reply to comments by fergus g f gibb and c michael b henderson on mafic ultramafic sills new insights from m and s shaped mineral and whole rock compositional profiles the comments by fergus gibb and michael henderson on a recent and some previous publications are most welcome and i am glad of the opportunity to clarify some of the issues they raise recent studies of chemical zonation in mafic dykes chistyakova latypov 2009a 2009b 2010 2011 2012 dolerite sills latypov egorova 2012 egorova latypov 2013 and layered intrusions latypov et al 2011 egorova latypov 2012a 2012b have provided several new and important constraints on the initial stages in the development of intrusive bodies in particular we have found that the an content of plagioclase cores in the marginal zones of mafic sills and layered intrusions systematically increases inwards indicating that these zones were not formed from a single pulse of parental magma of uniform composition rather they resulted from an early stage of filling when the inflowing magma became increasingly more primitive this and other findings resulted in an abandonment of soret differentiation a hypothesis that i had supported earlier for the origin of marginal reversals latypov 2003a 2003b in favour of the leading edge fractionated magma hypothesis see latypov 2014 this is quite an old concept in petrology that implies the initial emplacement of batches of evolved magma produced by three principal mechanisms 1 the early stages of fractional melting without complete mixing in the mantle source 2 magma stratification in a subjacent chamber 3 fractional crystallization of magma while flowing through conduits in accepting this hypothesis as an explanation for marginal reversals i referred to morse 1979 1981 2008 who has been supporting this idea for many years for layered intrusions i fully agree however that it was a grave omission not to mention the work of gibb and henderson who proposed essentially the same process for mafic ultramafic sills gibb henderson 1978 2006 henderson gibb 1987 henderson et al 2000 references to their publications would certainly have made our case even stronger it should be noted that the conclusion about the formation of basal reversals by inflowing magma that gradually becomes more primitive is not trivial no absolutely unequivocal evidence for this process has been forthcoming from petrological studies including those by gibb and henderson of mafic ultramafic sills owing to their enrichment in olivine this is because the primary composition of olivine is commonly altered to varying degree by reaction with interstitial melt making this mineral unreliable for deciphering igneous processes it is therefore understandable that most workers considered such sills as having formed from a single pulse of magma followed by gravitational accumulation of olivine and or pyroxene either already present in the magma at the time of emplacement marsh 1996 ubide et al 2012 or that grew in the intrusion itself frenkel et al 1989 worster et al 1993 ariskin yaroshevsky 2006 lo pez moro et al 2007 this crystallization model suggests that an upward increase in whole rock mgo in basal reversals is a consequence of a decreasing solidification rate that ensures an increase in the amount of olivine able to settle to the bottom of the magma in other words basal reversals are considered to be mixtures of melt and cumulus olivine

thrust fault growth and segment linkage in the active ostler fault zone new zealand abstract thrust faulting is a fundamental mode of crustal deformation yet many of the key geometrical attributes of thrust faults and the controls on fault rupture growth and linkage remain poorly resolved numerous surface rupturing thrust faults cut through upper quaternary glacial outwash terraces within the ostler fault zone an active thrust system in the southern alps new zealand we use these deformed marker surfaces to define the three dimensional deformation field associated with their surface expression and to map displacement and length on 40 fault segments displacement transfer across two fault segment arrays occurs in distinctly different styles in one displacement is transferred between en echelon fault segments to produce a smooth linear displacement gradient in the other large scale folding and a population of small faults transfer displacement between two non overlapping fault segments with a residual displacement minimum within the transfer zone size distribution of fault segment length and maximum displacement follow a power law scaling relationship maximum displacement d max scales linearly with and represents 1 of segment trace length l d max l data from the segments of the ostler fault zone display similar scaling to a global fault dataset this similarity is surprising given that the observed displacements along the ostler fault represent only 20 ky of slip on fault segments that are likely to be many times older

on the development of internal chemical zonation in small mafic dykes three dolerite dykes small 3 2 cm middle 13 5 cm thick 50 cm from torsholma island sw finland reveal distinctly different internal zonation that becomes more complicated with increasing thickness of the dykes the small dyke shows a systematic inward increase in normative pl an ab or and a decrease in normative an 100 an an ab whole rock mgo mg number 100 mg mg fetotal tio2 k 2o and zr the middle dyke exhibits the same compositional pattern at the margins while the centre is distinguished by an abrupt increase in normative pl and an whole rock sr and mg number from the margins inwards the thick dyke displays first a compositional pattern identical to that observed in the small dyke and the margins of the middle dyke this is followed by a region where whole rock mgo mg number and normative an start increasing inwards while the transition to the centre of the dyke is characterized by a compositional pattern similar to that in the centre of middle dyke the origin of chemical zonation in these dykes is attributed to the operation of three independent physico chemical processes namely the small dyke formed exclusively by progressive changes in the composition of inflowing magma the middle dyke by changes in composition of inflowing magma margins and concentration of plagioclase and olivine phenocrysts by flow differentiation centre the thick dyke by changes in composition of inflowing magma margins in situ cumulate growth against dyke sidewalls middle and flow differentiation centre systematic changes in these processes and as a result in internal chemical zonation likely take place in response to crystallization of magma under less supercooled conditions with increasing dyke thickness a comprehensive geochemical study of the internal zonation of small mafic dykes worldwide is required to develop a complete understanding of the processes operating in mafic dykes

flow differentiation phenocryst alignment and compositional trends within a dolerite dike at rockport massachusetts systematic variations in the volume percent size and orientation of plagioclase phenocrysts up to 12 0 cm long occur across a 5 6 m thick porphyritic alkaline dolerite dike in rockport massachusetts field measurements indicate that phenocryst concentrations increase from nearly zero at the dike margin to 46 0 vol at its center average phenocryst size increases inward from 4 1 2 2 mm at the dike margin to 19 2 7 9 mm at the center the increase in size and abundance of phenocrysts toward the center of the dike is interpreted as resulting from flow differentiation the magma flow direction is assumed to have been upward and parallel to the dike margins n7 w stiike 88 e dip the strikes and dips of all elongate phenocrysts viewed in cross section within one traverse across the dike were measured and compared to the dike attitude to determine the degree of flow alignment across the dike average phenocryst strike deviations from dike strike increase inward 21 8 from the dike margin to its midpoint phenocryst dip angle deviations from dike dip increase inward by 18 8 this more pronounced clow alignment of phenocrysts nearer the dike margins is interpreted as being a function of the more extreme velocity gradients and resulting shear due to flow within the marginal zones of the magma than within its interior at least the outer few centimetres of phenocryst free chilled dike margins may form primarily by rapid quenching of phenocryst free magma rather than by flow differentiation whole rock major and minor element trends across this dike may be produced in part by flow differentiation a1 2 o 3 cao p 2 o 5 and na 2 o increase inward with plagioclase phenocryst concentrations whereas sio 2 k 2 o feo tio 2 mgo and mno decrease this inward decrease in certain oxides together with an inward within dike decrease in the anorthite content of the cores of plagioclase phenocrysts cannot be attributed to flow differentiation the inward decreasing chemical trends are believed to have resulted from one or a combination of several of the following processes the concentration of silica and incompatible elements in glass now devitrified within chilled dike margins compared to interiors plagioclase fractionation continuous tapping of partial melts increasingly depleted of silica and incompatible elements tapping of a zoned magma chamber and greater crustal contamination of marginal liquids superposed on the chemical trends the inward decrease in plagioclase anorthite content resulted from fractional crystallization

composition and stable isotope geochemistry of natural gases from kansas midcontinent u s a abstract more than 28 1012 ft 3 79 1010 m3 of natural gas and 5 3 109 bbl 8 4 108 m3 of oil have been produced in kansas u s a from paleozoic carbonate and sandstone reservoirs on structural uplifts and shallow embayments along the northern margin of the anadarko basin a heavily explored geologically well characterized state kansas is an excellent place to study hydrocarbon migration and to test geochemical models for the origin of natural gases immature to marginally mature rocks of eastern kansas cherokee and forest city basins produce mixed microbial and thermogenic gases gases in this region have wetness 0 03 51 methane 13c 65 to 43 and methane d 260 to 150 gases from central and western kansas nemaha uplift to hugoton embayment are entirely thermogenic and have wetness 4 51 methane 13c 48 to 39 and methane d 195 to 140 ethane and propane 13c values throughout kansas vary from 38 to 28 and from 35 to 24 respectively mature thermogenic gas generated from source rocks in southwestern kansas and the anadarko basin with 1 0 ro 1 4 is recognized throughout the state lateral migration into shallow reservoirs on the central kansas and northern nemaha uplifts and in the cherokee basin probably occurred along basal pennsylvanian conglomerates and weathered lower paleozoic carbonates at the regional sub pennsylvanian unconformity early thermogenic gas generated by local source rocks with ro 0 7 is recognized in isolated fields in the salina and forest city basins in ordovician reservoirs beneath the sub pennsylvanian unconformity in the cherokee basin and in reservoirs generally above the unconformity in the cherokee and sedgwick basins the eastern central kansas uplift and the hugoton embayment

comments on mafic ultramafic sills new insights from m and s shaped mineral and whole rock compositional profiles by v egorova and r latypov j petrology 54 2155 2191 2013

seismicity and geometry of a 110 km long blind thrust fault 2 synthesis of the 1982 1985 california earthquake sequence during 1982 1985 three 5 4 mw 6 5 earthquakes migrated 65 km along the north half of a string of quaternary folds at the east front of the california coast ranges there is no surface fault associated with these earthquakes but the fold chain oriented parallel to the san andreas fault 30 km to the west takes up contraction normal to the san andreas fault identification of active blind thrust faults is hindered by the absence of a fault trace but may be revealed by the presence of growing folds at the surface and by earthquakes at depth because of excellent seismic geodetic and geologic data this earthquake sequence illuminates the geometry of the blind faults and enables us to probe their mechanics we relocate seismicity and compute focal mechanisms in a three dimensional velocity space and model the vertical deformation associated with the 1983 m 6 5 coalinga earthquake the aftershock zones abut at echelon offsets in the fold axes and the mainshocks display reverse slip perpendicular to the axes suggesting that the folds conceal a contiguous segmented thrust fault background seismicity concentrates at bends and breaks in the fold chain sites that may correspond to tears and ramps in the thrust fault at depth seismic reflection profiles reveal thrust and reverse faults dipping toward the san andreas fault at depths of 5 10 km with several kilometers of cumulative slip and high angle reverse faults in the anticlines with several hundred meters cumulative slip coseismic fold uplift accompanied the coalinga and kettleman hills north dome earthquakes suggesting that fold growth is episodic and coupled closely to repeated earthquakes on the underlying thrusts the north half of the fold chain has been the site of several 6 m 6 5 earthquakes since 1885 thus kettleman hills middle dome the next fold segment to the south has an elevated seismic potential the aftershock zones of the three main shocks are diffuse and occupy a region much larger than the site of seismic slip aftershocks occur 5 7 km from the fault regions where on the basis of a boundary element model the shear strain increase caused by the fault slip exceeds 20 ppm equivalent to about 0 7 mpa we argue that the broad aftershock zone is a product of high sustained off fault stress caused by repeated displacement on faults that do not cut the earth s surface the fault tip stresses lead to the formation of secondary faults which can become sites of aftershocks and postseismic creep

structure and evolution of the seismically active ostler fault zone new zealand based on interpretations of multiple high resolution seismic reflection profiles abstract to improve our understanding of active faulting away from the main plate boundary on new zealand s south island we have acquired high resolution seismic data across the ostler fault zone twelve 1 2 km long lines perpendicular to fault strike and a 1 6 km long crossline were collected in a region of the mackenzie basin where surface mapping delineates significant complexity in the form of two non overlapping reverse fault strands separated by a transfer zone characterised by multiple smaller strands and increased folding interpretation of the resultant images includes a 45 55 west dipping principal fault and two 25 30 west dipping subsidiary faults one in the hanging wall and one in the footwall of the principal fault the geologically mapped complexities are shown to be caused by shallow variations in the structure of the principal fault which breaks the surface in the north and south but not within the transfer zone where it forms a triangle zone with associated backthrusting and minor faulting these complexities only extend to 300 m depth structures below this level are markedly simpler and much more 2d in nature with the principal fault strand extending over a much longer distance than the individual strands observed at the surface since longer faults are susceptible to larger earthquakes than shorter ones seismic hazard at the study site may be higher than previously thought multiple surface fault strands that give way to a single more major stand at relatively shallow depths may be a common feature of segmented fault systems the deepest layered reflections at our site are consistent with the presence of a late cretaceous tertiary basin underlying the present day mackenzie basin structural restoration of the seismic images back to the base of quaternary fluvioglacial terraces and back to the top of a late pliocene pleistocene fluviolacustrine unit indicate that compression was initiated prior to the late pliocene and that it has continued at a comparatively steady rate of about a millimetre per year to the present day the fluviolacustrine unit has experienced 440 800 m of along fault vertical offset and 870 1080 m of horizontal shortening since that time our study demonstrates that structural reconstructions based on high resolution seismic reflection data provide critical displacement information that can be used to estimate slip rates

chemical and mineralogic variations within four dikes of the columbia river basalt group southeastern columbia plateau four dikes within the western portion of the chief joseph dike swarm of the mio pliocene columbia river basalt group show systematic major element mineralogic and textural trends across their widths two of the dikes are of wanapum basalt dodge chemical type and served as source vents for two flows of dodge chemistry and petrography that are exposed in the study area a third dike of saddle mountains basalt served as a vent for the wenaha flow elephant mountain chemical type also present in the area two additional dikes of probable saddle mountains basalt cannot be correlated unambiguously with any flows exposed in the area but one of them closely resembles the buford flow chemically and petrographically the chemical variations across all four dikes indicate that the chilled dike margins are slightly enriched in felsic components and incompatible elements sio 2 p 2 o 5 tio 2 and k 2 o and depleted in mgo and feo compared to dike interiors most of these chemical trends can be related to the marked enrichment in glass at chilled dike margins compared to their more crystalline interiors microprobe analyses of glasses from chilled dike margins when compared to whole rock analyses from dike interiors agree with the above described trends for sio 2 tio 2 mgo and probably k 2 o feo is also concentrated in the three glasses analyzed producing an opposing and stronger trend increase than shown by the whole rock data this probably reflects the greater concentration of opaque oxides within the marginal tachylite compared to the more crystalline dike interiors which lack tachylite this variation in glass content is of course controlled by the rapid quenching of magma against the relatively cold country rock and the progressively decreasing cooling rate toward the interior of a dike as intrusion continues in addition to variations in crystallinity fractionation and or crustal contamination may also have contributed to or modified these major element trends mineralogic trends inward from dike margins are from mafic to felsic with plagioclase anorthite content and perhaps the ca content of augite decreasing orthopyroxene hypersthene bronzite is present only in the chilled margin of the wenaha dike and exhibits well developed reaction rims of augite these mafic to felsic mineralogic trends were superposed on the felsic to mafic chemical trends

sandbox experiments of inverted listric and planar fault systems abstract the kinematic and geometric evolution of basement controlled inversion structures has been analyzed using a plane strain sandbox apparatus the results of two representative scaled analogue models comprising rigid listric and planar detachment faults that both have cut off angles of 60 to the horizontal are described in detail the hangingwall above these detachment geometries was constructed from alternate layers of sand and mica in order to simulate an anisotropic sedimentary sequence in both experiments initial shortening at the onset of inversion was accommodated by bulk strain this was followed by reactivation of the basal detachment together with the main basin controlling planar and listric faults which propagate upwards through the post rift sequence at approximately the same angle as the upper part of the detachment fault i e 60 reactivation of relatively steep intra basinal extensional faults within the cover was restricted to nucleation of reserve faults and thrusts in the region of the tips during approximately the first 10 to 15 contraction this resulted in gently dipping thrusts that propagated upwards through the post rift sequence to produce harpoon shaped structures later in the inversion phase after approximately 15 contraction backthrusts cut through and displaced the original antithetic extensional graben faults producing downward tapering wedge shaped structures at the margins of the basin although deformation in these experiments was limited to purely dip slip displacement the nature of the original extensional faults and their reactivated tip regions resulted in cross sectional geometries that have a marked resemblance to strike slip induced flower structures uplift was asymmetric and centred above the upper part of the main detachment above the listric fault but was more symmetrical and centred above the soling out point of the detachment in the case of the planar fault geometry the results of these experiments show distinct similarities to structures seen on seismic sections form the southern north sea and other inverted sedimentary basins

orientation of tabular mafic intrusions controls convective vigour and crystallization style the microstructure in basaltic dykes is significantly different from that in sills and lava lakes of the same bulk composition for a given width of intrusion or depth of lava lake vertical tabular bodies are coarser grained than horizontal bodies with an invariant plagioclase shape across the intrusion when comparing samples from sills and dykes for which the average grain size is the same the dyke samples contain fewer small grains and fewer large grains than the sill samples in contrast the variation of median clinopyroxene plagioclase plagioclase dihedral angles in dykes correlates precisely with that observed in sills and is a function of the rate of diffusive heat loss these patterns can be accounted for if the early stages of crystallization in dykes primarily involve the growth of isolated grains suspended in a well mixed convecting magma with the final stage during which dihedral angles form occurring in a crystal rich static magma in which heat loss is primarily diffusive in contrast crystallization in sills occurs predominantly in marginal solidification fronts suggesting that any convective motions are insufficient to entrain crystals from the marginal mushy layers and to keep them suspended while they grow an exception to this general pattern is provided by members of the mull solitdykes which propagated 100 1000 km se from the mull palaeogene igneous centre scotland through the shallow crust these dykes where sampled 100 km from mull have a microstructure indistinguishable from that of a sill of comparable thickness we suggest that sufficient nucleation and crystallization occurred in these dykes to increase the viscosity sufficiently to damp convection once unidirectional flow had ceased

two independent processes responsible for compositional zonation in mafic dykes of the aland aboland dyke swarm kestio island sw finland abstract detailed sampling across three dolerite dykes of different size small 7 cm middle 75 cm and thick 675 cm of the aland aboland dyke swarm has revealed an internal zonation of an anomalous nature the small almost glassy dyke exhibits a systematic inward decrease in whole rock mgo and mg indicating a normal fractionation trend together with a simultaneous increase in normative an and cpx and decrease in whole rock zr y cao tio 2 indicating a reverse fractionation trend the middle dyke shows similar compositional trends across its narrow margins but in the more crystalline interior whole rock mgo and mg gradually but steadily increase inwards as a result normal and reverse fractionation trends of the margins grade to exclusively reverse fractionation trends of the interior the thick almost totally crystalline dyke exhibits an internal zonation similar to that of the middle dyke with fractionation trends becoming only much more pronounced in the centre of the dyke the almost glassy nature of small dyke suggests that its anomalous compositional zonation most likely resulted from temporal changes in the composition of magma as it formed the dyke the mechanism s responsible for such systematic changes in composition of inflowing magma remains however unknown the margins of middle and thick dyke form in a similar way whereas their interiors formed by in situ cumulate growth against dyke sidewalls this process resulted in a gradual inward increase in the proportion of cumulus phases owing to magma crystallization in progressively less supercooled conditions with increasing distance from cold country rocks the compositional zonation of these dolerite dykes is thus produced by two independently operating mechanisms successive changes in composition of inflowing magma an external liquid state process and an in situ cumulate growth on dyke sidewalls an internal crystal liquid process based on the relatively minor development of internal zonation in interiors of middle and thick dykes the former mechanism appears to be several times more effective in causing magma differentiation than the latter it remains to be determined whether these two processes are a general reason for the formation of marginal reversals in mafic ultramafic dykes sills and large layered intrusions

petrology of the grenville swarm of gabbro dikes canadian precambrian shield the grenville tholeiitic dikes of late proterozoic or early paleozoic age cut marbles and gneisses of the grenville province within and adjacent to the ottawa rift structure where traversed the swarm consists of about 40 large dikes up to 100 m wide representing a crustal extension of 1 km the principal minerals are olivine augite pigeonite plagioclase magnetite ilmenite k feldspar and quartz crystals of pigeonite around olivine and complex augite pigeonite composite grains suggest that the reactions olivine melt pigeonite and pigeonite melt augite have taken place conspicuous zoning and grain to grain variation in the composition of augite are consistent with fractional crystallization but crystal melt equilibrium during crystal growth is indicated by a restricted range in pyroxene paleotemperatures of 1180 1060 c rock textures subophitic combined ophitic subophitic and equigranular in dike centres are related to dike width and are determined principally by the influence of

soret separation of mid ocean ridge basalt magma chemical differentiation of an initially homogeneous mid ocean ridge basalt morb liquid has been experimentally observed in a temperature gradient above the liquidus the magnitude of this effect in producing differences in composition is comparable to that of crystal liquid fractionation for a given temperature difference however the chemical changes produced by the two processes soret and crystal liquid fractionation are different soret separations resemble those observed in a third process silicate liquid immiscibility this similarity is a reflection of the fact that the soret separable components are the same network former network modifier structural components which segregate during silicate liquid immiscibility

solidification and turbulence non laminar during magma ascent insights from 2d and 3d analyses of bubbles and minerals in an etnean dyke

channel width response to differential uplift 1 the role of channel width and slope adjustments to differential uplift in rivers within actively deforming terrains remains contentious here high resolution topographic surveying of formerly antecedent outwash channels demonstrates marked changes in channel width as a primary response to differential uplift for five late quaternary alluvial paleochannels crossing small folds along the active ostler fault zone of southern new zealand nearly continuous measurements of paleochannel width and concomitant incision reveal abrupt narrowing of widths toward minimum values at channel positions coincident with the initial uplift when the magnitude of differential uplift is sufficiently small narrowing alone permits these channels to remain antecedent in the context of a unit stream power model for fluvial erosion observed limits on the magnitude of channel narrowing suggest that above some threshold amount of differential uplift continued incision requires concomitant changes in channel gradient thus when crossing small growing folds alluvial rivers simply narrow their channels whereas larger folds that demand greater incision prompt an initial narrowing followed by channel steepening

the obliquely convergent plate boundary in the south island of new zealand implications for ancient collision zones abstract the alpine fault of new zealand forms the western boundary of a zone of distributed deformation formed by the oblique convergence of continental crust belonging to the pacific and australian plates structural and geodetic data from the alpine fault show that a large proportion of the total plate displacement is accommodated by rapid oblique slip on the fault the remaining displacement is distributed over a 200 km wide zone to the east the collision may be modelled as a two sided deforming orogen with the partitioning of deformation being controlled by erosional differences between the narrow high strain inboard and broad low strain outboard sides in ancient collision zones little evidence may remain of the nature and amount of displacement on the inboard side partitioning of deformation among pre existing structures complicates interpretation of the outboard zone radiometric ages may post date collision by several tens of millions of years and indicate slow isostatic uplift and unroofing collision ages if preserved may be recognized by high uplift rates calculated from muscovite biotite pairs

adcumulate mafic dykes in layered intrusions a case study of a late stage dyke in the bayantsagaan layered intrusion mongolia we have discovered an adcumulate late stage dyke in the bayantsagaan layered intrusion the 11 cm thick dyke is composed of fresh troctolite with no signs of chilling against the host leucotroctolite texturally both the dyke and its host are medium grained plagioclase olivine magnetite cumulates the dyke is however finer grained and contains less interstitial material two geochemical features characterize the dyke it is compositionally more evolved than the host as indicated by its lower real and normative an content in plagioclase whole rock cr and mg number and it is highly depleted in all incompatible components e g k 2 o y and rare earth elements or rees that have much lower concentrations than in the host the depletion in rees is extreme and has not been reported earlier for any troctolitic rocks it has an internal reverse zonation with an inwards increase in compatible mgo and tio 2 and a decrease in all incompatible elements suggesting an inwards decrease in the amount of trapped melt we interpret this late stage dyke as having formed from a residual melt that was channelled along a fissure in solidifying cumulates the flow of the melt resulted in the very efficient removal of a boundary layer of evolved liquid from crystals growing on the walls of the dyke this resulted in an almost perfect adcumulate that is extremely depleted in incompatible components

fine scale chemical zonation in small mafic dykes kestio island sw finland detailed centimetre scale sampling across two small dolerite dykes 7 and 21 cm wide of kestio island sw finland has revealed a well developed internal zonation with surprisingly systematic compositional variations from the margins inwards the dykes exhibit a steady decrease in whole rock mgo mg number 100mg mg fe total and normative opx indicating a normal fractionation trend with simultaneous increase in normative an 100an an ab and decrease in incompatible zr y tio 2 and p 2 o 5 indicating a reverse fractionation trend in addition marginal rocks of dykes contain normative corundum that is apparently associated with their significant depletion in whole rock cao the extent of margin to centre differentiation of dykes in terms of most components is slight to modest although in some petrochemical parameters it is quite high e g 15 mol of normative an the dykes are almost glassy and uncontaminated by host rocks suggesting that their compositional profiles are primary and most likely reflect temporal changes in composition of magma filling the dykes a mechanism responsible for the systematic changes in composition of inflowing magma remains elusive however since no known processes are able to force magma to evolve simultaneously along both normal and reverse fractionation trends the study thus appears to indicate some not yet specified process of magma differentiation

eohimalayan fold and thrust belt implications for the geodynamic evolution of the nw himalaya india 1 in the himalayas the eocene deformation phase is called the eohimalayan event by means of a forward and backward balanced cross section along a classical traverse through the tethyan himalaya we constrain eohimalayan sw vergent folding and sw directed thrusting in a belt above a basal thrust at 10 km depth this thrust is located at the structural position of the southern tibetan detachment system with a ne directed normal sense displacement suggesting miocene reactivation of a major eocene contractional fault stepwise palinspastic restoration demonstrates that this eocene contractional fault has been subsequently openly folded due to southwestward propagation of the himalayan thrust system

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

testing the validity of the petrological hypothesis no phenocrysts no post emplacement differentiation an extravagant hypothesis no phenocrysts no post emplacement differentiation has been put forward by marsh in a series of papers for the development of mafic ultramafic intrusions this hypothesis is based on an assertion that the majority of these intrusions are structureless and undifferentiated because they lack residual granitic rocks to explain this the hypothesis postulates that phenocryst free magmas are not able to differentiate in crustal chambers because all evolved interstitial liquid is locked in solidification fronts producing compositionally uniform magmatic bodies layered well differentiated intrusions are attributed to the successive emplacement of magma pulses with phenocrysts of different phase and chemical compositions rather than to slow magma cooling and fractional crystallization as conventional models imply such phenocryst laden magma pulses are supposed to be derived from an underlying magmatic mush column however structureless undifferentiated mafic ultramafic bodies simply do not exist in nature all wellstudied mafic ultramafic bodies with or without residual granitic rocks that crystallized from parental magmas of non eutectic composition tend to reveal clear evidence of internal compositional differentiation in terms of crystallization sequences e g ol opx opx pl opx pl cpx mineral compositions e g an in plag en in cpx and compatible incompatible major and trace element geochemistry e g mg number cr rare earth elements this is especially evident in layered intrusions that represent the key evidence against the hypothesis essentially by denying the ability of magma to differentiate in intrusive bodies the hypothesis forbids magmatic differentiation in any sub chamber related to the entire magmatic mush column as a result magma pulses in which phenocrysts progressively change in composition cannot be derived from the column to form layered intrusions the hypothesis is thus contradictory baseless and fundamentally flawed it should be abandoned in favour of a classical fractional crystallization model based on the pioneering experiments of bowen and amply confirmed over almost a century by subsequent studies of layered intrusions the classical model was is and will most probably remain the best explanation for the origin of differentiated magmatic bodies

along strike growth of the ostler fault new zealand consequences for drainage deflection above active thrusts 1 rarely are geologic records available to constrain the spatial and temporal evolution of thrust fault growth as slip accumulates during repeated earthquake events here we utilize multiple generations of dated and deformed fluvial terraces to explore two key aspects of the along strike kinematic development of the ostler fault zone in southern new zealand over the past 100 k y accumulation of fault slip through space and time and fixed length thrust growth that results in patterns of drainage diversion suggestive of laterally propagating faults along the ostler fault surface deformation patterns revealed by topographic surveying of terrace profiles in nine transverse drainages define systematic variations in fault geometry and suggest deformation over both listric and planar thrust ramps kinematic modeling of folded terrace profiles and 100 fault scarp surveys along major fault sections reveals remarkably similar slip distributions for multiple successions of geomorphic surfaces spanning 100 k y spatially abrupt and temporally sustained displacement gradients across zones of fault section overlap suggest that either persistent barriers to fault propagation or interference between overlapping faults dominate the interactions of fault tips from the scale of individual scarps to the entire fault zone deformed terrace surfaces dated using optically stimulated luminescence and cosmogenic radionuclides indicate steady maximum rates of fault slip of 1 9 mm yr during the late quaternary slip data synthesized along the central ostler fault zone imply that displacement accumulated at approximately constant fault lengths over the past 100 k y a northward temporal progression of abandoned wind gaps along this section thus reflects lateral tilting in response to amplification of displacement rather than simple fault lengthening or lateral propagation oscillations of climate at 104 yr time scales modulate the formation and incision of geomorphic surfaces during successive glacial stages superimposed on apparently steadier rates of fault slip such climate dependent surfaces contribute to a pattern of progressive drainage deflection along the central ostler fault zone that is largely independent of fault propagation

magma differentiation and crystallization in basaltic conduits by two competing petrogenetic processes abstract magma differentiation processes that take place in conduits delivering basaltic magmas to the earth s surface are still poorly understood to get new insights into this problem we have studied in detail the whole rock geochemistry of a section across a dolerite dyke 21 m thick and three sections across its narrow apophysis 69 cm 29 cm and 17 cm thick from the russian fennoscandian shield the dyke is fresh aphyric and shows no evidence of in situ contamination by crustal rocks chemical zonation in the dyke changes systematically with the thickness of the sections in particular rocks become more primitive inwards mgo mg number and normative an increase and p 2 o 5 decreases in the main dyke while rocks become more evolved inwards in the apophysis in addition the chemical zonation of the apophysis is anomalous since compatible and incompatible elements behave in a manner inconsistent with fractional crystallization of basaltic magma to explain the chemical zonation we introduce a novel concept that attributes compositional trends in mafic dykes to competition between two processes a the filling of dykes with magmas that become increasingly more evolved with time as a result of fractionation in the deeper parts of conduits and b in situ crystal growth on dyke walls accompanied by effective removal of evolved melt by through flowing magma the processes have opposite effects on rock geochemistry with the first making dykes more evolved and the second more primitive inwards the key idea is that dykes become more evolved inwards when quenching of inflowing magmas controls the distribution of all components and become more primitive inwards when in situ crystal growth governs the distribution of all components anomalous compositional trends develop when these two processes control the distribution of different groups of chemical components the chemical zonation in the studied dyke can be attributed to a change from rocks mainly produced by quenching of progressively more evolved magmas in the apophysis to those predominantly formed by in situ crystal growth in the main dyke this happens in response to a decreasing degree of undercooling as sections of the magma conduit become thicker we believe that the competitive operation of these two petrogenetic processes is likely a general feature of magma differentiation and crystallization in basaltic conduits

incremental dilation of magma filled fractures evidence from dykes on the isle of skye scotland abstract localised swarms of narrow 10 120 mm basaltic dykes occur at offsets and terminations of some larger basaltic dykes in skye scotland these narrow dykes cut and chill against each other and the larger dyke and its country rock the narrow dykes can only be traced a short distance into the larger dyke before terminating some of these terminations show the central parts of both dykes merging as the chilled margins vanish at other terminations the later dyke outcrop narrows progressively to a point these all show that after initial dilation and some crystallisation of material in the dyke fissure there were additional up to 11 increments of dilation increments were sufficiently spaced in time for preceding injections to have become solid time spans separating initial and later dilation may be sufficient for local crystallisation of dykes up to 3 2 m thick away from these terminations the dyke fissure remained an open void occupied by flowing magma during the successive increments of dilation this paper demonstrates that fluid filled dyke fissures can vary in width with time an observation consistent with the modern theoretical models of dyke emplacement that relate dyke width to magma input pressures and other magmatic parameters dyke offsets and terminations with late dilational increments are shown to provide a variety of other information on flow crystallisation and sealing of dyke fissures

influence of syntectonic sedimentation on thrust geometry field examples from the iberian chain spain and analogue modelling abstract steep thrusts are usually interpreted as oblique slip thrusts or inverted normal faults however recent analogical and numerical models have emphasised the influence of surface mass transfer phenomena on the structural evolution of compressive systems this research points to sedimentation and erosion during deformation as an additional explanation for the origin of steeply dipping thrusts the present study uses both field observations and analogue modelling to attempt to isolate critical parameters of syntectonic sedimentation that might control the geometry of the upper part of thrust systems a field study of thrust systems bounding two compressive intermountain tertiary basins of the iberian chain is first briefly presented we describe the surface geometry of thrusts surrounding the montalban basin and the alto tajo syncline at the vicinity of deposits of oligocene early miocene alluvial fans at the footwall of faults field observations suggest that synthrusting sedimentation should influence the structure of thrusts indeed the faults are steeper and splitted at the edge of the syntectonic deposits effects of sedimentation rate on footwall of thrusts and of its change along fault strike are further investigated on two layer brittle ductile analogue models submitted to compression and syntectonic sediment supply two series of experiments were made corresponding to two end members of depositional geometries in the first series the sedimentation was homogeneously distributed on both sides of the relief developed above the thrust front in the second series deposits were localised on a particular area of the footwall of thrust front in all experiments the sedimentation rate controls the number and the dip of faults for low sedimentation rates a single low angle thrust develops whereas for high sedimentation rates a series of steeper dipping thrust is observed in experiments with changing sedimentation rate along fault strike the thrust geometry varies behind the areas with the thickest sediment pile

basal reversals in layered intrusions are evidence for emplacement of compositionally stratified magma basal reversals in layered intrusions are evidence for emplacement of compositionally stratified magma

the origin of basic ultrabasic sills with s d and i shaped compositional profiles by in situ crystallization of a single input of phenocryst poor parental magma an attempt is made to develop an in situ crystallization model based on the concept of soret fractionation to explain the origin of commonly observed s d and i shaped compositional profiles in sills formed from a single pulse of phenocryst poor parental magma the model envisages that the various compositional profiles observed in sills can be interpreted in terms of different combinations of four principal units basal zone and layered series forming the floor sequence and top zone and upper border series constituting the roof sequence the basal and top zones represent mirror images of the layered and upper border series respectively and therefore are referred to as basal and top reversals it is proposed that the formation of basal and top reversals takes place through the non equilibrium soret differentiation of liquid boundary layers which form as a consequence of the temperature gradient imposed by the cold country rock in contrast the layered and upper border series originate predominantly through the crystal liquid boundary layers developing in equilibrium conditions the model permits the production of s d and i shaped compositional profiles from the same magma composition all that is necessary to produce a specific shape of compositional profile is an appropriate temperature gradient imposed by the cold country rock on the liquid boundary layers of a parental magma of a given composition

geochemical consequences of flow differentiation in a multiple injection dike trinity ophiolite n california abstract a clinopyroxene rich dike of the trinity ophiolite sheeted dike complex shows three different magmatic pulses probably injected in a short period of time no well developed chilled margin and important variations of the clinopyroxene and plagioclase percentages between its core highly porphyritic and margins aphyric this variation interpreted as related to a flow differentiation phenomenon mechanical phenocryst redistribution has important geochemical consequences it produces increases in the feo mgo cao cr and ni contents from the margin to the core together with increases in the clinopyroxene percentage and decreases in the sio 2 zr y nb and ree contents together with a decrease in the percentage of the fine grained groundmass toward the core of the dike this mineralogical redistribution which also affects the incompatible trace element ratios because of the difference in plagioclase and clinopyroxene mineral liquid partition coefficients illustrate the importance of fractionation processes outside of a magma chamber

surface breakthrough of a basement fault by repeated seismic slip episodes the ostler fault south island new zealand 1 the ostler fault is one of the major active reverse faults in the piedmont of the southern alps se of the alpine fault we present a new geological and morphotectonic map of the southern ostler fault integrated with two seismic reflection profiles across the active central segments of the fault segmented subparallel scarps define a n s belt 40 km long and 2 3 km wide of pure reverse faults which upthrow and back tilt a panel of plio pleistocene terrestrial units 2 4 1 0 ma plus the overlying glacial outwash 200 ka uplift gradients the chronology of newly faulted markers and tectonically controlled diversion of paleodrainages all indicate progressive s to n breakthrough of the surface trace of the ostler fault in the last 2 4 ma the new seismic data define a main fault segment dipping 50 60 w to depths of 1 5 km with a vertical throw of 800 m and a shortening of 30 the fault geometry and kinematics and the subsurface data favor the interpretation that the ostler fault propagated updip across the plio quaternary terrestrial sequence as the emerging high angle splay of an inherited late cretaceous paleocene normal fault that underwent repeated cycles of compressional reactivation in the last 2 4 ma

relay zones between mesoscopic thrust faults in layered sedimentary sequences abstract we examine the geometry formation and destruction of relay zones in well bedded sedimentary sequences containing thrust fault segments with maximum observed displacements of 0 64 8 m contractional extensional and neutral relay zones are distinguished based on the stepping sense of the interacting fault segments and the orientation of the associated fault slip vectors large displacement gradients 0 17 1 0 in relay zones are mainly accommodated by folding with aggregate displacements maintained across segment boundaries and a significant component of the fault slip converted to fold related shortening folds in contractional relay zones verge in the direction of hanging wall motion with the steeper limb defining a parallelogram shaped zone between thrusts fault segment lengths are established after minimal displacement and folds in relay zones grow between segments as displacement accrues on the thrusts with increasing displacement upper and lower thrust tip lines in contractional and extensional relay zones are fixed at stratigraphic boundaries while the lateral thrust tip lines may propagate in a strike parallel direction upper and lower tip lines may eventually propagate to bypass relay zones that formed early in the fault growth history contractional relay zones remain intact at higher displacements than extensional relay zones

prolonged magma emplacement as a mechanism for the origin of the marginal reversal of the fongen hyllingen layered intrusion norway the 100 m thick marginal zone of the fongen hyllingen intrusion fhi consists of non layered highly iron enriched ferrodiorites that are overlain by a 6 km thick layered sequence of gabbroic to dioritic rocks of the layered series from the base upwards the marginal zone becomes more primitive as exemplified by a significant increase in whole rock mgo mg number and normative an the reverse trends are also evident from an upward increase in an content of plagioclase from 30 to 43 at and mg number of amphibole from 9 to 23 at and clinopyroxene from 23 to 33 at the marginal zone is abruptly terminated at the contact with the overlying layered series as is evident from a step like increase in mg number of mafic minerals and an content of plagioclase as well as a sharp increase in whole rock mgo and mg number in overlying olivine gabbronorites of the layered series based on these features the marginal zone of the fhi can be interpreted as an aborted marginal reversal reverse trends in whole rock and mineral compositions as well as a sharp break in these parameters are indicative of its formation in an open system with the involvement of the prolonged emplacement of magma that became increasingly more primitive such development of the marginal reversal was interrupted by the emplacement of a major influx of more primitive magma that produced the layered series the open system evolution of a basaltic magma chamber may represent a general mechanism for the origin of marginal reversals in mafic sills and layered intrusions

selkirk fan structure southeastern canadian cordillera tectonic wedging against an inherited basement ramp a revised cross section through the selkirk fan structure provides the basis for a new model for the middle jurassic tectonic evolution of the southern omineca belt canadian cordillera palinspastic restoration of this cross section shows that the southwest verging structures along the west flank of the selkirk fan structure formed as a result of tectonic wedging of distal north american strata clachnacudainn complex beneath more proximal north american strata and that the selkirk fan structure developed outboard from a crustal ramp dogtooth high inherited from late proterozoic early paleozoic rifting along the western margin of north america the first episode of mesozoic deformation in southeastern british columbia occurred between 187 and 173 ma and involved the northeastward juxtaposition of the intermontane superterrane over the outer part of the north american continental terrace wedge it resulted in deep burial 20 25 km of the outer margin of north america a crustal ramp localized along the western edge of the late proterozoic early paleozoic dogtooth high impeded the northeastward propagation of the orogenic wedge comprising the intermontane superterrane and the imbricate underlying northeast verging thrust sheets of north american supracrustal rocks tectonic wedging involving southwest verging deformation occurred within the orogenic wedge and the resulting crustal thickening established sufficient topography and gravitational potential to drive the propagation of the deformation eastward into the dogtooth range and the rocky mountains the southwest verging structures along the west flank of the selkirk fan developed between approximately 173 and 168 ma concurrent with synorogenic extension and 10 km of exhumation the initial subsidence of the foreland basin during kimmeridgian time ca 154 ma provides the first indication of tectonic loading and lithospheric flexure of the north american plate it is interpreted to mark the time at which the orogenic wedge overrode the crustal ramp of the dogtooth high and advanced onto relatively thick and rigid continental lithosphere the tectonic model proposed for the selkirk fan structure illustrates how the configuration of the rifted margin influenced the style of crustal thickening during subsequent compressional deformation

crustal structure and orogenic material budget in the west central pyrenees surface and subsurface data are combined to construct a crustal scale cross section of the western central pyrenees france and spain at the boundary between the european and iberian plates the position of moho reflections in the ecors arzacq reflection profile suggests a tectonic wedge of european crust and upper mantle had indented the iberian plate at lower crustal levels the european wedge is overlain by an upper iberian wedge thus constituting a double stacked wedge geometry the upper wedge was delaminated and deformed giving rise to the pyrenean orogenic prism manifested as a bivergent fan in upper crustal levels the underthrust lower iberian plate has been imaged to depths of 55 60 km but crustal budget considerations based on a palinspastic reconstruction require that this continental root subducted to depths up to 90 km total orogenic contraction calculated from surface structures is about 75 80 km which was accomplished between the latest cretaceous and the early miocene at an averaged rate of 1 2 mm yr consistent with these moderate values exhumation of the orogen is much less than in the more shortened eastern parts of the range paleozoic basement and preorogenic mesozoic rocks are little eroded and much of the exhumation involved cannibalization of early foreland basins which once covered the entire poorly emergent orogen at this transect this resulted in a continuous process of sediment recycling and coupled with a considerable lateral arrival of material a bulk negative erosion sedimentation budget

a three increase model for the origin of the marginal reversal of the koitelainen layered intrusion finland to gain insights into the long standing problem of marginal reversals we have studied in detail the 200 m thick marginal zone of the 3 km thick mafic koitelainen layered intrusion kli this marginal zone consists of pigeonite gabbros that are chilled against gneisses of the underlying basement but reveals a non chilled upper contact with orthopyroxenites of the overlying layered series there is a sharp textural and compositional break between the rocks of the marginal zone and the layered series of the kli the marginal zone is remarkable in showing systematic reverse fractionation trends from the bottom to the very top these are exemplified by a significant upward increase in whole rock and pyroxene mg number along with normative and actual an content of plagioclase as well as by an upward decrease in all incompatible components e g tio2 zr y ree this is accompanied by a systematic upward decrease in ratios of highly incompatible elements such as zr yand la yb and in initial whole rock end the uppermost rocks of the marginal zone are very fine grained and show well developed plagioclase lamination and ultra depletion in all incompatible elements e g zr1 4 0 5 ppm ce1 4 0 11ppm the marginal zone is interpreted as having developed by in situ crystallization of magma in a slowly opening fissure the origin of reverse compositional trends is attributed to three principal factors which we refer to as the threeincrease model 1 an increase in compositional primitivity of the magma that gradually filled the chamber 2 an increase in the degree of chemical equilibrium among phases associated with increasing distance from the cold country rocks 3 an increase in the proportion of cumulus minerals in response to more effective removal of evolved liquid from in situ growing crystals with distance from the intrusive contact the marginal reversal of the kli is distinct from typical reversals in layered intrusions in that its development was interrupted by the emplacement of a large volume of new magma that was parental to the overlying layered series this new hot magma caused significant textural and compositional reconstitution of the uppermost gabbroic rocks of the marginal reversal by their partial melting compaction and recrystallization this gave rise to a considerable decrease in grain size appearance of plagioclase lamination and ultra depletion in highly incompatible elements the anomalous nature of these rocks is thus a manifestation of their restitic rather than primary magmatic origin the proposed three increase model may represent a general explanation for the origin of marginal reversals in many mafic sills and layered intrusions