the progressive evolution of a continental climate in southeast central european lowlands during the middle pleistocene recorded in loess paleosol sequences 1 abstract little is known about the long term quaternary climate evolution of central and south east europe because suitable terrestrial paleoenvironmental records are scarce we present a multiproxy record of loess paleosol sequences in the middle and lower danube basins over the past 700 k y in these lowlands the continentality of interglacial climate progressively increased during the middle pleistocene corresponding trends are seen in other climate prox ies in the same region and in the lowlands of the northern black sea but not or less clearly in climate archives from outside these lowlands we conclude that a small scale increase in paleoelevation of central european mountain ranges the alps carpathians and dinarides during the middle pleistocene might be the cause of the progressive increase in climate conti nentality of southeast european lowlands

new gas geothermometers for geothermal exploration calibration and application calibration of five gas geothermometers is presented three of which used co2 h2s and h2 concentrations in fumarole steam respectively the remaining two use co2h2 and h2sh2 ratios the calibration is based on the relation between gas content of drillhole discharges and measured aquifer temperatures after establishing the gas content in the aquifer gas concentrations were calculated in steam formed by adiabatic boiling of this water to atmospheric pressure to obtain the gas geothermometry functions it is shown that the concentrations of co2 h2s and h2 in geothermal reservoir waters are fixed through equilibria with mineral buffers at temperatures above 230 c epidote prehnite calcite quartz are considered to buffer co2 two buffers are involved for h2s and h2 and two functions are therefore presented for the geothermometers involving these gases for waters containing less than about 500 ppm chloride and in the range 230 300 c pyrite pyrrholite epidote prehnite seem to be involved but pyrite epidote prehnite magnetite or chlorite for waters above 300 c and waters in the range 230 300 c if containing over about 500 ppm the gas geothermometers are useful for predicting subsurface temperatures in high temperature geothermal systems they are applicable to systems in basaltic to acidic rocks and in sediments with similar composition but should be used with reservation for systems located in rocks which differ much in composition from the basaltic to acidic ones the geothermometry results may be used to obtain information on steam condensation in upflow zones or phase separation at elevated pressures measured aquifer temperatures in drillholes and gas geothermometry temperatures based on data from nearby fumaroles compare well in the five fields in iceland considered specifically for the present study as well as in several fields in other countries for which data were inspected the results of the gas geothermometers also compare well with the results of solute geothermometers and mixing models in three undrilled icelandic fields

dust flux estimates for the last glacial period in east central europe based on terrestrial records of loess deposits a review loess paleosol sequences are significant records of the mineral dust cycle of glacial interglacial periods as dust particles give rise to direct and indirect radiative forcing obtaining a reliable picture of the global and regional patterns of mineral dust fluxes during glacial periods can lead to a better understanding of the contribution of mineral dust to past climate changes recent progress in absolute dating of loess deposits in the carpathian basin in east central europe made it possible to provide correct aeolian flux estimates for the last glacial period marine isotope stage mis 2 mass accumulation rates mars from chronological data of 33 loess sites exhibited a wide range of values from 150 to 1422 g m 2 a 1 centered around median and mean values of 338 and 417 g m 2 a 1 marpm10marpm10 and marpm2marpm2 estimates have been also calculated using grain size measurements of many loess samples and loess mars in order to facilitate comparison with models and since particles larger than 10 m have a negligible radiative effect here we show that some previous model simulations of the dust cycle at the last glacial maximum lgm significantly underestimated the real aeolian flux ranges of our estimates marpm10 34 324marpm10 34 324 and marpm2 9 3 88 2gm 2a 1 in east central europe for this reason some simulations of dust induced direct radiative forcing of the lgm climate failed to yield reliable results for this mid latitude region as they have been based on three dimensional dust field models that are not capable of estimating the real aeolian fluxes in central europe a recent global model of top of the atmosphere toa radiative forcing by mineral aerosols at the lgm that has been based on more realistic parameterization of dust sources transport and deposition revealed zonally averaged surface cooling of 2 c for the latitudes of our study area this surface cooling and toa radiative forcing 2 to 3 w m 2 are greater than recognized in other models and draws our attention to the importance of further modeling the impact of mineral dust on lgm climate in order to gain insight into the spatial pattern of radiative forcing and better understand resulting climate response in mid latitude loess regions such as east central europe

stratigraphy and spatial and temporal paleoclimatic trends in southeastern eastern european loess paleosol sequences abstract the loess paleosol sections batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine are presently located in areas of different types of steppe and are highly sensitive for recording climatic changes a stratigraphy for these three southeastern eastern european sections is presented based on pedostratigraphy and correlation of recently obtained susceptibility records with susceptibility data of other sections of the area koriten mostistea vyazivok of the chinese loess plateau and with the benthic 18o record of odp 677 six pedocomplexes were studied at the serbian and romanian sections and five at the ukrainian section the oldest are related to marine isotope stage mis 17 batajnica stari slankamen and mircea voda and mis 13 15 stary kaydaky some points concerning the existing loess chronostratigraphies of bulgaria ukraine and china are discussed comparative study of the profiles allows the tracing of paleoclimatic and paleoenvironmental changes in southeastern eastern europe in time and space reconstruction of paleoprecipitation based on susceptibility rainfall relationships and calculations of sedimentation rates are evaluated

groundwater recharge and hydrogeochemical evolution in the ejina basin northwest china groundwater plays a dominant role in the eco environmental protection of arid semi arid areas understanding sources and mechanisms of groundwater recharge in the ejina basin an arid inland river basin in northwest china is important for water resource planning in this ecologically sensitive area in this study 90 water samples were collected from rainfall rivers and lakes and springs and pumping wells in 2009 analysis of the aquifer system and hydrological conditions together with hydrogeochemical and isotope techniques were used to investigate groundwater sources and their associated recharge processes our results show that shallow phreatic and deep confined groundwater differ greatly in their compositions with a distinct spatial heterogeneity of phreatic groundwater tds from 365 mg l to 5833 mg l which increase along the shallow groundwater flow paths groundwater chemical evolution is mainly controlled by rock dominance and the evaporation crystallization process and the dominant anion species change systematically from hco3 to so4 to cl and the dissolved ions within the groundwater system from na and k rich minerals and sulfate phases also contribute significantly to the groundwater composition the stable isotope levels delta o 18 and delta h 2 of the surface water and the shallow phreatic groundwater confirm that the heihe river and badain jaran desert groundwater are the main sources recharging the phreatic aquifer in the ejina basin thus river infiltration and desert front recharge should be considered as the two main recharge mechanisms of the ejina aquifer however recharge from the badain jaran desert aquifer to the ejina basin has occurred at a lower rate due to acidification since the middle holocene for this reason the sustainable improvement of the ecological environment should be based on the shallow groundwater recharge of the phreatic aquifer in the ejina delta which mainly takes place via seepage through the riverbed and direct infiltration during periods of environmental flow control c 2012 elsevier b v all rights reserved

the crvenka loess paleosol sequence a record of continuous grassland domination in the southern carpathian basin during the late pleistocene abstract in this study we compare two independent paleoenvironmental proxies for a loess sequence in northern serbia in the southern carpathian basin novel n alkane biomarkers and traditional land snail assemblages both are associated with other more widely used proxy data for loess sections such as environmental magnetism grain size and geochemical indices together these paleoenvironmental proxy records provide evidence for the continued dominance of grasslands during the late pleistocene in the southern carpathian basin it is contrary to other european loess provinces which are characterized by high diversity of late pleistocene environments ranging from tundra like to deciduous forest habitats these findings highlight the southeastern part of carpathian basin as an important but still insufficiently investigated biogeographical refugium and biodiversity preservation zone the reason for this is a mostly stable paleoclimate for much of the late pleistocene

occurrence and hydrogeochemistry of fluoride in alluvial aquifer of weihe river china fluoride f has significant impacts on human health high fluoride groundwater up to 1 90 mg l has been found in upper confined aquifer underlying the first terrace of weihe river during a hydrogeological investigation for water supply in 2005 to reveal the occurrence and hydrogeochemistry of high f groundwater hydrogeochemical tools such as saturation index ionic ratios and correlation analysis were used in this study the study shows that the concentrations of most physiochemical parameters from phreatic water influenced by intensive evaporation and anthropogenic activities such as unregulated sewage and excreta disposal and agricultural practices in the area are higher than those of confined water the f concentration in phreatic water is within the acceptable limits set by china and the world health organization who while that of upper confined water shows a decreasing trend northwestward as the weihe river approaches with f concentration in the first terrace beyond the national and the who standards high f groundwater is observed in alkaline environment associated with high na ph hco3 and low ca2 and mg2 the enrichment of f is controlled by geologic and hydrogeological conditions fluorine bearing minerals presented in alluvial formations and their dissolution precipitation under the alkaline environment along groundwater flow ion exchange human activities and the mixing of different recharge waters may influence the enrichment of f as well

weathering intensity and pedostratigraphy of the middle to upper pleistocene loess palaeosol sequence of wels aschet upper austria abstract on top of a fluvioglacial terrace near wels aschet a complex loess palaeosol sequence has been investigated to date the terrace is classified as a classical gunz unit older deckenschotter sedimentological and mineralogical analyses were carried out on the basis of palaeopedological field data the results show that in terms of mineralogical composition the palaeosols can clearly be differentiated and are characterised throughout by interglacial weathering intensity bulk mineralogical as well as clay mineralogical data allow a five stage ranking of weathering intensity based on indicator minerals from the bulk mineralogical perspective slightly weathered loess still contains carbonate minerals and primary chlorite whereas the intensely weathered soil horizons are characterised by the total or near absence of carbonate minerals and primary chlorite micas and feldspars in clay mineralogical results chlorite and the relation of 14 a and 18 a vermiculites as well as mixed layer minerals play an important role in determining the weathering stage primary chlorite can be present in slightly weathered loess loams and vermiculite 14 a is dominant there stage 1 and 2 from weathering stage 3 onwards the amount of vermiculite 18 a increases considerably and dominates the following stage 4 most intensive weathering causes the absence of illite stage 5 generally the studied interglacial palaeosols belong to at least stage 3 with the applied methodology four interglacial palaeosols have been demarcated as well as a highly weathered palaeosol within the terrace gravels of the gunz in wels aschet pedostratigrapy points to a classification of the older deckenschotter in mis 14 at minimum however since this glacial period was of low intensity and the weathering intensity of the basal palaeosol was significantly enhanced a correlation of the gunz terrace with mis 16 also seems possible

hydrogeochemistry and geothermometry of the carbonate evaporite aquifers controlled by deep seated faults using major ions and environmental isotopes abstract carbonate aquifers probably constitute the most important thermal water resources in non volcanic areas and are characteristic of great energy potential and easier production as the most ideal targets for development in the future the thermal waters in the aquifers within southeast chongqing sec of china occur in an extensive region with an area of 198 000 km2 which are mainly hosted in the cambrian and ordovician carbonate evaporite rocks the thermal waters are mainly in pristine conditions and their genesis has not yet been fully understood the occurrence of thermal waters in sec is closely related to the presence of deep seated faults which constitute pathways for the hydrothermal circulation in this study an investigation of water major ions and environmental isotopes from 14 hot springs and three drilled wells was carried out to examine their hydrogeochemical evolution and to estimate reservoir temperature the thermal waters have outflow temperatures from 19 to 54 2 c they are divided into two hydrochemical groups with the yushan fault as a boundary group a located to the west of the fault are characterized by facies of chloride sodium waters with higher tds group b to the east of the fault are more complicated sulfate bicarbonate chloride alkaline earth waters with lower tds the hydrochemical processes such as dissolution of carbonate gypsum and or anhydrite and halite the common ion effect and dedolomitization are evident based on the major ions and 34sso4 and 18oso4 the 18o and d compositions of the thermal waters suggest a meteoric recharge in a relatively wetter and colder climatic condition the silica geothermometers show that the average reservoir temperatures are 63 18 c for group a and 82 15 c for group b the corresponding average reservoir depths are estimated to be 2 5 0 7 km for group a and 3 2 0 7 km for group b the corrected 14c ages of the thermal waters average at 14 8 ka bp corresponding to the late pleistocene a conceptual circulation model is proposed for the thermal waters driven by gravity of topographic gradients the percolating groundwater circulates at a specific depth reaching a higher temperature and interacting with the host carbonate with imbedded evaporitic minerals gypsum and or anhydrite and additional halite for group a to be saline deep seated thermal fluids the fluids rise along faults and emerge at the surface as thermal springs the slow renewability rate of the thermal aquifers highlights the importance of assessing the resource before groundwater exploitation and extraction

mixing hydrology and chemical equilibria in bakreswar geothermal area eastern india abstract a group of alkaline thermal springs of bakreswar having varying temperatures 45 71 c and identical compositions emerges through a nearly n s trending fault in the gneissic basement the thermal springs are of na cl so 4 type and are rich in sio 2 and f contrary to the local groundwaters which are mostly of ca hco 3 type the springs undergo mild to moderate dilution by local groundwater which does not significantly affect their original compositions agnikund the main spring with the highest temperature mild dilution consistent composition and negligible tritium discharges almost pure deep seated thermal water original thermal water is at equilibrium with quartz in the deep reservoir and attains surface temperature largely by conductive cooling with no significant loss of dissolved sio 2 certain ionic ratios coupled with very low tritium contents in the springs are indicative of prolonged subsurface circulation of the original water xrd results of the spring site sediments and the bore hole rocks fairly corroborate the predicted saturation state of thermal water with respect to quartz feldspar calcite fluorite etc which is believed to control the major chemical compositions of the springs a geothermal reservoir having probable temperature of about 100 5 c and possibly occurring at a depth of 1 km is the source of thermal water for the springs the present study is aimed at understanding the mixing trend between thermal springs and local groundwaters as well as the water rock equilibria

origin of calcium sulfate type water in the triassic carbonate thermal water system in chongqing china a chemical and isotopic reconnaissance abstract chongqing located in the southwestern china was named as a spa city of the world it s most geothermal reservoirs are developed in carbonate rock aquifers and those thermal waters are characterized by high concentrations of sulfate and low hco3 however little was known about the origin and genesis of those thermal waters which is necessary for their protection and determination of regime of exploitation therefore thermal and surface waters were sampled seasonally and analyzed for hydrogeochemical and isotopic compositions 18o 2h 34s so4 18o so4 to decipher the origin of the thermal waters in the triassic carbonate aquifers in chongqing area key questions include the relative significance of hydrothermal processes and solute supply the results showed that 1 the major chemical composition of analyzed the thermal waters from chongqing area was characterized by ca so4 2 the 2h and 18o values of the thermal waters ranged from 48 6 to 63 1 with an average value of 54 2 and from 6 5 to 9 2 with an average value of 8 0 respectively indicating that the thermal waters originated from the local rain water with an elevation of 415 m to 1453 m above mean sea level 3 the estimated geothermal temperatures varied from 63 8 c to 78 3 c quartz indicating that the depth of the geothermal reservoir varied from 411 m to 1728 m which is located in the lower triassic jialingjiang formation 4 the 34s so42 and 18o so42 in the geothermal waters ranged from 29 7 to 34 1 with a mean value of 32 1 and from 12 5 to 16 5 with a mean value of 15 2 respectively suggesting that the high so42 concentrations resulted mainly from the dissolution of gypsum in the second part of the lower triassic jialingjiang formation 5 three processes of water rock interactions gypsum dissolution carbonate dissolution by carbonic acid and carbonate dissolution by sulfuric acid in the thermal system were unveiled by the hydrogeochemical and isotopic models among these three processes gypsum dissolution seems to be primarily responsible for solute composition of the thermal water this study also indicates the integration of hydrogeochemical and isotopic data is very useful tool to decipher the origin and genesis of the carbonate thermal waters

the current tectonic motion of the northern andes along the algeciras fault system in sw colombia abstract riedel synthetic and antithetic type faults principal displacement zones pdz pull apart basins such as lazy s shaped releasing bend extensive and rhomboidal shaped and releasing sidestep basins and minor folds located oblique to the main trace of the algeciras fault system afs are interpreted from landsat tm 5 images and geological mapping these tectonic features are affecting quaternary deposits and are related to major historical earthquakes and recent registered seismic events indicating neotectonic activity of the structure the afs is classified as a right lateral wrench complex structure with an important vertical component in which sedimentary cover and basement rocks are involved in addition the system represents a simple shear caused by the oblique convergence between the nazca plate and the northern andes the transpressive boundary in sw colombia was previously located along the eastern frontal fault system however this paper shows that the afs constitutes the actual boundary of the current transpressive regime along the northern andes which begins at the gulf of guayaquil in ecuador and continues into colombia and venezuela

tectonic implications of tomographic images of subducted lithosphere beneath northwestern south america we used seismic tomography to investigate the complex structure of the upper mantle below northwestern south america images of slab structure not delineated by previous seismicity studies help us to refine existing tectonic models of subducted caribbean pacific lithosphere beneath the study area beneath western venezuela and colombia we distinguish two slabs a maracaibo and a redefined bucaramanga slab the maracaibo slab coinciding with most of the bucaramanga slab previously defined by w d pennington dips in a direction of 150 at an angle of 17 to a depth of 275 km and correlates to the subducted late cretaceous oceanic plateau of the caribbean plate farther south a second slab dips at an angle of 50 in a direction of 125 to a depth of at least 500 km and correlates to the subducted oceanic crust of the nazca plate and the downdip extension of the panama island arc we refer to this slab as the redefined bucaramanga slab because it is different from the bucaramanga slab segment defined by pennington the area of the south american plate overriding both slabs is characterized by the absence of an active volcanic arc an anomalously wide topographically uplifted and tectonically active area and the northward escape of the maracaibo block along active strike slip faults in support of earlier studies we attribute this to the underthrusting of the caribbean oceanic plateau our shallowly dipping maracaibo slab along the base of the south american lithosphere and to the recent collision of the panama island arc rafted in on more steeply dipping crust of the nazca plate our redefined bucaramanga slab

groundwater recharge environments and hydrogeochemical evolution in the jiuquan basin northwest china the groundwater recharge environments and hydrogeochemical characteristics in the quaternary aquifer of jiuquan basin was investigated using a combination of chemical indicators stable isotopes and radiocarbon dating the d excess values of winter precipitation and surface water revealed that the meltwater from snow and ice played the dominant role in the basin s surface water supply the unconfined groundwater showed gradual enrichment of heavy isotopes along the flow path but delta o 18 and delta h 2 values were similar to those of surface water suggesting recent recharge as a result of rapid seepage along rivers combined with the effects of high evaporation the c 14 pmc values of unconfined groundwater was between 71 5 and 90 9 and since 80 modern carbon probably represents the upper limit of initial c 14 activity this suggests that the groundwater is relatively young the confined groundwater was depleted in heavy isotopes coupled with low c 14 values similar to 20 53 indicating that the groundwater was mainly recharged as palaeowater during the late pleistocene and holocene epochs under a cold climate the surface water and most groundwater samples were fresh rather than saline with tds 490 and 1000 mg l 1 respectively the chemistry of unconfined groundwater changed from hco3 dominated to no dominant ions and then to so42 dominated moving along the flow path from the jiuquan jiayuguan basin to the jinta basin and the confined water was so42 dominated the results have important implications for groundwater management in the basin where a high proportion of the water being used is in effect being mined i e extracted faster than its replacement rate thus significant changes are urgently needed in the regional water use strategy c 2012 elsevier ltd all rights reserved

garzon massif basement tectonics structural control on evolution of petroleum systems in upper magdalena and putumayo basins colombia abstract the garzon massif is an active laramide style basement uplift flanked by the upper magdalena valley umv and the putumayo basin in this paper we use new gravity magnetic well and seismic data for the first geophysical interpretation of the garzon massif the garzon algeciras fault has been previously interpreted as a right lateral strike slip fault the new seismic well and gravity data demonstrates that the garzon fault is also a low angle 12 17 andean age fault thrusting precambrian basement 10 17 km northwestward over miocene sediments of the umv in a prospective footwall anticline the new geophysical data as well as previous field mapping were used to produce the first gravity and magnetic maps and retrodeformable structural cross section of the northern garzon massif the new model distinguishes for the first time distinct episodes of thin skinned and thick skinned deformation in the garzon massif the model indicates approximately 43 km of early to middle miocene shortening by thin skinned imbricate thrusting contemporaneous with the uplift of the nearby southern central cordillera 9 16 ma and the main hydrocarbon expulsion event for the umv and putumayo basin this was followed by at least 22 km of late miocene 3 6 ma thick skinned andean shortening and 7 km of uplift on the symmetrical garzon thrust and a se verging basement thrust fault zone the andean uplift interrupted and exposed the hydrocarbon migration pathways to the putumayo basin 3 d volume fracture analysis was used for the first time in this paper together with the first seismic and well data published for the topoyaco and miraflor structures to test closure models for the topoyaco foothills intense fracturing is observed in the topoyaco basement monocline from the near surface to depths of over 3 5 km the high level of fracturing permitted freshwater flushing and oil biodegradation and hydrocarbon escape in contrast the miraflor 1 well located just southwest of the topoyaco block tested light gravity oil and is sealed from groundwater flushing and biodegradation by a backthrust

hydrochemical characterization of drinking groundwater with special reference to fluoride in an arid area of china and the control of aquifer leakage on its concentrations the objective of the study is to determine the distribution and origin of fluoride in two confined aquifers within the depth of 80 240 m mid deep confined aquifers in shizuishan city an arid area in northwest china based on geological and hydrogeological conditions the distribution patterns of fluoride in the two confined aquifers were studied correlation analysis was used to reveal the mechanisms and reactions influencing the groundwater chemistry the control of aquifer leakage induced by intense groundwater abstraction on fluoride concentrations was also discussed the results show that the concentration of f in some locations of the study area is beyond the limit of the standards for drinking water quality of china correlation analysis shows that the major reactions occurring in the confined aquifers are dissolution of gypsum fluorite and halite and precipitation of calcite and dolomite groundwater leakage from shallow aquifers is also responsible for the elevation of fluoride in mid deep confined aquifers the research is a scientific basis for the rational development and utilization of groundwater in this area and it may be referenced by international scholars for similar research in other parts of the world

mixed layer illite vermiculite as a paleoclimatic indicator in the pleistocene red soil sediments in jiujiang southern china abstract the mineralogy and chemical composition of the jiujiang red soil sediments were investigated using x ray diffraction xrd x ray fluorescence xrf and inductively coupled plasma mass spectrometry icp ms mixed layer illite vermiculite i v was confirmed based on the conditions that a broad peak of 1 0 to 1 4 nm appeared in xrd after mg saturation and its d spacing did not change after glycol treatment but collapsed to 1 0 nm after heating owing to the loss of water and hydroxy cations from its interlayer the mixed layer i v contents fluctuate throughout the section but show a decreasing trend upwards suggesting decreased weathering towards the surface of the section the chemical index of alteration cia values and rb sr ratios also exhibit upward decreasing trends jointly revealing the climate shift from warm humid to cool dry from the middle to the late pleistocene although the general climate evolution can be evaluated by cia values and rb sr ratios sub climatic events within the jiujiang red soil sediments cannot be identified the sio2 al2o3 al2o3 fe2o3 and sio2 fe2o3 ratios clearly fluctuate along the section especially within the net like red soil sediments but they do not reveal multiple climate cycles this is because of an inhomogeneous distribution of sio2 al2o3 and fe2o3 in the white veins and the red matrix and also non uniform sampling the variation in the content of mixed layer i v show a strong positive correlation with changes in magnetic susceptibility of loess paleosol sediments and in marine oxygen isotope ratios revealing multiple sub climate cycles on a global scale since the middle pleistocene therefore the mixed layer i v contents not only reveal the whole climate trend documented in the red soil sediments since the middle pleistocene but also disclose the sub climate cycles related to the deposit pedogenesis process

tectonic implications of tomographic images of subducted lithosphere beneath northwestern south america tomographic images and deep seismicity of the mantle beneath northwestern south america support the existence of extensive and continuous subducted slabs which may be important controls on the neotectonic deformation of the overriding south america plate using tomographic data we have estimated lateral continuity regional dip downdip length and approximate convergence direction of two largely aseismic slabs tomographic data suggests that the cauca slab previously defined using earthquakes beneath southern colombia extends 300 km into the mantle beneath northern colombia has an average dip of 50 degrees and is the downdip extension of eocene to miocene panama island arc and oligocene miocene oceanic crust of the nazca plate the maracaibo slab of northern colombia and western venezuela extends up to 450 km into the mantle at an average angle of 16 degrees and is the downdip extension of late cretaceous oceanic plateau crust of the caribbean sea the boundary between the two slabs is less than 50 km in width the maracaibo and northern cauca slabs are generally aseismic and not associated with an overlying volcanic arc instead both slabs are overlain by broad zones of diffuse active faulting and topography in the northern andes the shallow dip angle of oblique subduction andmore thickness of the maracaibo slab may produce crustal deformation including northward tectonic escape of the maracaibo block a triangular wedge of continental crust in the overriding south america plate less

geochemistry and genesis of geothermal well water from a carbonate evaporite aquifer in chongqing sw china thermal water is an important natural resource the hydrogeochemistry and geothermometry of thermal water from the qianyi well twqw which is associated with the tongjing warm springs located in the eastern sichuan fold belts in chongqing sw china was investigated the reservoir of this region consists of upper and middle triassic carbonate and evaporite rocks the twqw was of ca mg so4 type with water temperature of 47 3 c plotting on the giggenbach na k mg diagram indicates that the twqw was immature due to a mixing of shallow karst groundwater and thermal water the mixing model indicates that the twqw was composed of 49 deep thermal water and 51 shallow karst groundwater geothermometers suggest a reservoir temperature of about 79 c locating this aquifer at a depth of 2 5 km the d and 18o values plot near the local meteoric water line suggesting that the twqw originates from local meteoric water at recharge elevations of 780 1160 m a s l a conceptual model of the genesis for tongjing warm springs was developed rainfall infiltrates via karst outcrops in the elevated areas of the northern tongluoxia anticline extracts heat from reservoir rocks at depth dissolves minerals and becomes thermal water the thermal water is driven by gravity flows through the carbonate evaporite aquifer and follows the tongluoxia anticline of the eastern sichuan fold belts to the southwest the thermal water ascends to the surface along the incision created by the wentang river and mixes with shallow karst groundwater to create warm springs this study may be relevant to other karst geothermal reservoirs in china

geochemical and isotope characterization of geothermal spring waters in sri lanka evidence for steeper than expected geothermal gradients summary seven geothermal springs from the precambrian high grade metamorphic terrain of sri lanka were investigated to assess their formation processes and to determine reservoir temperatures based on their chemical compositions silica based geothermometric calculations for the marangala and nelumwewa springs showed the highest average reservoir temperatures of 122 c and 121 c respectively samples of low temperature

processes of loess lithogenesis during the pleistocene holocene southeast siberia regional studies have been conducted on loess deposits cohesive sands and loess like neoformations in the technogenesis zones in southeast siberia cryogenic processes and distribution of geological formations have been ascribed to influential factors of loess lithogenesis the processes of loess formation are active in the present environment

quaternary extension in southern tibet field observations and tectonic implications we summarize evidence for quaternary and active faulting collected in the field during three sino french expeditions to southeastern tibet 1980 1982 detailed mapping of quaternary and active faults as well as microtectonic measurements indicate that normal faulting has been the dominant tectonic regime north of the himalayas in the last 2 0 5 m y the maximum horizontal principal stress in south tibet appears to be only the intermediate principal stress 2 1 being vertical south of the chord joining the eastern and western syntaxes of the himalayan arc extensional strains are principally localized within seven regularly spaced rift zones three of which have been studied in some detail the extension direction is determined to be n96 e 7 mainly from statistical averaging of strikes of newly formed normal faults throw rates on normal faults are evaluated for different time spans 2 0 5 m y 60 40 kyr and 10 2 kyr b p using structural and topographic reliefs as well as synglacial and postglacial vertical offsets the rate of quaternary extension is about 1 m y 1 along an 1100 km long ese traverse across south tibet this corresponds to a spreading rate of 1 0 6 cm yr this rate and the divergent horizontal projections of slip vectors of earthquakes along the himalayan front constrain the rate at which rigid india underthrusts southern tibet to be 2 1 cm yr although most of the normal faults appear to be independent of and nearly orthogonal to the e w mesozoic tertiary tectonic fabric the yadong gulu rift appears to be guided for over 130 km by the older oblique ne sw nyainqentanglha range and fault zones along it this reactivated zone is the most prominent left lateral strike slip fault system in se tibet excepting this zone and the vicinity of the se extremity of the karakorum fault quaternary strike slip faulting is rare in south tibet i e south of the chord between the syntaxes of the himalayan arc north of the chord the tectonic style is different there minor conjugate strike slip faulting is widespread and appears to control quaternary normal faulting which is more diffuse and subdued than in south tibet along the chord the presence of a major zone of active right lateral en echelon strike slip faults karakorum jiali fault zone probably reflects the greater facility of eastward extrusion in north central tibet in response to the northward push of india the eastern himalayan syntaxis may be an obstacle to such extrusion movements south of the chord

an integrated analysis of transverse structures in the northern apennines italy abstract the northern apennines have been the object of numerous studies both from a morphological and a structural point of view at present much debate is going on about the existence and interpretation of ne sw alignments described by geomorphologists boccaletti m coli m napoleone g 1977 nuovi allineamenti strutturali da immagini landsat e rapporti con l attivita sismica negli appennini boll soc geol it 96 679 694 signorini r 1953 linee tettoniche trasversali nell appennino settentrionale rend acc naz lincei 6 42 45 and partly denied by structural geologists we show new microtectonic and morphological data which contribute to a more comprehensive interpretation of these elements stress axis determination and different morphotectonic analyses have been combined the analysis of the drainage networks and of two different digital elevation models have also been considered the results lead us to interpret the ne sw alignments as large and diffuse deformation zones which may represent old transfer zones active with left lateral strike slip movements during the mountain building

stable oxygen and hydrogen isotopes as indicators of lake water recharge and evaporation in the lakes of the yinchuan plain the yinchuan plain has more than 2000 years of history of irrigation by diverting water from the yellow river currently the amount of water diverted from the yellow river is about 21 7 times the water formed on the plain as a result of precipitation and inflow of groundwater under the intensive influence of irrigation the plain changed from a desert into a rich and populous area earning its name as south china beyond the great wall with lakes scattered across the yinchuan plain just as stars in the sky in this research 17 representative lakes were sampled to analyze and study 2h and 18o content the results showed that lakes on the plain have undergone obvious non equilibrium evaporation recharges of the lakes can be divided into three types recharge from the yellow river from groundwater and from both of these the craig gordon non equilibrium evaporation model for isotope fractionation was used to estimate the evaporation proportion of each lake the results showed that evaporation from lakes on yinchuan plain is generally extensive under the dry climatic conditions most lakes have an evaporation proportion of over 25 with the largest originating from shahu lake and gaomiaohu lake in the northern part of the plain at 42 5 and 42 8 respectively the evaporation proportions calculated on the basis of 18o and 2h are very close to each other this shows that the method used in this paper is feasible for estimating the evaporation proportions of lakes in areas with a heavy anthropogenic influence copyright 2013 john wiley sons ltd

evaluation of groundwater hydrochemical characteristics and mixing behavior in the daying and qicun geothermal systems xinzhou basin this paper examines groundwater hydrochemical characteristics during mixing between thermal and non thermal groundwater in low to medium temperature geothermal fields a case study is made of daying and qicun geothermal fields in the xinzhou basin of shanxi province china the two geothermal fields have similar flow patterns with recharge sourced from precipitation in mountain areas heated through a deep cycle before flowing into overlying quaternary porous aquifers via fractures hydrochemical features of 60 ground and surface water samples were examined in the context of hydrogeologic information the average temperatures of the deep geothermal reservoirs are estimated to be 125 degrees c in daying field and 159 degrees c in qicun field based on na k mg geothermometry while slightly lower estimates are obtained using silica geothermometers hydrochemical features of thermal water are distinct from cold water thermal groundwater is mainly cl center dot so 4 na type with high tds while non thermal groundwater is mostly hcl 3 ca center dot mg and hco 3 ca type in the daying and qicun regions respectively hydrogeochemical processes are characterized by analyzing ion ratios in various waters higher contents of some minor elements in thermal waters such as f si b and sr are probably derived from extended water rock interaction and these elements can be regarded as indicators of flow paths and residence times mixing ratios between cold and thermal waters were estimated with cl na and b concentrations using a mass balance approach mixing between ascending thermal waters and overlying cold waters is extensive the proportion of water in the quaternary aquifer derived from a deep thermal source is lower in daying geothermal field than in qicun field 5 3 7 3 vs 6 3 49 3 mixing between thermal and non thermal groundwater has been accelerated by groundwater exploitation practices and is enhanced near faults shallow groundwater composition has also been affected by irrigation with low temperature thermal water c 2009 elsevier b v all rights reserved

pleistocene environmental dynamics recorded in the loess of the middle and lower danube basin abstract the substantial loess deposits of the middle and lower danube basin in southeastern europe represent one of the thickest and most comprehensive terrestrial palaeoenvironmental records on the continent yet are also the least well understood environmental conditions over the last million years have resulted in relatively continuous deposits uninterrupted by glaciation and tundra conditions which nevertheless reflect oscillations between relatively warm humid interglacial and cold dry glacial intervals this relative environmental stability may have proven important for hominins migrating into and through the region the loess stratigraphy comprises distinct loess paleosol sequences reflecting glacial interglacial phases which can be quantified for intensity using environmental magnetism and geochemistry these phases are emphasised by variations in vegetation and malacofauna which respond to climatic change the loess deposits demonstrate broadly similar sedimentological characteristics across the basin danubian loess deposits initiated in response to the tectonic formation of the pannonian basin retreat of the large palaeolakes and increased sediment supply from the danube the period from 1 ma 500 ka mis 27 13 was characterised by alternating loess deposition and pedogenesis during glacial and interglacial periods respectively in response to relatively humid forested conditions this period represents the opening of the danube corridor and provides the backdrop for initial hominin arrival into europe after 500 ka and particularly after mis 9 loess accumulation rates increased in response to relatively more steppic arid environments mis 9 and 13 15 were the most humid phases of the last 600 ky the mis 5 interglacial period was the warmest and relatively most humid period preceding the holocene and was followed by substantially increased loess accumulation during mis 4 which may be linked to north atlantic circulation the complexity of the mis 3 interstadial paleosol suggests that conditions were not uniformly warm and wet during this time mis 3 corresponds with the first arrival of anatomically modern humans to europe the last glacial maximum and younger dryas of mis 2 were characterised by substantially increased loess accumulation indicating cold steppe environments most likely influenced by the north atlantic although conditions were sufficiently mild that the region acted as a refugium for thermophilic biota as may also have been the case for most of the pleistocene glacial cycles the holocene soil represents relatively wamer and more humid conditions corresponding to the current interglacial

morphometry of late pleistocene holocene faulting and volcanotectonic relationship in the southern andes of colombia diffuse seismicity and the active galeras volcano characterize the southern andes of colombia whose inhabitants are prone to a high natural risk we used field geological structural and quantitative morphological data to define the geometry and kinematics of late quaternary faults and the volcanotectonic relationships in this area the main ne sw buesaco fault has a late pleistocene holocene 29 km rupture length offset of dated landforms yields 188 13 m of horizontal right lateral long term cumulative component of slip the vertical component of uplift of the nw block being 67 12 m the long term net slip rate is 1 48 0 12 mm yr the other main structure here named aranda fault also strikes ne sw and is 13 km long offset of landforms yields 160 10 m of horizontal right lateral long term component of slip and 3 9 1 9 m of vertical component of uplift of the nw block the long term net slip rate is 1 19 0 08 mm yr on the galeras edifice e w to nw se faults have normal motions and slip rates from 0 02 to 0 23 mm yr both the galeras and a late pleistocene pyroclastic cone lie along the ideal extension of the buesaco fault magma uprising in the crust can occur along the ne striking fractures when magma pressure mp is greater than the normal to fault component of tectonic 1 magma uprising in the uppermost crust i e in the cone can occur by rock cracking along e w planes with mp 3 up to nw se planes with mp greater than shear stress component of the horizontal greatest principal stress hmax

malacological characteristics of the middle to upper pleistocene transitional interval mis 7 5 observed in the batajnica locality serbia abstract the batajnica loess section is one of the most complete middle and late pleistocene records known in the vojvodina region serbia the main aim of the malacological investigations was to study the latest middle pleistocene cold interval and to see how the mollusc successions reacted to the climate changes during the cold warm transition the deposits which belong to the upper part of pedocomplex v s2 v l2 loess and partly to the v s1 soil were sampled the penultimate glacial loess v l2 of the batajnica site corresponds to the cold interval marine isotope stage mis 6 the molluscs indicate moderate or sometimes warm climate and dry or moderate steppe like environment composed of adjacent mosaics of drier and humid habitats the mollusc complexes of v s2 soil mis 7c v l2 loess mis 6 and v s1 paleosol mis 5e show almost the same species composition which suggests the existence of a comparatively moderate or warm climate during the late middle pleistocene cold interval in contrast the mollusc complexes mis 6 from western and eastern europe have less species and few individuals compared with the batajnica section comparison with the late middle pleistocene mollusc associations from the northern and southern margins of the fruska gora mountain confirms its environmental originality the northern side of the mountain was characterized by a humid and relatively colder environment than the other areas of the vojvodina region batajnica irig and ruma the mollusc fauna obtained in the batajnica site suggests that this adjacent area represented a refugium for the thermophilous and arid tolerant species where they were able to survive during the cold periods of the pleistocene and thus confirms the hypothesis of p sumegi

structure of the hanmer strike slip basin hope fault new zealand hanmer basin 10 x 20 km located in northern south island new zealand is evolving where two major segments of the dextral strike slip hope fault are projected to converge across a 6 to 7 km wide releasing step over the structural geometry and development of hanmer basin does not conform to traditional pull apart basin models the respective fault segments do not overlap but are indirectly linked along the southwest margin of the basin by an oblique normal fault the hope river segment terminates in an array of oblique normal faults along the northwestern basin range front and east west striking normal faults on the west hanmer plain faulted holocene alluvial fan surfaces indicate west hanmer basin is actively subsiding evolving under north south extension the conway segment along the southeastern margin of the basin terminates in a complex series of active fault traces small pop up ridges and graben depressions early basin fill sediments of pleistocene age are being folded elevated and dissected as the eastern part of hanmer basin is progressively inverted and destroyed by north south contraction the north margin of the basin is defined by a series of topographic steps caused by normal faulting outside of the area of the releasing step over these normal faults we interpret to reflect large scale upper crustal collapse of the hanging wall side of the hope fault new seismic reflection data and geologic mapping reveal a persistent longitudinal and lateral asymmetry to basin development four seismic stratigraphic sequences identified in the eastern sector of the basin thicken and are tilted southward with insequence lateral onlaps occurring to the north and east and also onto basement near the fault controlled basin margins the basin depocenter currently contains 1000 m of sediment adjacent to the south margin and is disrupted by faulting only at depth in the western part of the basin the sediment fill is thinner today the rate of basin deepening under transtension at the western end is matched by its progressive inversion and destruction under transpression in the eastern sector with the oldest basin fill now being recycled we propose a hybrid model for hanmer strike slip basin one in which geometric elements of a fault wedge basin downward and upward tipped spindle shaped ends are combined with those of a pull apart basin step over region between the major fault segments we also conclude that changes in fault geometry releasing and restraining bends and step overs at a variety of scales and over short distances control the development of the extensile and contractile parts of the basin and three dimensional basin asymmetry strain partitioning is complex and cannot be related simply to local reorientation of the regional stress field

the late pleistocene belotinac section southern serbia at the southern limit of the european loess belt environmental and climate reconstruction using grain size and stable c and n isotopes the belotinac loess section is one of the southernmost loess paleosol environmental archives for the late quaternary in serbia the climate at this site is intermediate between the continental and the mediterranean realms which makes this loess archive potentially highly sensitive to past climatic changes this paper presents new insights into the paleoenvironmental history during the last glacial period in southern serbia using grain size and isotope proxy data the grain size parameters from the belotinac section reveal variations in the paleowind dynamics and weathering intensity and suggest the nearby valley of the ju na morava river as an important source of aeolian sediments in this area based on a multiproxy dataset alternating phases of weak interstadials and phases of enhanced loess deposition at this site were identified nitrogen isotope data suggest that during marine isotope stage 3 ecosystems of high biomass productivity and rather open n cycles prevailed during marine isotope stage 2 productivity was reduced and the n cycle was more strongly closed probably due to a shorter growing season and more pronounced temperature decline carbon isotope data indicate a possible contribution of c4 plants to the holocene vegetation but not to the glacial and interstadial ecosystems of the late pleistocene changes in atmospheric co2 level are not reflected in the carbon isotope record these findings are discussed in the light of paleoclimate proxy datasets from the morava river valley and carpathian basin as well as through comparison of carbon isotope records from loess sections in se central europe and in the rhine valley two different loess provinces exist in terms of glacial interglacial humidity changes a province of glacial drying and a province of glacial humidification the first includes loess sites under more oceanic influence where loess 13c records indicate humid interglacials and interstadials and relatively drier glacial periods the second includes the loess sites of the carpathian basin and especially the southern serbian loess area of belotinac where loess 13c records indicate more intensive aridity during interglacials but a reduced soil moisture deficit and a more humid climate due to lower evapotranspiration in interstadials and even more in glacial periods

cenozoic contractional reactivation of mesozoic extensional structures in the eastern cordillera of colombia 1 the eastern cordillera of colombia is key to understanding the role of inherited basement anisotropies in the evolution of active noncollisional mountain belts in particular the rio blanco guatiquia region of the eastern cordillera is exemplary in displaying a variety of phenomena that document the importance of the orientation geometry and segmentation of preorogenic anisotropies we document the first unambiguous evidence that extensional basement structures played an important role in determining the locus of deformation during contractional reactivation in the eastern cordillera detailed structural field mapping and analysis of industry seismic reflection profiles have helped to identify the inherited san juanito naranjal and servita normal faults and associated transfer faults as important structures that were inverted during the cenozoic andean orogeny apparently the more internal faults in the former rift basin were not properly oriented for an efficient reactivation in contraction however these faults have a fundamental role as strain risers as folding is concentrated west of them in contrast reactivated normal faults such as the more external servita fault are responsible for uplifting the eastern flank of the eastern cordillera in addition these structures are adjacent and intimately linked to the development of thin skinned faults farther east in part the superimposed compression in this prestrained extensional region is compensated by lateral escape the dominant presence of basement involved buckling and thrusting and the restricted development of thin skinned thrusting in this inversion orogen makes the eastern cordillera a close analog to the intraplate atlas mountains of morocco and other inverted sectors of the andean orogen farther south

isotopic characteristics of precipitation surface and ground waters in the yinchuan plain northwest china the isotopic characteristics of hydrogen and oxygen of various water bodies in the yinchuan plain were investigated a total of 131 water samples were collected and another 99 water samples collected by other scholars and the international atomic energy agency were referred to in the study the stable isotopic compositions of precipitation and lake waters are influenced by dry climate and strong evaporation of the area and the slope of local meteoric water line and lake water line are smaller than that of global meteoric water line the isotopic compositions of the yellow river water are significantly lower than the weighted averages of local atmospheric precipitation and are controlled by the runoff of upstream areas the isotopes of phreatic water suggest that the single phreatic water is predominantly recharged by the bedrock fissure water of helan mountain while the phreatic water in multilayer structure area is recharged by multiple sources the confined waters in the area may be recharged under cooler climate conditions than the present which makes the heavy isotopes depleted the 3h contents of various water bodies are in the following order the yellow river water multilayer phreatic water single phreatic water lake water drainage ditch water upper confined water lower confined water this is in accordance with the recharge discharge and circulation conditions of the specific water bodies the isotope compositions of waters in the yinchuan plain are mainly affected by external water recharge rather than local precipitation this study is meaningful and helpful in understanding the groundwater flow systems and water cycle in the area

the eastern foothills of the eastern cordillera of colombia an example of multiple factors controlling structural styles and active tectonics we decipher the geometry timing and kinematics of deformation of a region in the eastern foothills of the eastern cordillera of colombia we assess the influence of inherited structural fabrics changes in basin geometry erosional denudation and the characteristics of the tectonic stress field with respect to the evolution of the structural styles of the deformation front in the eastern cordillera detailed structural and geomorphic mapping of an area of 5000 km 2 analysis of seismic reflection profiles cross section balancing tectonic stress field indicators and new apatite fission track data are used to characterize the partitioning of late cenozoic deformation in the eastern foothills of the eastern cordillera of colombia during the late miocene pliocene in the eastern cordillera deformation migrated from inverted master normal faults to low elevation low amplitude structures in the foreland however this shift in the locus of deformation was not spatially uniform the deformation front is wider in a northern sector of the cordilleran foothills where sedimentary units are thicker and shortening is perpendicular to the structures this shortening direction is identical to the direction of the greatest horizontal stress s hmax as seen in borehole breakouts during the late miocene pliocene basement ranges are passively uplifted by younger more frontal thrusts the eastern foothills of the eastern cordillera thus reveal a complex combination of factors responsible for the structural styles and partitioning of active deformation in an inversion orogen over time the most important factor changes from the role of inherited structural fabrics to the geometries of basin fills

geochemical characterization and origin of southeastern and eastern european loesses serbia romania ukraine abstract the loess paleosol sections of batajnica stari slankamen serbia mircea voda romania and stary kaydaky ukraine were geochemically characterized based on discriminant analysis of major and trace elements the ratios of al ti fe ti and al fe the a cn k ternary plot and element enrichment depletion relative to the average composition of the upper continental crust the origin of the loess material in the southern pannonian basin vojvodina the lower danube basin dobrudja and the dnieper area was evaluated by comparison with the representative element composition of possible source areas and by considering the geomorphodynamic setting also the background values of the initial magnetic susceptibility of the loesses were taken into account for the lower danube basin dobrudja and the ukraine paleowind direction was reconstructed based on the geographic distribution of sandy soil texture and dunes related to river systems finally loesses were evaluated as possible samples of the average upper continental crust our results show that danube and dnieper loess areas can be clearly distinguished the former reveal higher al and fe contents the latter higher si zr hf content and indications of effective mineral and grain size sorting we can confirm that vojvodina loess originated from danube alluvial material and loess of the dnieper area from glaciofluvial sediments of the fennoscandinavian ice sheet the dobrudja loess derived also predominantly from danube alluvium but shows significant contribution of a second loess source probably the glaciofluvial sediments of the ukraine this was forced by northerly katabatic winds from the fennoscandinavian ice sheet whereas wnw winds prevailed in the western walachian plain the studied loesses reflect the average composition of the upper continental crust yet biases exist due to selective mineral element enrichment and depletion in the course of previous sedimentary recycling phases respectively material of all studied loess deposits seems to derive originally from sedimentary rocks

response of alluvial rivers to slow active tectonic movement alluvial rivers respond to valley slope deformation caused by active tectonics in various ways depending on the rate and amount of surficial deformation and on the type of river on the basis of experimental results and field examples hypothetical models of river response to anticlinal uplift and synclinal subsidence were developed for different types of alluvial rivers an experimental braided channel responded to anticlinal uplift across the channel with degradation and terrace formation in the central part of the uplift with subsidence aggradation in the central reach was the main response transverse bars developed downstream of the subsidence axis an experimental meandering channel responded to slope steepening with a sinuosity increase bank erosion and point bar growth occurred downstream of the anticlinal axis and upstream of the synclinal axis upstream of the uplift axis and downstream of the subsidence axis where the slope was flattened water flooded over bars local convexity in longitudinal profiles of the middle rio grande new mexico is considered to be formed by a domal uplift local aggradation and degradation could be explained by the effect of uplift the san joaquin river california which is now highly controlled does not show clear adjustment to the rapid subsidence due to ground water withdrawal it shows however a channel pattern adjustment to active tectonic subsidence that has been occurring for a long time the san antonio and guadalupe rivers in texas both increase their sinuosity significantly where monoclinal movements steepen valley slopes

the belotinac section southern serbia at the southern limit of the european loess belt initial results abstract the palaeoclimate record preserved in loess deposits in s serbia is poorly understood this is in strong contrast to the situation in the north of the country vojvodina region where similar deposits have been intensively investigated in recent years this study presents a first detailed description initial proxy analysis magnetic susceptibility colour total organic carbon and preliminary luminescence chronology of a loess palaeosol sequence that is exposed in an abandoned quarry at belotinac near the city of nis s serbia the sequence is about 10 m thick and preserves three loess units and three weakly developed palaeosol units although its potential remains to be fully tapped the preliminary results demonstrate that the sequence offers a unique record of climate and environmental change during the late pleistocene at the transition between mediterranean and continental europe

the role of late pleistocene holocene tectono sedimentary history on the origin of patches of savanna vegetation in the middle madeira river southwest of the amazonian lowlands abstract savanna patches are features of the amazonian landscape that have been long under intense debate but there are still questions about the main factors that have determined their establishment and evolution within the rainforest matrix in particular their geological substrates were poorly documented the aim of this work is to reconstruct the tectono sedimentary history of four savanna patches in the middle madeira river southwest amazonia and discuss its potential control over the development of the savanna communities the approach consisted in the integration of geomorphological sedimentological chronological and floristic data the results revealed that the savanna substrates are sandy deposits aged between 118 9 and 35 6 ky overlain by late pleistocene to holocene muddier successions

strike slip deformation within the colombian andes the colombian andes are characterized by a dominant ne structural trend which is offset by ene trending right lateral and nw trending left lateral structures ne trending faults are either dip slip or oblique thrusts generated as a result of a transpressive regime active since at least palaeogene times nw trending faults are considered to be reactivated pre cretaceous extensional structures right lateral shear on ene trending faults has resulted from oblique convergence between the nazca plate and the northern andes major changes in the geometry of the oblique plate convergence between the nazca and south american plates have generated the northward escape of the northern andes and stress strain partitioning within the mountain belt these strike slip structures have exerted important controls on sedimentation source rock distribution fluid flow and ore mineralization during cenozoic times the interpretation of the northern andes as a mountain belt affected by strike slip deformation provides a structural context in which to reassess the exploration plays each of these cordilleras has a different composition and evolution as a result of different tectonic processes that have affected the region since mesozoic times the central cordillera originated in response to triassic subduction and consequent volcanic and igneous activity barrero et al 1969 barrero vesga 1976 bartok et al 1981 triassic and jurassic backarc rifting generated a predominantly ne sw structural trend that influenced the sedimentation in the adjacent magdalena valley and eastern cordillera the western cordillera is composed of oceanic crust and deformed deep marine sediments representing an accretionary complex established in the late cretaceous de freitas et al 1997 the eastern cordillera represents the inversion of thick mesozoic and tertiary sedimentary basins see taboada et al 2000 eastward subduction of the nazca plate beneath the northern andes occurs at c 60 mm a 1 trenkamp et al 2002 along the western margin of ecuador and colombia fig 1 additionally north of latitude 8 n the caribbean plate is moving ese at an average velocity of 20 mm a 1 trenkamp et al 2002 as a result of the oblique convergence of both the nazca and the caribbean plates with the northern andes the andean block fig 1 is moving northeastwards relative to the south american plate pennington 1981 kellogg et al 1985 the colombian andes have been interpreted as an assemblage of terraines that have been accreted to south america with a dominant nne structural trend etayo serna et al 1983 lopez barrero 2003 this interpretation has led to the assumption of plane strain deformation orthogonal to the strike of the main structures which in colombia is almost parallel to the continental margin fig 1 for this reason the colombian andes have been described as a classical fold and thrust belt mojica franco 1990 schamel 1991 cooper et al 1995 however oblique ene and nw strike slip deformation has been recognised in the region feininger 1970 boinet et al 1986 diederix et al 1987 cuervo 1995 velandia komuro 1998 montes 2001 ujueta 2001 branquet et al 2002 acosta et al 2004 and the importance of these structures in the evolution of the belt has for the most part been neglected in this paper a variety of geological geophysical geodetic and geodynamic information has been integrated to examine the origin and evolution and of some of these strike slip fault systems within the colombian andes

late quaternary kinematics slip rate and segmentation of a major cordillera parallel transcurrent fault the cayambe afiladores sibundoy system nw south america abstract we describe the recent activity of the cayambe afiladores sibundoy fault casf and recognise it as one of the major potential active structures of northwestern south america based on field observations stereoscopic aerial photos of offset late pleistocene holocene deposits and landforms and crustal seismic activity the casf runs for at least 270 km along the sub andean zone of northern ecuador and southern colombia we measured systematic latest pleistocene holocene right lateral strike slip motion and right lateral reverse motion consistent with earthquake focal mechanism solutions and estimated a 7 7 0 4 to 11 9 0 7 mm yr slip rate magnitudes of the earthquakes that could be generated by possible fault segment reactivation range up to m 7 0 0 1 the casf should be considered as a major source of possible future large magnitude earthquakes presenting a seismic hazard for the densely populated regions to the west the casf is part of the tectonic boundary of the north andean block escaping nne wards with respect to the stable south american plate

hydrogeochemical characteristics and formation of the hot springs occurring in the plunging ends of an anticline in chongqing eastern sichuan basin china hot springs occurring in two plunging ends of a very long and narrow anticline is unique this study focuses on the hydrogeochemical characteristics and formation of the anticline controlled thermal groundwater which may provide a perspective for geothermal resources potential the low to middle temperature thermal groundwater of the taozidang anticline in the sichuan basin china was examined to estimate the temperature of the deep reservoir and identify the main hydrogeochemical processes affecting the composition of hot water during circulation and evolution the occurrences of thermal groundwater of these springs strongly controlled by anticline are in the two plunging ends of the anticline and differ from that of the more common deep fault circulation controlled by faults or by faults and anticlines incongruent dissolution of the gypsum or anhydrite of the lower triassic jialingjiang and middle triassic leikoupo groups is affected by the anticline structures and results in hot water of so4 ca type meteoric water infiltrates through the karst channels and fissures at the outcropping area of carbonates to feed the groundwater part of the groundwater flows to depth and circulate along the two flanks of the anticline after heated it issues in the form of hot springs or wells in the plunging ends of the anticline another part of the groundwater undergoing a shallow circulation forms the normal temperature spring near the hot springs this study of the anticline controlled thermal groundwater is important for exploitation and utilization of geothermal energy tourism and provides a perspective for the anticline controlled geothermal resources potential

middle and late pleistocene loess sequences at batajnica vojvodina serbia abstract loess sequences in the vojvodina region northern serbia reveal a continuous record of paleoclimatic variations during the middle and late pleistocene the most detailed stratigraphic information comes from remarkable exposures on the cliffs of the right danube bank from vukovar to belgrade the batajnica loess section has been recognized as one of the most complete middle and late pleistocene records in this region a more than 40 m thick loess paleosol succession represents environmental transition from relative thin loess layers and rubified soils in lower part of profile to thick loess and fossil chernozems characterizing the last three glacial interglacial cycles the proposed stratigraphic model is based on a detailed magnetic susceptibility ms record which is related to the deep sea isotope stratigraphy and on correlation with other eurasian loess records using the distinct ms pattern of selected loess paleosol couplets this new stratigraphic model suggests serious revision of previous chronological interpretations ms as function of depth shows a well known pattern of low values in loess and high values in paleosols indicating strong enhancement of magnetic minerals during soil formation with the exception of the recent soil v s0 which is strongly contaminated by archaeological artifacts the third paleosol v s3 reveals the highest values in ms and a very distinct double peak the rock magnetic signal at batajnica resembles the typical pattern of the enviromagnetic records determined from other eurasian loess sites the paleopedological interpretations rubification index values and rock magnetic record at batajnica yield valuable data for the reconstruction of paleoclimatic fluctuations for the last 5 glacial interglacial cycles at least moreover the record provides an important link between the classical central european loess sites and the central asian and chinese loess provinces

roles of sorting and chemical weathering in the geochemistry and magnetic susceptibility of xiashu loess east china abstract uncertainties in paleoenvironmental interpretations for traditional chemical analysis of bulk samples result from different grain size sub populations of sediments containing variable distributions of elements and minerals therefore it is important to understand the elemental and mineral distribution in different grain sizes in determining the quantitative relationship between chemical weathering and climatic change we sieved a series of xiashu loess samples into three sub populations of different grain sizes 45 m respectively and then analyzed each population for rubidium rb strontium sr rare earth elements and magnetic susceptibility in comparison with elemental concentrations of bulk samples clay mineralogy and illitic crystallinity our results show that distinct elemental distributions and magnetic susceptibilities for different grain size sub populations are controlled by sorting and or chemical weathering although we also suggest that the xiashu loess may have the same provenance as the central chinese loess maximum concentrations of rb and fine grained magnetic minerals in the less than 2 m sub population coupled with our finding of maximum sr in the larger than 45 m fraction indicate that sr was lost during chemical weathering grain size sub population analysis is therefore an effective method for extracting paleoenvironmental information because individual sub populations show minimal variations in initial rb sr ratios compared to bulk analysis of all sizes together furthermore a negative correlation between rb sr ratios and sr concentrations for the r 2 0 97 may indicate that clay is a sensitive indicator of intensity of chemical weathering and is an ideal sub population for determining rb sr ratios but not for magnetic susceptibility

evidence for a neoproterozoic carbonate ramp on the northern edge of the central african craton relations with late proterozoic intracratonic troughs during late proterozoic times the archaean central african craton was affected by trough faulting which led to the formation of grabens the sangha aulacogen being the main structure of this type in the studied area this transverse basin connects with other basins on the northern and south western borders of the craton during the cryogenian this network of basins was filled with fluvio deltaic and lacustrine periglacial deposits the glacio eustatic transgression in neoproterozoic iii end proterozoic times flooded extensive areas of shelf on the northern edge of the craton leading to the development of carbonate sedimentation in a broad outer shelf environment associated with nearshore barriers and evaporitic lagoons these facies are similar to those developed in the west congolian schisto calcaire shale limestone ramp succession the north central african ramp succession sediment slope contains an example of tidal rhythmites in vertical accretion which occurs beneath the barrier deposits on the subtidal outer shelf mathematical analysis of the bedding pattern yields a period of 29 30 days for the lunar month a result which is in agreement with astrophysical evidence for this epoch i e 650 ma ago major subsidence and seismic activity on this gently sloping platform associated with the proximity of the sangha aulacogen caused the triggering of carbonate turbidites and mass flow deposits the proliferation of microbial mats under euphotic conditions on an extensive shelf led to the build up of a carbonate platform during early neoproterozoic iii times the west congolian and north central african ramps prograded northwards and southwards respectively into the sangha aulacogen the sea at that time was restricted to a long graben like basin while a remaining area of marine sedimentation persisted into the palaeozoic thus the pattern of end proterozoic carbonate sedimentation on the borders of the central african craton can be interpreted in terms of an overall gently sloping ramp model with progradation converging towards the sangha aulacogen

an introduction to the middle and upper pleistocene loess paleosol sequence at ruma brickyard vojvodina serbia abstract six loess units and five paleosols are preserved in the 20 m thick exposure of middle and late pleistocene sediments at ruma brickyard vojvodina serbia amino acid geochronology provides stratigraphic correlations between loess paleosol units sl l1 s1 sl l2 s2 sl l3 s3 and sl l4 at ruma with loess of glacial cycles b c and d and e respectively at other central and southeastern european localities the profile represents one of the best potential sections in the region for reconstructing detailed paleoclimates and paleoenvironments of the last ca 350 000 yr initial sedimentological magnetic and malacological evidence indicate many episodes of drier conditions in the region than in other parts of central and southeastern europe during the later part of the middle and late pleistocene

investigation of active faults in morocco using morphometric methods and drainage pattern analysis a survey has been done of recently active faults in morocco in addition to field observations morphometric methods were applied and an analysis was made of the drainage pattern in the morphometric analysis a map of vertical deformation was established from the elevations of summit level surfaces this enables the recognition of neotectonic discontinuities and lithological contrasts the actual discrimination of different rock types can only be achieved by comparison with field observations the analysis of drainage patterns including their perturbations and anomalies can also reveal the presence of features due to neotectonics structural control or lithological variation certain faults can be detected which correspond to structures known from field geology or remote sensing ne sw and nw se oriented sets some new faults are observed which belong to these sets as well as others which define a new n s trending set the present analysis leads to a distinction between ancient faults and currently active faults the results of this study are shown on a map of recently active faults where the respective vertical displacements are also indicated

principles of drainage basin analysis from multisource data application to the structural analysis of the zaire basin abstract classifications which attempt to combine descriptive and genetic aspects of types of drainage basins must take into account the application of new techniques satellite imagery high precision topographic maps and digital terrain models in addition the use of new concepts such as neotectonics and drainage basin history will lead to a reassessment of classification schemes after a review of current classifications we propose a genetic scheme that is based on the development of drainage networks and which includes integration of local and regional scale perturbations state of the art methods of drainage basin analysis are applied to the zaire basin to provide new information on deep structures the influence of basin and block tectonics is revealed in the context of major late proterozoic shear faults which have been rejuvenated up to the present day this is demonstrated from an analysis of the drainage network in the light of geological and geophysical observations

iron mineralogical proxies and quaternary climate change in se european loess paleosol sequences abstract the loess paleosol sequences batajnica stari slankamen serbia and mircea voda romania represent key archives for the climate and landscape development of the middle and lower danube basin during the last 700 000 years for deciphering the quaternary climate evolution in these regions the batajnica stari slankamen and mircea voda sites are for the first time studied by a multi proxy approach based on iron mineralogical parameters changes in the iron mineralogical composition are identified and characterized by rock magnetic investigations diffuse reflectance spectroscopy drs and munsell color based proxies the results show that environmental conditions during mid and early middle pleistocene interglacials were more favorable for hematite formation suggesting a more oxidizing pedoclimate as in the more recent interglacials this is also reflected in a gradual increase of the anhysteretic remanent magnetization vs saturation isothermal remanent magnetization arm sirm ratio in the studied profiles changes in this ratio can be linked to a preferential hematitization of coarse grained ferrimagnetica and relates to warmer climate conditions and a more extended estival dry period at the same time rock magnetic parameters indicate a preferential destruction of fine grained magnetic particles in older paleosols resulting from seasonal excess moisture a progressive cooling and decrease of rainfall during the middle and late pleistocene is evidenced not only for interglacial pedocomplexes but also for glacial loess layers this finding is in line with previously published proxy records of silicate weathering and clay formation at these sites and similar trends reported from other sites in the european steppe belt relating iron mineralogical proxies to paleopedological characteristics and proxies of silicate weathering additionally a change in the seasonal pattern of the interglacial temperature and precipitation regime from a mediterranean type to a steppe type climate is revealed highlighting the potential of such a multi proxy approach possible triggers for this paleoenvironmental evolution are discussed as well finally highlighting a quaternary uplift hypothesis which best could explain the inferred trend of cooling aridification and increasing continentality accordingly changes in atmospheric circulation and rain shadow effects induced by small scale uplift of european mountain belts alps carpathians dinaric alps would provide a driving mechanism for the westward extension of the eurasian steppe belt into central and se europe during the quaternary

pedology and mineralogy of loess profiles at kapela batajnica and stalac serbia abstract profiles with multiple paleosols developed in loess at kapela batajnica and stalac were studied by chemical physical and mineralogical methods to determine paleoclimatic changes through the pleistocene the cyclic nature of sedimentary and pedogenetic processes is indicated by the caco 3 content and silt and clay mineralogy stalac is 200 km south of kapela batajnica and differences between individual paleosols at the two sites are attributed to local differences in soil parent material composition weathering intensity or erosion of the paleosols the profile at stalac provides an important link between typical middle european and se european loess paleosol sequences and indicates the relative influences of the mediterranean and continental climates statistical analysis of values for the hydrolytic alteration index of thorez and other mineral ratios calculated at 0 5 m vertical intervals suggests a steady decrease in interglacial weathering rates since the gunz mindel pedocomplexes f8 and f9 and a gradual change from warm humid to temperate dry conditions the climatic curve for the kapela batajnica sequence suggests continental conditions and correlates well with the nw european climatic curve up to the gunz mindel interglacial pedocomplex f8 the curve for the lower part of the stalac sequence shows a stronger mediterranean influence and correlates well with the curve for greece but the upper part of the stalac sequence above the riss 1 riss 2 pedocomplex f6 shows an increased continental climatic influence

the chemistry of geothermal waters in iceland i calculation of aqueous speciation from 0 to 370 c abstract a computer programme has been developed to calculate the composition and aqueous speciation of geothermal reservoir waters including ph redox potential and gas partial pressures the programme is specifically suited to handle geochemical data from wet steam wells hot water wells and boiling hot springs but it may also be used for non thermal waters solubility data for selected geothermal minerals are incorporated to facilitate the study of solution mineral equilibria the programme may also be used to study chemical changes in water chemistry accompanying boiling variable degassing and cooling and how these changes disturb solution mineral equilibria

empirical calibration of the clinopyroxene garnet magnesium isotope geothermometer and implications the large equilibrium mg isotope fractionation between clinopyroxene and garnet observed in eclogites makes it a potential high precision geothermometer but calibration of this thermometer by natural samples is still limited here we report mg isotopic compositions of eclogite whole rocks as well as mg and o isotopic compositions of clinopyroxene and garnet separates from 16 eclogites that formed at different temperatures from the dabie orogen china the whole rock 26mg values vary from 1 20 to 0 10 among them 11 samples display limited 26mg variations from 0 36 to 0 17 similar to those of their protoliths the mineral separates exhibit very different 26mg values from 0 39 to 0 39 for clinopyroxenes and from 1 94 to 0 81 for garnets the clinopyroxene garnet mg isotope fractionation 26mgclinopyroxene garnet 26mgclinopyroxene 26mggarnet varies from 1 05 to 2 15 the clinopyroxene garnet o isotope fractionation 18oclinopyroxene garnet 18oclinopyroxene 18ogarnet varies from 1 01 to 0 98 equilibrium mg isotope fractionation between clinopyroxene and garnet in the investigated samples is selected based on both the 26mgclinopyroxene versus 26mggarnet plot and the state of o isotope equilibrium between clinopyroxene and garnet the equilibrium 26mgclinopyroxene garnet and corresponding temperature data obtained in this study together with those available so far in literatures for natural eclogites are used to calibrate the clinopyroxene garnet mg isotope thermometer this yields a function of 26mgclinopyroxene garnet 0 99 0 06 106 t2 where t is temperature in kelvin the refined function not only provides the best empirically calibrated clinopyroxene garnet mg isotope thermometer for precise constraints of temperatures of clinopyroxene and garnet bearing rocks but also has potential applications in high temperature mg isotope geochemistry

mineral composition vs soil forming processes in loess soils a case study from krakow southern poland abstract the mineral composition of soil parent material has a clear impact on soil formation soil properties especially chemical properties and mineral transformation in soil environment despite many studies concerning loess soils detailed quantitative studies on the mineral composition and transformation of clay minerals in loess soils formed during holocene and the influence of the mineral composition of parent material on the properties of loess soils are rare the main aims of the present study were 1 to determine the influence of loess mineral composition on soil genesis and 2 to determine layer silicate transformations and clay mineral formation in loess soils in relation to soil forming processes using qualitative and quantitative x ray diffraction analyses xrd and qxrd the obtained results show that the occurrence of carbonate minerals i e calcite and their influence on chemical properties of soil play a crucial role in the evolution of loess soils in loess that does not contain carbonates dispersion and translocation of clay particles including clay minerals down the profile occur this leads to the formation of luvisols and albeluvisols in carbonate loess clay minerals and soil organic matter form stable humus mineral complexes leading to the accumulation of humus and the formation of chernozems the transformation of mica and or smectite and or vermiculite to hydroxy interlayered minerals hims is the dominant process in the studied loess soils developed in a temperate climate because intense weathering of layer silicates is possible after removal of carbonates from soil profile this indicates that the occurrence of carbonates which maintain soil ph on a level of about 7 or higher is most likely the main factor controlling the rate of weathering of layer silicates in a loess soil environment in carbonate loess the dissolution and leaching of carbonates prevail over the weathering of silicates it is highly likely that the continuous leaching of carbonates assuming that the climate will not change will lead to more intense weathering of layer silicates

pleistocene slip rates on the bocono fault along the north andean block plate boundary venezuela the bocono fault is a strike slip fault lying between the north andean block and the south american plate which has triggered at least five mw 7 historical earthquakes in venezuela the north andean block is moving toward nne with respect to a stable south american plate this relative displacement at 12 mm yr 1 in venezuela within the maracaibo block was measured by geodesy but until now the distribution and rates of quaternary deformation have remained partially unclear we used two alluvial fans offset by the bocono fault yaracuy valley to quantify slip rates by combining 10be cosmogenic dating with measurements of tectonic displacements on high resolution satellite images pleiades based upon a fan dated at 79 ka and offset by 1350 1580 m and a second fan dated at 120 273 ka and offset by 1236 1500 m we obtained two pleistocene rates of 5 0 11 2 and 20 0 mm yr 1 consistent with the regional geodesy this indicates that the bocono fault in the yaracuy valley accommodates 40 to 100 of the deformation between the south american plate and the maracaibo block as no aseismic deformation was shown by insar analysis we can assume that the fault is locked since the 1812 event this implies that there is a slip deficit in the yaracuy valley since the last earthquake ranging from 1 to 4 m corresponding to a mw 7 7 6 earthquake this magnitude is comparable to the 1812 earthquake and to other historical events along the bocono fault

a critical reevaluation of palaeoclimate proxy records from loess in the carpathian basin abstract in the carpathian basin loess is the most important archive of quaternary palaeoclimate evolution but only in the past two decades systematic and high resolution investigations were conducted those studies remarkably improved our knowledge of the regional past environmental change palaeoclimate inferences based on the magnetic susceptibility and grain size distribution as the most commonly used palaeoenvironmental proxies for the carpathian basin loess indicate colder and drier climatic conditions during glacials when compared to interglacials with an increasing number of studies using novel proxies in loess research such a traditional understanding of dry and cold glacials and humid and warm interglacials in the carpathian basin has been questioned as an illustrative example mollusc based climate reconstructions suggest generally warm and very dry summer conditions with mean july temperatures up to 21 c for the southern carpathian basin during the last glacial results based on stable carbon isotopes strongly oppose such high summer temperatures but studies based on n alkanes are in general agreement with the mollusc data when it comes to the vegetation reconstruction indicating mostly steppic conditions however n alkanes studies contradict warm and dry glacial conditions as indicated by mollusc based reconstructions pointing instead to cold and relatively humid glacials in addition there is an ongoing debate whether or not millennial scale climatic oscillations can be observed in the carpathian basin loess as well as whether this area was an important northern hemisphere dust source or rather a sink of far distance dust transport consequently the current state of the art of the palaeoclimate reconstructions from loess in the carpathian basin is rather inconsistent in order to make sense of the existing palaeoclimate data from the carpathian basin loess we have reevaluated and reinterpreted the available data we discuss and propose a coherent interpretation of rock magnetic grain size malacological stable carbon and nitrogen isotope n alkane and bacterial membrane lipid data for the last glacial cycle loess archives from the carpathian basin we show that glacial conditions in the carpathian basin led to a notable increasing north south gradient in temperature and an even stronger expressed decreasing trend in humidity and that most of the biomarker proxy data conducted in loess for the very dry southern part of the carpathian basin show a strong bias towards arid conditions in particular palaeotemperature reconstructions seem to be misleading glacial conditions were drier and colder than previously proposed summer temperatures likely under 15 c during glacials but notably warmer than in other parts of western central and eastern europe the vegetation consisted mostly of steppic environments during both glacials and interglacials we indicate that the carpathian basin has a potential to be a major dust source of the northern hemisphere during glacials although it was at the same time exposed to the deposition of fine far distance travelled dust moreover the main issues in the regional and continental correlation of loess are highlighted as well as the sensitivity of the carpathian basin loess to the millennial scale climate variability recorded in other northern hemisphere records finally we suggest that the onset of loess formation in the investigated area occurred during the middle pleistocene transition and it was probably related to intensive silt production related to glacier dynamics in the alpine ice cap

seismicity fault plane solutions depth of faulting and active tectonics of the andes of peru ecuador and southern colombia the intracontinental seismicity of the andes of peru ecuador and southern colombia is concentrated along the easternmost flank of the cordillera beneath the western margin of the sub andes the focal depths and fault plane solutions of the largest events were constrained by comparing the observed long period p waves with synthetic waveforms in general the fault plane solutions show reverse faulting on steeply dipping nodal planes striking northwest southeast and reflect crustal shortening perpendicular to the range probably in response to the subduction of the nazca plate to the west earthquakes in the sub andes occur at depths of between 8 and 38 km indicating that much of the crust deforms in a brittle manner the seismicity seems to reflect antithetic underthrusting of the brazilian shield beneath the eastern margin of the andes however the earthquakes are too deep and their nodal planes are too steep to be associated with the thin skinned decollement of the sedimentary cover instead they appear to reflect the tectonic deformation of the underthrust basement west of the zone of active deformation at the surface in the sub andes hence the earthquakes on the east side of the andes may reflect the style of deformation in the hinterland of fold and thrust belts such as in the canadian rockies while much of the decollement farther east occurs aseismically in contrast normal faulting occurs in the high andes on planes parallel to the strike of the mountain belt thus there is a delicate balance between the compressive stress applied to the andes in the direction of subduction which causes thrust faulting in the sub andes and the gravitational body forces acting on the topographically higher parts and the crustal root of the andes which may cause normal faulting at high elevation

the garzon fault active southwestern boundary of the caribbean plate in colombia we propose active right lateral strike slip motion on the garzon fault zone of the neiva basin colombia based on the identification of two active right stepping releasing bend basins along the fault using stereoscopic analysis of 1 250000 spot images the garzon fault connects the bocono pamplona guaicaramo fault zones of venezuela and colombia with the romeral dolores and guayaquil faults of colombia together these faults form a continuous active right lateral fault between accreted terranes in northwestern south america and a more stable south america plate we infer 5 km right lateral offset of the garzon fault based on the width of the algeciras releasing bend basin

subduction of the eastern panama basin and seismotectonics of northwestern south america spreading along the cocos nazca plate boundary since the breakup of the farallon plate in the miocene has resulted in the formation of the panama basin and a complex interaction of plates in and near northwestern south america current plate boundaries have been defined and segments of subducted lithosphere identified through selection of hypocentral locations of earthquakes considering only well located events and through focal mechanism determinations the existence of relict plate boundaries bathymetric features and the panamanian isthmus has affected the subduction process of the nazca plate beneath south america and determined the present day configuration of the subducting lithospheric plate there is no single triple junction separating the caribbean south american and nazca plates instead the panamanian isthmus and surrounding areas are accommodating east west compression and a lesser degree of north south compression along a series of thrust faults striking nw to ne and the andean ranges of ecuador colombia and venezeula are moving as a block nne relative to the rest of the south american plates along a system of faults following the front of the eastern cordillera the subducted portions of the panama basin and old farallon plate have become segmented into three pieces recognized in this study from north to south they are 1 a bucaramanga segment continuous with the caribbean seafloor northwest of colombia 2 a cauca segment continuous with oceanic crust nazca plate currently being subducted beneath south america at the colombia ecuador trench and 3 an ecuador segment at the northern end of the subducted lithospheric plate which is dipping at a small angle to the east beneath northern peru the segmentation of the subducted plate can be explained by the buoyancy of bathymetric features which have been partially subducted

structural variety and tectonic evolution of strike slip basins related to the philippine fault system northern luzon philippines the northern part of the philippine fault zone in luzon corresponds to a complex braided system of left lateral strike slip faults the nw oriented main active branch which emerges from the philippine sea splits into an array of north striking splays responsible for the tectonic evolution of the central cordillera this complex fault pattern has favored local stress field variations strike slip basins have evolved in this framework along or in the vicinity of the main splays of the philippine fault apart from the classical pull apart tectonics on a releasing fault termination overlap or bend we describe other mechanisms such as the strike slip tilting or the warping of a strip limited by two strike slip faults the strike slip basins are good recorders of the evolution of the philippine fault system those located along the north striking cordilleran faults individualized in late early pliocene to pleistocene time when the present day philippine fault initiated but their main control is the fault shape acquired in upper middle miocene time the recent tectonic evolution of the fault system is best recorded in central luzon where the active basins trace an asymmetrical v shape with the longest branch trending ne parallel to the east luzon trough and the shortest one trending nw related to the philippine fault both the fault pattern and the basin distribution demonstrate the influence of the benham rise in the tectonic evolution of luzon the structural setting is interpreted as the result of an early miocene collision event between the benham rise and the eastern margin of luzon and subsequent inception of the nw striking strand of the philippine fault the present locations of the basins result from the interaction between the structural heritage and the present day regional plate motion