episodic growth of the kodiak convergent margin convergent plate boundaries have long been recognized as zones where deep sea sediments become accreted to plate margins causing the margin to grow with time1 however our understanding of the evolution of these margins is limited because accreted rocks are often too poorly exposed to unravel the complex history theyrecord recent results from field deep sea drilling and high resolution seismic reflection studies indicate that various processes can occur in time along a specific margin2 for example both the middle america and japan trenches are believed to record a history of strike slip faulting and or tectonic erosion before the periods of subduction accretion which presently characterize these margins3 4 here we propose that growth of the kodiak continental margin in south west alaska one of the largest accretionary prisms in the world has been dominated by two relatively short episodes of accretion the first in the late cretaceous and the second in the early eocene these two periods of growth appear to account for 70 of the margin growth during the past 75 100 myr

deformation paths in the shallow levels of an accretionary prism the eocene shimanto belt of southwest japan detailed structural analysis of coherent turbidites in a part of the eocene shimanto belt on the muroto peninsula shikoku island japan reveals a structural evolution that is typical of the shallow levels of accretionary prisms in style and sequence of deformational fabrics but anomalous in that it includes both a marked rotation in shortening direction and a major out of sequence thrust deformation throughout a history of progressive lithification and burial was dominated by subhorizontal shortening and seaward vergent shear structures evolved from predominantly mesoscale thrusts and folds to larger more brittle faults and finally to kilometer scale amplified fault bend folds with an associated pressure solution cleavage this structural progression is consistent with increasing strength of the rocks decreasing fluid pressures and increasing temperature and pressure as the sediments were dewatered lithified and accreted to the prism in contrast to this straightforward structural evolution the prism scale deformation of the eocene shimanto belt is difficult to reconcile with simple models of prism developmentthat assume orthogonal subduction and seaward stepping imbrication a 50 counterclockwise rotation in the shortening direction and a major out of sequence or intraprism thrust are recorded by two distinct structural domains in both the earliest structures are clastic dikes and faults indicative of north south shortening one domain is characterized by east striking regional scale folds and cleavage that are transected by an east northeast trending cleavage however the other is characterized by northeast striking folds and cleavage that are transected by a slightly more north striking cleavage the different deformation histories of the two do mains require that they be separated by a major intraprism fault this fault carries tectonic melange containing blocks of pillow basalt and chert indicating that it rooted in the decollement zone beneath the prism the tectonostratigraphy and deformation histories of the two domains suggest that both before and after the out of sequence fault developed higher structural levels of the prism experienced significant subhorizontal shortening whereas lower structural levels bypassed this zone of deformation

late eocene and maastrichtian paleomagnetic poles for the pacific plate implications for the validity of seamount paleomagnetic data abstract mean paleomagnetic poles for the pacific plate have been calculated for the late eocene 39 ma and the maastrichtian 69 ma the former is located at 77 6 n 7 6 e the latter at 69 9 n 0 9 e although these pole positions are little changed from previous calculations they are better constrained with additional data slightly less than half of the data are derived from the inversion of seamount magnetic fields providing an excellent opportunity to compare such data with other paleomagnetic data of the same age as no significant systematic difference between the two types of data is evident it is inferred that most seamount paleomagnetic data are probably useful indicators of the paleomagnetic field direction

stable isotopes reveal human influences on southern new zealand soils abstract a multi isotopic soil study across a southern new zealand transect has been undertaken as part of a geochemical baseline survey to identify human impacts on new zealand s landscape and characterise different land uses and anthropogenic effects carbon nitrogen and sulphur isotopes from two soil depths 0 30 and 50 70 cm were acquired across a variety of land uses including pristine national parks urban centres intensively farmed pastoral land climates dry 6000 mm annual rainfall altitude sea level to 2300 m above sea level and soil parent material lithology sandstone schist basalt detrital organic matter accumulated more in lowlands than at higher altitudes with higher carbon and nitrogen contents found in river valleys carbon isotopes clearly differentiated between drier higher altitude or open pastoral sites more positive values and wetter forested sites more negative values nitrogen isotopes reflect anthropogenic human influence with elevated values around urban and intensively farmed sites and lower values characterising indigenous forests and pristine sites sulphur isotopes either show more positive values typical of fertilisers rain or sea spray in open pastoral sites or more negative values consistent with weathered geological sources such as metamorphic sulphides found in schist in some river valley sites the study demonstrates that regional isotope studies are a potential tool to understand the long and short term impacts on landscapes and may be useful for future mineral exploration urban health studies agricultural site remediation and land use control and regulation

carbon delivery to deep mineral horizons in hawaiian rain forest soils 1 this study aimed to better understand the mechanisms for soil organic matter delivery to and accumulation in mineral horizons of tropical rain forest volcanic soils we used soil morphology lysimetry isotopes and spectroscopy to investigate the role of preferential flow paths in the delivery of carbon c to the subsoil high rainfall high primary productivity and the dominance of highly reactive short range order minerals combine to sequester substantial stocks of soil c with long mean residence times the soils have large peds separated by wide cracks which form a network of channels propagating downward through the top 40 to 60 cm facilitating macropore flow the channel infillings and crack surfaces were enriched in organic material om with lower c n ratios and had higher ammonium oxalate extractable al and lower ammonium oxalate extractable fe than the adjacent mineral bulk soil cp mas 13c nmr spectra of om accumulating at depth showed strong signal intensities in the carboxyl and carbonyl c regions indicative of organic acids while decaying roots showed greater contributions of aromatic and o alkyl c the ratios of alkyl to o alkyl c in the organic infillings were more similar to those of the bulk bh and to dissolved organic matter than to those of decaying roots radiocarbon based ages of om infillings at 50 cm depth were significantly younger than the mineral soil 2000 years versus 7000 years respired co2 from incubated soils showed that om accumulating at depth is a mixture of modern and much older c providing further evidence for the downward movement of fresh c

paleogene evolution of the kodiak islands alaska consequences of ridge trench interaction in a more southerly latitude the kodiak islands of alaska are principally composed of a late cretaceous and paleogene complex of accreted deep sea rocks an early paleocene magmatic event invaded the accretionary complex with mid ocean ridge basalt morb andesite and granodiorite geochemical evidence suggests both the andesite and granodiorite are mixtures of morb and sediment the volcanic rocks are interlayered with coarse clastic sediments and deformed with the latter the granodioritic intrusions with k ar ages as old as 62 ma postdate emplacement of the early paleocene sedimentary and volcanic rocks interaction of the subduction complex with the kula farallon ridge most simply explains this early paleocene magmatic episode paleomagnetic studies of the volcanic rocks indicate this interaction occurred at 40 3 6 north latitude which is 25 3 9 south of the expected position of the kodiak islands relative to north america the magmatic arc presently northwest of the kodiak accretionary complex was active during the late cretaceous and early paleocene diminished after the ridge trench interaction and resurged from late eocene into miocene time the magmatic resurgence is coeval with the obductive offscraping of eocene to oligocene submarine fan deposits in the kodiak islands the petrology of these fan deposits indicates they are the most likely proximal equivalent for the zodiac fan thereby limiting its relative motion with respect to the kodiak islands possible models accounting for the northward motion of the kodiak accretionary complex include 1 coupling the accretionary complex and possibly related arc to the northward moving kula plate and closing an ocean basin north of the arc in paleogene time 2 emplacing the kodiak accretionary complex at the northward limit of the paleomagnetic data with subsequent northward motion accomplished by closure of a small back arc basin and or intracontinental shortening and 3 transcurrent faulting and northward motion of the kodiak accretionary complex without the presently adjacent arc

paleothermal structure of the point san luis slab of central california effects of late cretaceous underplating out of sequence thrusting and late cenozoic dextral offset late cretaceous shale and sandstone turbidites of the point san luis slab are isoclinally folded locally sheared and faulted but their severity of stratal disruption is relatively mild when compared to adjacent polymictic melange of the franciscan complex we tested the interpretation of a trench slope basin origin for these strata by documenting their paleothermal structure including contacts between turbidites and melange values of mean random vitrinite reflectance rm from turbidites are 0 9 1 7 estimates of maximum paleotemperature are 135 200 c melange matrix samples yield rm values of 1 1 2 5 with an average of 1 5 and peak temperatures between 160 and 240 c the turbidite over melange contact is locally cooler over warmer and was folded after peak heating the relatively high paleotemperatures cast doubt on a shallow slope basin model i e 1 2 km burial depth we suggest instead that thermal maturation of the point san luis slab occurred much deeper in an accretionary prism 10 15 km where offscraped trench wedge deposits were faulted against underplated melange the paleothermal structure was offset and tilted after peak heating by two out of sequence faults late oligocene to pliocene strata rest unconformably above the franciscan and there is a significant gap in thermal maturity across this unconformity with no evidence to show that franciscan rocks were reset thermally following the main episode of uplift and erosion three dimensional orientations of isoreflectance surfaces on opposite sides of the san gregorio san simeon hosgri fault system also can be used to test interpretations of strike slip neotectonics the failure to match these geometries among suspected piercing points at point san luis cambria and point sur favors a suggestion that differential post thermal peak dextral offset of franciscan basement has not exceeded 10 15 km

turnover and storage of c and n in five density fractions from california annual grassland surface soils 1 we measured 14c 12c in density fractions from soils collected before and after atmospheric thermonuclear weapons testing to examine soil organic matter som dynamics along a 3 million year california soil chronosequence the mineral free particulate organic matter fpom 2 2 g cm 3 consists of relatively om free sand and om rich clays three indicators of decomposition c n 13c and 15n all suggest increasing som decomposition with increasing fraction density the 14c derived som turnover rates suggest that 90 of fpom turns over in 10 years the four mineral associated fractions contain 69 86 stabilized decadal som with the remainder assumed to be passive millenial som within each soil the four mineral associated fractions display approximately the same residence time 34 42 years in 200 kyr soil 29 37 years in 600 kyr soil and 18 26 years in 1 3 myr soils indicating that a single stabilized som pool exists in these soils and may turn over primarily as a result of soil disruption

effects of internal structure and local stresses on fracture propagation deflection and arrest in fault zones the way that faults transport crustal fluids is important in many fields of earth sciences such as petroleum geology geothermal research volcanology seismology and hydrogeology for understanding the permeability evolution and maintenance in a fault zone its internal structure and associated local stresses and mechanical properties must be known this follows because the permeability is primarily related to fracture propagation and their linking up into interconnected clusters in the fault zone here we show that a fault zone can be regarded as an elastic inclusion with mechanical properties that differ from those of the host rock as a consequence the fault zone modifies the associated regional stress field and develops its own local stress field which normally differs significantly both as regard magnitude and orientation of the principal stresses from the regional field the local stress field together with fault rock heterogeneities and interfaces discontinuities fractures contacts determine fracture propagation deflection along discontinuities interfaces and arrest in the fault zone and thereby its permeability development we provide new data on the internal structure of fault zones in particular the fracture frequency in the damage zone as a function of distance from the fault core new numerical models show that the local stress field inside a fault zone modelled as an inclusion differ significantly from those of the host rock both as regards the magnitude and the directions of the principal stresses also when the mechanical layering of the damage zone due to variation in its fracture frequency is considered the numerical models show abrupt changes in local stresses not only between the core and the damage zone but also within the damage zone itself abrupt changes in local stresses within the fault zone generate barriers to fracture propagation and contribute to fracture deflection and or arrest also analytical solutions of the effects of material toughness the critical energy release rate of layers and their interfaces show that propagating fractures commonly become deflected into and often arrested at the interfaces generally fractures propagating from a compliant soft layer towards a stiffer one tend to become deflected and arrested at the contact between the layers whereas fractures propagating from a stiff layer towards a softer one tend to penetrate the contact thus it is normally easier for fractures to propagate from the host rock into the damage zone than vice versa similarly it is easier for fractures to propagate from the outer stiffer parts of the damage zone to the inner softer parts and from the stiff host rock to the outer damage zone than in the opposite directions these conclusions contribute to increased understanding as to how fractures propagate and become arrested within fault zones and how the fault zone thickness is confined at any particular time during its evolution

modern and ancient seismogenic out of sequence thrusts in the nankai accretionary prism comparison of laboratory derived physical properties and seismic reflection data 1 to investigate characteristics of a seismogenic out ofsequence thrust oost imaged as a strong reflection on seismic profiles in the nankai accretionary prism we determined acoustic properties of discrete samples from an fossil nobeoka oost outcrop under confining pressures and compared the acoustic properties with those of an active oost in the nankai accretionary prism we observed anisotropy of velocity and attenuation in the hanging wall of nobeoka oost attributed to foliation of pelitic phyllite in contrast the footwall is composed of brittlely deformed chaotic shales and fine sandstones and velocities in the footwall are lower than those in the hanging wall amplitude variation with offset avo modeling utilizing contrasts in p and s wave velocities and densities between the hanging wall and footwall of the nobeoka oost indicates that fractures filled with overpressured fluid likely account for angle dependent reflection amplitudes of the active oost in the nankai trough citation tsuji t g kimura s okamoto f kono h mochinaga t saeki and h tokuyama 2006 modern and ancient seismogenic out ofsequence thrusts in the nankai accretionary prism comparison of laboratory derived physical properties and seismic reflection data geophys res lett 33 l18309 doi 10 1029 2006gl027025

closely spaced fractures in layered rocks initiation mechanism and propagation kinematics spacings of opening mode fractures joints and veins in layered sedimentary rocks often scale with the layer thickness field observations reveal that the ratio of fracture spacing to the thickness of the fractured layer s tf ranges from less than 0 1 to greater than 10 there is a critical spacing to layer thickness ratio that defines the condition of fracture saturation and explains the observed spacing ratios between 0 8 and 1 2 values of s tf 1 2 are explained as the results of the fracturing process having not reached the saturation level to explain ratios of s tf 0 8 we study the possibility for further fracture infilling by considering flaw distributions between adjacent fractures loaded by extension of the layer results show that infilling fractures grow more easily from flaws located near the interface than from those in the middle of the fractured layer the propagation of a flaw located in the middle of the fractured layer is unstable but for the flaw to propagate toward the interfaces its height has to be greater than a critical size this critical size decreases with increasing s tf the propagation behavior of a flaw with one of its tips at the interface depends on s tf the propagation is unstable when s tf is greater than a critical value when s tf is less than this critical value the propagation is first unstable then stable and then unstable again an infilling fracture can cut through the fractured layer only if s tf is greater than another critical value otherwise the infilling fracture can only partially cut the fractured layer for models with the same elastic constants for the fractured layer and the neighboring layers this critical value is 0 546 and the minimum spacing to layer thickness ratio of fractures formed by the in filling process under extension is 0 273

kinematic analysis of melange fabrics examples and applications from the mchugh complex kenai peninsula alaska permian to cretaceous melange of the mchugh complex on the kenai peninsula south central alaska includes blocks and belts of graywacke argillite limestone chert basalt gabbro and ultramafic rocks intruded by a variety of igneous rocks an oceanic plate stratigraphy is repeated hundreds of times across the map area but most structures at the outcrop scale extend lithological layering strong rheological units occur as blocks within a matrix that flowed around the competent blocks during deformation forming broken formation and melange deformation was noncoaxial and disruption of primary layering was a consequence of general strain driven by plate convergence in a relatively narrow zone between the overriding accretionary wedge and the downgoing generally thinly sedimented oceanic plate soft sediment deformation processes do not appear to have played a major role in the formation of the melange a model for deformation at the toe of the wedge is proposed in which layers oriented at low angles to s1 are contracted in both the brittle and ductile regimes layers at 30 458 to s1 are extended in the brittle regime and contracted in the ductile regime and layers at angles greater than 458 to s1 are extended in both the brittle and ductile regimes imbrication in thrust duplexes occurs at deeper levels within the wedge many structures within melange of the mchugh complex are asymmetric and record kinematic information consistent with the inferred structural setting in an accretionary wedge a displacement field for the mchugh complex on the lower kenai peninsula includes three belts an inboard belt of late triassic rocks records west to east directed slip of hanging walls a central belt of predominantly early jurassic rocks records north south directed displacements and early cretaceous rocks in an outboard belt preserve southwest northeast directed slip vectors although precise ages of accretion are unknown slip directions are compatible with inferred plate motions during the general time frame of accretion of the mchugh complex the slip vectors are interpreted to preserve the convergence directions between the overriding and underriding plates which became more oblique with time they are not considered indicative of strain partitioning into belts of orogen parallel and orogen perpendicular displacements because the kinematic data are derived from the earliest preserved structures whereas fabrics related to strain partitioning would be expected to be superimposed on earlier accretion related fabrics 1999 elsevier science ltd all rights reserved

contribution of induced magnetization to magnetization of seamounts a fundamental assumption in modelling seamount magnetic anomalies is that the contribution of induced magnetization is negligible the general consistency of seamount and non seamount palaeopoles scarcity of poles skewed toward the present field direction and the high ratio of remanent to induced magnetization koenigsberger ratio of many oceanic basalts have been cited as evidence supporting this assumption1 2 recent discussions concerning the dominance of normally magnetized seamounts have focused attention on the possible role of viscous and induced magnetization in seamount anomalies3 6 here we determine natural remanent magnetization initial volume susceptibility and the koenigsberger ratio for more than 2 000 samples from a subaerially exposed seamount section on la palma canary islands table 1 by contrast to results from the oceanic crust and ophiolites these data indicate that a variety of rock types are potential magnetic sources the significant induced component of intrusives underscores the importance of the lithological distribution in determining the character of seamount magnetic anomalies the la palma data together with a plausible lithological distribution indicate that induced magnetization may account for one sixth of seamount magnetization

late holocene tectonics and paleoseismicity southern cascadia subduction zone holocene deformation indicative of large subduction zone earthquakes has occurred on two large thrust fault systems in the humboldt bay region of northern california displaced stratigraphic markers record three offsets of 5 to 7 meters each on the little salmon fault during the past 1700 years smaller and less frequent holocene displacements have occurred in the mad river fault zone elsewhere as many as five episodes of sudden subsidence of marsh peats and fossil forests and uplift of marine terraces are recorded carbon 14 dates suggest that the faulting subsidence and uplift events were synchronous relations between magnitude and various fault offset parameters indicate that earthquakes accompanying displacements on the little salmon fault had magnitudes of at least 7 6 to 7 8 more likely this faulting accompanied rupture of the boundary between the gorda and north american plates and magnitudes were about 8 4 or greater

out of sequence thrust faults developed in the coseismic slip zone of the 1946 nankai earthquake mw 8 2 off shikoku southwest japan a multi channel seismic mcs reflection survey was conducted to study the subsurface structure of the coseismic slip zone of the 1946 nankai earthquake mw 8 2 off shikoku island in 1997 we could identify a splay fault system consisting of several sigmoid out of sequence thrust ost faults dipping landward with slope 10 25 on the poststack depth migrated mcs profiles most of the osts are apparently developed from the subducting oceanic basement to the seafloor in the forearc region cutting both underthrust sediments and the overriding accretionary prism in addition most of the osts are within the coseismic zone of the 1946 nankai earthquake and the interseismic locked zone the osts are considered to be related to large interplate earthquakes including the 1946 nankai earthquake these osts may be responsible for tsunami generation following deformation of forearc accretionary wedge

structural and fluid evolution of a young accretionary complex the hoh rock assemblage of the western olympic peninsula washington the hoh rock assemblage of the western olympic peninsula washington was deposited in eocene to miocene time and accreted deformed uplifted and eroded by the late miocene northeast dipping fault zones within the hoh are characterized by intensely deformed mud matrix melange and they range from 200 m to 1 000 m thick kinematic indicators within the matrix indicate thrusting to the west southwest both hanging wall and footwall sections are strongly folded and faulted wall rock sections are lithostratigraphically distinct with hanging walls composed of massive coarse sandstone and conglomerate and footwall sections composed of thin to medium bedded sandstone and siltstone folds within the wall rock sections are oblique to and are truncated by the later fault zone melanges indicating that the fault zones postdate folding evidence of fluid involvement in the hoh rocks includes petroliferous outcrops carbonate and clay cement and veins of carbonate and laumontite the progressive evolution of veins and cements paragenetic sequence can be interpreted in terms of crystallization under conditions of increasing consolidation decreasing salinity and changing fluid composition suppressed carbonate luminescence may reflect crystallization under reducing conditions perhaps related to the sulfate reduction zone the presence of hydrocarbons or clay dehydration although deformational features may be associated with the earliest phase of veining most of the localized grain breakage and matrix shear zones formed after the early micritic veins and before the last phase of sparitic carbonate laumontite veins laumontite occurred syn deformationally and in equilibrium with carbonate and also post deformationally the paragenetic sequences observed in all samples from the hoh rock assemblage can be correlated suggesting that the sources and processes controlling the fluid emplacement were similar across a wide region in addition the paragenetic sequence in the hoh rocks is similar to that documented in autochthonous coeval basins of southwest washington this similarity suggests that the precipitates formed during the evolution of the hoh rocks involved fluids that originated within the matrix and did not involve exotic or far traveled fluids

signals of watershed change preserved in organic carbon buried on the continental margin seaward of the waipaoa river new zealand abstract holocene sediments buried on the continental shelf seaward of the waipaoa river northeastern new zealand preserve a stratigraphic record of terrestrial environmental change the well characterized long term record of storms volcanism and human disturbance in this region provides an opportunity to examine how such changes are reflected in the character of organic carbon oc buried on the continental margin complimentary evidence obtained from analyses of the 14 c content and the elemental and stable carbon isotopic composition of different sedimentary fractions including charcoal wood and clay sized isolates indicates that these perturbations led to mobilization of oc components with variable storage histories in the watershed charcoal transported in the modern waipaoa river and buried in offshore depocenters includes a highly aged component that has apparently been slowly released from storage in soil or alluvial terraces the charcoal fraction ages become dramatically younger in sediments deposited after the taupo volcanic eruption 1717 cal yr bp and then polynesian settlement ca 700 cal yr bp both signaling biomass burning the mean age of woody plant fragments and clay bound oc deposited on the shelf also varies over time with older material having accumulated in the middle holocene and since human occupation deposition of older than average wood fragments and clay bound oc between about 5 and 3 6 kyr bp correlates with evidence for a period of increased storm frequency in the region and may reflect the enhanced delivery of aged soil and sedimentary rock mobilized from hill slopes via earthflows and or deep seated landslides similarly the deposition of older wood and clay bound oc commensurate with the first anthropogenic disturbance ca 700 years ago is consistent with accelerated mass wasting due to deforestation at the same time a change in the elemental and stable isotopic composition of bulk and clay bound oc buried on the shelf may reflect increased marine primary productivity and or mobilization of oc from deep levels in soil profiles deforestation of the waipaoa headwaters by european settlers beginning in the middle 19th century is evinced by a sharper rise in the age of clay associated oc buried offshore today deep gully incision into fractured sedimentary bedrock is a major source of sediment and kerogen to the river and this process has left its mark on the age of sedimentary oc delivered to the adjacent margin

formation of compound strike slip fault zones mount abbot quadrangle california abstract numerous strike slip fault zones in granitic rocks of the mount abbot quadrangle california developed from steeply dipping subparallel joints these joints generally were less than 50 m long and were spaced several centimeters to several meters apart some joints subsequently slipped and became small faults simple fault zones formed as oblique dilatant fractures splay fractures linked non coplanar faults side to side and end to end these simple fault zones are as much as 1 km long and accommodated displacements as great as 10 m compound fault zones formed as splay fractures linked small faults and simple fault zones they are as much as several kilometers long and accommodated displacements as great as 100 m these zones are distinctly different from riedel shear zones and the mechanics of their formation are unlikely to be described well by mohr coulomb mechanisms simple and compound fault zones are composed of non coplanar segments that join at steps or bends splay fracture length determines step widths the longest splay fractures occur along the longest fault zones allowing step widths to increase as the length and displacement across the zones increase these findings are consistent with the structure of some active seismogenic faults and they provide a mechanically consistent field based conceptual model for fault zones that grow in basement rocks from a preexisting set of joints

mesoscale strike slip faults and damage zones at marsalforn gozo island malta well exposed strike slip faults in limestones in the north western part of gozo show damage zones that can be grouped into three categories based on their location along faults tip damage linking damage and distributed damage the predominant fracture types within damage zones include extension fractures and secondary faults tip damage zones usually show wedge shaped patterns formed by antithetic faults and extension fractures commonly accompanied by block rotation several fractures are combined at linking damage zones typically with the concentration of a high intensity of fractures structures in distributed damage zones are typically similar to the classical riedel shear pattern evolutionary and 3d models are proposed in terms of the geometries of damage zones for small displacement strike slip fault zones different evolutionary routes depend on fault tip modes and locations

simulating brittle fault growth from linkage of preexisting structures many researchers have proposed conceptual models of fault development that are based on the linkage of preexisting structures such as isolated faults joints or veins to date such models largely use theoretical mechanics to explain the detailed damage zone geometries observed in linkage structures in this paper we present the first numerical simulations of the temporal and spatial development of geometrically complex fault linkage structures using the finite element model for fault damage zone evolution mopedz simulations show spatial and temporal fault zone evolution for a range of preexisting joint or fault geometries and stress conditions simulations show that linkage geometries are governed by three key factors the stress ratio the original joint geometry such as contractional or dilational configurations and the orientation of the principal stress simulated linkage structures display close correspondence to field observations of fault zone geometry with all secondary and tertiary damage features being reproduced the research also demonstrates that given information on the regional stress conditions numerical modeling can be used to predict fault zone geometries and hence identify the most and least likely structures for promoting fluid flow

very low frequency earthquakes within accretionary prisms are very low stress drop earthquakes 1 we report characteristic p wave spectra and stress drops of very low frequency vlf earthquakes that occurred within the accretionary prism along the nankai trough southwestern japan although many vlf earthquakes showed no distinct phases on a raw seismogram a few showed slightly distinct phases the arrival times of some phases were consistent with the calculated p wave arrival times the corner frequencies of the vlf earthquakes were calculated using the stacked p wave spectra assuming an omega square spectrum stress drops were very low i e in the range of 0 1 10 kpa which corresponds to 0 1 1 of those of ordinary earthquakes such extremely low stress drops of the vlf earthquakes suggest that the fault strength within the accretionary prism may have weakened due to the existence of a fluid within the thrust fault system of the accretionary prism

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

structural style and kinematics of an underplated slate belt kodiak and adjacent islands alaska the kodiak formation composed of coherent maastrichtian turbidites is a slate belt whose dominant structures developed during underplating to an accretionary wedge in the latest cretaceous it consists of about 80 coherent landward dipping thrust packets zones of disrupted sandstone associated with a scaly argillite matrix constitute the remainder about half of these disrupted sandstone zones are related to pre accretion deformation and the rest formed along late stage strike slip faults that postdate development of slaty cleavage the formation is divided into three structural belts the landward and seaward belts include steeply dipping structures and the central belt contains shallowly dipping structures and rocks that have experienced the highest strain the central belt probably acted as a low angle southeast verging floor thrust zone beneath the landward belt the structural history of the kodiak formation includes 1 early soft sediment disruption 2 tectonic stratal disruption 3 thrust faulting slaty cleavage s 1 development and folding f 1 4 intrusion of granodioritic plutons dikes and sills and associated normal faulting 5 development of crenulations f 2 and crenulation cleavage s 2 6 thrust faulting and 7 development of right lateral strike slip faults event 3 produced the dominant northwest dipping structural grain and caused the greatest amount of shortening the timing of event 7 relative to events 5 and 6 is not certain the dominant structures of the kodiak formation are interpreted as developing during underthrusting underplating and intra wedge shortening during latest cretaceous time within an accretionary wedge the maximum time from deposition to emplacement was about 12 m y and the timing is constrained by the maximum depositional age 74 m y and the age of plutonic rocks 62 m y that crosscut the dominant fabric pre cleavage zones of stratal disruption reflect deformation on the lower plate during underthrusting slaty cleavage thrusts and f 1 folds developed during underplating that also resulted in the formation of duplexes crenulations are probably related to post underplating subhorizontal shortening of sediments within the accretionary wedge syn deformation dynamic recrystallization of quartz minimum syn accretion metamorphic temperatures between 205 and 250 c and pressures of at least 2 65 kb recorded during the earliest stages of deformation suggest underplating at 10 km

strike slip relay ramps areas of reorientated bedding at contractional oversteps between strike slip faults are here called strike slip relay ramps metre scale examples are described from the jurassic sediments at east quantoxhead somerset u k larger strike slip relay ramps occur in the rio de peixe basin ne brazil along the newport inglewood trend california and in the bovey basin sw england although the geometry and development of strike slip relay ramps are similar to those of relay ramps in normal fault systems there are differences in the structures which accommodate the transfer of displacement between the overstepping faults whereas strike slip relay ramps are typically transpressional with pressure solution often occurring relay ramps in normal fault systems are dominated by extension or transtension care needs to be taken when interpreting areas of reorientated bedding between overstepping faults particularly when displacement directions are unknown for example when using seismic data this is because relay ramps can occur in both strike slip and normal fault zones

deformation and fluid flow of a major out of sequence thrust located at seismogenic depth in an accretionary complex nobeoka thrust in the shimanto belt kyushu japan 1 nobeoka thrust in kyushu southwest japan was investigated to understand the relationship between the seismogenic out of sequence thrust ost and fluid flow in accretionary prisms the nobeoka thrust is a fossilized ost being active at seismogenic depth the hanging wall exhibits a penetrative plastic deformation while a brittle cataclastic melange like occurrence characterizes the footwall although both of them have same shale and sandstone dominant protolith vitrinite reflectance analyses indicate that the maximum temperatures of the hanging wall and footwall are approximately 320 and 250 c respectively this thermal gap across the thrust corresponds to 8 6 14 4 km of displacement assuming a 28 47 c km geothermal gradient the brittle damage zone of the thrust is asymmetric only 2 m for hanging wall side and 100 m for footwall three types of mineral veins quartz and carbonate are well developed especially in the damaged footwall the tension crack filling vein the fault filling vein and postmelange one the first is harmonious with fabric perpendicular to the p surface fluid inclusion geothermobarometry indicates the p t of fluid in the intensively damaged zone of the footwall is 300 c 230 250 mpa higher than that from vitrinite reflectance which suggests that hydrothermal fluid flow is associated with deformation the same type vein in the lowest portion of the footwall damaged zone includes a much lower p t fluid this difference suggests that continuous underplating caused the damaged zone to propagate downward with cooling and shallowing which differs from faults characterized by shear localization and might be unique to aquiferous ost in accretionary complexes

age dependent variation in the magnetization of seamounts the magnetization of pacific seamounts shows a surprisingly large variation when viewed as a function of time similar to normal upper oceanic crust the basalts that form the external shell of volcanic seamounts have a high average magnetization immediately after formation this high magnetization decays rapidly with time resulting in a factor of 5 reduction in intensity in less than 500 000 years because submarine volcanoes appear to consist of the same basalts that form the upper part of the seafloor low temperature oxidation of the magnetic mineral titanomagnetite is assumed to be responsible for the reduction in magnetization for both types of crust some large oceanic volcanoes are of sufficient volume that the upper capping rocks erupt subaerially and submerge completely due to thermal subsidence only after several million years these capping rocks can be locally abundant i e hawaii are exposed to a different post formation environment and can have a magnetic mineralogy that is different from submarine volcanoes in spite of these differences the magnetization of subaerially erupted rocks of the hawaii emperor chain also may show a similar rapid reduction in intensity with age finally seamounts of cretaceous age show a factor of 2 higher average magnetization when compared to tertiary seamounts similar to the previously observed increased magnetization of cretaceous seafloor basalts recovered from deep sea drilling project ocean drilling project cores this increase in cretaceous magnetization appears to be reflected in the increased amplitude of magnetic anomalies in some but not all of the ocean basins prior and subsequent to the cretaceous normal superchron the processes potentially responsible for the elevated cretaceous magnetization values include a high geomagnetic field intensity large scale variations in whole rock major element geochemistry of the extrusive rocks or a systematic acquisition of a secondary magnetization during the cretaceous normal superchron

seismic and geodetic evidence for extensive long lived fault damage zones during earthquakes slip is often localized on preexisting faults but it is not well understood how the structure of crustal faults may contribute to slip localization and energetics growing evidence suggests that the crust along active faults undergoes anomalous strain and damage during large earthquakes seismic and geodetic data from the calico fault in the eastern california shear zone reveal a wide zone of reduced seismic velocities and effective elastic moduli using seismic traveltimes trapped waves and interferometric synthetic aperture radar observations we document seismic velocities reduced by 40 50 and shear moduli reduced by 65 compared to wall rock in a 1 5 km wide zone along the calico fault observed velocity reductions likely represent the cumulative mechanical damage from past earthquake ruptures no large earthquake has broken the calico fault in historic time implying that fault damage persists for hundreds or perhaps thousands of years these fi ndings indicate that faults can affect rock properties at substantial distances from primary fault slip surfaces and throughout much of the seismogenic zone a result with implications for the amount of energy expended during rupture to drive cracking and yielding of rock and development of fault systems

nonuniform magnetization of jasper seamount paleopoles derived from seamounts have been used to reconstruct the tectonic history of ocean basins however the interpretation of seamount magnetization models and the validity of seamount paleopoles may be affected by inhomogeneous magnetization multibeam bathymetric data sea surface and deep tow magnetic field data and paleomagnetic analyses of dredged samples were used to examine the origin of nonuniform magnetization within jasper seamount 30 27 n 122 44 w models indicate that the seamount is predominantly reversely magnetized with local zones of normal polarity as corroborated by deep tow measurements lithologies likely to be volumetrically important in a seamount edifice show highly variable magnetic properties basalts have high intensities 0 5 27 0 a m high koenigsberger ratios q and low viscous remanence vrm acquisition low q ratios and high vrm acquisition coefficients of coarse grained material and volcaniclastics suggest that they may have substantial viscous and induced components models for jasper are characterized by low uniform intensities and far sided paleopoles the shallow model inclinations may be attributed to nondipolar components in the time averaged geomagnetic field the low intensities of the uniform models and the large nonuniform component in the seminorm solutions imply a complex distribution of magnetization sources within jasper this nonuniformity may result from either lithological variability or construction of the seamount spanning two or more polarity intervals

a multiisotope c and n modeling analysis of soil organic matter turnover and transport as a function of soil depth in a california annual grassland soil chronosequence 1 we examine soil organic matter som turnover and transport using c and n isotopes in soil profiles sampled circa 1949 1978 and 1998 a period spanning pulse thermonuclear 14c enrichment of the atmosphere along a 3 million year annual grassland soil chronosequence temporal differences in soil 14c profiles indicate that inputs of recently living organic matter om occur primarily in the upper 20 30 cm but suggest that om inputs can occur below the primary rooting zone a three pool som model with downward transport captures most observed variation in 14c percentages of c and n 13c and 15n supporting the commonly accepted concept of three distinct som pools the model suggests that the importance of the decadal som pool in n dynamics is greatest in young and old soils altered hydrology and possibly low ph and or p dynamics in highly developed old soils cause changes in soil c and n turnover and transport of importance for soil biogeochemistry models

paleothermal structure of the shimanto accretionary prism shikoku japan role of an out of sequence thrust vitrinite reflectance study on the cretaceous shimanto accretionary prism of southwest japan shows that the vitrinite reflectance varies from 0 6 to 3 0 corresponding to the estimated maximum paleotemperature variation of 90 210 c the thermal structure shows a sharp discontinuity across an out of sequence thrust separating it into two thermal blocks in each block vitrinite reflectance values increase systematically toward the prism younging direction and the thermal structure is clearly overprinted on the tectonic imbrication of turbidite and melange units this provided us with a set of data to calculate the geometry and displacement of the out of sequence thrust the fission track zircon partial annealing ages indicate that this thrust was active about 43 ma probably in response to the accretion of eocene rocks this study shows that initial thickening of the accretionary prism in an order of several kilometres was mainly controlled by out of sequence thrust

new insights into the magmatism in the northern margin of the south china sea spatial features and volume of intraplate seamounts the extensive intraplate seamounts are obvious features in the northern south china sea scs however the distribution volume and origin of these seamounts are not well understood which greatly hinders our understanding of magmatism in the scs based on high resolution bathymetric data and 147 seismic profiles and combining gravity and magnetic data we first identify 45 seamounts in the northern margin of the scs and simulate their shape with elliptical cones results show that the total volume of these 45 seamounts above seafloor is estimated at about 1885 3078 km3 and the total volume of intrusive magma above moho is about 0 15 mkm3 which is close to the estimates for classic large igneous provinces across the world these seamounts are mostly located on the continental slope with thin crust approximately 12 18 km which reduces the overlying pressure and shortens the magmatic conduits the dominant azimuth of elliptical major axis in seamounts is consistent with the synrift and synspreading fault strikes ne nee indicating that these pre existing faults provide magmatic conduits for the subsequent postrift intraplate seamounts based on three existing clues i e 1 the intraplate seamounts high velocity layer and hainan mantle plume are contiguous in 3 d space 2 the high velocity layer is thicker beneath the continental shelf but thinner beneath the slope and 3 the basalts dredged from certain seamounts show oib type geochemical features we propose a magmatic upwelling pattern which contains hainan mantle plume to explain the spatial and morphological characteristics of these intraplate seamounts

cyclic fluid flow through a regionally extensive fracture network within the kodiak accretionary prism two types of periodic textures observed in veins from the kodiak accretionary prism attest to cyclic fluid flow through a regionally extensive fracture network buried at 8 12 km depth 1 crack seal microstructures with bands of mica inclusions and 2 collapse microstructures with jagged bands of residue embedded within euhedral crystals of quartz the difference in texture reflects the closure of cracks crack seal microstructures record the complete chemical sealing of the crack after each fracture event whereas the collapse features record longer fluid filled periods followed by more rapid draining of fractures collapse features consist of pressure solution selvages trapped within veins and in the wall rock adjacent to euhedral growth terminations the high concentrations of immobile elements in these selvages indicate that these fractures closed by collapse and penetration of quartz crystals into wall rock analysis of chemical composition on either side of four large euhedral growth veins and whole rock analysis of slates across the kodiak formation reveal local depletion of silica adjacent to veins but no evidence for long distance silica transport within the system both crack seal and collapse textures are observed in a regionally extensive vein system that displays a regular geometry with thin closely spaced 0 5 3 cm near vertical crack seal veins that connect vertically and laterally with thicker euhedral growth veins arranged in widely spaced 500 mm southeast dipping en echelon sets the mesoscopic distribution and textural variability of the vein network suggests that the development of the vein system involved early nucleation and growth of vertical hydrofractures as the fracture density increased arrays of fractures locally provided zones of weakness and southeast dipping brittle ductile shear zones nucleated these en echelon cracks remained open and provided small reservoirs of fluid textures show that en echelon fractures remain open but periodically grow by upward and downward propagation crack tips are then sealed with locally derived silica and fluid drains back into en echelon fracture arrays this local fluid movement is punctuated by less frequent events where the system links up over a greater distance fractured reservoirs become interconnected and the fluid within reservoirs is drained upward or laterally periodic inflation and deflation of en echelon arrays may reflect periodic slip on crosscutting faults and rupture of the seals that separate reservoirs

implications of carbon flux from the cascadia accretionary prism results from long term in situ measurements at odp site 892b a 403 day in situ field experiment at ocean drilling program site 892b sought to quantify the flux of methane along a fluid active fault and to experimentally determine rates of methane hydrate and authigenic carbonate deposition associated with fluid expulsion from the borehole an instrument package was deployed that osmotically sampled fluid measured borehole pressure and flow rates and contained reaction chambers in which deposition of gas hydrates and carbonates was anticipated and from which microbial communities might be extracted flow is highly variable in the three phase water methane system that exists at site 892b flow rates fluctuate over two orders of magnitude in response to tidally induced pressure variations and gas hydrate formation and dissociation hydrate formation began 45 days into the experiment and reduced the initial flow 2 l day to 20 ml day unexpectedly the hydrate destabilized after about 125 days tidally induced flow reversals are common 25 of time in this setting characterized by overpressured pore waters these reversals pump sulfate rich bottom water into near surface sediments where archaea anaerobically oxidize ch4 and induce carbonate precipitation at the sediment water interface authigenic carbonates are undergoing dissolution methanotrophs dominated the microbial community where fluid is discharged to ambient seawater all expelled methane is apparently oxidized in the water column

the great sumatra andaman earthquake of 26 december 2004 the two largest earthquakes of the past 40 years ruptured a 1600 kilometer long portion of the fault boundary between the indo australian and southeastern eurasian plates on 26 december 2004 seismic moment magnitude mw 9 1 to 9 3 and 28 march 2005 mw 8 6 the first event generated a tsunami that caused more than 283 000 deaths fault slip of up to 15 meters occurred near banda aceh sumatra but to the north along the nicobar and andaman islands rapid slip was much smaller tsunami and geodetic observations indicate that additional slow slip occurred in the north over a time scale of 50 minutes or longer

paleomagnetism of cretaceous pacific seamounts revisited the paleomagnetism of cretaceous pacific seamounts is reexamined herein techniques for nonuniform magnetic modeling are applied to determine paleomagnetic pole positions and their associated confidence limits modeling techniques are presented for reconstruction of both uniform and nonuniform components of the seamount magnetization the uniform component yields an estimate of the paleomagnetic pole position and the nonuniform component accounts for irregularities in the seamount magnetization a seminorm minimization approach constructs maximally uniform magnetizations and is used to represent seamount interiors a statistical modeling approach constructs random nonuniform magnetizations and is used to determine the confidence limits associated with each pole position mean paleopoles are calculated for groups of seamounts including their associated error bounds the mean paleopole for seven reliably dated upper cretaceous seamounts is located close to the position predicted by pacific hotspot relative motion the paleopole for five seamounts with cretaceous minimum dates is located west of the hotspotpredicted apparent polar wander path and may represent a lower cretaceous or upper jurassic pole

relationship of pore water freshening to accretionary processes in the cascadia margin fluid sources and gas hydrate abundance 1 drilling in the cascadia accretionary complex enable us to evaluate the contribution of dehydration reactions and gas hydrate dissociation to pore water freshening the observed freshening with depth and distance from the prism toe is consistent with enhanced conversion of smectite to illite driven by increase in temperature and age of accreted sediments although they contain gas hydrate as evidenced by discrete low chloride spikes the westernmost sites drilled on hydrate ridge show no freshening trend

seamount magnetic polarity and cretaceous volcanism of the pacific basin in this paper we examine the magnetic polarity for pacific basin seamounts exclusive of the hawaiian ridge on pacific crust older than 65 ma seamounts of normal polarity predominate on crust younger than 65 ma seamounts exhibit normal and reversed polarity as well as mixed polarity we show that viscous components do not dominate seamount magnetization and we suggest that a large number of normal seamounts were formed during a major magmatic event postulated for the period 110 70 ma this period overlaps with the long cretaceous normal period 118 84 ma and corresponds to 85 normal polarity for earth9s magnetic field the correspondence of a period of high magmatic activity with a long period of normal polarity supports the possible correlation between those processes responsible for magma production and for magnetic field generation

the illite crystallinity technique a critical appraisal of its precision analysis of the precision of the illite crystallinity technique shows that machine errors are 0 8 it is necessary that contours should be at intervals of 0 1 2 which is equivalent to subdivision of the anchizone into upper and lower units where previous interpretations have relied upon an isocryst method of contouring at less than 0 1 2 the conclusions must be regarded as unsubstantiated centrifuge separation of clay fractions based on a stokes law application gives separations in which a significant but variable percentage of grains have long axes greater than the size calculated for the typical 2 m fraction utilized some 20 of grains lie in the 2 4 m range although the proportion is not believed to have a significant effect upon crystallinity values the formula is applicable for grain sizes down to 0 5 m illite crystallinity values on samples prepared by an ultrasonic disaggregation method show a small increase on those prepared by ball mill crushing the differences are minimal at the epi anchizone level but increase to some 10 at the anchizone diagenetic level the effect on grade determinations is again thought to be minimal and indicates that concern over unsuitability of the ultrasonic disaggregation method is unfounded

fault terminations and barriers to fault growth abstract field observations of strike slip faults in jointed granitic rocks of the central sierra nevada california combined with a mechanical analysis of fault interaction provide insight into how fault terminations vary with scale we document here a strike slip fault system 2 3 km long clustered about the west end of the fault system are several dozen faults that parallel the three main fault zones in the system we interpret this cluster of small faults as a barrier that inhibited growth of fault zones in the fault system a two dimensional mechanical analysis shows that a cluster of small faults flanking the tip of a large fault zone will tend to diffuse the stress concentration near the fault zone tip an analogous effect in engineering is known as crack tip shielding near tip stress concentrations promote fault growth and processes that decrease these stress concentrations inhibit fault growth as faults lengthen and grow they interact with features at greater distances and over a broader area so the potential for tip shielding effects will increase as fault length increases this effect can account for why the mechanisms and character of fault terminations would tend to vary as a function of scale

fluid rich damage zone of an ancient out of sequence thrust kodiak islands alaska 1 the uganik thrust is a fossil out of sequence thrust fault which was active over a period of 3 ma during the early tertiary until activity ceased with the subduction of the kula farallon spreading ridge at 57 ma during this period the fault experienced at least 1 km of throw and developed a strongly asymmetric damage zone the brittle damage zone in the footwall of the fault acted as a conduit for fluid advection during the active faulting a similar asymmetrical footwall damage zone has been interpreted as a fluid conduit at the nobeoka thrust shimanto belt sw japan thermal indicators in the uppermost footwall give similar maximum paleotemperatures to those in the hanging wall 280 c while previous work elsewhere in the footwall formation suggests maximum burial temperatures of 240 c in this case similar to the irish canyon thrust in the franciscan accretionary complex the location of the thermal anomaly is spatially offset from the structural fault which caused it owing to thermal overprinting in the vicinity of the fault

evidence for a remanent contribution in magsat data from the cretaceous quiet zone in the south atlantic indirect evidence for the presence of a trm component in the magsat elevation data in the south atlantic is found through forward modeling of the prominent positive anomaly overlying the walvis ridge the anomaly contrast between the ridge and adjacent angola and cape basins is too large to be easily explained by induced magnetization of even alkali basaltic crust however most of the walvis ridge and portions of the adjacent basins lie within the cretaceous quiet zone where prolonged normal polarity may have produced enough volume of material to cause a measureable contribution at satellite elevation an additional 3 a m spread over the entire layer 2 thickness trm contribution is required to account for the walvis ridge anomaly this value is within the range found for the cretaceous quiet zone anomalies in the magsat data in the north atlantic

tectonically driven fluid flow in the kodiak accretionary complex alaska sandstone and chert boudins that have syntectonic extensional veins are dominant structural elements in melanges of the kodiak accretionary complex alaska detailed analyses of cogenetic methane rich and water rich fluid inclusions in syntectonic quartz veins indicate that fluid pressures dropped by 20 to 45 during crystal growth this drop occurred faster than uplift of the rock and probably represents the local effect of fluid escaping to shallow levels in the subduction complex during melange deformation possibly along an interconnected fracture network an important implication of channelized fracture flow to higher levels in a subduction complex is that fluids may transport heat and solutes thereby generating thermal and chemical anomalies along shallow faults

stable and radioactive carbon in forest soils of chhattisgarh central india implications for tropical soil carbon dynamics and stable carbon isotope evolution abstract soils from two sites viz kotumsar and tirathgarh located 5 km apart in a tropical reserve forest 18 52 n 81 56 e in central india have been explored for soil organic carbon soc content its mean residence time mrt and the evolution of stable carbon isotopic composition 13c soc stocks in the upper 30 cm of soil layers are 5 3 kg m2 and 3 0 kg m2 in the upper 110 m are 10 7 kg m2 and 7 8 kg m2 at kotumsar and tirathgarh respectively soc decreases with increasing depth bomb carbon signature is observed in the upper 10 cm organic matters in the top soil layers 0 10 cm have mrts of the order of a century which increases gradually with depths reaching 3500 5000 yrs at 100 cm 13c values of soc increase with depth the carbon isotopic fractionation is obtained to be 1 2 and 3 for soils at kotumsar and tirathgarh respectively confirmed using rayleigh isotopic fractionation model the evolution of 13c in soils was also studied using a modified rayleigh fractionation model incorporating a continuous input into the reservoir the depth profiles of 13c for soc show that the input organic matter from surface into the deeper soil layers is either insignificant or highly labile and decomposes quite fast in the top layers thus making little contribution to the residual biomasses of the deeper layers this is an attempt to understand the distillation processes that take place in soc assess the extent of decomposition by microbes and effect of percolation of fresh organic matter into dipper soil layers which are important for stable isotope based paleoclimate and paleovegetation reconstruction and understanding the dynamics of organic carbon in soils

dynamic deformation of the accretionary prism excites very low frequency earthquakes 1 we have detected anomalous very low frequency earthquakes within the accretionary prism along the nankai trough southwestern japan centroid moment tensor inversion analysis reveals that the earthquake hypocenters are distributed at 10 km depth above the upper surface of the subducting philippine sea plate and within 50 70 km landward of the trough axis the focal mechanisms indicate reverse faulting their hypocenters are distributed beneath a deformation zone of an accretionary prism in sea floor topography these observations suggest that the occurrence of very low frequency earthquakes is related to numerous reverse fault systems within the accretionary prism and that the earthquakes reflect the dynamics of deformation within this accretionary prism

warm fluid migration along tectonic melanges in the kodiak accretionary complex alaska analyses of methane water fluid inclusions from syntectonic quartz veins in melange boudins of the kodiak accretionary complex alaska indicate fluid temperatures ranging from 215 to 290 c at depths between 10 and 14 km these fluid temperatures are significantly higher than those predicted by conductive heat flow models of subduction zones given the available geological constraints this discrepancy is interpreted as the result of migration of warm fluids from deeper structural levels along active fault zones during subduction related underthrusting of these units this interpretation requires more careful consideration of how migrating fluids affect the general thermal structure of subduction zones

distant off fault damage and gold mineralization the impact of rock heterogeneity field observations have established that fault related damage can occur at locations far from the principal slip surface which are well outside the fractured region currently predicted by models of fault damage we use a finite element model to simulate fracture initiation due to fault linkage and show how variations in rock properties allow off fault damage to develop at surprisingly large distances away from the main fault off fault damage continues to grow even after two adjacent closely spaced fault segments have interacted and linked we demonstrate that this process was important for the formation of fracture hosted gold deposits in the mount pleasant goldfield western australia the strength of lithological contacts also has a significant impact on off fault damage location and intensity our approach may go some way to explaining the non intuitive distribution of mineralization in certain mineral systems as well as being applicable to predict subsurface fracturing and fluid flow in hydrothermal geothermal reservoirs

magnetization of the la palma seamount series implications for seamount paleopoles paleopoles determined from seamount magnetic anomalies constitute the major data source for the pacific apparent polar wander path but relatively little is known about the processes of remanence acquisition in seamounts since magnetic anomalies reflect both natural remanence nrm and the induced field it is important first to assess whether the nrm is likely to represent an original field direction and second to constrain the magnitude of the induced component to this end we present paleomagnetic data from an uplifted subaerially exposed section through a seamount on la palma canary islands the pliocene seamount series of la palma comprises a 6 km sequence of alkalic extrusives and intrusives which includes all lithologies likely to be volumetrically important in seamounts the structural tilt of the seamount series allows separation of early thermal or chemical remanence from magnetization components acquired after tilting e g viscous remanence the nrm provides a poor indication of the original magnetization direction although the characteristic magnetization of many la palma samples is compatible with the original pretilt direction hydrothermal alteration has resulted in the production of ti poor magnetite and an increasing contribution of hematite with increasing degree of alteration more importantly well defined magnetization directions which deviate from any reasonable geomagnetic direction at la palma can be attributed to hydrothermal alteration in a different polarity than prevalent during the original magnetization based on a comparison of the magnitude of low stability components of magnetization and laboratory acquisition of viscous remanence and previous estimates of the induced magnetization we conclude that viscous and induced magnetization probably account for 15 25 of the total magnetization of seamounts the resulting paleopole bias is a function of the polarity and paleolatitude of the seamount and ranges from 4o to 16 o for cretaceous seamounts in the pacific

mechanisms of coal metamorphism case studies from paleozoic coalfields controls on coal metamorphism can be complex in this paper we examine four paleozoic coalfields the western kentucky portion of the illinois basin the pennsylvania anthracite fields the south wales coalfield and the bowen basin an increase in temperature with depth of burial is certainly a factor in coal metamorphism in many coalfields however including the coalfields reviewed here it has become apparent that such a simple mechanism does not explain the coal rank patterns observed the flow of hydrothermal fluids through the coals has been proposed as a cause of coal metamorphism evidence includes inverted rank gradients elevated cfl as an indicator of brine fluids isotopic evidence for hydrothermal fluids and vein and cleat mineral assemblages in any case multiple hypotheses must often be evaluated in the examination of any coalfield since the simple paradigm of coal rank increases with a simple increase in temperature with increasing depth does not fit the evidence observed in many cases

fluid flow paths in the middle america trench and costa rica margin the hydrology of the subducting plate and its dewatering behavior through the shallow subduction zone is linked to the structure and deformation of the forearc prism the nature of the seismogenic zone the composition of seawater for selected elements and the composition of the residual slab subducted to depths of magma generation at the volcanic arc two locally independent systems of fluid flow govern the transport of heat and chemistry through the costa rica subduction complex a dominantly nonaccretionary subduction zone one fluid system is the margin wedge decollement and underthrust sediment section fluid sources include local sediment compaction and mineral dehydration at depth a second flow system occurs in basement beneath the sedimentary sequence on the incoming plate this region is characterized by extremely low conductive heat flow and the sediment overlying basement has pore water geochemistry similar to that of seawater flow nearly parallel to the trench could be directed by permeability associated with faults and driven by a combination of differential heating and earthquake strain cycling

thickening of fault zones a mechanism of melange formation in accreting sediments sediments accreted at subduction zones undergo stratal disruption and form a type of melange the thickness of the disrupted zones grows with progressive deformation this suggests that initial fault surfaces are abandoned and deformation propagates into adjacent undeformed sediment factors causing the abandonment of fault surfaces during continuing deformation include 1 strengthening owing to porosity loss during consolidation 2 localized drops in fluid pressure on fault surfaces that act as dewaterinig conduits and 3 reorientation of fault surfaces the disruptive processes occurring in accretionary prisms result principally from the deformation of a consolidating sediment mass

dynamics of decadally cycling carbon in subsurface soils subsurface horizons contain more than half of the global soil carbon c yet the dynamics of this c remains poorly understood we estimated the amount of decadally cycling subsurface c 20 to 60 cm depth from the incorporation of bomb radiocarbon 14c using samples taken over 50 years from grassland and forest soils in the sierra nevada mountains california the radiocarbon content of all organic matter fractions roots low density lf high density hf and non oxidizable hf increased from the pre to post bomb samples indicating 1 6 kgc m 2 or about half of the subsoil c consists of c fixed since 1963 low density lf c represented 20 years for the arrival of bomb 14c to this fraction a two pool fast cycling and passive model including 20 year time lag showed that 28 73 of the subsoil mineral associated c had turnover times of 10 95 years microbially respired c was enriched in bomb14c compared to both lf and hf fractions in 2009 overall we estimate that c fluxes through decadally cycling pools in the subsurface are equivalent to 1 9 grassland to 10 54 forest of the surface litterfall at these sites our results demonstrate the importance of decadally cycling c for ecosystem c balance and that a lagged response of the large subsurface c stores to changes in environmental conditions is possible

paleomagnetic evidence for cretaceous age of two volcanoes on the south flank of the island of hawaii apuupuu and dana seamounts are located on the south flank of the island of hawaii near the active submarine volcano loihi though previous work suggests that they are older inactive volcanoes their ages and relationship to hawaiian volcanism are uncertain we make age estimates for these two seamounts by comparing paleomagnetic poles derived using a magnetic inversion technique to the pacific apparent polar wander path the paleopoles of apuupuu and dana seamounts are located at 65 8 n 9 2 e and 66 7 n 358 7 e respectively both poles are insignificantly different and located on the late cretaceous part of the polar wander path between the 82 and 72 ma mean poles suggesting that the seamounts formed contemporaneously long before their part of the pacific plate drifted over the hawaiian hot spot

transition of accretionary wedge structures around the up dip limit of the seismogenic subduction zone the nankai accretionary prism is divided into three segments outer and inner wedges and their transition zone these wedges reflect different aspects of wedge taper internal deformation and basal plate boundary fault the outer wedge is characterized by narrow critical taper internal deformation by in sequence fold and thrust and aseismic decollement the inner wedge represents a stable narrow taper weakly deformed internal structure and seismogenic plate boundary fault along its base the transition zone between the two wedges shows large critical taper with steep surface slope internal structure of out of sequence thrust and step down of decollement onto the sediment oceanic basement interface the trench slope break and oceanward margin of forearc basin is located around the landward edge of this transition zone these common aspects might be related to the lithification of both accreted and underthrust sediments and the resultant switch of the plate boundary fault deformation and lithification process recorded in exhumed on land melange of accretionary complexes suggest that the step down of the plate boundary decollement occurs around the up dip limit of seismogenic subduction zone

duplex accretion and underplating in an ancient accretionary complex kodiak islands alaska the landward belt of the kodiak formation represents a sequence of lower maastrichtian turbidites that was underplated to the kodiak accretionary complex by duplex accretion evidence for duplexes exists on the mesoscopic and map scale at the microscopic scale incremental strain histories are consistent with early shear during underthrusting abrupt landward rotation of individual thrust slices over fault ramps and locking of thrust packets in steeper orientations duplex geometries at the mesoscopic scale are represented by high angle reverse faults bounded either above or below by low angle southeast verging detachments at the map scale different structural belts can be related to a low angle detachment zone central belt flooring a more landward duplex landward belt duplex underplating can result in the uplift and thickening of accretionary prisms without necessarily deforming the overlying previously accreted material and slope sediments

using a reactive transport model to elucidate differences between laboratory and field dissolution rates in regolith the reactive transport model flotran was used to forward model weathering profiles developed on granitic outwash alluvium over 40 3000 ka from the merced california usa chronosequence as well as deep granitic regolith developed over 800 ka near davis run virginia usa baseline model predictions that used laboratory rate constants km measured fluid flow velocities v and bet volumetric surface areas for the parent material a o m were not consistent with measured profiles of plagioclase potassium feldspar and quartz reaction fronts predicted by the baseline model are deeper and thinner than the observed consistent with faster rates of reaction in the model reaction front depth in the model depended mostly upon saturated versus unsaturated hydrologic flow conditions rate constants controlling precipitation of secondary minerals and the average fluid flow velocity va unsaturated hydrologic flow conditions relatively open with respect to co2 g resulted in the prediction of deeper reaction fronts and significant differences in the separation between plagioclase and potassium feldspar reaction fronts compared to saturated hydrologic flow relatively closed with respect to co2 g under saturated or unsaturated flow conditions the rate constant that controls precipitation rates of secondary minerals must be reduced relative to laboratory rate constants to match observed reaction front depths and measured pore water chemistry additionally to match the observed reaction front depths va was set lower than the measured value v for three of the four profiles the reaction front gradients in mineralogy and pore fluid chemistry could only be modeled accurately by adjusting values of the product kma o m by assuming km values were constrained by laboratory data field observations were modeled successfully with tst like rate equations by dividing measured values of a o m by factors from 50 to 1700 alternately with sigmoidal or alinhibition rate models this adjustment factor ranges from 5 to 170 best fit models of the wetter hydrologically saturated davis run profile required a smaller adjustment to a o m than the drier hydrologically unsaturated merced profiles we attributed the need for large adjustments in va and a o m necessary for the merced models to more complex hydrologic flow that decreased the reactive surface area in contact with bulk flow water e g dead end pore spaces containing fluids that are near or at chemical equilibrium thus rate models from the laboratory can successfully predict weathering over millions of years but work is needed to understand how to incorporate changes in what controls the relationship between reactive surface area and hydrologic flow

the development of folds and cleavages in slate belts by underplating in accretionary complexes a comparison of the kodiak formation alaska and the calaveras complex california the development of folds and cleavages in slate and graywacke belts is commonly attributed to arc continent or continent continent collisions however the kodiak formation of southern alaska and the calaveras complex of the western sierra nevada california are two slate and graywacke belts in which folds and slaty cleavages developed during simple underthrusting and underplating within accretionary wedges the maastrichtian kodiak formation is composed dominantly of coherent turbidites but includes lesser pebbly mudstone minor conglomerate and rare chert the kodiak formation is part of a large accretionary complex that youngs in age seaward but bedding tops generally show landward younging a progression of structures has been determined by crosscutting relationships and includes 1 syndeformational depositional features 2 broken formation 3 slaty cleavage folds and thrust faults 4 crenulations and crenulation cleavage 5 late brittle thrust faults and 6 right lateral strike slip faults broken formation slaty cleavage thrust faults and folds developed during underthrusting and underplating within an accretionary wedge crenulations and brittle thrust faults are related to subsequent intrawedge shortening based on peak metamorphism in the uppermost zeolite to prehnite pumpellyite facies underplating occurred at a minimum depth of 10 km the calaveras complex is composed of argillite chert graywacke pebbly mudstone limestone and volcanic rocks its age of deposition has a maximum range from permian to early jurassic overall the unit appears to young westward but local facing indicators show eastward younging of individual blocks the sequence of structures developed in the calaveras complex is 1 syn depositional olistostromes 2 broken formation 3 slaty cleavage folds and thrust faults and 4 younger jura triassic folds and crenulation cleavages broken formation and slaty cleavage developed during underthrusting and underplating in an accretionary wedge in an analogous fashion to the kodiak formation greenschist facies metemorphism during underplating suggests that the calaveras complex was accreted at deeper levels or in a wedge with a higher geothermal gradient than the kodiak formation some other probable examples of slate graywacke belts that became folded and well foliated during underplating include part of the dunnage zone newfoundland the southern uplands complex scotland the torlesse terrane new zealand part of the hamburg klippe pennsylvania and the taconic allochthons new york peak metamorphism in these belts indicates that they were accreted in accretionary wedges with geothermal gradients higher than usually assumed for such tectonic settings such wedges may have been fairly common features at convergent margins

archaean au ag mineralisation at racetrack near kalgoorlie western australia a high crustal level expression of the archaean composite lode gold system the racetrack au ag deposit in the archaean yilgarn block western australia is hosted by a porphyritic basalt in a low greenschist facies setting and is associated with a brittle strike slip fault system three distinct and successive stages of hydrothermal activity and late quartz carbonate veining resulted in multiple veining and or brecciation stages i and ii are au bearing whereas stage iii and late veins are barren the ore shows features of both classic epithermal and mesothermal deposits alteration assemblages typified by sericitization carbonization silicification and chloritization are similar to those of mesothermal gold deposits wheras the quartz vein textures including comb rosette plumose and banded ore mineralogyof arsenopyrite pyrite chalcopyrite sphalerite galena freibergite tetrahedrite tennantite fahlore electrum and gold and metal associations cu as ag sn sb w au and pb are more characteristics of epithermal deposits fluid inclusions related to stage ii are two phase and aqueous with 1 8 average 4 wt nacl equiv and co2 content of 0 85 molal pressure corrected homogenisation temperatures range from 190 c to 260 c mineral assemblages indicate that ore fluid ph ranged between 4 2 and 5 3 fo 2 between 10 38 8 and 10 39 6 bars and m s between 10 3 2 and 10 3 6 calculated chemical and stable isotope compositions require a component of surface water in the ore fluid depositing the mineralisation but evidence for deep crustal pb indicates that deeply sourced fluids were also involved the deposit is interpreted to have formed in a shallow environment via mixing of deeply sourced fluids from at least as deep as the base of the greenstone belt with surface waters it therefore represents the upper crustal end member of the crustal depth spectrum of archaean lode gold mineralisation

damage and permeability around faults implications for mineralization mineral deposits are commonly hosted by small displacement structures around jogs in major faults but they are rarely hosted by the major fault itself this relationship may be explained by time dependent fracturing and healing in and around major faults and associated permeability evolution a damage mechanics formulation is used here to explore the spatial temporal evolution of damage in and around a fault following a fault slip event we show that regions of increased damage rate correspond to the location of mineral deposits and that these areas correspond to areas of aftershocks predicted by stress transfer modeling the fault itself enters a healing regime following the slip event hence it is expected to become less permeable than the fracture network outside the fault our results support the hypothesis that mineralization occurs in a fracture network associated with aftershocks this may be due to the higher time integrated permeability of the fracture network relative to the main fault

thermal maturity in the shimanto accretionary prism southwest japan with the thermal change of the subducting slab fluid inclusion and vitrinite reflectance study abstract the p t path of the cretaceous shimanto accretionary complex western shikoku southwest japan was determined by a combination of vitrinite reflectance data and homogenization temperatures of fluid inclusion analysis within the complex the p t paths of the upper cretaceous yokonami melange and surrounding coherent strata were compared no p t difference was found between the yokonami melange and surrounding strata at least two types of fluids methane rich and water rich fluids migrated at different stages during metamorphism within the complex the methane rich fluid was initially trapped in vein quartz under pressures of 260 mpa and a geothermal gradient of 24 c km the water rich fluid was included in calcite at 95 125 mpa and a geothermal gradient of 50 c km the complex sequence of occurrence of the vein minerals and radiometric age data suggest that the water rich fluid was trapped during the kula pacific ridge subduction into the shimanto accretionary complex the paleoheat flow values for the two stages of subduction are consistent with the changes in the inferred slab age the metamorphism of the shimanto accretionary complex was predominantly controlled by the thermal condition of the subducting plate

comparison of vertical transport of 137cs and organic carbon in agricultural cracking soils abstract the movement of soil organic carbon soc down the soil profile has been compared to that of the environmental tracer 137 cs at two neighbouring field sites sharing the same land management history but comprising clay soils with different cracking characteristics cracking black vertisol and a red luvisol a finite element model fem simulation of the vertical transport of soc and 137 cs was developed for each site which accommodates the differing spatial and temporal trends of input and decay of the two species from these models the diffusion and convection coefficients which best describe the movement of 137 cs at each site were determined both convection and diffusion coefficients were found to be substantially higher in cracking vertisol soils d cs 721 mm 2 yr v cs 0 84 mm yr than in the neighbouring luvisol soils d cs 94 mm 2 yr v cs 0 mm yr finally the 137 cs transport coefficients determined for each site were used in modelling the soc profile the excellent match between predicted and observed soc profiles suggests that transport of the soc and 137 cs down the soil column at the luvisol site follows the same pathways while the match between predicted and observed soc profiles at the vertisol site was weaker this was concluded to be more likely due to the impact of extensive soil cracking which is not explicitly accounted for in the soc fem rather than the result of the use of 137 cs transport coefficients

simulating brittle fault evolution from networks of pre existing joints within crystalline rock many faults grow by linkage of smaller structures and damage zones around faults may arise as a result of this linkage process in this paper we present the first numerical simulations of the temporal and spatial evolution of fault linkage structures from more than 20 pre existing joints the initial positions of which are based on field observation we show how the constantly evolving geometry and local stress field within this network of joints contribute to the fracture pattern markedly different fault zone trace geometries are predicted when the joints are at different angles to the maximum compressive far field stress ranging from evolving smooth linear structures to complex stepped fault zone trace geometries we show that evolution of the complex fault zone geometry is governed by 1 the strong local variations in the stress field due to complex interactions between neighbouring joints and 2 the orientation of the initial joint pattern with respect to the far field stress

emplacement of the kodiak batholith and slab window migration the kodiak batholith is one of the largest most elongate intrusive bodies in the forearc sanak baranof plutonic belt located in southern alaska this belt is interpreted to have formed during the subduction of an oceanic spreading center and the associated migration of a slab window individual plutons of the kodiak batholith track the location and evolution of the underlying slab window six u pb zircon ages from the axis of the batholith exhibit a northeastward decreasing age progression of 59 2 0 2 ma at the southwest end to 58 4 0 2 ma at the northeast tip the trench parallel rate of age progression is within error of the average slab window migration rate for the entire sanak baranof belt 19 cm yr structural relationships u pb ages and a model of new gravity data indicate that magma from the kodiak batholith ascended 5 10 km as a northeastward younging series of 1 8 km diameter viscoelastic diapirs individual plutons ascended by multiple emplacement mechanisms including downward flow collapse of wall rock stoping and diking stokes flow xenolith calculations suggest ascent rates of 5 100 m yr and an effective magmatic viscosity of 10 7 10 8 pa s pre existing structural or lithologic heterogeneities did not dominantly control the location of the main batholith instead its location was determined by migration of the slab window at depth

gold mineralisation at the lady bountiful mine western australia an example of a granitoid hosted archaean lode gold deposit the lady bountiful granitoid hosted lode gold deposit located in the mid greenschist facies metamorphosed ora banda greenstone sequence is hosted predominantly by the late tectonic liberty granodiorite gold mineralisation is localised along quartz veined sinistral brittle fault zone s that transect the boundary between the liberty granodiorite and mt pleasant sill quartz vein textures indicate two stages of a single gold related vein development event with high grade gold mineralisation restricted to the second stage ore minerals include pyrite chalcopyrite pyrrhotite galena sphalerite au ag bi pb tellurides and native gold fluid infitration has resulted in narrow 1 m bleached wallrock alteration envelopes to the fault zones comprising albite k mica chlorite calcite rutile assemblages temperature pressure conditions varied from stage i 300 50 c 2 kbar to stage ii 250 50 c 0 5 to 2 kbar with the hydrothermal fluid in both stages characterised by x co2 0 15 and moderate salinity 1 28 m nacl intermittent phase separation of stage ii mineralising fluids initiated by pressure fluctuations in dilational sites and or fluid dominated fluid wallrock interaction are invoked as the dominant depositional mechanisms the granitoid hosted lady bountiful lode gold deposit shares many features with other granitoid hosted lode gold deposits in the yilgarn craton and the superior province granitoid hosted lode gold deposits such as the lady bountiful deposit provide additional evidence that the dominant control on the localisation of gold mineralisation within a granitoid host is structure with competency contrasts playing a significant role furthermore the hydrothermal wallrock alteraction and orefluid chemistry characteristics of the granitoid hosted lode gold deposits are comparable to those established for greenstone hosted lode gold mineralisation

edaphic influences on plant community adaptation in the chiquibul forest of belize abstract edaphic variables figure significantly in plant community adaptations in tropical ecosystems but are often difficult to resolve because of the confounding influence of climate within the chiquibul forest of belize large areas of ultisols and inceptisols occur juxtaposed within a larger zone of similar climate permitting unambiguous assessment of edaphic contributions to forest composition wet chemical analyses x ray diffraction and x ray fluorescence spectroscopy were employed to derive chemical ph exchangeable cations cec total and organic c total trace elements and physical texture mineralogy properties of four granite derived ustults from the mountain pine ridge plateau and four limestone derived ustepts from the san pastor region the soils of these two regions support two distinct forests each possessing a species composition reflecting the many contrasting physicochemical properties of the underlying soil within the mountain pine ridge forest species abundance and diversity is constrained by nutrient deficiencies and water holding limitations imposed by the coarse textured highly weathered ultisols as a consequence the forest is highly adapted to seasonal drought frequent fires and the significant input of atmospherically derived nutrients the nutrient rich inceptisols of the san pastor region conversely support an abundant and diverse evergreen forest dominated by sabal mauritiiformis cryosophila stauracantha and manilkara spp moreover the deep fine textured soils in the depressions of the karstic san pastor landscape collect and retain during the wet season much available water thereby serving as refugia during particularly long periods of severe drought to the extent that the soils of the chiquibul region promote and maintain forest diversity they also confer redundancy and resilience to these same forests and to the broader ecosystem of which they are a central part

seismic investigations of a vent field associated with gas hydrates offshore vancouver island 1 a three dimensional seismic reflection survey was carried out over a gas hydrate field offshore vancouver island in the area of ocean drilling program leg 146 site 889 890 the area of investigation is located on the accretionary prism of the cascadia margin in water depths of 1200 1500 m several seismic blank zones were observed in the seismic data over a frequency range from 30 hz to 3 5 khz where the degree of blanking increases with seismic frequency time slices and selected horizon slices were used to define the spatial distribution of the blank zones the zones range from 80 m to several hundred meters in width one blank zone almost circular with a diameter of 400 m has a distinct seafloor expression it shows the characteristics of a mud carbonate mound and is probably associated with free gas expulsion hydrate was found at four sites with a piston corer within this blank zone at depths of 3 8 m below the seafloor we present a tectonic model that explains the blank zones to be a result of differential uplift along thrust faults the blank zones represent conduits for fluids and gas migrating upward blanking of the seismic energy is believed to be mainly the result of increased hydrate formation in lenses within the faults the blanking effect is enhanced locally because of scattering at carbonates formed at the seafloor

weathering profiles in granitoid rocks of the sila massif uplands calabria southern italy new insights into their formation processes and rates abstract in this paper we characterized several weathering profiles developed on granitoid rocks in the sila massif upland calabria southern italy integrating detailed macro and micromorphological observations with physico mechanical field tests and petrographic mineralogical and geochemical analyses we focused our attention on the main weathering and pedogenetic processes trying to understand apparent discrepancies between weathering grade classes based on field description and geomechanical properties and two common weathering indices such as the micropetrographic index ip and the chemical index of alteration cia our results showed that sericite on plagioclase and biotite chloritization that represent inherited features formed during late stage hydrothermal alteration of granitoid rocks may cause an overestimation of the real degree of weathering of primary mineral grains under meteoric conditions especially in lower weathering grade classes moreover the frequent identification of fe mn oxides and clay coatings of illuvial origin rather than or in addition to those formed in situ both at the macro and microscale may also explain an overestimation of the weathering degree with respect to field based classifications finally some apparent inconsistencies between field geomechanical responses and chemical weathering were interpreted as related to physical weathering processes cryoclastism and thermoclastism that lead to rock breakdown even when chemical weathering is not well developed hence our study showed that particular caution is needed for evaluating weathering grades because traditional field and geochemical petrographic tools may be biased by inherited hydrothermal alteration physical weathering and illuvial processes on the basis of chronological constraints to soil formation obtained from a 42 ka old volcanic input mixed to granite parent materials detected in the soil cover of the sila massif upland a first attempt to estimate soil formation rates was achieved for different depths of corresponding weathering profile zones soil formation rates ranged from 0 01 0 07 mm a 1 for a and bw horizons weathering class vi to 0 04 0 36 mm a 1 for the underlying saprolite c and cr layers class v by comparing these results with the corresponding erosion rates available in the literature for the study area that range from

thermal metamorphism in the lesser himalaya of nepal determined from raman spectroscopy of carbonaceous material the determination of metamorphic conditions is critical to the understanding of the formation of mountain belts however all collisional mountain belts contain large volumes of accreted sediments generally lacking metamorphic index minerals and are therefore not amenable to conventional petrologic investigations by contrast these units are often rich in carbonaceous material making it possible to determine thermal metamorphism through raman spectroscopy of carbonaceous material rscm method a technique that has been recently calibrated beyssac et al j metamorph geol 20 2002 859 871 the lesser himalaya lh is one of these problematic cases with a very poor mineralogy but a key structural position within the himalayan system that makes lh considered as diagnostic of the overall thermal behaviour of the orogen this work demonstrates the performance of the rscm technique and shows that this technique might thus be used to detect inter sample variations as small as 10 15 c but absolute temperatures can only be determined to 50 c due to the uncertainty on the calibration this study reveals that the lh has undergone a large scale thermal metamorphism with temperature decreasing progressively from about 540 c at the top to less than 330 c within the deepest exhumed structural levels

oblique slip and the geometry of normal fault linkage mechanics and a case study from the basin and range in oregon abstract map patterns of normal fault linkages near summer lake oregon show a systematic relationship between echelon step sense oblique slip sense and the position of linking faults where the step sense is the same as the sense of oblique slip e g left step and left oblique slip the faults are linked in the lower part of their relay ramp where the step sense and slip sense are opposite e g left step and right oblique slip the faults are linked in the upper part of the ramp a boundary element code is used to calculate the stress field around echelon normal faults during oblique slip and the model results reveal a relationship similar to the field observations if step sense and oblique slip sense are the same there is a greater potential for deformation ahead of the tip of the front fault and in the lower part of the ramp if step sense and oblique slip sense are opposite there is a greater potential for deformation ahead of the tip of the rear fault and in the upper part of the ramp the field model comparison confirms that oblique slip modifies the mechanical interaction among fault segments and thus influences fault growth and the geometry of fault linkage

orientation history and rheology in slates kodiak and afognak islands alaska abstract theoretical and experimental studies have shown that slates have a roughly parabolic yield curve in and space where is the orientation of cleavage relative to the maximum compressive stress is the orientation of cleavage relative to the incremental shortening direction and is the deviatoric stress deformation mechanisms that operate in low grade rocks such as diffusive mass transfer in a grain boundary fluid dislocation creep and frictional grain boundary sliding may have stress strain rate relationships that depend on during a progressive strain history and may vary as a function of the strain path thus the sequence of dominant deformation mechanisms as well as the stress strain history may depend on the orientation history or variations in as strain accumulates in the kodiak formation a slate belt in southwest alaska the orientation history and deformation mechanisms were evaluated using incremental strain indicators and microstructures there are four successive textural events 1 development of a slaty cleavage s2 with antitaxial growth of fibrous quartz and mica in pressure shadows fi2 2 static growth of siderite and chlorite porphyroblasts 3 10 70 rotation of porphyroblasts relative to s2 with growth of curved syntaxial siderite fibers and 4 antitaxial growth of fibrous quartz and micas with local development of a crenulation cleavage s3 cumulative incremental strain and progressive finite strain histories were determined in 23 samples from syntectonic fibers and orientation histories were reconstructed from information provided by cumulative incremental strain histories textural and strain analyses indicate that 1 the strain history of nearly all samples can be approximated by two coaxial strain accumulations separated by a rigid rotation 2 development of crenulation cleavages was dependent on the orientation history and the magnitude of the early strain accumulation i e the degree of mica alignment at the completion of d2 3 unstable behavior or buckling occurred when suggesting that the angle of internal friction was close to 0 i e basal slip in micas may have been more important than frictional grain boundary sliding and 4 diffusive mass transfer was accompanied by anisotropic plastic deformation so the orientation history could be used to reconstruct the history

variations in temperature gradients identify active faults in the oregon accretionary prism abstract a multi channel seismic survey mcs yields high resolution images of geologic structures within the oregon accretionary prism in addition to revealing the internal geometry of the prism a prominent bottom simulating reflector bsr provides indirect estimates of temperature gradients the bsr marks the phase transition within the pore space of the sediments of small amounts of solid gas hydrate above the reflector to free gas below although the absolute value of temperature gradients depends on assumptions of gas hydrate stability conditions velocity functions and seafloor temperature relative differences reflecting regional trends and local anomalies are unaffected by the assumptions involved in calculation of temperature gradient from the position of the bsr broad scale landward decreases in temperature gradient reflect the increasing depth to the oceanic crust across the accretionary prism correlation of anomalously high temperature gradients with two out of sequence thrusts indicates that these structures are currently acting as conduits for warm fluids

rough faults distributed weakening and off fault deformation 1 we report systematic spatial variations in fault rocks along nonplanar strike slip faults cross cutting the lake edison granodiorite sierra nevada california sierran wavy fault and lobbia outcrops of the adamello batholith in the italian alps lobbia wavy fault in the case of the sierran fault pseudotachylyte formed at contractional fault bends where it is found as thin 1 2 mm fault parallel veins epidote and chlorite developed in the same seismic context as the pseudotachylyte and are especially abundant in extensional fault bends we argue that the presence of fluids as illustrated by this example does not necessarily preclude the development of frictional melt in the case of the lobbia fault pseudotachylyte thickness varies along the length of the fault but the pseudotachylyte veins thicken and pool in extensional bends we conduct a quantitative analysis of fault roughness microcrack distribution stress and friction along the lobbia fault numerical modeling results show that opening in extensional bends and localized thermal weakening in contractional bends counteract resistance encountered by fault waviness resulting in an overall weaker fault than suggested by the corresponding static friction coefficient the models also predict static stress redistribution around bends in the faults which is consistent with distribution of microcracks indicating significant elastic and inelastic strain energy is dissipated into the wall rocks due to nonplanar fault geometry together these observations suggest that damage and energy dissipation occurs along the entire nonplanar fault during slip rather than being confined to the region close to the dynamically propagating crack tip

mid cretaceous to early tertiary apparent polar wander path of the pacific plate pacific apparent polar wander was delineated for mid cretaceous to early tertiary time using 22 seamount paleomagnetic poles 11 paleocolatitudes from azimuthally unoriented cores five effective inclinations from two dimensional magnetic anomaly inversions and one magnetic lineation relative amplitude datum three of the seamount paleomagnetic poles were new data calculated in this study the apparent polar wander path was defined with six mean poles having ages of 39 66 76 82 85 and 94 ma an alternate path was constructed combining data from two pairs of mean poles 66 and 76 ma 85 and 94 ma that were statistically indistinguishable the apparent polar wander path is hook shaped with a nearly right angle bend at 82 ma its post 82 ma section trends north south the pre 82 ma part east west the path indicates uneven polar wander unresolvable polar motion occurred between 66 76 ma and 85 94 ma suggesting stillstands however the large distances between the 85 and 82 ma poles 15 2 3 8 and 82 and 76 ma poles 11 3 2 8 imply rapid polar wander at rates of 5 1 1 3 m y and 1 9 0 5 m y respectively both the sharp bend and rapid polar wander occurred at the end of the cretaceous normal polarity superchron the mid cretaceous paleomagnetic data show a trend suggestive of southward motion of the pacific plate that may be the end of a period of southward drift postulated by others to have begun in the jurassic the evolution of various features of the apparent polar wander path are discussed in terms of plate motion true polar wander and time varying non dipole geomagnetic fields we argue that the overall shape of the polar wander path resulted from the change of pacific plate motion from southward to northward perhaps brought about by the beginning of the subduction of the plate beneath asia

decoupling of sulfur and nitrogen cycling due to biotic processes in a tropical rainforest abstract we examined the terrestrial sulfur s cycle in the wet tropical luquillo experimental forest lef puerto rico in two previously instrumented watersheds icacos and bisley chemical and isotopic measurements of carbon c nitrogen n and s were used to explore the inputs in soil processing and losses of s through comparison to the n cycle additionally the impact of soil forming factors particularly climate organisms topography and parent material on s cycling in this system was considered atmospheric inputs 34 s values of 16 1 2 8 from a mixture of marine and anthropogenic sources delivered an estimated 2 2 g s m 2 yr at icacos and 1 8 g s m 2 yr at bisley bedrock n and s inputs to soil were minimal we estimated a hydrologic export of 1 7 0 1 g s m 2 yr at icacos and 2 5 0 2 g s m 2 yr at bisley stream baseflow s isotope data revealed significant bedrock s in the hydrologic export at bisley with a distinctive 34 s values of 1 6 0 7 but not at icacos pore water data supported the co occurrence of at least three major biological s fractionating processes in these soils plant uptake oxidative degradation of organic s and bacterial sulfate reduction the rates and relative importance of these processes varied in time and space vegetation litter was 3 5 depleted in 34 s compared to the average pore water providing evidence for fractionation during uptake and assimilation out of all abiotic soil forming factors climate especially the high rainfall was the main driver of s biogeochemistry in the lef by dictating the types and rates of processes topography appeared to impact s cycling by influencing redox conditions c n and s content decrease downslope at all sites and the bisley lower slope showed strongest evidence of bacterial sulfate reduction parent material type did not impact the soil s cycle significantly to compare the fate of s and n in the soil we used an advection model to describe the isotopic fractionation of total s and n associated with downward movement of organic matter in both dissolved and solid fractions this model worked well for n but the assumption of a constant fractionation factor with depth failed to describe s transformations this result revealed a fundamental difference between n and s cycling in these soils indicating an apparent greater sensitivity of s isotopes to fluctuating redox conditions

structural evolution of underthrusted sediments kodiak islands alaska the late cretaceous to early tertiary sediments of the kodiak accretionary complex preserve the earliest deformation associated with underthrusting along a thickly sedimented convergent margin because of the thick trench fill this early deformation resulted in the formation of two distinct structural terranes 1 coherent terranes of layered turbidites and 2 melange terranes the earliest deformation d1 in the coherent terranes is marked by normal faults mineralized layer perpendicular veins in sandstones and microfaults in shales these features suggest that 1 was vertical and that 3 was horizontal and nw trending during d1 we interpret d1 structures as hydrofractures that formed in flat lying sediments with high fluid pressures caused by rapid tectonic loading in contrast the melanges appear to record a more protracted and complex history that culminated in structures similar to the d1 structures above we have recognized three successive transitional stages in the melanges i breakup of sand beds along cataclastic shear zones with dispersal of sand inclusions within a relatively ductile shale matrix resulting in the blocks in matrix character of the melange ii development of ductile shear bands that crosscut the melange fabric at a low angle and iii hydrofracturing with the formation of calcite and quartz filled veins in sandstone inclusions and microfaults in the shales the sequence of microstructures associated with stages i iii records increased cohesion of the sediments during deformation dominated by layer parallel shear intense mineralization and microfaulting during stage iii suggest that the melanges are zones of concentrated fluid flow with a fracture dominated permeability stage iii structures are texturally indistinguishable and contemporaneous with the less pervasive d1 structures in the coherent terranes based on these observations we believe that the melanges are major shear zones that formed at the top of the subducting pile and immediately below a major decollement the coherent terranes represent the structurally and stratigraphically lowest sediments and they bypassed the stage i and ii deformations of the melanges because they were the greatest distance from the decollement when they were deformed moreover both the melange and coherent terranes appear to have bypassed the shallow zone of intense horizontal shortening that dominates the toe of the overriding accretionary prism