evidence of a shallow water submarine hydrothermal field off zannone island from morphological and geochemical characterization implications for tyrrhenian sea quaternary volcanism discoveries from multibeam bathymetry and geochemical surveys performed off zannone island western pontine archipelago tyrrhenian sea provide evidence of an undocumented hydrothermal field characterized by ongoing fluid emissions and morphologically complex giant depressions located in shallow water 250 m that host pockmarks mounds small cones and active fluid vents and which are interpreted as complex fluid escape features developed both through vigorous explosive events and steady seepage their spatial distribution suggests that the ne sw trending faults bounding the ponza zannone structural high and the shallow fractured basement are favorable conditions for the upward migration of hydrothermal fluids moreover we performed a detailed geochemical study to investigate the source of the hydrothermal fluids the geochemical signature of the collected fluids provides information of active co2 dominated degassing with a significant contribution of mantle volatiles with measured 3he 4he values 3 0 ra that are similar to those recorded at stromboli and panarea volcanoes the hydrothermal system produces volatiles that may originate from residual magma batches similar to the pleistocene trachytes cropping out in the se sector of ponza island that were probably intruded in the shallow crustal levels and never erupted the discovery of the zannone hydrothermal field updates the record of active hydrothermal areas of the mediterranean sea moreover the recognition of several giant hydrothermal depressions characterized by a complex morphology is peculiar for the mediterranean sea

active degassing across the maltese islands mediterranean sea and implications for its neotectonics abstract the maltese islands located in the central mediterranean sea are intersected by two normal fault systems associated with continental rifting to the south due to a lack of evidence for offshore displacement and insignificant historical seismicity the systems are thought to be inactive and the rift related deformation is believed to have ceased in this study we integrate aerial marine and onshore geological geophysical and geochemical data from the maltese islands to demonstrate that the majority of faults offshore the archipelago underwent extensional to transtensional deformation during the last 20 ka we also document an active fluid flow system responsible for degassing of ch4 and co2 the gases migrate through carbonate bedrock and overlying sedimentary layers via focused pathways such as faults and pipe structures and possibly via diffuse pathways such as fractures where the gases seep offshore they form pockmarks and rise through the water column into the atmosphere gas migration and seepage implies that the onshore and offshore faults systems are permeable and that they were active recently and simultaneously the latter can be explained by a transtensional system involving two right stepping right lateral nw se trending faults either binding a pull apart basin between the islands of malta and gozo or associated with minor connecting antitethic structures such a configuration may be responsible for the generation or reactivation of faults onshore and offshore the maltese islands and fits into the modern divergent strain stress regime inferred from geodetic data

gas geochemistry of the hot spring in the litang fault zone southeast tibetan plateau abstract the southeast tibetan plateau is a region with high level seismic activity and strong hydrothermal activity several large 7 5 m 7 historical earthquakes have occurred in the litang fault zone lfz eastern tibetan plateau since 1700 litang ms 5 1 earthquake occurred on sept 23 2016 indicating the reactivation of the lfz this study was undertaken to elucidate spatial temporal variations of the hot spring gas geochemistry along the lfz from jun 2010 to april 2016 the chemical components he ne and c isotropic ratios of bubbling gas samples taken from 18 hot springs along lfz were investigated helium isotope ratios 3he 4he measured in hot springs varied from 0 06 to 0 93 ra ra air 3he 4he 1 39 10 6 with mantle derivd he up to 11 1 in the lfz assuming r ra 8 for mantle indicated the fault was a crustal scale feature that acts as a conduit for deep fluid from the mantle co2 concentrations of the majority of hot spring gas samples were 80 vol co2 3he ratios varied from 1 4 to 929 5 1010 and 13cco2 values varied from 19 2 to 2 3 vs pdb the proportions of mantle derived co2 varied from 0 to 1 8 crustal marine limestone was the major contributor 75 to the carbon inventory of the majority of hot spring gas samples before litang ms 5 1 earthquake the 3he 4he ratios obviously increased in the heni spring from may 2013 to apr 2016 the geographical distribution of the mantle derivd he decreased from east to west along 30 n in the southeast tibetan plateau relative to a corresponding increase in the radiogenic component the gas geochemical data suggested that the upwelling mantle fluids into the crust play an important role in seismic activity in the strike slip faults along 30 n in the southeast tibetan plateau

seismogenic sources potentially responsible for earthquakes with m 6 in the eastern southern alps thiene udine sector ne italy summary new geomorphological and structural data permitted to define the active faulting framework of the eastern southern alps ne italy all the active faults detected in the investigated area are thrust segments of the complex thrust system which has been responsible for the latest building of the eastern southalpine chain esc geomorphological investigations were performed to identify the surficial traces of recent fault activity generally represented by gentle scarps connecting uplifted palaeolandscapes of quaternary age with the flat and lower areas of the venetian and friulian plains surficial and subsurficial data the latter from reflection seismic profiles available for the investigated faults indicate that the thrusts have been responsible for the displacement of the entire wedge of quaternary deposits in the western sector of the investigated area the six recognized fault segments represent portions of a 100 km long thrust system at the boundary between the alpine relief and the plain areas in the eastern sector active tectonics is the result of parallel thrust segments located both in the alpine mountainous area and in the friulian plain the 3 d geometry of the active thrust segments has been derived from new structural surficial surveys and the interpretation of reflection seismic profiles for a total length of 1700 km on this basis we defined the geometry of 10 seismogenic sources whose dimensions are consistent with the occurrence of earthquakes with m 6 the comparison between the source geometry and the highest intensity data point distribution of large historical earthquakes has permitted to make hypotheses on the association of past seismic events to specific seismogenic sources this procedure indicated that no large historical events can be attributed to three sources montello conegliano arba ragogna medea this may indicate an elapsed time since the last activation of more than eight centuries based on the completeness of the historical catalogues the available data define therefore sources and related areas for which a high level of seismic hazard may be invoked

middle late miocene 10 ma formation of the main boundary thrust in the western himalaya three independent data sets from northwestern india and pakistan suggest initial displacement along 1000 km of the main boundary thrust prior to 10 ma at least 5 m y earlier than previously reported regionally extensive changes in the depositional characteristics and rates of the foreland basinfill between 11 and 9 5 ma are interpreted to reflect new hinterland loading due to the formation of the main boundary thrust sediment accumulation rates sandstone siltstone ratios and thickness and amalgamation of individual sandstone bodies all substantially increase after 11 ma in well dated stratigraphic sections from pakistan to nepal across the indo gangetic foreland basin in the himachal pradesh reentrant of northwestern india a newly discovered 8 7 ma conglomerate derived from the hanging wall of the main boundary thrust indicates that source area uplift and denudation must have occurred prior to 9 ma and probably prior to 10 ma assuming a gravelprogradationrateof3cm yr threeapatitefission trackages fromstructuresattheleadingedgeofthemainboundarythrustin the kohat region of northwest pakistan indicate that rapid cooling below 105 c1 2 m y earlier these data indicate that the main boundary thrust in the western himalaya formed synchronously along strike in the middle late miocene has a displacement rate of 10 mm yr and has a displacement history that is coeval with late displacement on the main central thrust

travertine deposits deep thermal metamorphism and tectonic activity in the longmenshan tectonic region southwestern china abstract recently a series of high magnitude earthquakes including the 2008 wenchuan earthquake m 8 0 have occurred in the longmenshan tectonic region of southwestern china many researchers are currently examining the geological aspects of the activity but little attention has been given to the huge travertine deposits along large fault zones carbon isotopes were measured in 106 samples and the results indicate that the travertine originated from 13 c enriched co 2 sourced from deep reservoirs and can be characterized by notable positive 13 c values co 2 is thought to have originated from isotopic equilibrium fractionation under thermal metamorphism temperature conditions within 350 850 c the re equilibrium fractionation between the deep co 2 and the dissolved carbonate composition during travertine formation is due to the declining temperature of thermo genetic co 2 which in turn leads to higher 13 c carb values based on oil drilling data and geochemical thermometry modeling the depth of the 13 c enriched co 2 source is inferred to be below 4643 m which coincides with the measured focal depth of the wenchuan earthquake and subsequent aftershocks the variation of tectonic activity intensity and the quantity of co 2 from deep formations are mainly responsible for the 13 c fluctuations observed in the travertine the 13 c values in travertine deposits have increased dramatically which implies the rapid upwelling of the co 2 bearing fluid the enhancement of thermal metamorphism and the continuous increase of the internal pressure in deep reservoirs these findings may contribute to a better understanding of the deep seismic activity and high frequency aftershocks in the longmenshan region

significant late neogene east west extension in northern tibet field mapping in northern tibet reveals that the normal slip along late cenozoic northsouth trending faults is comparable to that estimated for equivalent structures in southern tibet the orientation of fault striations in two north south trending rifts suggests an eastnortheast west northwest direction of extension in northern tibet which in turn implies that northeast striking active faults in northern tibet have significant left slip components initiation of rifting in northern tibet postdates the early oligocene and possibly occurred after 4 ma the broad similarities in the magnitude of slip and the direction of extension for normal faults in both northern and southern tibet imply that the entire plateau has been extending this precludes significant eastward extrusion of north tibet relative to south tibet and requires a regional boundary condition as the cause of east west extension for the entire tibet plateau

evidence for tibetan plateau uplift before 14 myr ago from a new minimum age for east west extension important changes in south asian climate occurred in the late miocene epoch 8 myr ago 1 2 and these have been attributed by some researchers to uplift of the tibetan plateau at about the same time3 5 unfortunately this link has been difficult to test because the timing of plateau uplift remains poorly constrained by independent evidence one way to determine the minimum age of uplift is to establish the initiation age of the north striking normal fault systems in southern tibet that are widely regarded6 10 as being related to gravitational collapse of the tibetan plateau here we report an40ar 39ar age of 14 myr for hydrothermal mica from an extensional fracture belonging to such a fault system in north central nepal this age implies that east west extension began before 14 myr ago in at least some parts of the tibetan plateau suggesting that the plateau attained its high mean elevation well before late miocene time

southward propagation of the karakoram fault system southwest tibet timing and magnitude of slip the net slip on the southern portion of the karakoram fault system in southwest tibet is estimated by restoring a piercing line defined by two key surfaces in the south kailas thrust system a regional counter thrust along the indus yalu suture assuming that the thrust system is planar across the karakoram fault we calculate 66 5 5 km of normal right slip documentation of the south kailas thrust active at 13 ma implies that the karakoram fault in southwest tibet did not initiate until after the cessation of motion on the thrust however field investigations of the central portion of the karakoram fault system document the fault to have been active at 17 ma and to have accumulated a maximum of 150 km of right slip we suggest that these along strike variations in the magnitude of slip and timing constraints are best explained by southward propagation of the karakoram fault system this is inconsistent with major right lateral slip on the fault system which was used in support of extrusion models for tibet

palynological evidence for vegetation development and climatic change in the sub himalayan zone neogene central nepal abstract a palynological study on miocene pleistocene sediments exposed at surai khola in central nepal yields new information on vegetation and climate change over the last 11 5 ma our results show that during the late middle miocene to early late miocene 11 5 8 ma lower siwalik the himalayan foothills and the gangetic floodplain of nepal were mainly forested with subtropical to temperate broad leafed b l taxa e g quercus lithocarpus castanopsis alnus and tropical forest taxa respectively grasses were present at the time but were not abundant between the early to late late miocene 8 6 5 ma lower middle siwalik grassland replaced subtropical and temperate b l forest this change may be related to disturbance of the vegetation on the slopes due to uplift perhaps enhanced by intensification of the monsoon between late late miocene to pliocene early pleistocene 6 5 potamogeton and better preservation of all specimens enhanced seasonal flooding in the system during the pliocene 5 5 3 5 ma top middle siwalik may have produced local lacustrine conditions on the overbanks evidenced by an abundance of algae spirogyra and pteridophytes in the pollen assemblages evidence of climatic cooling between 6 5 5 ma ago is indicated by the onset of steppe taxa decrease of tropical forest taxa and disappearance of certain dipterocarpaceae pollen assemblages from the surai khola section suggest complex vegetation changes of which the shift to c 4 grass dominance was only one global climatic cooling the intensification of the monsoon and the late miocene uplift may all have contributed to the phytogeography in the sub himalayan zone

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

late neogene environmental changes in the central himalaya related to tectonic uplift and orbital forcing the linkage between tectonic forces and climate evolution remains a matter of much debate and speculation here we present high resolution oxygen and carbon isotope data from an ancient lake basin in the central himalaya these data together with sedimentologic evidence reveal major changes in drainage systems and depositional settings at 7 2 5 5 and 3 2 ma these environmental changes appear to be driven by regional scale tectonics the oxygen isotope record also reveals alternating wet and dry climates with periodicities of 24 and 100 kyr that were likely controlled by orbital forcing paleo temperatures estimated using a fossil based oxygen isotope paleo thermometer are 21 6 ca t 7 ma which is 19 6 c higher than the present day mean annual temperature in the same area the much warmer environment inferred here is consistent with fossil mammalian and pollen assemblages and sediment clay mineralogy as well as carbon isotope data from fossil tooth enamels and paleosol carbonates the estimated temperature difference would require the study area to have been raised by 2 2 5 km since 7 ma to its current elevation of 4100 4500 m above sea level this result can be interpreted as either indicating the presence of a low altitude intermountain basin in the hanging wall of the already formed main central thrust or a protracted development of a north trending rift basin that has experienced changes in drainage system and depositional environment through time

the structure and rate of late miocene expansion of c4 plants evidence from lateral variation in stable isotopes in paleosols of the siwalik group northern pakistan this study uses stable isotope variation within individual mio pliocene paleosols to investigate subkilometer scale phytogeography of late miocene vegetation change in southeast asia between ca 8 1 and 5 ma a time interval that coincides with dramatic global vegetation change we examine trends through time in the distribution of low latitude grasses c4 plants and forest c3 plants on indo gangetic floodplains using carbon 13c and oxygen isotopic 18o values in buried soil carbonates in siwalik series sediments exposed in the rohtas anticline north central pakistan revised high resolution magnetostratigraphy and a new 40ar 39ar date provide improved age control for the 2020 m rohtas section carbon isotope results capture lateral variability of c3 versus c4 plants at five stratigraphic levels r11 8 0 ma r15 6 74 6 78 ma r23 5 78 ma r29 4 8 4 9 ma and upper boundary tuff ubt 2 4 ma using detailed sampling of paleosols traceable laterally over hundreds of meters paleosols and the contained isotopic results can be assigned to three different depositional contexts within the fluvial sediments channel fill crevassesplay and floodplain environments 13c results show that near the beginning 8 0 ma and after 4 0 ma the period of major ecological change vegetation was homogeneously c3 or c4 respectively regardless of paleo landscape position in the intervening period there is a wide range of values overall with c4 grasses first invading the drier portions of the system floodplain surfaces and c3 plants persisting in moister settings such as topographically lower channel swales although abrupt on a geologic timescale changes in abundance of c4 plants are modest 2 per 100 000 yr compared to rates of vegetation turnover in response to glacial and interglacial climate changes in the quaternary earlier research documented a sharply defined c3 to c4 transition in pakistan between 8 1 and 5 0 ma based on vertical sampling but this higher resolution study reveals a more gradual transition between 8 0 and 4 5 ma in which c3 and c4 plants occupied different subenvironments of the siwalik alluvial plain 18o values as well as 13c values of soil carbonate increase up section at rohtas similar to isotope trends in other paleosol records from the region spatially however there is no correlation between 13c and 18o values at most stratigraphic levels this implies that the changes in soil hydrology brought about by the shift from forest to grassland i e an increase in average soil evaporation did not produce the shift through time in 18o values we interpret the trend toward heavier soil carbonate 18o values as a response to changes in external climatic factors such as a net decrease in rainfall over the past 9 ma

large scale geometry offset and kinematic evolution of the karakorum fault tibet the total offset lifespan and slip rate of the karakorum fault zone kfz western tibet are debated along the southern fault half ongoing oblique slip has exhumed dextrally sheared gneisses intruded by synkinematic leucogranites whose age v23 ma u pb on zircon indicates that right lateral motion was already in progress in the late oligocene ar ar k feldspar thermochronology confirms that rapid cooling started around 12 ma likely at the onset of the present dextral normal slip regime correlation of suture zones across the fault requires a total offset greater than 250 km along the active northern fault branch an average long term slip rate of 1 0 3 cm yr is inferred assuming that this offset accrued in a time span of 23 34 ma southwest of the ladakh karakorum range the large scale boudinage of ophiolitic units suggests that an offset of several hundreds of kilometers exists along another southern branch of the kfz towards the southeast in the mount kailas region the fault zone does not end at gurla mandatha but continues eastwards as a transpressive flower structure along the indus tsangpo suture our new data thus suggest that the kfz contributed to absorb hundreds of kilometers of india asia convergence

diet and environment of a mid pliocene fauna from southwestern himalaya paleo elevation implications a mid pliocene fauna 4 2 3 1 ma was recently uncovered in the zanda zhada basin in the southwestern himalaya at an elevation of about 4200 m above sea level these fossil materials provide a unique window for examining the linkage among tectonic climatic and biotic changes here we report the results from isotopic analyses of this fauna and of modern herbivores and waters as well as paleo temperature estimates from the zanda basin the 13c values of enamel samples from modern wild tibetan asses and domesticated horses cows and goats in the area are 9 4 1 8 which indicate a diet comprising predominantly of c3 plants and are consistent with the current dominance of c3 vegetation in the region the enamel 13c values of the fossil horses rhinos deer and bovids are 9 6 0 8 indicating that these ancient mammals like modern herbivores in the area also fed primarily on c3 vegetation and lived in an environment dominated by c3 plants the lack of significant c4 plants in the basin suggests that the area had reached high elevations 2 5 km by at least the mid pliocene taking into account the changes in the 13c of atmospheric co2 in the past the enamel 13c values suggest that the average modern equivalent 13c value of c3 vegetation in the zanda basin in the mid pliocene was 1 2 lower than that of the c3 biomass in the basin today this would imply a reduction in annual precipitation by about 200 400 mm in the area since then assuming that the modern c3 13c precipitation relationship applied to the past consistent with this inference from the 13c data the enamel 18o data show a significant shift to higher values after the mid pliocene which also suggests a shift in climate to much drier conditions after 4 3 ma paleo temperature estimates derived from a fossil bone based oxygen isotope temperature proxy as well as the carbonate clumped isotope thermometer for the mid pliocene zanda basin are higher than the present day mean annual temperature in the area after accounting for late cenozoic global cooling these paleo temperature estimates suggest that the paleo elevation of the zanda basin in the mid pliocene was similar to or slightly less than 1 km lower than its present day elevation which is consistent with the inference from the 13c data

spatial and temporal variations of co2 emissions from the active fault zones in the capital area of china abstract the chemical and isotopic composition of 26 soil gas wells and 11 springs along the active fault zones in the capital area of china was determined to investigate the origin of co2 the spatial and temporal variations of co2 emission and their mechanisms the chemical and isotopic data indicated that biogenic co2 was the primary source for co2 from the soil gas wells in both the basin and orogen regions the crust derived and mantle derived co2 could have ascended through the deep cut faults and got into the springs with a few diffusing into the soil gas wells minor air could have intruded into the soil gas wells in the orogen region through the faults cutting the surface owing to the barometric pressure fluctuation relatively high he concentration co2 concentration and flux of soil gas from wells were observed in the basin region than those in the orogen region a significant amount of co2 is produced during the process of oxidation of organic matter in the basin where the organic matter accumulates in thick clayey strata further amounts of co2 are produced by interactions between groundwaters and carbonates which are widely represented in the basin region and by intruded air into the soil gas wells in the orogen region due to barometric pressure fluctuations temporal variations of co2 concentration and co2 flux were observed in soil gas wells in the basin region where seismic activity is more frequent compared to those in the orogen indicating that seismic activity could be responsible for the jumpily temporal variations of co2 concentration and flux in wells monitoring activities of soil gas co2 concentrations and co2 fluxes in active fault zones should be carried out

late miocene movement within the himalayan main central thrust shear zone sikkim north east india in the sikkim region of north east india the main central thrust mct juxtaposes high grade gneisses of the greater himalayan crystallines over lower grade slates phyllites and schists of the lesser himalaya formation inverted metamorphism characterizes rocks that immediately underlie the thrust and the large scale south tibet detachment system stds bounds the northern side of the greater himalayan crystallines in situ th pb monazite ages indicate that the mct shear zone in the sikkim region was active at c 22 14 15 and 12 10 ma whereas zircon and monazite ages from a slightly deformed horizon of a high himalayan leucogranite within the stds suggest normal slip activity at c 17 and 14 15 ma although average monazite ages decrease towards structurally lower levels of the mct shear zone individual results do not follow a progressive younging pattern lesser himalaya sample kbp1062a records monazite crystallization from 11 5 0 2 to 12 2 0 1 ma and peak conditions of 610 25 c and 7 5 0 5 kbar whereas in the mct shear zone rock chg14103 monazite crystallized from 13 8 0 5 to 11 9 0 3 ma at lower grade conditions of 525 25 c and 6 1 kbar the p t t results indicate that the shear zone experienced a complicated slip history and have implications for the understanding of mid crustal extrusion and the role of out of sequence thrusts in convergent plate tectonic settings

miocene sn polymetallic mineralization in the tethyan himalaya southeastern tibet a case study of the cuonadong deposit abstract the cuonadong deposit is located in the cuonadong gneiss dome of the eastern tethyan himalaya and is characterized as a large to superlarge scale sn polymetallic deposit in the himalaya orogen the mineralization pattern includes skarn w sn mineralization in the strong shear zone of the dome mantle hydrothermal sn w veins controlled by north south trending rifts nstrs and be rb mineralization in pegmatitic leucogranite the results of this study show that the zircon u pb age of undeformed postkinematic leucogranites is 15 5 0 1 ma n 28 mswd 1 4 the cassiterite u pb age of the vein type sn w orebody is 14 3 0 5 ma n 40 mswd 3 2 and the muscovite ar ar age of beryl bearing pegmatitic leucogranite is 15 2 0 2 ma mswd 1 5 the isotopic dating results demonstrate that the cuonadong sn w be rb mineralization has a close genetic relationship with the miocene ca 16 14 ma leucogranite magmatic hydrothermal activity in the cuonadong dome the deformed synkinematic two mica granite 18 ma was cut by the sn w ore veins 14 ma faulted by nstrs indicating that the e w trending extension of the nstrs initiated at ca 18 14 ma the himalaya leucogranite belongs to a highly fractionated granite with high sn content 15 ppm in conclusion the himalaya leucogranite is considered to be tin granite in this study and therefore the himalaya presents high potential for sn polymetallic mineralization prospecting

lower altitude of the himalayas before the mid pliocene as constrained by hydrological and thermal conditions abstract contradictory paleoaltitudinal histories of the himalayas arrived at using isotopic paleoaltimeters and ecological evidences have constrained our further exploration of the geodynamic mechanisms driving the india eurasia collision and the resultant interaction between tectonic uplift and climate change in this study based on evidence derived from glycerol dialkyl glycerol tetraethers gdgts the hydrogen isotopes of leaf wax n alkanes 2 h alk we estimated the paleoaltitude of the gyirong basin gb central himalayas for the 7 0 3 2 ma period the paleoaltitudinal reconstruction based on 2 h alk values 6 3 km above sea level asl was consistent with that of the revised 18 o c values 5 6 km asl and higher than the present day altitude 4 km asl the reconstructed paleotemperatures based on brgdgts 14 2 4 5 c for the lake surface 7 5 3 3 c for terrestrial organic matter source areas were consistent with the ecological evidences indicating a low altitude paleoenvironment this proves that a systemic bias exists between the isotopic paleoaltimeters and the ecological evidence rather than a problem with specific indicators the reconstructed paleoaltitudinal differences between the 2 h alk and 18 o c values are similar to those of brgdgt reconstructions seemingly representing the paleoaltitudinal differences between the source areas of terrestrial organic matter inputs and the lake surface and suggesting that the isotopic palaeoaltimeters do not specifically record the higher altitude parts of the basinal topography further paleoenvironmental analysis indicated that the warmer and wetter environment present during the late miocene to mid pliocene would on the face of it be better suited to the application of brgdgt paleothermometers and this in turn would potentially lead to a systemic overestimation by isotopic paleoaltimeters we therefore adopted the paleoaltitudinal reconstructions which used brgdgts and concluded that the lake surface of the gb during the late miocene to mid pliocene was 2 5 0 8 km asl and that the surrounding mountains exceeded 3 6 km asl in height implying that the central himalayas underwent a rapid uplift of 1 5 km after the mid pliocene

high times on the tibetan plateau paleoelevation of the thakkhola graben nepal east west extension in the tibetan plateau is generally assumed to have resulted from gravitational collapse following thickening and uplift on the basis of this assumption several studies have dated east west extensional structures to determine when the plateau attained its current high elevation however independent estimates of elevation are needed to determine whether extension occurred before during or after the plateau achieved its current elevation because the isotopic composition of meteoric water decreases with increasing elevation significant change in local elevation throughout the thakkhola graben depositional history should be recorded by change in 18 o values of fluvial and lacustrine carbonates the 18 o values of 16 to 23 of thakkhola graben carbonates reflect meteoric water values similar to modern values and suggest that the southern tibetan plateau attained its current elevation prior to eastwest extension initiation of thakkhola graben extension is constrained between 10 and 11 ma based on magnetostratigraphy of the older tetang formation the 13 c values of soil carbonates suggest an age younger than 8 ma for the base of the thakkhola formation

carbon dioxide emissions from soils at hakkoda north japan 1 a soil gas and co2 efflux survey was carried out at hakkoda north japan to investigate the spatial distribution and origin of the gas which caused the accidental death of three japanese soldiers on 12 july 1997 in the study area no fumarolic and or thermal activity is observed chemical composition of the gas from areas with high co2 effluxes 5 000 g m 2 d 1 and high co2 contents 15 vol indicate a strong deep sourced contribution for co2 whereas air and or air saturated water is suggested for the rest of the discharged gases which are mainly released from a shallow aquifer isotopic analysis of soil gas and hot spring discharges suggests a combination of magmatic degassing and thermal decarbonation with magmatic degassing being the main contributior to the high co2 emission approximately 74 t d 1 of deep seated magmatic plus thermal decarbonation origin co2 were estimated to contribute to the total output of co2 from this area

field evidence for active normal faulting in tibet crustal thickening does not now occur in southern tibet field observations made during the chinese french expedition of 1980 support an earlier hypothesis based on a combined analysis of satellite images and fault plane solutions of earthquakes immediately north of the highest peaks of the himalayas the tectonic regime is dominated by east west extension we have mapped a large number of north south normal faults which sharply cut the glacial and post glacial morphology and followed several recent earthquake breaks along faults detected on satellite and aerial photographs microtectonic measurements in the quaternary suggest that the maximum principal stress is vertical

geochemical precursors to seismic activity studies of earthquake precursory phenomena during the last several decades have found that significant geophysical and geochemical changes can occur prior to intermediate and large earthquakes among the more intensely investigated geochemical phenomena have been 1 changes in the concentrations of dissolved ions and gases in groundwaters and 2 variations in the concentrations of crustal and mantle volatiles in ground gases the concentration changes have typically showed no conanomalies trend either increasing or decreasing and the spatial and temporal distribution of the observed anomalies have been highly variable as a result there is little agreement on the physical or chemical processes responsible for the observed anomalies mechanisms proposed to account for precursory groundwater anomalies include ultrasonic vibration pressure sensitive solubility pore volume collapse fracture induced increases in reactive surfaces and aquifer breaching fluid mixing precursory changes in soil gas composition have been suggested to result from pore volume collapse micro fracture induced exposure of fresh reactive silicate surfaces and breaching of buried gas rich horizons an analysis of the available field and laboratory data suggests that the aquifer breaching fluid mixing ab fm model can best account for many of the reported changes in temperature dissolved ion and dissolved gas concentrations in groundwater ultrasonic vibration and pressure sensitive solubility models cannot reasonably account for the geochemical variations observed and although the pore collapse model could explain some of the observed chemical changes in groundwater and ground gas uncertainties remain regarding its ability to generate anomalies of the magnitude observed other geochemical anomalies in particular those associated with hydrogen and radon seem best accounted for by increases in reactive surface areas irsa model that may accompany precursory deformation around the epicenter of an impending earthquake analysis of the probable response of these models to the earthquake preparation process as well as to other environmental factors suggests that geochemical monitoring programs can provide information that may be valuable in forecasting the probability of an earthquake however because of the complexity of the earthquake preparation process the absolute prediction of seismic events using geochemical methods alone does not presently appear to be feasible

compositions and flux of soil gas in liu huang ku hydrothermal area northern taiwan abstract soil co 2 flux has been considered a useful proxy to remotely monitor volcanic activity in a hydrothermal area within a safe distance the liu huang ku lhk area which is close to the taipei basin and many existing active fumaroles and hot springs was chosen for the first systematic soil gas study in a hydrothermal area of taiwan in 2004 and 2006 the soil co 2 flux was measured by the closed chamber method with a non dispersive infrared detector soil co 2 emission rate was estimated 19 8 0 2 t day 1 and 582 t km 2 day 1 in 2004 and 22 4 0 2 t day 1 and 659 t km 2 day 1 in 2006 respectively these values are close to those reported for other active high co 2 flux hydrothermal areas of the world it implies that magmatic gases are actively degassing from subsurface in northern taiwan helium and carbon isotopic data reveal that soil gas in lhk is mainly derived from the mantle and is mixed with a small amount of crustal and air components the abundance of soil co 2 shows a positive correlation with the 3 he 4 he ratios and total sulfur contents which are considered as magmatic sensitive indicators for the fumarolic samples therefore soil co 2 could be used as a good proxy for future monitoring of magmatic activity in this area

tibetan uplift prior to the eocene oligocene climate transition evidence from pollen analysis of the xining basin uplift of the tibetan plateau and the himalayas since the onset of the indo asia collision is held responsible for asian aridifi cation and monsoon intensifi cation but may also have gradually cooled global climate leading to the 34 ma eocene oligocene transition to unravel the interplay between tibetan uplift and global climate proxy records of asian paleoenvironments constrained by accurate age models are needed for the paleogene period here we report the 38 ma appearance of high altitude vegetation recovered from palynological assemblages in precisely dated lacustrine sediments from the xining basin of the northeastern tibetan plateau region this result confi rms previous evidence for important regional uplift in the central and northern tibetan plateau regions during the early stage of the indo asia collision this is consistent with the idea that the associated increase in rock weathering and erosion contributed to lowering of atmospheric co 2 leading to the eocene oligocene transition

helium and carbon isotopes in the dissolved gases of friuli region ne italy geochemical evidence of co2 production and degassing over a seismically active area abstract the first geochemical data showing the existence of an active degassing activity over a large seismically active sector of the southern alps friuli region ne italy are presented the dissolved gases helium and carbon isotopic systematics of 46 water samples taken from 13 sites running along e w and ne sw faults besides the natural degassing of a 5000 km 2 wide area are investigated the chemical composition of the dissolved gases revealed that a co 2 rich gas phase feeds the local groundwaters 3 he 4 he ratios r normalized to the atmospheric 3 he 4 he ratio ra 1 39 10 6 and corrected for the atmospheric contamination r ra c range from 0 29 to 1 as a result of a two component radiogenic and atmospheric mixing the 13 c values of total dissolved inorganic carbon tdic ranging from 15 28 to 0 75 vs pdb show the occurrence of multiple gas water interactions the mixing between the atmospheric air and a crustal source and the gas water interactions occurring at various extents appears to be the main control on the observed he c systematics the natural co 2 degassing was evaluated by a soil gas survey carried out by a grid of about 100 measuring sites located over the area that generated destructive seismic sequences e g the gemona sequence of 1976 main shocks m6 4 of 6th may and m6 1 of 11th and 15th september the results obtained show that a significant amount of crustal originated gases are released over the continental area of eastern southern alps the evidence that carbon dioxide is associated with radiogenic type helium denotes the lack of the mantle as primary energy and degassing source highlighting the possibility that co 2 is produced by thermo mechanical processes occurring at seismogenic depth the information provided here may be used to start up a long term geochemical monitoring of this seismically active area and could be able to detect the modifications occurring to the circulating fluids to gain a better insight on the relationships between the fluids geochemistry and the activity of the local seismogenic faults

magnetostratigraphy of the neogene siwalik group in the far eastern himalaya kameng section arunachal pradesh india abstract the siwalik group was deposited from the mid miocene to the pliocene in the foreland of the himalaya and records the unroofing history of the mountain belt in this study we provide the first magnetostratigraphic data for the eastern himalayan foreland basin we analyzed two sections of the lower to upper siwalik group along the kameng river in arunachal pradesh india magnetostratigraphic data were acquired from 395 sites within a 5 8 km thick molassic series thermal demagnetization and magnetic rock property analyses indicate a relatively low temperature 150 340 c characteristic remanent magnetization chrm yielding reliable primary directions carried by iron sulfides such as greigite the results show local counter clockwise rotation of the thrust sheets which is consistent with partitioning of arc normal and left lateral strain along the himalaya nineteen polarity zones have been identified in the two sections detrital fission track data from the top and bottom of the sections are used to constrain correlations with the geomagnetic polarity time scale gpts from chron c5ar 1n to chron c2an 2n from these results we propose that the siwalik formation in arunachal pradesh was deposited between 13 and 2 5 ma the transition between the lower and middle siwaliks is dated at about 10 5 ma and the middle to upper siwaliks transition is dated at 2 6 ma these results coupled with sedimentological observations suggest that the eastern himalayan chrono stratigraphic record is nearly synchronous with that analyzed in other parts of the neogene himalayan foreland basin nevertheless some differences in the evolution of the sedimentation rate and in the thickness of the middle siwaliks suggest that indian plate flexure in the east is different from that observed in other parts of the indian foreland basin and could be affected by the presence of the shillong plateau to the south

dynamic fluvial systems and gravel progradation in the himalayan foreland although the large scale stratigraphy of many terrestrial foreland basins is punctuated by major episodes of gravel progradation the relationships of such facies to hinterland tectonism and climate change are often unclear structural reentrants provide windows into older and more proximal parts of the foreland than are usually exposed and thus provide key insights to earlier phases of foreland evolution our magnetostratigraphic studies show that although the major lithofacies preserved within the himachal pradesh structural reentrant in northwestern india resemble neogene facies in pakistan they have a much greater temporal and spatial variability from 11 5 to 7 ma major facies boundaries in himachal pradesh vary by as much as 2 3 m y across distances of 20 30 km and are controlled by the interference between a major southeastward flowing axial river and a major southwestward flowing transverse river a thick but highly confined middle to late miocene conglomerate facies includes the oldest extensive siwalik conglomerates yet dated 10 ma and implies the development of significant erosional topography along the main boundary thrust prior to 11 ma our studies document extensive syntectonic gravel progradation with conglomerates extending tens of kilometers into the undeformed foreland during a period of increased subsidence rate and within 1 2 m y of major thrust initiation overall gravel progradation is modulated by the interplay among subsidence sediment supply and the proportion of gravels in rivers entering the foreland

mantle degassing on a near shore volcano se tyrrhenian sea the presence of a seamount like structure located a few nautical miles offshore the capo vaticano promontory western calabria s italy was revealed by combined geophysical and geochemical investigation the edifice covers 55 km2 with a top located at a depth of about 70 m below sea level and consists mainly of a nw trending structure orthogonally interrupted by minor ridges the largest of which is affected by extensional faults the top of the edifice hosts active vents injected fluids that have been investigated for dissolved volatiles gas analyses revealed high co2 and ch4 contents several orders of magnitude above the atmospheric type values expected for shallow coastal marine waters and a noteworthy enrichment in mantle derived 3he which is an unambiguous indicator of the mantle origin of the fluids our results combined with available data from the literature suggest that the edifice is a tectonically controlled volcanic system which presence near the calabria region changes the role played by faults in the frame of the subduction process

uplift driven climate change at 12 ma a long δ18o record from the ne margin of the tibetan plateau carbonates from fluvial and lacustrine sediments were sampled from multiple measured sections in the linxia basin of western china based on textural and mineralogical evidence lacustrine carbonates are primary precipitates from lake water a 29 million year record of the oxygen isotope composition of meteoric water is inferred from the n 18 o values of these carbonates this inference is based on the most negative n 18 o values in the lake carbonates which represent lake waters that have experienced the least evaporative enrichment carbonate n 18 o values a proxy for rainfall n 18 o are v310 5x throughout the interval of 29 12 ma at 12 ma there is a shift to 39x a value that remains into the pliocene this implies a major reorganization of atmospheric circulation patterns and a shift to more arid conditions at the ne margin of the tibetan plateau with the post 12 ma system similar to that of today the 12 ma event may represent the time at which the tibetan plateau achieves sufficient elevation to block the penetration of moisture from the indian ocean or south pacific into western china the period of greatest aridity is from 9 6 to 8 2 ma a time interval which agrees well with other climate records 2003 elsevier b v all rights reserved

insights into mantle type volatiles contribution from dissolved gases in artesian waters of the great artesian basin australia abstract the geochemical features of the volatiles dissolved in artesian thermal waters discharged over three basins millungera galilee and cooper basin of the australian great artesian basin gab consistently indicate the presence of fluids from multiple gas sources located in the crust e g sediments oil reservoirs granites as well as minor but detectable contributions of mantle magma derived fluids the gases extracted from 19 water samples and analyzed for their chemical and isotopic composition exhibit amounts of co2 up to about 340 mlstp lh2o marked by a 13ctdc total dissolved carbon ranging from 16 9 to 0 18 vs pdb while ch4 concentrations vary from 4 4 10 5 to 4 9 mlstp lh2o helium contents were between 9 and 2800 times higher than equilibrium with air saturated water asw with a maximum value of 0 12 mlstp lh2o helium isotopic composition was in the 0 02 0 21 ra range ra air normalized 3he 4he ratio the three investigated basins differ from each other in terms of both chemical composition and isotopic signatures of the dissolved gases whose origin is attributed to both mantle and crustal volatiles mantle he is present in the west central and hottest part of the gab despite no evidence of recent volcanism we found that the partial pressure of helium significantly higher in crustal fluids than in mantle type volatiles enhances the crustal he signature in the dissolved gases thus masking the original mantle contribution neotectonic activity involving deep lithospheric structures and magma intrusions highlighted by recent geophysical investigations is considered to be the drivers of mantle magmatic volatiles towards the surface the results although pertaining to artesian waters from a vast area of 542 000 km2 provide new constraints on volatile injection and show that fluids geochemistry can provide additional and independent information on the geo tectonic settings of the great artesian basin and its geothermal potential

geochemical evidence of seismogenic induced anomalies in the dissolved gases of thermal waters a case study of umbria central apennines italy both during and after the 1997 1998 seismic swarm 1 in this paper we present the first geochemical data set regarding long term monitoring of dissolved gases in thermal waters from a seismic area three sites in umbria central apennines italy were studied both for the chemical and for the helium isotopic composition of the dissolved gases data were collected during and after the seismic crisis that struck the region in 1997 1998 the chemical composition of the dissolved gases revealed that a co2 rich gas phase was always mixed with an atmospheric derived component dominated by n2 a normal faulting marked the beginning of the seismic activity enhancing the release of co2 on a regional scale variations in both the chemical and isotopic compositions of the dissolved gases were also observed as preseismic synseismic and postseismic phenomena related to the seismic shock of march 1998 those geochemical modifications were interpreted as being the consequence of a drop in the co2 degassing rate in good agreement with the compressive focal mechanism of that seismic event furthermore this interpretation was also consistent with the geologic and tectonic setting of the study area and induced us to postulate that changes in the local rock permeability due to crustal deformations i e coseismic deformation and postseismic release were responsible for the geochemical modifications observed on the basis of the foregoing we have concluded that the geochemistry of dissolved gases in groundwaters represents a useful tool for the investigation of the relationships between circulating fluids and seismic activity

geochemistry of dissolved gases from the eastern carpathians transylvanian basin boundary abstract we show the results of a study on the volatiles dissolved in mineral waters discharged over a 200 km long transect along the rodna b rg u area and c limani gurghiu harghita volcanic chain eastern carpathians romania all of the collected mineral water samples carry dissolved gas with carbon dioxide content up to 1 99 cm 3 stp gh 2 o and helium content up to 2 3 10 5 cm 3 stp gh 2 o carbon 13 c tdic total dissolved inorganic carbon ranging from 15 6 to 5 32 vs vpdb he systematics he isotopes in the range of 0 38 0 99 ra ra air normalized 3 he 4 he ratio and co 2 3 he ratio spanning over four orders of magnitude from morb like values of 2 92 10 9 to crustal type values of 3 02 10 13 coherently indicate the presence of fluids from different crustal sources e g sediments hydrocarbon reservoirs besides minor but detectable contributions of mantle magmatic derived fluids up to 16 45 our investigations show that the wide range of chemical and isotopic composition can be explained in terms of mixings among different gas sources feeding the groundwater and the contemporary occurrence of gas water interactions like degassing and deposition of carbonates affecting the circulating waters after their infiltration

origin of carbon in fumarolic gas from island arcs abstract we have measured 3 he 4 he ratios 13c values and co 2 3 he ratios of fumaroles and hot spring gases in three volcanic areas in japan the 3 he 4 he ratios 13c values and co 2 3 he ratios vary from 02 05 ratm 9 7 to 2 7 and from 7 74 109 to 1 18 1011 respectively based on these data and those in the literature we present the first quantitative estimates of the upper mantle sediment and limestone including slab components in co2 of volcanic and hydrothermal fluids from subduction zones taking compiled c isotopic data of limestone and organic sediment assuming that the co 2 3 he ratio and 13c value of mid ocean ridge basalt morb are representative of the upper mantle component and that later isotopic and elemental fractionations are minimal it is possible to deconvole each fraction of c on the basis of simple mixing equations up to 20 of the carbon in high temperature volcanic gases in subduction zones is derived from a morb type source while the major fraction of the gases is attributable to co2 produced by decarbonation of subducted marine limestone and slab carbonate

geochemical applications of noble gases abstract noble gases are unique tracers due to their rarity on earth and their inertness several of their isotopes are produced by nuclear reactions whereas others were trapped when the earth formed they have been widely used for understanding the evolution and structure of the earth dating geological events processes characterizing magma genesis and volcanism in different tectonic environments tracing mantle crust interaction even in non volcanic areas and for monitoring earthquake and volcanic activities some of these topics were presented at the 9th international conferences on gas geochemistry that was held in 2007 in taipei taiwan this special volume includes twelve papers which cover a wide range of applications of noble gases geochemistry such as tracing the thermal evolution of the early earth understanding the mantle source of continental basalts establishing the spatial variations of gas compositions in hot springs and fumaroles from volcanic and forearc areas as well as in key non volcanic areas such as faults and seismic zones and tracing the origin and evolution of ore forming fluids of uranium deposits reproducing the noble gas behavior during faulting and finally using argon as a tracer of large scale geologic processes

enhanced global continental erosion and exhumation driven by oligo miocene climate change surface erosion is the most significant process responsible for the recycling of continental crust into the upper mantle and controls both exhumation in mountain belts and the long term global climate via chemical weathering earlier studies have highlighted the importance of climate instability since the onset of northern hemispheric glaciation similar to 3 ma as being the primary influence causing high erosion rates since that time here i show that synchronous pulses of erosion and exhumation occurred across eurasia in north america and in africa starting after 33 ma with a prominent peak around 16 ma correlation of these erosional events with changes in global climate suggests that they are controlled by surface processes because these climate events involve both cooling and warming periods the importance of increased seasonality is emphasized as being the key factor in controlling global erosion and exhumation throughout the cenozoic citation clift p d 2010 enhanced global continental erosion and exhumation driven by oligo miocene climate change geophys res lett 37 l09402 doi 10 1029 2010gl043067

intensification of monsoon microclimate and asynchronous c4 appearance isotopic evidence from the indian siwalik sediments article i nfo analysis of the d h ratio of pedogenic clay and the 18 o 16 o ratio of carbonate nodules collected from siwalik sediments in india indicates three episodes of monsoon intensification at 11 ma 6 ma and 3 ma these episodes coincide with major pulses of tectonic uplift in the himalayas suggesting causal link between monsoon intensity and uplift in addition variation in the carbon isotope ratio of carbonate nodules and residual organic matter indicates a change in vegetation regime from pure c3 type to a mix of c3 c4 type during this time span isotopic analysis of samples collected from different locations of the himalayan siwalik shows that the late miocene c4 appearance was locally asynchronous by 3 ma similar to what is seen on a global scale the lack of synchronous emergence of c4 plants in various parts of siwalik probably indicates a combined effect of microclimate e g varying monsoon intensity and habitat disturbance e g forest fire in contrast subsequent expansion of c4 plants during the late miocene pliocene time could be entirely due to monsoon intensification that favoured c4 respiration in a warm and seasonally variable rainfall regime 2010 elsevier b v all rights reserved

simultaneous miocene extension and shortening in the himalayan orogen the south tibetan detachment system separates the high grade metamorphic core of the himalayan orogen from its weakly metamorphosed suprastructure it is thought to have developed in response to differences in gravitational potential energy produced by crustal thickening across the mountain front geochronologic data from the rongbuk valley north of qomolangma mount everest in southern tibet demonstrate that at least one segment of the detachment system was active between 19 and 22 million years ago an interval characterized by large scale crustal thickening at lower structural levels these data suggest that decoupling between an extending upper crust and a converging lower crust was an important aspect of himalayan tectonics in miocene time

late cenozoic genus fupingopollenites development and its implications for the asian summer monsoon evolution an extinct palynomorph fupingopollenites was used as the basis for a discussion of the late cenozoic asian summer monsoon asm evolution and its possible driving forces based on the spatial and temporal variations in its percentages across inner and east asia we found that fupingopollenites mainly occurred in east asia with boundaries to the ne of ca 42 degrees n 135 degrees e and nw of ca 36 degrees n 103 degrees e during the early miocene ca 23 17 ma this region enlarged westwards reaching the eastern qaidam basin ca 36 degrees n 97 5 degrees e during the middle miocene ca 17 11 ma before noticeably retreating to a region bounded to the nw at ca 33 degrees n 105 degrees e during ca 11 5 3 ma the region then shrank further in the pliocene with the ne boundary shrinking southwards to about 35 degrees n 120 degrees e the area then almost disappeared during the pleistocene 2 6 0 ma the flourishing and subsequent extinction of fupingopollenites is indicative of a narrow ecological amplitude with a critical dependence on habitat humidity and temperature most likely mean annual precipitation map 1000 mm and mean annual temperature mat 10 degrees c therefore the fupingopollenites geographic distribution can indicate the humid asm evolution during the late cenozoic revealing that the strongest asm period occurred during the middle miocene climate optimum mmco similar to 17 14 ma after which the asm weakened coincident with global cooling we argue that the global cooling played a critical role in the asm evolution while the tibetan plateau uplifts made a relatively small contribution c 2015 international association for gondwana research published by elsevier b v all rights reserved

gas geochemistry and seismotectonics a review abstract publications on soil and spring gases have been examined regarding their relationships with both tectonic and seismic activities the main sources behaviours and uses of species detected in soils and springs are displayed and their mode of sampling and analysing briefly described the main patterns of degassing in soils are described and we outline the wide range of geochemical signatures as the result of both permeability and mineralogical contrasts because thermomineral waters have been in contact with great volumes of crustal rocks at various depths spring gases might be more representative of the local environment than soil gases moreover gas signature comparisons show that spring gases are much more enriched with deep gases and slightly contaminated by atmospheric gases therefore they can be considered as better samples for identifying precursors of earthquakes environmental perturbations are examined and it is shown from divergent cases that pressure temperature soil moisture or earth tides may generate very high perturbations of the degassing process such effects demonstrate that no systematic correction law can be proposed and that removing external contributions from gas concentrations must be performed case by case this demonstrates therefore the need for the simultaneous measurement of external parameters during gas monitoring a qualitative examination of about 150 claimed precursors proposed in the literature has been reviewed as noted by previous authors anomalies appear at distances sometimes much greater than typical source dimensions and occur in the field of strain higher than 10 9 most of them being in the field of strain higher than 10 8 taking into account the very high heterogeneity of such a set of data we can suggest that amplitudes of gas anomalies are independent of both magnitudes and epicentral distances of related earthquakes suggesting local conditions to control amplitudes on the contrary precursory time and duration of anomalies seem to increase both with magnitudes and epicentral distances abundant evidence demonstrates the major role of crustal fluids in the earthquake cycle many works have outlined the fact that crustal instabilities can appear as the result of low stress strain perturbations during loading it has been suggested that motion of fluids may occur at various scales from microcrack fluid transfer up to changes of hydraulic levels of water tables the study of subsequent anomalies is expected to supply a tool for earthquake prediction following previous authors we outline the need for further methodological improvements including the setting up of multiparameter station networks and the simultaneous recording of the main external parameters atmospheric pressure water and air temperature soil moisture for signal processing

late miocene through early pliocene deep water circulation and climate change viewed from the sub antarctic south atlantic benthic foraminiferal stable isotope records for the past 11 myr from a recently drilled site in the sub antarctic south atlantic site 1088 ocean drilling program leg 177 41 s 15 e 2082 m water depth provide for the first time a continuous long term perspective on deep water distribution patterns and southern ocean climate change from the late miocene through the early pliocene i have compiled published late miocene through pliocene stable isotope records to place the new south atlantic record in a global framework carbon isotope gradients between the north atlantic south atlantic and pacific indicate that a nutrient depleted watermass probably of north atlantic origin reached the sub antarctic south atlantic after 6 6 ma by 6 0 ma the relative proportion of the northernprovenance watermass was similar to today and by the early pliocene it had increased to greater than the modern proportion suggesting that thermohaline overturn in the atlantic was relatively strong prior to the early pliocene interval of inferred climatic warmth site 1088 oxygen isotope values display a two step increase between v7 4 ma and 6 9 ma a trend that parallels a published n 18 o record of a site on the atlantic coast of morocco this is perhaps best explained by a gradual cooling of watermasses that were sinking in the southern ocean i speculate that relatively strong thermohaline overturn at rates comparable to the present day interglacial interval during the latest miocene may have provided the initial conditions for early pliocene climatic warmth the impact of an emerging central american seaway on atlantic pacific ocean upper water exchange may have been felt in the north atlantic beginning in the latest miocene between 6 6 and 6 0 ma which would be v1 5 myr earlier than previously thought 9 2002 elsevier science b v all rights reserved

expansion of c4 grasses in the late miocene of northern pakistan evidence from stable isotopes in paleosols stable isotopic clay mineralogic and bulk chemical analyses were conducted on paleosols of the neogene siwalik sections in northern pakistan in order to reconstruct floodplain environments over the past 17 ma the stable carbon isotopic composition of soil carbonate mean 13c pdb 10 2 and associated organic matter mean 13c pdb 24 1 in paleosols representing 17 7 3 ma reveal that floodplain vegetation was dominated by c3 plants at 7 3 ma a shift toward more positive carbon isotopic values began signaling the gradual expansion of c4 grasses onto the floodplain from 6 ma to present carbon isotopic values for paleosol carbonate mean 13c pdb 0 6 and organic matter mean 13c pdb 14 4 are uniformly enriched in 13c indicating the presence of nearly pure c4 grassland the scarcity of kaolinite and abundance of smectite and pedogenic carbonate in most paleosols suggest that rainfall in the region remained 1 0 1 25 m yr or less for the entire 17 ma of record paleosols in the lower portion of the section lack organic a horizons but have reddish b horizons often containing secondary iron oxide nodules leaching depths of soil carbonate in these older paleosols are typically greater than those in the plio pleistocene part of the section where organic a horizons are common and b horizons are markedly more yellow the combined evidence suggests that the mature paleosols in the pre 7 3 ma part of the record are dominantly calcareous alfisols or mollisols that once underlay nearly pure c3 vegetation perhaps trees and shrubs while calcareous mollisols underlying c4 grassland dominate the upper part of the record the carbon and oxygen isotopic trends in the paleosol record in pakistan are also evident in the diet of fossil mammals and in paleosols from nepal thus demonstrating that these paleoenvironmental changes in floodplain vegetation may be continent wide local effects such as the development or intensification of the asian monsoon driven by uplift of the tibetan plateau may have led to the expansion of c4 grasses if however the expansion of c4 grasses proves globally synchronous then a larger scale cause such as a marked decrease in co2 may be the driving mechanism

climatic and tectonic uplift evolution since 7 ma in gyirong basin southwestern tibet plateau clay mineral evidence climate evolution associated with the uplift in gyirong southern margin of the tibetan plateau was investigated based on the clay mineralogy of the gyirong sediments using x ray diffraction and scanning electron microscopy methods the chlorite illite kaolinite smectite ratio and the illite crystallinity index suggest the trend of paleoclimate evolution in gyirong basin during 7 1 7 ma bp with a warm and humid climate in 7 0 5 8 ma a relative cool and dry climate in 5 8 5 5 ma a relative warm and humid climate in 5 5 2 5 ma and a much warmer climate in 2 5 1 7 ma respectively the fluctuating kaolinite smectite index and calcite content and the frequent occurrence of gypsum in the episode of 6 7 5 5 ma suggest intense climatic fluctuations between humid and more seasonal humid conditions five peaks exhibit at 5 8 4 9 4 3 3 6 and 2 5 ma in the curves of illite and chlorite content and illite crystallinity the intense uplift and tectonic forced cooling at 5 8 and 4 3 ma were indicated by the high illite crystallinity index and illite and chlorite content a remarkable increase in illite and chlorite content associated with only little increase in illite crystallinity at 3 6 ma indicates a rapid uplift but no significant climate change and a sharp increase in illite crystallinity while small change in illite and chlorite content at 2 5 ma suggests that no remarkable relief was produced by the uplift which may take place in the whole south tibet plateau while cooling at 4 9 ma is probably a record of the global climate cooling

anomalies of mantle derived helium during the 1997 1998 seismic swarm of umbria marche italy more than 100 he 4he isotope ratios were measured in co2 dominated gas samples collected during the 1997 1998 seismic crisis that shook the umbria marche central apennines italy although the gas emissions were located in a typical crustal environment the measured values delineate variable mixing proportions between mantle derived and crustal helium during the monitoring period anomalous he 4he ratios were observed together with a significant increase of fluid outflows the observed he 4he anomalies appear to be driven by stress induced crustal deformations affecting micro fracturing and bulk permeability and in turn by a seismogenic induced modification of the crustal permeability of rocks since crustal deformations can also occur aseismically the geochemical anomalies must be considered indicators of processes occurring below the surface which could eventually help to estimate the probability increase of an impending earthquake instead of pure empirical precursors

late miocene topographic inversion in southwest tibet based on integrated paleoelevation reconstructions and structural history article investigations of the deformation history of the himalayan orogen support interpretations of rapid and striking changes in the landscape of the tibetan himalaya and high himalaya we examine this issue by integrating oxygen isotope based paleoelevation reconstructions of the zada basin in southwestern tibet with information on the structural evolution of the high and tibetan himalaya between 79 e and 84 30 e 18 opsw values were calculated from 18 occ values from pristine fluvial miocene gastropod shells analyses comparing the most negative 18 osw and reconstructed 18 opsw values to 18 osw versus elevation relationships based on both thermodynamic models and an empirical data set suggest a decrease in the mean watershed elevation of 1 to 1 5 km since the late miocene geologic mapping and structural data from crustal scale fault systems in the zada region and regions to its east indicate a phase of arc normal shortening and vertical thickening since the middle miocene followed by ongoing arc parallel extension and vertical thinning these results suggest that regions in this part of the orogen transitioned from undergoing arc normal shortening to arc parallel extension in the late miocene and that arc parallel extensional structures root deeply within the himalayan thrust wedge when combined with data on the distribution age and provenance of sedimentary basins our geologic mapping structural data and paleoelevation results suggest that this transition from shortening to extension was accompanied by a topographic inversion from mountains to basins in b4 m y these observations can be explained by a foreland propagating fault system that accommodates outward radial expansion of the himalayan orogen

late cenozoic eolian deposition in the north pacific asian drying tibetan uplift and cooling of the northern hemisphere a newly constructed record of eolian dust accumulation from the central north pacific shows that dust deposition increased by an order of magnitude quite rapidly at 3 6 ma we associate this sudden drying with the uplift of at least the northern portion of the tibetan plateau shutting off the indian ocean moisture source to central and western china this ten fold increase in atmospheric dust loading appears to be associated with the 1 m y long shift toward heavy 18o values that occurred at 3 6 2 6 ma the dust grain size record of wind intensity begins its late cenozoic coarsening a million years before the drying event at 4 5 ma the northern hemisphere cooling that results in intensification of the subpolar westerly winds may have as its ultimate cause the drawdown of atmospheric co2 in the latest miocene and the early pliocene closing of the panamanian seaway

east west extension and miocene environmental change in the southern tibetan plateau thakkhola graben central nepal east west extensional basins are distributed across the southern half of the tibetan plateau at an elevation of 4 km these basins have generated much interest because of their potential implications for the regional tectonics and force distribution in the plateau this study documents the sedimentology of the miocene pliocene thakkhola graben fill in order to reconstruct basin evolution and paleoenvironment analysis of depositional systems paleodrainage patterns and conglomerate clast provenance of the 1 km thick graben fill sets limits on the timing of activity of the basin bounding faults and the development of southward axial drainage in the basin during the deposition of the oldest basin fill tetang formation ca 11 9 6 ma probably in a restricted basin minor motion occurred on the basin bounding fault systems an angular unconformity separates the tetang and overlying thakkhola formations where this contact can be observed in the southern part of the basin southward axial drainage was established by ca 7 ma with the onset of deposition of the thakkhola formation several episodes of damming of this drainage system are recorded by widespread lacustrine deposits in the southern part of the basin facies distribution and the progressive rotation of strata in the thakkhola formation indicate that the dangardzong fault on the western edge of the basin was active at this time and drainage ponding may have been related to displacement on normal faults associated with the south tibetan detachment system to the south of thakkhola graben contrasts between deposits of the tetang and thakkhola formations provide evidence for environmental change in the basin in the tetang formation the abundance of lacustrine facies the pollen record and the absence of paleosol carbonate suggest that conditions were more humid than during subsequent deposition of the thakkhola formation environmental change in the thakkhola graben coincided with environmental change observed in the siwalik foreland basin sequence arabian sea and bay of bengal at ca 8 7 ma although this climate change event has been previously attributed to intensification of the asian monsoon in response to uplift of the tibetan plateau paleoaltimetry data indicate that this region had already attained a high elevation by ca 11 ma thus the thakkhola graben stratigraphic record suggests that uplift of the southern tibetan plateau and the onset of the asian monsoon as inferred from paleoclimatic indicators were not directly related in a simple way

a paleoclimatic enigma major glaciations began in the northern hemisphere around 2 75 million years ago after a long prior interval of climatic cooling numerous observations reveal how climate cooled before glacial onset but our understanding of the driving forces behind the cooling remains incomplete

extended stratigraphy palynology and depositional environments record the initiation of the himalayan gyirong basin neogene china here we report new sedimentological and paleontological data from a 603 5 m thick neogene sequence woma section in the gyirong basin a basin induced by east west extension in the himalayas of southern tibet we document the conglomeratic danzengzhukang formation at the base of the section and the overlying finer grained woma formation that includes a hipparion fauna based on stratigraphic correlations and earlier thermochronology and magnetostratigraphic results we bracket the depositional age of this section between 10 8 ma and 1 7 ma lithology paleo current directions and provenance analysis together with palynological and paleontological data have revealed three depositional environments for the deposition of the studied section 1 alluvial fan to braided river environments with ese transport directions danzengzhukang formation 1 7 ma with increased denudation and wsw paleo currents was associated with a deciduous coniferous and broad leaved mixed forest that suggests an increase in climate variability our data indicate that the gyirong basin was under overall warm and humid conditions throughout most of its history in agreement with high resolution oxygen and carbon isotope data collected from the same section this issue we interpret our warm climate in the gyirong basin to reflect the prevalence of the monsoonal influence and the distal pollen sources to result from orographic effects

geochemical monitoring of the 2012 po valley seismic sequence a review and update abstract a seismic swarm characterized by a ml 5 9 mainshock occurred in the po valley northern italy in 2012 the area has been studied for active compressional tectonics since the beginning of the twentieth century a variety of geophysical and geochemical parameters have been utilized with the purpose of identifying possible precursory signals this paper considers groundwater level data and geochemical data both in groundwaters and in gases all considered parameters have led to the conclusion that possible long and medium precursory trends have been identified in geofluids no short term precursors have been clearly identified hydrogeological and geochemical monitoring could be more effectively utilized in a different geological context and seismic hazard reduction procedures could benefit from geofluid monitoring

palaeolatitude and age of the indo asia collision palaeomagnetic constraints summary ongoing controversies on the timing and kinematics of the indo asia collision can be solved by palaeomagnetically determined palaeolatitudes of terranes bounding the indo asia suture zone we show here based on new palaeomagnetic data from the linzizong volcanic rocks 54 47 ma near the city of lhasa that the latitude of the southern margin of asia was 22 8 4 2 n when these rocks were deposited this result combined with revised palaeomagnetic results from the northernmost sedimentary units of greater india and with apparent polar wander paths of india and eurasia palaeomagnetically constrain the collision to have occurred at 46 8 ma 95 per cent confidence interval these palaeomagnetic results are consistent with tomographic anomalies at 15 25 n that are interpreted to locate the tethyan oceanic slab that detached following collision and with independent 56 46 ma collision age estimates inferred from the timing of slowing down of india high pressure metamorphism the end of marine sedimentation and the first occurrence of suture zone and arc detritus on the greater indian margin when compared with apparent polar wander paths of india and eurasia the 46 ma onset of collision at 22 8 4 2 n implies 2900 600 km subsequent latitudinal convergence between india and asia divided into 1100 500 km within asia and 1800 700 km within india

late cenozoic uplift of southeastern tibet the age of surface uplift in southeastern tibet is currently unknown but the initiation of major river incision can be used as a proxy for the timing of initial uplift the topographically high eastern plateau and gently dipping southeastern plateau margin are mantled by an elevated low relief relict landscape that formed at a time of slow erosion at low elevation and low tectonic uplift rates prior to uplift of the eastern tibetan plateau thermochronology from deep river gorges that are cut into the relict landscape shows slow cooling between ca 100 and ca 10 20 ma and a change to rapid cooling after ca 13 ma with initiation of rapid river incision at 0 25 0 5 mm yr between 9 and 13 ma a rapid increase in mean elevation of eastern tibet beginning at this time supports tectonic climate models that correlate the lateral eastern expansion of high topography in tibet with the late miocene intensification of the indian and east asian monsoons

seismicity in idaho and montana triggered by the denali fault earthquake a window into the geologic context for seismic triggering we present a case study of dynamically triggered seismicity in idaho and western montana from the 2002 mw 7 9 denali fault earthquake to investigate the relationship between measured geological discriminants and propensity for trig gering we first establish triggering we find events that are not reported in the advanced national seismic system catalog in idaho and yellowstone following the denali fault earthquake by filtering broadband waveforms an ml 4 6 earthquake is discovered near new meadows idaho during the passage of the rayleigh waves and another earthquake probably located near yellowstone we find that central western idaho and yellowstone have statistically significant seismicity increases by applying a b test to the cataloged events in the 48 hr after the denali fault earthquake in idaho and surrounding regions we also find that pine idaho may have triggered events but the measurement is not robust because of uncertainty in the background seismicity rate both central western idaho and yellowstone triggered previously during the 1992 landers earthquake we then try to determine the local geological conditions necessary for triggered seismicity to occur geothermal regions with high total dissolved solids and background seismicity appear to be favorable conditions to trigger earthquakes in the study

development of asian monsoon revealed by marked ecological shift during the latest miocene in northern pakistan carbon isotopes from soil carbonate1 4 and soil organic matter5 6 yield palaeoecological information because the carbon in the soil carbonate forms in isotopic equilibrium with local soil co2 refs 1 7 the isotopic composition of which is in turn determined by local plant cover siwalik group sediments in northern pakistan contain a well exposed palaeosol record spanning the past 18 myr here we report on stable carbon isotope results from associated pedogenic carbonate which indicate a dramatic ecological shift from to dominated floodplain biomass beginning 7 4 7 0 myr ago the earlier c3 floodplain biomasses were probably mainly composed of trees and shrubs whereas c4 grasslands dominated in the plio pleistocene oxygen isotopes also exhibit a shift in the latest miocene probably corresponding to a major climate change which may have induced the forest to grassland transition this dramatic ecological shift in the latest miocene may mark the inception or a marked strengthening of the asian monsoon system

new field and geophysical data about transpressional deformation an improved model for the structural style of sha gou fault area in southern ningxia northeastern edge of tibetan plateau china abstract situated near the northeastern edge of the tibetan plateau the sha gou fault area sgfa represents an important area to understand cenozoic regional interactions between northeastern ne tibetan plateau and southwestern sw liupan shan basin within this region several km scale arcuate fault systems such as the lijun fault and the madong shan piedmont fault accommodate the transpressive deformation but their structural style is still controversial predecessors regarded these bow like faults as southwest dipping thrust systems with large scale nappes however this opinion is not compatible with the new field and geophysical data in this study we aim to ascertain the structural pattern of this area based on the analyses of field observation data interpretation of seismic reflection profiles and two dimensional gravity forward modeling according to the present fieldwork the structural cleavages low angle slickenlines sub vertical fault surfaces ribbon effect as well as the linear geomorphic features in plane view indicate that these faults belong to a strike slip system newly acquired seismic profiles characterized by distinct positive flower structures strongly suggest that this area is again a strike slip fault system rather than a thrusting system furthermore gravity forward modeling results show that the reverse strike slip model without large scale thrust nappes is closer to the present structural style of this area the gravity forward modeling is an effective method to identify km scale thrust nappes which could be used for reference by the structural style analysis in other similar regions based on these evidences a new transpressional shear model for the structural pattern is proposed the overall structural style of the sgfa is not characterized by large scale thrust nappes but is dominated by a transpressional shear system with significant strike slip faulting such a new model can be an additional evidence for the tectonic escape that is going on in the area north of the himalaya and is dominated by reverse strike slip deformation the stepwise morphology i e the pre cretaceous strata in the west of strike slip faults are higher than those in the east successively in this model is also caused by the uplift of the tibetan plateau furthermore the strike slip deformation indicates that the sw liupan shan basin is a continental sub basin segmented by several km scale strike slip faults rather than the imbricated style of purely contractional system in typical foreland basin

active tectonics of the adriatic region from gps and earthquake slip vectors 1 to investigate the kinematics of the adriatic region we integrate continuous and episodic gps measurements with mw 4 5 earthquake slip vectors selected from the regional centroid moment tensor catalogue coherent motion of gps sites in the po valley in apulia and in the hyblean plateau allows us to estimate geodetically constrained angular velocities for these regions the predictions of the gps inferred angular velocities are compared with the earthquake slip vectors showing that the seismically expressed deformation at the microplate boundaries is consistent with the observed geodetic motion the remarkable consistency between geodetic seismological and geological evidence of active tectonics suggests that active deformation in the central adriatic is controlled by the relative motion between the adria and apulia microplates the microplates angular rotation rates are then compared with the rotation rates calculated with a simple block model supporting the hypotheses 1 that apulia forms a single microplate with the ionian sea and possibly with the hyblean region and 2 that adria and apulia rotate in such a way as to accommodate the eurasia nubia relative motion we suggest that the present day microplate configuration follows a recent fragmentation of the adriatic promontory that during the neogene rigidly transferred the africa motion to the orogenic belts that now surround the adriatic region

origin and interactions of fluids circulating over the amik basin hatay turkey and relationships with the hydrologic geologic and tectonic settings abstract we investigated the geochemical features of the fluids circulating over the amik basin se turkey syria border which is crossed by the northern extension of the dsf dead sea fault and represents the boundary area of three tectonic plates anatolian arabian and african plates we collected 34 water samples thermal and cold from natural springs and boreholes as well as 8 gas samples bubbling and gas seepage besides the gases dissolved in the sampled waters the results show that the dissolved gas phase is a mixture of shallow atmospheric and deep components either of mantle and crustal origin coherently the sampled waters are variable mixtures of shallow and deep ground waters the latter being characterised by higher salinity and longer residence times the deep groundwaters from boreholes deeper than 1000 m have a ch 4 dominated dissolved gas phase related to the presence of hydrocarbon reservoirs the very unique tectonic setting of the area includes the presence of an ophiolitic block outcropping in the westernmost area on the african plate as well as basalts located to the north and east on the arabic plate the diffuse presence of co 2 enriched gases although diluted by the huge groundwater circulation testifies a regional degassing activity fluids circulating over the ophiolitic block are marked by h 2 dominated gases with abiogenic methane and high ph waters the measured 3 he 4 he isotopic ratios display contributions from both crustal and mantle derived sources over both sides of the dsf although the serpentinization process is generally independent from mantle type contribution the recorded helium isotopic ratios highlight variable contents of mantle derived fluids due to the absence of recent volcanism over the western side of the basin african plate we argue that co 2 rich volatiles carrying mantle type helium and enriched in heavy carbon are degassed by deep rooted regional faults rather than from volcanic sources

conjugate strike slip faulting along the bangong nujiang suture zone accommodates coeval east west extension and north south shortening in the interior of the tibetan plateau this is the published version copyright 2002 american geophysical union all rights reserved

rate of diffuse carbon dioxide earth degassing estimated from carbon balance of regional aquifers the case of central apennine italy central italy is characterized by an anomalous flux of deeply derived co2 in the western tyrrhenian sector of central italy co2 degassing occurs mainly from focused emissions vents and strong diffuse degassing and thermal springs whereas in the eastern apennine area deep co2 is dissolved in cold groundwaters of regional aquifers hosted by mesozoic carbonate evaporite formations influx of deep co2 into 12 carbonate aquifers 12 500 km2 of the central apennine is computed through a carbon mass balance that couples aquifer geochemistry with isotopic and hydrogeological data mass balance calculations estimate that 6 5 1010 mol yr 1 of inorganic carbon are dissolved in the studied aquifers approximately 23 of this amount derives from biological sources active during the infiltration of the recharge waters 36 comes from carbonate dissolution while 41 is representative of deep carbon sources characterized by a common isotopic signature 13c 3 the calculated deep co2 influx rate ranges from 105 to 107 mol yr 1 km 2 increasing regionally from east to west in the study area

magnetic polarity stratigraphy of the neogene siwalik group at khutia khola far western nepal the middle miocene pliocene siwalik group was deposited in the himalayan foreland basin in response to uplift and erosion in the himalayan fold thrust belt results of thermal demagnetization experiments on samples from the siwalik group in central and western nepal demonstrate that laminated siltstones yield paleomagnetic data useful for tectonic and magnetostratigraphic studies sandstones and paleosols of the siwalik group however generally display highly erratic paleomagnetic behavior during thermal demagnetization on the basis of these observations siltstones from a well exposed 2423 m thick section of the siwalik group in khutia khola far western nepal were sampled for magnetic polarity stratigraphy the siwalik group is composed of informal lower middle and upper members correlation of the resulting polarity stratigraphy with the geomagnetic polarity timescale indicates that the exposed section spans 13 30 to 7 65 ma the lower middle siwalik boundary occurs at 11 05 ma near the beginning of chron c5n the rate of sediment accumulation increases upsection similar to rate changes previously observed in the pakistan siwalik group and probably in response to increasing proximity of the himalayan thrust belt in the khutia khola section a discordant declination indicates that this region has rotated about a vertical axis 16 6 counterclockwise with respect to the indian subcontinent measurements of 13 c in paleosol carbonate indicate the predominance of c 3 plants until 7 65 ma and the clear presence of c 4 plants higher in the undated portion of the section

the late miocene through present paleoelevation history of southwestern tibet recent research using stable isotopes of carbon and oxygen from carbonates and fossil teeth seems to support both a pre and post mid miocene uplift of the southern tibetan plateau we examined this issue by analysis of well preserved fossil mollusks and plant remains from the zhada basin in southwestern tibet which ranges in age from 9 2 to paleoenvironmental modeling and physical evidence shows that the climate in zhada basin was cold and arid indistinguishable from modern the 13cpm values of well preserved vascular plant material increase from 23 4 to 26 8 permil at the base of the zhada formation to as high as 8 4 permil above 250 to 300 m this shift denotes the expansion of c4 biomass in this high arid watershed at 7 ma and thus corresponds to the c3 c4 transition observed in neogene deposits of the northern indian sub continent

cenozoic vertebrate evolution and paleoenvironment in tibetan plateau progress and prospects abstract due to its lofty height the tibetan plateau features some of the harshest environments in the world with extreme coldness low oxygen high uv radiation and in places severe aridity these harsh environments have served as the main driver of vertebrate evolution during the cenozoic that produced a low productivity low diversity high endemicity community environmental forcing seems to be a dominant mechanism for mammalian evolution in marginal habitats mammals have acquired special adaptations for thermal insulation oxygen transport dna damage repair and others while broadly similar to faunal assemblages in north china and central asia tibetan faunas often show initiation of cold adapted lineages that predate ice age megafauna our out of tibet hypothesis thus postulates that cold tolerant species in pliocene high tibet were pre adapted to conditions that were to become widespread during the subsequent pleistocene ice age and tibet had thus become a cradle for ice age megafauna the best examples of the out of tibet scenario include the tibetan woolly rhinoceros coelodonta thibetana tibetan bharal pseudois asian hunting dog sinicuon and ancestral snow leopard panthera blytheae our third pole to north pole linkage of an extinct pliocene tibetan fox vulpes qiuzhudingi with the late pleistocene and extant arctic fox vulpes lagopus is a subset of the out of tibet hypothesis one of the iconic tibetan mammals the endemic tibetan antelope pantholops has the longest residence in tibet going back to the late miocene suggesting a long history of perfecting its adaptations to cold environments stable carbon and oxygen isotope analyses of fossils from the tibetan plateau reveal significant spatial and temporal variations in the evolution of herbivores diets and environments during the late cenozoic the diets of modern tibetan herbivores consist primarily of c3 plants reflecting the present day c3 dominance in high elevation cold habitats the available carbon isotope data however show that warm climate c4 grasses were a significant dietary component of ancient herbivores in the gyirong basin central himalayas in the late miocene and in shangri la southeastern tibetan plateau in the pliocene and likely in the qaidam basin ne tibetan plateau from late miocene to early pliocene and in kunlun pass basin northeastern tibetan plateau in the pliocene this suggests that c4 grasses spread into the tibetan plateau in the late miocene and had persisted in some places to early pleistocene but have since disappeared or become insignificant in the region the retreat of c4 grasses from the tibetan plateau is most likely driven by decreases in local temperatures to below the cross over temperature unfavorable to c4 grasses as a result of tectonic uplift and or global climate change the available isotope data also show that high elevation cold climatic conditions that favor c3 over c4 grasses arrived earlier in southwestern tibetan plateau than in southeastern and northeastern parts of the plateau this would imply that the tibetan plateau had not uniformly reached its present height as recent as early pleistocene future research should focus on determining intra regional patterns of ecological and climatic changes in order to tease apart the effects of tectonic uplift and global climate change on local and regional environmental changes and to better understand the linkage between tectonics and climatic and biotic changes

controls on cenozoic exhumation of the tethyan himalaya from fission track thermochronology and detrital zircon u pb geochronology in the gyirong basin area southern tibet the gyirong basin southern tibet contains the record of miocene pliocene exhumation drainage development and sedimentation along the northern flank of the himalaya the tectonic controls on basin formation and their potential link to the south tibetan detachment system stds are not well understood we use detrital zircon zft and apatite aft fission track analysis together with detrital zircon u pb dating to decipher the provenance of gyirong basin sediments and the exhumation history of the source areas results are presented for nine detrital samples of gyirong basin sediments aft zft and u pb two modern river sediment samples zft and aft and six bedrock samples zft from transect across the gyirong fault bounding the basin to the east the combination of detrital zircon u pb and fission track data demonstrates that the gyirong basin sediments were sourced locally from the tethyan sedimentary sequence this provenance pattern indicates that deposition was controlled by the gyirong fault active since 10 ma whose vertical throw was probably 5000 m rather than being controlled by normal faults associated with the stds the detrital thermochronology data contain two prominent age groups at 37 41 and 15 18 ma suggesting rapid exhumation at these times a 15 18 ma phase of rapid exhumation has been recorded widely in both southern tibet and the himalaya a possible interpretation for such a major regional exhumation event might be detachment of the subducting indian plate slab during the middle miocene inducing dynamic uplift of the indian plate overriding its own slab

development of active low angle normal fault systems during orogenic collapse insight from tibet active north trending rifts in tibet vary significantly in their character as a function of extension magnitude most rifts are characterized by internally drained basins bounded by high angle normal faults with paleogene or older rocks in the footwall however the central part of the yadong gulu rift near lhasa and the newly documented lunggar rift in west central tibet are bounded by low angle normal faults detachments with mylonitic rocks and miocene granites in the footwall and exhibit active basin incision and intrabasin topographic highs in areas of inferred maximum extension we suggest that tibetan rifts initiate as high angle normal fault and half graben or graben basin systems and evolve in response to increasing extension and footwall isostatic rebound into detachment systems that are active at uppermost crustal levels and above which rift basin fill is being uplifted and eroded

sedimentology sedimentary petrology and paleoecology of the monsoon driven fluvio lacustrine zhada basin sw tibet abstract in this paper we present sedimentologic petrographic and paleoecologic data from a 810 m thick section of late neogene ca 9 7 to 1 ma fluvio lacustrine deposits in the high elevation zhada basin of sw tibet the tectonic evolution of the zhada basin region located between the himalayan mountains in the s and the transhimalayan mountains in the n is poorly understood but sediment accumulation was probably initiated in response to the middle late miocene uplift of the gurla mandhata and leo pargil domes in the e and w respectively the sedimentary record can be subdivided into five stratigraphic units with distinctly different lithofacies associations la these are from bottom to top a bedload dominated fluvial la unit 1 0 90 m a nearshore lacustrine deltaic la unit 2 90 220 m an offshore lacustrine la unit 3 220 500 m a nearshore lacustrine fan delta la unit 4 500 600 m and a fan delta alluvial fan la unit 5 600 810 m clast and heavy mineral compositions revealed sediment supply from two different provenance areas one from the south and one from the north east based on catchment geology of the himalaya and transhimalaya ostracode faunal assemblages are largely comparable to those of modern tibetan lakes and allow the reconstruction of paleo lake environments including lake level changes and salinity the sedimentary pattern shows strong cyclicity at various scales m 10 s m and 100 m small scale cycles are interpreted as intrinsically controlled depositional processes of deltas lobe switching whereas medium and large scale cycles are most likely forced by climate fluctuations the overall evolution of the sedimentologic record includes a strong and rapid increase in fluvial discharge in the uppermost portion of unit 1 a transition from fluvial to lacustrine deposition during deposition of unit 2 rhythmic variations in the style of lacustrine sedimentation during deposition of unit 3 an increase in the supply of coarse clastics starting with deposition of unit 4 and a transition from lacustrine to alluvial sedimentation during deposition of unit 5 we speculate that the increase in discharge and presumably precipitation leading to the establishment of lacustrine conditions in the lower part of the section unit 2 is largely due to regional summer monsoon intensification during the late miocene and that the transition from lacustrine to alluvial sedimentation in the uppper part of the section reflects the onset of northern hemisphere glaciation and winter monsoon strengthening at 2 6 ma

evolution of fluvial style in the siwalik group in the foothills of the nepal himalaya abstract middle miocene to pleistocene fluvial sediments of the siwalik churia group are widely distributed in the southern frontal area of the himalaya the succession is about 6 km thick and was derived from denudation of the himalayan orogen the siwalik group in nepal is well exposed in the surai khola area western nepal and the hetauda bakiya khola area central nepal the group is separated into northern and southern belts by the central churia thrust cct eight facies associations fa1 to fa8 are recognized in the siwalik group in these areas they are interpreted as the deposits of fine grained meandering flood flow dominated fine grained meandering sandy meandering deep sandy braided comparatively shallow sandy braided anastomosed gravelly braided and debris flow dominated braided systems respectively fa6 fa7 and fa8 occur only in the southern belt in each area the sedimentary succession generally coarsens upwards the accumulation of these facies associations related to the paleomagnetic time frame indicates that flooding increased dramatically from about 10 5 to 9 5 ma and fluvial style changed from meandering to braided between 9 0 and 6 5 ma a gravelly fluvial system prevailed after 3 0 to 2 5 ma the evolution of these fluvial styles is intimately related to the uplift of the himalaya and associated thrust movements and consequent effects on atmospheric circulation and precipitation by comparison with the characteristics of the submarine bengal fan deposits it is apparent that an increase in flood flow is strongly influenced by increased precipitation due to onset and intensification of monsoon climate the sandy braided system was mainly induced by regional tectonic uplift and the gravelly fluvial system may have been formed due to regional thrust movements along the himalaya frontal area

normal faulting in central tibet since at least 13 5 myr ago tectonic models for the evolution of the tibetan plateau interpret observed east west thinning of the upper crust to be the result of either increased potential energy of elevated crust1 or geodynamic processes that may be unrelated to plateau formation2 3 4 5 6 a key piece of information needed to evaluate these models is the timing of deformation within the plateau the onset of normal faulting has been estimated to have commenced in southern tibet between about 14 myr ago7 and about 8 myr ago8 and in central tibet about 4 myr ago9 here however we report a minimum age of approximately 13 5 myr for the onset of graben formation in central tibet based on mineralization ages determined with rb sr and 40ar 39ar data that post date a major graben bounding normal fault these data along with evidence for prolonged activity of normal faulting in this and other tibetan grabens support models that relate normal faulting to processes occurring beneath the plateau thinning of the upper crust is most plausibly the result of potential energy increases resulting from spatially and temporally heterogeneous changes in thermal structure and density distribution within the crust and upper mantle beneath tibet this is supported by recent geophysical and geological data10 11 12 13 14 15 16 17 which indicate that spatial heterogeneity exists in both the tibetan crust and lithospheric mantle

ancient diets indicate significant uplift of southern tibet after ca 7 ma the uplift of the tibetan plateau plays a critical role in controlling global climate yet the history of the tibetan uplift is still a contentious issue in particular the elevation of the plateau during the neogene a crucial period in the development of the asian monsoons and c4 ecosystems remains uncertain here we present carbon isotopic evidence preserved in tooth enamel from 7 m y old horses and rhinos from the high himalayas which indicates that unlike modern herbivores in the area these ancient mammals ate substantial amounts of c4 grasses the presence of significant amounts of c4 grasses in the diets of these ancient mammals indicates that the climate in the area was much warmer and the elevation was much lower in the late miocene than today the carbon isotope data from the high himalayas after accounting for late cenozoic global cooling and paleoatmospheric co2 levels indicate that this part of southern tibet was less than 2900 3400 m above sea level in the latest miocene this implies that the present elevation of the area must have been attained after 7 ma much later than generally believed

nyainqentanglha shear zone a late miocene extensional detachment in the southern tibetan plateau a major low angle ductile shear zone containing s c mylonites involves metamorphosed granitic rocks at the southeastern edge of the nyainqentanglha mountain range southern tibet prominent triangular facet geomorphology is developed by valley erosion of the detachment surface defined by the top of the southeast dipping mylonitec shear zone kinematic criteria consistently indicate a top to southeast sense of shear the ductile shearing deformation is inferred from isotopic cooling ages to have occurred during the interval 11 5 ma late miocene we interpret the shear zone as a regional extensional detachment its development indicates when the extensional tectonics in this area started which in turn may mark the time when the maximum sustainable surface elevation and perhaps crustal thickness was reached in southern tibet

recent mantle degassing recorded by carbonic spring deposits along sinistral strike slip faults south central australia abstract the interior of the australian continent shows evidence for late quaternary to recent fault controlled mantle 3 he and co 2 degassing a series of interconnected nw striking sinistral faults the norwest fault zone nfz in south central australia are associated with travertine mounds the latter show a regular spacing of 50 70 km u series ages on 26 samples range from 354 7 to 1 19 0 02 ka 2 errors and suggest a clustering every 3 4 ka since 26 ka geochemical data demonstrate a remarkable mantle to groundwater connection isotopic data indicate that the groundwater is circulating to depths 3 km and interacting with neoproterozoic cambrian basement and mantle volatiles 3 he 4 he isotope ratios show that the he comes in part from the mantle this demonstrates that the nfz cuts through the entire crust and provides pathways for mantle degassing scaling relationships suggest that the series of sinistral faults that make up the nfz are interconnected at depths and have a significant strike length of 60 70 km or more the nfz occurs where a major compositional boundary and a significant heat flow anomaly occurs and a major step in lithospheric thickness has been mapped we discuss a tectonic model in which recent stress field heat flow and lithospheric structure in central australia reactivated a set of steeply dipping neoproterozoic faults which may now be growing into a crustal lithospheric scale structure

pakistan mammal tooth stable isotopes show paleoclimatic and paleoenvironmental changes since the early oligocene abstract this research presents an isotopic study of three large mammal groups elephantoid proboscideans hyracodontid and rhinocerotid rhinocerotoids equids of the hipparion group from the bugti hills sequence eastern balochistan pakistan combined with published data from the miocene siwalik group northern central pakistan these two exceptional fossil records from pakistan provide an unambiguous source of biotic information from the early oligocene up to the late miocene the 13 c c and 18 o c results from the same herbivore groups show several significant variations in environmental and climatic conditions throughout the 30 to 7 5 myr period in this region first from 30 to 22 myr the environment is characterized by a relatively dry but dense forest existing under a temperate to subtropical climate with a more closed tropical environment at 23 myr oligocene 18 o of the terrestrial herbivore teeth agrees with the marine foraminifera 18 o and mg ca trends suggesting that the pakistan region was affected by global climate rather than regional conditions after 22 myr the 18 o c mammal enamel results show a long term decreasing trend until 15 myr toward a wetter environment with the appearance of tropical forests in response to the probable onset of the asian monsoon this is a period of high tectonic activity with the india asia collision leading to uplift of the tibetan plateau and shrinkage of the epicontinental paratethys sea this activity modified the land sea distribution and the thermal contrast between ocean and continent the driving force of the monsoon climate the middle miocene environment in pakistan experienced moist conditions under an intense monsoon system with relatively closed rainforest after 12 myr the 18 o c enamel values record a positive shift until 9 3 myr toward a drier environment with an increase of seasonality as suggested by higher 18 o c variability after 9 3 myr these late miocene drier climatic conditions and the asian monsoon intensification could potentially favour the c 4 photosynthetic pathway and hence the development of grassland to the detriment of subtropical forests resulting in the higher enamel 13 c values recorded after 9 3 myr

co2 degassing over seismic areas the role of mechanochemical production at the study case of central apennines field observations coupled with experimental results show that co2 can be produced by mechanical energy applied to carbonate rocks becoming an unexpected additional gas source besides that degassed from the mantle or produced by thermometamorphism the evidence that a large amount of carbon dioxide associated with radiogenic type helium r ra as low as 0 01 0 08 is released through continental areas denotes the absence of a contribution from the mantle or from mantle derived fluids data collected during the seismic crisis which struck the central apennines in 1997 98 have shown an enhanced co2 flux not associated with the presence of mantle or thermometamorphic derived fluids on the other hand new experimental results highlight the possibility of producing co2 by mechanical energy that acts on the calcite crystalline lattice while the co2 released over the geothermal areas e g larderello geothermal field is obviously derived by mantlederived activities this is not the case of the huge amount of co2 released over the seismically active areas where the presence mantle derived products is ruled out we propose that mechanical energy e g released during seismic events microseismicity or creeping processes is a possible additional energy source able to produce co2 and thus could explain the presence of co2 degassing over tectonic areas where the influence of the mantle is low