late miocene coesite eclogite exhumed in the woodlark rift late miocene pliocene eclogites were exhumed in the woodlark rift of eastern papua new guinea an actively extending region west of the woodlark basin seafl oor spreading center we report the discovery of coesite in late miocene eclogite from the lower plate of one of the d entrecasteaux islands metamorphic core complexes within the woodlark rift zircon crys tallization temperatures 650 675 c and 238 u 206 pb age ca 8 ma and rutile thermometry 695 743 c combined with garnet pyroxene thermometry 600 760 c and garnet pyroxene phengite barometry 18 27 kbar indicate that the coesite eclogite was exhumed from mantle depths 90 km to the earth s surface at plate tectonic rates cm yr 1 this late miocene coesite eclogite is the youngest exhumed ultrahigh pressure uhp rock on earth and its preservation ahead of the westward propagating seafl oor spreading center forces reevaluation of models for uhp exhumation as well as the geologic and tectonic evolution of the woodlark rift

geodetic observations of the 2018 mw 7 5 sulawesi earthquake and its implications for the kinematics of the palu fault

large magnitude extensional deformation in the south mountains metamorphic core complex arizona paleomagnetic data are used to test controversial aspects of cordilleran metamorphic core complexes including the original dip of extensional structures origin of the mylonitic front and applicability of rolling hinge models we obtained paleomagnetic data 115 sites 82 accepted for analysis from the weakly deformed interior of a synkinematic footwall intrusive suite and proterozoic footwall rocks of the south mountains metamorphic core complex central arizona these rocks yield dual polarity high unblocking temperature and high to moderate coercivity magnetizations positive baked contact tests indicate that footwall rocks possess primary thermoremanent magnetizations trms or high temperature thermochemical remanent magnetizations tcrms acquired early in their cooling history and during ductile and brittle extensional deformation of structurally higher rocks this is consistent with thermochronologic data indicating rapid synkinematic cooling from crystallization through the range of laboratory unblocking temperatures for the magnetic mineralogy of these rocks between about 22 and 17 5 ma paleomagnetic data are considered as two populations based on the structural asymmetry of the south mountains metamorphic core complex 1 a front side characterized by northeast dipping 10 mylonitic fabrics and brittle extensional structures and 2 a back dipping side characterized by rollover of the mylonitic zone to form a southwest or back dipping 15 mylonitic front comparison of paleomagnetic data from these two sides suggests that the back dipping mylonitic front was synkinematically tilted about 10 down to the southwest the data support a folded shear zone hypothesis for origin of the mylonitic front and the interpretation that footwall rocks possess primary miocene age trms or tcrms a second regional fold test involved data from sites on both flanks of the topographically prominent northeast trending mountain range scale antiform the negative result from this fold test demonstrates that this structure formed early in the extensional history and prior to magnetization acquisition by the plutons we obtained a well grouped footwall grand mean from 62 front side and 20 back dipping site means n 82 d 1 0 i 51 7 k 41 8 95 2 5 we calculated this grand mean with the assumption that front side sites have remained structurally untilted whereas back dipping side sites require removal of 10 of southwest dip this grand mean is statistically indistinguishable 95 confidence level from time averaged miocene expected directions we thus conclude that the current gentle dip of front side mylonites and detachment faults is original therefore both ductile and brittle extensional deformations of the south mountains metamorphic core complex were accommodated along low angle structures dip of 15 our interpretation refutes the widespread applicability of models that predict metamorphic core complexes to represent tilted crustal blocks originally bounded by moderate angle normal faults and does not support rolling hinge models of metamorphic core complex evolution that require a moderate angle ramp

origin of eclogite bearing domed layered metamorphic complexes core complexes in the d entrecasteaux islands papua new guinea compositionally layered metamorphic rocks of the d entrecasteaux islands papua new guinea are folded into domes and antiforms bounded by faults parallel to metamorphic layering and foliation the structures are broadly similar to the metamorphic core complexes of western north america lenses of ultramafic rock lie on the bounding faults and the same faults have served as loci for quaternary andesitic volcanic activity metamorphic grade in the northern islands goodenough and fergusson is amphibolite facies with pockets of eclogite fergusson island only and granulite and is greenschist facies in the southern island normanby in all three islands there is a characteristic tectonostratigraphic sequence fmu sequence from felsic metamorphic rocks at base or internally through mafic metamorphic rocks to ultramafic rocks at top or externally the association of metamorphic and ultramafic rocks apparently developed in a north dipping paleogene subduction system and was exhumed to upper crustal level in the oligocene early miocene possibly by reversal of movement on faults in the former subduction system vigorous uplift and development of domes and antiforms in the pliocene was triggered by westward propagation of the woodlark basin spreading ridge and was accompanied by rifting rift related magmatism rapid erosion and deposition of coarse sediment in the adjacent trobriand basin

failure to bloom intense upwelling results in negligible phytoplankton response and prolonged co2 outgassing over the oregon shelf during summer upwelled water with elevated co2 partial pressure pco2 and nutrients outcrops over the oregon or inner shelf as this water transits across the shelf high rates of primary production fueled by the upwelled nutrients results in net atmospheric co2 drawdown upwelled source waters typically have pco2 approaching 1000 atm that is then reduced to 200 atm for almost the entire month of july 2008 strong and persistent upwelling brought cold 8 c saline 33 5 high pco2 600 atm water to our midshelf buoy site and high pco2 water was broadly distributed over the shelf chlorophyll levels as a proxy for phytoplankton biomass were low 2 mg m 3 on the shelf during the period of most intense upwelling and satellite data showed no evidence of a downstream phytoplankton bloom a small chlorophyll increase to 4 mg m 3 was observed at our buoy site following a decrease in the strength of southward wind stress 10 days after upwelling initiated chlorophyll levels further increased to 10 mg m 3 only after a cease in upwelling these higher levels were coincident with the appearance of water masses having temperature and salinity properties distinct from recently upwelled water we suggest that rapid offshore transport and subsequent subduction before phytoplankton populations could respond is the most likely explanation for the persistent low chlorophyll and elevated surface water pco2 throughout the july upwelling event this mechanism likely dominates under conditions of strong and persistent upwelling favorable winds that coincide with close proximity of low density offshore waters which may have implications for the biogeochemical functioning of this system under future climate scenarios

oceanic corrugated surfaces and the strength of the axial lithosphere at slow spreading ridges abstract we analyse the topography and gravity signature of 39 corrugated surfaces formed over the past 26 myrs in the footwall of axial detachment faults at the eastern southwest indian ridge these corrugated surfaces appear to have formed at a melt supply about half the global melt supply average for mid ocean ridges and we find that their presently elevated topography relative to adjacent non corrugated seafloor was mostly acquired at the end of their formation at the termination stage this configuration which also characterizes many off axis corrugated surfaces in other oceans suggests that the plate flexural rigidity was very low during the formation of the corrugated surface and increased significantly at the termination stage following buck 1988 we hypothesize that stresses related to bending of the plate cause internal deformation and damage in the footwall of the fault which is associated with weakening as a possible mechanism for enhanced footwall weakening while corrugated surfaces form we propose the formation of weak shear zones coated with hydrous minerals such as talc amphibole chlorite and serpentine in mantle derived ultramafics next to gabbro intrusions if this hypothesis is correct the amount of footwall weakening and roll over along axial detachment faults at slow spreading ridges may be controlled both by access to hydrothermal fluids in the footwall of the detachment and by the abundance and distribution of gabbros intrusions in exhumed ultramafics

estuary enhanced upwelling of marine nutrients fuels coastal productivity in the u s pacific northwest 2014 american geophysical union all rights reserved the pacific northwest pnw shelf is the most biologically productive region in the california current system a coupled physical biogeochemical model is used to investigate the influence of freshwater inputs on the productivity of pnw shelf waters using realistic hindcasts and model experiments that omit outflow from the columbia river and strait of juan de fuca outlet for the salish sea estuary outflow from the strait represents a critical source of nitrogen to the pnw shelf accounting for almost half of the primary productivity on the vancouver island shelf a third of productivity on the washington shelf and a fifth of productivity on the oregon shelf during the upwelling season the columbia river has regional effects on the redistribution of phytoplankton but does not affect pnw productivity as strongly as does the salish sea a regional nutrient budget shows that nitrogen exiting the strait is almost entirely 98 of ocean origin upwelled into the strait at depth mixed into surface waters by tidal mixing and returned to the coastal ocean from the standpoint of nitrogen availability in the coastal euphotic zone the estuarine circulation driven by freshwater inputs to the salish sea is more important than the supply of terrigenous nitrogen by rivers nitrogen rich surface waters exiting the strait follow two primary pathways to the northwest in the vancouver island coastal current and southward toward the washington and oregon shelves nitrogen flux from the juan de fuca strait and eddy region to these shelves is comparable to flux from local wind driven upwelling

modulation of the semidiurnal cycle of turbulent dissipation by wind driven upwelling in a coastal embayment with two 25 hour series of turbulent microstructure and currents observations carried out in august 2013 during spring chaos 1 and neap tides chaos 2 we investigated the semidiurnal cycle of turbulent dissipation in an embayment affected by coastal upwelling ria de vigo nw iberia at the time of sampling the bay hosted a net wind driven bi directional positive exchange flow and thermal stratification turbulent kinetic energy tke dissipation e at the interface between upwelled and surface waters was enhanced by two orders of magnitude during the ebbs 10 6 w kg 1 with respect to the floods 10 8 w kg 1 this pattern was caused by the constructive interference of the shear associated with the upwelling and tidal currents the vertical structure of the tidal currents was consistent with a deformation of tidal ellipses by stratification which was tightly coupled to the intensity of upwelling this two pronged interaction resulted in a modulation of the semidiurnal cycle of turbulent dissipation by coastal upwelling thus as a result of the upwelling relaxation conditions experienced during chaos 1 depth integrated interior tke dissipation rates were higher by a factor of 2 compared to chaos 2 by using a simple model we determined that observed variations in turbulent mixing had a limited influence on the tidal variations of stratification which were dominated by straining and advection the mixing mechanism described here is potentially relevant for the ecology of upwelling bays as it can stimulate the transport of nutrients from deep upwelled waters to the sun lit surface layers where primary production takes place

the rate of oceanic detachment faulting at atlantis bank sw indian ridge abstract the rates of slip on oceanic detachment faults and how those rates compare to sea floor spreading rates constitute fundamental data required to constrain how oceanic core complexes form and their role during crustal accretion we combine sea surface magnetic data with the magnetic polarity of shallow core samples and pb u shrimp ages of igneous zircon to determine the time averaged half spreading rate during oceanic detachment faulting at atlantis bank 100 km south of the ultraslow spreading southwest indian ridge swir the pb u zircon ages correlate well with the magnetic ages and so highlight that magmatic accretion and faulting were coeval for over 2 myr creating and exposing a 1 5 km thick layer of gabbro for 35 km parallel to spreading we use bivariate linear regression of distance age data and forward modeling of magnetic anomaly data to calculate a half spreading rate during detachment faulting of 14 1 1 8 1 5 km myr 95 confidence limits when integrated with regional constraints on spreading history we note that detachment faulting coincided with a short lived regional increase in the full spreading rate along the swir and for the ridge segment containing atlantis bank spreading was highly asymmetric with 80 of plate motion accommodated by detachment faulting consequently the detachment fault effectively formed the plate boundary at the surface in this spreading segment highly asymmetric spreading was confined to the spreading segment containing atlantis bank and to the duration of detachment faulting so the ridge segment containing atlantis bank migrated northward relative to its symmetrically spreading eastern neighbour such that the intervening non transform discontinuity shortened we suggest that the highly asymmetric spreading may be a characteristic feature of oceanic detachment faulting an inference supported by more poorly constrained half spreading rates determined at several other oceanic core complexes

low angle range flank faults in the panamint inyo and slate ranges california implications for recent tectonics of the death valley region four of the mountain ranges near death valley california display exhumed low angle normal faults on their flanks features originally referred to as turtleback structures these fault surfaces are smooth planar to curviplanar and defined by faceted spurs and coincident interfluve crests the lowest parts of these faults are overlain in tectonic contact by poorly indurated fanglomerate and locally by quaternary volcanic rocks steep fault scarps in alluvium are present at the foot of each turtleback type flank although these may be examples of active low angle normal faults it is difficult to establish the dip histories of these faults the problem with constraining the dip histories is one of missing and concealed information because the exposed hanging wall rocks are some of the youngest material cut and displaced by the currently shallow dipping faults another important relationship along these range flanks is the intersection between the low angle faults and steep scarp forming faults that cut alluvium at the range fronts although this relationship remains unconstrained in most of the ranges a shallow dipping fault is cut by one of the steep faults in panamint valley suggesting that in one area at least the low angle faults are not active the low angle faults and not the steep neotectonic faults are probably responsible for most of the opening of the present valleys because each low angle fault intersects the valley floor at the range front none of the low angle faults are perched high in the ranges as would be the case if the steep faults had uplifted them significantly therefore even if there has been a geologically recent transition from low angle normal faulting to steep normal with or without strike slip faulting the modern topography still reflects the former regime strictly speaking the death valley region may not be an example of active low angle normal faults and supradetachment basins

mechanics of extensional wedges the extensional wedges that overlie low angle basal detachment faults are characterized by a tapered cross section similar to that exhibited by a fold and thrust belt but with an opposite sense of shear on the basal fault such wedges are common in zones of crustal extension such as the basin and range province of the north american cordillera the north sea and the u s gulf coast this paper examines the mechanics of these upper crustal extensional wedges using a modification of the compressional coulomb critical taper model developed for fold and thrust belts and accretionary wedges if a compressional wedge is mechanically analogous to a wedge of soil being pushed up an incline by a moving bulldozer then an extensional wedge is analogous to the same wedge with the bulldozer moving in reverse gear down the incline a critically tapered extensional wedge is one that is on the verge of coulomb failure everywhere a wedge whose taper is narrower may be slid stably down the same incline without internal deformation a wedge whose taper is greater will fail by normal faulting and reduce its taper until it is critical after testing the quantitative predictions of this extensional critical taper theory in a series of laboratory experiments on dry sand wedges we apply the theory to a pair of active extensional wedges in the brazos area offshore texas both wedges are underlain by well imaged basal detachment faults dipping at 17 o down to depths of 10 km one wedge exhibits relatively little internal deformation whereas the other is pervasively faulted along a series of moderately dipping synthetic normal faults direct and indirect estimates of the pore fluid pressure distribution within the two wedges suggest that the undeformed wedge is stable whereas the pervasively faulted wedge is unstable but nearly critical regional values for the coefficients of basal and internal friction in excess of 0 3 together with vertical cohesion gradients in excess of 1 kpa m are consistent with the observed pore pressures and the geometry of the wedges as well as with in situ stress data acquired during drilling and the dips of active synthetic normal faults such values are comparable to values inferred from mechanical and thermal models of compressional wedges and they are consistent with laboratory rock mechanics data

potential and timescales for oxygen depletion in coastal upwelling systems a box model analysis a simple box model is used to examine oxygen depletion in an idealized ocean margin upwelling system near bottom oxygen depletion is controlled by a competition between flushing with oxygenated offshore source waters and respiration of particulate organic matter produced near the surface and retained near the bottom upwelling supplied nutrients are consumed in the surface box and some surface particles sink to the bottom where they respire consuming oxygen steady states characterize the potential for hypoxic near bottom oxygen depletion this potential is greatest for faster sinking rates and largely independent of production timescales except in that faster production allows faster sinking timescales for oxygen depletion depend on upwelling and productivity differently however as oxygen depletion can only be reached in meaningfully short times when productivity is rapid hypoxia thus requires fast production to capture upwelled nutrients and fast sinking to deliver the respiration potential to model bottom waters combining timescales allows generalizations about tendencies toward hypoxia if timescales of sinking are comparable to or smaller than the sum of those for respiration and flushing the steady state will generally be hypoxic and results indicate optimal timescales and conditions exist to generate hypoxia for example the timescale for approach to hypoxia lengthens with stronger upwelling since surface particle and nutrient are shunted off shelf in turn reducing subsurface respiration and oxygen depletion this suggests that if upwelling winds intensify with climate change the increased forcing could offer mitigation of coastal hypoxia even as the oxygen levels in upwelled source waters decline

detachment faults evidence for a low angle origin the origin of low angle normal faults or detachment faults mantling metamorphic core complexes in the southwestern united states remains controversial if sigma sub 1 is vertical during extension the formation of or even slip along such low angle normal faults is mechanically implausible no records exist of earthquakes on low angle normal faults in areas currently undergoing continental extension except from an area of actively forming core complexes in the solomon sea papua new guinea in light of such geophysical and mechanical arguments w r buck and b wernicke and g j axen proposed models in which detachment faults originate as high angle normal faults but rotate to low angles and become inactive as extension proceeds these models are inconsistent with critical field relations in several core complexes the rawhide fault an areally extensive detachment fault in western arizona propagated at close to its present subhorizontal orientation late in the tertiary extension of the region neither the wernicke and axen nor buck models predict such behavior in fact both models preclude the operation of low angle normal faults the authors recommend that alternative explanations or modifications of existing models are needed to explain the evidence that detachment faults form and operate with gentle dips

mesoscale biogeochemical responses to iron fertilization in the upper layers of the southern ocean iron experiment areas 1 during the southern ocean iron experiment sofex january february 2002 two iron fertilization experiments were conducted at the south 66 45 s 171 8 w and north 56 23 s 172 w patches the south patch was replete with all macronutrients whereas the north patch was nearly depleted of silicate using a towed water sampling measurement system high resolution three dimensional observations of temperature salinity co2 partial pressure pco2 and the concentrations of total co2 tco2 nitrate phosphate and silicate in the upper 100 m were obtained 10 and 28 days after initial iron additions in the south and north patches respectively tco2 and nutrient drawdowns observed in the south patch were small due to wind events that limited biological response in the early postfertilization period at the north patch drawdown signals were stronger resulting from the longer time since fertilization the north patch was dispersed along a frontal zone between two distinct waters with the denser subducted under the lighter subduction limited co2 uptake from the air but provided alternative mechanisms for vertical carbon export based on the biogeochemical drawdowns and published estimates of the rate of the entrainment of nonfertilized waters into the patch the mean net community productivity over 28 days was estimated to be 94 12 mmol carbon m 2 day 1 to which the air to sea flux contributed only 2 despite low silicate concentrations and potential limitation of growth of silicifying plankton in the north patch our estimates of the enhanced carbon uptake are similar to estimates from higher silicate environments citation hales b and t takahashi 2012 mesoscale biogeochemical responses to iron fertilization in the upper layers of the southern ocean iron experiment areas j geophys res 117 c01018 doi 10 1029 2011jc006956

convectively driven mixing in the bottom boundary layer closely spaced vertical profiles through the bottom boundary layer over a sloping continental shelf during relaxation from coastal upwelling reveal structure that is consistent with convectively driven mixing parcels of fluid were observed adjacent to the bottom that were warm by several millikelvin relative to fluid immediately above on average the vertical gradient of potential temperature in the superadiabatic statically unstable bottom layer was found to be 21 7 3 1024 km 21 or 6 0 3 1025 kg m24 in potential density turbulent dissipation rates increased toward the bottom but were relatively constant over the dimensionless depth range 0 4 1 0z d where d is the mixed layer height the rayleigh number ra associated with buoyancy anomalies in the bottom mixed layer is estimated to be approximately 1011 much larger than the value of approximately 10 3 required to initiate convection in simple laboratory or numerical experiments an evaluation of the data in which the bottom boundary layer was unstably stratified indicates that the greater the buoyancy anomaly is the greater the turbulent dissipation rate in the neutral layer away from the bottom will be the vertical structures of averaged profiles of potential density potential temperature and turbulent dissipation rate versus nondimensional depth are similar to their distinctive structure in the upper ocean during convection nearby moored observations indicate that periods of static instability near the bottom follow events of northward flow and local fluid warming by lateral advection the rate of local fluid warming is consistent with several estimates of offshore buoyancy transport near the bottom it is suggested that the concentration of offshore ekman transport near the bottom of the ekman layer when the flow atop the layer is northward can provide the differential transport of buoyant bottom fluid when the density in the bottom boundary layer decreases up the slope

shortening in the upper plate of the buckskin rawhide extensional detachment fault southwestern u s and implications for stress conditions during extension commonwealth post graduate research award u s geological survey national cooperative geologic mapping program under statemap g11ac20455

an assessment of source parameters of earthquakes in the cordillera of the western united states abstract source parameters for 50 earthquakes occurring between 1915 and 1988 have been used to examine the faulting characteristics of magnitude 5 5 to 7 8 earthquakes within the western u s cordillera an area extending from the eastern sierra nevada to the great plains and from northwestern montana to trans pecos texas source parameters used in this study include seismic information from first motion analyses body and surface waveform modeling geodetic studies and geological studies of surface faulting the principal results of this analysis include 1 all earthquakes occurred on faults dipping 38 or more and no evidence for listric of low angle planar faulting was found 2 all m 7 0 earthquakes occurred at depths 12 km and were composed of multiple subevents 3 most earthquakes 70 per cent had unilateral ruptures and 4 no individual subevent had a rupture length 21 km

seismic reflection evidence for seismogenic low angle faulting in southeastern arizona focal mechanisms for large m 6 earthquakes in extensional terranes suggest that seismogenic normal faults have dips that range from approximately 30 degree to approximately 70 degree geologic relations suggest that low angle faults have accommodated large scale upper crustal extension these disparate observations are often reconciled by arguments that low angle faults move aseismically or rotate to low angles from initially high angles seismic reflection data from the tucson basin in southeast arizona image a low angle normal fault the santa rita fault that crops out along the trend of late quaternary fault scarps caused by large magnitude m approximately 6 7 7 6 earthquakes velocity independent dip analysis from shot records of the santa rita fault indicates that it has a true dip of approximately 20 degree to a depth of at least 6km this observation suggests that low angle extensional faults indeed may be seismogenic and that actual mechanisms for accommodation of upper crustal extension depend on local conditions of stress and preexisting geologic structure

active normal faulting and crustal extension a world wide review of fault plane solutions and focal depths for large normal faulting earthquakes on the continents shows that the overwhelming majority of such earthquakes nucleate in the depth range 6 15 km on faults dipping between 30 and 60 in the few cases where levelling or seismic data are good enough these normal faults are shown to be approximately planar from the surface to their nucleation depth at the base of the brittle crust there is evidence that in some cases as a result of the enormous transitory increase in strain rate during large earthquakes rupture continues into the normally ductile lower crust on surfaces with substantially gentler dips these low angle surfaces may be analogous to some of the detachments seen in metamorphic core complexes of the western usa but the nature of the motion on them depends on strain rate as well as on rheological contrasts between the detachments and the blocks on either side such contrasts however are unlikely to introduce substantial curvature to an originally planar shear zone if the observed spread in active normal fault dips is caused by rotation of the faults and the blocks they bound during extension then a maximum value of 1 7 can be accommodated by seismic activity on a single generation of normal faults with continued extension either a new generation of steeper faults cutting the rotated first faults is likely to form or the deformation will continue aseismically on faults dipping at less than 30 large earthquakes have not been observed to nucleate on very low angle 20 normal faults within the continental crust anywhere in the world such faults can of course move aseismically but are unlikely to do so on a large scale within the upper crust in areas where steep normal faults are seismically active thus extensional models that require concentrated simple shear on large sub horizontal faults within the brittle upper crust will also require a spatial separation between aseismic very low angle faulting and seismic highangle faulting since seismogenic high angle faults dominate the topography of extending regions upper crustal very low angle faulting if it occurs on a large scale presumably does so in areas that are relatively fiat

realization of new production in coastal upwelling areas a means to compare relative performance a theoretical basis for analyzing new production of upwelling centers under various conditions and for comparing the relative performance of different upwelling centers has been developed using the concept of shift up or acceleration of n03 uptake no concentration at the beginning of an upwelling cycle determines the rate of acceleration the maximal specific no uptake rate and the maximal new production rate achieved the relationship between initial no concentration and new production rate is nonlinear and a doubling of initial no concentration results in a threefold increase in new production the tendency for new biomass to increase during an upwelling cycle varies widely between different upwelling regions and by comparing theoretical predictions with data the performance of an upwelling system can be judged against optimal expectations and the realization of potential new production by the system estimated among upwelling centers at cap blanc northwest africa 15 off the coast of peru and point conception california the least of this potential is realized at point conception new production that portion of the primary production based upon entry of new primary nutrient into the euphotic zone is the basis for net transfer of co2 from the atmosphere to the ocean and of the transport of c to the deep ocean by sinking of particles eppley and peterson 1979 martin et al 1987 one definition of new production is the productivity that results from the upward vertical flux of n03 dugdale and goering 1967 and consequently the uptake of that n03 by phytoplankton this flux proceeds relatively slowly over most of the oceans more actively along the equatorial divergences and very rapidly in coastal upwelling regions it follows that the coastal upwelling regions also must contribute a disproportionately large share of global new production ryther 1969 examination and modeling of the entire productivity cycle occurring in a coastal upwelling system yields information necessary

late miocene to pliocene crustal extension and lithospheric delamination revealed from the 5 ma palopo granodioritic intrusion in western sulawesi indonesia abstract recent studies have revealed that following collision between the western sulawesi and sula spur microcontinents during the early to middle miocene the western sulawesi microcontinent subsequently underwent extension however the geodynamic process that resulted in extension is unknown the petrogenesis of late miocene to pliocene granitoids in the region provides insights to the mechanism of extension to achieve this goal we studied the palopo granodioritic intrusion a well exposed representative pluton that crops out along the palu koro fault zircon u pb dating indicates a 4 8 4 7 0 1 ma crystallization age for the pluton compared with arc igneous rocks the pluton has high sr contents and low y and yb contents with relatively high sr y and lan ybn ratios these geochemical signatures are similar to those of typical adakites the samples exhibit high mgo 1 60 2 54 wt cr 46 65 ppm and ni 14 1 19 0 ppm contents relative to adakitic rocks derived from thickened lower crust in addition negative ehf t 9 7 to 5 5 and end t 8 5 to 11 1 values together with relatively low 143nd 144nd and high initial 87sr 86sr ratios reflect an origin through recycling of ancient crustal materials which is clearly different from adakites derived from melting of a subducting slab the most plausible mechanism for generation of the late miocene pliocene adakitic granodiorites in the western sulawesi microcontinent is partial melting of delaminated lower crust that interacted with the mantle we propose that the late miocene to pliocene crustal extension in the western sulawesi microcontinent was triggered by delamination of pre existing thickened lithosphere

possible seismogenic shallow dipping normal faults in the woodlark d entrecasteaux extensional province papua new guinea active normal faults dipping less than 30 have not been documented in the seismic record but they are commonly observed in geologic structures one interpretation is that seismogenic low angle faulting is physically impossible and that the geologic structures do not form at shallow dips to better examine this problem teleseismic body waves were inverted to determine source parameters for five large earthquakes in the woodlark d9entrecasteaux region a rare example of active continental extension associated with pliocene quaternary metamorphic core complexes the inversions show that at least two and possibly four events are consistent with normal dip slip on shallow dipping faults the largest earthquake m w 6 8 is located near the mapped core complexes the shallow dipping plane for this event determined to dip between 10 and 25 is nearly coplanar to the faults bounding the core complexes and may represent slip on these or other parallel low angle structures although slip on the conjugate high angle plane cannot be ruled out observations of quaternary uplift and the similarity to the adjacent core complex bounding structures favor motion on the low angle plane similar earthquake mechanisms have not yet been documented in most other extensional provinces perhaps because instances of active core complex exhumation are rare

cordilleran metamorphic core complexes in arizona a contribution from geomorphology cordilleran metamorphic core complexes consist of granitic cores surrounded by in an outward direction mylonite chloritic breccia and microbreccia these rocks are separated by a low angle detachment fault from typically unmetamorphosed but normally faulted rocks rocks above the detachment fault have been transported relative to the core rocks in one consistent direction giving a distinct lineation to rocks below the detachment fault dome shaped metamorphic core complex mountains show considerable structural control of landforms mylonitic rocks develop triangular dome facets around the margins and low relief areas in the central parts of the complexes chloritic breccia is much less resistant to erosion and has been almost completely removed from many complexes drainage patterns in metamorphic core complexes are mainly radial but an older set of drainage lines parallel to mylonitic lineation especially channels that drain down the crests of antiformal ridges suggests that drainage developed on a ramp on the detachment fault and the underlying breccia prior to lineation parallel arching

normal faulting in the upper continental crust observations from regions of active extension abstract observations of present day normal faulting in regions of active continental extension may be helpful when interpreting the geological record in older extensional basins the most obvious manifestation of active extension is normal faulting in earthquakes earthquake foci are mostly confined to the upper seismogenic continental crust whose thickness imposes a scale on the observed deformation large earthquakes move faults with lengths similar or large compared with the thickness of the seismogenic layer large seismogenic normal faults on the continents appear to be restricted to a dip range of around 30 60 dips significantly gentler than 20 have not been observed in fault plane solutions of large earthquakes large seismographic normal faults are approximately planar in cross section and cut through the base of the upper seismogenic layer rotating about a horizontal axis as they move a reasonable estimate of the regional extension can often be made from the dip of the large normal faults and the tilt of the blocks they bound the domino model such faults are rarely continuous for more than 15 20 km but commonly change strike or step in an en echelon fashion this segmentation may occur on a scale controlled by the thickness of the seismogenic layer and is an important influence on sedimentation and drainage these observations are common to large seismogenic normal faults from a variety of tectonic settings and suggest that the kinematics of normal faulting may not be strongly influenced by the forces responsible for the extension which can vary widely in nature and magnitude small earthquakes which move faults that are small compared with the seismogenic layer thickness show no simple pattern and often can be interpreted as internal deformation of blocks bounded by large faults in some places the seismogenic basement faults do not reach the surface but are decoupled from the sedimentary cover by layers of weak lithology faults in the sedimentary cover may be strongly curved in cross section requiring their hangingwalls to deform internally estimating extension from such faults is not straightforward and requires a knowledge of the hangingwall deformation estimates made in this way are often very non unique and prone to large errors we postulate that the thickness of the seismogenic upper crust controls both the maximum length of large normal fault segments along strike and the maximum size of blocks that can rotate coherently about a horizontal axis

experimental constraints on metal transport in fumarolic gases abstract metals are efficiently transported in a gas phase and the gas composition strongly affects transport rates of these metals in the gas phase here we present a new approach to systematically investigate metal transport and deposition from volcanic gases of different compositions we test the effect of sulfur and chlorine on the volatilization of 30 metal oxides and the phases deposited along a temperature gradient of 1250 300 c in evacuated silica glass tubes in water free systems in total we observe 30 different deposited phases including oxides sulfides and chlorides the experimental results are compared with closed system and open system thermochemical equilibrium calculations the closed system calculations provide insights into the metal speciation in the gas phase and the open system calculations provide thermodynamic predictions of the temperature ranges over which metals deposited from the gas phase both approaches only partially reproduce the experimental observations of the deposited phases in the silica glass tubes however when we compare our experimental results with records from fumaroles on three different volcanoes kudriavy volcano russia la fossa crater on vulcano italy and momotombo nicaragua we find that our experiments agree very well with natural observations we suggest that similar experimental investigations are powerful tools in the study of metal transport in ore forming systems involving gas phases and results may be applied to various processes in terrestrial and planetary environments

collision rotation and the initiation of subduction in the evolution of sulawesi indonesia the island of sulawesi indonesia has been shaped and deformed as a result of collision with the sula platform a sliver of continental material from the northern margin of australia new guinea the collision has resulted in rotation of the north volcanic arm of sulawesi and the development of the accretionary wedge of the north sulawesi trench the north sulawesi trench changes laterally from a zone of no active deformation in the eastern part to a wide accretionary wedge in the west early stages of thrusting produce a steep frontal slope 8 16 indicative of relatively high basal shear stress whereas the more advanced western zone of thrusting produces a gentle 2 slope consistent with low basal shear stress reported paleomagnetic data suggest post late eocene counter clockwise rotation of the north arm and the offshore geophysics are explained by a pivot of the north arm with respect to the celebes basin about the eastern end of the arc convergence between the north banda basin and southeast sulawesi is documented by the presence of the tolo thrust its outcrop is strongly arcuate and its accretionary wedge varies in width from a minimum of a few kilometers at each end to a maximum of 30 40 km in the central part the northern end transforms to the leftlateral matano fault with a reported offset of 20 km the southern end of the thrust projects toward the deformed rocks of buton but the structural relations there are not clear the matano fault zone appears to connect westward with the palu fault which forms the western transform of the north sulawesi trench the palu matano fault system acts as a trench trench transform between the north sulawesi trench and the tolo thrust and this system is described by the same rotation pole as that for the sulawesi north arm

flexural rotation of normal faults a conceptual model is proposed for the generation of low angle normal faults in metamorphic core complexes the model is based on three assumptions 1 the isostatic response to normal fault motion is of regional extent 2 when a fault segment is significantly rotated from the optimum angle of slip relative to the crustal stress field it is replaced by a new planar fault oriented in the optimum direction and 3 the fault cuts the entire upper crust and fault motion always nucleates in the same region at the base of the upper crust the stress field is considered to be uniform through the crust and the regional isostatic response of the crust to loads is computed using the thin plate flexure approximations active low angle normal faults are difficult to reconcile with rock mechanics theories earthquake focal mechanism studies and geochronologic results indicating rapid cooling of core complex rocks the model does not require active fault slip on low angle faults the flexural response to normal faulting is shown to be significantly affected by anelastic behavior of the crust and by loading due to sedimentation the anelastic response to large bending stresses results in significant reduction in the effective elastic rigidity of the upper crust this can explain the observed short wavelength of topographic response to normal fault loads the model results in 1 a nearly flat lying abandoned normal fault or detachment below slices of upper plate rocks and sedimentary infill 2 a strong contrast in metamorphic grade across the abandoned detachment 3 rapid movement of lower plate rocks from midcrustal depths to shallower depths these results are qualitatively in agreement with geologic observations for core complexes

noncohesive critical coulomb wedges an exact solution active fold and thrust belts or submarine accretionary complexes can be modeled as critically tapered wedges of material on the verge of coulomb failure everywhere overlying a basal decollement where frictional sliding is occurring ignoring cohesion the four strength parameters needed to describe a critical coulomb wedge are its internal and basal coefficients of friction and b and its internal and basal hubbert rubey fluid pressure ratios and b an exact relation between surface slope and basal dip of a noncohesive critical wedge with uniform properties is derived the state of stress within such a wedge has the same orientation everywhere and is constant if is and vice versa a coefficient of internal friction 1 1 is consistent with the known surface slope basal dip and pore fluid pressures in the active fold and thrust belt of western taiwan assuming that byerlee s law b 0 85 is valid on the base the wide variety of tectonic styles observed to occur along convergent margins including subduction erosion active accretion subduction without accretion and even extension and normal faulting may be controlled by relatively small spatial or temporal variations in either b or b

tectonic evolution of the priest river complex northern idaho and washington a reappraisal of the newport fault with new insights on metamorphic core complex formation new geologic mapping 40ar 39ar thermochronometry and geobarometry in the middle eocene priest river metamorphic core complex provide the basis for unraveling the role of en echelon fault systems in core complex formation and for determining the scale of crustal fragments that form during continental extension four faults occur in the priest river complex the east verging purcell trench fault zone on the eastern side consists of two distinct en echelon fault segments separated by an unfaulted homocline the u shaped newport fault system on the northwestern side is a conjugate normal fault set the west verging eastern newport fault terminates within the silver point wrencoe pluton which was intruded syntectonically into the fault zone the east verging western newport fault merges with the east verging spokane dome mylonite zone in the underlying infrastructure new geobarometric data show that this midcrustal shear zone which evidently forms part of the regional basal decollement of the cordilleran fold and thrust belt also records significant eocene extensional shearing rocks that formed beneath the mylonite zone at a depth of 30 35 km are juxtaposed against rocks that formed at a depth of 10 km above the zone eocene 40ar 39ar chrontours in the southern part of the infrastructure record progressive exhumation and quenching that becomes younger eastward in the northern fragment of the infrastructure alternating domains of progressive westward exhumation quenching and progressive eastward exhumation quenching occur beneath the eastern newport fault and the northern purcell trench fault respectively these relationships form the basis for a new model of the evolution of the priest river complex the southern part of the infrastructure was exhumed by a major east verging detachment system comprising the western newport fault and the reactivated eastern part of the spokane dome mylonite zone into which the western newport fault merges this master detachment fault which roots in the southern purcell trench on the east side of the core complex plunges beneath the northern part of the infrastructure the selkirk crest block below the detachment the infrastructure appears to be intact above the detachment the crust extended along a set of relaying conjugate detachment faults these faults are the eastern newport fault and the north and south purcell trench faults kinematic analysis shows that the selkirk crest block is a crustal scale extensional horse that was stranded as continued extension moved the underlying metamorphic infrastructure out from beneath it and toward the west along the master detachment this study shows that large tracts of midcrustal rocks can be translated and stranded as allochthonous fragments during continental crustal extension

on the role of isostasy in the evolution of normal fault systems the footwalls of west dipping normal faults that separate the west central colorado plateau from the basin and range province record at least 5 7 km and perhaps as much as 15 20 km of west side up neogene uplift with an axis just 10 20 km west of undeformed plateau strata the uplift is expressed as folding and steep faulting in pre tertiary cratonic and disconformably overlying neogene strata forming a basement cored anticline and coincident topographic high on the western margin of the plateau the authors interpret the uplift as a nonelastic response of the crust to buoyancy forces accompanying the tectonic denudation of the plateau margin profound isostatically driven deformation of the footwalls of major normal faults may be common in extensional terrains calling into question several assumptions fundamental to existing models of the evolution of normal fault systems

field tests of rolling hinges existence mechanical types and implications for extensional tectonics in rolling hinge models a locus of isostatic footwall uplift migrates together with the withdrawing hanging wall of a large displacement tens of kilometers normal fault a fault bend fold that migrates through the footwall results causing progressive deactivation of the updip part of the fault as it is tilted to a lower dip rolling hinge migration should leave a discernible geologic record but compelling tests are difficult to design because predictions of rolling hinge models are nonunique and alternative models commonly can explain individual data sets field tests based on thermochronology paleomagnetism and structural analysis are typically applied to footwall rocks whereas sedimentology geochronology of volcanic rocks and structural analysis are typically applied to upper plate rocks we review existing theoretical models and case studies in 14 detachment terranes some negative results are reasonably compelling but positive tests as yet tend to permit rather than demand a rolling hinge locally both positive and negative conclusions have been reached about the passage of a hinge within the same terrane such differences in interpretation may depend more on the scale of observation or on the specific model considered than on the geological development of the area subvertical simple shear and flexural failure mechanisms with or without significant induced flow of lower crustal material are thought to dominate hinge related footwall deformation in individual sites although rolling hinge models offer an alternative to low initial fault dips hinge related deformation does not demand a steep initial fault dip few areas in which rolling hinge tectonics are permissible had initially steep faults 35 rather where the evidence most strongly favors a rolling hinge detachment faults had initial dips 35 in the future conclusive results are most likely to be obtained if diverse tests are applied to both the upper and lower plates of detachment terranes where other geological sources of ambiguity are minimal at best the rolling hinge mechanism does not universally explain the observation that earthquakes are rare on low angle normal faults nor solve the mechanical problems of frictional slip on such faults

geometry and kinematics of shear zones formed during continental extension in eastern papua new guinea abstract the d entrecasteaux islands eastern papua new guinea lie in an area of continental extension that has been active since the mid miocene during the last 4 ma the metamorphic basement rocks composing most of the islands have been uplifted and tectonically exhumed from depths of approximately 35 km tectonic exhumation appears to have been controlled by deformation in broad kilometre scale mylonitic shear zones a progressive evolution is documented in the shear zones characterized by increasing localized deformation a change from dominantly ductile to dominantly brittle processes and decreasing metamorphic grade i e retrograde metamorphism the evolution is believed to be the result of uplift and cooling of the basement accompanying shear zone movement the kinematic history of the shear zones is complex a number of sinistrally offset extensional detachment zones separate a multiply deformed high grade metamorphic basement from a cover of largely undeformed ultramafic and mafic cover rocks the detachment zones are connected by transverse shear zones these transverse zones appear to act as sinistral strike slip zones which also accommodate transfer motion between the detachment zones

structural evolution of the dayman dome metamorphic core complex eastern papua new guinea a shallow dipping ductile mylonitic shear zone and concordant brittle detachment fault mai iu fault together make up the dominant geological structure that controls the orientation of dip slopes on the fl anks of mount dayman eastern papuan peninsula papua new guinea the dip slopes dip in all directions from the peak of mount dayman and form a domed landform that is much less dissected by streams compared to the adjacent mount suckling domed landform the orientation of megacorrugations on the domed surface of mount dayman footwall is consistent with nne directed transport of the hangingwall block which is composed of low grade undifferentiated volcanic and sedimentary rocks and minor ultramafi c rocks though previously documented as a thrust surface the geometry and style of structures and map relations presented in this study indicate an extensional origin for the domed mylonitic foliation s1 and mineral elongation lineation l1 the fi eld relationships are consistent with the domed landform comprising the core of a metamorphic core complex observations of dominantly nne trending regional lineaments in aerial photography and shuttle radar topography mission srtm data correlate with detailed fi eld analysis of mineral elongation lineations l1 in the main metamorphic core complex bounding shear zone field relationships show a crosscutting sequence of structures that includes 1 ductile s2 folia with ese plunging blue sodic calcic amphibole mineral elongation lineations 2 narrow steeply dipping ductile d2 shear zones and 3 semibrittle to brittle fault zones s c fabrics asymmetric strain shadows around porphyroclasts and fault drag indicate a top down to the nne sense of shear for most structures kinematic vorticity analysis of the highest grade ductile deformation indicates a kinematic vorticity number wk between 0 34 and 0 56 suggesting general shear for the early stage of deformation d1 the nne directed lineaments and l1 mineral elongation lineations are consistent with the australia woodlark eulerian pole for periods between the early pliocene 3 6 ma and pleistocene 0 52 ma this observation is consistent with ca 3 3 ma granite and monzonite intrusions that cut the mylonitic fabrics and limit the age of the mylonitic fabrics to older than 3 3 ma on mount suckling a se dipping sedimentary sequence gwoira conglomerate characterizes part of the hanging wall of the metamorphic core complex petrography of the clasts within the sedimentary rocks indicates that metabasite rocks were the dominant source the unit is in fault contact with the metabasite footwall across prehnite bearing d3 brittle fault zones

effects of western boundary current dynamics on the internal wave field of the southeast florida shelf 1 shelf sea internal wave fields are typically highly variable and dominated by wind and tidal forces however this is not necessarily true for outer shelf regions or very narrow shelves where remote physical processes originating over the slope or deep ocean may exert a strong influence on the internal wave climate during the summers of 2003 and 2004 observational studies were conducted to examine the effects of a western boundary current the florida current tides and wind on the mean currents and internal wave field on the outer southeast florida shelf wavelet analyses of nonstationary shelf currents coupled with altimetry images of the straits of florida reveal the strong influence of florida current fluctuations on outer shelf flows local winds were found to be a small factor in flows on the outer shelf region and tidal forcing diurnal and semidiurnal accounted for less than a third of the total barotropic variance high frequency internal waves dominate the internal wave field and result in bottom intensified currents and strong shoreward mass transport we present evidence that suggests that the florida current plays as large a role in the determination of the high frequency internal wave field as tidal forces these observations and analyses show that it is necessary to include the forcing from the florida current meanders and instabilities in order to predict accurately the episodic nature of the internal wave field on the southeast florida shelf

aragonite saturation state dynamics in a coastal upwelling zone 1 coastal upwelling zones may be at enhanced risk from ocean acidification as upwelling brings low aragonite saturation state ar waters to the surface that are further suppressed by anthropogenic co2 ar was calculated with ph pco2 and salinity derived alkalinity time series data from autonomous ph and pco2 instruments moored on the oregon shelf and shelf break during different seasons from 2007 to 2011 surface ar values ranged between 0 66 0 04 and 3 9 0 04 compared to an estimated pre industrial range of 1 0 0 1 to 4 7 0 1 upwelling of high co2 water and subsequent removal of co2 by phytoplankton imparts a dynamic range to ar from 1 0 to 4 0 between spring and autumn freshwater input also suppresses saturation states during the spring winter ar is less variable than during other seasons and is controlled primarily by mixing of the water column

coastal upwelling in the california current system abstract coastal upwelling in the california current system has been the subject of large scale studies off california and baja california and of small scale studies off oregon recent studies of the winds along the entire coast from 25 n to 50 n indicate that there are significant along shore variations in the strength of coastal upwelling which are reflected in the observed temperature distribution active upwelling appears to be restricted to a narrow coastal band about 10 25 km wide along the entire coast but the region influenced by coastal upwelling may be much wider intensive observations of the upwelling zone during summer off oregon show the presence of a southward coastal jet at the surface a mean vertical shear a poleward undercurrent along the bottom and persistently sloping isopycnals over the continental shelf most of the upwelling there occurs during relatively short periods several days long of upwelling favorable winds during the upwelling season off oregon the offshore ekman transport is carried by the surface ekman layer and the onshore return flow occurs through a quasi geostrophic interior it is not known whether the structure and dynamics observed off oregon are typical of the upwelling zone along the entire coast though some of the same features have been observed off baja california current and future research will eventually show whether the oregon results are also applicable in the region of persistently strong upwelling favorable winds off northern california and in the region of complex bathymetry off central and southern california

distribution and variability of iron input to oregon coastal waters during the upwelling season generally higher in spring mean of 2 1 and 33 9 nmol l 1 respectively than in summer means of 1 4 and 15 4 nmol l 1 in spring and summer high iron concentrations in surface waters were associated with both cold and saline recently upwelled waters and with fresh relatively warm water influenced by the columbia river comparison of total dissolvable iron in 0 45 mm filtered and in unfiltered samples indicated a substantial contribution from particulate iron iron concentrations in summer were generally lower than in spring throughout the water column with the exception of the near bottom where concentrations were generally higher in summer than spring optical backscatter data from moored sensors were used to infer the vertical and cross shelf transport of iron bearing particles during the upwelling season over a steep shelf cross correlation analysis showed downslope movement of particles from the deep inner shelf to the deep midshelf there was also evidence for sinking of biogenic particles at the midshelf and inner shelf but we found no evidence of upslope transport of benthic particles sufficient iron is available in this system to meet the demands of the phytoplankton which are able to make full use of available nitrate citation chase z b hales t j cowles r schwartz and a van green 2005 distribution and variability of iron input to oregon coastal waters during the upwelling season j geophys res 110 c10s12 doi 10 1029 2004jc002590

seasonal cycles of currents temperatures winds and sea level over the northeast pacific continental shelf 35 n to 48 n seasonal cycles of coastal wind stress adjusted sea level asl shelf currents and water temperatures off the west coast of north america 35 n to 48 n are estimated by fitting annual and semiannual harmonics to data from 1981 1983 longer records 9 34 years of monthly asl indicate that these two harmonics adequately represent the long term monthly average seasonal cycle and that the current measurement period is long enough to estimate the seasonal cycles we characterize the differences between fall winter and spring summer as follows for fall winter monthly mean winds north of 35 n are northward for 3 6 months longer in the north than in the south south of 35 n the mean winds are near zero or weakly southward monthly mean alongshore currents are northward over midshelf and shelf break at all locations sampled at depths of 35 m and deeper and are associated with high coastal sea levels and relatively warm water temperatures for spring summer monthly mean wind stresses are southward at all latitudes for 3 6 months longer in the south than in the north sea levels are low and water temperatures are relatively cool monthly mean currents at 35 m depth over the shelf are southward for 1 6 months longer at the shelf break than over midshelf and longer in the north than in the south while the deeper currents are less southward or northward the magnitudes of the seasonal cycles of all variables are maximum between approximately 38 n and 43 n generally decreasing slightly to the north and greatly to the south at each location the seasonal cycle of the alongshore current from 35 m depth at midshelf leads the sea level slightly and both lead the wind stress and temperatures by 1 2 months the seasonal cycles of all variables show a south to north progression south leads north by 1 2 months at 48 n annual mean currents at 50 m depth over the shelf break oppose the annual mean wind northward wind and southward current similarly at 35 n annual mean currents at 35 m depth over both midshelf and shelf break are opposed to the annual mean wind southward wind and northward current from 35 n to 43 n both summer and winter regimes are dominated by strongly fluctuating currents

tectonic versus magmatic extension in the presence of core complexes at slow spreading ridges from a visualization of faulted seafloor topography we develop a forward model of the generation of faulted seafloor topography visualization to estimate the relative roles of tectonic and magmatic extension in the presence of core complexes at slow spreading ridges the visualization assumes flexural rotation of 60 normal faults a constant effective elastic thickness te of young lithosphere and a continuous infill of the depressed hanging wall by lava flowing from the spreading axis we obtain a new estimate of te 0 5 1 km from the shapes of the toes of 6 well documented oceanic core complexes we model an 80 km long bathymetric profile in the equatorial atlantic across a core complex and the ridge axis at 13 20 n and estimate the variation in tectonic extension which yields the variation in the fraction of upper crust extension m by magmatic diking at the ridge axis core complex formation appears to be stable for all values of m 0 5 the visualization shows how gabbro emplaced at the base of the lithosphere during extension by magmatic diking is partitioned to each side of the spreading axis and predicts a high probability of finding gabbros in the domes of core complexes

widespread active detachment faulting and core complex formation near 13 n on the mid atlantic ridge oceanic core complexes are massifs in which lower crustal and upper mantle rocks are exposed at the sea floor1 2 3 they form at mid ocean ridges through slip on detachment faults rooted below the spreading axis2 3 4 5 6 to date most studies of core complexes have been based on isolated inactive massifs that have spread away from ridge axes here we present a survey of the mid atlantic ridge near 13 n containing a segment in which a number of linked detachment faults extend for 75 km along one flank of the spreading axis the detachment faults are apparently all currently active and at various stages of development a field of extinct core complexes extends away from the axis for at least 100 km our observations reveal the topographic characteristics of actively forming core complexes and their evolution from initiation within the axial valley floor to maturity and eventual inactivity within the surrounding region there is a strong correlation between detachment fault morphology at the ridge axis and high rates of hydroacoustically recorded earthquake seismicity preliminary examination of seismicity and seafloor morphology farther north along the mid atlantic ridge suggests that active detachment faulting is occurring in many segments and that detachment faulting is more important in the generation of ocean crust at this slow spreading ridge than previously suspected

low angle normal faults and seismicity a review although large low angle normal faults in the continental crust are widely recognized doubts persist that they either initiate or slip at shallow dips 30 because 1 global compilations of normal fault focal mechanisms show only a small fraction of events with either nodal plane dipping less than 30 and 2 andersonian fault mechanics predict that normal faults dipping less than 30 cannot slip geological reconstructions thermochronology paleomagnetic studies and seismic reflection profiles mainly published in the last 5 years reinforce the view that active low angle normal faulting in the brittle crust is widespread underscoring the paradox of the seismicity data for dip slip faults large enough to break the entire brittle layer during earthquakes m w 6 5 consideration of their surface area and efficiency in accommodating extension as a function of dip suggests average recurrence intervals of earthquakes r tan assuming stress drop rigidity modulus and thickness of the seismogenic layer do not vary systematically with dip if the global distribution of fault dip normalized to total fault length is uniform the global recurrence of earthquakes as a function of dip is shown to be r tan sin this relationship predicts that the frequency of earthquakes with nodal planes dipping between 30 and 60 will exceed those with planes shallower than 30 by a factor of 10 in good agreement with continental seismicity assuming major normal faults dipping more than 60 are relatively uncommon revision of andersonian fault mechanics to include rotation of the stress axes with depth perhaps as a result of deep crustal shear against the brittle layer would explain both the common occurrence of low angle faults and the lack of large faults dipping more than 60 if correct this resolution of the paradox may indicate significant seismic hazard from large low angle normal faults

miocene detachment faulting predating epr propagation southern baja california at the southern tip of the baja california peninsula we characterize the onshore structures and kinematics associated with crustal necking leading up to the pliocene breakup and early east pacific rise seafloor spreading from a combination of tectonic field investigations k ar and cosmogenic isotope dating and geomorphology we propose that the los cabos block represents the exhumed footwall of a major detachment fault this north trending detachment fault is marked by a conspicuous low dipping brittle ductile shear zone showing a finite displacement with top to the se ending to the ese this major feature is associated with fluid circulations which led to rejuvenation of the deformed cretaceous magmatic rocks at a maximum of 17 5 ma the detachment footwall displays kilometer scale corrugations controlling the present day drainage pattern this major detachment is synchronous with the development of the san jose del cabo basin where syntectonic sedimentation took place from the middle miocene to probably the early pliocene we propose that this seaward dipping detachment fault accommodates the proximal crustal necking of the baja california passive margin which predates the onset of formation of the east pacific rise spreading axis in the cabo puerto vallarta segment our data illustrate an apparent anticlockwise rotation of the stretching direction in baja california sur from 17 ma to the pliocene

turbulent nitrate fluxes in the amundsen gulf during ice covered conditions 3 2 5 10 3 m 2 s 1 and decreased exponentially to a depth of 50 m below which it was roughly constant at the background value kb 3 2 5 1 0 6 m 2 s 1 t he nitracline centered around 62 m depth was subject to an eddy diffusivity close to the background value kb and the mean diffusive nitrate flux across the nitracline was fnit 0 5 0 3 0 8 mmol m 2 d 1 these observations are compared with other regions and the role of vertical mixing on primary production in the amundsen gulf is discussed citation bourgault d c hamel f cyr j e tremblay p s galbraith d dumont and y gratton 2011 turbulent nitrate fluxes in the amundsen gulf during ice covered conditions geophys res lett 38 l15602 doi 10 1029 2011gl047936

large scale structure in wind forcing over the california current system in summer abstractthe wind that drives oceanic eastern boundary upwelling systems is highly variable in many locations the standard deviation of wind velocity on time scales of days to weeks is larger than the mean in the 1600 km long california current system ccs the spatial decorrelation scale of the wind fluctuations is 400 800 km suggesting wind fluctuations in the north and south ends of the system are not related yet there is also the suggestion in the literature of a larger scale structure in the fluctuations here empirical orthogonal function eof analysis of buoy and satellite wind velocities confirms the existence of that structure this analysis covers a larger spatial domain than previous eof studies in the ccs and to allow for propagation of the wind fluctuations includes an approach for calculating hilbert eofs from time series with gaps the large scale structure in the wind fluctuations is a quasi dipole pattern spanning the coastline from washington through california it accounts f

development of oceanic detachment and asymmetric spreading at the australian antarctic discordance 1 the largest known oceanic detachment terrains occur in segment b3 of the australian antarctic discordance aad using newly collected bathymetry magnetic and gravity data we show that segment b3 is divided into two contrasting second order segments the western subsegment b3w is characterized by well ordered ridge parallel abyssal hills and low mantle bouguer gravity anomalies the eastern subsegment b3e displays rough chaotic morphology and includes several megamullions characterized by high mantle bouguer gravity anomaly values the crust is estimated to be thinner by a maximum of 3 km in southern b3e the combination of chaotic morphology with thinner crust supports the idea that the megamullions are exposed footwalls of oceanic detachments megamullion terrains are characterized by higher magnetization than adjacent terrains most likely as a result of serpentinization of peridotite exposed at the detachment surfaces detachment surfaces constitute up to 70 of the total area of both ridge flanks younger than 2 ma in b3e indicating that oceanic detachments have played a major role in its development spreading in b3e has been extremely asymmetric with higher apparent rates associated with the large detachment surfaces where up to 75 of the total extension occurred similar asymmetric spreading on oceanic detachments is also recognized in segment b4 suggesting that this is the dominant mode of extension associated with cold mantle and low magma supply in this deepest part of the aad where it is confined to a mere 100 km long section of the aad spreading axis

high slip rate for a low seismicity along the palu koro active fault in central sulawesi indonesia accurate chronological records are critical for understanding the landformsevolution and in particular of alluvial fan sequences emplaced during glocal global climatic changes toward this end we measured in situ produced 10be in quartz boulders exposed on top surfaces of sulawesian late quaternary alluvial fans combined geomorphic study spot image and field analyses indicate that this site is composed of twoalluvial fan units in situ produced 10be concentrations suggest that they were emplaced during two successive major climatic events the calculated minimum exposure ages date the younger unit abandonment at 11 000 2 000 years and seem consistent with a late interglacial abandonment age 120 000years for the older unit this study demonstrates that using both the neutron and muon components implicated in the production of in situ10be surficial erosion rates can be estimated 6 m ma in sulawesi and alluvial fan surfaces dated in particular it shows that10be may be used to date fan surface emplacement during the last 120 ka under humid tropical conditions significantly helping to constrain continental paleo climatology in these regions

enhanced turbulence due to the superposition of internal gravity waves and a coastal upwelling jet to vertical aspect ratios of 10 2 to 10 3 median value 300 these patches are clearly defined by regions of low richardson number and occur where and when the linear superposition of the three dominant shear constituents near inertial m2 and thermal wind interferes constructively this is most pronounced at the base of the coastal jet where the thermal wind shear is largest while the effect of the turbulence stress divergence on the jet is small compared to geostrophy 1 it is significant in the second order force balance governing secondary circulation the timescale associated with the decay of the thermal wind shear via turbulence stress is o 10 days we confirm that the vertical salt flux due to mixing is comparable to the net ekman transport of salt onto the shelf within the bottom boundary layer because numerical models of coastal circulation lack turbulence in midwater column any vertical transport of scalars including salt and heat must be achieved inshore of the 40 m isobath this is inconsistent with the observations presented in this study in which significant vertical turbulent salt transport is found to exist across the entire shelf

irreversible nitrate fluxes due to turbulent mixing in a coastal upwelling system 1 detailed and repeated measurements of nitrate across the oregon shelf made coincident with turbulence measurements reveal the importance of cross isopycnal mixing via turbulence in providing nitrate to the upper water column spatial distributions of vertical gradients and turbulent fluxes in the oregon coastal ocean reveal variability that could not have been resolved with traditional sampling approaches nitrate rich near bottom waters are drawn up the shelf during upwelling and back down the shelf during downwelling continuous turbulent mixing in the bottom boundary layer increases nitrate on intermediate isopycnals by several m toward the shelf this increased nitrate is consistent with measured turbulent flux of nitrate of o 0 1 mol m 2 s 1 for a period of 3 days roughly the timescale for changes in the wind and hence to the upwelling circulation our flux estimates are consistent with high biomass nutrient replete incubation based primary productivity estimates in this area and suggest that turbulent vertical nitrate transport plays a significant role in supporting the high productivity seen here offshore of 30 m depth we estimate the irreversible transport of nitrate from nitrate rich near bottom waters to be about 25 of the rate at which it is provided by upwelling the total irreversible transport is greater by some unknown amount when we consider the transport inshore of 30 m depth we suggest that the onshore transport of offshore water whether deep water during upwelling or surface water during relaxation forces the juxtaposition of strong gradients and mixing regimes such that turbulent vertical fluxes are consistently elevated in the shoreward reaches of the coastal ocean

internal tide convergence and mixing in a submarine canyon abstractobservations from eel canyon located on the north coast of california show that elevated turbulence in the full water column arises from the convergence of remotely generated internal wave energy the incoming semidiurnal and bottom trapped diurnal internal tides generate complex interference patterns the semidiurnal internal tide sets up a partly standing wave within the canyon due to reflection at the canyon head dissipating all of its energy within the canyon dissipation in the near bottom is associated with the diurnal trapped tide while midwater isopycnal shear and strain is associated with the semidiurnal tide dissipation is elevated up to 600 m off the bottom in contrast to observations over the flat continental shelf where dissipation occurs closer to the topography slope canyons are sinks for internal wave energy and may have important influences on the global distribution of tidally driven mixing

gently dipping normal faults identified with space shuttle radar topography data in central sulawesi indonesia and some implications for fault mechanics abstract space shuttle radar topography data from central sulawesi indonesia reveal two corrugated domal landforms covering hundreds to thousands of square kilometers that are bounded to the north by an abrupt transition to typical hilly to mountainous topography these domal landforms are readily interpreted as metamorphic core complexes an interpretation consistent with a single previous field study and the abrupt northward transition in topographic style is interpreted as marking the trace of two extensional detachment faults that are active or were recently active fault dip as determined by the slope of exhumed fault footwalls ranges from 4 to 18 application of critical taper theory to fault dip and hanging wall surface slope and to similar data from several other active or recently active core complexes suggests a theoretical limit of three degrees for detachment fault dip this result appears to conflict with the dearth of seismological evidence for slip on faults dipping less than 30 the convex upward form of the gently dipping fault footwalls however allows for greater fault dip at depths of earthquake initiation and dominant energy release thus there may be no conflict between seismological and mapping studies for this class of faults

possible origin and significance of extension parallel drainages in arizona s metamorphic core complexes the corrugated form of the harcuvar south mountains and catalina metamorphic core complexes in arizona reflects the shape of the middle tertiary extensional detachment fault that projects over each complex corrugation axes are approximately parallel to the fault displacement direction and to the footwall mylonitic lineation the core complexes are locally incised by enigmatic linear drainages that parallel corrugation axes and the inferred extension direction and are especially conspicuous on the crests of antiformal corrugations these drainages have been attributed to erosional incision on a freshly denuded planar inclined fault ramp followed by folding that elevated and preserved some drainages on the crests of rising antiforms according to this hypothesis corrugations were produced by folding after subaerial exposure of detachment fault footwalls an alternative hypothesis proposed here is as follows in a setting where preexisting drainages cross an active normal fault each fault slip event will cut each drainage into two segments separated by a freshly denuded fault ramp the upper and lower drainage segments will remain hydraulically linked after each fault slip event if the drainage in the hanging wall block is incised even if the stream is on the flank of an antiformal corrugation and there is a large component of strike slip fault movement maintenance of hydraulic linkage during sequential fault slip events will guide the lengthening stream down the fault ramp as the ramp is uncovered and stream incision will form a progressively lengthening extension parallel linear drainage segment this mechanism for linear drainage genesis is compatible with corrugations as original irregularities of the detachment fault and does not require folding after early to middle miocene footwall exhumation this is desirable because many drainages are incised into nonmylonitic crystalline footwall rocks that were probably not folded under low temperature surface conditions an alternative hypothesis that drainages were localized by small fault grooves as footwalls were uncovered is not supported by analysis of a down plunge fault projection for the southern rincon mountains that shows a linear drainage aligned with the crest of a small antiformal groove on the detachment fault but this process could have been effective elsewhere lineation parallel drainages now plunge gently southwestward on the southwest ends of antiformal corrugations in the south and buckskin mountains but these drainages must have originally plunged northeastward if they formed by either of the two alternative processes proposed here footwall exhumation and incision by northeast flowing streams was apparently followed by core complex arching and drainage reversal

microblock rotations and fault coupling in se asia triple junction sulawesi indonesia from gps and earthquake slip vector data the island of sulawesi eastern indonesia is located within the triple junction of the australian philippine and sunda plates and accommodates the convergence of continental fragments with the sunda margin we quantify the kinematics of sulawesi by modeling gps velocities and earthquake slip vectors as a combination of rigid block rotations and elastic deformation around faults we find that the deformation can be reasonably described by a small number of rapidly rotating crustal blocks relative to the sunda plate the southwestern part of sulawesi makassar block rotates anticlockwise at 1 4 myr the northeastern part of sulawesi the bangai sula domain comprises three blocks the central north sula block moves toward the nnw and rotates clockwise at 2 5 myr the northeastern manado block rotates clockwise at 3 myr about a nearby axis and east sulawesi is pinched between the north sula and makassar blocks along the boundary between the makassar block and the sunda plate gps measurements suggest that the trench accommodates 15 mm yr of slip within the makassar strait with current elastic strain accumulation the tectonic boundary between north sula and manado blocks is the gorontalo fault moving right laterally at about 11 mm yr and accumulating elastic strain the 42 mm yr relative motion between north sula and makassar blocks is accommodated on the palu koro left lateral strike slip fault zone the data also indicate a pull apart structure in palu area where the fault shows a transtensive motion and may have a complex geometry involving several active strands sulawesi provides a primary example of how collision can be accommodated by crustal block rotation instead of mountain building