the paleohydrology of lower cretaceous seasonal wetlands isle of wight southern england abstract the floodplain deposits of the wealden group lower cretaceous of the isle of wight southern england were formed in a seasonal wetland setting a type of environment widespread today along higher order tropical and subtropical river systems but rarely identified in the geological record the unit consists of four main lithofacies sheet sandstones with dinosaur footprint casts green gray mudstones with vertebrate remains abundant lignite pyrite and siderite spectacularly color mottled mudstones with goethite and locally pseudo anticlines and red mudstones with pseudo anticlines hematite and carbonate nodules the sheet sandstones are interpreted as crevasse deposits the green gray mudstones were deposited in shallow ponds on the floodplain which acted as sinks for debris released by local floods following wildfires the mottled mudstones represent surface water gley soils formed in seasonally waterlogged areas and the red mudstones resemble present day vertisols that formed on topographically elevated areas only intermittently flooded these mudstones show vertical transitions from one to another and although they could be interpreted as components of simple catenas the absence of associated facies changes implies that topographic differences were not the only control it is proposed that these three mudstone types formed as seasonal wetland catenas in which differences in soil drainage conditions resulted from variations in the flooding hydroperiod affecting areas with minor relief differences rather than drainage variability simply reflecting static topographic differences such seasonal wetland systems are rarely documented in the stratigraphic record despite being a widespread environment in present day tropical regions and the wealden deposits are used to identify criteria for the recognition of this important environment in the rock record these southern english wetlands are compared with other lower cretaceous wetlands from northern spain enabling hydrological factors which controlled deposition to be recognized

structural and geochronological constraints on the tectonic evolution of the dulong song chay tectonic dome in yunnan province sw china abstract the dulong song chay tectonic dome lies on the border of china se yunnan province and northern vietnam and consists of two tectonic and lithologic units a core complex and a cover sequence separated by an extensional detachment fault these two units are overlain unconformably by late triassic strata the core complex is composed of gneiss schist and amphibolite shrimp zircon u pb dating results for the orthogneiss yield an age of 799 10 ma which is considered to be the crystallization age of its igneous protolith formed in an arc related environment a granitic intrusion within the core complex occurred with an age of 436 402 ma which probably formed during partial closure of paleotethys within the core complex metamorphic grades change sharply from upper greenschist low amphibolite facies in the core to low greenschist facies in the cover sequence there are two arrays of foliation within the core complex detachment fault and the cover sequence s 1 and s 2 the pervasive s 1 is the axial plane of intrafolial s 0 folds d 1 deformation related to this foliation is characterized by extensional structures the strata were structurally thinned or selectively removed along the detachment faults indicating exhumation of the dulong song chay tectonic dome the major extension occurred at 237 ma determined by shrimp zircon u pb and 39 ar 40 ar isotopic dating techniques regionally simultaneous tectonic extension was associated with pre indosinian collision between the south china and indochina blocks the s 2 foliation appears as the axial plane of nw striking s 1 buckling folds formed during a compressional regime of d 2 d 2 is associated with collision between the south china and indochina blocks along the jinshajiang ailao shan suture zone and represents the indosinian deformation the dulong granites intruded the dulong song chay dome at 144 2 140 2 and 116 10 ma based on 39 ar 40 ar measurement on muscovite and biotite the dome was later overprinted by a conjugate strike slip fault and related thrust fault which formed a vortex structure contemporaneously with late cenozoic sinistral movement on the ailao shan red river fault

cenozoic high k alkaline magmatism and associated cu mo au mineralization in the jinping fan si pan region southeastern ailao shan red river shear zone southwestern china northwestern vietnam abstract the jinping fan si pan jfp cenozoic magmatic and cu mo au metallogenic belt in the southeastern part of the ailao shan shear zone host the tongchang chang an habo and chinh sang cu mo au deposits these deposits form an integrated epithermal porphyry regional mineralization system associated with 40 32 ma high k alkaline magmatism the magmatic rocks in the belt have relatively low tio2

palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record interest in palustrine carbonates and calcretes has increased over the last 20 years since they contain significant environmental information much of the work performed in this area has focused on either of two types of terrestrial carbonate palustrine carbonates or calcretes pedogenic and groundwater yet their simultaneous study shows there may be a gradual transition from one form to the other revealing the interplay between pedogenic sedimentary and diagenetic processes three main factors control the formation of these carbonates the position of the water table the host rock and the period of sub aerial exposure in pedogenic calcretes precipitation of carbonate takes places mostly in the vadose zone above the water table and within a previous host rock or sediment in groundwater calcretes the precipitation of carbonate also occurs within a previous host rock and around the groundwater table in palustrine carbonates however the precipitation of lime mud occurs in a lacustrine water body palustrine carbonates necessarily form on previous lacustrine mud whereas both types of calcretes may form on any type of sediment or soil the sub aerial exposure time needed to form palustrine carbonates may by relatively short even a season whereas pedogenic calcretes need more time several years to millions of years groundwater calcretes do not form on the topographic surfaces so there is no need of sub aerial exposure however stable surfaces favour the development of thick groundwater calcretes small fluctuations in the water table cause gradual transitions of these three types of terrestrial carbonates and the subsequent mixture of their characteristic features causing difficulties in the interpretation of these carbonates the formation of these carbonates is controlled by palaeoenvironmental factors both commonly form in semi arid climates arid climates are also suitable for calcretes but sub humid conditions are more suitable for palustrine carbonates more indications of climatic conditions may be obtained through the analysis of the d18o content of both calcretes and palustrine carbonates and from the depth of the horizon containing carbonate nodules in pedogenic calcretes vegetation is also important in the formation of these types of carbonates data on the prevailing vegetation can be obtained from the analysis of the micro and macrofabric as well as from the d13c signal of the primary carbonates which in pedogenic carbonates has also been used to estimate atmospheric pco2 during the phanerozoic these terrestrial carbonates are widely distributed on floodplains and distal areas of alluvial basins their presence and characteristics can be used as indicators of aggradation subsidence or accommodation rates and therefore as indicators of different tectonic regimes even though the study of these carbonates has notably increased in recent years much less is known about them than about marine carbonates presently there is much emphasis on obtaining a general model for sequence stratigraphy in terrestrial basins with a need to include the carbonates analysed in this paper

slow slip near the trench at the hikurangi subduction zone new zealand the range of fault slip behaviors near the trench at subduction plate boundaries is critical to know as this is where the world s largest most damaging tsunamis are generated our knowledge of these behaviors has remained largely incomplete partially due to the challenging nature of crustal deformation measurements at offshore plate boundaries here we present detailed seafloor deformation observations made during an offshore slow slip event sse in september and october 2014 using a network of absolute pressure gauges deployed at the hikurangi subduction margin offshore new zealand these data show the distribution of vertical seafloor deformation during the sse and reveal direct evidence for sses occurring close to the trench within 2 kilometers of the seafloor where very low temperatures and pressures exist

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

distinguishing climate and time in the soil record mass balance trends in vertisols from the texas coastal prairie mass balance relationships of 10 major elements in a vertisol climosequence and chronosequence formed on alluvial terraces on the texas gulf coastal plain indicate that the soils develop characteristic element translocation patterns in response to climatic forcing and reach mass flux equilibrium within a relatively short period of time vertisols within the climosequence age 35 ka 800 1500 mm mean annual precipitation map approach a net mass flux of 16 3 of parent element contents corresponding to a weathering flux of 1 0 x 10 3 to 1 3 x 10 3 g cm 2 yr 1 when map exceeds 900 mm net mass flux assessments in a vertisol chronosequence 0 4 35 ka 1000 mm map show that this equilibrium is achieved within 5 6 k y below 900 mm map positive net mass fluxes indicate that vertisol profiles are gaining material at a rate of 0 2 x 10 3 g cm 2 yr 1 vertisols forming in drier map areas approach equilibrium with climate by different mechanisms and at different rates compared to their wetter counterparts and may not be as sensitive to millennial scale climate shifts

evidence from paleosols for the geological antiquity of rain forest kaolinitic claystones in paleozoic paleokarst underlying the middle pennsylvanian fort scott limestone near drake missouri contain abundant fossil root traces these include a surficial root mat as well as stout woody deeply penetrating root traces a rooting pattern similar to that under rain forest also similar to soils of rain forest is the deeply weathered clay of the paleosol in which minimal amounts of nutrient bases remain forest communities adapted to oligotrophic clayey substrates in humid climates existed at least 305 million years ago

structural petrological and thermal evolution of a tertiary ductile strike slip shear zone diancang shan yunnan the diancang shan a horst massif within the red river fault zone in yunnan people s republic of china preserves a structural petrological and thermal record of two distinct phases of tectonic activity a left lateral ductile shear that terminated between 20 and 17 ma and a ductile to brittle phase of normal faulting which began at 4 7 ma and remains active mylonitic rocks in the core of the range display an early steep high temperature ht schistosity and a horizontal stretching lineation that are both parallel to the trend of the belt kinematic indicators indicate that shear was left lateral the complex shape of the ht schistosity at the southern termination of the massif likely results from a large scale oblique left lateral c shear plane that dismembered the shear zone and separated the ailao shan and the diancang shan as left lateral deformation terminated thermochronological and thermobarometric results suggest that the gneisses were partially unroofed during this event along the eastern edge of the diancang shan the ht fabrics were overprinted by low temperature structures during activation of east dipping normal faults cooling associated with this normal right lateral faulting along the diancang shan and perhaps activation of the right lateral normal movement on the range front fault farther south along the ailao shan began at 4 7 0 1 ma these results tend to support the view that extrusion of indochina occurred along the left lateral red river shear zone between 35 and 19 17 ma initiation of right lateral normal slip during the late miocene may relate to eastward extensional collapse of the thickened tibetan crust or more probably to initiation of the second phase of extrusion

source and evolution of ore fluids in the zhenyuan orogenic gold deposit se tibet constraints from the s c o isotopes abstract orogenic gold deposits commonly have large variation of stable isotopic values of ore minerals induced by complicated ore fluids evolution which was considered to provide equivocal evidence for ore sources in contrast this study has revealed relatively narrow range of s and c o isotopes of pyrites and carbonate minerals in the zhenyuan gold deposit 100 t at 3 5 g t on ailaoshan shear zone southeastern margin of tibet the zhenyuan deposit is a disseminated orogenic gold deposit with mineralization and alteration occurring in various types of wall rocks including carbonaceous slate meta quartz sandstone lamprophyre quartz porphyry and meta basalt the pre ore pyrites include the diagenetic pyrites in carbonaceous slate and meta quartz sandstone and the barren hydrothermal pyrites in quartz porphyry diagenetic pyrites have much varied 34s values from 54 58 38 31 and barren hydrothermal pyrites have elevated positive 34s values 8 76 43 24 the ore related pyrites disseminated in all types of host rocks and commonly with repetitive gold rich zones are the most important gold bearing minerals they contain high concentration of au along with other trace elements including cu as sb tl pb and bi little difference of 34s values is observed for the pyrites in different types of host rocks and for the low au and high au zones in single pyrite grain all ore related pyrites display a relatively narrow range of 34s values 5 22 4 16 with a peak at 0 this narrow range implies that the deposition of gold from ore fluids at zhenyuan deposit was mainly controlled by sulfidation of iron bearing minerals in the wall rocks the 34s values of ore related pyrites are consistent with the explanation that the ore fluids were from the subcrustal source instead of the crustal source with much varied sulfide 34s values carbonate minerals from different types of host rocks also have consistent and relatively narrow range of 13cpdb 3 77 0 68 and 18osmow 14 85 20 77 values indicating that the composition of ore fluids were little affected by water rock reaction at deposit scale the 13cpdb and 18osmow values of carbonates minerals are between those of the mantle peridotite and marine carbonates which can be explained by that the ore fluids have experienced crustal carbonate contamination in the subcrustal level or and along the migration conduit of the ore fluids

paleosols below the ames marine unit upper pennsylvanian conemaugh group in the appalachian basin u s a variability on an ancient depositional landscape abstract a vertisol like paleosol complex ranging from 3 to 10 m thick is developed below the ames marine interval conemaugh group upper pennsylvanian in the appalachian basin eastern ohio western pennsylvania west virginia and adjacent parts of maryland and kentucky sub ames mudstones contain the following pedogenic features very large slickensides microsparitic calcite nodules nodules or coatings of radial calcite spar preserved soil microstructure soil compatible birefringence fabrics and prominent mottling commonly restricted to the lower part of the paleosolum soil formation comprised 1 long term pedogenesis in alluvial and probably lacustrine sediments and 2 rapid development of histosols harlem coal as much as 8 m thick encouraged by the approaching am s transgression pedogenic carbonates in the sub ames interval at three localities yielded 18o values ranging from 6 18 to 1 21 pdb average 4 02 pdb s d 1 42 and 13c values ranging 9 17 to 6 72 pdb average 8 12 pdb s d 0 59 a inary plot of these values suggests mixing probably seasonal of evaporative and meteoric effects on isotope partitioning the stratigraphy of the ames harlem coal interval the regional distribution and thickness of the harlem coal and features of the sub ames paleosol show that the pre ames landscape had significant local relief in the form of shallow paleovalleys with broad interfluves along the western to northern margin of the appalachian basin ohio southwestern pennsylvania the stratigraphic relationships of sub ames paleosols the harlem coal ames marine unit interval and the ames marine unit itself are compatible with a significant effect of eustatic sea level rise in this area greater regional tectonic subsidence was probably the strongest control on sub ames sedimenta ion and pedogenesis along the eastern to southern margin south central pennsylvania west virginia northeasternmost kentucky where there appears to have been very little relief the morphology and stable isotope geochemistry of sub ames paleosols are compatible with seasonally wet dry climates probably with moderate 500 1000 mm annual rainfall

equation for compaction of paleosols due to burial existing empirically derived compaction curves for marine sediments fail to estimate the compaction of paleosols flood plain sediments and peats as indicated by deformation of clastic dikes dinosaur footprints and sandstone paleochannels yet compaction estimates are vital to reconstructing paleoclimate and geochemical profiles of paleosols to modeling sediment accumulation rates of nonmarine rocks and to tectonic flexural modeling of molasse facies this paper presents a compaction equation and physically derived constants that make geologically realistic estimates of compaction of paleosols and other nonmarine sediments a protocol for the application of the equation is suggested that would allow the following equation to solve for burial compaction c as a fraction of original thickness given depth of burial d in km as c s i f e d k 1 this equation can be applied to nonmarine sedimentary rocks or paleosols given appropriate empirical data on the physical constants in the equation such as initial solidity s i initial porosity f and the corresponding curve fitting constant k data on physical constants useful for this equation are compiled here for a range of paleosol and nonmarine sediment types

2d spatial distribution of reflection intensity on the upper surface of the philippine sea plate off the boso peninsula japan abstract the region off the boso peninsula japan is a tectonically complex area where the pacific plate is subducting beneath both the landward plate and the philippine sea plate phs from the japan trench and the izu bonin trench as the phs is subducting under the landward plate from the sagami trough it is important to better determine the structure of this region to deepen our understanding of its seismicity previous seismic reflection studies have shown that reflections from the upper surface of the phs vary with depth being stronger in the main slip area of the slow slip events beneath the boso peninsula boso sses however the spatial relationship between the reflective area and the sses is poorly constrained this study mapped the distribution of the reflective area using data recorded by ocean bottom seismometers during an active source seismic experiment we constructed a 3d p wave velocity structure by using traveltimes of first arrivals from 18 ocean bottom seismometer records we also adapted the traveltime mapping method to reflection traveltimes projecting them to the depth distance domain to map the 2d distribution of strong reflections from the top of the phs these reflections were concentrated in two areas one near the main slip area of the boso sses and the other about 60 km to the east in the first area the absence of strong velocity contrasts near the top of the phs suggests that the reflections were generated by a thin low velocity layer in contrast the structure of the second area has a convex shape of high velocity with a high velocity gradient near the top of the phs this structure may represent boninitic material of the outer arc high partially serpentinized peridotite or gabbro displaced by intraoceanic reverse faults

emplacement and cooling of the dien bien phu granitic complex implications for the tectonic evolution of the dien bien phu fault truong son belt nw vietnam the dien bien phu dbp fault strikes nearly perpendicular to the general tectonic framework separating northwest vietnam into two compartments the dbp and muong lay granites are exposed respectively east and west of the fault the u pb age of 277 2 ma obtained for the muong lay granite is similar to the age of the chieng khuong complex exposed within the song ma structure east of the dbp fault these two magmatic intrusions are considered as belonging to a same tectonic structure related to the subduction of the song ma ocean under the indochina block during the indosinian orogeny the dbp fault with a total post permian dextral offset of 30 40 km shifts the song ma suture it could then be connected to the ailao shan shuanggou suture to the north the undeformed dbp granite gave a u pb age of 230 1 ma sealing the indosinian deformation on the fault the ladinian carnian activity of the fault is confirmed by the 40ar 39ar biotite age of 228 4 ma obtained from the paragneiss forming the fault zone a geodynamic model is proposed to describe the various tectonic phases recorded by on the dbp fault it associates field data stratigraphic observations and geochronology analyses u pb ar ar fission tracks following the late triassic exhumation of the granite and the end of the indosinian orogeny marked by the norian unconformity the granite was buried under jurassic and lower cretaceous sediments a strong cooling event during the early late cretaceous 100 ma is associated with the reactivation of the dbp fault and the accommodation of a southward thrusting of the song da terrane onto the truong son belt this newly recognised tectonic phase could be associated to the subduction of the paleo pacific plate under the indochina block no data are available yet to constrain the tertiary evolution of the dbp system however the tertiary deformation is likely similar to the cretaceous one

an oxygen isotope study of illite and calcite in three appalachian paleozoic vertic paleosols abstract the oxygen isotope compositions of pedogenic calcite and illite in three paleozoic vertic red bed paleosols record a complex history of pedogenic and diagenetic processes the paleosols are preserved in the upper mississippian chesterian mauch chunk pennsylvania hinton west virginia and pennington tennessee formations in the appalachian basin and were buried to 7 8 km 230 260 c 3 4 km 100 145 c and 1 5 3 km 70 100 c respectively the submicron size clay fractions of the paleosols are presently composed of r3 ordered illite smectite i s inferred from k ar dates and soil morphology to have been authigenically produced by the reaction of smectite to illite oxygen isotope fractionations calculated pore fluid compositions and k ar dates were used to constrain the conditions and timing of i s and pedogenic calcite re crystallization in each of the paleosols the data were interpreted in light of three possible end member environments for formation and recrystallization 1 the pedogenic environment 2 the burial diagenetic environment and 3 a burial environment dominated by hot tectonically driven fluid the 18o values of pedogenic calcite and authigenic i s in vertic red bed paleosols generally reflect recrystallization and exchange during burial diagenesis and are thus not suitable for interpretation of paleoenvironment or paleoclimate the involvement of orogenic fluids during burial cannot be ruled out but it is not required by any of the paleosols in the coastal margin pennington formation paleosol i s formation may have been initiated in the pedogenic environment in response to cyclical wetting and drying of the soil clay matrix continued smectite transformation and coarsening and ordering of i s during a long period of shallow burial led to its isotopic reequilibration with pore fluids at slightly elevated temperature but oxygen isotope compositions of pedogenic calcite in the paleosol are preserved

no red river capture since the late oligocene geochemical evidence from the northwestern south china sea abstract rare earth elements ree in the sediment samples of six industrial wells from the yinggehai song hong basin in the northwestern south china sea were analyzed and compared with the detrital zircon u pb data from earlier studies to extrapolate sediment provenance the results reveal that the red river song hong river hainan island and central vietnam have been the main provenances of the yinggehai song hong basin since the late oligocene the red river has been supplying sediments with positive eu anomalies from basic ultrabasic metamorphic and volcanic parent rocks to most parts of the basin while hainan island has delivered sediments with negative eu anomalies from granitic and sedimentary parent rocks to the eastern slope area of the basin the progradational downlap structures in the seismic profiles also support the finding that the sediment supply is mainly from the red river and from hainan island the metamorphic rocks which are widespread within the red river drainage not only provided high volumes of sediments to the basin but also contributed to the positive eu anomalies observed because their ree and u pb signatures are similar to those of the red river source the metamorphic and igneous rocks of the song ma suture zone kontum massif and jinghong area were probably parts of a large basic provenance region before being separated by strike slip movements along the ailao shan red river shear zone furthermore our results indicate that the red river drainage area has been relatively stable since the late oligocene therefore if a drainage capture from the red river occurred it is likely to have taken place before the late oligocene

geochronological and geochemical constraints on the coexistent n morb and ssz type ophiolites in babu area sw china and tectonic implications our detailed geological geochemical and geochronological investigations indicate the coexistence of late paleozoic 270 265 ma normal middle ocean ridge basalt n morb type and suprasubduction zone ssz type ophiolites in the babu area sw china metaperidotite samples from the babu ophiolites show high os concentrations and low re os 187 os 188 os and 187 re 188 os ratios and represent residual upper mantle metagabbro and metabasalt samples show light rare earth element lree depleted ree patterns and n morb like primitive mantle normalized spider diagrams without nb ta and zr hf anomalies and depleted sr nd isotopic compositions e nd t 6 9 8 3 these geochemical and re os sr nd isotopic data show that the babu ophiolites are derived from a depleted mantle source and represent ancient n morb like oceanic crust in addition peridotites basalts and boninites with ssz signatures e g nb ta negative anomalies were also reported in the babu ophiolites consistent with their generation in a forearc or arc setting in combination with the arc related high mg limburgite basalt and andesite these late paleozoic ultramafic mafic rocks are genetically related to paleotethyan subduction rather than being emeishan mantle plume related the coexisting n morb and ssz type ophiolites in the babu area show similar geochemical and geochronological characteristics to the jinshajiang ailaoshan song ma ophiolites supplementary material a description of the geology of the babu ultramafic mafic complex sample descriptions detailed analytical methods and results and a summary of previously published age data for late paleozoic magmatic rocks along the china vietnam border are available at https doi org 10 6084 m9 figshare c 4007569

new constraints on the structure thermochronology and timing of the ailao shan red river shear zone se asia new structural petrographic and 40ar 39ar data constrain the kinematics of the asrr ailao shan red river shear zone in the xuelong shan xls geochronological data reveal triassic early tertiary and oligo miocene thermal events the latter event 33 26 ma corresponds to cooling during left lateral shear in the fansipan fsp range thrusting of the sapa nappe linked to left lateral deformation and cooling of the fsp granite occurred at 35 ma rapid cooling resumed at 25 29 ma as a result of uplift within the transtensive asrr in the daynuiconvoi dncv foliation trends nw se but is deflected near large scale shear planes stretching lineation is nearly horizontal on steep foliations shear criteria indicate left lateral shear sense zones with flatter foliations show compatible shear senses petrographic data indicate decompression from 6 5 kbar during left lateral shear temperatures 700 c 40ar 39ar data imply rapid cooling from above 350 c to below 150 c between 25 and 22 ma without diachronism along strike along the whole asrr cooling histories show two main episodes 1 rapid cooling from peak metamorphism during left lateral shear 2 rapid cooling from greenschist conditions during right lateral reactivation of the asrr in the nw part of the asrr xls diancang shan we link rapid cooling 1 to local denudations in a transpressive environment in the sw part ailao shan and dncv cooling 1 resulted from regional denudation by zipper like tectonics in a transtensive regime the induced cooling diachronism observed in the ailao shan suggests left lateral rates of 4 to 5 cm yr from 27 ma until 17 ma dncv rocks always stayed in a transtensive regime and do not show cooling diachronism the similarities of deformation kinematics along the asrr and in the south china sea confirms the causal link between continental strike slip faulting and marginal basin opening

depth to pedogenic carbonate horizon as a paleoprecipitation indicator an analysis of 1168 modern soil profiles from the u s natural resources conservation service yields no correlation between mean annual precipitation and depth to the top of the carbonate horizon r 2 0 03 p 0 001 parent material and soil texture both play negligible roles in this regression when combined with similar published studies n 1481 r 2 improves slightly r 2 0 31 p 0 001 caution is therefore advised in using this or any previously published regression for inferring paleoprecipitation from paleosols however in the combined data set carbonate horizon bearing soils correlate with a mean annual precipitation of 760 mm p 0 05 thus the presence vs absence of pedogenic calcium carbonate is a good indicator of paleoprecipitation above or below this value

timing of left lateral shearing along the ailao shan red river shear zone constraints from zircon u pb ages from granitic rocks in the shear zone along the ailao shan range western yunnan china as the boundary between the indochina and the south china blocks the ailao shan red river asrr shear zone underwent a sinistral strike slip shearing which is characterized by ductile deformation structures along the ailao shan range the timing issue of left lateral shearing along the asrr shear zone is of first order importance in constraining the nature and regional significance of the shear zone it has been therefore focused on by many previous studies but debates still exist on the age of initiation and termination of shearing along the shear zone in this paper we dated 5 samples of granitic plutons dykes along the ailao shan shear zone zircon u pb ages of four sheared or partly sheared granitic rocks give ages of 30 9 0 7 36 6 0 1 25 9 1 0 and 27 2 0 2 ma respectively an undeformed granitic dyke intruding mylonitic foliation gives crystallization age of 21 8 1 ma the th u ratios of zircon grains from these rocks fall into two populations 0 17 1 01 and 0 07 0 08 reflecting magmatic and metamorphic origins of the zircons detailed structural and microstructural analysis reveals that the granitic intrusions are ascribed to pre syn and post shearing magmatisms the zircon u pb ages of these granites provide constraints on timing of the initiation later than 31 ma from pre shearing granitic plutons but earlier than 27 ma from syn shearing granitic dykes and termination ca 21 ma from the post shearing granitic dykes of strong ductile left lateral shearing which is consistent with previous results on the diancang shan and day nui con voi massifs in the literature we also conclude that the left lateral shearing along the asrr shear zone is the result of southeastward extrusion of the indochina block during the indian eurasian plate collision furthermore the left lateral shearing was accompanied by the ridge jump postdating the opening of the south china sea

tectonics and metallogeny of mainland southeast asia a review and contribution abstract the southeast asia region is endowed with a diversity of mineral resources notably porphyry related skarn epithermal and sediment hosted orogenic gold deposits formation of these deposits was associated with a long and complex tectonic history of gondwana supercontinent break up arc magmatism backarc basin development together with arc continent and continent continent collisions that created the present day mainland se asia this paper summarizes historical and current se asian geological research and ore deposit studies here we present a new tectonic and metallogenic model for phanerozoic mainland se asia from this model we conclude that incipient arc backarc basin magmatism is the key to the formation of many important ore deposits in the truong son and loei fold belts the two major metallogenic belts in mainland se asia in addition triassic to cenozoic arc continent and continent continent collisions have led to the formation of many sediment hosted orogenic gold deposits in the sukhothai and the sibumasu terranes oblique cretaceous to recent subduction along the andaman sunda trench was responsible for gold and copper gold molybdenum porphyry and epithermal mineralization along the kawlin wutho mt popa arc in myanmar in the north and the sumatran volcanic arc in the south we anticipate that the present emphasis on exploring for shallower level epithermal deposits will increasingly lead to exploration for deeper level porphyry and porphyry related skarn systems in the coming decades

igneous petrogenesis of the yakuno ophiolite japan in the context of the diversity of ophiolites an ophiolite complex includes three major members basaltic volcanics mafic ultramafic cumulates and residual peridotite from the aspect of igneous petrology three distinct types are recognized among the associations of the three members liguria type alkalic basalt plagioclase type cumulates and lherzolite yakuno type high alumina tholeiite clinopyroxene type cumulates and clinopyroxene bearing harzburgite papua type low alumina tholeiite orthopyroxene type cumulates and clinopyroxene free harzburgite in the light of recent experimental studies the three types represent cogenetic complementary products of low 30 degrees of partial melting in the lherzolitic source mantle respectively the cumulates of the yakuno ophiolite show structural and chemical continuity to the underlying residual peridotite and were recrystallized at high pressures 5 10 kb they originated in a deep soft floored magma chamber directly overlying the partially melted residual harzburgite from which the magma was extracted the three members of the yakuno ophiolite were cogenetically formed through a magmatic event induced by a moderate degree of partial melting in the mantle

paleosols in clastic sedimentary rocks their geologic applications interest in pre quaternary paleosols has increased over the past decade in large part because they have proved to be beneficial in solving diverse geological problems the majority of paleosols are described from continental deposits most commonly from alluvial strata criteria for recognizing these paleosols have been extensively described however classifying them has proved more complicated pre quaternary paleosols are generally classified according to one or more modern soil classification systems although one new classification has been proposed exclusively for paleosols to avoid problems using the modern soil classifications in addition to taxonomic classification paleosols can be categorized according to the interplay among deposition erosion and the rate of pedogenesis when they formed paleosols can be solitary if they formed during a period of landscape stability following the development of an unconformity such paleosols are commonly thick and extremely well developed more commonly paleosols are vertically stacked or multistory because they formed in sedimentary systems undergoing net aggradation if erosion was insignificant and sedimentation was rapid and unsteady compound paleosols generally formed if the rate of pedogenesis exceeded the rate of deposition composite paleosols developed thick cumulative paleosols indicate that erosion was insignificant and that sedimentation was relatively steady both autogenic and allogenic processes can influence depositional and erosion patterns and thus affect the kinds of soils that form consequently paleosols can help to interpret the history of sediment deposition and the autogenic and allogenic processes that influenced a sedimentary basin paleosols are also helpful in stratigraphic studies including sequence stratigraphic analyses they are used for stratigraphic correlations at the local and basinal scale and some workers have calculated sediment accumulation rates based on the degree of paleosol development in addition to their stratigraphic applications paleosols can be used to interpret landscapes of the past by analyzing paleosol landscape associations at different spatial scales ranging from local to basin wide in scope at the local scale lateral changes in paleosol properties are largely the result of variations in grain size and topography at the scale of the sedimentary basin paleosols in different locations differ because of basinal variations in topography grain size climate and subsidence rate paleosols are used to reconstruct ancient climates even to estimate ancient mean annual precipitation map and mean annual temperature mat ancient climatic conditions can be interpreted from modern soil analogs or by identifying particular pedogenic properties that modern studies show to have climatic significance stable carbon and oxygen isotopes are also used to interpret ancient climate and some effort has been made to estimate mat from isotopic composition on the basis of

mass balance reconstruction of a modern vertisol implications for interpreting the geochemistry and burial alteration of paleo vertisols abstract utilizing identical sampling and analytical techniques the morphological and chemical characteristics of a modern vertisol houston black series central texas can be directly compared with an upper mississippian paleo vertisol from the appalachian basin pennington formation east central tennessee mass balance reconstructions suggest retention of primary pedochemical patterns in the paleo vertisol including patterns of soil volume change strain and transport functions translocations of many major and trace elements retention of primary pedochemical patterns suggests that vertisols constitute nearly closed systems during burial diagenesis chemical and mineralogical changes associated with burial diagenesis of the paleo vertisol include oxidation of organic carbon oc illitization of smectites dehydration and recrystallization of fe mn oxyhydroxides and dolomitization of pedogenic calcite significant differences in the chemical behavior of gilgai microhigh and microlow pedons in modern vertisols have implications for interpretation of geochemical data obtained from paleo vertisols overall wetter soil conditions and variable redox potential under gilgai microlows promote greater depths of leaching and mobility of redox sensitive trace elements including co cr cu mn ni and v gilgai microhighs behave as evaporative wicks that draw moisture and soluble phases towards the soil surface resulting in precipitation of metal hydrosylate complexes and sulfates gypsum at the capillary fringe and shallower depths of leaching and fixation of trace elements paleoprecipitation estimates from paleosols based on the depth to the top of the pedogenic carbonate horizon should therefore utilize field petrographic and geochemical data for characterizing maximum depths of leaching loss or gain of exchangeable bases and calcification rather than relying solely upon field data

geodetic data inversion based on bayesian formulation with direct and indirect prior information summary mechanical interaction between adjacent plates which causes crustal deformation in plate boundary zones is rationally represented by tangential displacement discontinuity fault slip at plate interfaces given fault slip distribution we can compute surface displacements on the basis of elastic dislocation theory thus we can determine the functional form of a stochastic model to extract information about unknown fault slip distribution from observed surface displacement data in addition to observed data we usually have prior information for example plate tectonics postulates that primary fault slip is parallel to relative plate motion this is direct prior information that bounds the values of model parameters within certain ranges from physical consideration we may impose prior constraint on the roughness of fault slip distribution this is indirect prior information that regulates the structure of stochastic models by combining the direct and indirect prior information with observed data in a proper way we constructed a bayesian model for geodetic data inversion which has a hierarchic flexible structure controlled by hyper parameters the optimum values of hyper parameters are objectively determined from observed data by using akaike s bayesian information criterion abic the inversion formula derived from the bayesian model unifies the jackson matsu ura formula with direct prior information and the yabuki matsu ura formula with indirect prior information in a rational way we demonstrated the effectiveness of the unified inversion formula through the analysis of the surface displacement data associated with the 1923 kanto earthquake in the analysis with direct and indirect prior information we obtained the bimodal distribution of fault slip almost parallel to plate convergence on the north american philippine sea plate interface if we ignore the direct prior information in the analysis additional significant distribution of fault slip perpendicular to plate convergence appears to the east which is incomprehensible from plate tectonics

the cretaceous southeast bohol ophiolite complex central philippines a highly disaggregated supra subduction zone ophiolite abstract the southeast bohol ophiolite complex seboc represents a complete ophiolite sequence with a pelagic chert cap yielding an early cretaceous age the residual peridotite suite of this ophiolite complex is dominated by harzburgite with rare occurrences of lherzolite and dunite pods layered ultramafic cumulate rocks made up of clinopyroxenite wehrlite dunite and massive to layered mafic cumulate rocks consisting of gabbro and norite are present although disaggregated the ophiolite complex includes a sheeted dike complex and a preponderance of sheet flows over pillow lavas in the volcanic section geologic observations such as gabbro pods included within residual harzburgite and deep water sedimentary and volcanic rocks directly overlying the harzburgite have often been reported from the mid atlantic ridge and other slow spreading centers however such situations are never encountered in the seboc geochemical data on seboc show that this ophiolite complex exhibits transitional mid ocean ridge basalt island arc tholeiite geochemical affinities this suggests formation in a subduction related marginal basin the field geological characteristics of seboc show that aside from being a harzburgite ophiolite type this crust mantle sequence was formed in a fast spreading center later tectonic events resulted in its emplacement as a forearc ophiolite

imaging of the early acceleration phase of the 2013 2014 boso slow slip event we analyze gps and seismic data to examine the spatiotemporal evolution of a slow slip event sse near boso peninsula central japan from december 2013 to january 2014 the evolution of this sse and its associated seismicity is divided into two distinct phases slip initially accelerated slowly with low slip rates low propagation speeds and no accompanying seismicity during the early phase and then accelerated more rapidly with higher slip rates a higher propagation speed and local earthquake swarm activity during the later phase the seismicity was highly correlated in space and time with slip rate suggesting that the swarm activity was triggered by stress loading due to the slow slip the transition from the slow to faster phase shares some similarities with the nucleation of megathrust earthquakes inferred from foreshock activities suggesting that sses may provide insights into the nucleation of large earthquakes

comparison of modern and ancient vertisols developed on limestone in terms of their geochemistry and parent material identification of paleosol parent material can be difficult a common simplistic assumption is that nonpedogenic strata directly beneath paleosols are representative of the parent material field relationships petrography and geochemical massbalance were used to test the simple hypothesis that the parent material of both an early carboniferous late mississippian vertic vertisol like paleosol and a modern analog soil vertisol was immediately subjacent marine carbonate rock an alternative hypothesis also tested was that the paleosol formed primarily from siliciclastic sediment deposited on top of the carbonate the modern ancient analog comparison is valid because both the paleosol and the modern soil have high clay contents extensive shrink swell features and rest directly on top of marine carbonate substrates field and thin section observations indicate minor assimilation of marine carbonate into both the paleosol and soil matrices mass balance of both the paleosol and soil calculated assuming that the subjacent carbonate was the parent material and that ti was immobile during weathering indicated 25 75 net volume loss during weathering and 25 99 net losses of many alkali alkaline earth and redox sensitive elements however calculations based on an alternative hypothesis of clayshale parent material for the paleosol indicated only 10 25 volume loss and lower translocation losses for weathering of this material the insoluble residue content of the dolostone would require that a fourfold volume reduction during weathering occurred if the dolostone were the only parent material if the paleosol formed from clayshale then significantly less volume loss characterised weathering these results collectively illustrate that the simplest interpretation of paleosol parent material may not always be correct and that paleosols can be derived from weathering of more than one parent material d 2002 elsevier science b v all rights reserved

permo triassic granitoids in the northern part of the truong son belt nw vietnam geochronology geochemistry and tectonic implications abstract the northern segment of the truong son belt of northwestern vietnam is composed of three granitoid complexes chieng khuong dien bien and song ma respectively our new la icp ms u pb dating results of magmatic zircons from five granitoid samples in the dien bien and the chieng khuong complexes reveal the existence of three age populations of magma emplacement and crystallization from 276 to 202 ma the new data show that the quartz diorite of the chieng khuong complex is dated to be 271 ma however the previously named dien bien complex exposed at different localities has various ages from 281 to 202 ma of magmatic crystallization the chieng khuong quartz diorite exhibits high mg value 60 7 and enriched sr nd isotopic features i sr 0 713822 end t 11 34 with subduction related geochemical features e g depletion in nb ta and ti and enrichment in rb and la the dien bien gabbroic diorite at muong lay is characterized by relatively depleted isotopic data i sr 0 705050 end t 0 09 and extensive depletion in nb and ta by contrast the dien bien granodiorite and quartz monzonite at dien bien are high k calc alkaline to calc alkaline with high mg values 45 5 to 54 4 and they display enriched sr nd isotopic data i sr 0 714912 to 0 716430 end t 9 58 to 8 85 and post collisional geochemical characteristics e g enrichment in total alkali lile and lree and depletion in eu sr p ti and nb under the framework of regional tectonic evolution the permo triassic magmatism along the northern truong son belt is thus grouped into an early stage from ca 280 to 250 ma and a late stage from 229 to 202 ma the early permian early triassic arc magmatism 280 270 ma and 250 245 ma which is widely distributed in the truong son belt provides reliable information on the continuous subduction of the song ma oceanic plate beneath the indochina block furthermore the magmatism of the dien bien complex at dien bien was formed during post collisional extension at ca 229 to 202 ma diachronous suturing of the eastern tethyan evolution is characterized by the differences in the ages of subduction post collisional evolution along the ailaoshan and the song ma belts

physical compaction of vertic palaeosols implications for burial diagenesis and palaeo precipitation estimates burial compaction is one of several major obstacles to estimating palaeoprecipitation from depth to pedogenic carbonate in favourably preserved palaeosols palaeosols must be decompacted and the preburial depth to the pedogenic carbonate obtained vertic palaeosols may be particularly good candidates for palaeoprecipitation estimates because of their increased likelihood of preserving clastic dykes one of the best features for estimating burial compaction compaction estimates from clastic dykes and literature based depth of burial estimates suggest vertic palaeosols undergo significantly less burial compaction than may be commonly assumed late carboniferous vertic palaeosols buried to 2 5 3 0 km compacted to 93 of their original thickness in contrast clastic dykes in a nonpedogenic shale directly underlying one of the late carboniferous palaeosols records compaction to 70 of original thickness similarly obtained burial compaction and burial depth estimates for early carboniferous ordovician and proterozoic vertic palaeosols were used to test a burial compaction curve and equation specific to vertic palaeosols results suggest this vertic calibrated curve and equation can be used to estimate burial compaction for vertic palaeosols lacking clastic dykes but additional testing is needed naturally high bulk densities may have limited the compactibility of vertic palaeosols likewise high initial bulk density and an abundance of swelling clays may have severely limited the transmissivity of some vertic palaeosols as they passed from pedogenic to burial environments upon burial these vertic palaeosols may have behaved as closed systems which has implications for understanding their diagenetic modification additional efforts to understand burial compaction of vertic palaeosols also promises to improve our understanding of aquifer aquiclude and hydrocarbon reservoir seal relationships in sedimentary basins containing intercalated palaeosols

intraplate tectonics in asia a precise age for large scale miocene movement along the ailao shan red river shear zone china tertiary left lateral movement along the 1000 km long ailao shan red river shear zone appears to have played an important role in absorbing post collisional northward penetration of india into asia crustal strike slip shear along this zone caused the formation of a gneiss belt metamorphosed to amphibolite grade including anatectic melting both metamorphism and melting were induced by ductile deformation yielding the possibility to date the major tectonometamorphic event that shaped the ailao shan red river belt 17 u pb isotope analyses were performed on small size fractions of zircon monazite and xenotime extracted from two different leucogranitic layers the two samples are located about 50 km apart in the central segment of ailao shan in structurally well controlled settings where the melts crystallized within the strongly foliated gneisses during late stages of deformation all mineral u pb analyses had to be corrected for excess or deficit amounts of radiogenic 206 pb originating from initial 230 th disequilibrium in the 238 u decay series in monazite such disequilibrium 206 pb reaches 20 of total radiogenic 206 pb the corrected u pb ages of monazite and xenotime lie between 22 1 and 23 9 ma whereas zircon yields significantly discordant u pb ages between 30 5 and 33 9 ma pointing to precambrian material in the magma source region inherited components could also be detected in monazite the set of u pb data shows that monazite and xenotime formed simultaneously in both localities substantiating an early miocene age of 23 0 0 2ma for late kinematic crystallization of anatectic melts in the metamorphic belt of the ailao shan red river shear zone

an early miocene transition in deformation regime within the red river fault zone yunnan and its significance for indo asian tectonics recent work has tended to support the view that lateral extrusion of indochina along the red river fault zone was a significant factor in accommodating the convergence of india with asia to better understand the nature and timing of this feature 40ar 39 ar age spectrum analyses were undertaken on minerals from the ailao shan red river metamorphic belt in southern yunnan china interpreted using diffusion domain theory these results yield thermal histories in the temperature range 550 150 c discontinuities in cooling rates observed from these results suggest a transition in deformation style in the shear zone during the early miocene at least in the vicinity of our samples left lateral strike slip ductile deformation appears to have ceased by about 20 ma the mylonitic gneisses in the shear zone were subsequently obliquely unroofed probably due to a component of normal faulting along the eastern edge of the shear zone causing a brief locally 100 c m y cooling episode this transition may have resulted from a component of northeast southwest extension attributable to greater clockwise rotation of indochina relative to south china after 20 ma than that consistent with pure strike slip along the fault k ar ages on clay minerals from gouge within the normal faults bounding the ailao shan and diancang shan yield a range of ages between 20 and 185 ma but show a significant clustering at 20 25 ma these results suggest that early miocene movement on a precursor to the range front normal fault in the ailao shan caused oblique unroofing of the shear zone this early miocene event corresponds in time with a transition from low to very high denudation rates throughout the himalaya and southern tibet this coincidence may reflect that once left lateral strike slip motion on the red river fault zone slowed or was terminated accommodation of much of the continued northward convergence of india occurred on the main central thrust resulting in rapid uplift in the tethyan himalaya and gangdese belt

pedogenic translocation of fe in modern and ancient vertisols and implications for interpretations of the hekpoort paleosol 2 25 ga abstract many interpretations of oxygen levels in the precambrian atmosphere use interpretations of fe distributions measured in paleosols this article addresses the current lack of knowledge concerning baseline fe translocations in modern soil analogs for the 2 25 ga hekpoort paleosol at waterval onder south africa as well as the lack of understanding of diagnostic petrographic features related to fe translocation preserved in the precambrian paleosols petrographic features related to fe translocations include redox related fe depletions and enrichments and possibly fe mn nodules which compare favorably with similar pedogenic features in paleozoic paleo vertisols and modern analog vertisols additionally preservation of sepic plasmic microfabrics in the hekpoort paleosol which are characteristic of clay soils experiencing shrink swell supports previous paleo vertisol interpretations total fe losses in vertisols are 10 50 losses increase with increasing soil age and with increasing mean ann

3 d modelling of plate interfaces and numerical simulation of long term crustal deformation in and around japan we developed a 3 d simulation model for long term crustal deformation due to steady plate subduction in and around japan by incorporating viscoelastic slip response functions into a realistic 3 d plate interface model constructed on the basis of the topography of ocean floors and hypocenter distributions of earthquakes the lithosphere asthenosphere system is modelled by an elastic surface layer overlying a maxwellian viscoelastic half space kinematic interaction at plate interfaces is rationally represented by the increase of tangential displacement discontinuity fault slip across the interfaces with this model giving the steady slip rates at plate interfaces calculated from nuvel 1a we simulated long term crustal deformation due to steady plate subduction in and around japan the simulated crustal deformation pattern is characterized by steep uplift at island arcs sharp subsidence at ocean trenches and gentle uplift at outer rises the numerical results show the strong dependence of the deformation pattern on the 3 d geometry of plate interfaces

synchronous changes in the seismicity rate and ocean bottom hydrostatic pressures along the nankai trough a possible slow slip event detected by the dense oceanfloor network system for earthquakes and tsunamis donet abstract we detected long term hydrostatic pressure changes at ocean bottom stations of the dense oceanfloor network system for earthquakes and tsunamis donet along the nankai trough off southwestern japan we detected these changes after removing the contributions of ocean mass variations and sensor drift from the records in addition we detected a decrease in the background seismicity rate of a nearby earthquake cluster that was synchronous with the hydrostatic pressure changes we interpreted these observed hydrostatic pressure changes to reflect vertical deformation of the ocean floor of 3 8 cm and we consider the cause of the seafloor crustal deformation to be a slow slip event sse beneath the stations because the pressure changes were observed at stations with distances less than 20 km to each other we inferred that the sse occurred in the shallow part of the sedimentary wedge such as on a splay fault system the synchronous observation of an sse and a seismicity rate change suggests that both were triggered by a change in the regional stress that may be associated with stress accumulation and release processes occurring along the nankai trough these data show that continuous and careful monitoring of crustal activities by donet stations provides an effective way to detect seismic and geodetic signals related to the occurrence of megathrust or other types of large earthquakes

reappraisal of a 2200 ma old paleosol near waterval onder south africa abstract a fossil soil paleosol about 2200 ma old in a deep roadcut between the towns of waterval boven and waterval onder transvaal here called the waterval onder clay paleosol was formerly reported to have formed on the hekpoort basalt it is here thought to have developed on a thick formerly at least 5 5 m upward fining and thinning sequence of sandstone siltstone and shale derived from pre existing soils on hekpoort basalt within the basal portion of the fluvial dwaal heuvel formation in contrast to paleosols developed on hekpoort basalt the waterval onder clay paleosol is little deformed lacks corestones and shows compositional variation and berthierine rich laminae interpreted as relict bedding the paleosol has a ridge and swale topography linear or wavy gilgai and a subsurface structure mukkara typical of modern vertisols since there is considerable relict bedding it probably formed over a short period of time less than 7000 years and was not self plowing to the extent seen in modern vertisols clastic dikes filled with sandstone from the overlying rocks are evidence that the profile was periodically dry to depths of at least 2 m more drab colored rocks below that may represent the level of permanent water table iron and manganese stain of layers and claystone granules within the surface horizon of the profile have some characteristics of modern rock varnish and could be taken as evidence for life in the soil the high ratio of ferric to ferrous iron near the surface of the paleosol together with evidence from clastic dikes that this horizon was not waterlogged is an indication of an oxidizing atmosphere although probably one in which oxygen was much less abundant than it is today the very low amounts of acid titratable bases in the shaly parent material of this paleosol and surficial loss of these bases within the paleosol appear to have been produced by decarbonation reactions comparable to those found today in soils of vascular land plants a likely source of weathering acid during the precambrian is an elevated abundance of atmospheric carbon dioxide considering these likely atmospheric differences together with the distribution of comparable modern vertisols and other geological evidence the climate under which this soil formed was probably semiarid to subhumid seasonally dry and temperate

paleomagnetic results from the upper permian of the eastern qiangtang terrane of tibet and their tectonic implications abstract paleomagnetic samples were collected from red intercalations within the upper permian tuoba formation from the eastern qiangtang terrane of tibet progressive thermal demagnetization has revealed a prefolding possibly primary characteristic remanent magnetization chrm which yields a tilt corrected mean direction ofd i 25 2 6 7 95 8 6 the equatorial paleolatitude for the qiangtang terrane indicated by this result and the similarity of late permian fauna and flora shared by the qiangtang terrane and south china block scb suggest that the two terranes were in close proximity during the late permian a late permian paleogeographic reconstruction involving the major terranes of the present day east asia is constructed in which the songpan garze sea is surrounded by laurasia the north china block ncb the scb and the qiangtang terrane the permian development of the songpan garze sea appears to be related to the rifting of the qiangtang terrane off the scb its triassic evolution may resemble that of the solomon sea today in the southwestern pacific

stratigraphic units overlying the zambales ophiolite complex zoc in luzon philippines tectonostratigraphic significance and regional implications abstract the zambales ophiolite complex zoc on the island of luzon philippines is one of the most well studied crust mantle sequences in the region several massifs comprise the zoc one of which is the coto block overlain by clastic sedimentary units previously dated as eocene geochronologic studies from diabase granodiorites and other late stage magmatic products similarly yielded the same age succeeding tectonic models have therefore all been grounded on the assumption that the entire zoc is eocene recent investigations however revealed the presence of chert blocks within the early to middle miocene clastic formation overlying the acoje block in the northern part of the ophiolite complex radiolarians extracted from the cherts yielded a stratigraphic range that suggests a late jurassic to early cretaceous age the recognition of a much older age than previously reported of the zoc warrants a re examination of its actual distribution and genesis correlating with other similarly aged ophiolites we suggest defining a western mesozoic ophiolite belt largely extending from the west central portion of the archipelago to the northeastern tip of luzon island tentatively we attribute the mesozoic ophiolitic and associated rocks in western luzon to an arc continent collision involving the philippine mobile belt and the palawan microcontinental block in addition differences in the clastic compositions of the cenozoic sedimentary formations provide material not only for deciphering the zoc s unroofing history but also for constraining the timing of province linkage the intermittent appearance of lithic fragments and detrital minerals from the ophiolite in the units of the middle miocene candelaria limestone and the late miocene to early pliocene sta cruz formation indicates significant but geographically variable contributions from the ophiolite complex in the northern zambales range the sta cruz formation caps the coto block and the acoje block of the zoc providing a minimum age for their amalgamation

kilometre scale sheath fold at mattmark and implications for transport direction in the alps folds were the first tectonic features of rocks to be studied and as such are taken as a reference for the interpretation of other structures intuitively fold axes were assumed to be subperpendicular to the direction of transport nevertheless many studies of metamorphic belts showing intense ductile deformation describe folds with axes close to the transport direction in particular sheath folds1 9 are highly curvilinear folds elongated parallel to the direction of transport we discuss here a spectacular large sheath fold situated in a crustal shear zone in the monte rosa nappe swiss alps our analysis implies that both the geometry and significance of folds in the internal alps must be re examined we further demonstrate the existence of crustal ductile shear zones in an area of the alps where previously emphasis was generally placed on fold nappes the movements on these shear zones is often tens of kilometres

shortening of recurrence interval of boso slow slip events in japan a slow slip event occurred off the coast of the boso peninsula japan from approximately 28 december 2013 to 10 january 2014 the estimated aseismic slip expanded slightly southward and westward over time with a moment magnitude of 6 5 which was the smallest value since 1996 the recurrence interval has decreased from approximately 6 4 to 2 2 years from 1996 to 2014 one explanation of this shortening is the change in coulomb failure stress due to the 2011 mw9 0 tohoku earthquake and its afterslip another interpretation is related to a scenario observed in several numerical simulation studies in which the recurrence interval of slow slip becomes shorter as the time nears a large earthquake this case will constrain the physical processes of a slip cycle the boso slow slip events together with the tohoku earthquake and its afterslip changed the stress state for the anticipated interplate earthquake near the sagami trough

quantitative paleoenvironmental and paleoclimatic reconstruction using paleosols abstract paleosols fossil soils are preserved throughout the geologic record in depositional settings ranging from alluvial systems to between basalt flows until recently paleosols were studied using primarily qualitative methods in recent years paleopedology has shifted from a largely qualitative field based on comparisons with modern analogues to an increasingly quantitative endeavor some of this change has been a result of applying existing techniques to new materials but many of the innovations have been the result of applying new techniques to new materials including thermodynamic modeling of soil formation isotope geochemistry and applications of empirical relationships derived from modern soils a variety of semi quantitative and quantitative tools has been developed to examine past weathering and pedogenesis and to reconstruct both paleoenvironmental and paleoclimatic conditions at the time that the paleosols formed though it is often not possible to achieve the same temporal resolution as with marine records for paleoclimatic reconstructions proxies based on paleosols are potentially a much more direct means of making paleoclimatic reconstructions because soils form at the earth s surface in direct contact with the atmospheric and climatic conditions at the time of their formation paleoclimatic and environmental properties that may be reconstructed using the new proxies include provenance weathering intensity mean annual precipitation and temperature during pedogenesis nutrient fluxes into and out of the paleosols the atmospheric composition of important gases including co2 and o2 the moisture balance during pedogenesis the soil gas composition reconstructed vegetative covering and paleo altitude

zircon u pb ages hf isotope data and tectonic implications of early middle triassic granitoids in the ailaoshan high grade metamorphic belt of southeast tibet the ailaoshan tectonic belt where the effects of the paleo tethyan ocean evolution and indian eurasian plate collision are superimposed is one of the most significant geological discontinuities in western yunnan province of southeast tibet an ailaoshan micro block within the belt is bounded by the ailaoshan suture zone to the west and the red river fault to the east and consists of low and high grade metamorphic belts late permian middle triassic granitoids that are widely distributed to the west of the ailaoshan suture zone and within the ailaoshan micro block may yield significant information on the tethyan tectonic evolution of the ailaoshan tectonic belt this study reports new la icp ms zircon u pb geochronology and hf isotope data of four granitoids from the ailaoshan high grade metamorphic belt zircon grains from the yinjie granitoid do not have inherited cores and yield a weighted mean u pb age of 247 1 2 0 ma the zircon e hf t values range from 7 8 to 12 1 and hf model ages from 775 to 546 ma indicating that the granitoid was derived from juvenile crust the rims of zircons from the majie and yuanjiang granitoids yield weighted mean u pb ages of 239 5 1 8 and 237 9 2 6 ma respectively whereas the cores yield ages of 1608 352 ma the e hf t values of zircon rims range from 20 4 to 5 3 yielding hf model ages from 2557 to 1606 ma and suggesting that the source magma of the majie and yuanjiang granitoids was derived from ancient crust an additional granitoid located near the majie village yields a zircon u pb age of 241 2 1 0 ma based on our geochronological and geochemical data combined with geological observations we propose that the ailaoshan micro block was derived from the western margin of the yangtze block and is comparable to the zhongzan and nam co micro blocks the presence of late permian mafic rocks with rift related geochemical characteristics within the ailaoshan micro block together with granitoids derived from partial melting of ancient juvenile crust indicates the presence of an ailaoshan rift this possible rift may correspond to the ganzi litang ocean to the northwest and the jinping song da rift to the southeast it is suggested that westward subduction of the jinshajiang ailaoshan song ma oceanic lithosphere triggered the separation of the zhongzan ailaoshan and nam co micro blocks from the western passive continental margin of the yangtze block through the opening of the ganzi litang ailaoshan jinping song da ocean rift this ocean rift may represent a subsidiary branch of the paleo tethyan ocean along the western margin of the yangtze block

pennsylvanian deposystems and paleoclimates of the appalachians abstract central appalachian basin rocks indicate major changes in source areas base level and climate for late mississipian through late pennsylvanian time through time dominant source areas change from craton and northeastern orogen to southeastern orogenic mountains the mississipian pennsylvanian uncomformity correlates with a worldwide eustatic event early pennsylvanian rocks contrast markedly with underlying mississippian mauch chunk redbeds in composition and texture yet the source areas and alluvial plain setting were similar seas transgressed northeastward during middle and earliest late pennsylvanian time along axes of the pocahontas and dunkard basins while fluvial dominant deltas prograded northwestward this progradation 1 progressively extended the coastal plain 2 provided coastal swamp environments for peat accumulation and 3 eventually cut off the narrow seaway of dunkard basin from the central interior by late pennsylvanian and transformed it into a large shallow freshwater lake redbeds calcium carbonate concretions and gilgai paleosol structures of late mississippian and late pennsylvanian rocks suggest seasonally dry tropical climate whereas the lithologies of the earlier pennsylvanian rocks are indications of everwet tropical climates with their quartz rich fluvial sandstones high quality coals and aluminum rich clay deposits streams change from predominantly bedload to suspended load generally from early to late pennsylvanian in response to changes in paleoslope gradient distance from source area unvegetated highland and change from everwet to intermittently dry tropical climate greater dryness is suggested for increased alkaline conditions observed in paleosols carbonates and coal beds of late pennsylvanian time but sufficiently wet to prevent evaporite deposition

closure of the east paleotethyan ocean and amalgamation of the eastern cimmerian and southeast asia continental fragments abstract the phanerozoic record of southeast asia preserves the history of opening and subsequent consumption of the paleotethyan ocean and the assembly of continental fragments into asia as part of the broader scale reconstruction of pangea however uncertainty remains as to which of the many suture zones in southeast asia represents the relict of the main ocean when final ocean closure occurred and the assembly history of the eastern cimmerian and southeast asia continental fragments our overview of the geological features of the suture zones the bounding continental fragments and their magmatic metamorphic and sedimentary records resolves many of these key issues the sedimentary biogeographical structural lithological geochemical and geochronological data from the changning menglian inthanon and bentong raub suture zones argue for their linkage with the longmu co shuanghu suture zone in central tibet and together constitute the main east paleotethyan ocean relict the eastward subduction of the ocean resulted in the development of a series of magmatic arc back arc basin and continental fragments in southeast asia including from west to east the lincang sukhothai east malaya arc the jinghong nan sa kaeo back arc basin the simao west indochina fragment the luang prabang loei back arc basin the south indochina fragment the wusu and truong son back arc basins the north indochina fragment the jinshajiang ailaoshan song ma branch back arc basin and the south china block assembly of these fragments resulted in indosinian high temperature and high pressure metamorphism and related tectonothermal event available data indicate a switch from subduction of the main east paleotethyan ocean to the collision of the sibumasu with simao indochina blocks at 237 ma with subsequent syn and post collisional events at 237 230 ma and 230 200 ma respectively along the changning menglian inthanon and bentong raub suture zones the timing of initial syn and post collision events along the jinshajiang ailaoshan song ma suture zone with its record of back arc basin closure is at 247 ma 247 237 ma and 237 200 ma generally 10 ma older than that along the changning menglian inthanon and bentong raub suture zones our synthesis of all available data enables establishment of a comprehensive geodynamic model for the east paleotethyan evolution this model links the spatial temporal pattern across southeast asia into a series of tectonic events including ocean back arc basin opening subduction closure subsequent assemblage and orogenic collapse along with associated igneous metamorphic and sedimentary activities

palaeoclimatic and site specific conditions in the early permian fossil forest of chemnitz sedimentological geochemical and palaeobotanical evidence abstract as significant indicators of deep time palaeoclimate a number of new palaeontological pedological and geochemical characteristics are provided for the chemnitz fossil lagerstatte to depict more precisely its environmental conditions for the first time several lines of evidence indicate that this fossil forest instantaneously preserved by volcanic deposits once received an annual precipitation of around 800 1100 mm but grew on a nearly unweathered palaeosol although the composition of this rich and diverse t0 assemblage suggests a hygrophilous dense and multi aged vegetation dominated by conservative lineages the habitat was affected by environmental disturbances and pronounced seasonality repeated changes in local moisture availability are suggested by geochemical proxies the co occurrence to intergrowth of calcic and ferric glaebules in the palaeosol and developmental traits of perennial vegetational elements specific substrate adaptation is reflected by different root systems and cyclic growth interruptions recorded in the stems branches and roots of long lived woody plants many differentially adapted terrestrial animals complete the more comprehensive reconstruction of a late sakmarian ecosystem and its climatic and preservational controls albeit spatially confined this diverse in situ record may contribute to understand wetland dryland dynamics of sub tropical northern hemisphere pangaea

neoproterozoic active margin of the sw south china block constraints from upb ages srnd isotopes and geochemical data for the gabbro and granodiorite along the ailaoshan tectonic belt abstract the yangtze block plays a crucial role in the revelation of the precambrian geology of the south china block scb a series of neoproterozoic igneous rocks have been reported along the north west and east yangtze block over the past two decades in this study gabbros and granodiorites in the south yangtze block are investigated with the aim of constraining the timing and tectonic background of the scb during the neoproterozoic representative samples for the gabbro and granodiorite yielded similar zircon u pb ages of ca 780 ma the gabbros have low nb u ratios nb ta and light rare earth element lree content and have end t values of 2 10 to 6 15 the granodiorites exhibit enrichments in th u zr hf and lree depletions in high field strength elements hfses e g nb ta and eu and end t values of 3 01 to 11 85 petrogenetic analysis of the gabbros suggests that two different mantle sources i e e morb and n morb existed in the region and the granodiorites originated from partial melting of lower continental crust with the input of mantle materials our data combined with the available geological observations show that the gabbros and granodiorites in the ailaoshan tectonic belt were generated in an active continental margin the scb was an isolated continent and continuous oceanic crust subduction occurred around it during the neoproterozoic ca 876 706 ma

tethys tectonic evolution and its bearing on the distribution of important mineral deposits in the sanjiang region sw china abstract the sanjiang region in se tibet plateau and nw yunnan is known to have formed by amalgamation of gondwana derived continental blocks and arc terranes as a result of oceanic subduction followed by continental collision from paleozoic to mesozoic in this paper we provide a synthesis of tectonic evolution magmatism and metallogeny in the region based on data from literatures early paleozoic ophiolites 473 439 ma in the changning menglian belt indicate the existence of a proto tethys ocean in this region two episodes of subduction related magmatism in the early paleozoic one occurred in the baoshan and tengchong blocks at 502 455 ma and the other occurred in the simao block at 421 401 ma are regarded as evidence for two different events of subduction of the proto tethys ocean at different locations the proto tethys was succeeded in early devonian by the paleo tethys which comprised the main ocean and three branches ailaoshan jinshajiang and garze litang the changning menglian main ocean existed from middle devonian to middle triassic the remnants of the oceanic crust are preserved in a few places in the longmu tso shuanghu suture as well as in the changning menglian ophiolite belt the eastward subduction of the main oceanic plate from early permian to early triassic formed a prominent arc terrane stretching 1500 km from yunnan to eastern tibet from the waning stage of subduction to post subduction numerous s type granite plutons with ages varying between 230 and 219 ma such as the lincang batholith in yunnan were emplaced at or close to the suture this event produced several hydrothermal w sn deposits in the region the tectonic evolution and associated magmatism of the jinshajiang and ailaoshan branch oceans are generally comparable to those of the main ocean however the branch oceans were subducted westward instead the garze litang branch ocean also underwent westward subduction from middle devonian to late triassic arc related high sr y porphyry intrusions and associated porphyry skarn cu mo au deposits are common in the jinshajiang ailaoshan region especially in the yidun arc which formed prior to jurassic the vms deposits in the sanjiang region formed in diverse tectonic settings including middle silurian back arc basins carboniferous oceanic islands paleozoic subduction zones and triassic post subduction rifting environments the mesozoic and early cenozoic evolution of the baoshan and tengchong blocks was largely influenced by eastward oceanic subduction of the meso and neo tethys from late permian to middle cretaceous and from late cretaceous to 50 ma respectively abundant early cretaceous granitoids and associated skarn type pb zn and sn fe deposits in the baoshan and tengchong blocks were produced in the background of the shan boundary oceanic slab subduction to the west and the break off of the nujiang bitu oceanic slab to the north the subduction of the neo tethys oceanic plate beneath the tengchong block from late cretaceous to paleogene formed abundant s type granitoids and many skarn type and greisen type sn w deposits granitoids formed at 105 to 81 ma and contemporaneous hydrothermal w mo ag and au deposits which temporally coincided with the subduction of the neo tethys are common in the yidun arc terrane

characteristic silent earthquakes in the eastern part of the boso peninsula central japan 1 analysis of global positioning system gps data shows transient crustal deformation in the boso peninsula central japan for about fifty days from october 2002 the southeastward horizontal displacements detected suggest the occurrence of interplate aseismic slip between the philippine sea plate and the north american plate six years after a similar event in 1996 we estimate an area of aseismic slip with moment magnitude mw 6 6 centered off the boso peninsula adjacent to associated seismic activity slip evolution of the 2002 aeismic slip started on october 4 and migrated from north to south for about ten days followed by gradual subsidence and restarting of slip which lasted until december 2 propagating more southward similarities in focal area and slip process between the 1996 and the 2002 events suggest the boso aseismic slips as characteristic silent earthquakes together with the repetitive occurrence of seismic swarm in a similar region every six to seven years a more tightly coupled southern area that did not release enough energy in the 1996 event may have caused the differences in magnitude central slip area and duration between the 1996 and the 2002 events if the hypothesized recurrence interval for strain accumulation is true based on swarm seismicity

slow slip events and seismic tremor at circum pacific subduction zones 1 it has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements however only recently has a fuller spectrum of strain release processes including normal slow and silent earthquakes or slow slip events and continuous and episodic slip been observed and generated by numerical simulations of the earthquake cycle despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive the concurrence of seismic tremor with slow slip episodes in cascadia and southwestern japan provides insight into the process of slow slip a perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface alternatively evidence is accumulating to support the notion that tremor results from shear failure during slow slip global observations of the location spatial extent magnitude duration slip rate and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation most slow slip events occur just downdip of the seismogenic zone consistent with rate and state dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation at a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault bringing it closer to or farther from earthquake failure respectively this paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide with a focus on circum pacific subduction zones trends in global observations of slow slip events suggest that 1 slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it 2 different frictional properties likely control fast versus slow slip 3 the depth range of slow slip may be related to the thermal properties of the plate interface and 4 the equivalent seismic moment of slow slip events is proportional to their duration mo different from the mo 3 scaling observed for earthquakes

a petrogenetic grid for pelitic schists in the system sio 2 al 2 o 3 feo mgo k 2 o h 2 o a quantitative petrogenetic grid for pelitic schists in the system kfmash that includes the phases garnet chlorite biotite chloritoid cordierite staurolite talc kyanite andalusite sillimanite and pyrophyllite with quartz h2o and muscovite or k feldspar in excess is presented the grid is based on thermodynamic data of berman et al 1985 and berman 1988 for endmember kfash and kmash equilibria and natural fe mg partitioning for the kfmash system calculation of p t slopes and the change in fe fe mg along reactions in the kfmash system were made using the gibbs method in addition the effect on the grid of mno and cao is evaluated quantitatively the resulting grid is consistent with typical buchan and barrovian parageneses at medium to high grades at low grades the grid predicts an extensive stability field for the paragenesis chloritoid biotite which arises because of the unusual facing of the reaction chloritoid biotite quartz h2o garnet chlorite muscovite which proceeds to the right with increasing t in the kfmash system however the reaction proceeds to the left with increasing t in the mnkfash system so the assemblage chloritoid biotite is restricted to bulk compositions with high fe fe mg mn typical metapelites will therefore contain garnet chlorite at low grades rather than chloritoid biotite

geology and geochemistry of the shuanggou ophiolite ailao shan ophiolitic belt yunnan province sw china evidence for a slow spreading oceanic basin origin abstract the early carboniferous shuanggou ophiolite lies in the middle segment of the ailao shan orogenic belt between the south china block to the north and the indochina block to the south the ophiolite consists of meta peridotite gabbro diabase and basalt capped by radiolarian bearing siliceous rocks no layered gabbros or sheeted dikes have been observed the meta peridotite underwent low degrees of partial melting consistent with the low magma budget of this oceanic lithosphere whole rock rare earth element analyses of gabbro indicate a geochemical affinity with normal mid ocean ridge basalts consistent with the crystallization order of plagioclase followed by clinopyroxene recognized in the gabbros the ophiolite is believed to have formed in a small slow spreading oceanic basin collision of the indochina block with the south china block in the late paleozoic was responsible for the closure of the oceanic basin and emplacement of the ophiolite in the ailao shan orogenic belt

paleopedology and paleoclimatic implications of late ordovician vertic paleosols juniata formation southern appalachians abstract claystone paleosols with abundant vertic features occur in upper ordovician ashgillian red beds of the juniata formation in the southern appalachians the beans gap claystone paleosol formed during late ordovician pedogenesis of estuarine and upper tidal flat mud deposits pedogenic processes were dominated by shrinking and swelling of clay in a subtropical to warm temperate paleolatitude 30 35 south paleoclimate characterized by a seasonal moisture deficit dry 4 8 months year large scale pedogenic slickensides are abundant and locally define pseudo anticline structures the predominance of sepic paleosol micro fabrics compares favorably with holocene vertisol micromorphology post pedogenic marine transgression resulted in erosion of the upper parts of paleosols followed by marine bioturbation and introduction of marine fluids changes in whole rock chemistry associated with early marine diagenesis include elevated na2o cao mgo mno and p2o5 in the preserved top of each paleosol reduction of fe3 to fe2 resulted in a decrease in fe2o3 and formation of drab halos around burrows the original smectitic mineralogy was converted to a well ordered 2m1 illite through progressive burial diagenesis

collision tectonics in the cenozoic orogenic zone bordering china india and burma abstract the southeast region of the qinghai tibetan plateau is the region where the indian subcontinent collided with eurasia to form arcuate mountain chains along what is now the border area of china india and burma on the basis of cenozoic deformation metamorphism and magmatic activity we can divide this orogenic zone into three tectonic sections the external medial and internal arcuate belts these in turn are divided into seventeen major nappes delineated in a sw to ne cross section through the orogenic zone the external belt composed of the western nappes contains traces of late mesozoic and cenozoic sutures which have undergone significant disruption due to cenozoic orogenesis and its paleozoic strata show affinities to the gondwanaland facies the medial belt including most notably the nappes of the jinsha river region contains the remains of an ancient ocean very probably the paleo tethys which separated the gondwana and yangzi paleolandmasses in late paleozoic early triassic time the internal belt composed of the eastern nappes consists mainly of flysch from china s largest triassic sedimentary basin and its paleozoic strata belong to the yangzi plate

the permo triassic paleotethys in mainland southeast asia and adjacent parts of china aspects of the geodynamic evolution of mainland southeast asia and china are discussed in consideration of the permo triassic paleotethys problem it is shown that all sutures in thailand vietnam and yunnan already closed during the paleozoic era and that the entire region must be regarded as part of the northern continents the permo triassic paleotethys must be expected south of tibet and in burma

slow and delayed deformation and uplift of the outermost subduction prism following ets and seismogenic slip events beneath nicoya peninsula costa rica abstract two odp cork ocean drilling program circulation obviation retrofit kit borehole hydrologic observatory sites deployed in 2002 at the toe of the subduction prism off nicoya peninsula costa rica were visited in december 2013 the five years of seafloor and formation fluid pressure data collected since the previous visit include clear signals associated with an episodic tremor and slip ets event off the coast of nicoya peninsula in 2009 and a mw 7 6 subduction thrust earthquake beneath the peninsula in 2012 formation pressure anomalies associated with the ets event are similar to ones observed following ets events observed previously here as well as ones following very low frequency earthquake swarms within the nankai accretionary prism off southwestern japan positive and negative impulsive transients in the hanging wall and foot wall of the subduction thrust respectively suggest contractional and dilatational strain generated by local slip propagating up the thrust fault beneath the outermost prism in the case of the 2009 event the transients occurred roughly two weeks after the initiation of slip observed at gps sites along the adjacent coast at the same time a decrease in seafloor pressure at the prism site relative to the subducting plate was observed indicating concurrent uplift of the prism of 1 2 cm other events at the prism toe following ets events closer to the coast are seen in 2006 2007 2008 2010 and 2011 the time between the initiation of ets slip constrained by gps and the onset of the prism toe transients suggest up dip rupture propagation along the seaward part of the subduction thrust at rates of a few km day in the case of the 2009 event the slip at the prism toe c 11 cm estimated from the 1 2 cm uplift and the local dip on the decollement 6 is roughly a factor of 5 greater than the slip further landward estimated from gps data by dixon et al in press in other cases slip at the toe is less or unresolvable similar uplift and formation fluid pressure transients occurred two days after the 2012 nicoya thrust earthquake then episodically unrelated to aftershocks every 1 3 weeks over the next few months slip rates at the prism toe estimated from the magnitude and duration of these and ets related uplift events are roughly 5 cm day such rates are much too slow for tsunamigenesis or seismogenesis total slip of the outermost prism after the 2012 earthquake determined from the uplift accumulated until the end of the observation period and the estimated local fault dip is roughly 75 cm a significant fraction of the seismogenic slip of the mw 7 6 earthquake itself a maximum of over 3 m negative steps in formation pressure are observed at both the prism and subducting plate sites simultaneous with the 2012 thrust earthquake the sign of these steps is inconsistent with the contractional deformation predicted by an elastic fault dislocation model with slip limited to the seismogenic zone highly compliant low shear modulus sediment below the decollement or very low stress deformation along splay faults may be responsible for the co seismic dilatation observed in the outermost prism and incoming plate

temperatures heat flux and frictional stress near major thrust faults we examine the two dimensional advective and conductive transport of heat in a region of thrust faulting both simple theoretical considerations and numerical experiments show that the steady state temperatures near the fault are reduced by a divisor s 1 b z vsin below what they would be with the same heat sources but in the absence of advection in this expression z is the depth to the fault v is the slip rate is the component of the dip of the fault in the direction of underthrusting is thermal diffusivity and b is a dimensionless factor that is essentially equal to one for most forms of heating initial changes in temperatures near the fault are given by t z t t z 0 12vsin t z 0 z these simple formulae are successful because of the neglible influence of lateral conduction of heat at least for slip rates of a few mm yr or more two time constants govern the transition from the initial change in temperature to steady state t1 u v where u is the distance along the fault in the direction of underthrusting from the surface to the depth in question and t2 z 2 2 where z is the depth to the fault when elapsed times exceed the sum of these two time constants temperatures differ from their steady state values by only about 10 percent the numerical experiments indicate that the simple formulae are sufficiently accurate that sophisticiated numerical modeling of temperatures in specific regions is unwarranted putain an application of these simple formulae to measurements of conductive heat flow at island arcs implies that shear stresses at island arcs approach 100 mpa and are greater than 30 mpa calculations of temperatures appropriate for the himalaya suggest that shear stresses of 100 mpa on the main central thrust probably are required to account for the tertiary granites of the region if melting took place after slip began on the thrust similarly the cut off in seismicity at a depth of about 15 km in the himalaya if due to temperatures exceeding 350 to 450 c implies a deviatoric stress close to 100 mpa

vertisol carbonate properties in relation to mean annual precipitation implications for paleoprecipitation estimates abstract previous publications combining the properties of multiple soil orders show that depth to carbonate dtc increases systematically between 350 and 1000 mm of mean annual precipitation map we hypothesize that carbonate in vertisols clay rich shrink swell soils respond differently to water flux than other soil orders because of lower permeability to test this hypothesis we compiled soil description and characterization data from multiple published sources across a late pleistocene climosequence of the coast prairie of texas to assess the relationship between map 700 1400 mm and dtc the dtc of carbonate nodules represents an index of accumulation and the dtc of calcium carbonate equivalent total carbonate 2 0 mm diam an index of leaching the dtc for 1 2 and 5 abundances were assessed using regression analysis the r2 values were highest for the dtc of 2 nodules and of 1 calcium carbonate equivalent in vertisol microlows surprisingly relatively high r2 values were calculated

zircon u pb and hf isotope constraints from the ailao shan red river shear zone on the tectonic and crustal evolution of southwestern china abstract the ailao shan red river asrr shear zone one of the most prominent geologic strike slip shear zones in southeast asia consists of high grade metamorphic complexes that provide a rare opportunity to sample the mid crustal rocks along the western margin of the yangtze block of south china here we report combined in situ analyses of zircon u pb and lu hf isotopes of eight gneisses from the diancang shan and ailao shan segments of the asrr shear zone our zircon u pb data indicate that the rocks contain abundant magmatic zircons ranging in age from 1785 to 25 ma with peak ages at ca 770 350 and 240 ma suggesting three major periods of protolith formation the 350 ma zircons observed only in an orthogneiss from the diancang shan show uniform initial hf isotopic ratios marked by high and positive e hf t values from 16 to 10 this is in contrast with the other two zircon populations that are more common occurring in both the diancang shan and ailao shan and overall delineate very heterogeneous hf isotopic compositions with e hf t values ranging from 15 to 16 many zircons reveal distinctive core rim age variations zircon rims formed between ca 34 and 26 ma show significant variations in th u ratios 5 0 01 and e hf t values 14 to 10 that suggest complicated magmatic and metamorphic zircon overgrowth during the oligocene the presence of both metamorphic and magmatic overgrowths on zircons suggests that the metamorphism reached upper amphibolite facies corresponding to mid crustal level p t conditions as also suggested by structural and petrologic data our data furthermore suggest that the asrr gneisses were not produced solely by shear heating during the tertiary strike slip faulting but are uplifted mid crustal basement rocks that formed essentially during two major stages of magmatism represented by the neoproterozoic kangding complex and late permian emeishan large igneous province as a result of the india asia collision these basement rocks underwent regional magmatic and metamorphic overprinting in the oligocene that based on our relevant work searle et al 2010 geosphere 6 1 23 predated the initial left lateral movement along the asrr shear zone the 350 ma protolith which requires a dominant depleted mantle input in the petrogenesis cannot be linked to any major magmatic events in south china but may be interpreted as part of the paleotethys remnants that were later incorporated into the asrr shear zone

neoproterozoic granitoids from the phan si pan belt northwest vietnam implication for the tectonic linkage between northwest vietnam and the yangtze block abstract several neoproterozoic granitic intrusions including the phin ngan intrusion and some smaller ones from the sin quyen cu mine have been identified in the phan si pan belt northwest vietnam whole rock geochemical and sm nd isotopic data and zircon u pb age and hf o isotopes have been determined for these intrusions in order to constrain their ages petrogenesis and tectonic implications the phin ngan intrusion mainly composed of syenogranite was emplaced at 824 4 ma rocks from this intrusion have high sio 2 72 1 73 5 wt and k 2 o 5 14 5 52 wt with a cnk values ranging from 1 02 to 1 06 they have negative whole rock e nd t 8 4 to 5 2 and zircon e hf t values 8 1 to 5 5 and high zircon 18 o values 9 7 10 9 these geochemical features suggest that the phin ngan intrusion was derived from ancient k rich crustal sources granitic intrusions from the sin quyen mine occur as stocks or dykes intruding ores and ore hosting rocks they are composed of monzogranite and granodiorite emplaced between 736 8 and 758 6 ma they have high sio 2 68 2 76 7 wt and k 2 o na 2 o 6 93 8 54 wt and low mgo 0 19 0 87 with a cnk values ranging from 0 91 to 1 14 their whole rock e nd t values range from 6 6 to 0 mostly clustered between 6 6 and 4 3 their zircon e hf t values vary from 6 7 to 11 1 mostly lower than 2 0 such geochemical data indicate that these intrusions were produced mainly through partial melting of ancient crustal materials coupled with subordinate involvement of mantle juvenile crust derived components the phin ngan intrusion and intrusions from the sin quyen mine are sub alkaline in nature and have arc like trace element compositions compiled with other broadly synchronous igneous rocks with arc like affinities in the region the neoproterozoic magmatism in the phan si pan belt was generated in a subduction related setting the neoproterozoic intrusions in the phan si pan belt are geochronologically and geochemically correlated with the neoproterozoic subduction related igneous rocks along the western yangtze block thus the phan si pan belt represents the southern most part of the giant arc system of the western yangtze block

effective resolution and drift of paroscientific pressure sensors derived from long term seafloor measurements 1 starting with the installation of the noaa tsunami early warning system dart in 1983 the paroscientific digiquarz broadband depth sensor has been deployed for long term ocean bottom pressure measurements in numerous marine investigations the sensor turned out to be very reliable with a good signal repeatability within a broad measuring range and high resolution however up to now its long term drift noise level and effective resolution under in situ conditions at the seafloor are only known from a few published studies and for a few sensors in this study we analyze 118 long term seafloor pressure time series longer than 2 months and up to a maximum time period of 9 years to investigate effective resolution and long term drift under in situ conditions the data are from dart ifm geomar lolem and cork stations the noise level of the data and therefore the mean sensor resolution are lower than an upper threshold of 20 7 pa corresponding to 2 07 mm equivalent water level for stations installed directly on the seafloor the noise level of cork sensors is much larger with a median value of 127 pa long term sensor drift is assumed to be composed of an initial exponential part and a subsequent linear drift in situ mean drift is 0 88 0 73 kpa a determined from all available data with a slight increase of drift with deployment depth for the first time we are able to quantify effective pressure resolution and drift of the widely used paroscientific pressure gauges under in situ conditions our results provide important constrains for the interpretation of seafloor pressure records however in situ self calibration procedures for the paroscientific sensors are still needed in order to benefit from high effective resolution and long term stability and also to increase accuracy especially for the monitoring of geodynamic processes at the seafloor

fluvial sequence stratigraphy the wapiti formation west central alberta canada abstract outcrop exposures and high resolution subcrop data allow the description and mapping of four stratigraphic discontinuities in the fully nonmarine strata of the campanian maastrichtian wapiti formation western interior foreland basin alberta canada this framework defines four unconformity bounded depositional sequences a d based on sequence stratigraphic methodology well log patterns and facies analysis in ascending order sequence a records the transition from the underlying marine facies of the puskwaskau formation into the wapiti fluvial facies and consists of strongly progradational and aggradational stacking patterns sequences b and c show a similar pattern of basal amalgamated channel fill deposits that grade upwards into floodplain dominated strata finally sequence d is dominated by channelized sediments and extensive overbank facies an aggradational stacking pattern suggests deposition under high accommodation conditions maximum flooding surfaces are interpreted within fine grained deposits in the upper portions of sequences c and d they are tied to regionally extensive coals that accumulated more than 250 km away from the coeval shoreline this study provides new evidence that major coal seams may represent the extension of marine maximum flooding surfaces into the downstream controlled fluvial realm furthermore the new stratigraphic framework of subaerial unconformities and maximum flooding surfaces provides the means of subdividing the previously undifferentiated fully nonmarine wapiti formation into depositional sequences and component systems tracts

distinguishing climate in the soil record using chemical trends in a vertisol climosequence from the texas coast prairie and application to interpreting paleozoic paleosols in the appalachian basin u s a a suite of vertisols clay rich soils with high shrink swell potential were examined across a climosequence climatic transect in twelve soil pits from the coast prairie of texas in order to determine if mean annual precipitation map exerts a control on the chemistry of these soils and if the observed chemical trends are useful for interpreting paleoclimate records of paleovertisols in the geologic record the precipitation regime of the climosequence spans a range between 144 and 86 cm year with moisture regimes classified as udic udic ustic ustic and aridic ustic in a general northeast to southwest direction other soil forming factors such as soil age 35 40 ka parent material fluviodeltaic beaumont formation of late pleistocene age landscape low relief coastal plain and vegetation prairie or mixed woody shrubs are relatively constant across the climosequence climate sensitive chemical proxies of map identified include dithionite citrate extractable fe fedith acid oxalate extractable fe feoxal caco3 equivalent caco3equiv s and ammonium acetate extractable na k and mg naacet kacet and mgacet respectively which vary across the climosequence because of differences in effective depths of leaching and intensity of wetting and drying cycles these standard usda wet chemical climate proxies are related to bulk oxide or element chemistry of soils and paleosols measured using xrf which supports the use of geochemical climate proxies for interpreting the paleoclimate records of paleovertisols application of the chemical index of alteration minus potash cia k geochemical climofunction to late mississippian paleosols from the appalachian basin of the eastern u s demonstrates evidence for a shift from a lower to a higher map paleoclimate that is consistent with previous paleoclimate models and with observed morphological changes in the paleosols we advocate actualistic research using bulk chemistry of soils and paleosols as a means of obtaining soil information useful for interpreting paleosols in the geological record

bounds on strain in large tertiary shear zones of se asia from boudinage restoration we have used surface balanced restoration of stretched boudinaged layers to estimate minimum amounts of finite strain in the mylonitic gneisses of the oligo miocene red river ailao shan shear zone yunnan china and of the wang chao shear zone thailand the layer parallel extension values thus obtained range between 250 and 870 we discuss how to use such extension values to place bounds on amounts of finite shear strain in these large crustal shear zones assuming simple shear these values imply minimum total and late shear strains of respectively 33 6 and 7 3 at several sites along the red river ailao shan shear zone for the wang chao shear zone a minimum shear strain of 7 4 is deduced assuming homogeneous shear would imply that minimum strike slip displacements along these two left lateral shear zones which have been interpreted to result from the india asia collision have been of the order of 330 60 km red river ailao shan and 35 20 km wang chao

paleovertisols as indicators of climate abstract clay rich paleosols are common in the rock record in upper delta plain fluvial floodplain marginal lacustrine and playa deposits in environments characterized by a marked seasonality of precipitation these soils are generally vertisols modern vertisols contain over 35 clay predominantly smectite have a distinctive slickensided ped structure and locally develop surface microrelief and carbonate nodules the optimum development of vertisols is in subtropical to tropical monsoonal climates surface microrelief gilgai is common in subhumid and semiarid but not arid climatic regimes carbonate nodules are common in both drab and pigmented vertisols in semiarid climates in the transition to subhumid regimes carbonate nodules are likely to be either absent or restricted to drab vertisols vertisol pigmentation appears to be a function of inherited color or the development of organic complexes and thus only indirectly controlled by climate changing precipitation patterns can cause the production or destruction of evaporites or carbonates in a vertisol profile in contrast the slickensided ped structure has a high preservation potential and is probably modified little during changes in climate and subsequent burial unlike marine and profundal lacustrine clays vertisols have a high bulk density and appear to be affected little by burial compaction syndepositional cementation in the form of veins and nodules of low mg calcite i e calcrete is common however major changes in the clay mineralogy of these paleosols may occur during diagenesis including the transformation of smectite into mixed layer clays illite or kaolinite end of article last page 239

triassic tectonics of the ailaoshan belt sw china early triassic collision between the south china and indochina blocks and middle triassic intracontinental shearing in se yunnan the ailaoshan belt has been extensively studied for the ductile shearing coeval with the left lateral cenozoic activity of the red river fault however the late triassic unconformity of the continental red beds upon metamorphic and ductilely deformed rocks demonstrates that the ailaoshan belt was already built up by early mesozoic tectonics from west to east the belt is subdivided into western central eastern ailaoshan and jinping zones the western ailaoshan and central ailaoshan zones correspond to a carboniferous permian magmatic arc and an ophiolitic melange respectively the eastern ailaoshan and the jinping zones consist of deformed proterozoic basement and paleozoic to early triassic sedimentary cover series both belonging to the south china block this litho tectonic zonation indicates that the ailaoshan belt developed through a sw directed subduction followed by the collision between indochina and south china blocks crustal thickening triggered per aluminous magmatism dated at ca 247 240 ma field and microscope scale top to the ne ductile shearing observed only in the pre late triassic formations but never in late triassic or younger formations complies with this geodynamic polarity furthermore the late collisional two mica granitoids and felsic per aluminous volcanites record a ductile deformation that argues for a continuing crustal shearing deformation after the early triassic collision up to the middle triassic therefore a two stage tectonic evolution accounts well for the documented structural and magmatic features the triassic architecture of the ailaoshan belt and its geodynamic evolution correlate well to the south and north with the north vietnam orogens and the jinshajiang belt respectively

geodetic data inversion using a bayesian information criterion for spatial distribution of fault slip summary we developed a new inversion method to reconstruct static images of seismic sources from geodetic data using akaike s bayesian information criterion abic coseismic surface displacements are generally related with a slip distribution on a fault surface by linear integral equations parametric expansion of the fault slip distribution by a finite number of known basis functions yields a set of observation equations expressed in a simple vector form incorporating prior constraints on the smoothness of slip distribution with the observation equations we construct a bayesian model with unknown hyperparameters the optimal values of the hyperparameters which control the structure of the bayesian model are objectively determined from observed data by using abic once the values of hyperparameters are determined we can use the maximum likelihood method to find the optimal distribution of fault slip we examined the validity of this method through a numerical experiment using theoretical data with random noise we analysed geodetic data associated with the 1946 nankaido earthquake ms 8 2 by using this method the result shows that the fault slip distribution of this earthquake has two main peaks of 4 and 6 m located off kii peninsula and muroto promontory these two high slip areas are clearly separated by a low slip zone extending along kii strait such a slip distribution corresponds with the fact that the rupture process of this earthquake in the western part is notably different from that in the eastern part

episodic slow slip events in the japan subduction zone before the 2011 tohoku oki earthquake abstract we describe two transient slow slip events that occurred before the 2011 tohoku oki earthquake the first transient crustal deformation which occurred over a period of a week in november 2008 was recorded simultaneously using ocean bottom pressure gauges and an on shore volumetric strainmeter this deformation has been interpreted as being an m6 8 episodic slow slip event the second had a duration exceeding 1 month and was observed in february 2011 just before the 2011 tohoku oki earthquake the moment magnitude of this event reached 7 0 the two events preceded interplate earthquakes of magnitudes m6 1 december 2008 and m7 3 march 9 2011 respectively the latter is the largest foreshock of the 2011 tohoku oki earthquake our findings indicate that these slow slip events induced increases in shear stress which in turn triggered the interplate earthquakes the slow slip event source area on the fault is also located within the downdip portion of the huge coseismic slip area of the 2011 earthquake this demonstrates episodic slow slip and seismic behavior occurring on the same portions of the megathrust fault suggesting that the faults undergo slip in slow slip events can also rupture seismically

the central ailaoshan ophiolite and modern analogs abstract the central ailaoshan cal ophiolite represents an important tectonic component of the jinshajiang ailaoshan song ma suture zone separating the south china and indochina blocks in the mainland se asia the cal ophiolite occurs as a complex tectonic melange and preserves the history of the opening and closure of the once vast jinshajiang ailaoshan song ma branch of the paleotethys new and existing geological data indicate that the cal ophiolite contains magmatic rocks generated by 1 l devonian e carboniferous ca 380 330 ma volcanic passive margin breakup development in the nw gondwana margin 2 l permian ca 258 ma emeishan large igneous province related continental rift magmatism together with and intruded by 3 earliest m triassic ca 244 ma continent continent syn collisional s type granitoids the devono carboniferous suites of the cal ophiolite are highly comparable with many continental margin type alpine tethyan ophiolites in addition the various cal magmatic suites have strong south china block affinities with coeval magmatism particularly in the western south china block jinshajiang song ma and song da terranes

an integrated perspective of the continuum between earthquakes and slow slip phenomena slow slip a mechanism by which faults can relieve stress was thought to be distinct from earthquakes however a global review of slow slip phenomena suggests that instead there is a continuum between the two types of event