porous fluid flow enables oceanic subduction initiation on earth 1 although most of the presently active intra oceanic subduction zones are relatively young and initiated during the cenozoic subduction initiation process remains poorly understood previous models of subduction initiation assumed excessive weakening of tectonic plate boundaries that does not reconcile with laboratory rock strength measurements the weakening was assumed to be caused by fluids present along tectonic fractures however no self consistent solid fluid model of subduction initiation has been developed so far here we present new numerical hydro thermo mechanical model of spontaneous intra oceanic subduction initiation where solid rock deformation and fluid percolation are fully coupled based on 2 d numerical experiments we demonstrate that although subduction fails to initiate under fluid absent conditions it can naturally start when porous fluid is present inside oceanic crust and along the plate boundaries fluid percolation is localized along spontaneously forming faults where high fluid pressure compensates lithostatic pressure thus dramatically decreasing friction along the incipient subduction zone through the parametric study we conclude that the most important parameter for subduction initiation is the solid matrix permeability paradoxical at first lowering the permeability indeed favors subduction initiation by maintaining high fluid pressure and thus decreasing friction along active faults

minas fault zone late paleozoic history of an intra continental orogenic transform fault in the canadian appalachians abstract the minas fault zone mfz defines the boundary between the avalon and meguma terranes in the canadian appalachians and is exposed in mainland nova scotia and southern new brunswick these terranes originated along the gondwanan margin but had accreted to laurentia by the middle devonian the surface trace of the mfz is adjacent to the southern margin of the latedevonian permian maritimes basin the late devonian late carboniferous evolution of the mfz involves several episodes of oblique dextral shear that resulted in basin formation and inversion and at various times the zone was the focus of magmatism regional fluid flow and mineralization in the late devonian early carboniferous asymmetric rifting accompanied by dextral shear produced two coeval sequences the horton group which is dominated by continental clastic strata and the fountain lake group which consists predominantly of bimodal volcanic rocks that overlie high level plutons emplaced along active shear zones the overall tectonic environment may have been dominated by dextral transtension along the southern margin of laurentia which corresponded with the northern flank of the rheic ocean a major change in the evolution of the minas fault zone occurred in the late mississippian early pennsylvanian and produced the e w chedabucto fault clockwise rotation of pre existing structures local zones of transtension and transpression as well as regional fluid flow and extensive mineralization this major change may reflect the onset of laurentia gondwana oblique collision the effects of which continued into the latest carboniferous with coeval development of flower structures and pull apart basins in zones of local transpression and transtension

significant sink of ocean eddy energy near western boundaries ocean eddies generated through instability of the mean flow are a vital component of the energy budget of the global ocean modelling combined with satellite altimetry data suggests that the energy from westward propagating eddies is scattered and eventually dispersed when they reach the western boundary of an ocean basin

a mesozoic crustal suture on the gondwana margin in the new zealand region 1 marine crustal multichannel seismic data recorded offshore south island new zealand are used to provide constraints on the evolution of the gondwana margin in this region lower crustal and upper mantle seismic reflectivity off southeastern stewart island south of south island is interpreted in terms of a northeast dipping paleosubduction zone this inferred suture is considered to be related to the docking of the brook street oceanic island arc terrane to the gondwana margin in the triassic the junction of which is now largely covered by the median batholith a similar lower crustal upper mantle feature has been imaged off western south island both inferred sutures have similar strikes and are approximately collinear after restoration of the region for major cenozoic horizontal deformation it is proposed that they are parts of the same paleosuture that was oriented subparallel to the former gondwana margin and to the present paleozoic and mesozoic terranes forming south island

petrology chronology and sequence of vein systems systematic magmatic and hydrothermal history of a major intracontinental shear zone canadian appalachians abstract intra continental shear zones developed during continental collision may experience prolonged magmatism and mineralization the cobequid shear zone formed part of a ne sw trending orogen parallel shear system in the late devonian early carboniferous where syn tectonic granite gabbro plutons and volcanic rocks 4 km thick were progressively deformed in late carboniferous to permian alleghanian collision of africa with laurentia formed the e w trending minas fault zone reactivating parts of the cobequid shear zone the 50 ma history of hydrothermal mineralization following pluton emplacement is difficult to resolve from field relationships of veins but sem study of thin sections provides clear detail on the sequence of mineralization the general paragenesis is albite quartz chlorite monazite biotite calcite allanite pyrite fe carbonates fe oxides minor sulfides calcite and synchysite chronology was determined from literature reports and new u pb la icpms dating of monazite and allanite in veins vein mineralization was closely linked to magmatic events vein emplacement occurred preferentially during fault movement recognised from basin margin inversion as a result of fractures opening in the damage zone of master faults the sequence of mineralization from ca 355 ma riebeckite and albite veins to ca 327 305 ma siderite magnetite and sulfide mineralization resembles precambrian iron oxide copper gold iocg systems in the literature the abundant magmatic na halogens and co2 in veins and some magmatic bodies characteristic of iocg systems were derived from the deeply subducted rheic ocean slab with little terrigenous sediment regional extension of the magdalen basin caused asthenospheric upwelling and melting of the previously metasomatized sub continental lithospheric mantle crustal scale strike slip faulting facilitated the rise of magmas resulting in high heat flow driving an active hydrothermal system

temporal variation of titanite morphology and chemistry in a long lived shear zone the clarke head syenite in the minas fault zone nova scotia abstract the mineral chemistry of titanite has been studied in hydrothermally altered syenite preserved as blocks in a salt wall within a regional intracontinental shear zone the study focusses on the controls on temporal variation in rees zr nb u and th several generations of titanite are recognised on the basis of morphology chemistry and relationship to other secondary minerals magmatic euhedral to subhedral titanite has ti and zr contents characteristic of magmatic titanite in other studies but does not have a magmatic abundance of ree rather it is 102 104 times depleted in lree and only slightly depleted in hree the leaching of lree began during a regionally recognised phase of potassic alteration as amphibole and biotite in gabbro and diorite recrystallized along shear zones and released k ca and f later some 15 ma after emplacement the alkali feldspar in the syenite was largely altered to scapolite and analcime by interaction with adjacent halite and gypsum deposits titanite formed at that time from dissolution reprecipitation reactions in large rutile crystals is less depleted in lree as a result of the dominance of cl in hydrothermal waters following that event f dominated hydrothermal waters prevailed again resulting in more lree depletion in previously formed titanite and in neoformed hydrothermal titanite at that time there was also depletion in zr and u the trace elements in hydrothermal titanite are thus very informative on the hydrothermal history of the rocks a combination of morphology and trace element signature allows different hydrothermal stages to be distinguished

interactions between geostrophic eddies and the mean circulation over large scale bottom topography abstract the presence of intense recirculations in the abyssal oceans has been revealed by both observations and modeling studies a suggested mechanism is the interactions between geostrophic eddies and the mean circulation in the presence of variable bottom topography here such interactions are studied using an idealized numerical model consisting of a single active abyssal layer overlying variable bottom topography an initial ensemble of eddies quickly organize themselves to generate a mean anticyclonic circulation around seamounts during this rearrangement energy is approximately conserved while potential enstrophy is dissipated consistent with previous studies of geostrophic turbulence a parameterization of geostrophic eddies is formulated in terms of an eddy induced transport u based on results from the eddy resolving experiments it is hypothesized that u should dissipate potential enstrophy while conserving energy using variational methods a solution for u is found that dissipates pote

instabilities and multiscale interactions underlying the loop current eddy shedding in the gulf of mexico abstracta recently developed tool the multiscale window transform along with the theory of canonical energy transfer is used to investigate the roles of multiscale interactions and instabilities

ocean eddy energetics in the spectral space as revealed by high resolution general circulation models abstractin this study the global eddy kinetic energy eke budget in horizontal wavenumber space is analyzed based on 1 10 ocean general circulation model simulations in both the tropical and mi

mylonitic mafic granulite in fault megabreccia at clarke head nova scotia a sample of avalonian lower crust the clarke head fault megabreccia was produced within a major late palaeozoic transcurrent structure the minas fault system which separates the displaced meguma terrane of southern nova scotia from rocks more typical of the avalon superterrane a large clast of anomalously high grade metabasite embedded in the clay matrix of the fault megabreccia displays a fresh granulite facies mineralogy 2 pyroxene garnet plagioclase and mylonitic to ultramylonitic textures induced by anhydrous shearing deep in the roots of the fault zone whole rock geochemistry reveals the granulite protolith to have been a continental within plate mafic magma transitional between theoleiitic and alkaline the original geochemical signature has survived strong dynamic recrystallization at granulite grade well preserved ree abundances testify to a lack of metasomatic fractionation during high grade shearing under water absent conditions sm nd data indicate that the basic granulite has a t dm age of c 1 ga isotopic comparisons with adjacent areas reveal similar t dm ages both north and south of the minas fault system the high grade clast may be typical of the lower crust in nova scotia and is thought to offer a rare window into the deep crust of the avalon superterrane in north america

lithospheric extension from rifting to continental breakup at magma poor margins rheology serpentinisation and symmetry the symmetry or asymmetry of the process of continental breakup has been much debated over the last 20 years with various authors proposing asymmetric simple shear models others advocating more symmetric pure shear models and some combinations of the two the unroofing of vast expanses of sub continental mantle at non volcanic margins has led some authors to argue in favour of simple shear models but supporting evidence is lacking subsidence evidence from conjugate margin pairs is equivocal and the detailed crustal and lithospheric structure of such pairs not generally well enough known to draw firm conclusions in the porcupine basin where the final stages of break up are preserved the development of structural asymmetry is demonstrable and apparently related to late stage coupling of the crust to the mantle following the complete embrittlement of the crust this agrees with theoretical modelling results which predict that asymmetric models can develop only on a lithospheric scale when the crust and mantle are tightly coupled however whether such asymmetry is maintained during continued exhumation of the mantle is unclear

revised pacific antarctic plate motions and geophysics of the menard fracture zone a reconnaissance survey of multibeam bathymetry and magnetic anomaly data of the menard fracture zone allows for significant refinement of plate motion history of the south pacific over the last 44 million years the right stepping menard fracture zone developed at the northern end of the pacific antarctic ridge within a propagating rift system that generated the hudson microplate and formed the conjugate henry and hudson troughs as a response to a major plate reorganization 45 million years ago two splays originally about 30 to 35 km apart narrowed gradually to a corridor of 5 to 10 km width while lineation azimuths experienced an 8 counterclockwise reorientation owing to changes in spreading direction between chrons c13o and c6c 33 to 24 million years ago we use the improved pacific antarctic plate motions to analyze the development of the southwest end of the pacific antarctic ridge owing to a 45 counterclockwise reorientation between chrons c27 and c20 61 to 44 million years ago this section of the ridge became a long transform fault connected to the macquarie triple junction following a clockwise change starting around chron c13o 33 million years ago the transform fault opened a counterclockwise change starting around chron c10y 28 millions years ago again led to a long transform fault between chrons c6c and c5y 24 to 10 million years ago a second period of clockwise reorientation starting around chron c5y 10 million years ago put the transform fault into extension forming an array of 15 en echelon transform faults and short linking spreading centers

early carboniferous deformation and mineralization in the cobequid shear zone nova scotia an 40ar 39ar geochronology study latest devonian to early carboniferous igneous rocks along the cobequid shear zone of central nova scotia record a complex history of intrusion volcanism deformation and hydrothermal alteration twenty new 40ar 39ar age determinations have been made on biotite and hornblende separates from rocks that constrain these events the mafic plutons of the cobequid shear zone are synchronous with the previously dated granitoid plutons 363 355 4 ma with the exception of the younger folly lake gabbro 355 350 4 ma high temperature shear deformation continued along the cobequid shear zone during this entire period of pluton emplacement several samples from mylonitic and hydrothermally altered rocks with dates ca 340 ma indicate renewed movement along the cobequid shear zone at this time accompanied by minor magmatism younger 330 320 ma ages reflect final movement along the rockland brook fault resulting in mid namurian uplift of the cobequid highlands following this regional alleghenian event ther

evolution of late palaeozoic shearing in the cobequid highlands constraints on the fragmentation of the appalachian orogen in nova scotia along intra continental shear zones

incipient subduction at the contact with stretched continental crust the puysegur trench a seismic benioff zone and plate kinematics show puysegur trench south of new zealand transitioning to subduction because the local structure and its influence on subduction initiation is poorly understood we conducted a seismic survey with ocean bottom seismometers and multichannel seismic profiles our early results show that the overriding pacific plate beneath the solander basin is composed of block faulted and thinned continental crust and the inner trench wall of northern puysegur ridge is composed of folded and faulted sediment the megathrust interface has been imaged and shows 500 m of downgoing undisturbed sediments combining plate kinematic history with seismic velocity inferred density we show that the density difference across the plate boundary changed as oblique strike slip plate motion juxtaposed dense oceanic crust with thinned continental crust the density difference rapidly increased 18 to 15 ma coincident with subduction initiation suggesting that compositional differences have a large influence on subduction initiation

geochemical variation of amphiboles in a type granites as an indicator of complex magmatic systems wentworth pluton nova scotia canada abstract the wentworth pluton is the most complex intrusion among a series of a type granitic plutons emplaced along an active shear zone in the cobequid highlands of nova scotia during the latest devonian earliest carboniferous this pluton consists of a type granites of different generations and a large gabbroic body among all late paleozoic plutons in the cobequid highlands only the wentworth granites contain both primary calcic edenite hornblende and sodic amphiboles arfvedsonite whole rock and mineral chemical data were examined along with estimated magmatic parameters such as temperature emplacement pressure oxygen fugacity and volatile contents in order to understand the geological factors responsible for this mineralogical variation the granites with calcic amphiboles show systematically lower e nd values magmatic temperatures and f in melt contents and appear geochemically less evolved compared to the granites with the sodic amphiboles all granites however appear geochemically homogeneous with limited evidence of fractionation specific chemical differences between these two types of granites indicate the presence of two coeval but distinct granitic systems in the wentworth pluton the granites with the calcic amphiboles were formed from a geochemically less evolved hydrous relatively calcic melt whereas the granites with sodic amphiboles were emplaced at structurally deeper levels and were derived from a relatively drier sodic melt which had a larger mantle component and was enriched in fluorine coexistence of these two magmas is indicated by the presence of interstitial sodic calcic amphiboles in a late granitic dyke this study provides evidence that in a type granites where fractional crystallization is limited extreme variation in the type of amphibole can be the result of a very complex magmatic history

fracture zone subduction and reactivation across the puysegur ridge trench system southern new zealand a two dimentional kinematic model for lithospheric thrusting that considers the flexural interaction between the underriding and overriding plates was used to assess the mechanical implications of subducting trench parallel fracture zones on the topography and free air gravity anomalies of the puysegur ridge trench system fracture zones in the underriding plate are simulated by vertical discontinuities across which bending and shearing stresses cannot be supported the implication of reactivating fracture zones on the outer trench slope is to suppress the flexural bulge creating topographic relief between the fracture zone and the trench and reducing the trench gravity anomaly in the studied region the trench subparallel l atalante fracture zone accounts for the lack of a flexural bulge strong outer trench slope and gravity gradients the southward decrease of the trench fracture zone distance results in a decrease of the trench gravity anomaly the effect of subducting and vertically reactivating fracture zones within the underriding plate is to segment the load of the overriding plate creating a trough located above the underthrust fracture zone the vertical offset and gravity modifications are functions of the fracture zone position relative to the trench this model explains the 3500 m deep troughs and the 1700 m subsidence observed at the puysegur ridge we speculate that reactivating underthrust fracture zones can facilitate strike slip faults development within the upper plate in case of oblique subduction and are conducive to the formation and dispersion of terranes at convergent margins this process can account for basal tectonic erosion

a description of local and nonlocal eddy mean flow interaction in a global eddy permitting state estimate abstractthe assumption that local baroclinic instability dominates eddy mean flow interactions is tested on a global scale using a dynamically consistent eddy permitting state estimate interactions are divided into local and nonlocal if all the energy released from the mean flow through eddy mean flow interaction is used to support eddy growth in the same region or if all the energy released from eddies through eddy mean flow interaction is used to feed back to the mean flow in the same region eddy mean flow interaction is local otherwise it is nonlocal different regions have different characters in the subtropical region studied in detail interactions are dominantly local in the southern ocean and kuroshio and gulf stream extension regions they are mainly nonlocal geographical variability of dominant eddy eddy and eddy mean flow processes is a dominant factor in understanding ocean energetics

stratigraphy and depositional environments of the upper mississippian codroy group port au port peninsula western newfoundland upper mississippian middle visean biohermal limestones siliciclastics evaporites and red beds of the lower codroy group correlative with the lower windsor group in nova scotia bevel a rugged paleokarst of late devonian early mississippian age on the port au port peninsula western newfoundland laminated limestones ship cove formation and overlying evaporites codroy road formation are similar to the sequence in the bay st george subbasin southwestern newfoundland in the port au port region this sequence is laterally equivalent to biohermal limestones and plant bearing siliciclastics of the proposed big cove formation and red beds of the lower cove formation lithostratigraphic correlation is supported by miospore and conodont biostratigraphies use of macrofaunal subzones is cautioned because there is evidence for the need to reevaluate the ranges of fossils that have previously been considered key indicators e g martinia galataea bell for parts of the codroy and windsor groups the na

scapolite and analcime monitors of magmatic fluid metasomatism in a major shear zone abstract scapolite and analcime are uncommon alteration minerals in syenite here we describe a syenite body in a fault zone that hosts these minerals and we elucidate the unusual chemical conditions that led to their formation the clarke head syenite is part of a regional late devonian early carboniferous back arc a type granitoid suite in the cobequid highlands of nova scotia canadian appalachians the syenite contains magmatic rutile and analcime magmatic k feldspar has been largely replaced by scapolite of marialite composition which shows a temporal transition from more cl rich to more carbonate rich varieties scapolite veins cut both the syenite and associated gabbro and diorite analcime i occurs as a late stage interstitial magmatic mineral analcime ii forms by alteration of albite lamellae in perthite replaced by scapolite analcime iii vugs that cross cut scapolite and analcime iv occurs in late veins cross cutting earlier analcime phases and scapolite the regional a type granite plutonism was na and halogen rich with widespread late magmatic albitization and f related mobility of ree minerals however only at clarke head is there extreme na and cl rich metasomatism indicated by scapolite and cl rich hastingsite with 1 wt cl content cl rich fluids were derived from regional halite evaporites at faulted basin margins the main circulating fluids were likely of magmatic origin based on the 18o of both replacement and vein scapolite as the nacl supply was reduced scapolite became more ca rich halogen rich fluids also mobilized ti and zr which were reprecipitated in hydrothermal rutile and zircon as the halogen activity diminished scapolite replacement of k feldspar released large amounts of k into the circulating fluids which converted ferromagnesian silicates in fault zones to secondary biotite

occurrence and origin of marialitic scapolite in the humboldt lopolith n w nevada the occurrence and origin of marialitic scapolite in the humboldt lopolith was investigated in the field and in the laboratory using petrographic and experimental techniques scapolite occurs in three modes as a pervasive replacement of plagioclase and other minerals in gabbro diorite and extrusive rocks as a poikiloblastic mineral in scapolitite dikes and as a fracture filling mineral with analcime albite and sphene in scapolite veins additional secondary minerals associated with scapolite include epidote prehnite hornblende and diopside salite clinopyroxene relations with these minerals suggest that most marialitic scapolite grew at temperatures around 400 c scapolite composition varies from eqan12 to eqan37 containing from 72 to 96 atomic cl in the r position experiments on systems of similar compositions indicate that nacl h2o fluid having more than 40 mol nacl is needed to stabilize the scapolite

equilibration of a warm pumped lens on a β plane abstract the dynamics of a warm lens created by a surface buoyancy flux and ekman pumping in an initially homogeneous unbounded fluid on a plane is studied in a set of high resolution numerical experiments a simple analytical model for the equilibrium structure of the lens is developed that assumes that the input of vorticity and buoyancy from the ekman layer is balanced through transfer by baroclinic eddies that carry the warm fluid laterally away from the lens the importance of eddy induced diapycnal flux in the western intensification region is emphasized by developing a boundary layer theory based entirely on the cross frontal mass exchange due to eddies the theory is successfully tested against direct numerical eddy resolving simulations possible oceanographic implications of the study for understanding subtropical gyres and the antarctic circumpolar current are discussed

can we infer diapycnal mixing rates from the world ocean temperature salinity distribution abstractthe turbulent diapycnal mixing in the ocean is currently obtained from microstructure and finestructure measurements dye experiments and inverse models this study presents a new method that infers the diapycnal mixing from low resolution numerical calculations of the world ocean whose temperatures and salinities are restored to the climatology at the difference of robust general circulation ocean models diapycnal diffusion is not prescribed but inferred at steady state the buoyancy equation shows an equilibrium between the large scale diapycnal advection and the restoring terms that take the place of the divergence of eddy buoyancy fluxes the geography of the diapycnal flow reveals a strong regional variability of water mass transformations positive values of the diapycnal flow indicate an erosion of a deep water mass and negative values indicate a creation when the diapycnal flow is upward a diffusion law can be fitted in the vertical and the diapycnal eddy diffusivity is obtained throu

persistent mafic igneous activity in an a type granite pluton cobequid highlands nova scotia the west moose river pluton is one of a series of latest devonian early carboniferous plutons of granite and gabbro diorite in the cobequid highlands southern edge of avalon zone intrusion of minor gabbro preceded emplacement of the granite which is fractured and cut by later mafic dykes of which some predate and others postdate a namurian compressive deformation minor hybrid phases reflect mixing of mafic and felsic magmas which are also represented by basalt and rhyolite in the synchronous fountain lake group the mafic rocks are continental tholeiites reflecting regional early carboniferous extension later dykes are more fractionated with high p2o5 tio2 and other high field strength elements the dykes are pervasively altered probably by residual fluids from the granite hydrothermally circulated by the hot mafic rocks higher ga al hf and zn content in basalts than dykes suggests upward increase in halogen complexing in the mafic plumbing system late stage fluids concentrated k rb an

metasomatism of gabbro mineral replacement and element mobilization during the sveconorwegian metamorphic event widespread metasomatism affected the 100 km long and 25 km wide proterozoic bamble and modum kongsberg sectors south norway resulting in the chemical and mineralogical transformation of wide segments of continental crust scapolitization was associated with veining and was followed by albitization transforming metagabbros pervasively over large areas fluids played an active role in these reactions forming h2o co2 and cl bearing phases at the expense of the primary volatile free minerals causing depletion in fe and infiltration of k mg na b and p the transformation of gabbro to scapolite metagabbro is observed as a fluid front replacing the primary magmatic mineral assemblage in three stages during an incipient amphibolitization stage the primary mafic minerals were replaced by anthophyllite or hastingsite followed by pargasitic and edenitic ca amphibole magnetite was dissolved while rutile formed by the breakdown of ilmenite plagioclase was replaced by cl rich scapolite me19 42 reflecting cl saturation while k and mg saturation produced phlogopite enstatite sapphirine and rare corundum the high modal contents of chlorapatite and tourmaline in the scapolite metagabbro imply infiltration of b and p the albitites consist dominantly of albite ab95 98 with varying generally small amounts of chlorite calcite rutile epidote and pumpellyite they formed from a h2o co2 fluid rich in na the gabbro yields a zircon u pb age of 1149 7 ma and tonalite 1294 38 ma whereas rutile from scapolite metagabbro and albitite has u pb ages of 1090 1084 ma and phlogopite produced during scapolitization rb sr ages of 1070 1040 ma temperature conditions for the scapolitization are inferred to have been 600 700 c the reported ages combined with mineralogical and petrographic observations and inferred p t conditions indicate that the metasomatism was a part of the regional sveconorwegian amphibolite facies metamorphic phase initial 87sr 86sr of the scapolite ranges from 0 704 to 0 709 the sr signature the cl and b rich environment and regional distribution of lithologies suggest that the fluid may have originated from evaporites that were mobilized during the regional metamorphism

scapolite phenocrysts in a latite dome northwest arizona u s a abstract a latite dome in northwest arizona contains a rare occurrence of primary so 4 rich scapolite phenocrysts the total phenocryst assemblage consists of plagioclase an 20 an 33 hornblende biotite and scapolite me 68 microphenocrysts include allanite and oxidized low ti magnetite electron microprobe analyses show that the scapolite contains about 1 74 wt s which indicates an atomic s s c of 0 58 although scapolite occurs in xenoliths in volcanic rocks and diatremes as well as a metamorphic mineral in granulites its occurrence as a primary igneous mineral is extremely rare ca rich scapolite has been crystallized experimentally by others from melts with a wide range of sio 2 cao and na 2 o contents at temperatures above 825 c and pressures ranging from 3 to 15 kbar comparison of scapolite from this latite with synthetic scapolite crystallized from nepheline syenite melt suggests that the arizona phenocrysts crystallized under conditions of 850 to 900 c 3 6 kbar total pressure and unusually high co 2 and so 2 the rarity of scapolite as a phenocryst mineral suggests that high partial pressures of co 2 and so 2 are rare in the magmatic environment

cretaceous high p granulites at milford sound new zealand metamorphic history and emplacement in a convergent margin setting granulite facies orthogneiss of the arthur river complex arc at milford sound western fiordland records a complex early cretaceous magmatic and orogenic history for the pacific gondwana margin that culminated in the emplacement and burial of a dioritic batholith the western fiordland orthogneiss wfo enstatite bearing mafic to intermediate protoliths of the arc and wfo intruded the middle to upper crust the early deformation history of the arc is preserved in the pembroke granulite where two pyroxene s1 assemblages that reflect p 750 c were only patchily recrystallized during later deformation s1 is cut by garnet bearing leucogabbroic to dioritic veins which are cut by distinctive d2 fractures involving anorthositic veins and garnet diopside plagioclase bearing reaction zones these zones are widespread in the arc and wfo and record conditions of p 14 kbar and t 750 c garnet clinopyroxene bearing corona reaction textures that mantle enstatite in both the arc and wfo reflect early cretaceous burial by approximately 25 km of continental crust most of the arc is formed from the milford and harrison gneisses which contain steeply dipping s4 assemblages that envelop the pembroke granulite and involve garnet hornblende diopside clinozoisite rutile and plagio clase with or without kyanite the p t history of rocks in western fiordland reflects pronounced early cretaceous convergence related tectonism and burial possibly related to the collision and accretion of island arc material onto the pacific gondwana margin

high temperature chlorine rich fluid in the martian crust a precursor to habitability abstract we report scapolite in a melt inclusion in olivine in nakhla which is the first occurrence of cl scapolite found in a martian meteorite using terrestrial metamorphic experiments and modeling we constrain its origin cl rich scapolite in nakhla is consistent with formation from either a late stage cl rich water poor magma or magmatic cl rich hydrothermal brine at a minimum temperature of 700 c the temperature of hydrothermal activity recorded by the cl scapolite is significantly higher than the temperatures recorded by alteration minerals in nakhla and the fluid was cl rich not co 2 rich our results demonstrate that high temperature cl rich fluids were present within the martian crust and any potential biologic activity would have to survive in these high temperatures and saline fluids halophiles can thrive in nacl rich systems but at significantly lower temperatures than those recorded by the scapolite during cooling of the fluid the system could have reached a habitable state for halophiles importantly halophiles can survive the conditions of space if they are encased in salt crystals and therefore chlorine rich phases present an opportunity to investigate for extant life both on the surface of mars and in martian meteorites

representing topographic stress for large scale ocean models abstract interaction of eddies with seafloor topography can exert enormous systematic forces on the ocean circulation this interaction has been considered previously under idealized circumstances theoretical results are here simplified and extended toward practical application in large scale ocean circulation models among the suggestions is that coarse resolution models can correct a depth independent part of the velocity field toward a velocity given by z flh where z is the vertical unit vector f is coriolis form l is a length scale o 10 km and h is the total depth absence of this tendency may be implicated in a number of systematic defects that appear in present ocean models

on the patterns of wind power input to the ocean circulation pathways of wind power input into the ocean general circulation are analyzed using ekman theory direct rates of wind work can be calculated through the wind stress acting on the surface geostrophicflow however because that energy is transported laterally in the ekman layer the injection into the geostrophic interior is actuallycontrolledby ekmanpumping with a patterndeterminedby the windcurl ratherthanthe wind itself regions of power injection into the geostrophic interior are thus generally shifted poleward compared to regions of direct wind power input most notably in the southern ocean where on average energy enters the interior 108 south of the antarctic circumpolar current core an interpretation of the wind power input to the interior is proposed expressed as a downward flux of pressure work this energy flux is a measure of the work done by the ekman pumping against the surface elevation pressure helping to maintain the observed anomaly of sea surface height relative to the global mean sea level

truncation and translation of appalachian promontories mid paleozoic strike slip tectonics and basin initiation accreted terranes of the appalachian iapetan and peri gondwanan realms display structural trends that are mainly concordant with promontories and embayments in the laurentian margin indicating that during accretion the shape of the continental margin acted as a template around which accreted terranes were molded in north carolina and new foundland post accretion transcurrent motion appears to be recorded by displaced outboard portions of promontories no longer concordant with those in laurentia a bend in structural trends confined to the peri gondwanan realm at the north carolina south carolina state line is interpreted to represent the dextrally displaced outboard portion of the virginia promontory in newfoundland the hermitage flexure is interpreted as a dextrally displaced laurentian promontory that originated along strike to the northeast in both places promontories were truncated and dextrally translated for 220 250 km by a devonian mississippian orogen parallel transcurrent system which may well have extended for the length of the eastern laurentian margin south of the nearby st lawrence promontory extreme thinning of appalachian crust beneath the maritimes basin is consistent with extension at a releasing stepover estimates of extension are consistent with those obtained from promontory offsets

vertical eddy energy fluxes in the north atlantic subtropical and subpolar gyres eddy energy generation and energy fluxes are examined in a realistic eddy resolving model of the north atlantic over 80 of the wind energy input is found to be released by the generation of eddies through baroclinic instability the eddy energy generation is located near the surface in the subtropical gyre but deeper down in the subpolar gyre to reconcile the mismatch between the depth of eddy energy production and the vertical structure of the horizontal dispersion of eddy energy the vertical eddy energy flux is downward in the subtropical gyre and upward in the subpolar gyre

eddy induced diapycnal fluxes and their role in the maintenance of the thermocline abstract high resolution numerical experiments are diagnosed to study the integral effects of geostrophic eddy fluxes on the large scale ocean circulation three characteristic large scale flows are considered 1 an anticyclonic single gyre 2 a double gyre and 3 an unblocked zonal flow a simple analog of the antarctic circumpolar current it is found that buoyancy and potential vorticity budgets in the presence of eddies are dominated by a balance between vertical advection into the control volume by ekman pumping and eddy transfer across the density surfaces achieved by diapycnal eddy fluxes with small scale mixing making only a minor contribution possible oceanographic implications of the results are discussed

implementation of a geometrically informed and energetically constrained mesoscale eddy parameterization in an ocean circulation model abstractthe global stratification and circulation as well as their sensitivities to changes in forcing depend crucially on the representation of the mesoscale eddy field in a numerical ocean circ

underthrusting at the hjort trench australian pacific plate boundary incipient subduction 1 the southernmost portion of the macquarie ridge complex mrc comprises the hjort ridge trench and plateau the topographic expression of the australian pacific plate boundary south of new zealand on the basis of marine geophysical swath bathymetry reflectivity seismic reflection gravity magnetic data teleseismic data and gravity modeling we argue that the australian plate is actively underthrusting the pacific plate along the hjort trench but self sustaining subduction does not yet appear to have commenced we interpret a crustal discontinuity in the trench as a shallowly dipping thrust splay off a sub vertical transform fault in the crest of the hjort ridge hjort fault the hjort fault separates oceanic crust generated at the southeast indian ridge seir crust located to the south from oceanic crust generated at the extinct australian pacific spreading center located to the north mrc crust oblique convergence on the transform has initiated a significant plate boundary decollement in the trench but our estimate of 50 km of underthrusting does not support the existence of an eastwardly dipping australian slab below 20 km depth for the length of the hjort ridge and trench system oblique convergence is partitioned between the decollement in the trench and the hjort fault south of 57 5 s the trench decollement accommodates thrusting north of 57 5 s the boundary parallel component of convergence becomes dominant the trench gradually shallows and the trench decollement evolves into a low angle oblique slip fault the trench decollement and strike slip system in the hjort ridge are structural boundaries that contain tectonic slivers of inferred seir crust of the western flank of the hjort ridge that currently belong to neither the australian nor the pacific plates

mylonite to megabreccia tracking fault events within a transcurrent terrane boundary in nova scotia canada transcurrent terrane boundaries commonly evolve into long lived faults that preserve little evidence for early docking events a remarkable exception is exposed at clarke head along the appalachian meguma terrane boundary in nova scotia canada where a late carboniferous fault megabreccia contains devonian 369 ma u pb zircon granulite grade mylonite fractured by veins filled with visean amphibole ca 335 ma ar ar this fractured mylonite was later mixed with early carboniferous sedimentary rocks during megabrecciation ca 315 310 ma these three fault events are reflected in the tectonostratigraphic record devonian ca 370 360 ma transpressional terrane docking ramped meguma up against avalonia and shed clastic detritus across the fault system the visean brittle deformation recorded by the amphibole veins was coeval with marine regression at surface the late namurian megabrecciation event similarly produced unconformity followed by renewed nonmarine clastic sedimentation the clarke head megabreccia therefore preserves an episodic late paleozoic fault history spanning some 55 m y during convergence between laurentia and gondwana and the assembly of the pangean supercontinent

evolving force balance during incipient subduction nearly half of all active subduction zones initiated during the cenozoic all subduction zones associated with active back arc extension have initiated since the eocene hinting that back arc extension may be intimately associated with an interval several tens of myr following subduction initiation that such a large proportion of subduction zones are young indicates that subduction initiation is a continuous process in which the net resisting force associated with forming a new subduction zone can be overcome during the normal evolution of plates subduction initiation is known to have occurred in a variety of tectonic settings old fracture zones transform faults and extinct spreading centers and through polarity reversal behind active subduction zones although occurring within different tectonic settings four known subduction initiation events izu bonin mariana ibm along a fracture zone tonga kermadec along an extinct subduction boundary new hebrides within a back arc and puysegur fiordland along a spreading center were typified by rapid uplift within the forearc followed by sudden subsidence other constraints corroborate the compressive nature of ibm and tonga kermadec during initiation using an explicit finite element method within a two dimensional domain we explore the evolving force balance during initiation in which elastic flexure viscous flow plastic failure and heat transport are all considered in order to tie theory with observation known tectonic settings of subduction initiation are used as initial and boundary conditions we systematically explore incipient compression of a homogeneous plate a former spreading center and a fracture zone the force balance is typified by a rapid growth in resisting force as the plate begins bending reaching a maximum value dependent on plate thickness but typically ranging from 2 to 3 1012 n m for cases that become self sustaining this is followed by a drop in stress once a shear zone extends through the plate the formation of a throughgoing fault is associated with rapid uplift on the hanging wall and subsidence on the footwall cumulative convergence not the rate of convergence is the dominant control on the force balance viscous tractions influence the force balance only if the viscosity of the asthenosphere is 1020 pa s and then only after plate failure following plate failure buoyancy of the oceanic crust leads to a linear increase with crustal thickness in the work required to initiate subduction the total work done is also influenced by the rate of lithospheric failure a self sustaining subduction zone does not form from a homogeneous plate a ridge placed under compression localizes subduction initiation but the resisting ridge push force is not nearly as large as the force required to bend the subducting plate the large initial bending resistance can be entirely eliminated in ridge models explaining the propensity for new subduction zones to form through polarity reversals a fracture zone fz placed in compression leads to subduction initiation with rapid extension of the overriding plate a fz must be underthrust by the older plate for 100 150 km before a transition from forced to self sustaining states is reached in fz models the change in force during transition is reflected by a shift from forearc uplift to subsidence subduction initiation is followed by trench retreat and back arc extension moderate resisting forces associated with modeled subduction initiation are consistent with the observed youth of pacific subduction zones the models provide an explanation for the compressive state of western pacific margins before and during subduction initiation including ibm and tonga kermadec in the eocene and the association of active back arcs with young subduction zones on the basis of our dynamic models and the relative poles of rotation between pacific and australia during the eocene we predict that the northern segment of the tonga kermadec convergent margin would have initiated earlier with a progressive southern migration of the transition between forced and self sustaining states

isopycnal mixing in ocean circulation models abstract a subgrid scale form for mesoscale eddy mixing on isopycnal surfaces is proposed for use in non eddy resolving ocean circulation models the mixing is applied in isopycnal coordinates to isopycnal layer thickness or inverse density gradient as well as to passive scalars temperature and salinity the transformation of these mixing forms to physical coordinates is also presented

subduction initiation at relic arcs although plate tectonics is well established how a new subduction zone initiates remains controversial based on plate reconstruction and recent ocean drilling within the izu bonin mariana we advance a new geodynamic model of subduction initiation si we argue that the close juxtaposition of the nascent plate boundary with relic oceanic arcs is a key factor localizing initiation of this new subduction zone the combination of thermal and compositional density contrasts between the overriding relic arc and the adjacent old pacific oceanic plate promoted spontaneous si we suggest that thermal rejuvenation of the overriding plate just before 50 ma caused a reduction in overriding plate strength and an increase in the age contrast hence buoyancy between the two plates leading to si the computational models map out a framework in which rejuvenated relic arcs are a favorable tectonic environment for promoting subduction initiation while transform faults and passive margins are not

global observations of large oceanic eddies 1 ten years of sea surface height ssh fields constructed from the merged topex poseidon t p and ers 1 2 altimeter datasets are analyzed to investigate mesoscale variability in the global ocean the higher resolution of the merged dataset reveals that more than 50 of the variability over much of the world ocean is accounted for by eddies with amplitudes of 5 25 cm and diameters of 100 200 km these eddies propagate nearly due west at approximately the phase speed of nondispersive baroclinic rossby waves with preferences for slight poleward and equatorward deflection of cyclonic and anticyclonic eddies respectively the vast majority of the eddies are found to be nonlinear

energetics of eddy mean flow interactions in the gulf stream region a detailed energetics analysis of the gulf stream gs and associated eddies is performed using a highresolution multidecadal regional ocean model simulation the energy equations for the time mean and timevaryingflowsarederivedasatheoreticalframeworkfortheanalysis theeddy meanflowenergycomponents and their conversions show complex spatial distributions in the along coast region the cross stream and cross bump variations are seen in the eddy mean flow energy conversions whereas in the off coast region a mixed positive negative conversion pattern is observed the local variations of the eddy mean flow interaction are influenced by the varying bottom topography when considering the domain averaged energetics theeddy meanflowinteractionshowssignificantalong streamvariability upstreamofcapehatteras the energy is mainly transferred from the mean flow to the eddy field through barotropic and baroclinic instabilities upon separating from the coast the gs becomes highly unstable and both energy conversions intensify when the gs flows into the off coast region an inverse conversion from the eddy field to the mean flow dominates the power transfer for the entire gs region the mean current is intrinsically unstable and transfers 28 26gw of kinetic energy and 26 80gw of available potential energy to the eddy field the mesoscaleeddykineticenergyisgeneratedbymixedbarotropicandbaroclinicinstabilities contributing28 26 and 9 15gw respectively beyond directly supplying the barotropic pathway mean kinetic energy also provides 11 55gw of power to mean available potential energy and subsequently facilitates the baroclinic instability pathway

fractured latest devonian granites of the west moose river pluton along the cobequid shear zone nova scotia implications for regional mineralization latest devonian 365 358 ma a type granites in the cobequid highlands host complex sequences of rare earth element ree and other hydrothermal minerals the west moose river pluton is the only pluton truncated and brittly deformed by the mid carboniferous 327 ma strike slip minas fault zone during the alleghanian orogeny fractures in the granite provide a record of several deformational and hydrothermal events with distinct mineral assemblages early sodic alteration produced albitisation of feldspar and riebeckite and tourmaline veins the 18 o of albite and albitised granite 5 6 is similar to other regional granites suggesting a mantle source of albitising fluids nearby halite deposits are younger and thus not a source of na early chlorite veins were followed by potassic alteration and hydrothermal biotite and by diabase and lamprophyre dyke emplacement euhedral magnetite occupies new cross cutting fractures and vugs correlated with regional iron oxide carbonate sulphide

vertical heat transport in eddying ocean models 1 the effect of mesoscale eddies on the vertical heat transport of the ocean is examined using two eddy resolving numerical models the global heat transport by the mean flow and diffusion are both downwards and are balanced by an upward eddy heat flux mean and eddy advective heat fluxes dominate the subpolar regions while diffusive flux is important primarily in the subtropics in the subtropical abyss the mean advective heat flux is balanced by a combination of eddy and diffusive fluxes and the classical munk type advective diffusive heat balance must be modified the munk and wunsch 1998 expression for the vertical turbulent diffusivity over estimates the diffusivity by as much as a factor of four near the base of the main thermocline this implies that the mixing required to close the meridional overturning circulation determined by munk and wunsch 1998 may be an over estimate due to the neglect of mesoscale eddies

impact of synoptic atmospheric forcing on the mean ocean circulation abstractthe impact of synoptic atmospheric forcing on the mean ocean circulation is investigated by comparing simulations of a global eddy permitting ocean sea ice model forced with and without synoptic atmospheric phenomena consistent with previous studies transient atmospheric motions such as weather systems are found to contribute significantly to the time mean wind stress and surface heat loss at mid and high latitudes owing to the nonlinear nature of air sea turbulent fluxes including synoptic atmospheric forcing in the model has led to a number of significant changes for example wind power input to the ocean increases by about 50 which subsequently leads to a similar percentage increase in global eddy kinetic energy the wind driven subtropical gyre circulations are strengthened by about 10 15 whereas even greater increases in gyre strength are found in the subpolar oceans deep convection in the northern north atlantic becomes significantly more vigorous which in turn leads to an increa

bottom enhanced diapycnal mixing driven by mesoscale eddies sensitivity to wind energy supply abstractit has been estimated that much of the wind energy input to the ocean general circulation is removed by mesoscale eddies via baroclinic instability while the fate of this energy remains a subject of research arguments have been presented suggesting that a fraction of it may get transferred to lee waves that upon breaking result in bottom enhanced diapycnal mixing here the authors propose several parameterizations of this process and explore their impact in a low resolution ocean climate model focusing on their impact on the abyssal meridional overturning circulation moc of antarctic bottom water this study shows that when the eddy energy is allowed to maintain diapycnal mixing the abyssal moc generally intensifies with increasing wind energy input to the ocean in such a case the whole system is driven by the wind wind steepens isopycnals and generates eddies and the parameterized eddies generate small scale mixing driving the moc it is also demonstrated that if the model diapycn

systematic mineralogical diversity in a type granitic intrusions control of magmatic source and geological processes the origin and causes of mineralogical diversity of a type granites are debated the series of a type granite plutons with distinct mineralogical differences emplaced along an upper paleozoic crustal scale shear zone in the cobequid highlands nova scotia provide an opportunity to examine the origin of different a type plutons in a similar tectonic setting based on the ferromagnesian minerals present the plutons are classified into sodic granites with sodic amphibole calcic granites with calcic amphibole and biotite granites sodic and calcic granites occur exclusively in complex intrusions with subequal amounts of gabbro in the eastern shear zone whereas plutons in the western shear zone with lesser gabbro are solely biotite granites trace elements and radiogenic isotopes show that the three granite types have different sources intensive parameters including temperature pressure and water in melt contents were estimated from mineralogical and geochemical data modeling of these geochemical data suggests that the biotite and calcic granites were derived by 20 40 partial melting of intracrustal feldspathic rocks whereas the sodic granites are extreme fractionates 90 of coeval mafic magma we propose that supply of upper paleozoic mafic magma probably related to regional extension and decompression melting beneath the magdalen basin created a deep crustal hot zone in the eastern cobequid highlands and extreme fractionation of underplated mafic sills produced the sodic granites heat transfer from crystallizing mafic magma induced partial melting of the surrounding crust creating batches of biotite and calcic granitic melts in different depths fractionated and crustally derived melts segregated along crustal scale faults constructing the complex plutons in the east melting of the crust was further facilitated by the release of water from the crustal rocks upon heating in the eastern shear zone water was released predominantly by magmatic rocks and in lesser amounts compared to the west where neoproterozoic sedimentary and volcaniclastic rocks are more abundant the volatile rich granitic melts in the western part of the shear zone were crystallized rapidly stabilizing only biotite this study demonstrates that the mineralogical variations in a type granites arise from rather similar magma compositions but they are important petrogenetic indicators of varying sources specific magmatic processes and emplacement conditions

internal control of fluid compositions in amphibolite facies scapolitic calc silicates mary kathleen australia unaltered metasediments of the mary kathleen fold belt are composed predominantly of layered amphibolite facies scapolitic calc silicate rocks in which minimal infiltration of externally derived fluids occurred during regional metamorphism there were substantial differences in volatile activities between different layers in the layered sequences in particular a co2 a h 2 o inferred from reaction progress estimates and analysis of biotite clinopyroxene fluid phase relations a nacl a h 2 o inferred from scapolite compositions and a hcl a h 2 o inferred from biotite compositions in one outcrop in which a clinopyroxene producing reaction dominated differences in approximate x co 2of up to 0 25 occurred between several samples collected over 50 metres variations in a h 2 o a hcl of up to one order of magnitude are inferred at 1 to 50 m scales from biotite cl contents and variations in nacl contents of scapolite from 0 0 to up to 0 6 cl atoms in the cl co3 so4 site reflect a large variation of a nacl in the coexisting fluid at similar scales most calcsilicate layers internally buffered fluid compositions in the h2o co2 nacl hcl system local occurrences of nacl rich scapolite suggest that some layers may have been in equilibrium with halite during early prograde metamorphism at peak metamorphic temperatures disolution of halite was complete but layers containing high nacl scapolite continued to buffer fluid at high values of a nacl fluid immiscibility does not appear to have affected the progress of the devolatilization reactions although fluid was predominantly internally buffered moderate quantities of fluid were released by prograde mineral reactions in many layers up to 30 cm3 fluid per 100 cm3 rock numerous episodes of fluid escape were required probably via microfractures such that the released fluid did not obviously influence reaction progress in the layers through which it passed the anomaly of beautifully preserved internal buffering signatures and the requirement for produced fluid locally to pass across layers in a deforming rock sequence suggest that the escaping fluid did not leave any readily observable tracks this is explained by rapid rates of fracture propogation and fluid migration therein this internally buffered system contrasts strongly with adjacent calc silicate rocks that show evidence for infiltration of externally derived fluids at high fluid rock ratios and highlights the broad range of fluid behaviour that can be expected in deforming heterogeneous rock sequences

crustal structure and inferred rifting processes in the northeast south china sea abstract taiger project deep penetration seismic reflection profiles acquired in the northeastern south china sea scs provide a detailed view of the crustal structure of a very wide rifted continental margin these profiles document a failed rift zone proximal to the shelf a zone of thicker crust 150 km from the shelf and gradually thinning crust toward the cob spanning a total distance of 250 300 km such an expanse of extended continental crust is not unique but it is uncommon for continental margins we use the high quality images from this data set to identify the styles of upper and lower crustal structure and how they have thinned in response to extension and in turn what rheological variations are predicted that allow for protracted crustal extension upper crustal thinning is greatest at the failed rift uc 7 5 but is limited farther seaward uc 1 2 we interpret that the lower crust has discordantly thinned from an original 15 17 km to possibly less than 2 3 km thick beneath the central thick crust zone and more distal areas this extreme lower crustal thinning indicates that it acted as a weak layer allowing decoupling between the upper crust and the mantle lithosphere the observed upper crustal thickness variations and implied rheology lower crustal flow are consistent with large scale boudinage of continental crust during protracted extension

the instabilities and multiscale energetics underlying the mean interannual eddy interactions in the kuroshio extension region abstractusing a recently developed energetics diagnostic methodology namely the localized multiscale energy and vorticity analysis ms eva this study investigates the intricate nonlinear mutual interactions among the decadally modulating mean flow the interannual fluctuations and the transient eddies in the kuroshio extension region it is found that the mean kinetic energy maximizes immediately east of the izu ogasawara ridge while the transient eddy kinetic energy does not peak until 400 km away downstream the interannual variabilities which are dominated by a jet trapped rossby wave mode provide an energy reservoir comparable to the other counterparts in the upstream strong localized barotropic and baroclinic transfers from the mean flow to the eddies are observed whereas those from the interannual variabilities are not significant besides fueling the eddies the unstable mean jet also releases energy to the interannual scale processes between 144 and 154 e both transfers from the mean

influence of preexisting fault fabric on inversion related deformation a case study of the inverted fundy rift basin southeastern canada 1 preexisting zones of weakness significantly influenced the structural development of the fundy basin during rifting and subsequent basin inversion the preexisting fabric consisting of ne striking faults with gentle dips and east striking faults with steeply dipping upper segments and gently dipping lower segments formed during paleozoic and older orogenic activity during mesozoic rifting the preexisting fabric was reactivated creating a border fault system composed of linked ne and east striking extensional fault zones with anomalous dips gentle and steep compared to those of newly formed normal faults during inversion the preexisting fabric was again reactivated as the hanging wall of the composite border fault system moved nne relative to the footwall inversion was highly oblique on the ne striking fault zones producing gentle fault parallel buttress folds and fault perpendicular detachment folds above the low angle fault zones inversion was moderately oblique on the east striking fault zone producing relatively tight fault parallel buttress and detachment folds above the gently dipping lower fault segments and reactivating the steeply dipping upper fault segments as left lateral strike slip faults thus inversion related deformation on the east striking fault zone was partitioned at shallow levels i e partitioned updip our work shows that the geometry of preexisting extensional faults and their obliquity relative to the shortening direction profoundly affect deformation style during basin inversion namely the type of inversion related faults the type and shape of inversion related folds and the distribution of deformation e g updip partitioning depend in part on the geometry of the preexisting extensional faults and the variations in these geometries with depth and along strike