are we studying deformed rocks in the right sections best practices in the kinematic analysis of 3d deformation zones abstract a standard procedure in kinematic analyses of deformed rocks is studying samples only on the foliation perpendicular lineation parallel section based on the assumption that the rotational component of deformation is restricted to that plane the theoretical background for this procedure is that deformation is plane strain which is often useful but fails to account for all relevant features observed in many natural cases more general 3d kinematic models reproduce several of these features and help to better understand 3d deformation likely predominant in nature so they are a more appropriate starting point for deformation zone analysis theoretical and natural 3d deformation examples suggest that the section with highest degree of asymmetry the vorticity normal section vns and the corresponding vorticity vector are independent from the finite strain fabric and thus may present varied orientations with respect to the tectonic foliation and lineation the vns orientation depends on the kinematics resulting from boundary conditions whereas the strain fabric orientation also depends on accumulated strain the orientation of the vns is itself an essential element of shear zone kinematics hence it cannot be pre assumed but must be determined independently

applying a general triclinic transpression model to highly partitioned brittle ductile shear zones a case study from the torcal de antequera massif external betics southern spain abstract oblique convergence and subsequent transpression kinematics can be considered as the general situation in most convergent and strike slip tectonic boundaries to better understand such settings progressively more complex kinematic models have been proposed which need to be tested against natural shear zones using standardized procedures that minimise subjectivism in this work a protocol to test a general triclinic transpression model is applied to the torcal de antequera massif tam an essentially brittle shear zone our results given as kinematic parameters of the transpressive flow transpression obliquity extrusion obliquity and kinematic vorticity number wk suggest that the bulk triclinic transpressive flow imposed on the tam was partitioned into two different flow fields following a general partitioning type as such one flow field produced narrow structural domains located at the limits of the tam where mainly dextral strike slip simple shear dominated transpression took place outer domains ods in contrast the remaining part of the bulk flow produced pure shear dominated dextral triclinic transpression at the inner part of the tam inner domain id a graphical method relating internal wk to far field dip of the shear zone boundary angle of oblique convergence transpression parameters is proposed to obtain the theoretical horizontal velocity vector v which in the case of the tam ranges between 099 and 118 these results support the applicability of kinematic models of triclinic transpression to brittle ductile shear zones and the potential utility of the proposed protocol

stratigraphy composition and form of the deccan basalts western ghats india in the western ghats between latitudes 18 20 n and 19 15 n 7000 km2 of deccan basalt have been mapped with the primary objective of establishing a flow stratigraphy as a guide to the volcanic history of the flood basalts using over 70 measured vertical sections major and trace element analyses of nearly 1200 samples and rare earth and87sr 86sr determinations for over 60 samples we divide the basalt into three subgroups and ten formations in this paper we describe the seven principal formations in the area and the most prominent individual flows

aridity changes in the eastern qilian mountains since ad 1856 reconstructed from tree rings abstract this paper presents a drought reconstruction for the eastern qilian mountains based on a tree ring width chronology developed from three sites of the qinghai spruce picea crassifolia kom the drought reconstruction spanning the years 1856 2009 was developed by calibrating tree ring data with the regional averaged palmer drought severity index pdsi the reconstruction explains 49 9 of the actual pdsi variance during the calibration period from 1951 to 2005 the reconstruction shows droughts occurred in the 1900s the 1920s and early 1930s and at the turn of the 21st century multi taper method spectral analysis indicates the existence of some significant peaks at 2 6 4 2 and 56 9 years drought variations in the study area are significantly correlated with sea surface temperatures in eastern equatorial pacific ocean northern indian ocean eastern china sea and the atlantic ocean suggesting a possible connection with the el nino southern oscillation the asian monsoon and the westerlies

variscan intra orogenic extensional tectonics in the ossa morena zone evora aracena lora del rio metamorphic belt sw iberian massif shrimp zircon u th pb geochronology

recurrent early cretaceous indo madagascar 89 86 ma and deccan 66 ma alkaline magmatism in the sarnu dandali complex rajasthan 40 ar 39 ar age evidence and geodynamic significance abstract the sarnu dandali alkaline complex in rajasthan northwestern india is considered to represent early pre flood basalt magmatism in the deccan traps province based on a single 40 ar 39 ar age of 68 57 ma rhyolites found in the complex are considered to be 750 ma malani basement our new 40 ar 39 ar ages of 88 9 86 8 ma for syenites nephelinite phonolite and rhyolite and 66 3 0 4 ma 2 melanephelinite provide clear evidence that whereas the complex has deccan age 66 ma components it is dominantly an older by 20 million years alkaline complex with rhyolites included basalt is also known to underlie the early cretaceous sarnu sandstone sarnu dandali is thus a periodically rejuvenated alkaline igneous centre active twice in the late cretaceous and also earlier many such centres with recurrent continental alkaline magmatism sometimes over hundreds of millions of years are known worldwide the 88 9 86 8 ma 40 ar 39 ar ages for sarnu dandali rocks fully overlap with those for the indo madagascar flood basalt province formed during continental breakup between india plus seychelles and madagascar recent 40 ar 39 ar work on the mundwara alkaline complex in rajasthan 120 km southeast of sarnu dandali has also shown polychronous emplacement over 45 million years and 84 80 ma ages obtained from mundwara also arguably represent post breakup stages of the indo madagascar flood basalt volcanism remnants of the indo madagascar province are known from several localities in southern india but hitherto unknown from northwestern india 2000 km away additional equivalents buried under the vast deccan traps are highly likely

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

40ar 39ar age of the st mary s islands volcanics southern india record of india madagascar break up on the indian subcontinent abstract the felsic volcanics rhyolites and rhyodacites of the st mary s islands smi southern india 13 n were originally interpreted as a distant outlier of the 65 ma deccan volcanic province of west central india comprising dominantly flood basalts later the smi volcanics were dated at 93 ma by the k ar technique however this k ar age was dubious being merely an average of five out of six widely varying dates and arbitrary data selectivity being involved in this averaging our first 40ar 39ar dating of the smi volcanics yields excellent plateau and isochron ages and their weighted mean isochron age is 85 6 0 9 ma 2 interestingly the southern indian precambrian terrain is intruded by numerous mafic doleritic dyke swarms ranging in age from proterozoic to the latest cretaceous 69 65 ma deccan related and indeed two regional dykes a leucograbbro and a felsite from the kerala region of southwestern india remain previously dated at 85 ma but again with the k ar technique however this age for the smi volcanics also corresponds excellently with 40ar 39ar ages of 89 85 ma weighted mean isochron age 87 6 1 2 ma 2 equivalent to 88 1 1 2 ma corresponding to mmhb 1 age of 523 1 2 6 ma for the madagascar flood basalt province together therefore the madagascar flood basalt province the smi volcanics and possibly the kerala dykes could represent volcanic activity associated with the break up of greater india india plus seychelles and madagascar thought to have occurred in the upper cretaceous at 88 ma

finite strains in transpression zones with no boundary slip abstract a mathematical model describing finite strains has been developed for transpression zones where no slip is allowed in any direction at the zone boundaries this has been adapted to model transpression zones where the boundaries are inclined the model can also be used to describe finite strain patterns where material is incorporated into the deforming zone from one or both sides after the initiation of deformation so that the deforming zone remains at a constant width thus allowing large transpressional strains to be accommodated without the deforming zone closing to zero thickness this model of steady state transpression can be used to explain some of the features of the south mayo trough a late silurian transpression zone in the west of ireland

mylonites from the towaliga fault zone central georgia products of heterogeneous non coaxial deformation abstract retrograde mylonitic rocks occur in the segment of the towaliga fault southeast of jackson georgia mylonite protoliths are heterogeneous quartz feldspathic gneisses upper amphibolite facies sillimanite zone from the pine mountain and piedmont terranes protoliths contain no distinctive lithological markers that can be used to determine fault displacement shear sense can only be determined using microstructural criteria and type porphyroclast systems shear bands asymmetric microfolded quartz ribbons subgrain fabrics in quartz ribbons the most common porphyroclast system developed in mylonites and ultramylonites is type type systems do not have readily identifiable tails but do produce distinctive asymmetrical pile ups in the matrix such that the angle of intersection between the perturbed zone and the mylonitic foliation points in the shear direction differences in morphology between and type systems can be related to differences in the recrystallization rate deformation rate ratio r reflecting changes in ductility contrast between matrix and porphyroclast that controls the amount of recrystallized material in a porphyroclast mantle that is potentially available to form tails in early stages of mylonitization with low ductility contrasts and large r ratios large mantles occur around porphyroclasts and tailed systems develop in advanced stages of mylonitization with large ductility contrasts and small r ratios either very small or partially or totally missing mantles occur and type systems develop microstructural criteria ubiquitously record a right lateral strike slip motion component to the deformation textural evidence e g unidirectional shear bands consistent vorticity recorded by porphyroclasts and asymmetrical microfolds suggest that the mylonites are the products of non coaxial deformation the local presence of fabrics with coaxial symmetry result from heterogeneity in the deformation the right lateral offset on the towaliga fault most likely occurred during the late paleozoic alleghanian orogeny

high pressure metamorphism in the early variscan subduction complex of the sw iberian massif abstract several units exposed in the boundary area of the ossa morena zone omz and the south portuguese zone spz preserve petrographic and thermobarometric evidence for an early metamorphic episode m1 developed under a high p low to intermediate t gradient related to early variscan subduction in the sw iberian massif in the omz these are the cubito moura unit p min 9 2 kbar and t 395 45 c blueschists from its basal melange p min 12 4 kbar and t 310 11 c and the underlying fuenteheridos group p 10 9 0 4 kbar and t 449 31 c the equivalent units in the spz are the la minilla formation p 8 7 0 4 kbar and t 388 16 c and the lawsonite pseudomorphs bearing pulo do lobo formation all these units formed part of an approximately ne verging orogenic wedge present coordinates developed by the accretion of subducted slabs of the outermost margin of gondwana and other elements of the rheic ocean realm from at least the middle devonian to the lowermost tournaisian high pressure rocks were subsequently emplaced on more internal zones of the omz that only experienced a younger high t low to intermediate p metamorphism m2 this high t event was coeval with magmatic activity from the uppermost devonian to the middle mississippian probably as a consequence of transtensional lithospheric thinning and or delamination of the lower crust and mantle lithosphere of the gondwana margin pre late devonian synorogenic sedimentation in forearc and back arc basins of the subduction complex evolved to a late devonian middle mississippian foreland basin system in early collisional stages finally a new middle late mississippian fold and thrust belt with opposite sw vergence and new foreland basins developed during late collisional stages

progressive development of structures in a ductile shear zone in the singhbhum shear zone of eastern india successive generations of folds grew in response to a progressive ductile shearing during this deformation a mylonitic foliation was initiated and was repeatedly transposed the majority of fold hinges were formed in an arcuate manner at low angles to the y axis in an e w trending subhorizontal position and major segments of the fold hinges were then rotated towards the down dip northerly plunging x axis the striping and intersection lineations were rotated in the same manner the down dip mylonitic lineation is a composite structure represented by rotated early lineations and newly superimposed stretching lineations the consistent asymmetry of the folds the angular relations between c and s surfaces and the evidence of two dimensional boudinage indicate that the deformation was non coaxial but with a flattening type of strain with 1 2 the degree of non coaxiality varied both in space and time from the progressive development of mesoscopic structures it is concluded that the 2 3 km wide belt of ductile shear gave rise to successive anastomosing shear zones of mesoscopic scale when a new set of shear lenses was superimposed on already sheared rocks the preexisting foliation generally lay at a low angle to the lenses no new folds developed where the acute angle was sympathetic to the sense of shear displacements where the acute angle was counter to the sense of shear the pre existing foliation lying in the instantaneous shortening field was deformed into a set of asymmetric folds

40ar 39ar ages of bombay trachytes evidence for a palaeocene phase of deccan volcanism we present 40ar 39ar ages of 60 4 0 6 ma and 61 8 0 6 ma 2 for deccan trap trachytes from manori and saki naka bombay situated in the tectonized panvel flexure zone along the western indian rifted continental margin these ages provide clear evidence that i these trachytes are of palaeocene age and therefore substantially younger than the lower part of the main flood basalt sequence exposed in the western ghats which precedes the k t boundary in age and ii the formation of the panvel flexure along the west coast must have been subsequent to 60 ma considering early alkaline deccan rocks previously dated at 68 5 ma the total duration of deccan volcanism was at least 8 my

the southern iberian shear zone a major boundary in the hercynian folded belt a long ductile shear zone extending across the northern parts of sevilla and huelva provinces southwest spain and very probably stretching further west into portugal is characterized by a conspicuously developed l s fabric and the existence of various mylonitic textures the shear zone closely associated with amphibolites of tholeiitic affinity represents an important oceanic suture of the hercynian belt in europe the sense of displacement inferred from microstructures is consistent with southwest directed upthrusting evolving to a left lateral shearing movement

analogue modelling of inclined brittle ductile transpression testing analytical models through natural shear zones external betics abstract the combination of analytical and analogue models gives new opportunities to better understand the kinematic parameters controlling the evolution of transpression zones in this work we carried out a set of analogue models using the kinematic parameters of transpressional deformation obtained by applying a general triclinic transpression analytical model to a tabular shaped shear zone in the external betic chain torcal de antequera massif according to the results of the analytical model we used two oblique convergence angles to reproduce the main structural and kinematic features of structural domains observed within the torcal de antequera massif 15 for the outer domains and 30 for the inner domain two parallel inclined backstops one fixed and the other mobile reproduce the geometry of the shear zone walls of the natural case additionally we applied digital particle image velocimetry piv method to calculate the velocity field of the incremental deformation our results suggest that the spatial distribution of the main structures observed in the torcal de antequera massif reflects different modes of strain partitioning and strain localization between two domain types which are related to the variation in the oblique convergence angle and the presence of steep planar velocity and rheological discontinuities the shear zone walls in the natural case in the 15 model strain partitioning is simple and strain localization is high a single narrow shear zone is developed close and parallel to the fixed backstop bounded by strike slip faults and internally deformed by r and p shears in the 30 model strain partitioning is strong generating regularly spaced oblique to the backstops thrusts and strike slip faults at final stages of the 30 experiment deformation affects the entire model box our results show that the application of analytical modelling to natural transpressive zones related to upper crustal deformation facilitates to constrain the geometrical parameters of analogue models

deformation path partitioning within a transpressive shear zone marble cove newfoundland detailed study of the structures in marble cove newfoundland indicates that they formed during a single transpressional event during which deformation was partitioned between dominantly strike slip and dominantly dip slip domains marble cove exhibits steeply dipping foliations steeply to shallowly plunging stretching lineations greenschist facies mineral assemblages and abundant quartz veins within the broad domain where stretching lineations plunge steeply sense of shear indicators and asymmetry of quartz c axis distributions in mylonitized quartz veins indicate dominantly reverse motion with a component of dextral shear adjacent greenschists exhibit orthorhombic symmetry and apparently accommodated pure shear the abrupt transition to a narrow high strain domain of shallowly plunging stretching lineations is accommodated by a rheologically distinct serpentinite body shear bands in this domain indicate dextral strike slip movement with a reverse component smaller conjugate shear bands are evident in thin section indicating a component of pure shear sense of shear indicators and asymmetry of c axis distributions in mylonitized quartz veins also record dextral strike slip and reverse shear with a component of pure shear crenulations and asymmetric folds in foliation overprint all other fabrics in marble cove and record a final phase of reverse shear with a dextral component with partitioning of this kind structures recording strike slip movement may be limited in areal extent and therefore less likely to be exposed than structures recording dip slip motion such partitioning within transpressional shear zones may therefore impede recognition of strike parallel motions within orogenic belts

porphyroclast systems as kinematic indicators porphyroclasts of relatively strong minerals in mylonites commonly have an internal monoclinic shape symmetry defined by tails of dynamically recrystallized material the geometry of a porphyroclast and its tails called a porhyroclast system can serve as a valuable indicator of the sense of vorticity porphyroclast systems have been divided into and types on the basis of the geometry of the tails types have wedge shaped recrystallized tails whose median lines lie on opposite sides of a reference plane parallel to the tails and containing the symmetry axis for the system types are further subdivided into a a types in which the porphyroclast is isolated in a relatively homogeneous matrix and b types in which the porphyroclast system is associated with a shear band foliation in the matrix types typically have narrow recrystallized tails whose median lines cross the reference plane adjacent to the porphyroclast consequently embayments of matrix material occur adjacent to the porphyroclasts and the tails display characteristic bends a porphyroclast system in a mylonite develops when the relatively weak dynamically recrystallized grain aggregate in the porphyroclast mantle changes its shape due to non coaxial flow in the adjacent matrix this behaviour has been modelled in shear box experiments passive marker lines around rigid cylinders embedded in silicone putty were subjected to simple shear the experiments were modified to simulate a change in recrystallization rate r with respect to rate of deformation by decreasing the diameter of the rigid cylinder during deformation at variable rates the ratio r appears to be one of the most important factors in determining which porphyroclast system will develop at high r values flow of recrystallized material away from the porphyroclast is continuously appended by the production of new grains and wedge shaped a type tails develop at low r values relatively few new grains are added to the tails which become thinned and deflected by drag due to the spinning motion of the porphyroclast in addition most porphyroclast systems at low shear strains are of a type or lack monoclinic symmetry whereas types are only developed at high shear strain values complex porphyroclast systems characterized by two generations of tails are observed in many of the natural and model shear zones studied and may form due to fluctuating r conditions that allow isolated a and type porphyroclast systems to be used as sense of vorticity indicators are the systems should have a monoclinic shape symmetry matrix grain size should be small with respect to porphyroclast size matrix fabric should be homogeneous deformation history should be simple and observations should be made on sections normal to the inferred bulk vorticity vector for the mylonite

late cretaceous india madagascar fit and timing of break up related magmatism a u pb zircon age of 91 2 0 2 myr from western india st mary islands confidently links india with the late cretaceous magmatic province in madagascar 84 92 ma and the u pb age is within analytical error of the u pb age of the analalava gabbro pluton 91 6 0 3 myr in northeastern madagascar palaeomagnetic data from india and madagascar allow us to postulate a new india madagascar fit euler latitude 14 24 longitude 38 8 and rotation angle 69 2 this fit is applicable to the late cretaceous directly prior to and during the early phase of madagascar india separation in our late cretaceous reconstruction south west india runs roughly subparallel with the first known break up related magnetic anomaly a34 it maintains a close connection between mada gascar and india but places india slightly rotated compared to the eastern margin of madagascar and more northerly compared with some reconstructions st mary magmatism is linked to the initial break up between india and madagascar and magmatism probably resulted from rift related extensional processes initially induced by the marion hotspot underlying southern madagascar during the late cretaceous

development of lattice preferred orientation in clinoamphiboles deformed under low pressure metamorphic conditions a sem ebsd study of metabasites from the aracena metamorphic belt sw spain the mechanical properties of the lower continental crust are intimately related to the rheology of calcic clinoamphibole naturally deformed clinoamphibole typically shows brittle behaviour under a wide range of deformation conditions whereas crystal plasticity is rarely observed in this study the microfabric of clinoamphiboles from metabasites deformed under low pressure medium to high temperature metamorphic conditions is presented amphiboles from all samples have developed lpo that can be attributed to different deformation mechanisms depending on deformation temperature fluid content structure and phase strength contrasts rigid body rotation of amphibole prisms within a weaker plagioclase matrix corresponds to metabasites deformed under medium deformation temperatures that show a weak layer structure and a high phase strength contrast between plagioclase and clinoamphibole lower temperatures and the presence of fluids mean that one of the studied rocks was affected also by dissolution precipitation creep and cataclastic flow in the final sample dislocation creep was accommodated by recovery and subgrain rotation dynamic recrystallization in monominerallic hornblende layers at higher temperatures which could be representative of the rheology of amphiboles in a lower continental crust at high temperature conditions

the karnataka late cretaceous dykes as products of the marion hot spot at the madagascar india breakup event evidence from 40ar 39ar geochronology and geochemistry two late cretaceous mafic dykes with an ene strike that is orthogonal to the west coast of india and located nearly 200 km inland around huliyardurga karnataka state yield 40ar 39ar plateau ages of 90 0 1 0 and 87 5 0 9 ma these fe ti enriched tholeiites are essentially co eval with at least four other igneous suites widely scattered in southern india namely the south and north kerala dykes the agali anaikatti dykes of central kerala tamil nadu and lavas of st mary islands off the west coast of india the karnataka cretaceous dykes are also co eval and compositionally very similar to the fe ti enriched tholeiitic lavas and dykes around mananjary a major phase of late cretaceous magmatism along the eastern rifted margin of madagascar which are believed to be products of the marion hot spot that extruded at 88 ma synchronous with the india madagascar break up event the age and compositional similarities between these late cretaceous magmatic rocks from india and madagascar constitute a clear evidence for extension of the thermal manifestations deep into the indian peninsula

geochemical provinciality in the cretaceous basaltic magmatism of northern madagascar mantle source implications the northern part of the late cretaceous flood basalt province of madagascar is formed by lava flows dykes and intrusive complexes these range from tholeiitic to weakly alkaline and have composition from basalts to basaltic andesites with rare more evolved rocks the magmatic evolution is dominated by low pressure crystal fractionation of olivine cr spinel plagioclase and clinopyroxene the erupted rocks form two subprovinces in terms of incompatible element concentrations or ratios and geographical position the mafic and intermediate samples from the western subprovince have low abundances of high field strength elements e g nb 2 9 ppm zr 50 230 ppm negative nb anomalies on mantle normalized diagrams and a wide range of initial 88 ma 143 nd 144 nd 0 51293 0 51197 e nd 7 9 to 10 9 these elemental and isotopic variations are compatible with melting of predominantly n morb like mantle and variable low pressure crustal contamination the mafic samples of the eastern subprovince are mildly enriched in incompatible elements e g nb 6 25 ppm zr 109 330 ppm with the highest values found in tholeiites from the east mahajanga basin tampoketsa kamoreen and tamatave they also have a comparatively narrow range of initial 143 nd 144 nd 0 51276 0 51258 e nd 5 1 to 1 0 consistent with derivation from incompatible element enriched mantle sources and minor subsequent crustal contamination the marked differences in the chemical and isotopic characteristics of the samples imply variable degrees of partial melting of hotter than normal chemically heterogeneous mantle sources at pressures where spinel to garnet are residual phases no clear evidence is seen for a chemical component similar to that represented at present by the marion hotspot lavas

comment on the late devonian variscan suture of the iberian massif a correlation of high pressure belts in nw and sw iberia tectonophysics 654 96 100 by r fernandez and r arenas abstract a vast variscan nappe spreading from the allochthonous complexes of nw iberia to the ossa morena zone in sw iberia has been proposed by diez fernandez and arenas 2015 based on the correlation of different outcrops of high pressure and morb type rocks this interpretation conflicts with well known geological and geophysical data regarding the sw iberian variscides which point to i major kinematic and geometric inconsistencies come up when interpreting the ossa morena zone as an allochthonous unit ii the outcrops of high pressure and morb type rocks belong to two different sutures rather than a single one and iii sw iberia is characterized by transpressional deformation related to a very oblique left lateral continental collision while nw iberia features a rather frontal collision

characterization of tectono metamorphic events using crystal size distribution csd diagrams a case study from the acebuches metabasites sw spain crystal size is one of the main characteristics of a metamorphic rock since it is the result of several processes including prograde metamorphism as well as retrometamorphism and static and dynamic recrystallisation in this paper crystal size histograms mean crystal size crystal size distribution diagrams mean aspect ratio and proportion of prismatic sections of amphiboles have been used to describe two tectono metamorphic events that affected the acebuches metabasites in the southwestern part of the iberian massif the diagrams depicting the crystal size distribution csd of metamorphic rocks show typically a straight segment that reflects the kinetic conditions during prograde metamorphism as well as retrometamorphic and dynamic recrystallisation processes and a bell shaped curve formed during the last stages of growth the geometrical characteristics of the straight lines of csd diagrams from different samples of the acebuches metabasites vary consistently with the structural and metamorphic features indicative of the tectono metamorphic history suffered by these rocks this suggests that csd diagrams can be a useful tool of microstructural analysis in metamorphic rocks

correlations between silicic volcanic rocks of the st mary s islands southwestern india and eastern madagascar implications for late cretaceous india madagascar reconstructions abstract the st mary9s islands southwestern india expose silicic volcanic and sub volcanic rocks rhyolites and granophyric dacites emplaced contemporaneously with the cretaceous igneous province of madagascar roughly 88 90 ma ago the st mary9s islands rocks have phenocrysts of plagioclase clinopyroxene orthopyroxene and opaque oxide moderate enrichment in the incompatible elements e g zr 580 720 ppm nb 43 53 ppm la yb n 6 9 7 2 relatively low initial 87 sr 86 sr 0 7052 0 7055 and near chondritic initial 143 nd 144 nd 0 51248 0 51249 they have mineral chemical whole rock chemical and isotopic compositions very close to those of rhyolites exposed between vatomandry ilaka and mananjary in eastern madagascar and are distinctly different from rhyolites from other sectors of the madagascan province we therefore postulate that the st mary9s and the vatomandry ilaka mananjary silicic rock outcrops were adjacent before the late cretaceous rifting that split madagascar from india if so they provide a valuable tool to check and aid traditional cretaceous india madagascar reconstructions based on palaeomagnetism matching precambrian geological features and geometric fitting of continental shelves supplementary material mineral analyses mass balance calculations and locality information are available at http www geolsoc org uk sup18332

the terrace like feature in the mid continental slope region off trivandrum and a plausible model for india madagascar juxtaposition in immediate pre drift scenario abstract bathymetry of the southwestern continental margin of india reveals the presence of an anomalous terrace like feature in the mid continental slope region off trivandrum the genesis of this terrace of large areal extent 9000 sq km is yet to be established based on exercises with several existing paleogeographic reconstruction models and updated compilation of identified offshore tectonic elements this study attempts to identify a plausible model of india madagascar juxtaposition in immediate pre drift scenario which provides idea about genesis of this terrace it is inferred that the terrace off trivandrum and an anomalous bathymetric notch located in the northern madagascar ridge are conjugate features related to india madagascar separation and the rifted and sheared segments of the pre drift plate boundary have shaped their outlines the drifting of india from madagascar is suggested to have commenced at about 86 5 ma

major shear zone within the greater himalayan sequence and sequential evolution of the metamorphic core in sikkim india abstract the greater himalayan sequence ghs bounded by the south tibetan detachment system and the main central thrust mct constitutes majority of the himalayan metamorphic core recent studies identified several shear zones within the ghs which played significant role in its evolution here we report the presence of a major shear zone the chungthang thambi thrust ctt which is situated within the ghs in sikkim eastern india the ctt exhibits zone type geometry with mylonite core flanked by protomylonite zones and its thickness varies from 1 km to 5 6 km along the transport direction new 40ar 39ar mica ages and apatite fission track dates from this study when integrated with published u th pb monazite and lu hf garnet ages indicate that the ctt the mct and the munsiari thrust mt at base of the crystalline lesser himalayan sequence lhcs developed in sequence between 27 ma and 12 ma and controlled the sequential evolution of the metamorphic core ghs lhcs in sikkim our imbricate model suggests that the upper middle ghs was initially underthrusted below the tethyan unit and underwent prograde metamorphism from 37 ma to 28 ma thrusting on the ctt exhumed the middle ghs and underthrusted the lower ghs between 27 ma and 22 5 ma the mct exhumed the lower ghs between 22 5 ma and 12 1 ma and underthrusted the lhcs which was later exhumed by the mt between 12 ma and 10 ma the thrust sheets exhumed to near surface conditions between 2 6 and 0 5 ma during growth of the underlying lesser himalayan duplex the mct showed protracted activity till 7 2 ma and leading edge of the ctt was later reactivated at 13 5 ma and at 1 8 ma the ctt is equivalent to the high himalayan discontinuity and forms part of a regional structure that spans 800 km arc length of the himalaya from sikkim to west central nepal

crustal structure of the transpressional variscan orogen of sw iberia sw iberia deep seismic reflection profile iberseis 1 iberseis a 303 km long 20 s deep seismic reflection profile was acquired across the variscan belt in sw iberian peninsula the acquisition parameters were designed to obtain a high resolution crustal scale image of this orogen the seismic profile samples three major tectonic terranes the south portuguese zone the ossa morena zone and the central iberian zone which were accreted in late paleozoic times these terranes show a distinctive seismic signature as do the sutures separating them late strike slip movements through crustal wedges are apparent in the seismic image and have strongly modified the geometry of sutures the upper crust appears to be decoupled from the lower crust all along the seismic line but some deformation has been accommodated at deeper levels a sill like structure is imaged in the middle crust as a 1 2 s thick and 175 km long high amplitude conspicuous reflective band it is interpreted as a great intrusion of mafic magma in a midcrustal decollement taking into account surface geological data and the revealed crustal architecture a tectonic evolution is proposed for sw iberia which includes transpressional collision interacting during early carboniferous with a mantle plume the moho can be identified along the entire transect as subhorizontal and located at 10 to 11 s indicating a 30 35 km average crustal thickness its seismic signature changes laterally being very reflective beneath the south portuguese zone and the central iberian zone but discontinuous and diffuse below the ossa morena zone

a model for the development of crenulations in shear zones with applications from the southern appalachian piedmont abstract two sets of crenulations are associated with a major alleghanian dextral shear zone which deformed stratigraphic and structural boundaries in the eastern piedmont of south carolina both sets of crenulation planes are oblique to the boundaries of the shear zone the morphologies and orientations of the crenulation sets and their spatial distributions indicate that they are related to slip along foliation planes and that they serve to compensate for displacement components of foliation slip normal to the overall movement direction in the shear zone the crenulations act to maintain the initial thickness of the shear zone our evaluation of the recent literature on shear zones suggests that crenulations related to foliation slip are abundant and constitute a reliable sense of shear indicator

geological and 40ar 39ar age constraints on late stage deccan rhyolitic volcanism inter volcanic sedimentation and the panvel flexure from the dongri area mumbai abstract post k pg boundary deccan magmatism is well known from the mumbai area in the panvel flexure zone represented by the salsette subgroup it shows characters atypical of much of the deccan traps including rhyolite lavas and tuffs mafic tuffs and breccias spilitic pillow basalts and intertrappean sedimentary or volcanosedimentary deposits with mafic intrusions as well as trachyte intrusions containing basaltic enclaves the intertrappean deposits have been interpreted as formed in shallow marine or lagoonal environments in small fault bounded basins due to syn volcanic subsidence we report a previously unknown sedimentary deposit underlying the dongri rhyolite flow from the upper part of the salsette subgroup with a westerly tectonic dip due to the panvel flexure we have obtained concordant 40ar 39ar ages of 62 6 0 6 ma 2 and 62 9 0 2 ma 2 for samples taken from two separate outcrops of this rhyolite the results are significant in showing that i danian inter volcanic sedimentary deposits formed throughout mumbai ii the rock units are consistent with the stratigraphy postulated earlier for mumbai iii shale fragments known in some dongri tuffs were likely derived from the sedimentary deposit under the dongri rhyolite iv the total duration of extrusive and intrusive deccan magmatism was at least 8 9 million years and v panvel flexure formed or continued to form after 63 ma possibly even 62 ma and could not have formed by 65 64 ma as concluded in a recent study

triclinic transpression zones with inclined extrusion data from natural transpressional shear zones reveal a large range of lineation orientations that can spread along complete girdles one possible way to account for such a type of fabrics is variation in the extrusion direction this work presents a new theoretical model of oblique transpression with inclined extrusion the model is kinematic and the flow is considered as homogeneous and steady the angle between the simple shear direction and the extrusion direction is one of the main parameters controlling the final fabric low values of 40 can generate strain ellipsoids very close to the abscissa axis of the flinn plot depending on the vorticity of the flow the finite strain and the actual value of the angle the model predicts the generation of lineation fabrics ranging from point maxima to patterns with opposite plunge senses these patterns can display monoclinic nearly monoclinic or clearly triclinic symmetry lineation patterns spreading along complete girdles can be obtained by allowing the extrusion direction to deviate less than 30 about the vertical in either direction

transpressional deformations within the sanandaj sirjan metamorphic belt zagros mountains iran abstract polyphase deformation structures of the sanandaj sirjan metamorphic belt in the neyriz area zagros mountains iran are consistent with dextral transpressional deformation which is related to the oblique collision between the african arabian continent and the iranian microcontinent the collision started in the late cretaceous and is continuing to the present day quantitative kinematic analyses quartz textures suggest localized shear zones deformed with a significant pure shear component spatial orientation of lineation and semi quantitative kinematic indicators indicate shear zone parallel stretching and shear zone perpendicular shortening the occurrence of a horizontal stretching component parallel to the deformation zone boundary allows a kinematic model of combined transpression and lateral extrusion for this part of the zagros orogeny

remobilization of granitoid rocks through mafic recharge evidence from basalt trachyte mingling and hybridization in the manori gorai area mumbai deccan traps products of contrasting mingled magmas are widespread in volcanoes and intrusions subvolcanic trachyte intrusions hosting mafic enclaves crop out in the manori gorai area of mumbai in the deccan traps the petrogenetic processes that produced these rocks are investigated here with field data petrography mineral chemistry and whole rock major trace and pb isotope chemistry local hybridization has occurred and has produced intermediate rocks such as a trachyandesitic dyke feldspar crystals have complex textures and an unusually wide range in chemical composition crystals from the trachytes cover the alkali feldspar compositional range and include plagioclase crystals with anorthite contents up to an47 crystals from the mafic enclaves are dominated by plagioclase an72 90 but contain inclusions of orthoclase and other feldspars covering the entire compositional range sampled in the trachytes feldspars from the hybridized trachyandesitic dyke yield mineral compositions of an80 86 an47 54 a b94 99 o r45 60 a nd or96 98 all sampled within individual phenocrysts we show that these compositional features are consistent with partial melting of granitoid rocks by influx of mafic magmas followed by magma mixing and hybridization of the partial melts with the mafic melts which broadly explains the observed bulk rock major and trace element variations however heterogeneities in pb isotopic compositions of trachytes are observed on the scale of individual outcrops likely reflecting initial variations in the isotopic compositions of the involved source rocks the combined data point to one or more shallow level trachytic

madagascar basalts tracking oceanic and continental sources extensive upper cretaceous volcanism in southern madagascar was fed in part by mantle sources resembling those expressed today in the indian ocean at marion and prince edward islands and on the central southwest indian ridge in addition very low end t to 17 4 high 87sr 86sr t to 0 72126 tholeiites in southwestern madagascar were variably but highly contaminated by ancient continental material broadly like that affecting the bushe and poladpur formations of the later deccan traps in india alkalic dikes in southwestern madagascar have a rough analogue in the mahabaleshwar formation of the deccan in that they document the influence of a low 206pb 204pb negative end relatively low 87sr 86sr reservoir a very similar reservoir is manifested at present in mid ocean ridge basalts on the central southwest indian ridge near 40 e the original location of this end member appears likely to have been in the madagascan lithospheric mantle a portion of which may have been removed in the middle cretaceous by the action of the marion hotspot or the rifting of indo madagascar an origin within the hotspot itself also may be possible however recent products of the hotspot appear to lack completely the necessary low 206pb 204pb low end signatures

structural analysis of an accretionary prism in a continental collisional setting the late paleozoic pulo do lobo zone southern iberia abstract models concerning the tectonic evolution of accretionary complexes typically relate outcrop scale to plate scale multiphase deformation as a smooth variation of strain on all scales however at oblique convergent margins regional scale brittle faults in the shallow crust are commonly parallel to the main orogenic grain these faults impose a strong structural anisotropy and can subsequently control deformation at subordinate scales as a result finite strain in each domain may not record local kinematics consistent with the overall orogenic scale motion implying that structural data must be analyzed selectively from a large area in order to relate outcrop scale kinematics to global plate scale dynamics field mapping and preliminary structural analysis of the late devonian pulo do lobo pdl formation and suspect exotic south portuguese zone spz in southern iberia indicate tectonic juxtaposition of diverse deposits such as foreland basin flysch sedimentary and tectonic melange and passive margin sediments showing an overall geometry consistent with an accretionary wedge setting variations in finite strain lithology and regional structure were used as proxies for defining tectonic domains for structural analysis numerous local kinematic indicators within the pdl suggest a complex regional deformation with several enigmatic features that can be explained by sequential compartmentalization of strain during the development of the imbricate stack followed by late stage bulk strain imposed across the entire complex structural data produced by local strain partitioning reveals kinematic indicators which contradict the overall regional structural style e g spatial juxtaposition of sinistral and dextral fabrics when viewed at larger scales i e regional scale however these data indicate that significant sinistral strike slip movement occurred in conjunction with both an extension and shortening outcrop scale deformation in polydeformed domains is controlled by local conditions resulting from brittle deformation coeval with orogenic scale bulk strain the entire pulo do lobo zone is dominated by a pervasive late stage vertical to sub vertical e w cleavage axial planar to chevron folds which overprint earlier deformation in the older passive margin units this overprinting suggests that in the late stages of the evolution of the accretionary complex bulk strain was imposed over the entire complex as a result of internal locking of the accretionary complex and reduced strain rates during the waning stages of collision between gondwana and laurussia stereographic analysis of fabric elements from each distinct tectonic domain together with regional geological constraints support this hypothesis and are indicative of progressive deformation imposed on the pdl during the variscan orogeny

radiometric discrimination of pre variscan amphibolites in the ediacaran serie negra ossa morena zone sw iberia new results on the geochronology of metabasites hosted by the neoproterozoic late ediacaran serie negra of the ossa morena zone iberian massif are presented these rocks record a protracted subduction at least since the latest cryogenian followed in a continuum by early cambrian rifting the serie negra country rocks are continental crust forearc segments of the thinned continental margin of gondwana the metabasite suite exhibits e and n morb as well as volcanic arc signatures and discloses the existence of a diverse late ediacaran early cambrian magmatism across the ossa morena zone protoliths of the e morb metabasites are clearly ediacaran they exhibit geochemical characteristics typical of younger island arcs notably of their forearc zones affected by extension soon after the initiation of subduction radiometric dating of n morb metabasites shows that these rocks are significatively younger than their country rocks whose age has been stratigraphically and paleontologically constrained as ediacaran they record early cambrian rifting developed in a continuum after a protracted subduction metabasite petrological zonation permits to reconstruct a single ediacaran subduction zone located to the s of the current omz and dipping towards the n in present day geographical coordinates

age constraints to the relationships between magmatism metamorphism and tectonism in the aracena metamorphic belt southern spain the aracena metamorphic belt amb southwest iberian peninsula is characterized by the following geological elements a a high temperature low pressure ht lp metamorphic belt a few kilometres wide and more than 200 km long b a linear belt of oceanic amphibolites with a low pressure inverted metamorphic gradient c crustal scale ductile shear zones and d mafic noritic intrusions of high mg andesite boninite composition the relationships between these elements led to the proposal of a model of ridge subduction for this sector of the hercynian belt of europe this interpretation is supported by the age relationships displayed between the main rock units considered representative of the main tectonic and petrological processes responsible for the geological elements mentioned previously the results of a geochronological study ar ar rb sr and sm nd clearly support a late paleozoic tectonic evolution at an active continental margin the time evolution of the metamorphism in the oceanic domain ranging from 342 6 0 6 ma in the west to 328 4 1 2 ma in the east over a distance of 70 km along the metamorphic belt support a tectonic model of triple junction migration responsible for the creation at depth of a slab free window with decisive consequences for the thermal evolution of the region the origin of the linear metamorphic belt of ht lp regime may be explained by the migration along a continental margin of a punctual thermal anomaly induced by the creation of a triple junction at the continental margin

rb sr isotope dating of neoproterozoic malani group magmatism from southwest rajasthan india evidence of younger pan african thermal event by 40ar 39ar studies abstract this paper reports rb sr isotope ages of the neoproterozoic volcanics and associated granitoids of the trans aravalli belt of northwestern india all these rocks along with the earlier reported 779 10 ma old felsic volcanics from diri and gurapratap singh of pali district rajasthan constitute the malani group the study indicates that different rock suites belonging to the malani group represent a polyphase igneous activity which spanned for about 100 ma ranging from 780 to 680 ma the granitoids of the malani group i e peraluminous jalore type and peralkaline siwana type were emplaced around 730 and 700 ma ago respectively these plutonic suites represent two different magmatic episodes within a short time interval the initial sr ratios of these granitoids suggest lower crustal derivation of the magma the peralkaline granitoids and the associated peralkaline rhyolites pantellerites are coeval and cogenetic the ultrapotassic rhyolite exposed at manihari of pali district represents the youngest magmatic activity at 681 20 ma having a very high initial sr ratio of 0 7135 0 0033 the high initial sr ratio of these rocks may be due to incorporation of radiogenic 87 sr from the country rock by assimilation or fusion into the residual fraction of the magma in the crust which gave rise to other differentiated rocks of the group 40 ar 39 ar studies of two jalore granite samples indicate presence of post crystallisation thermal disturbance between 500550 ma ago the timing of this thermal overprinting on the malani rocks is related to the widespread pan african thermo tectonic event which is witnessed and magmatically manifested in different part of the indian shield

tectonometamorphic evolution of the aracena metamorphic belt sw spain resulting from ridge trench interaction during variscan plate convergence 1 the aracena metamorphic belt is a high temperature low pressure ht lp band located at the southern end of the european variscan chain it marks a suture between armorica and avalonia this belt is characterized by 1 the presence of mid ocean ridge basalt derived metabasites that were affected by an inverted ht lp metamorphism related to sw verging thrusting whose thermal peak diachronously migrated eastward 2 the occurrence of a ht lp metamorphism related to an extensional event affecting continental rocks belonging to the ossa morena zone with peak temperatures that are 150 c higher than that recorded in the oceanic metabasites and 3 the presence of near trench magmatism with high mg andesite composition these and other characteristics can be interpreted in terms of a ridge trench trench triple junction that migrated along the armorican margin during variscan oblique convergence

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

relationships between kinematic indicators and strain during syn deformational exhumation of an oblique slip transpressive plate boundary shear zone the alpine fault new zealand abstract in order to assess how different elements of plate boundary scale shear zone tectonite fabrics reflect the boundary kinematics and strain history we have examined a range of such structures within the active alpine fault mylonite zone new zealand in this oblique slip zone we find that quartz cpo fabric symmetry and individual mica grain lineations reflect incremental stretches but develop stable orientations parallel to the finite stretching direction s 1 this s 1 trends oblique to the plate motion vector because the shear zone experiences some extrusion toward the free surface conversely asymmetric structures such as shear bands and mica fish reflect simple shear dominated deformation late in the shear zone history parallel to the imposed relative plate motion vector finally linear fabrics are a poor record of the mylonitic deformation in this zone because 1 they are dominantly inherited and have been only partially re oriented during mylonitisation and 2 macroscopically they become less visible at higher strains due to fabric homogenisation generally these results indicate that particularly in heterogeneous polyphase shear zones a full understanding of the movement history can only be obtained by considering kinematic information from as many different sources as possible

physical experiments of vertical transpression with localized nonvertical extrusion abstract previously proposed models of vertical walled transpression implicitly assume that material extrudes upwards during deformation this assumption is not necessarily valid at all scales given that a in areas of diverse lithologies local zones of relatively rigid materials may cause extruding material to deflect around those zones and b ductile strain often forms anastomosing geometries of shear zones therefore it is possible that a local extension direction in otherwise classic transpression may be nonvertical for rocks deforming at depth using an analogue experiment we have modeled a transpression zone with localized nonvertical extrusion this extrusion is accomplished by the addition of a side leak that allows sideways extrusion in addition to vertical extrusion the net extension direction depends on the material s position within the deforming zone resulting in a significant range of lineation orientations with deformation the strain patterns produced by transpression with localized nonvertical extrusion may explain the wide array of lineation orientations found in some natural ductile transpression zones

the structure of the temsamane fold and thrust stack eastern rif morocco evolution of a transpressional orogenic wedge abstract the structure of the temsamane fold and thrust stack corresponds to four units limited by anastomosing ductile shear zones cutting a trend of south verging recumbent folds this ductile stack was formed in an inclined left handed transpressional zone at the north african paleomargin during chattian to langhian times producing two main deformational events the first event d p produced a s p l p planar linear fabric generated in a non coaxial deformation with a top to the wsw sense of movement and was associated to metamorphic p t conditions varying from late diagenesis in the southernmost temsamane outcrops to epizone in the north according to the 40 ar 39 ar ages this deformation occurred at chattian aquitanian times the second deformational event d c event generated ene wsw trending folds with sse vergence and a set of anastomosing shear zones with s m l m planar linear fabric the latter units were generated at around 15 ma langhian and indicate a strong localization of the simple shear component of the transpression moreover this orientation is compatible with the kinematics of the temsamane detachment which can explain most of the uplift of the temsamane rocks from the middle to the uppermost crust the described evolution indicates that collision between the western mediterranean terranes and the north african paleomargin and the formation of the rifean orogenic wedge occurred at chattian to langhian times

testing the model of oblique transpression with oblique extrusion in two natural cases steps and consequences abstract kinematic models of various types of transpression have been used to explain fabric features and strain in many natural deformation studies here a mathematical model that encompasses all monoclinic and triclinic transpressional deformations including triclinic deformation with inclined simple shear and or inclined extrusion orientations can be tested using a step by step approach with available field evidence two cases are presented the first case from the wabigoon quetico boundary in the archean superior province utilizes both fabric orientation and quantified strain data the best fit of the field evidence to the model indicates that deformation likely took place along subvertical shear zones via transpression with subhorizontal simple shear 0 20 and variable inclined extrusion direction extrusion can be either east or west and typically indicates extrusion orientations between 0 and 50 from vertical the second case of the south iberian shear zone has fabric orientation data but no quantifiable strain possibilities the best fit of the field evidence to the model indicates that deformation likely took place along a moderately inclined shear zone via transpression with subhorizontal simple shear 0 20 and variable inclined extrusion direction values between 0 and 80 from the true dip of the shear zone using this protocol in other examples of natural deformation will allow further constraints to be applied to kinematic models

secondary cleavages in ductile shear zones abstract secondary cleavages developed at late stages in ductile shear zones show several features that are inconsistent with progressive simple shear in the zone these are the orientation of a single secondary cleavage oblique to the shear zone boundaries conjugate sets with opposite senses of shear and multiple sets with the same sense of shear these features can be explained if the bulk flow is partitioned into slip along discrete failure planes parallel to the primary foliation s coaxial stretching along the foliation and spin

application of the analytic model of general triclinic transpression with oblique extrusion to an active deformation zone the alhama de murcia fault se iberian peninsula abstract we have applied the analytic model of general triclinic transpression with oblique extrusion to an active shear zone in southeastern spain this study opens a new methodological approach in the study of active fault zones we are able to constrain the triclinic transpression model with absolute measures of active deformation such as gps velocity gradients and have exhaustively explored the predictions of the model and compared them to the orientation data of field kinematic markers fault slip data and reorientation of fold hinges during progressive deformation gps data and the kinematic study of the fault gouge that is developed at the alhama de murcia fault the combined analysis allows the values of the kinematic vorticity number the orientation of the vorticity vector the orientation of the local and regional convergence vectors the angle of extrusion in the shear zone and the amount of extrusion to be constrained the results point to a highly partitioned heterogeneous shear zone with domains deforming in response to the same boundary conditions but are displaying different kinematic responses that reflect both their intrinsic properties and geometric effects related to competency contrasts we propose that the alhama de murcia fault is an incompletely coupled fault zone with two different domains a low competency domain comprising the fault gouge ductilely deformed with low vorticity values which probably experienced a steady state aseismic slip that reflects regional convergence vectors convergence eurasia nubia and a domain outside of the fault gouge with episodic brittle failure with higher vorticity values and showing convergence vectors which are parallel to the local convergence vectors calculated from the gps velocity field

complex rift geometries resulting from inheritance of pre existing structures insights and regional implications from the barmer basin rift abstract structural studies of the barmer basin in rajasthan northwest india demonstrate the important effect that pre existing faults can have on the geometries of evolving fault systems at both the outcrop and basin scale outcrop exposures on opposing rift margins reveal two distinct non coaxial extensional events on the eastern rift margin northwest southeast extension was accommodated on southwest and west striking faults that form a complex zig zag fault network on the western rift margin northeast southwest extension was accommodated on northwest striking faults that form classical extensional geometries combining these outcrop studies with subsurface interpretations demonstrates that northwest southeast extension preceded northeast southwest extension structures active during the early previously unrecognised extensional event were variably incorporated into the evolving fault systems during the second in the study area an inherited rift oblique fault transferred extension from the rift margin to a mid rift fault rather than linking rift margin fault systems directly the resultant rift margin accommodation structure has important implications for early sediment routing and depocentre evolution as well as wider reaching implications for the evolution of the rift basin and west indian rift system the discovery of early rifting in the barmer basin supports that extension along the west indian rift system was long lived multi event and likely resulted from far field plate reorganisations

mixing in flow perturbations a model for development of mantled porphyroclasts in mylonites abstract the presence of a rigid object such as a porphyroclast in simple shear flow induces a flow perturbation with a relatively simple geometry domains of closed and open flow lines are bounded by a separatrix that surrounds the porphyroclast the concept of a separatrix to describe heterogeneous flow gives rise to some new insights in the development of porphyroclasts with a mantle of recrystallized material in mylonites the final shape of the recrystallized mantle depends on separatrix shape but also on the degree of intersection of the mantle and the separatrix and therefore on relative mantle width this model can explain the coexistence of several types of mantled porphyroclast in a single mylonite sample the occurrence of porphyroclasts that lack wings at high strain values and the presence of symmetric winged mantled porphyroclasts in ductile shear zones

the ezhimala igneous complex southern india possible imprint of late cretaceous magmatism within rift setting associated with india madagascar separation abstract the gabbro granophyre granite complex of ezhimala emplaced along the western rifted continental margin of india preserves evidence for bimodal magmatism with related magma mixing and mingling processes here we report petrological geochemical zircon u pb geochronological and lu hf isotopic data from the ezhimala igneous complex eic that provide insights into the late cretaceous magmatic activity field investigations and petrographic observations in zircon u pb data from the granophyres show emplacement ages of 93 21 0 6 ma and 94 26 0 92 ma the evolved lu hf isotopic systematics for these rocks are indicative of the involvement of older crustal material during magma genesis the geochemical systematics together with isotopic data suggest magma generation in a rift related setting and interaction with or melting of neoproterozoic basement rocks the timing of magmatism broadly correlates with the late cretaceous marion hotspot activity which is considered to be responsible for the break up of india and madagascar we thus interpret the eic to be one of the rare signatures in southern india for the final phase of rifting of gondwana

geometry classification and kinematics of s c and s c fabrics in the mushandike area zimbabwe planar fabrics in small dextral shear zones in the mushandike area of the zimbabwe archaean craton consist of a sigmoidal primary foliation s displaced by discrete shears c or c these planar fabrics can be divided into porphyroclastic megacrystic and banded types depending mainly on the values of the angles between s and c or c surfaces the structures that define s surfaces and the spacing of c or c surfaces the values of the angles between the foliations are proposed as the basis for a general classification of planar fabrics in shear zones the values of the angles depend on microstructures and strain microstructural evidence shows that slip did not occur on s surfaces but only on c or c surfaces a model for the development of the fabrics proposes that s surfaces lie parallel to the xy plane of the local finite strain ellipsoid in domains of simple shear between c or c surfaces c surfaces may form in the orientation of a coulomb failure surface the field evidence suggests that an increase in bulk strain is at least partly accommodated by an increase in local strain in domains between c or c surfaces as the s surfaces rotate with the local finite strain ellipsoid

the deformation matrix for simultaneous simple shearing pure shearing and volume change and its application to transpression transtension tectonics simultaneous simple shearing and pure shearing with or without additional volume change can be combined into a single upper triangular deformation matrix the off diagonal term is named the effective shear strain and is a simple function of the pure shearing and simple shearing components a three dimensional deformation matrix for the simultaneous combination of coaxial deformation with or without additional volume change and up to three simple shearing systems with mutually orthogonal shear planes is also presented by using this matrix one can easily extract the various properties of incremental as well as finite strain and the progressive as well as finite rotation of passive markers during deformation the case of transpression transtension is revised using the unified deformation matrix the orientation of the major axis of the strain ellipsoid 1 is always horizontal if the deformation is transtensional switches from horizontal to vertical during transpressional wrenching 1 wk 0 81 for constant vorticity deformations and is always vertical for highly transpressional deformations wk 0 81 for transpression material lines initially rotate towards the horizontal shearing direction but generally turn to rotate towards the vertical axis after a certain strain for transtension all material lines rotate towards a direction in the horizontal plane which is oblique to the shearing direction

inclined transpression in the neka valley eastern alborz iran three major nappes in the neka valley in the eastern alborz mountains of iran allow the cimmerian to present convergence following the oblique collision between iran and the southern margin of eurasia this work reports the identification of an inclined transpression zone recognized by field investigations and strain analyses of the geometries of formations and detailed mesoscopic structural analyses of multiple faults folds and a cleavage the main structures encountered include refolded recumbent asymmetric fold nappes highly curved fold hinges in a transpression zone that dips 37 to the nw between boundaries thrusts striking from n050 to n060 the angle the angle between the zone boundary and direction of horizontal far field shortening is about 80 the north west and south east boundaries of this zone coincide with the haji abad thrust and the shah kuh thrust respectively fold axes generally trend ne sw and step to both right and left as a result of strike slip components of fault displacements strain analyses using fry s method on macroscopic ooids and fusulina deformed into oblate ellipsoids indicate that the natural strain varies between 2 1 and 3 14 the estimated angle between the maximum instantaneous strain axis isamax and the transpression zone boundary is between 6 and 20 the estimated oblique convergence angle therefore ranges between 31 and 43 the average kinematic vorticity number wk is 0 6 in a zone of sinistral pure shear dominated inclined triclinic transpression these results support the applicability of kinematic models of triclinic transpression to natural brittle ductile shear zones

the elusive nature of the rheic ocean suture in sw iberia the rheic ocean suture resulted from pre carboniferous oceanic subduction followed by late devonian carboniferous variscan collision in sw iberia this suture has been classically located along the boundary between the ossa morena and south portuguese zones based on the presence of three units i a conspicuous metamafic unit beja acebuches that crops out along this boundary and has been interpreted as a pre carboniferous rheic ocean ophiolite ii a low grade metasedimentary unit with minor mid ocean ridge basalt like lithologies pulo do lobo unit thought to represent a rheic ocean subduction related accretionary prism and iii the allochthonous cubito moura unit that contains high pressure and ophiolitic like rocks we report new structural and geochronological data that allow us to reinterpret the origin and internal structure of the beja acebuches and the pulo do lobo units thus both the beja acebuches protoliths and the pulo do lobo metabasalts would have been formed in the context of an intracollisional extensional stage that interrupted the variscan collision at early carboniferous time after the rheic ocean consumption and the first continental collision later on collision was resumed in an oblique left lateral regime that gave way to coeval frontal folds and thrusts and lateral shear zones and strike slip faults structures with variable pressure temperature conditions and space distribution along time as a consequence of the superposition of transtension and complex transpression the rheic suture in sw iberia has an obscure nearly cryptic appearance

structural evidence for slip partitioning and inclined dextral transpression along the se sanandaj sirjan zone iran the structural evolution of the sanandaj sirjan zone is the result of the convergence of the iranian microcontinent and the afro arabian continent the study area at khabr in the se sanandaj sirjan zone in the hinterland of the zagros orogen consists of paleozoic mesozoic and cenozoic rocks in this area deformation phases were distinguished in different rock units based on structural and stratigraphical evidence and the deformational events are divided into two stages 1 a late triassic event and 2 a late cretaceous to miocene event the late triassic deformation event caused regional metamorphism in the paleozoic units these units are overlain by unmetamorphosed jurassic clastic sequences fabrics and structural evidence confirm that the f1 folding recumbent and refolded folds were synchronous with the metamorphism of the paleozoic units and terminated in the early jurassic the time table of the orogenic phases shows that this deformation event is related to the cimmerian orogenic phase from a geodynamic point of view the early cimmerian deformation in the southeastern iranian margin suggests that the se sanandaj sirjan zone was an active margin at that time the early cimmerian discordance recorded the onset of a contractional component related to the oblique subduction of neo tethys beneath the central iranian microcontinent structures related to the late cretaceous to miocene deformation phase are observed in jurassic to oligocene units which contain moderately inclined and plunging folds comparing these folds with domains of deformation generated in models of transpression shows that the folding was caused by a combination of contractional and dip slip components of movement eventually resulting in the formation of a thrust system the khabr thrust systems consist of five sheets of oblique thrusts duplex structures and shear zones the shear zones generally strike e w and dip moderately n 30 40 the occurrence of asymmetric folds with hinges that are either parallel to strike or plunge down dip demonstrates an oblique slip component in these thrust shear zones the stretching lineation in the mylonites within the shear zones is defined by the long axes of ellipsoidal grains of quartz calcite plagioclase and garnet in general stretching lineations trend from n40 w to n80 w with an intermediate 35 plunge the geometry of foliation and lineation within these shear zones shows the effect of dip and oblique slip shearing deformation continued with strike slip faulting becoming important during the last stages of deformation from the miocene to the present day the results of this study demonstrate that the evolution of the se sanandaj sirjan zone from late triassic to miocene is compatible with an inclined dextral transpression along this zone

geochemistry and paleomagnetism of late cretaceous mafic dikes in kerala southwest coast of india in relation to large igneous provinces and mantle plumes in the indian ocean region new geochemical and paleomagnetic results are presented on two late cretaceous dikes of the 85 90 ma leucogabbroic and doleritic dikes and the 65 70 ma dolerites in kerala india the dikes are rich in incompatible elements have fractionated patterns with light rare earth element enrichment and are akin geochemically to cretaceous basalts on the east coast of madagascar the magmas were formed at garnet lherzolite depths above the marion plume constituting part of a large igneous province in madagascar in contrast the 65 70 ma dolerites are moderately depleted in incompatible elements with almost flat rare earth element patterns and resemble the upper formations of the deccan traps and the tholeiitic dikes of the seychelles these dolerites were formed by melting of spinel lherzolite over the reunion plume paleomagnetic data from the dikes and the other coeval igneous units from south india provide the 90 ma pole latitude 24 longitude 293 a 95 5 9 n 18 sites for india the 65 70 ma dolerites possess both normal and reverse polarities and the mean pole latitude 36 longitude 283 a 95 5 7 n 10 sites compares well with the deccan superpole paleolatitude estimates indicate 5 southward migration for the marion plume and a northward migration for the reunion plume in conformity with global mantle circulation models however distinguishing migration of the reunion plume from the effects of true polar wander is difficult furthermore the geodynamic reconstructions extending the shear zones of southern madagascar into south india are not tenable

shear senses and viscous dissipation of layered ductile simple shear zones velocity profiles and shear heat profiles for inclined layered newtonian simple shear zones are considered reverse fault like simple shear of the boundaries and upward net pressure gradient act together in such shear zones as the velocity of the boundary increases the point of highest velocity shifts from the lower layer of less viscosity into the upper layer the shear heat profile shows a temperature peak inside the lower layer for a more viscous upper layer the point of highest velocity is located inside the upper layer and shifts towards the upper boundary of the shear zone the shear heat profile shows a maximum temperature within the upper layer depending on the flow parameters of the two layers the slip rate of the boundary and the dip and thickness of the shear zone a shear sense in reverse to the relative movement of the shear zone boundaries may develop these models can decipher thermo kinematics of layered shear zones in plate scale hot orogens

palaeostress perturbations near the el castillo de las guardas fault sw iberian massif use of stress inversion methods on faults measured at 33 sites located at the northwestern part of the south portuguese zone variscan iberian massif and analysis of the basic dyke attitude at this same region has revealed a prominent perturbation of the stress trajectories around some large crustal scale faults like the el castillo de las guardas fault the results are compared with the predictions of theoretical models of palaeostress deviations near master faults according to this comparison the el castillo de las guardas fault an old structure that probably reversed several times its slip sense can be considered as a sinistral strike slip fault during the moscovian these results also point out the main shortcomings that still hinder a rigorous quantitative use of the theoretical models of stress perturbations around major faults the spatial variation in the parameters governing the brittle behaviour of the continental crust and the possibility of oblique slip along outcrop scale faults in regions subjected to general non plane strain

tree ring based drought reconstruction for the central tien shan area in northwest china 1 a robust ring width chronology developed from two sites of picea schrenkiana in the central tien shan area of northwest china was employed to study regional drought variability our analyses demonstrate both temperature and precipitation have significant effects on tree growth thus both should be considered for climate reconstruction regional drought history 1675 2002 a d was therefore reconstructed by calibrating with the palmer drought severity index pdsi our reconstruction not only captured well those extreme drought events recorded in local historical archives but also revealed the long term pattern of drought variability especially the trend of increasing moisture during the 20th century multi taper method spectral analysis indicates the existence of some low and high frequency cycles 146 171 11 5 10 6 9 7 6 1 3 9 3 4 3 2 2 4 and 2 1 yr overall our study indicates the feasibility of combining tree rings and the pdsi to reconstruct large scale drought patterns over this area

age of seychelles india break up many continental flood basalt provinces are spatially and temporally linked with continental break up establishing the relative timing of the two events is a key step in determining their causal relationship here we investigate the example of the deccan traps and the separation of india and the seychelles whilst there has been a growing consensus as to the age of the main phase of the deccan emplacement 65 5 1 ma chron 29r the age of the rifting has remained unclear we resolve this issue through detailed seafloor magnetic anomaly modeling supported by wide angle and reflection seismic results of the north seychelles and conjugate laxmi ridge gop rift margins and geochemistry and 40ar 39ar geochronology of rocks from the north seychelles margin we show that syn rift volcanics offshore the seychelles islands in the form of seaward dipping reflectors were most likely erupted during chron 28n and the first organized seafloor spreading at the carlsberg ridge also initiated during this chron at 63 4 ma the severing of the seychelles occurred by a south eastward ridge propagation that was completed by the start of chron 27n 62 ma a brief pre 28r phase of seafloor spreading occurred in the gop rift possibly as early as 31r 32n 71 ma initial extension at the margin therefore preceded or was contemporaneous with the deccan emplacement and separation of the seychelles was achieved less than 3 5 ma afterwards this is the shortest time interval between flood basalt emplacement and break up yet reported for any continental flood basalt rifted margin pair a contributing factor to the apparently short interval in the deccan case may be that rifting occurred by a ridge jump into already thinned continental lithosphere however we conclude that external plate boundary forces rather than the impact of a mantle plume were largely responsible for the rifting of the seychelles from india

determination of the fluid absent solidus and supersolidus phase relationships of morb derived amphibolites in the range 4 14 kbar experiments on a morb mid ocean ridge basalt derived amphibolite have been conducted in order to determine fluid absent solidus and supersolidus phase relationships the solidus has been determined in the range 4 14 kbar by using the incremental heating technique tested against classical procedures peritectic clinopyroxene was produced below 10 kbar and epidote was the stable peritectic phase at pressures greater than 10 kbar for temperatures near the solidus garnet was the peritectic phase for temperatures above 800 c and pressures of 10 to 14 kbar the shape of the solidus was similar to previous estimations but the temperature interval between the high and low pressure regions was strongly reduced with these new estimations the possibilities for melting of the oceanic crust at p below 10 kbar are increased and consequently the number of tectonic scenarios needed for magma generation from amphibolite sources is enlarged in the absence of free water the solidus in the pressure region above 10 kbar is at higher t than previous estimations

kinematic analysis of the southern iberian shear zone and tectonic evolution of the acebuches metabasites sw variscan iberian massif 1 the acebuches metabasites constitute a slice of oceanic crust located at the variscan suture between the ossa morena and the south portuguese zones iberian massif the emplacement of the metabasites onto the accretionary prism was associated with the activity of the southern iberian shear zone careful measurements of the fabrics and structures related to this shear zone show consistent kinematic criteria pointing to the presence of a simple shear component with an oblique predominantly left lateral sense of displacement the data are consistent with existing models of triclinic or oblique shear zones considering coeval simple shear and pure shear components these models provide a satisfactory explanation of the observed spatial variations in the foliation lineation and fold hinge data the kinematics of other shear deformations older and younger than the southern iberian shear zone have also been established these results offer new insights into the tectonic evolution of this suture of the variscan belt and show how complex transpressional strains can arise during oblique crustal deformation associated with the motions of tectonic plates

a late cretaceous ca 90 ma kimberlite event in southern india implication for sub continental lithospheric mantle evolution and diamond exploration abstract we report groundmass perovskite u pb sims ages perovskite nd isotopic la icpms composition and bulk rock geochemical data of the timmasamudram diamondiferous kimberlite cluster wajrakarur kimberlite field in the eastern dharwar craton of southern india the kimberlite pipes gave similar mesoproterozoic ages of 1086 19 ma tk 1 microcrystic variant and 1119 12 ma tk 3 however a perovskite population sampled from the macrocrystic variant of tk 1 gave a much younger late cretaceous age of ca 90 ma this macrocrystic kimberlite phase intrudes the mesoproterozoic microcrystic phase and has a distinct bulk rock geochemistry the nd isotope composition of the 1100 ma perovskites in the cluster show depleted end t values of 2 1 0 6 to 6 7 0 3 whereas the 90 ma perovskites have enriched end t values of 6 3 1 3 the depleted mantle dm model age of the cretaceous perovskites is 1 2 ga whereas the dm model age of the proterozoic perovskites is 1 2 to 1 5 ga bulk rock incompatible trace element ratios la sm gd lu la nb and th nb of all timmasamudram kimberlites show strong affinity with those from the cretaceous group ii kimberlites from the bastar craton india and kaapvaal craton southern africa as the late cretaceous age of the younger perovskites from the tk 1 kimberlite is indistinguishable from that of the marion hotspot linked extrusive and intrusive igneous rocks from madagascar and india we infer that all may be part of a single madagascar large igneous province our finding constitutes the first report of cretaceous kimberlite activity from southern india and has significant implications for its sub continental lithospheric mantle evolution and diamond exploration programs

late cretaceous magmatism in madagascar palaeomagnetic evidence for a stationary marion hotspot late cretaceous basaltic volcanics in the morondava basin sw madagascar possess high quality and pre fold palaeomagnetic data declination 353 5 inclination 54 8 95 2 4 the palaeomagnetic data are all of normal magnetic polarity and remanence acquisition is linked to the terminal stages of the cretaceous normal superchron 83 ma this is sustained by an 40ar 39ar age of 83 6 1 6 ma from one of the tested basaltic flows a precise u pb zircon baddeleyite age from northeast madagascar demonstrates magmatism at least back to 91 6 0 3 ma thus reliable isotope ages for the madagascar cretaceous igneous province span a range of 8 million years late cretaceous palaeomagnetic data obtained from volcanics and dolerites all over madagascar are directionally concordant and the combined palaeomagnetic pole latitude 68 5 n longitude 230 3 e a95 5 5 n 8 studies sampling age range ca 84 90 ma represents one of the best late cretaceous poles for the former gondwanan elements the collective palaeomagnetic data yield a palaeolatitude of 45 3 s 5 3 4 7 for the proposed focal point of the marion plume volcan de l androy southeast madagascar during the late cretaceous this is in perfect agreement with hotspot controlled reconstructions that place the marion hotspot 46 0 s beneath southeast madagascar during the late cretaceous setting true polar wander aside hotspot movements in the indian ocean do not appear to exceed ca 0 75 cm yr and the marion hotspot appears stationary within the resolution power of palaeomagnetic data

petrofabric of forsterite marbles and related rocks from a low pressure metamorphic terrain almaden de la plata massif ossa morena zone sw spain and its kinematic interpretation abstract a fabric study of forsterite marble and calc silicate rock paragenetic minerals is presented for samples collected in the almaden de la plata massif of sw spain that experienced variscan low pressure metamorphism related to the tectonic evolution of the suture between the ossa morena and south portuguese zones of the iberian massif two tectonically stacked metamorphic units contain marble metacarbonate and variably impure dolomitic rocks that record contrasting thermal conditions of the upper greenschist structuraly upper unit and the upper amphibolite granulite facies structuraly lower unit different reactional paths lead to formation of forsterite marbles in both units dolomite and calcite petrofabrics disclose their contrasting rheological behaviour during syn metamorphic ductile deformation under temperatures between 500 and 700 c dolomite formed harder porphyroclast systems and boudinaged bands whereas weaker calcite underwent dynamic recrystallization in both cases deformation was facilitated by activation of various intracrystalline slip systems complemented by other deformation mechanisms the fabrics of other paragenetic metamorphic minerals also denote crystal plasticity and exhibit close geometrical relationships with respect to the macroscopic foliation and mineral stretching lineation including a systematic asymmetry suggestive of non coaxial deformation components foliations and lineations are interpreted as solid state flow planes and directions bearing a kinematic significance in particular regional sinistral shear at mid deep crustal realms coeval with low pressure metamorphism explains the imbrication of metamorphic units and their exhumation concomitant with the overall wrench tectonic framework ruling the tectonic evolution of the ossa morena south portuguese suture between the late devonian 360 ma and the latest carboniferous 300 ma

experimental modelling of mantled porphyroclasts abstract mantled porphyroclasts are commonly used as sense of shear indicators in mylonites analogue experiments have been carried out to model the development of such objects rigid spheres mantled by a viscous plasticene putty mixture with power law behaviour were suspended in an optically transparent newtonian polymer matrix the samples were deformed between two cylinders one placed within the other and with coinciding axes this induces a non coaxial flow between the cylinders and allows the achievement of high finite strain the viscous mantle around the rigid sphere remained undeformed deformed into an ellipsoid or developed wings the final geometry depends mainly on the induced viscosity contrast between the mantle and the matrix which is a function of the flow induced stress on the surface of the mantle winged mantles only develop if the induced viscosity contrast between the mantle and the matrix polymer is sufficiently small if this critical induced viscosity contrast is exceeded the mantled sphere remains undeformed or obtains a stable ellipsoidal shape even at high finite strain shaped winged mantles only develop in simple shear flow if the mantle around a rigid sphere is thin

40ar 39ar dating of the mumbai tholeiites and panvel flexure intense 62 5 ma onshore offshore deccan magmatism during india laxmi ridge seychelles breakup

the discovery of the barmer basin rajasthan india and its petroleum geology the discovery of oil and gas in the barmer basin in northwest india was one of the more significant global discoveries in the decade 2001 2010 the basin s presence was suspected from gravity and magnetic data in the late 1980s but not confirmed until 1999 from seismic and drilling the basin is a lacustrine failed rift biostratigraphic data however indicate it was intermittently connected to marine waters via either the cambay basin the kutch basin or across the devikot high temporarily forming a large shallow estuary at least six major tectono stratigraphic events have caused relative lake level falls and translation of clastic reservoirs basinward upward of 6 km 20 000 ft of cenozoic and mesozoic sedimentary rocks have been preserved prolific source rocks occur from the mesozoic through eocene strata tectonically the basin is divided into a northern and a southern province the north province continues to undergo inversion and erosion and has not been buried as deeply as the south kinetics of the major source facies in the north are substantially different from those in the south as well as the present day and paleo heat flow these differences have made the northern part of the basin predominantly an oil province and the southern part a mixed oil and gas province the prolific paleocene fatehgarh formation contains the bulk of the 7 3 billion barrels of stock tank oil in place stoip identified to date but other reservoirs from the mesozoic to the late cenozoic are common and may yield significant future resource additions

testing models for obliquely plunging lineations in transpression a natural example and theoretical discussion theory predicts that stretching lineations in an ideal vertical transpressional zone should be either vertical or horizontal many field descriptions of transpressional zones however indicate a range of lineation orientations between these extremes several theoretical models have been developed to explain such departures from expected lineation orientation and we discuss these in the context of a field example from the archean superior province in the north american craton existing models are insufficient to explain obliquely plunging lineations in this example because 1 obliquely plunging lineations cannot be accounted for by shear zone boundary effects imposed by a no slip condition 2 foliations and lineations vary independently 3 the vorticity normal section is subhorizontal limiting possibilities for inclined simple shear 4 high vorticity is needed for finite strains and lineations to match previously proposed triclinic models but vorticity is relatively low and 5 juxtaposed east and west plunging lineations are unlikely in the previously proposed triclinic models because existing theoretical models are not applicable to our field example we contemplate a new model to explain obliquely plunging lineations within quasi homogeneous transpression

deformation mechanics in inclined brittle ductile transpression zones insights from 3d finite element modelling abstract most natural examples of transpression zones developed at oblique convergence regime are inherently 3d and have inclined boundaries a 3d finite element model with an elasto plastic rheology is used to investigate the structural and mechanical evolution of inclined transpression zones in a rock sequence above a frictional basal detachment inelastic constitutive relationships allow permanent strains to develop in response to the applied loads fe modelling results show that oblique convergence is accommodated by discrete deformation at the main pre existing inclined faults 70 and by distributed brittle and ductile deformation at active blocks oblique contraction at the active blocks resulted mainly in layer parallel shortening orthogonal to the model outer boundaries whereas thickening in the horizontal and vertical directions was accommodated via layer parallel fault strike parallel extension and up dip extrusion i e inclined extrusion lateral extrusion should have compensated the rest and or volume loss took place folding and thickening of the mobile backstop produced a non cylindrical asymmetric bi vergent anticline where permanent strains developed principally in the steep forelimb secondary conjugate fault zones also accommodate oblique slip and contribute to uplift displacement vectors within the transpression zone are rotated counter clockwise ca 20 30 with respect to vectors in the fixed backstop areas with higher rotation values seem to correlate with those showing higher ellipticity values the presence of pre existing faults favored strain partitioning from the onset of deformation fe modelling results compared with analytical natural example and analogue modelling results show that our mechanical modelling can overall match inclined transpression zones geometry that present different modes of strain partitioning and localisation

how do lineations reflect the strain history of transpressive shear zones the example of the active alpine fault zone new zealand abstract lineations within mylonites exhumed in the hanging wall of new zealand s active alpine fault zone have a complicated relationship to contemporary plate kinematics the shear zone is triclinic and macroscopic object lineations are not usually parallel to the simple shear direction despite high total simple shear strains 150 this is mostly because the lineations are inherited from pre mylonitic fabrics and have not been rotated into parallelism with the mylonitic stretching direction which pitches c 44 in the fault plane furthermore some lineations have been variably rotated depending on whether they are present in shear bands or microlithons which accommodated bulk strains with different vorticities total strains required to obtain parallelism between the finite maximum principal stretching direction calculated from transpression models and these mylonitic lineations are pure shear stretch s 1 3 5 simple shear 11 7