crustal strain in central greece from repeated gps measurements in the interval 1989 1997 summary a 66 station gps network spanning central greece first observed in 1989 has been occupied fully on three occasions june 1989 october 1991 and may 1993 subsets of this network bounding the gulf of korinthos have also been occupied in june 1995 october 1995 may 1996 and september october 1997 the first three occupations were processed using a fiducial gps methodology whereas later surveys were processed using code precise orbits combination of data from different surveys to yield smooth site velocities requires global network translations at each epoch to compensate for errors in the realization of the reference frame this method provides a posteriori estimates of the relative coordinate errors and reference frame noise only one earthquake the 1995 june 15 egion event has caused significant local coseismic displacement and its effects on the interseismic velocity field are removed using an elastic dislocation model we constrain the orientation of the 100 yr triangulation gps velocity estimates of davies et al 1997 using 14 sites common to the two networks the goodness of fit of this transformation indicates that the short term and 100 yr geodetic estimates of deformation are highly compatible we infer that short term geodetic studies are capable of determining longer term deformation rates provided that transient local effects can be modelled from the combined velocity field we estimate principal strains and rigid body rotation rates at points on a regular grid using data from neighbouring sites strain rates are high within the gulf of korinthos and much lower elsewhere the extension rate across the gulf of korinthos increases from east to west comparison of the extension rate with historical and recent rates of seismic release of strain reveals significant medium term seismic hazard in the western gulf of korinthos and may also indicate long term aseismic strain

paleomagnetic evidence for long term 104 year memory and periodic behavior in the earth s core dynamo process a new paleomagnetic secular variation psv record from the late quaternary wilson creek beds of mono lake california contains a distinctive periodic vector waveform that follows and is almost certainly related to the mono lake excursion a comparison of all published psv results from the wilson creek beds suggests that the magnetic field at mono lake went through an interval 36 000 28 000 ybp of very low amplitude psv followed by the mono lake excursion 28 000 27 000 ybp and four subsequent recurrences 27 000 12 500 ybp of the excursion waveform with relatively diminished amplitudes lower than the excursion amplitude but higher than psv amplitudes at mono lake since 12 500 ybp this pattern clearly suggests that the mono lake excursion is related to typical psv it also suggests that the core dynamo process responsible for psv is capable of near impulse onset persistence over a time scale of 15 000 years and quasi periodic behavior that is non wave length dispersive in time

late cenozoic to recent transtensional deformation across the southern part of the gaoligong shear zone between the indian plate and se margin of the tibetan plateau and its tectonic origin abstract within the southeastern part of the tibetan plateau the gaoligong shan shear zone forms the boundary between the tengchong and baoshan blocks and is one of the main cenozoic strike slip fault systems of the eastern himalayan syntaxis the mountain ranges rise to a maximum elevation of 3623 m with a width of 20 km and a length of 400 km the core of the shear zone consists of a narrow belt of mylonitic rocks with right lateral strike slip fabrics formed during the northward movement of india relative to eurasia in oligocene and miocene time to the south the mountains decreases in elevation and end against the wanding fault the latter is one of a series of ne sw striking active left lateral strike slip faults within the southeastern part of the tibetan plateau the cause and timing for the change in elevation of the gaoligong shan is unknown but based on our recent structural and fission track geochronological work the decrease in elevation is the result of east west extension across the southern part of the gaoligong shear zone inferred from the late cenozoic and active normal faults along its eastern and western boundaries southward the eastern boundary fault system merges with a series of splays of the wanding strike slip fault while the western boundary fault system is bent into parallelism with the wanding fault this geometric relationship suggests that the normal faulting along the eastern and western boundary of the gaoligong shear zone was caused by transfer of the ne sw left lateral movement along the wanding fault into e w extension on faults to the northeast the resultant normal faulting caused the lowering of the topography in the southern part of the shear zone fission track data from 11 samples from the mylonitic rocks in the footwall of the ruili oblique slip fault left lateral thrust slip yielded ages between 8 4 and 0 9 ma coeval with volcanism within the jietou and mangbang basins the left lateral strike slip movement along the wanding and ruili faults is interpreted to have accommodated differential clockwise rotation of the gaoligong shear zone and its adjacent tectonic units during late cenozoic to recent time during the northward movement of the indian plate with respect to the southeastern margin of the tibetan plateau along the right lateral sagaing fault

coastal submarine hydrothermal activity off northern baja california 2 evolutionary history and isotope geochemistry a geochemical model of the punta banda submarine hydrothermal system pbshs and ensenada quadrangle subaerial hot springs is developed using sup 18 o sup 16 o d h sup 34 s sup 32 s sup 3 h water and gas chemistry the pbshs water is a primary high temperature acid reducing fluid of old seawater origin which has been titrated by cold alkaline groundwater of meteoric origin the final exiting solutions represent a 1 1 mixture of the two primary mixing components in contrast the subaerial hot spring waters are of unmixed meteoric origin the subaerial hot spring gas is predominantly atmospheric n sub 2 while the pbshs contains large amounts of ch sub 4 and n sub 2 derived from trapped marine sediments of cretaceous age deltas sup 34 values of sampled hydrothermal waters are similar to cretaceous marine sulfate values and suggest that the waters contacted cretaceous marine sedimentary strata the presence of the alisitos and rosario marine sedimentary formations of cretaceous age within the ensenada punta banda quadrangel renders support to the above hypothesis the data also demonstrate the pyrite mineralization and deposition in submarine hydrothermal environments result from the complexing of ferrous iron with elemental sulfur and sulfide and that submarine hydrothermal activity acts as a major source of silica more ca sup 2 and trace metals and as a major sink for seawater mg sup 2 and so sub 4 sup 2 less

late brunhes polarity excursions mono lake laschamp iceland basin and pringle falls recorded at odp site 919 irminger basin abstract component natural remanent magnetizations derived from u channel and 1 cm3 discrete samples from odp site 919 irminger basin indicate the existence of four intervals of negative inclinations in the upper brunhes chronozone according to the age model based on planktic oxygen isotope data these excursional intervals occur in sediments deposited during the following time intervals 32 34 ka 39 41 ka 180 188 ka and 205 225 ka these time intervals correspond to polarity excursions detected elsewhere known as mono lake laschamp iceland basin and pringle falls the isotope based age model is supported by the normalized remanence paleointensity record that can be correlated to other calibrated paleointensity records for the 0 500 ka interval such as that from odp site 983 for the intervals associated with the mono lake and laschamp excursions virtual geomagnetic poles vgps reach equatorial latitudes and mid southerly latitudes respectively for intervals associated with the iceland basin and pringle falls excursions repeated excursions of vgps to high southerly latitudes indicate rapid directional swings rather than a single short lived polarity reversal the directional instability associated with polarity excursions is not often recorded probably due to smoothing of the sedimentary record by the process of detrital remanence drm acquisition

submarine groundwater discharge as a source of dissolved nutrients to an arid coastal embayment la paz mexico submarine groundwater discharge sgd was investigated in the southeastern portion of la paz bay baja california mexico using radon 222rn as a natural tracer in the absence of permanent surface flows in this arid region we hypothesize sgd is a major regional source of dissolved nutrients four spatial surveys showed higher radon and nutrient nh4 no3 no2 po4 and sio4 values in the winter than summer lagging rainfall by 3 4 months the surveys revealed two sites balandra and merito with a stronger radon signal intensive time series 12 24 h measurements at those sites were used to estimate sgd fluxes using a radon mass balance approach in balandra sgd was estimated to be 0 18 m3 m 2 day 1 and significant correlations between radon and nutrients no3 and sio4 were observed in merito sgd rates were estimated to be 0 10 m3 m 2 day 1 and no correlations between nutrients and 222rn were observed the difference between the two sites was interpreted to be related to different components dominating sgd i e fresh sgd in balandra and saline sgd in merito the estimated sgd derived nutrients fluxes were 2 52 0 04 0 94 7 164 mmol m2 day 1 for dissolved inorganic nitrogen phosphate and silicate respectively these fluxes could explain between 5 and 20 of the regional marine primary productivity values

hydrochemical isotopic and hydrogeological conceptual model of the las tres virgenes geothermal field baja california sur mexico abstract based on geological structural hydrochemical and isotopic data a hydrogeological conceptual model for the geothermal reservoir shallow wells and springs at the las tres virgenes geothermal field and its surroundings is proposed the model explains the genesis of different types of thermal and cold groundwater in the nw el azufre valley las tres virgenes and aguajito complex ne reforma complex and s sierra mezquital areas shallow groundwater of sulfate type in the nw zone is explained by the rise of co2 h2s vapor from a shallow magma chamber and the subsequent heating up of a shallow aquifer vertical communication between the reservoir and the surface is facilitated by a series of extensional nw se trending normal faults forming the graben structures of the santa rosalia basin low permeability characteristics of the geological formations of the study area support the hypothesis of a fracture and fault dominated subterranean flow circulation system the na cl hco3 composition of springs in the ne and se zones indicates influence of ascending geothermal fluids facilitated by radial fault systems of the reforma caldera and probably the existence of a shallow magma chamber close to the surface the rising geothermal fluids are mixed up with meteoric water from a shallow aquifer the las tres virgenes and the reforma complex are separated by younger n s trending lateral shearing faults such as the cimarron fault such disposition explains the genesis of different hydrogeological flow regimes on both sides hco3 type surface water from the southern zone between san ignacio and mezquital is of typical meteoric origin with no influence of geothermal fluids due to arid climatic conditions in the study zone recent recharge in the geothermal area seems improbable thus recent interaction between the surface and the geothermal reservoir can be excluded furthermore isotopic and hydrochemical data exclude the presence of marine water from the gulf of california in the deep reservoir both conditions indicate recharge of the reservoir by meteoric water during glacial periods in holocene or pleistocene time or a magmatic origin of the reservoir fluids the slightly positive slope of the 18o d line of geothermal fluids and its intermediate isotopic composition between the surface samples and magmatic andesitic water indicate that magmatic andesitic water contributes approximately 30 to the geothermal fluid composition whereas fossil meteoric water represents the major component 70 the geothermal reservoir is considered to represent a hydrostatic stagnant flow system based on the observed linear correlation between the isotopic composition and the altitude of the surface manifestations the isotopic composition and altitude of the former recharge were determined as 18 o 9 7 and d 67 3 and 350 m a s l respectively this altitude is interpreted as mean average recharge elevation scarcity of permanent rivers low density of springs and domestic wells as well as low precipitation rates reflect restricted distribution of shallow groundwater systems in the study zone these systems are related to isolated local aquifers composed of valley fillings

226ra and222rn contents of galapagos rift hydrothermal waters the importance of low temperature interactions with crustal rocks abstract hydrothermal waters collected by alvin from the galapagos spreading center are enriched in 222 rn by factors of 50 200 over bottom waters the 226 ra in the same samples however is enriched by less than a factor of four over bottom waters enrichments of 222 rn result primarily from recoil from rock surfaces while 226 ra enrichments are dominantly produced by high temperature alteration of cooling ridge volcanics the abundances of both nuclides exhibit positive correlations with temperature the data extrapolate to bottom water temperatures and compositions demonstrating the importance of seawater mixing different vents however have different mixing lines and vents with high 222 rn have low 226 ra we propose these patterns result from variations in the extent of low temperature crustal interaction with the hydrothermal fluids low temperature crustal waters can maintain high steady state 222 rn contents due to the recoil additions to the fluids the 226 ra however is strongly adsorbed at low temperatures resulting in low concentrations of this nuclide in low temperature crustal waters thus physical mixing of a crustal water component with hydrothermal waters or variable crustal path lengths of the hydrothermal fluids can account for the variable mixing lines and 222 rn 226 ra values of the hot springs the 222 rn 226 ra value appears to be a sensitive indicator of low temperature crustal interaction values 100 have experienced extensive crustal interaction and are indicative of diffuse hydrothermal flow values between 1 and 10 are indicative of primary hydrothermal fluids which have not experienced significant interaction with the crust values of 222 rn 226 ra between 10 3 and 10 4 are indicative of interaction of the hydrothermal fluids with sediments such values are observed in water samples from the galapagos hydrothermal mounds

diachronous cooling along the mogok metamorphic belt shan scarp myanmar the trace of the northward migration of the indian syntaxis abstract we present new observations and new mineral ages eight by the 40 ar 39 ar and nine by the 40 k 40 ar methods from high grade metamorphic and foliated intrusive rocks collected along the mogok metamorphic belt of central myanmar that complete preliminary results we previously published all 30 ages presented here confirm the oligocene to middle miocene age of the mogok metamorphism moreover the ages are young from the gulf of martaban in the south to the china myanmar border in the north showing a clear diachronism these results confirm a northward migration of the tectonic event responsible for the cooling of our samples at a velocity similar to the india relative to indochina velocity at the same period in addition intensive field work along a 800 km long section of the mogok metamorphic belt has revealed the numerous ductile structures that resulted from a strong nnw sse trending extension from the analogy between the present day local extrusion around the eastern indian syntaxis and the extension observed along the mogok metamorphic belt and from the diachronism we document we suggest that the central part of myanmar has recorded the northward passage of the eastern indian syntaxis with respect to indochina from oligocene to middle miocene

age and correlation of a paleomagnetic episode in the western united states by 40ar 39ar dating and tephrochronology the jamaica blake or a new polarity episode high resolution paleomagnetic records from two sites near pringle falls oregon are compared with similar records from summer lake oregon 170 km to the southeast paoha island in mono lake 660 km to the southeast and benton crossing in long valley approximately 700 km to the southeast in east central california the sequences at pringle falls contain a distinctive coarse pumice lapilli tephra layer which we have dated as 218 10 ka by 40ar 39ar step heating of plagioclase feldspar stratigraphically this tephra is closely associated with a suite of several other tephra layers that bracket the interval studied paleomagnetically each tephra layer is distinguished by the unique chemical composition of its volcanic glass shards the pumice layer dated at pringle falls is correlated with layers at three of the other localities using all the tephra layers we can correlate the lake stratigraphic sequences and associated paleomagnetic records among the four distant localities additional age control is obtained from a fifth locality at tulelake in northern california where the stratigraphic interval of interest is bracketed between 171 43 and approximately 140 ka characteristics of the paleomagnetic records indicate virtually identical paleofield variation particularly the geometry of a normal to normal n n geomagnetic polarity episode the observed paleofield behavior resembles the blake geomagnetic polarity episode but is significantly older than the generally accepted age of the blake episode either the age of the blake episode is significantly underestimated or the polarity episode documented here is older perhaps the jamaica episode or is an as yet unreported episode a corollary of the latter option is that paleomagnetic polarity episodes of different ages may have similar transition polar paths a conclusion implying that a common mechanism is involved

tide influenced acidic hydrothermal system offshore ne taiwan elemental sulfur and hydrogen sulfide emitted offshore of northeastern taiwan known to local fishermen for generations but never studied until recently are found to have originated from a cluster of shallow 92 with small amounts of h2s helium isotopic ratios 7 5 times that of air indicate that these gases originate from the mantle high temperature hydrothermal fluids have measured temperatures of 78 116 degrees c and ph 25 degrees c values as low as 1 52 likely the lowest to be found in world records low temperature vents 30 65 degrees c have higher ph values continuous temperature records from one vent show a close correlation with diumal tides suggesting rapid circulation of the hydrothermal fluids c 2005 elsevier b v all rights reserved

mono lake excursion in mono basin california and at carson sink and pyramid lake nevada summary a restudy of the mono lake excursion in the mono basin california using two new localities 20 km apart shows that the palaeomagnetic record in the basin is the most complete and accurate for the entire excursion the excursion is also recorded in exposed sediment from pleistocene lake lahontan in northwestern nevada about 250 km north of the mono basin sampling of the lake lahontan sediment was done at pyramid lake and in the carson sink following the initial discovery of the mono lake excursion by denham cox 1971 liddicoat coe 1979 showed that the excursion consists of two parts split by a volcanic ash bed at pyramid lake and in the carson sink the older half of the excursion is not recorded but the younger half can be recognized two factors appear to have contributed to the partial recording of the excursion at pyramid lake and in the carson sink 1 the relative strength of the palaeomagnetic field low during the older half of the excursion and high during the younger half and 2 the slower sedimentation in lake lahontan estimated to be about half the rate of deposition for the lacustrine sediment in the mono basin tephrochronology and carbon 14 dates indicate an age of 28 000 yr for the middle of the mono lake excursion on the assumption that the sedimentation rate was a constant 25cm kyr 1 in the mono basin the span of the full excursion is about 2000 yr

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

a tidal influenced hydrothermal system temporarily cooled by a tropical storm abstract the lutao hydrothermal field is an intertidal arc volcanic system located offshore southeast taiwan hosting a zhudanqu zdq vent and a huwaichi hwc spring with strongly contrasting fluid chemistry low mg moderately enriched cl and h with respect to seawater indicate that the zdq endmember was derived from the brine phase that was formed during low degree subcritical phase separation in contrast the endmember for the hwc vent fluids is related to the vapor phase temperature and pressure of the phase separation were estimated as 150 c and 7 bar respectively the water rock ratio was roughly calculated as about 2 the lutao hydrothermal system was slightly affected by semi diurnal tides by some combination of tidal loading and tidal currents the time delay between tides and the response of the hydrothermal system was about 3 h while freshwater was almost absent in the hwc vent fluids at normal conditions the typhoon fung wong on sep 21st 2014 led to intrusions of freshwater into the vent fluids with a percentage of 16 both the zdq and the hwc endmember compositions showed some changes after the typhoon event suggesting a cooling of the reaction zone after the typhoon passed by the hydrothermal system began to recover evidenced by increasing percentages of the hwc endmember and decreasing freshwater contributions the flux of the hwc endmember was estimated as 460 560 l h 1 based on these observations this study for the first time reports a shallow depth tidal influenced hydrothermal system that was temporarily cooled by a tropical storm

vent fluid chemistry in bahia concepcion coastal submarine hydrothermal system baja california sur mexico abstract shallow submarine hydrothermal activity has been observed in the bahia concepcion bay located at the gulf coast of the baja california peninsula along faults probably related to the extensional tectonics of the gulf of california region diffuse and focused venting of hydrothermal water and gas occurs in the intertidal and shallow subtidal areas down to 15 m along a nw se trending onshore offshore fault temperatures in the fluid discharge area vary from 50 c at the sea bottom up to 87 c at a depth of 10 cm in the sediments chemical analyses revealed that thermal water is enriched in ca as hg mn ba hco3 li sr b i cs fe and si and it has lower concentrations of cl na so4 and br than seawater the chemical characteristics of the water samples indicate the occurrence of mixing between seawater and a thermal end member stable isotopic oxygen and hydrogen composition of thermal samples plot close to the local meteoric water line on a mixing trend between a thermal end member and seawater the composition of the thermal end member was calculated from the chemistry of the submarine samples data by assuming a negligible amount of mg for the thermal end member the results of the mixing model based on the chemical and isotopic composition indicate a maximum of 40 of the thermal end member in the submarine vent fluid chemical geothermometers na li na k ca and si were applied to the thermal end member concentration and indicate a reservoir temperature of approximately 200 c the application of k mg and na li geothermometers for vent fluids points to a shallow equilibrium temperature of about 120 c results were integrated in a hydrogeological conceptual model that describes formation of thermal fluids by infiltration and subsequent heating of meteoric water vent fluid is generated by further mixing with seawater

the breakup of east gondwana assimilating constraints from cretaceous ocean basins around india into a best fit tectonic model published models for the cretaceous sea oor spreading history of east gondwana result in unlikely tectonic scenarios for at least one of the plate boundaries involved and or violate particular constraints from at least one of the associated ocean basins we link east gondwana spreading corridors by integrating magnetic and gravity anomaly data from the enderby basin off east antarctica within a regional plate kinematic framework to identify a conjugate series of east west trending magnetic anomalies m4 to m0 126 7 120 4 ma the mid ocean ridge that separated greater india from australia antarctica propagated from north to south starting at 136ma northwest of australia and reached the southern tip of india at 126 ma sea oor spreading in the enderby basin was abandoned at 115 ma when a ridge jump transferred the elan bank and south kerguelen plateau to the antarctic plate our revised plate kinematic model helps resolve the problem of successive two way strike slip motion between madagascar and india seen in many previously published reconstructions and also suggests that sea oor spreading between them progressed from south to north from 94 to 84 ma this timing is essential for tectonic ow lines to match the curved fracture zones of the wharton and enderby basins as greater india gradually began to unzip from madagascar from 100 ma in our model the 85 east ridge and kerguelen fracture zone formed as conjugate anks of a leaky transform fault following the 100ma spreading reorganization our model also identi es the afanasy nikitin seamounts as products of the conrad rise hotspot

estimating groundwater discharge into the northeastern gulf of mexico using radon 222 abstract submarine groundwater discharge sgd may provide important chemical constituents to the ocean but the dispersed nature of this process makes locating and quantifying its input extremely difficult since groundwater contains 3 4 orders of magnitude greater radon than seawater 222rn may be a useful tracer of this process if all other sources of radon to bottom waters can be evaluated we report development of a sgd tracing tool based on radon inventories in a coastal area of the northeastern gulf of mexico we evaluated factors that influence the concentration of radon in the water column i e production decay horizontal transport and loss across the pycnocline using a linked benthic exchange horizontal transport model total 222rn benthic fluxes 2420 dpm m 2 day 1 measured with in situ chambers are of the magnitude required to support measured sub pycnocline 222rn inventories while estimates of molecular diffusion show that this input is relatively small 230 dpm m 2 day 1 using this model approach together with measurements of the radon inventory we estimated a regional subsurface fluid flow ranging from 180 to 710 m3 sec 1 into the 620 km2 study area this discharge equivalent to an upward advective velocity of approximately 2 10 cm day 1 dispersed over this entire study area is equivalent to approximately 20 first magnitude springs

a detailed record of paleomagnetic field change from searles lake california 1 long term secular variation bounding the gauss matuyama polarity reversal more than 33 m of 2 5 ma sediment from searles lake california was studied in order to construct a record of secular variation sv across the gauss matuyama g m normal to reverse polarity transition the behavior of the field preceding and following the reversal is considered here while in a companion paper glen et al this issue the details of the transition are discussed the record encompasses an interval of roughly 183 000 years beginning 50 kyr 9 m before and extending more than 128 kyr 23 m beyond the transition while the main phase of the transition lasts for nearly 5 kyr 1 m because the core was rotary drilled and declinations lost sv was characterized by the inclination and its angular dispersion inclination only statistics reveal that 1 the record displays overall higher than expected values of angular dispersion normal s 20 reverse s 19 expected s 15 5 suggesting that the field proximal to transitions may be more noisy than the distal field in addition normal data from immediately before the transition display higher s than reverse data immediately following it implying that the postransitional field is more stable than the pretransitional field one of the most prominent features of this record is an excursion of the field occurring roughly 4 kyr prior to the onset of the reversal a record of the g m transition from chinese loess r zhu et al submitted manuscript 1999 displays a similar event also occurring roughly 4 kyr before the transition this and the fact that the event is associated with anomalously low intensities suggest that the disturbance may be global in nature the fact that comparable features are associated with other transitions hartl and tauxe 1996 clement 1992 intimates that the field may commonly show signs of early instability this precursory event is actually one of a sequence of oscillations in inclination and intensity preceding the transition that these fluctuations occur at roughly 4 kyr intervals leading up to the reversal which also appears at this same interval strongly suggests that an oscillatory disturbance in the core active over at least 15 kyr prior to the transition had eventually triggered the reversal in addition that these waveforms are absent from the postransitional record suggests the reversal process actively rejuvenates and stabilizes the field

relative paleointensity and environmental magnetism since 1 2 ma at iodp site u1305 eirik drift nw atlantic abstract integrated ocean drilling program iodp expedition 303 to the north atlantic in 2004 recovered rapidly deposited deep sea sediments at iodp site u1305 on eirik drift located south of greenland at 3460 m water depth along the path of the western boundary under current wbuc about 200 m of sediment was sampled with u channels from the composite section providing a continuous record of paleomagnetic field directions and relative paleointensity rpi variations covering the past 1 2 myr the age model based on an oxygen isotope record is consistent with the fit of the rpi record to a calibrated template and indicates higher sedimentation rates during interglacials relative to glacial epochs magnetite grain size and concentration proxies indicate higher concentrations of magnetite with larger grain sizes during interglacials enhanced interglacial deposition can be attributed to a combination of elevated entrainment of terrigenous detritus into the wbuc due to glacial retreat on continents flanking the upstream path of the wbuc east greenland and iceland and of increased bottom current wbuc vigor leading to elevated transport and deposition at the site during interglacials this pattern is opposite to observations of flow of the antarctic circum polar current acc in the south indian ocean which suggests an inter hemispheric antiphase in marine circulation at the milankovitch scale with strong circulation in the deep north atlantic when the acc is weak and vice versa

repeating waveform initiated by a 180 190 ka geomagnetic excursion in western north america implications for field behavior during polarity transitions and subsequent secular variation new paleomagnetic lithologic and stratigraphic data are presented from the sediments of lake chewaucan in the summer lake basin oregon the new data place better age constraints on the sediments and improve the accuracy of the previously published paleomagnetic record from this locality a complex yet distinct waveform is observed in all three components of the paleomagnetic vector the waveform begins as the 180 190 ka pringle falls long valley summer lake ii geomagnetic excursion and continues for two cycles after the excursion until the record is interrupted by an unconformity that we correlate to the oxygen isotope stage 6 5e boundary the waveform s directional morphology in virtual geomagnetic pole vgp space is defined by two clockwise loops followed by a distinctive counterclockwise clockwise counterclockwise looping sequence the vgp paths of the two cycles after the excursion are rotated 180 about earth s spin axis with respect to the vgp paths of the excursion cycle the waveform also consists of a relative paleointensity variation which repeats during the two cycles after the excursion the average paleointensity of the postexcursion waveform repetitions is high relative to the extremely low values that occur during the excursion this observation indicates that excursion initiated secular variations can occur after the field fully recovers from the low intensities which commonly typify excursions because of the similarities noted previously between this excursion and full polarity transitions trie et al 1991 our new observations constrain models for a wide range of field behavior including polarity transitions excursions and secular variation

coastal groundwater dynamics off santa barbara california combining geochemical tracers electromagnetic seepmeters and electrical resistivity this paper presents repeat field measurements of 222 rn and 223 224 226 228 ra electromagnetic seepage meter derived advective fluxes and multi electrode stationary and continuous marine resistivity surveys collected between november 2005 and april 2007 to study coastal groundwater dynamics within a marine beach in santa barbara california the study provides insight into magnitude and dynamics of submarine groundwater discharge sgd and associated nutrient loadings into near shore coastal waters where the predominant sgd drivers can be both spatially and temporally separated rn 222 and 223 224 226 228 ra were utilized to quantify the total and saline contribution respectively of sgd the two short lived 224 223 ra isotopes provided an estimate of apparent near shore water mass age as well as an estimate of the ra derived eddy diffusion coefficient kh 224 ra 2 86 0 7 m 2 s 1 223 ra 1 32 0 5 m 2 s 1 because 222 rn t 3 8 day and 224 ra t

deep sea and shallow water hydrothermal vent communities two different phenomena hydrothermal vent communities from 76 areas lying at depths from 0 to 4100 m were split into two groups bdeepq and bshallow waterq based on the occurrence of vent obligate restricted to hydrothermal vents taxa of a high rank genus and family the two groups were then compared based on a large set of environmental faunistic and community parameters the degree of obligacy of fauna sharply changes at the depth of approximately 200 m in 21 shallow water areas located at depths b200 m vent obligate taxa are absent or their taxonomic rank does not exceed a species the total number of vent obligate species in shallow water is 8 and their obligacy is uncertain data from 55 areas lying at depths from 200 to 4100 m indicate there are ca 400 obligate species in 47 of these areas obligate vent taxa of the genus or the family rank are present obligate taxa of the genus rank appear at 200 m depth and of the family rank at 386 m the depth ca 200 m corresponds well with differences in community structure and composition and environmental parameters deep sea n200 m hydrothermal communities differ from shallow water ones b200 m in a much higher ratio of vent obligate taxa deep sea vent communities are also distinguished by the lack of diatom and algae bacterial mats phytoplankton lower species richness the development of large sulphide structures higher role of active vents in structuring communities in space replication of a set of dominant taxa in communities within large regions reproduced through the succession at newly formed vent fields more pronounced concentric and vertical zonality higher biomass of macrofauna the important role of symbiotrophic forms dominating the biomass the ratio of species with a bpointq species range endemic to small areas is higher in the deep sea there are no significant differences between the vent and non vent biogeography both in shallow waters and the deep ocean modern deep sea hydrothermal vent communities have a longer evolutionary history than their shallow water counterparts to explain major differences between deep and shallow water hot vent communities evolutionary processes need to be analysed over long geological periods and within global vertical zones it is suggested that the proportion of organic matter derived from chemosynthesis and photosynthesis plays a crucial role in evolution when calculated for global zones this proportion increases with depth to a certain critical level that separates deep and shallow water hot vent communities and fauna vertical zonation in the distribution of obligate taxa in hydrothermal vent communities indicates that this level is reached at approximately 200 m depth

the driving forces of porewater and groundwater flow in permeable coastal sediments a review abstract advective flows rapidly transport water solutes and particles into and out of permeable sand beds and significantly affects the biogeochemistry of coastal environments in this paper we reviewed the drivers of porewater and groundwater advection in permeable shelf sediments in an attempt to bridge gaps among different disciplines studying similar problems we identified the following driving forces 1 terrestrial hydraulic gradients 2 seasonal changes in the aquifer level on land moving the location of the subterranean estuary 3 wave setup and tidal pumping 4 water level differences across permeable barriers 5 flow and topography induced pressure gradients 6 wave pumping 7 ripple and other bed form migration 8 fluid shear 9 density driven convection 10 bioirrigation and bioturbation 11 gas bubble upwelling and 12 sediment compaction while these drivers occur over spatial scales ranging from mm to km and temporal scales ranging from seconds to years their ultimate biogeochemical implications are very similar i e they are often a source of new or recycled nutrients to seawater and transform organic carbon into inorganic carbon drivers 2 12 result in no net water input into the ocean taking all these mechanisms into account we conservatively estimate that a volume equivalent to that of the entire ocean is filtered by permeable sediments at time scales of about 3000 years quantifying the relative contribution of these drivers is essential to understand the contribution of sediments to the global cycles of matter

mn ba hg mineralization at shallow submarine hydrothermal vents in bahia concepcion baja california sur mexico coastal submarine hydrothermal venting occurs on the west shore of the fault bounded bay of bahia concepcion along a stretch of about 700 m of rocky shoreline diffuse hydrothermal seepage of water and continuous gas bubbling mainly co2 and n2 take place through the sediment covered seafloor at shallow depth 5 to 15 m in addition at about 500 m se a cluster of hot springs occurs within the intertidal zone the temperature and ph of the hydrothermal fluids varies from 72 to 87 c and 5 95 to 6 02 in the submarine diffuse venting area and reaches 62 c and ph of 6 68 in the intertidal hot springs mn ba hg mineralization is presently forming as a result of the hydrothermal venting at the intertidal hot springs moss like crusts of manganese oxides and structureless detrital aggregates cemented by opal a barite and calcite occur around the main discharge conduits these aggregates are overlaid by silica carbonate fine layered stromatolitic aggregates that extend some meters from the hot springs forming crusts and coalescing rims over volcanic pebbles and boulders manganese crusts are made up of barium rich x ray amorphous todorokite like and romanechite phases and represent a rare example of a manganese deposit formed in a shallow submarine hydrothermal environment in the submarine diffuse venting area the hydrothermal precipitates are less conspicuous and consist in millimeter thick iron oxyhydroxide coatings on volcanic cobbles and boulders these coatings are composed of poorly crystallized six line ferrihydrite accompanied by minor cinnabar and fine grained colloform pyrite textures and fabrics of the mineral assemblages suggest microbial mediation for mineral deposition the vent precipitates display a significant enrichment of hg as and sb arsenic is probably adsorbed onto mn and fe oxide substrates the nasc north american shale composite normalized ree patterns of the vent precipitates show a pronounced positive eu anomaly that is probably inherited from the hydrothermal fluid

tertiary diachronic extrusion and deformation of western indochina structural and 40ar 39ar evidence from nw thailand the wang chao and three pagodas fault zones cut the western part of the indochina block and run parallel to the red river fault evidence of intense ductile left lateral shear is found in the lansang gneisses which form a 5 km wide elongated core along the wang chao fault zone dating by 40 ar 39 ar shows that such deformation probably terminated around 30 5 ma the wang chao and three pagodas faults offset the north striking lower mesozoic metamorphic and magmatic belt of northern thailand 40 ar 39 ar results suggest that this belt suffered rapid cooling in the tertiary probably around 23 ma these results imply that the extrusion of the southwestern part of indochina occurred in the upper eocene lower oligocene it probably induced rifting in some basins of the gulf of thailand and in the malay and mekong basins in the oligo miocene the continuing penetration of india into asia culminated with the extrusion of all of indochina along the ailao shan red river fault this occurred concurrently with the onset of e w extension more to the south plotting in a geographical reference frame the diachronic time spans of movement on left lateral faults east and southeast of tibet implies that the northward movement of the indian indenter successively initiated new strike slip faults located farther and farther north along its path

record of the younger part of the pringle falls excursion at long valley california summary the younger of two closely spaced palaeomagnetic excursions at pringle falls oregon is recorded in lacustrine silts that crop out in long valley california assigned an age of about 220 000 years the virtual geomagnetic poles of the younger excursion form a clockwise loop that reached 35 s latitude east of south america before returning to the northern hemisphere in the pacific ocean west of central america the poles then form a narrow band across north america while moving to high northern latitudes this record matches extremely well feature b of the original excursion record from pringle falls reported by herrero bervera et al 1994 and is similar to this excursion at summer lake oregon negrini et al 1994 in that the pole path is confined primarily to the east central pacific ocean on the basis of an assumed sedimentation rate of 30 cm per thousand years the younger excursion feature b at pringle falls spans an estimated 1200 years and followed by about 1000 years a larger excursion feature a at pringle falls previously discovered at the same long valley site at a second long valley site 30 m away the younger excursion feature b is only partially recorded because of a presumed small hiatus in the sedimentary section

mechanisms of mass and heat transport during barrovian metamorphism a discussion based on field evidence from the central alps switzerland northern italy 1 tectonic and metamorphic data for the central alps switzerland italy are used to discuss this classic example of a barrovian metamorphic terrain notably the evolution of its thermal structure in space and time available p t t data indicate variable contributions of advective and conductive heat transport during collision and subsequent cooling and exhumation some areas experienced a prolonged period of partial melting while other areas at the same time show but moderate heating the barrow type metamorphic field gradient observed in the final orogen is the result of two distinct tectonic processes with their related advective and conductive heat transport processes the two tectonic processes are 1 accretion of material within a subduction channel related to decompression and emplacement of high pressure units in the middle crust and 2 wedging and related nappe formation in the continental lower plate the second process postdates the first one wedging and underthrusting of continental lower plate material produces heat input into lower crustal levels and this process is responsible for predominantly conductive heat transport in the overlying units the interacting processes lead to different maximum temperatures at different times producing the final barrovian metamorphic field gradient the south experienced rapid cooling whereas the north shows moderate cooling rates this discrepancy principally reflects differences in the temperature distribution in the deeper crust prior to cooling differences in the local thermal gradient that prevailed before the cooling also determined the relationships between cooling rate and exhumation rate in the different areas citation berger a s m schmid m engi r bousquet and m wiederkehr 2011 mechanisms of mass and heat transport during barrovian metamorphism a discussion based on field evidence from the central alps switzerland northern italy tectonics 30 tc1007 doi 10 1029 2009tc002622

structural development of the mid tertiary doi suthep metamorphic complex and western chiang mai basin northern thailand abstract the northern western ranges of thailand contain mylonitic gneisses of the doi suthep metamorphic complex dsmc near chiang mai mylonitic foliations outline a southeast trending dome and stretching lineations trend n80 w low grade metasedimentary rocks and tertiary fanglomerates flank the dome on the east and widespread chloritic breccia marks the intervening doi suthep detachment fault we interpret that the metamorphic complex developed between triassic and early miocene with detachment faulting mylonitization and uplift during oligocene to miocene within the dsmc dikes of mutually cross cutting hence coeval granitic pegmatite and aplite cut mylonitic orthogneiss although the contacts of the dikes are sharp the dikes contain a mylonitic fabric that parallels the fabric in the surrounding mylonitic orthogneiss thus we infer that intrusion occurred during mylonitization east of doi suthep tertiary fanglomerates of the mae rim formation overlie the doi suthep detachment fault variable strikes with dips of 10 50 and several outcrop scale fold hinges suggest that the mae rim formation is deformed into a set of non cylindrical folds numerous variably striking high angle normal faults suggest either multiple deformations or deformation in a three dimensional strain field the discovery of an intraformational angular unconformity confirms that the mae rim formation accumulated during folding

the timing of strike slip shear along the ranong and khlong marui faults thailand 1 the timing of shear along many important strike slip faults in southeast asia such as the ailao shan red river mae ping and three pagodas faults is poorly understood we present 40ar 39ar u pb shrimp and microstructural data from the ranong and khlong marui faults of thailand to show that they experienced a major period of ductile dextral shear during the middle eocene 48 40 ma centered on 44 ma which followed two phases of dextral shear along the ranong fault before the late cretaceous 81 ma and between the late paleocene and early eocene 59 49 ma many of the sheared rocks were part of a pre kinematic crystalline basement complex which partially melted and was intruded by late cretaceous 81 71 ma and early eocene 48 ma tin bearing granites middle eocene dextral shear at temperatures of 300 500 c formed extensive mylonite belts through these rocks and was synchronous with granitoid vein emplacement dextral shear along the ranong and khlong marui faults occurred at the same time as sinistral shear along the mae ping and three pagodas faults of northern thailand a result of india burma coupling in advance of india asia collision in the late eocene 37 ma the ranong and khlong marui faults were reactivated as curved sinistral branches of the mae ping and three pagodas faults which were accommodating lateral extrusion during india asia collision and himalayan orogenesis

tracing submarine hydrothermal inputs into a coastal bay in baja california using radon abstract hydrothermal fluid fluxes into deep ocean environments can be obtained from heat balance approaches however in shallow systems hydrothermal heat fluxes can be masked by solar heating in this paper we use radon 222rn as a naturally occurring geochemical tracer to map the location of hydrothermal fluid inputs as well as low temperature groundwater discharges and quantify fluxes into concepcion bay baja california mexico this fault bound bay contains intertidal seeps with salinities ranging from 5 3 to 25 6 temperatures reaching 64 c and nitrate reaching 900 m the bay is subject to natural eutrophication and frequent red tide events a detailed 222rn survey around the 100 km perimeter of concepcion bay allowed us to map the location of enhanced submarine groundwater inputs moorings at three contrasting coastal sites indicated that radon concentrations were higher at low tide and during the winter modeled hydrothermal fluid inputs ranged between 0 4 cm day in the middle of the bay and 43 9 cm day at the largest hydrothermal coastal seep site apparently faults allow meteoric water to be heated and serve as conduits for its subsequent discharge through permeable marine sediments when conservatively extrapolated to the entire bay using weighted distributions these fluxes are estimated at 17 5 m3 s a flow much higher than local ephemeral rivers about 42 of the fluxes described consisted of fresh groundwater with the remaining made up of recirculated seawater new nitrogen inputs associated with groundwater pathways are estimated to directly account for at least 15 of the local primary productivity our combined spatial survey time series strategy can be very useful to quantify hydrothermal fluid inputs in particular at vent sites where a temperature signal in shallow surface waters is difficult to be observed

tectonics and history of the andaman sea region abstract the andaman sea is an active backarc basin lying above and behind the sunda subduction zone where convergence between the overriding southeast asian plate and the subducting australian plate is highly oblique the effect of the oblique convergence has been formation of a sliver plate between the subduction zone and a complex right lateral fault system the late paleocene collision of greater india and asia with approximately normal convergence started clockwise rotation and bending of the northern and western sunda arc the initial sliver fault which probably started in the eocene extended through the outer arc ridge offshore from sumatra through the present region of the andaman sea into the sagaing fault with more oblique convergence due to the rotation the rate of strike slip motion increased and a series of extensional basins opened obliquely by the combination of backarc extension and the strike slip motion these basins in sequence are the mergui basin starting at 32 ma the conjoined alcock and sewell rises starting at 23 ma east basin separating the rises from the foot of the continental slope starting at 15 ma and finally at 4 ma the present plate edge was formed alcock and sewell rises were separated by formation of the central andaman basin and the faulting moved onshore from the mentawai fault to the sumatra fault system bisecting sumatra

structure and kinematics of the indo burmese wedge recent and fast growth of the outer wedge 1 the northern sunda subduction zone offshore burma and the associated indo burmese wedge mark the active eastern boundary of the burma platelet jammed between the india plate and the sunda plate the aim of this paper is to provide a structural and kinematics analysis of the indo burmese wedge based on seismic reflection geodetic and geological field data we found out that the indo burmese wedge is the place of diffuse strain partitioning right lateral shearing in the innermost part and e w shortening in the outermost part in the outer wedge thick skinned deformation overprints thin skinned deformation it can be explained by the required preservation of the critical taper after the fast westward propagation of the outer wedge above a very efficient clayey decollement layer the thick skinned deformation is here characterized by major right lateral strike slip faults the kaladan fault and the chittagong coastal fault and yet a typical internal deformation of the indo burmese wedge we suggest that the westward migration of internal right lateral shear deformation allows preservation of the strain partitioning ratios between internal n s trending right lateral shearing and external e w shortening some seismic lines show that the outer wedge deformation is not older than 2 ma its propagation could have been enhanced by the large amount of sediments filling up the sylhet flexural basin formed after the pliocene tectonic uplift of the shillong plateau

gondwana to asia plate tectonics paleogeography and the biological connectivity of the indian sub continent from the middle jurassic through latest eocene 166 35 ma abstract using the most up to the date information available we present a considerably revised plate tectonic and paleogeographic model for the indian ocean bordering continents from gondwana s middle jurassic break up through to india s collision with asia in the middle cenozoic the landmass framework is then used to explore the sometimes complex and occasionally counter intuitive patterns that have been observed in the fossil and extant biological records of india madagascar africa and eastern eurasia as well those of the more distal continents although the paleogeographic model confirms the traditional view that india became progressively more isolated from the major landmasses during the cretaceous and paleocene it is likely that at various times minor physiographic features principally ocean islands provided causeways and or stepping stone trails along which land animals could have migrated to from the sub continent aside from a likely link albeit broken by several marine gaps to africa for much of this time it is notable that the present day recent biota of madagascar indicates that the ancestors of five land mammal orders plus bats crossed the 400 km wide mozambique channel at different times in the cenozoic it is possible that the kerguelen plateau connected india and australia antarctica in the mid cretaceous approximately 115 90 ma later the seychelles mascarene plateau and nearby elevated sea floor areas could have allowed faunas to pass between southern india and madagascar in the late cretaceous from around 85 65 ma with an early cenozoic extension to this path forming as a result of the reunion hot spot trace islands growing on the ocean floor to the ssw of india the modelling also suggests that india s northward passage towards asia with eventual collision at 35 ma involved the ne corner of the sub continent making a glancing contact with sumatra followed by burma from 57 ma late paleocene onwards a scenario which is compatible with the fossil record indicating that india asia faunal exchanges began occurring at about this time finally we contend that a number of biologically based direct terrestrial migration routes that have been proposed for last 15 m y of the cretaceous asia to india antarctica to madagascar and or india can probably be dismissed because the marine barriers likely varying from 1000 up to 2500 km were simply too wide

hydrothermal venting of greenhouse gases triggering early jurassic global warming abstract the climate change in the toarcian early jurassic was characterized by a major perturbation of the global carbon cycle the event lasted for approximately 200 000 years and was manifested by a global warming of 6 c anoxic conditions in the oceans and extinction of marine species the triggering mechanisms for the perturbation and environmental change are however strongly debated here we present evidence for a rapid formation and transport of greenhouse gases from the deep sedimentary reservoirs in the karoo basin south africa magmatic sills were emplaced during the initial stages of formation of the early jurassic karoo large igneous province and had a profound influence on the fate of light elements in the organic rich sedimentary host rocks total organic carbon contents and vitrinite reflectivity data from contact aureoles around the sills show that organic carbon was lost from the country rocks during heating we present data from a new type of geological structures termed breccia pipes rooted in the aureoles within the shale of the western karoo basin the breccia pipes are cylindrical structures up to 150 meters in diameter and are mainly comprised of brecciated and baked black shale thousands of breccia pipes were formed due to gas pressure build up during metamorphism of the shales resulting in venting of greenhouse gases to the toarcian atmosphere mass balance calculations constrained by new aureole data show that up to 1800 gt of co2 was formed from organic material in the western karoo basin about 15 times this amount of co2 27 400 gt may have formed in the entire basin during the intrusive event u pb dating of zircons from a sill related to many of the pipes demonstrates that the magma was emplaced 182 5 0 4 million years ago this supports a causal relationship between the intrusive volcanism the gas venting and the toarcian global warming

aborted reversal of the palaeomagnetic field in the brunhes normal chron in east central california summary exposed pleistocene lake sediments in long valley california record a palaeomagnetic field of reversed polarity of short duration in the brunhes normal chron that is interpreted as an aborted reversal the virtual geomagnetic poles for that field reach a southern mid latitude and form a large clockwise directed loop when traced from old to young the poles enter the southern hemisphere about 90 east of long valley and exit about 90 west of it part of the record is present in exposed lake sediments in mono basin 40 km northwest of long valley along with the palaeomagnetic record tephrochronology is used to correlate and date the stratigraphy at the two localities assuming the sedimentation rate in both lakes was a constant 25cm per thousand years the recorded anomalous field behaviour is estimated to span about 4000 yr and be about 280 000 yr old

petrogenesis of malaysian granitoids in the southeast asian tin belt part 2 u pb zircon geochronology and tectonic model in our complementary geochemical study part 1 the malaysian granitoids of the southeast asian tin belt were divided into a middle permian to late triassic i type dominated eastern province indochina terrane and a triassic to early jurassic transitional i s type main range province sibumasu terrane separated by the bentong raub suture zone which closed in the late triassic previous geochronology has relied on only a few u pb zircon ages together with k ar and whole rock rb sr ages that may not accurately record true magmatic ages we pre sent 39 new high precision u pb zircon ion microprobe ages from granitoids and vol canics across the malay peninsula our results show that ages from the eastern province granitoids span 289 220 ma with those from the main range province granitoids being entirely late triassic spanning 227 201 ma a general westerly younging magmatic trend across the malay peninsula is considered to refl ect steepening and roll back of the bentong raub subduction zone during progressive closure of paleo tethys the youngest ages of subduction related granites in the eastern province roughly coincide with the youngest ages of marine sedimentary rocks along the paleo tethyan suture zone our petrogenetic and u pb zircon age data support models that relate the eastern province granites to pre collisional andean type magmatism and the western main range province granites to syn and post collisional crustal melting of sibumasu crust during the late triassic tin mineralization was mainly associated with the latter phase of magmatism two alternative tectonic models are discussed to explain the triassic evolution of the malay peninsula the fi rst involves a second late triassic to jurassic or early cretaceous east dipping subduction zone west of sibumasu where subduction related hornblende and biotite bearing granites along sibumasu are paired with main range crustal melt tinbearing granites analogous to the bolivia cordilleran tin bearing granite belt the second model involves westward underthrusting of indochina beneath the west malaya main range province resulting in crustal thickening and formation of tin bearing granites of the main ranges cretaceous granitoids are also present locally in singapore ubin diorite on tioman island in the noring pluton of the stong complex eastern province and along the sibumasu terrane in southwest thailand and burma myanmar refl ecting localized crustal melting

magnitudes of submarine groundwater discharge from marine and terrestrial sources indian river lagoon florida 1 magnitudes of terrestrial fresh and marine saline sources of submarine groundwater discharge sgd are estimated for a transect across indian river lagoon florida two independent techniques seepage meters and pore water cl concentrations show terrestrial sgd decreases linearly to around 22 m offshore and these techniques together with a model based on the width of the outflow face indicate a cumulative discharge of between 0 02 and 0 9 m3 d per meter of shoreline seepage meters and models of the deficiencies in 222rn activity in shallow sediments indicate marine sgd discharges of roughly 117 m3 d per meter of shoreline across the entire 1800 m wide transect two surface streams nearest the transect have an average discharge of about 28 m3 d per meter of shoreline marine sgd is thus 4 times greater then surface water discharge and more than 2 orders of magnitude greater than terrestrial sgd the magnitude of the terrestrial sgd is limited by the amount of regional precipitation evaporation recharge and groundwater usage while marine sgd is limited only by processes circulating marine water into and out of the sediments the large magnitude of marine sgd means that it could be important for estuarine cycling of reactive components such as nutrients and metals with only slight modification from estuarine water compositions the small magnitude of terrestrial sgd means that large differences from estuarine water composition would be required to affect chemical cycling

odp site 1063 bermuda rise revisited oxygen isotopes excursions and paleointensity in the brunhes chron an age model for the brunhes chron of ocean drilling program odp site 1063 bermuda rise is constructed by tandem correlation of oxygen isotope and relative paleointensity data to calibrated reference templates four intervals in the brunhes chron where paleomagnetic inclinations are negative for both u channel samples and discrete samples are correlated to the following magnetic excursions with site 1063 ages in brackets laschamp 41 ka blake 116 ka iceland basin 190 ka pringle falls 239 ka these ages are consistent with current age estimates for three of these excursions but not for pringle falls which has an apparent age older than a recently published estimate by 28 kyr for each of these excursions termed category 1 excursions virtual geomagnetic poles vgps reach high southerly latitudes implying paired polarity reversals of the earth s main dipole field that apparently occurred in a brief time span 2 kyr in each case several times shorter than the apparent duration of regular polarity transitions in addition several intervals of low paleomagnetic inclination low and negative in one case are observed both in u channel and discrete samples at 318 ka mis 9 412 ka mis 11 and in the 500 600 ka interval mis 14 15 these category 2 excursions may constitute inadequately recorded category 1 excursions or high amplitude secular variation

geomagnetic events and relative palaeointensity variations during the past 300 ka as recorded in kolbeinsey ridge sediments iceland sea indication for a strongly variable geomagnetic field magnetostratigraphic analyses of five sediment cores recovered from the kolbeinsey ridge area revealed consistent records of several geomagnetic events linked with low relative palaeointensities within the past 300 ka interpretation of various rock magnetic parameters clearly rule out the possibility that the recorded non normal polarity directions are linked to a deviating magnetomineralogical fraction or a distorted magnetic fabric therefore these directions are interpreted as true recordings of geomagnetic field variations hysteresis parameters and thermomagnetic measurements revealed pure pseudo single domain psd magnetite with curie temperatures of 580 c as the dominant remanence carrier mineral due to the homogeneity of the rock magnetic parameters the sediments are also suitable for relative palaeointensity determinations oxygen isotope stratigraphies for two of the cores provided a time frame to estimate the age ranges for the recorded geomagnetic field variations the obtained record of ten events of up to 12 ka duration during the past 300 ka and the related record of relative palaeointensity indicate a fairly dynamic character of the earth s magnetic field which is in clear contrast to published polarity time scales

the basins of sundaland se asia evolution and boundary conditions abstract most of the basins developed in the continental core of se asia sundaland evolved since the late cretaceous in a manner that may be correlated to the conditions of the subduction in the sunda trench by the end of mesozoic times sundaland was an elevated area composed of granite and metamorphic basement on the rims which suffered collapse and incipient extension whereas the central part was stable this promontory was surrounded by a large subduction zone except in the north and was a free boundary in the early cenozoic starting from the palaeogene and following fractures initiated during the india eurasia collision rifting began along large faults mostly n s and nnw sse strike slip which crosscut the whole region the basins remained in a continental fluvio lacustrine or shallow marine environment for a long time and some are marked by extremely stretched crust phu khanh natuna n makassar or even reached the ocean floor spreading stage celebes flores western sundaland was a combination of basin opening and strike slip transpressional deformation the configuration suggests a free boundary particularly to the east trench pull associated with the proto south china sea subduction java sulawesi trench subduction rollback in the early miocene australian blocks reached the sunda subduction zone and imposed local shortening in the south and southeast whereas the western part was free from compression after the indian continent had moved away to the north this suggests an important coupling of the sunda plate with the indo australian plate both to se and nw possibly further west rollback had ceased in the java sumatra subduction zone and compressional stress was being transferred northwards across the plate boundary the internal compression is expressed to the south by shortening which is transmitted as far as the malay basin in the late miocene most of the sunda plate was under compression except the tectonically isolated andaman sea and the damar basins in the pliocene collision north of australia propagated toward the north and west causing subduction reversal and compression in the short lived damar basin docking of the philippine plate confined the eastern side of sundaland and created local compression and uplift such as in nw borneo palawan and taiwan transpressional deformation created extensive folding strike slip faulting and uplift of the central basin and arakan yoma in myanmar minor inversion affected many thailand rift basins all the other basins record subsidence the uplift is responsible for gravity tectonics where thick sediments were accumulated sarawak ne luconia bangladesh wedge

tectonic evolution of the mogok metamorphic belt burma myanmar constrained by u th pb dating of metamorphic and magmatic rocks 1 the mogok metamorphic belt mmb extends for over 1500 km along the western margin of the shan thai block from the andaman sea north to the eastern himalayan syntaxis previous geochronology has suggested that a long lasting jurassic early cretaceous subduction related event resulted in emplacement of granodiorites and orthogneisses 171 120 ma and a poorly constrained tertiary metamorphic event on the basis of new u pb isotope dilution thermal ionization mass spectrometry and u th pb laser ablation multicollector inductively coupled plasma mass spectrometer geochronology presented here we propose two tertiary metamorphic events affected the mmb in burma the first was a paleocene event that ended with intrusion of crosscutting postkinematic biotite granite dikes at 59 ma a second metamorphic event spanned late eocene to oligocene at least from 37 possibly 47 to 29 ma this resulted in the growth of metamorphic monazite at sillimanite grade growth of zircon rims at 47 43 ma sillimanite muscovite replacing older andalusite and synmetamorphic melting producing garnet and tourmaline bearing leucogranites at 45 5 0 6 ma and 24 5 0 7 ma these data imply high temperature sillimanite muscovite metamorphism peaking at 680 c and 4 9 kbar between 45 and 33 ma to around 606 656 c and 4 4 4 8 kbar at 29 3 0 5 ma the later metamorphic event is older than 24 5 0 3 ma the age of leucogranites that crosscut all earlier fabrics our structural and geochronological data suggest that the mmb links north to the unexposed middle or lower crust rocks of the lhasa terrane south tibet and east to high grade metamorphic core complexes in northwest thailand

the kinematic history of the khlong marui and ranong faults southern thailand abstract the khlong marui fault kmf and ranong fault rf are major nne trending strike slip faults which dissect peninsular thailand they have been assumed to be conjugate to the nw trending three pagodas fault tpf and mae ping fault mpf in northern thailand which experienced a diachronous reversal in shear sense during india eurasia collision it follows that the kmf and rf are expected to show the opposite shear sense and a slip sense reversal at a similar time to the tpf and mpf new field data from the kmf and rf reveal two phases of ductile dextral shear separated by campanian magmatism paleocene to eocene post kinematic granites date the end of this phase while a brittle sinistral phase deforms the granites and has exhumed the ductile fault rocks the timing of these movements precludes formation of the faults in response to himalayan extrusion tectonics instead they formed near the southern margin of a late cretaceous paleocene orogen and may have been influenced by variations in the rate of subduction ahead of india and australia north south compression prior to reactivation of the subduction zone around southern sundaland in the eocene caused widespread deformation in the over riding plate including sinistral transpression on the kmf and rf

nutrient biogeochemistry in a gulf of mexico subterranean estuary and groundwater derived fluxes to the coastal ocean we hypothesize that biogeochemical processes in a subterranean estuary in the northeastern gulf of mexico significantly alter nutrient concentrations that are discharged into the ocean via submarine groundwater discharge sgd this subterranean estuary is a site of steep gradients over small spatial scales so selecting the appropriate groundwater endmember for flux calculations is difficult two endmember mixing models typically applied to investigate biogeochemical processes in surface estuaries are not useful in this case because of aquifer heterogeneity and complex solid fluid interactions groundwater residence times redox potential source strength and aquifer matrix appear to be the most important drivers for dissolved organic carbon doc and nutrient concentrations in this pristine coastal plain aquifer the distribution of dissolved species was consistent with a sequence of reactions in a narrow 2 m surface layer in which nitrate is initially exhausted likely because of denitrification organic nitrogen is remineralized releasing ammonium and some doc remains on the basis of a 222rn derived non steady state box model total terrestrial marine sgd rates were estimated to oscillate around 11 cm d21 the sgd is composed almost entirely of recirculated seawater accounting for 95 of total sgd fluxes conservative estimates of groundwater derived nitrogen inputs into the coastal ocean were 8 2 6 1 2 mmol m22 d21 consisting of ammonium 58 organic nitrogen 28 and nitrate 14 we suggest that these mainly represent recycled rather than new nutrient additions when extrapolated to the florida gulf coast the nitrogen and doc fluxes were comparable to the main regional rivers supporting the proposition that sgd plays a major role in coastal biogeochemistry the biogeochemical implications of submarine groundwater discharge sgd into coastal environments are becoming increasingly recognized globally groundwater discharge has been estimated to be only a few percent of the total freshwater flux to the oceans burnett et al 2006 in spite of that small fraction the input of nutrients to coastal environments via groundwater pathways could be globally more important because nutrient concentrations in groundwater are often much higher than those in river water in addition high dissolved n p ratios in groundwater relative to surface waters might drive the coastal ocean toward p limitation within the coming decades perhaps changing the present n limited coastal primary production slomp and van cappellen 2004

complex slab subduction beneath northern sumatra 1 new data provided by the 2004 2005 sumatra andaman great earthquake sequences allow us to image with improved detail the p wave velocity structure beneath sumatra and adjacent regions below northern sumatra we find that the slab is folded at depth exhibiting geometry similar to that of the volcanic arc and the trench at the surface we speculate that this fold plays a major role in the segmentation of the sumatra megathrust and may impede rupture propagation in the region north of sumatra significant slab material in the mantle transition zone is imaged for the first time and we infer the presence of a major tear between the upper mantle and transition zone there

carbon dioxide dynamics driven by groundwater discharge in a coastal floodplain creek summary dissolved carbon dioxide co 2 may be highly enriched in groundwater however the contribution of groundwater discharge as a source of co 2 to rivers estuaries and coastal waters is poorly understood we performed high resolution measurements of radon 222 rn a natural groundwater tracer and the partial pressure of co 2 p co 2 in a highly modified tidal creek and estuary north creek richmond river new south wales australia to assess whether co 2 in surface waters was driven by groundwater discharge a spatial survey revealed increasing 222 rn activities up to 17 3 dpm l 1 and p co 2 up to 11 151 atm in the upstream direction the enrichment occurred in a drained coastal acid sulphate soil wetland upstream of a mangrove forest time series experiments 24 h were performed at two stations upstream and downstream of the p co 2 enrichment area upstream measurements demonstrated a significant correlation between p co 2 and 222 rn while downstream values resulted in a significant inverse relationship between p co 2 and dissolved oxygen apparently as a result of respiration in nearby mangroves measurements taken 2 days after a 245 mm precipitation event revealed the highest recorded 222 rn activities up to 86 1 dpm l 1 and high p co 2 up to 11 217 atm showing a strong groundwater influence after flooding these observations imply that groundwater discharge drove co 2 dynamics at the upstream station while multiple complex processes drove co 2 at the downstream station a 222 rn mass balance model demonstrated that groundwater discharge accounted for about 76 of surface water in this floodplain creek the co 2 evasion rates 799 225 mmol m 2 d 1 were driven primarily by currents rather than wind groundwater derived co 2 fluxes into the creek averaged 1622 mmol m 2 d 1 a value twice as high as atmospheric co 2 evasion and consistent with carbon uptake within the creek and downstream exports these results demonstrate that groundwater seepage was a major factor driving co 2 evasion to the atmosphere from the creek groundwater discharge should be accounted for in co 2 budgets in coastal systems

nutrient inputs through submarine groundwater discharge in an embayment a radon investigation in daya bay china abstract daya bay a semi closed bay of the south china sea is famous for its aquaculture agriculture and tourism although routine environmental investigations in the bay have been conducted since the early 1980s evaluations of submarine groundwater discharge sgd an important process in exchange between groundwater and coastal seawater and its environmental impacts have never been reported in this study naturally occurring radon isotope 222 rn was measured continuously at two sites north west and middle east sites and used as a tracer to estimate sgd and associated nutrient inputs into the bay the sgd rates estimated based on the 222 rn mass balance model were on average 28 2 cm d at north west site and 30 9 cm d at middle east site the large sgd rate at middle east site may be due to the large tidal amplitude and the sandy component with high permeability in sediments the sgd driven nutrient fluxes which were calculated as the product of sgd flux and the difference of nutrient concentrations between coastal groundwater and seawater were 3 28 10 5 mol d for dissolved nitrates no 3 n 5 84 10 3 mol d for dissolved inorganic phosphorous dip and 8 97 10 5 mol d for reactive silicate si these nutrient inputs are comparable to or even higher than those supplied by local rivers in addition these sgd driven nutrients have a nitrogen phosphorous ratio as high as 43 which may significantly affect the ecology of coastal waters and lead to frequent occurrence of harmful algal blooms

estimation of heat and chemical fluxes from a seafloor hydrothermal vent field using radon measurements the circulation of seawater through newly formed ocean crust at mid ocean ridge spreading centres is important in the oceanic heat and chemical budgets the heat transfer in submarine hydrothermal systems accounts for 25 of the total global heat loss1 the transfer of mass resulting from basaltic alteration affects the geochemistry of seawater2 and is responsible for the formation of ore deposits on and beneath the seafloor3 various geophysical techniques have been employed in efforts to determine the heat output from hydrothermal vent fields4 9 however the magnitudes of the heat and chemical fluxes through these systems remain uncertain here we introduce a geochemical approach for estimating the flux from a vent field based on radon 222rn measurements in the overlying effluent plume this method was applied successfully in september 1986 during a 23 day expedition to an active vent field on the 170 km endeavour segment of the juan de fuca ridge fig la we estimate the heat flux from this site to be l 5 l09 w

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

deformation history and u pb zircon geochronology of the high grade metamorphic rocks within the klaeng fault zone eastern thailand abstract in eastern thailand the klaeng fault zone includes a high grade metamorphic rock assemblage named nong yai gneiss which extends about 30 km in a nw se direction along the fault zone the rocks of this brittle fault strand consist of amphibolite to granulite grade gneissic rocks structural analysis indicates that the rocks in this area experienced three distinct episodes of deformation d1 d3 the first d1 formed large scale nw se trending isoclinal folds f1 that were reworked by small scale tight to open folds f2 during the second deformation d2 d1 and d2 resulted from ne sw shortening during the triassic indosinian orogeny before being cross cut by leucogranites d1 and d2 fabrics were then reworked by d3 sinistral shearing including shear planes s3 and mineral stretching lineations l3 la mc icp ms u pb zircon dating suggested that the leucogranite intrusion and the magmatic crystallization took place at 78 6 0 7 ma followed by a second crystallization at 67 1 to 72 1 0 6 ma both crystallizations occurred in the late cretaceous and it is suggested were tectonically influenced by se asian region effects of the west burma and shan thai sibumasu collision or development of an andean type margin the sinistral ductile movement of d3 was coeval with the peak metamorphism that occurred in the eocene during the early phases of the india asia collision

rock falls in high alpine rock walls quantified by terrestrial lidar measurements a case study in the mont blanc area 1 the global warming observed in recent decades and its future increase may affect permafrost distribution on high mountain faces with consequences for their stability in this paper we show that rock falls from high alpine rock walls can be computed with a decimetre resolution using lidar measurements a laser scanner was used to create point clouds and triangulated irregular network models on the east face of the tour ronde at 3792 m asl mont blanc massif comparison of the models realised from measurements of july 2005 and july 2006 enabled quantification of rock falls with reduced uncertainty the volume of rock fall reached a total of 536 m3 in the scanned area which matches an erosion rate of 8 4 mm yr 1 this rate slightly higher to the ones reported in former studies enable to assume that this rock fall may be the consequence of the permafrost degradation in this rock face

submarine groundwater borne nutrients in a tropical bay maowei sea china and their impacts on the oyster aquaculture submarine groundwater discharge sgd has been recognized as an important pathway for nutrients into estuaries coasts and the adjacent seas in this study 222rn was used to estimate the sgd associated nutrient fluxes into an aquaculture area in a typical tropical bay maowei sea china the sgd into the maowei sea during june of 2016 was estimated to be 0 36 0 33 m d 1 and was associated with sgd derived dissolved inorganic nitrogen din dissolved inorganic phosphorus dip and dissolved silicon dsi fluxes mol d 1 of 4 5 5 5 106 5 3 9 1 104 and 9 4 9 3 106 respectively the sgd derived nutrients i e din dip and dsi were more than 1 9 0 9 and 3 6 times the amounts in the local river input and served as dominant sources in the nutrient budgets in the maowei sea moreover the n p ratios in the sgd around the maowei sea were high mean 64 and these ratios likely exceeded the environmental self purification capacity thereby enhancing the biomass and changing the phytoplankton community structure therefore sgd processes with derived nutrients may affect the biogeochemical cycles and marine ecological environment in the maowei sea furthermore the n p ratios 67 in oysters are very close to those in the sgd in the maowei sea this coincidence suggests that the high n p ratios in the sgd are likely to be one of the most important sources that support oyster aquaculture which might weaken the burden of water eutrophication in the maowei sea

submarine groundwater discharge from the yellow river delta to the bohai sea china 1 spatial and temporal variations of submarine groundwater discharge sgd have been evaluated by automated seepage meters from the yellow river delta to 7 km offshore in the bohai sea china we identified three zones from the coast to offshore based on different relationships between tidal and sgd changes our results indicate that the point of maximum sgd shifted 2 km offshore from september 2004 to september 2006 this spatial change is thought to be caused by sediment deposition near the coast integrating submarine fresh groundwater discharge sfgd along the coastline of the yellow river delta using measured values of sfgd per unit length of shoreline shows that discharge of fresh groundwater along the entire delta would be equivalent to 4 5 to 7 0 of the river discharge

a possible lacustrine paleomagnetic record of the blake episode from pringle falls oregon u s a abstract we have studied a high resolution paleomagnetic record of a magnetic polarity episode recovered from a 20 m section of diatomaceous lacustrine sediments from pringle falls near la pine oregon 43 7 n 238 6 e a total of 474 samples 982 specimens were collected at about 5 cm intervals from the 20 m section the age of this record is at present constrained between 0 6 ma and 18 000 yr based upon a pollen date from the older part of the lakebed sequence and the age of the younger glacial deposits that overlie the lakebeds the characteristic magnetization of the samples was determined by alternating field af demagnetization to 15 mt the average normal polarity stable declination and inclination of the non magnetic polarity episode sampled section 61 95 2 6 is statistically equivalent to that expected at this site for a geocentric axial dipole 62 the record provides a virtual geomagnetic pole vgp path that identifies a well defined clockwise ne sw loop with a radius of 60 followed by a second younger feature that traces out a counter clockwise loop 15 in radius residing in the ne quadrant and characterized by low latitudes interpretation of the natural remanent magnetization anhysteretic remanent magnetization nrm arm ratios for the samples indicates that the field intensity may have fallen and then increased above the average dipole field intensity the low intensity interval ends before the onset of the polarity episode as defined by directions and may suggest that the episode is a result of an unstable regeneration of the field after a significant lowering of overall field intensity these two characteristic features are similar to the two features present in the blake geomagnetic polarity episode at 114 000 and 105 000 yr bp observed in different parts of the world

early india australia spreading history revealed by newly detected mesozoic magnetic anomalies in the perth abyssal plain the seafloor within the perth abyssal plain pap offshorewestern australia is the only section of crust that directly records the early spreading history between india and australia during the mesozoic breakup of gondwana however this early spreading has been poorly constrained due to an absence of data including marine magnetic anomalies and data constraining the crustal nature of key tectonic features here we present new magnetic anomaly data from the pap that shows that the crust in the western part of the basin was part of the indian plate the conjugate flank to the oceanic crust immediately offshore the perth margin australia we identify a sequence of m2 and older anomalies in the west pap within crust that initially moved with the indian plate formed at intermediate half spreading rates 35 mm yr consistent with the conjugate sequence on the australian plate more speculatively we reinterpret the youngest anomalies in the east pap finding that the m0 age crust initially formed on the indian plate was transferred to the australian plate by a westward jump or propagation of the spreading ridge shortly afterm0 time samples dredged from the gulden draak and batavia knolls at the western edge of the pap reveal that these bathymetric features are continental fragments rather than igneous plateaus related to broken ridge these microcontinents rifted away from australia with greater india during initial breakup at 130ma then rifted from india following the cessation of spreading in the pap 101 103ma

exhumation of west sundaland a record of the path of india abstract the indian plate commenced its northward migration towards eurasia in the early cretaceous the lateral effect of this migration on the western edge of the sunda plate in southeast asia still remains equivocal in order to assess this effect we evaluate several key sectors characterized by deep crustal exhumation along a n s transect from the southern malay peninsula to the east himalayan syntaxis the evaluation is aided by a structural analysis of vertical movements and basin development five major metamorphic domes with similar geodynamic evolution maximum p t burial conditions and exhumation are studied exhumation of these domes migrated with time between late cretaceous in the stong complex north malaysia in the south and late miocene in the gaoligong shear zone south china in the north as documented by published work and our new fission track data presented herein deformation is characterized by a n s oriented extension that followed the more regional e w oriented plate tectonic shortening creating local core complexes and syn kinematic magmatism in the footwall of crustal scale detachments which displays a consistent temporal northward migration the n s extension was associated with the onset of hanging wall deposition in the sedimentary basins of western sundaland e g malay sumatra and thai basins during continuous exhumation of the footwall to upper brittle levels our multifaceted analysis of structural and thermochronological data shows a similar succession of tectonic thermal and sedimentary events in west sundaland that was driven by the gradual northward migration of india starting from cretaceous times we infer that the principal mechanism was driven by the subduction of an excess topography of greater india rifted continental margin during its underplating resulting in uplift thermal anomalies extensional exhumation and associated subsidence