mass balance were performed every month on zongo glacier bolivia simultaneously water discharge temperature and precipita tion data were obtained the first year of the survey 1991 92 was marked by an enso el nino southern oscillation event with high temperature and low precipitation whilst the following year 1992 93 was normal results point to the early and late wet season october december and march may as playing a critical role in the determination of the annual mass balance the wet season is the warmest period of the year and consequently the duration of the wet season is a highly relevant variable in determining mass balance both glaciological and hydrological methods for the determination of the mass balance provide similar results our study confirms that enso events have a major influence on the rapid glacier retreat currently affecting this part of the andes

kinematic evolution of thrust related structures in the umbro romagnan parautochthon northern apennines italy in the internal part of the umbro marchean romagnan apennines the foredeep clastic wedge constituting the neogene part of the sedimentary cover is completely detached from the underlying mesozoic palaeogene succession the resulting umbro romagnan parautochthon consists of tectonostratigraphic units with a general geometry of broad synclinal blocks separated by narrow faulted anticlines thrust related structures observed in the field require thrust ramp propagation to have occurred within already folded rocks therefore they cannot be restored using simple fault bend fold or fault propagation folding models evidence for a passive fold origin in the studied rocks suggests that an early detachment folding episode preceded ramp propagation the latter was facilitated by the enhanced thickness of incompetent material in the cores of detachment anticlines which became the preferential sites where thrust ramps cut up section depending on the trajectory of such thrust ramps different types of fault related structures could develop hanging wall anticlines which give way to monoclinal structures higher up in the section are associated with listric thrust ramps whereas hanging wall monoclines approximately parallel to the underlying fault surface are associated with straight trajectory ramps this kinematic evolution which occurred partly during syn depositional compression also accounts for the observed lithofacies distribution the latter reflects an early differentiation of the foredeep trough into sub basins that are progressively younger towards the foreland the detachment anticlines that originally bounded such sub basins were the site of later thrust propagation leading to a tectonic juxtaposition of different tectonostratigraphic units consisting of broad nw se elongate synclinal blocks

hot ice glaciers in the tropics are making the press tropical glaciers international hydrology series by georg kaser and henry osmaston eds cambridge university press unesco cambridge uk 207 pp isbn 0 521 6333 8 hardcover published 2002

growth processes and melange formation in the southern apennines accretionary wedge abstract the southern apennines owe their present geometry to the subduction of an apulian continental lithospheric slab and are thus best interpreted as an accretionary wedge southward the apenninic thrust front branches on to the still active ionian wedge which is related to the present calabro sicilian subduction the interpretation of conventional seismic reflection profiles and exploration wells combined with geologic field studies biostratigraphy and structural geology provide constraints for a geodynamic model for the post messinian growth of the apenninic prism our model for the apennines is a good analogy for submerged oceanic accretionary prisms in both instances features such as out of sequence thrusts underplating and duplexes are viewed as processes to explain the thickening of accretionary wedges syntectonic terrigenous deposits have accumulated in the synclines developed above the flats of pliocene thrust faults these depocenters represent piggy back basins younger accretion at the eastern border of the accretionary wedge has led to a progressive uplifting and tilting of the already emplaced thrust sheets including a continous westward migration of the depocenters in the piggy back basins during pliocene and early quaternary times a contrary west to east migration of the depocenters locally occurred where preexisting flats of pliocene thrust faults have been refolded rather than only being rotated dewatering processes and effects of overpressures on undercompacted sediment deformations can also be studied in the southern apennines melanges and broken formations form an important component of the trench apparently restricted to the base of tectonic nappes listric normal faults are a major structural element which preserves in combination with the erosion of topographic highs and resedimentation in the piggy back basins a uniform geometric shape critical taper for the prism the age and location of these distensive or gravitational effects are also discussed

frontal part of the northern apennines fold and thrust belt in the romagna marche area italy shallow and deep structural styles in this study surface geological data resulting from a detailed field survey including structural and biostratigraphic analysis have been integrated with subsurface seismic lines and well logs data in order to reconstruct the tectonic evolution of the external zones of the northern italian apennines in the romagna marche foothills and adriatic sea areas this integrated analysis shows 1 a late messinian to lower pleistocene progression of structural development from the hinterland to the foreland of the studied sector of the thrust belt 2 relatively limited 20 southward increasing amounts of shortening obtained by the construction of line length balanced and restored geological cross sections 3 a regional deformation style characterized by the presence of backthrusts associated with most foreland vergent thrust ramps leading to quasi symmetric uplift and a low critical taper for the wedge typical of foreland fold and thrust belts with a weak basal decollement triassic anhydrites in the present case 4 an important influence of basement faulting which despite a general basement cover decoupling appears to control stress localization in the latter producing linkage of basement and cover stuctures in a combination of thin and thick skinned tectonic styles and 5 contrasting structural styles characterizing deep features as imaged by seismic reflection profiles and shallow ones deep stuctures consist of growth anticlines bounded by major thrust ramps and back limb back thrusts separated by broader open synclines both involving a mesozoic paleogene mainly carbonate passive margin succession in the crestal zones of major anticlines shallow structures affecting neogene terrigenous foredeep sediments show a complex pattern of upright to recumbent folds of tens to hundreds of meters wavelength related to minor thrusts and backthrusts deformation of the mesozoic paleogene multilayer appears to be dominated by thrust propagation in the cores of early formed anticlines developed by buckling instabilities the overlying neogene deposits are detached from the carbonate substratum along the base of the foredeep succession bedding parallel slip occurring along this detachment level appears to be accommodated by the complex structures in the crests of major anticlines where the thrusts lramp to the surface cutting up section complex shallow structures interpreted to accommodate at shallow structural levels the deep deformation would therefore represent a geometrical requirement for maintaining strain compatibility across the shallow detachment level located at the base of the foredeep succession

active tectonics in the central apennines and possible implications for seismic hazard analysis in peninsular italy abstract the central apennines fault system cafs of peninsular italy overprints earlier structures of a neogene fold and thrust belt and includes segments characterized by diffuse seismicity distributed within a nnw sse trending zone 50 60 km wide the system has been analysed by means of morphotectonic and structural analysis of exposed active fault segments the resulting fault structure consists of an interconnecting network of roughly n s trending left lateral strike slip segments and mostly nw se oriented transtensional to normal faults evidence for recent activity of cafs structures is provided by faulted middle pleistocene holocene deposits including 30 40 ka old pyroclastites and 40 ka old palustrine sediments fresh scarps in both bedrock and late quaternary continental deposits and decametric lateral offsets locally affecting the post wurmian drainage pattern of the area the regional stress field responsible for the development and evolution of the cafs as inferred from fault slip data is characterized by a nw se compression and by a ne sw extension the cafs pattern and its present day kinematics have been related to left lateral strike slip motion on north south trending crustal faults the existence of deep seated strike slip faults in the central apennines has implications for seismic hazard analysis motion along these structures suggests in fact that coseismic surface faulting is distributed and that cumulative displacements include normal transtensional and strike slip components the seismogenic potential of cafs structures can therefore be best described by multiple rupture models and be better analysed in terms of partial contributions of lower rank features constituting congruent structural associations within the system

episodic rifting and subsidence in the south china sea the south china sea experienced at least three stages of rifting and two intervening stages of sea floor spreading since the early cretaceous its evolution can be described by an episodic model of tectonism one of thermal cooling and subsidence pulsed by temporally and spatially confined heating events analysis of regional geologic and geophysical data suggests episodes of rifting and associated thermal activities initiated during the late cretaceous the late eocene and the late early miocene the rift system corresponding to the first episode trends northeast southwest whereas those of the second and third trend east west these two trends coincide with the orientations of the major tectonic lineations within the basin age estimates from heat flow and bathymetric data suggest the oceanic crust in the southwest subbasin is considerably older 55 ma than that in the northwest 35 36 ma or east 32 ma subbasins the episodic tectonic model is supported by basin subsidence analysis subsidence especially subsidence rate curves derived from the regional well data demonstrates that unlike a classic atlantic passive margin thermal subsidence in the south china sea was punctuated by rapid subsidence events which are chronologically consistent with the rifting episodes in terms of hydrocarbon potential the episodes of rifting and drifting would be conducive to the development of overprinted structures and the deposition of several discrete transgressive packages of source rocks and reservoirs separated by widespread unconformities the thermal maturity of sedimentary organic matter affected by episodic rifting and subsidence may be greater than expected on a purely passive margin of equivalent age that had not experienced repeated heating

evolution of glacial flow and drainage during the ablation season proglacial discharge is controlled by the geometry of the glacial drainage network and by meltwater processes the glacial drainage systems of some alpine glaciers have been characterised using a model based on a proglacial discharge analysis in this paper we apply high frequency systemic analysis to data collected from the baounet glacier french alps during two successive ablation seasons our approach is based on an analysis of the evolution of daily recession curves during the ablation period the observed data are fitted by a single coefficient dependant recession law changes in are compared to variations in the daily discharge amplitude and the time lag between air temperature and proglacial discharge the changes in the values do not appear to be related to changes in the time lag and the amplitude of the daily discharge there were significant variations in the coefficient during the two ablation periods studied here even if there was no time lag or the daily discharge amplitude change high values of correspond to high drainage velocities therefore increases in values can be used as an indicator of the evolution of the glacier s internal drainage network

three dimensional reconstruction of geological surfaces an example of growth strata and turbidite systems from the ainsa basin pyrenees spain the external and internal geometry of four turbidite systems outcropping around the buil syncline ainsa basin spanish pyrenees has been reconstructed with reservoir scale resolution in three dimensions 3 d the irregular geometry of the syncline and the resolution required for the reconstruction cannot be resolved with cross sections therefore reconstruction has been carried out with a new methodology that applies a 3 d dip domain geometrical model and 3 d restoration techniques to achieve reservoir scale resolution in kilometric scale reconstructions this methodology is aimed at resolving 3 d geometries in folded areas and regions with variable thickness stratigraphy the 3 d reconstruction of the buil syncline reveals the synsedimentary growth of an intrabasinal anticline and the foreland lithospheric flexure associated with tectonic loading north of the ainsa basin

structural constraints on the tertiary plate tectonic evolution of italy abstract eight cross sections six of which were balanced and restored using the principles of thin skinned tectonics demonstrate the reinterpretation of the apennine and sicilian mountains as a detached fold and thrust belt the thin skinned interpretation constrains the extent of the restored continental margins and the amount percentage direction and timing of tectonic shortening allowing the development of a plate tectonic model late cretaceous and paleogene subduction to the north beneath the corsica sardinia calabria csc microplate causes rifting from se france and the development of oceanic crust between the two in the oligo miocene the late oligocene collision of adria and northernmost csc pins the northern edge of the csc plate causing its counter clockwise rotation and its mid miocene suturing between italy and sicily the n s convergence of africa and europe with counter clockwise rotation of italy causes shortening in the nne ssw direction in italy and sicily from 20 10 ma the n s compression extrudes calabria to the se causing mio pliocene compression in southern italy and eastern sicily at the same time as extension and alkaline volcanism in central italy

tropical glacier meltwater contribution to stream discharge a case study in the cordillera blanca peru original abstract discharge measurements climate observations and hydrochemical samples gathered monthly 1998 99 in the yanamarey and uruashraju glacier fed catchments of the cordillera blanca peru permit an analysis of the glacier meltwater contribution to stream flow these glacier catchments feed the rio santa which discharges into the pacific ocean based on a water balance computation glacier melt contributes an estimated 35 of the average discharge from the catchments for comparison a volumetric end member mixing model of oxygen isotopes shows glacier melt contributes 30 45 to the total annual discharge based on stream geochemistry discharge from the yanamarey glacier catchment provides 30 of the annual volume discharged from the querococha watershed which is 10 glacierized by analogy the larger rio santa watershed also 10 glacierized receives at least 12 of its annual discharge from melting glacier ice tributary watersheds to the rio santa with larger fractions of glacier cover have less variable runoff and enhanced discharge demonstrating that the glaciers effectively buffer stream discharge seasonally with continued glacier melting stream flow will likely become more variable and there will be less dry season runoff

late local glacial maximum in the central altiplano triggered by cold and locally wet conditions during the paleolake tauca episode 17 15 ka heinrich 1 the timing and causes of the last deglaciation in the southern tropical andes is poorly known in the central altiplano recent studies have focused on whether this tropical highland was deglaciated before synchronously or after the global last glacial maximum 21 ka bp in this study we present a new chronology based on cosmogenic 3he 3he c dating of moraines on cerro tunupa a volcano that is located in the centre of the now vanished lake tauca 19 9 s 67 6 w these new 3he c ages suggest that the tunupa glaciers remained close to their maximum extent until 15 ka bp synchronous with the lake tauca highstand 17 15 ka bp glacial retreat and the demise of lake tauca seem to have occurred rapidly and synchronously within dating uncertainties at 15 ka bp we took advantage of the synchronism of these events to combine a glacier model with a lake model in order to reconstruct precipitation and temperature during the lake tauca highstand this new approach indicates that during the tauca highstand 17 15 ka bp the centre of the altiplano was characterized by temperature 6 5 c cooler and average precipitation higher by a factor ranging between 1 6 and 3 compared to the present cold and wet conditions thus persisted in a significant part of the southern tropical andes during the heinrich 1 event 17 15 ka bp this study also demonstrates the extent to which the snowline of glaciers can be affected by local climatic conditions and emphasizes that efforts to draw global climate inferences from glacial extents must also consider local moisture conditions

silica phase transformations during diagenesis within petrified woods found in fluvial deposits from thailand myanmar abstract transitions in petrified wood samples from several thailand myanmar sites included opal a to opal ct opal a to metastable crystobalite and reordered opal ct quartz the moganite in the samples indicates a potential volcanic silica source for the wood petrifactions silica phase transitions evident under sem include opal a opal ct opal a cuboid quartz pseudocubic and opal ct quartz certain stages of silica transformation and transition processes seem to overlap such overlapping results when lepisphere blades transform to the high crystallinity of prismatic quartz through a solid state mechanism the results provide some insights into the petrified wood genesis in the region thermal inputs into the silicification process may have pre dated final burial of woods in flood deposits

tectonic patterns and cenozoic basalts in the western margin of the south china sea abstract the allochthonous fragments indosinia sibumasu east malaya and southwest kalimantan rifted from gondwanaland and drifted northward indosinia collided with the yangzi huanan terranes in devonian or early carboniferous period and became part of the east asia continent sibumasu collided with east asia continent and east malaya during the indosinian orogeny 220 200 ma the southwest kalimantan terrane probably rifted from the northeast margin of indosinia in the cretaceous at about 50 ma the collision of the indian continent into the eurasian continent led to the fragmentation of asia and was followed by the opening of the andaman sea the clockwise rotation of the indochina plate and the rifting and the opening of the south china sea the late cretaceous alkaline intrusions in the red river area of northern vietnam formed during initial stage of rifting of the south china sea the indian eurasian collision has successively pushed the indochina peninsula in the east southeast direction most of the middle tertiary movements probably occurred along the left lateral red river tonle sap mekong faults concurrent with the opening of most of the eastern south china sea the extensional tectonics along these predominantly strike slip faults may be responsible for the pliocene pleistocene alkaline basalts which extend from the mekong delta northwestward into thailand some basalt outcrops in thailand kampuchea and vietnam appear to trend north south the composition of basalts ranges from tholeiitic to alkalic the basanitoid basalts contain abundant megacrysts of zircon ruby sapphire and spinel the megacrysts probably originated through assimilation of metamorphic rocks deep in the continental crust the cores from the south china sea indicate that the increase in subsidence rate appears in wells during the quaternary it may be related to the increase in quaternary basalt and high heat flow in the western part of the south china sea basin

holocene paleohydrology of the tropical andes from lake records two century scale time series in northern bolivia constrain the ages of abrupt changes in the physical geochemical and biological characteristics of sediments obtained from lakes that formed during deglaciation from the late pleistocene glacial maximum the watersheds of laguna viscachani 16 12 s 68 07 w 3780 m and lago taypi chaka kkota 16 13 s 68 21 w 4300 m located on the eastern and western slopes of the cordillera real respectively contain small cirque glaciers a high resolution chronology of the lake sediments is provided by 23 ams14c dates of discrete macrofossils late pleistocene glaciers retreated rapidly exposing the lake basins between 10 700 and 970014c yr b p the sedimentary facies suggest that after 890014c yr b p glaciers were absent from the watersheds and remained so during the middle holocene an increase in the precipitation evaporation balance is indicated above unconformities dated to 230014c yr b p in both lago taypi chaka kkota and laguna viscachani an abrupt increase in sediment accumulation rates after 140014c yr b p signals the onset of neoglaciation a possible link exists between the observed millennial scale shifts in the regional precipitation evaporation balance and seasonal shifts in tropical insolation

deep penetration seismic soundings across the northern margin of the south china sea twenty reversed two ship expanding spread profiles esps with maximum source receiver offsets of 100 km were collected in three transects across the rifted northern margin of the south china sea source receiver offset versus two way travel time x t data were mapped into the intercept time versus ray parameter p domain and velocity depth solutions were obtained by a combination of sum inversion in the p domain and ray tracing in both the p and x t domains arrivals from the moho were detected on 17 of the esps the depths to moho determined for individual esp interpretations have reproducibilities of 0 1 km to 3 km in most cases the moho depth has been determined to within 1 5 km moho depths determined in this investigation represent a significant improvement over previous estimates of moho along the margin from gravity data variations in present day crustal thickness measured from top of prerift basement to moho are one measure of the amount and nature of the crustal thinning associated with the rifting of continental crust preceding the formation of the adjacent south china sea basin the esp interpretations reveal that across the eastern portion of the south china margin the crust appears to thin more or less continuously toward the continent ocean boundary in the west esp interpretations also show a general trend of seaward crustal thinning but in addition indicate at least two instances of focused localized crustal thinning crustal velocities and the relative proportion of upper crust vp 6 4 km s are used to identify areas of the south china margin with similar and contrasting crustal structures variations in these properties are believed to result primarily from contrasting prerift crustal structure across the margin however magmatic underplating during rifting depth dependent extension and pleistocene igneous intrusions may also have contributed to the variations in present crustal structure reliable information about variations in crustal thickness and velocity structure across and along the south china margin is an important prerequisite to understanding better the nature of the spatially variable rifting processes which dominated the formation of this margin

extension tectonics the neogene opening of the north south trending basins of central thailand paleomagnetic samples were collected from late neogene basalt flows from thailand all of these flows are horizontal and are relatively unaltered in thin section these rocks possess a stable magnetization which is believed to be primary samples from 48 lava flows were collected from sites located within the khorat plateau the chao phraya phitsanulok basin and the mountainous terrane west of the chao phraya phitsanulok basin these data were combined with previously reported late neogene data from five flows from western thailand although the average inclination from the 53 sites is indistiguishable from the expected dipole inclination the average declination has a net clockwise rotation of 13 5 5 8 from the geocentric dipole field furthermore the mean declination values from the 29 flows from the khorat plateau are indistinguishable from the present dipole field direction dm 4 3 7 5 and indistinguishable from the mean declination from 28 late neogene volcanic flows from vietnam in contrast the mean declinations from 24 flows collected from central and western thailand are deflected significantly clockwise dm 24 4 7 7 from the geocentric dipole field direction the differential rotation between western and central thailand versus the khorat plateau suggests that indochina is composed of at least two structural blocks which underwent a different rotational history these observations when combined with geologic and geophysical data from the chao phraya phitsanulok basin gulf of thailand and the intermontane basins of western thailand suggest that the rotations are recording a late neogene phase of e w extension of these basins we suggest that the formation of these basins and the related basaltic volcanism developed in reponse to subduction of the indian plate under western burma we envision the tectonics of this region is similar in style to the basin and range region of the western united states last we have observed field relationships from some of the rhyolites located in the central basin although these rhyolites are reported to be mesozoic or paleozoic in age our field observations and a k ar age date show that at least some of these rhyolites are younger than the basalts we suggest that the rhyolites form a bimodal suite with the basaltic rocks which were erupted in the later stages of the extension

multidecadal to century scale arid episodes on the northern altiplano during the middle holocene abstract we present reconstructions of multidecadal to centennial scale shifts in the hydrologic balance of the northern altiplano during the middle holocene using stable isotopic geochemical and sedimentologic evidence from lake titicaca sediments large downcore changes in the 13corg of bulk organic matter previously shown to be a site specific lake level proxy indicate that extended periods of lake level regression occurred in response to sustained reductions in mean annual precipitation and or increases in air temperature supporting evidence from a floating interval of finely laminated sediments indicates that salinity and stratification were enhanced at lake titicaca during the middle holocene the age model used in this study is based on 7 ams 14c age dates estimated from bulk decalcified sediment from a 60 cm sequence spanning 7200 5600 14c cal yr bp simulations from a hydrological energy balance model of the titicaca basin indicate that the 38 m drop in lake level that preceded the maximum lowstand at 6200 yr bp would require a significant decrease in mean annual precipitation of up to 50 and or a significant increase in mean annual temperature of up to 8 c today the altiplano is often affected by drought during periods of enhanced summertime westerly wind flow which reduces the delivery of moisture from the east this investigation supports the idea of sustained periods of enhanced westerly air flow during the mid holocene and provides additional submillennial scale information about the timing and magnitude of regional drought results of our frequency domain analysis of the floating lamination interval indicate significant power at a decadal periodicity 10 12 yr associated with the schwabe cycle of solar activity frequency domain analysis also reveals power in a 75 year time series of modern lake level we suspect that solar influence on large scale atmospheric circulation features results in changes to the moisture balance in the titicaca basin over decadal and possibly century scale time periods

anomalous heat and mass budget of glaciar zongo bolivia during the 1997 98 el nino year during el nino southern oscillation enso warm events outer tropics glaciers usually experience a deficit of precipitation an increase of air temperature and a strongly negative mass balance at glaciar zongo bolivia this was particularly striking during the vigorous 1997 98 el nino event one of the strongest of the century and which resulted in an annual depth of runoff two thirds higher than normal we compare the energy balance on the glacier between two contrasting cycles 1996 97 la nina year and 1997 98 el nino year due to a 1 3 c increase of annual mean air temperature the sensible heat flux slightly increases from 6 1 to 9 8 w m 2 during the el nino year sublimation is reduced leaving more energy for melting le 18 1 w m 2 in 1996 97 and le 11 6 w m 2 in 1997 98 the main factor responsible for the dramatic increase in melting is the net all wave radiation which is three times higher in 1997 98 than in 1996 97 48 7 and 15 8 w m 2 respectively this sharp increase of net all wave radiation is related to the decrease of albedo due to the precipitation deficit

flow separation on zongo glacier cordillera real bolivia meltwaters collected from the proglacial stream escaping from zongo glacier 2 1 km2 bolivia 16 s have been monitored in order to analyse the internal drainage system of an andean glacier electrical conductivity has been measured sporadically between february 1995 and march 1996 during 16 one day field surveys under various meteorological conditions in summer and winter the mixing model technique based on the electrical conductivity is used for a quantitative separation of discharge which is derived from continuous water level registration tracer experiments mainly uranine dye and nacl salt have been carried out from march to june 1997 to obtain information about the internal drainage system in the tropical andes accumulation only occurs in austral summer whereas ablation occurs throughout the year and is higher during the accumulation season between november and march the assumptions involved in the use of mixing models for analysis of glacial drainage structure are applicable for tropical glaciers because glacial conduits do not suffer complete closure and are permanently supplied by meltwaters even in wintertime two components of discharge are separated an englacial flow originating from surface meltwater which is routed without chemical enrichment and offering low electrical conductivity and a subglacial one routed in contact with bedrock or sediments showing high ionic concentrations electrical conductivity of meltwater varies diurnally inversely to discharge fluctuations according to this behaviour total discharge is mainly formed by the englacial component the drainage structures for englacial and subglacial flow have to be widely interconnected as indicated by diurnal variations of the subglacial discharge comparison of hydrograph separation based on conductivity and on 18o isotope confirms that the subglacial flow is influenced by surface melting a hydrograph separation of the subglacial flow is proposed between a diurnal variable component composed of water coming from the englacial network and a base flow which may vary seasonally the dye tracing experiments confirm the drainage complexity of zongo glacier and demonstrate the interest of identifying three main drainage components 1998 john wiley sons ltd

fission track dating of alluvial zircons and heavy mineral provenance in northeast tasmania three alluvial zircon concentrates from the blue tier region have been fission track dated in a heavy mineral provenance study of cenozoic sediments in ne tasmania zircons in one concentrate are euhedral and are fine grained mostly 0 1 to 0 3 mm dating gave a combined age of 367 15 ma confirming their derivation from upper devonian granites zircons from the other concentrates are rounded and coarser grained mostly 2 5mm they gave a combined age of 46 7 0 6 ma this agrees with the k ar radiometric dates obtained from three blue tier basalts sutherland wellman pers comm some of the geological implications of this study are outlined in this paper

the pearl river mouth basin a rift basin and its geodynamic relationship with the southeastern eurasian margin abstract based on multichannel seismic reflection profiles exploration well data and gravity studies the tectonic development of the pearl river mouth basin is discussed in terms of the geodynamic evolution of the southeastern eurasian margin the area around the pearl river mouth basin has been dominated by two episodes of rifting of the attenuated continental crust along the south china margin from the late cretaceous to the early oligocene the rifting brought about ruptures of various magnitudes in various segments of the basin regional normal faults have been produced and resulted in the formation of three major subbasins zhu 1 zhu 2 and zhu 3 which are separated by local uplifts and are characterized by horst and graben structures regional subsidence prevailed throughout the late oligocene recent period and resulted in a tilted continental shelf upon which rests a unified rift basin the pearl river mouth basin a three stage model involving doming rifting and drifting is proposed for the tectonic evolution of the pearl river mouth basin the uplifting and rifting of the continental crust along the south china margin are related to the late episodes of the yanshan orogeny during the late cretaceous early oligocene period when the intensity of rifting decreased the thermal subsidence of the continental margin of south china prevailed during the late oligocene recent period of the himalaya orogeny

three dimensional visualization of the neogene structures of an external sector of the northern apennines italy a three dimensional 3 d visualization technique is used to build a structural model linking a complex series of thrust sheets in an external area of the northern apennines central italy this foreland fold and thrust belt consists of faulted anticlines and broad syn clines involving a triassic paleogene succession that is detached from the underlying basement reactivation of basement faults has influenced the geometry and kinematics of the overlying structures in a mix of thin skinned and thick skinned tectonics upper de tachment horizons within the sedimentary succession form shallow structures in the crestal zone of the major anticlines all the struc tures are scantily cylindrical and the model demonstrates the soft linkages between oblique and frontal structures through relay ramps

mass balance of glaciar zongo bolivia between 1956 and 2006 using glaciological hydrological and geodetic methods the longest continuous glaciological mass balance time series in the intertropical zone of south america goes back to 1991 on glaciar zongo bolivia photogrammetric and hydrological data have been used to i check the specific net balance over long periods and ii extend the mass balance time series over the last 50 years these data reveal a bias in the glaciological mass balance which can be explained by the field measurement sampling network our study shows a large temporal variability of the surface mass balances in the ablation area and reveals strong relationships between independent surface mass balance data coming from selected ablation areas with numerous data it demonstrates the very large contribution 80 of low elevation ranges one third of the surface to the specific mass balance and consequently the importance of the reduction of the area of the tongue with these new results glaciar zongo offers the longest and most accurate mass balance series in any andean country the dataset shows that glaciar zongo experienced a relatively steady state over the period 1956 75 with even a slight mass gain over 1963 75 and a rapid and continuous decrease since then

late cenozoic subduction complex of sicily abstract besides remnants of hercynian deformations in the peloritani nappe and of pre oligocene alpine structures in the troiani nappe most compressive structures observed in the sicilian accretionary wedge result from the late cenozoic tortonian to present continental subduction of the apulia iblei block and are thus synchronous with distensive structures related to the opening of the tyrrhenian sea syntectonic deposits fill southward migrating foredeeps in a sequential fashion and the dating of these deposits helps to constrain the timing of deformation similarly plio quaternary sediments eroded from the accreted units rest on top of the allochthon in either compressive piggy back depressions or extensional basins the age and configuration of these overlap deposits constrain our reconstructions of the subsurface geometry of the underlying peri tyrrhenian detachment faults or s verging thrust faults post depositional erosion normal faulting and syntectonic filling of basins contribute to maintaining the critical taper of the prism whose geometry is continuously altered owing to frontal accretion underplating and isostatic uplift

australasian impact crater buried under the bolaven volcanic field southern laos the crater and proximal effects of the largest known young meteorite impact on earth have eluded discovery for nearly a century we present 4 lines of evidence that the 0 79 ma impact crater of the australasian tektites lies buried beneath lavas of a long lived 910 km3 volcanic field in southern laos 1 tektite geochemistry implies the presence of young weathered basalts at the site at the time of the impact 2 geologic mapping and 40ar 39ar dates confirm that both pre and postimpact basaltic lavas exist at the proposed impact site and that postimpact basalts wholly cover it 3 a gravity anomaly there may also reflect the presence of a buried 17 13 km crater 4 the nature of an outcrop of thick crudely layered bouldery sandstone and mudstone breccia 10 20 km from the center of the impact and fractured quartz grains within its boulder clasts support its being part of the proximal ejecta blanket

el nino southern oscillation enso influence on a sajama volcano glacier bolivia from 1963 to 1998 as seen from landsat data and aerial photography sajama volcano located in the bolivian altiplano is the southernmost tropical glacier and owing to its situation approximately 100 km east of the pacific coast is well suited to study the el nino southern oscillation phenomenon landsat data from 1972 to 1998 and a 1963 aerial photograph are used to monitor the snow line fluctuations on a selected part of sajama volcano we assume that a few months after the rainy season the snow line is representative of the previous rainy season if no recent snowfall has occurred by observing precipitation from the stations surrounding sajama volcano and by verifying snow presence on surrounding summits we detect images with recent snowfall likely to disturb the climatic significance of the snow line a snow line evolution model takes into account the different image acquisition dates and adjusts the snow line elevation accordingly for the middle of the dry season a progressive rise of the snow line elevation is observed from 1963 to 1998 with a sustained rise from 1984 to 1990 the snow line altitude is related to the southern oscillation index even after the high precipitation of the 1996 1997 wet season the following el nino 1997 1998 leads to a substantial rise of the snow line the snow line elevation is related primarily to the total rainy season precipitation and to a lesser degree to the maximum monthly mean temperature of the warmest month thus confirming a greater snow line sensitivity to precipitation than to temperature

fluctuations of glaciers in the tropical andes over the last millennium and palaeoclimatic implications a review abstract the aim of this paper is to document the evolution of glaciers in the tropical andes between 10 n and 16 s for the last millennium based on moraines dated by lichenometry and radiocarbon lake sediment records and historical documents viewed collectively several glacial advances occurred synchronously the first advance is dated around ad 1200 1350 the maximum glacial extent mge defined as the furthest down valley extent recorded synchronously by the majority of glaciers occurred around 1630 1680 in bolivia and peru the outer tropics and around ad 1730 in ecuador colombia and venezuela the inner tropics subsequently during the 18th and 19th centuries glaciers retreated continuously with only minor synchronous readvances in the outer tropics minor glacial advances occurred around 1730 1760 1800 1850 and 1870 in the inner tropics synchronous minor advances occurred around 1760 1820 and 1880 between the mge and the early 20th century glaciers lost about 30 of their total length the retreat was slow between the 17th and 18th centuries but then became more marked use of the accumulation area ratio aar method or historical observations in the different cordilleras revealed an increase in the equilibrium line altitude ela of about 300 m from the mge onward palaeoclimatic hypotheses based on glaciological models run in different countries suggest a cool and humid period in the 16 18th centuries followed by a colder and drier period in the 19th century the reduction of glaciers observed from the middle of the 19th century is due to increasingly warmer conditions than before here quantitative estimates are proposed to explain the evolution of the glaciers in venezuela results indicate for the period 1250 1820 that mean air temperatures were 3 2 1 4 c cooler and precipitation was about 22 higher than at present in ecuador temperatures of between 0 8 and 1 1 c lower than today and between 25 and 35 higher accumulation than today appear to have occurred in the 18th century followed by a short drier but colder period at the beginning of the 19th century in bolivia the mge could be a consequence of a decrease in temperature of 1 1 to 1 2 c and a 20 to 30 increase in accumulation or an increase in cloudiness of about 1 2 10 we discuss not only external climatic forcing but also the coincidence between glacier expansion and a decrease in solar irradiance dating uncertainties however have made the role of volcanism in glacier fluctuations impossible to determine finally we discuss the relationships between enso and glacier fluctuations in recent centuries which do not match directly with current knowledge of modern teleconnections between tropical pacific ssts and variations in glacier mass balance

rates of deglaciation during the last glaciation and holocene in the cordillera vilcanota quelccaya ice cap region southeastern peru abstract moraine chronology is combined with digital topography to model deglacial rates of paleoglacier volumes in both the huancane valley on the west side of the quelccaya ice cap and the upismayo valley on the northwest side of the cordillera vilcanota the fastest rates of deglaciation 39 10 5 to 114 10 5 km3 yr 1 and 112 10 5 to 247 10 5 km3 yr 1 for each valley respectively were calculated for the most recent paleoglaciers corresponding to the last few centuries these results are consistent with observations in the venezuelan andes showing high rates of deglaciation since the little ice age these rates also fall within the range of 20th century rates of deglaciation measured on the quelccaya ice cap 29 10 5 to 220 10 5 km3 yr 1 brecher and thompson 1993 thompson 2000 these results imply that rates of deglaciation may fluctuate significantly over time and that high rates of deglaciation may not be exclusive to the late 20th century equilibrium line altitude ela depressions for the ice volumes of the last glaciation modeled here were computed as 230 m for the quelccaya ice cap and 170 m for the cordillera vilcanota maximum ela depressions are lower than previously published

miocene unconformities in the central apennines geodynamic significance and sedimentary basin evolution abstract this paper shows the results obtained from an integrated study geology biostratigraphy and geochemistry carried out on the miocene edimentary deposits in central italy in order to define the timing of the sedimentary basin evolution this paper deals also with the causes of the unconformities recorded in these basins in the miocene deposits of the latina valley and the ernici simbruini mts several unconformities which distinguish different stratigraphic sequences have been recognized d 0 d 1 d 2 d 3 and d 4 for each unconformity a general description together with a geodynamical significance is provided in particular d 0 unconformity appears to be related to a regional tectonic event adria europe collision as a consequence the adria lithosphere folded and the area underwent a regional erosive event d 1 d 2 and d 3 unconformities have had a more local tectonic control since they represent the stratigraphic record of the migration of the apennines thrust belt foredeep system d 1 and d 2 unconformities are related to the late tortonian foredeep stage whereas d 3 is linked to the early messinian piggy back stage moreover the d 4 unconformity which took place during the messinian piggy back stage is strictly linked to the sea level drop of the messinian salinity crisis in this paper the genesis and evolution of a late tortonian foreland basin is also stressed latina valley foredeep basin finally taking into account sequence boundaries nannofossil biostratigraphy and geochemistry isotopic data a comparison with the curve of the 3rd order of the relative coastal onlap haq et al 1988 has been attempted in order to distinguish the unconformities controlled either by tectonic or eustatic processes

the south china sea margins implications for rifting contrasts abstract implications regarding spatially complex continental rifting crustal extension and the subsequent evolution to seafloor spreading are re examined for the northern and southern rifted margins of the south china sea previous seismic studies have shown dramatic differences in the present day crustal thicknesses as the manifestations of the strain experienced during the rifting of the margin of south china although the total crustal extension is presumed to be the same along the margin and adjacent ocean basin the amount of continental crustal extension that occurred is much less along the east and central segments of the margin than along the western segment this difference was accommodated by the early formation of oceanic crust creating the present day south china sea basin adjacent to the eastern margin segment while continued extension of continental crust was sustained to the west using the observed cross sectional areas of extended continental crust derived from deep penetration seismics two end member models of varying rift zone widths and varying initial crustal thicknesses are qualitatively examined for three transects each model implies a time difference in the initiation of seafloor spreading inferred for different segments along the margin the two models examined predict that the oceanic crust of the south china sea basin toward the west did not begin forming until sometime between 6 12 my after its initial formation 32 ma toward the east these results are compatible with crustal age interpretations of marine magnetic anomalies assuming rifting symmetry with conjugate margin segments now residing along the southern portions of the south china sea basin implies that the total width of the zone of rifting in the west was greater than in the east by about a factor of two we suggest the most likely causes of the rifting differences were east west variations in the rheology of the pre rift crust and associated east west variations in the thermal structure of the pre rift lithosphere the calculated widths of rifted continental crust for the northern and southern margins when combined with the differential widths of seafloor generated during the seafloor spreading phase indicate the total crustal extension that occurred is about 1100 km and is remarkably consistent to within 10 for all three eastern central western segments examined

geological development of the central and south vietnamese margin implications for the establishment of the south china sea indochinese escape tectonics and cenozoic volcanism abstract the vietnamese margin forms a key region to the understanding of escape tectonics and the development of the south china sea scs the existing geological reconstructions of the region are restricted to studies of single basins are based on limited amounts of geophysical data or analysis of onshore geological features these models are critically assessed on the basis of interpretation of the most comprehensive 2 d digital seismic database published to date within the area combined with a thorough analysis of existing literature and a new model is presented the vietnamese margin is underlain by a series of paleogene rift basins established through southeastward extrusion of indochina the east vietnam boundary fault evbf forms the almost 1000 km long seaward continuation of the left lateral ailao shan red river shear zone asrrsz toward the southern half of the phu khanh basin the evbf breaks up into discrete segments and splays into the se directed tua hoa fault zone paleogene faults splayed from the evbf and the mae ping shear zone and accommodated the coeval motion of these two major left lateral structural lineaments during the late oligocene basin inversions offshore occurred contemporaneously with initial right lateral inversion along the mae ping shear zone and the onset of major uplift of the metamorphic core complexes along the asrrsz it is suggested that a dramatic change of the regional stress pattern occurred in response to the northward movement of india and the effective coupling of the west burma block and india the later resulting in broadening of the indenting continental mass after the mid oligocene left lateral movements across the offshore evbf decreased and eventually ceased later onshore sinistral movements were accommodated by internal shortening and local clockwise block rotations within the shan thai terrain renewed rifting offshore south vietnam resulted from the jump of the scs spreading axis and subsequent neogene southwestward propagation of continental break up the neogene opening of the scs is viewed as a consequence of a slab pull associated with subduction of the proto scs underneath borneo as offshore neogene escape tectonism had virtually ceased during this phase of rifting right lateral transtension is inferred along n to nw oriented fault zones in the phu khanh and the nam con son basins rifting and by inference seafloor spreading continued until the end of middle miocene time although at significantly reduced rates during the final 5 10 ma termination of seafloor spreading is marked by a distinct latest middle miocene unconformity in the nam con son and the southern phu khanh basins neogene volcanism resulted in the build up of several magmatic structures across the central and south vietnamese margin and induced reactivation of older faults in the phu khanh basin the offshore magmatism heralded widespread volcanism onshore southern indochina associated with a latest neogene uplift and denudation event the uplift led to significantly increased siliciclastic accumulation rates offshore which repressed widespread carbonate deposition

the petrology and mineralogy of mt popa volcano and the nature of the late cenozoic burma volcanic arc mt popa is situated on a line of widely spaced calc alkaline volcanic centres in the central lowlands of burma latites rhyodacites and ignimbrites are interbedded with strongly folded arenaceous sediments of topmost miocene and pliocene age these are overlain unconformably by a composite cone of basalt and basaltic andesite lavas and pyroclastic deposits of pleistocene or early recent age the two groups of lavas are regarded as a single petrographic suite in which several continuous and discontinuous mineral reaction series are recognized phenocryst phases analysed by microprobe are olivine bronzite hypersthene biotite diopsidic augite salite magnesio hastingsite magnesio hornblende titaniferous magnetite bytownite oligoclase and sanidine whole rock analyses are characterized by relatively high k ba sr rb and zr high mg mg fe ratios of 0 85 to 0 65 in both phenocrysts and whole rock high k rb 767 and low sr 87 sr 86 0 70431 and rb sr 0 0155 ratios suggest that the basalts are relatively primitive mantle derived compositions modified slightly by fractionation with negligible crustal contamination the more siliceous lavas may have been derived by fractional crystallization of such magmas at crustal levels this high k calc alkaline suite is typical of a continental margin orogenic environment analyses of contemporaneous lavas from elsewhere in burma define three n s volcanic lines which become more alkaline from w to e the magmatism is attributed to the waning stages of orogeny as eastward subduction of the indian plate beneath china gave way to strike slip movement associated with the andaman sea spreading centre within this tectonic model magmas were probably generated by hydrous mantle melting above dehydrating oceanic crust of the subduction zone

zircon and monazite upb dating of the doi inthanon core complex northern thailand implications for extension within the indosinian orogen abstract the doi inthanon metamorphic core complex occupies a prominent central position within the northwestern thai gneiss belt which has been inferred to be as old as precambrian and as young as permo triassic u pb dating of zircon from core orthogneisses of the complex suggests that the orthogneisses were derived from granitic protoliths with essentially the same late triassic early jurassic age as the mae cham pluton 205 3 4 ma to the west of the doi inthanon complex monazite ages from the orthogneisses indicate that low pressure and high temperature metamorphism and migmatitization occurred in the late cretaceous 84 72 ma limited published radiometric age data from elsewhere in the migmatitic gneiss belt suggest that widespread minor plutonism accompanied this thermal event a younger u pb data of 26 8 0 5 ma for zircon and monazite from the mae klang granite which intruded mylonitic gneisses on the eastern side of the doi inthanon complex indicates that there was also significant plutonism in the late oligocene these u pb ages constrain the development of the complex and hence of the migmatitic gneiss belt as a whole to an interval between late cretaceous and early miocene ductile shearing uplift and tectonic denudation via detachment faulting chronologically overlap the initiation of extensional basin development to the east and southeast of the gneiss belt and imply a genetic connection thus oligocene early miocene thermal rifting from the gulf of thailand northward into mainland thailand may have been the direct product of crustal extension rather than the transtensional product of regional strike slip faulting

geological evolution regional perspectives and hydrocarbon potential of the northwest phu khanh basin offshore central vietnam abstract seismic stratigraphic and structural analyses of the northwest phu khanh basin offshore central vietnam based on 2 d seismic data indicate that the initial rifting began during the latest cretaceous or palaeogene controlled by left lateral transtension along the east vietnam boundary fault zone evbfz and northwest southeast directed extension east of the evbfz rifting stopped due to transpression during middle oligocene times but resumed by left lateral transtension during the late oligocene thick sequences of lacustrine and alluvial sediments were deposited during the palaeogene rift periods the late oligocene rifting ended due to inversion triggered by right lateral wrenching near the palaeogene neogene boundary following the onset of this inversion regional uplift and volcanism took place in the southern half of the study area and contemporaneous subsidence and transgression took place farther north leading to widespread carbonate deposition as the right lateral wrenching decreased during the early neogene thermal subsidence and siliciclastic sedimentation became dominant resulting in the buildup and southward propagation of the shelf slope sediment accumulation and subsidence rates increased after the middle miocene times due to eastward tilting of central vietnam and the adjacent offshore area potential direct hydrocarbon indicators dhis in the phu khanh basin include common amplitude anomalies gas chimney like features and seafloor gas seeps in addition oil seeps are found at dam thi nai immediately landward of the basin geochemical analyses of the oil seeps indicate the existence of at least two early to peak mature source rocks maturation modelling combined with the seismic analysis suggests the likely presence of oil kitchens 40 50 km downdip in the basin and a fairly simple oil migration route the basin is probably charged from lacustrine syn rift mudstones humic coals and fore reef marls potential reservoirs are turbidite lowstand delta shelf and coastal sandstones as well as platform and reef carbonates and fractured basement various structural and stratigraphic traps formed during the palaeogene and early neogene prior to the main stage of petroleum generation