ultracataclasite structure and friction processes of the punchbowl fault san andreas system california abstract the punchbowl fault is an exhumed 40 km displacement fault of the san andreas system in the devil s punchbowl the fault contains a continuous ultracataclasite layer along which the punchbowl formation sandstone and an igneous and metamorphic basement complex are juxtaposed the fabric of the ultracataclasite layer and surrounding rock indicate that nearly all of the fault displacement occurred in the layer by analogy with nearby active faults we assume that the punchbowl fault was seismogenic and that the ultracataclasite structure records the passage of numerous earthquake ruptures we have mapped the ultracataclasite layer at 1 1 and 1 10 to determine the mode of failure and to constrain the processes of seismic slip on the basis of color cohesion fracture and vein fabric and porphyroclast lithology two main types of ultracataclasite are distinguished in the layer an olive black ultracataclasite in contact with the basement and a dark yellowish brown ultracataclasite in contact with the sandstone the two are juxtaposed along a continuous contact that is often coincident with a single continuous nearly planar prominent fracture surface pfs that extends the length of the ultracataclasite layer in all exposures no significant mixing of the brown and black ultracataclasites occurred by offset on anastomosing shear surfaces that cut the contact or by mobilization and injection of one ultracataclasite into the other the ultracataclasites are cohesive throughout except for thin accumulations of less cohesive reworked ultracataclasite along the pfs structural relations suggest that 1 the black and brown ultracataclasite were derived from the basement and sandstone respectively 2 the black and brown ultracataclasites were juxtaposed along the pfs 3 the subsequent final several kilometers of slip on the punchbowl fault occurred along the pfs and 4 earthquake ruptures followed the pfs without significant branching or jumping to other locations in the ultracataclasite by comparison with rock friction experiments the slip localization along the pfs in the ultracataclasite implies rate weakening behavior with a critical slip distance similar to laboratory values and thus relatively small nucleation and breakdown dimensions for earthquake ruptures of the various mechanisms proposed to explain the low strength of the san andreas and to produce dynamic weakening of faults those that require or assume extreme localization of slip are most compatible with our observations

fluidized breccias a record of brittle transitions during ductile deformation abstract unusual breccias of caledonian age are described in relation to the tectonic and metamorphic history of their greywacke sandstone and siltstone parent rocks the variety of field and textural relationships displayed by the breccias indicate a combination of dilational and non dilational components in a fluidized system of breccia development the velocity of the escaping fluid phase and the viscosity of the fluidized suspension are strongly influenced by competency controls due to their finer grained nature the pelite based breccias allow a greater mobility of the fluid phase and locally record a turbulent expanded bed stage of the fluidized system however the sandstone based breccias lacking the intricate flow patterns retain a replacive non dilational fracture network the breccias occur in a zone of intense d2 deformation the age relationships of the breccias indicate a repeated pattern of brecciation with syntectonic temporal and partly genetic affinities to the s 2 cleavage development the syntectonic dilational elements involving boudinage and hydraulic fracture are coupled with intense pressure solution and conjugate cleavage development metamorphism to lower greenschist facies is synchronous with deformation and brecciation a focussing of the metamorphic fluid phase within the breccia zones is indicated contributing the non dilational components of the brecciation process a simple shear model of the d2 deformation within this zone is proposed the orientation of the breccia zones suggests that their localization is determined by tensional components within the overall d2 stress field the cyclical pattern of the brecciation during the d2 deformation is considered to represent rapid brittle transitions during the ductile deformation stratigraphie controls on the generation of the increased fluid pressures are identified the presence of an impermeable barrier facilitating the necessary conditions for the excess fluid pressures to accumulate is indicated it is suggested that the brecciation process is fundamentally controlled by a seismic pumping phenomenon following periodic shear failure on a major basement fault at depth

a geochemical reconstruction of oil generation in the barrow sub basin of western australia abstract a suite of crude oils and petroleum source rock extracts from the barrow sub basin of western australia have been analysed for biological marker compounds by capillary gc ms and for volatile hydrocarbons by whole oil capillary gc these analyses were used to calculate values for twenty three biomarker parameters in order to assess aspects of source type maturity migration and biodegradation of the hydrocarbons the crude oils had a source in the upper jurassic dingo claystone formation these hydrocarbons accumulated in the reservoir sands and in some cases were biodegraded several accumulation and biodegradation episodes have been recognised while the basin continued to subside which resulted in a suite of oils showing marked differences in composition

meso cenozoic tectonic evolution of the se brazilian continental margin petrographic kinematic and dynamic analysis of the onshore araruama lagoon fault system abstract the ararauama lagoon fault system composes one of the most prominent set of lineaments of the se brazilian continental margin it is located onshore in a key tectonic domain where the basement inheritance rule is not followed this fault system is characterized by ene wsw silicified tectonic breccias and cataclasites showing evidences of recurrent tectonic reactivations based on field work microtectonic kinematic and dynamic analysis we reconstructed the paleostresses in the region and propose a sequence of three brittle deformational phases accountable for these reactivations 1 ne sw dextral transcurrence 2 nnw sse dextral oblique extension that evolved to nnw sse pure extension 3 ene wsw dextral oblique extension these phases are reasonably correlated with the tectonic events responsible for the onset and evolution of the se onshore rift basins between the neocretaceous and holocene however based on petrographic studies and supported by regional geological correlations we assume that the origin of this fault system is older related to the early cretaceous south atlantic rifting this study provides significant information about one of the main structural trends of the se brazilian continental margin and the tectonic events that controlled its segmentation since the gondwana rifting and compartmentalization of its onshore sedimentary deposits during the cenozoic

uplift of deep crust during orogenic extensional collapse a model based on field studies in the sogn sunnfjord region of western norway the western gneiss region wgr in norway experienced high pressure metamorphism during silurian devonian continent continent collision the eclogite bearing lower crust is separated from the middle and upper crust by major detachment zones formed during extensional collapse of the orogen formation of the devonian basins is related to the extension the footwall of the detachment zones comprises three structural and metamorphic zones the upper zone zone 1 is characterized by penetrative homogeneous down to the west simple shear developed under retrograde greenschist facies metamorphism zone 2 suffered inhomogeneous simple shear of the same polarity petrography and mineral chemistry data from the lower zone zone 3 show a record of initial eclogite facies metamorphism at 600 c and 16 kbar which was decompressed almost isothermally to amphibolite facies conditions at 550 c and 10 12 kbar both the eclogite and amphibolite facies metamorphism developed in a regime of pure shear with vertical shortening the rapid decompression records an approach of approximately 20 km to the surface related to uplift that was probably the result of the removal of a thickened thermal boundary layer in the mantle lithosphere the pure shear regime which developed initially in the lower crust was truncated by zones of simple shear as the lower crust was uplifted to middle and upper crustal levels extension by simple shear in the upper crust was rooted in the lower crust where extension occurred by pure shear the shear zones in zones 1 and 2 did not penetrate the pure shear regime of the lower crust a considerable amount of tectonic stripping of the orogenic welt predates deposition of the devonian sedimentary basins

the brittle plastic transition in experimentally deformed quartz aggregates deformation experiments have been conducted to provide constraints on the processes responsible for the brittle plastic transition in quartz aggregates a correlation between mechanical behavior and distinctive microstructural characteristics indicates that the brittle plastic transition in nonporous quartzite involves at least three transitions in deformation mechanism that occur with increasing temperature and or pressure first there is a transition from cataclastic faulting to semibrittle faulting microstructural observations indicate that this transition occurs due to the activation of dislocations in addition faulting is more stable in the semibrittle faulting regime due to the blunting of the stresses at the advancing fault tip by dislocation glide second there is a transition from semibrittle faulting to semibrittle flow this transition corresponds to a change from localized to distributed deformation microstructural observations indicate that microcracks nucleate in response to stress concentrations at dislocation pileups in the semibrittle flow regime we conclude that the transition to semibrittle flow occurs when the stress intensity at crack tips is insufficient to allow propagation across grain boundaries third there is a transition from semibrittle flow to dislocation creep microstructural observations suggest that this transition occurs as a result of an increase in grain boundary mobility with increasing temperature in addition microstructural observations indicate that a transition from dominantly mode i axial to mode ii shear microcracking occurs with an increase in confining pressure from 0 4 to 0 8 gpa regardless of temperature the differential stresses supported by the experimentally deformed samples are higher than those expected under geologic conditions however a comparison of the experimentally produced microstructures to those reported from natural fault zones suggests that similar processes are operative in the laboratory and in the earth the results of this study provide further evidence to indicate that the brittle plastic transition in the continental crust occurs over a relatively wide range of conditions

fluid rock reaction weakening of fault zones the presence of weak phyllosilicates may explain the low shear strengths of fault zones if they define well developed fabrics the growth of phyllosilicates is favored in meteoric water dominated granitic fault systems where mineral aqueous fluid equilibria predict that modal phyllosilicate will increase via feldspar replacement reactions in deeper more alkaline rock dominated regimes the reactions reverse and feldspars tend to replace phyllosilicates in mg rich mafic rocks however phyllosilicates chlorite biotite can replace stronger framework and chain silicates in both shallower approximately 10 km meteoric h sub 2 o dominated and in deeper alkaline rock dominated regimes where these phyllosilicates precipitate in active fault zones they contribute directly to reaction softening because low temperature deformation of phyllosilicates is not governed by frictional processes alone but can occur by pressure independent dislocation glide the strength of phyllosilicate rich fault rocks can be low at all depths low strain rate creep during interseismic periods can align phyllosilicate grains in foliated gouge and phyllonites where preferred orientations are strong and contiguity of phyllosilicates is large strengths of rocks within fault zones may approach minimum strengths defined by single phyllosilicate crystals fault zones containing localized high concentrations of phyllosilicates with strong preferred orientations in well defined folia can exhibit aseismic slip especially where mafic mg rich rocksmore occur along the fault like parts of the san andreas fault 104 refs 6 figs 1 tab less

biological markers and carbon isotope composition of organic matter in the upper cretaceous coals and carbonaceous shale succession jiza qamar basin yemen origin type and preservation abstract bituminous coals and carbonaceous shales located in the jiza qamar basin on the eastern yemen were analysed based on a combined investigation of organic geochemistry and petrology to define the palaeodepositional environment condition organic matter inputs and their thermal maturity carbon isotope compositions and various biomarkers were performed on coals and carbonaceous shales within the upper cretaceous mukalla formation in the jiza qamar basin the 13 c values range from 29 2 to 24 5 with average values around 26 7 whereas the organic carbon contents in most sediment samples are consistently high 3 indicating that the organic matter in the mukalla coal and carbonaceous shale sediments has a predominantly terrigenous origin with slightly marine influence during burial this has also been identified from kerogen microscopy which is characterized by dominance of vitrinite and liptinite organic matter the investigated biomarkers indicated that the mukalla coals and carbonaceous shales contain high contribution of land plants with a minor aquatic organic matter input that was deposited in a fluvial to deltaic environments and preserved under relatively oxic conditions this has been achieved from acyclic isoprenoids terpane and sterane biomarkers of a saturated hydrocarbon and dibenzothiophene alkylnaphthalene and methylphenanthrene biomarkers of an aromatic hydrocarbon based on the analysed biomarker thermal maturity indicators it may be deduced that the mukalla coals and carbonaceous shales in the jiza qamar basin have entered an early mature to mature stages for hydrocarbon generation this is also supported by vitrinite reflectance values of 0 63 0 83 ro indicative that these sediments have reached oil window maturity

segmentation of the caledonian orogenic infrastructure and exhumation of the western gneiss region during transtensional collapse the ultra high pressure western gneiss region of the norwegian caledonides represents an archetypical orogenic infrastructure of a continent continent collision zone to test established exhumation models we synthesize the geochronology and structures of major basement windows and provide new ages from poorly dated areas migmatite u pb zircon samples date melt crystallization at c 405 ma in the oygarden complex expanding the spatial extent of devonian migmatization micas from shear zones in the oygarden and gulen domes yield 40ar 39ar ages mostly between 405 and 398 ma recording the exhumation of metamorphic core complexes on a larger scale the youngest ages of various geochronometers in different segments of the western gneiss region show abrupt breaks 10 30 myr across low angle detachments and sinistral transfer zones which also correspond to metamorphic and structural discontinuities we explain the segmentation of the orogenic infrastructure by partitioned post orogenic transtension due to lateral and vertical rheological contrasts in the orogenic edifice strong cratonic foreland and orogenic wedge v soft infrastructure differential crustal stretching dragged out deep levels of the orogenic crust below low angle detachments and became progressively dominated by sinistral transfer zones collapse obliterated the syn collisional structure of the orogenic root and resulted in the diachronous exhumation of distinct infrastructure segments supplementary material complete analytical results are available at https doi org 10 6084 m9 figshare c 5241710

dynamic development of fault rocks in a crustal scale detachment an example from western norway 1 the nordfjord sogn detachment nsd zone of western norway juxtaposes eclogites and gneisses of lower crustal affinity with sedimentary deposits suggesting that the zone experienced substantial displacement during devonian extensional denudation of the caledonides renewed activation occurred in permian and jurassic cretaceous times the detachment zone consists of a succession of fault related rocks reflecting various crustal positions and deformation mechanisms during activation and unroofing in more detail the lower 1 2 km thick section of the nsd zone consists of mylonites with various protoliths showing a general upward decrease in metamorphic grade the mylonitic section is truncated by the nsd fault defining the boundary toward hanging wall nappe rocks that are topped by sedimentary basins in an attempt to provide precise descriptions of the observed fault rocks we classify these rocks into 1 noncohesive breccias 2 cemented and indurated breccias of secondary cohesion and 3 cataclasites phyllonites and mylonites formed with primary cohesion along and across strike sections of the fault reveal the spatial and temporal relationships of the nsd fault the fault zone consists of a lower section of phyllonites and cataclasites reaching a total thickness of 50 70 m significant volumes of pseudotachylyte were injected into these fault rocks and were later reworked reactivation of the fault is suggested by overprinting carbonate cemented breccias that are cut by a discrete fault itself associated with breccias and gouge by comparing the various fault rocks and their formation mechanisms some constraints can be applied to the unroofing history the nsd fault developed in the ductile brittle transition zone of the crust where it experienced an initial shift from mainly frictional to plastic flow caused by reaction softening before hardening caused a return to frictional flow at the same time repeated pulses of pseudotachylyte were generated possibly lubricating the fault zone and contributing to strain localization these pseudotachylyte pulses also show that the fault was affected by seismic slip events before returning to a creep regime within a wider section than that ruptured by earthquakes younger cemented breccias and noncohesive breccias and gouge reflect earthquake rupturing and frictional flow within the seismogenic crust

the molecular composition of cretaceous ambers identification and chemosystematic relevance of 1 6 dimethyl 5 alkyltetralins and related bisnorlabdane biomarkers abstract one of the major components of the organic solvent extractable fraction of cretaceous ambers is 1 6 dimethyl 5 isopentyltetralin a compound that has been incorrectly or not identified in previous reports on the molecular composition of cretaceous ambers here the purification and structural identification of 1 6 dimethyl 5 isopentyltetralin is reported from amber samples of the cretaceous penacerrada ii deposit at penacerrada alava basque cantabrian basin spain the structural identification of 1 6 dimethyl 5 isopentyltetralin allowed the complete identification of related compounds comprising the family of 1 6 dimethyl 5 alkyltetralins this suggests that those compounds with concentrations up to 27 of the total organic extract of amber from penacerrada are characteristic for labdane type biomarkers in cretaceous fossil resins and their distributions indicate different compositional families related to their botanical and topographic origin also the name amberene is proposed for the main molecule of this group the relative proportion of the amberene type compounds suggests three compositional families for the cretaceous spanish ambers

evidence for paleoseismic slip on a continental low angle normal fault tectonic pseudotachylyte from the west salton detachment fault ca usa abstract the potential of continental low angle normal faults lanf to nucleate large 6 0 m w earthquakes at low angles remains unclear despite much focused research we document evidence for ancient seismicity along a continental lanf detachment fault that formed and slipped at low angles and produced tectonic pseudotachylyte these thick and laterally persistent pseudotachylyte accumulations along the west salton detachment fault wsdf salton trough usa preserve convincing evidence for a frictional melt origin including spherulitic microlites ductile flow structures preservation of high temperature phases as clasts and injection veins cumulative thickness of pseudotachylyte along the fault ranges from 0 1 to 1 5 m and pseudotachylyte cataclasite in the fault core and damage zone are exposed along 2 6 km length of the fault reworked fragments of pseudotachylyte in cataclasites and multiple generations of cataclasites provide evidence for the preservation of multiple earthquake cycles the limited exposure

early carboniferous unroofing in western norway a tale of alkali feldspar thermochronology abstract 40ar 39ar thermochronologic data from an extensional detachment zone in western norway document punctuated late paleozoic through mesozoic tectonothermal activity diffusion and thermal modeling of alkali feldspars sampled in a profile through the detachment replicate laboratory argon release patterns when feldspars comprise three or four diffusion domains with differing activation energies that represent high intermediate and low closure temperatures these domains correspond to distinct changes in late paleozoic cooling rates 1 slow cooling at 0 4 2 2 c m yr from ca 380 360 ma 2 rapid cooling at 15 c m yr in late devonian early carboniferous time 360 340 ma 3 slow cooling at 0 4 1 7 c m yr after ca 340 ma with partial argon loss in permian and late jurassic early cretaceous times the early carboniferous rapid cooling event recorded by the feldspars links the western norway margin to contemporaneous unconformities regional extension basin inversion and igneous activit

monazite geochronology of uhp and hp metamorphism deformation and exhumation nordoyane western gneiss region norway u th pb monazite geochronology is combined with previous structural analysis and quantitative estimates of metamorphic conditions to date the thermotectonic evolution of uhp and hp plates 820 c 39 kbar 780 c 18 kbar metamorphosed during the late silurian early devonian collision between baltica and laurentia the upper plate contains a microdiamond bearing kyanite garnet graphite gneiss and associated kyanite eclogites independently indicating probable diamond forming conditions in situ dating of monazite in the microdiamond sample using the shrimp ii at the geological survey of canada yielded ages of 415 6 8 ma for those included in garnet and 398 6 ma for those in the matrix these ages compare to 408 0 5 6 and 397 5 4 4 ma determined using the electron microprobe at the university of massachusetts both methods also identified complexly zoned detrital cores up to 150 micrometers in diameter with ages of 1100 950 ma and scattered grains with ages of 900 500 ma but no ages of 1680 1650 ma equivalent to the local baltica basement were found agreement between the two techniques allowed evaluation of monazite age domains 198 analyses from the microdiamond rock and a kyanite garnet sillimanite mylonite produced from it using a combination of high resolution element imaging and trace element analysis of u th pb and y this comparison yielded three mean ages of 407 0 2 1 ma 394 8 2 3 ma and 374 6 2 7 ma combining this geochronology with previous p t estimates we propose that the uhp unit reached its maximum depth of 125 km at a maximum age of 407 ma when monazite was included in garnet and experienced 65 km of exhumation at an average rate of 10 9 mm year during top southeast thrusting that brought it into contact with the hp unit following these events both units were exhumed together at an average rate of 3 8 mm year until reaching a depth of 37 km at 395 ma where these rocks experienced extensive re equilibration and top west and left lateral shearing after 395 ma these units continued to be exhumed at an average rate of 0 8 to 1 4 mm year until 375 ma the time of last equilibration of asymmetric monazite porphyroclasts in the mylonite the exhumation histories of these units record a change in mechanism from syncollisional exhumation through late to post orogenic collapse that was a consequence of plate reorganization

deformation and metamorphism of devonian rocks in the outer solund area western norway implications for models of devonian deformation many modern accounts of the devonian rocks of western norway which emphasise the extensional processes by which the basins were formed tend to ignore or gloss over the deformation and metamorphism which these rocks have suffered during contractional deformation the present account describes extensive ductile folding penetrative cleavage formation and low grade regional metamorphism developed in the devonian strata of the outer solund region although the deformation in this area is more intense than in other devonian basins it belongs to the same movement plan it will also be shown that the devonian rocks of the scandinavian caledonides apparently share a common tectonothermal development this regional contractional event conceptually may relate either to a mid late devonian arc continent collision or to a transpressional strain regime

the effects of thermal maturity on distributions of dimethylnaphthalenes and trimethylnaphthalenes in some ancient sediments and petroleums abstract the distributions of di and trimethylnaphthalenes in two sedimentary sequences from western australia have been examined by capillary gas chromatography and combined gas chromatography mass spectrometry a general decrease was observed in the relative proportions of dimethylnaphthalenes and trimethylnaphthalenes with increasing thermal maturity similar trends were also observed for six crude oils which have very different ratios of ethylcholestane epimers indicating very different thermal histories these results suggest that changes in the relative abundances of certain methyl substituted naphthalenes may be useful indicators of thermal maturity of sedimentary organic matter and the use of a number of isomer ratios is illustrated

structural analysis of the smeaheia fault block a potential co2 storage site northern horda platform north sea abstract smeaheia a prominent fault block located on the horda platform northern north sea is identified as a potential subsurface co2 storage site we utilise the gn1101 3d seismic survey to generate a high resolution subsurface geomodel to inform the structural style and evolution of the fault block to investigate geological controls on proposed co2 storage and provide a geometric framework as a basis for future analyses two basement involved first order north south trending fault systems the vette fault zone vfz and the oygarden fault complex ofc bound the 15 km wide fault block the vfz bifurcates down section where it is hard linked with two separate basement structures a phenomenon we term as dual rooted apart from activity during the permo triassic rift phase 1 and the late jurassic early cretaceous rift phase 2 we present evidence that rifting in this part of the north sea continued into the late cretaceous with minor reactivation in the palaeocene eocene two segments of the vfz interacted and linked at a relay ramp during rift phase 2 second order thin skinned faults show basement affinity and developed during rift phase 2 in two distinct pulses a population of polygonal faults intersects the overburden and developed during the eocene to middle miocene we have revised the areal extent of two structural closures that define the smeaheia fault block alpha vfz footwall and beta ofc hanging wall which consist of upper jurassic viking group target formations simplified cross fault juxtaposition analysis of the vfz and second order intra block faults are presented and inform pressure communication pathways between the smeaheia and tusse fault block as well as reservoir integrity and compartmentalisation the geomodel further identifies important geological controls on co2 storage in the fault block including a thinning caprock above the alpha structure and identification of hard linkage between deep tectonic faults and shallow polygonal faults

late orogenic extension in mountain belts insights from the basin and range and the late paleozoic variscan belt from two examples of orogenic domains some general mechanisms significant of late orogenic tectonic processes in mountain belts are characterized the basin and range province and the variscan belt in the french massif central have both suffered important compressional orogenic crustal thickening and the results of late orogenic processes can be observed in the field both areas are covered by deep seismic profiling providing constraints on the geometry of a crust which has been restored to a normal thickness late orogenic features from the two domains are compared at different scales and their tectonic significance for extension mechanisms is discussed at the scale of the orogenic domains the most prominent tectonic features are the metamorphic core complexes mcc which expose deformed rocks from the middle crust generally affected by high temperature low to medium pressure metamorphism partial melting and widespread granite emplacement in these mcc large scale extensional shear zones present an intense mylonitic deformation characterized by low dipping foliations and pervasive stretching lineations they show a complete evolution from early deep seated ductile deformation generally achieved under high temperature low to medium pressure metamorphism to a late shallow brittle stage characterized by cataclastic deformation the late detachment stage generally controls the development of asymmetrical extensional sedimentary basins filled by continental deposits two main geometries of mcc are defined that are characterized by differing geometry and kinematics of low angle shear zones in the first case two low angle shear zones with opposite vergence develop along the flanks of a roughly symmetrical mcc often one system is dominant over the other the second geometry characterizes asymmetrical mcc bounded by a single normal shear zone which is upwarped during uplift and doming of the core caused by tectonic denudation detailed strain analysis performed in several extensional shear zones shows that the deformation regime is heterogeneous and results from general noncoaxial flow deformation along the shear zones evolves progressively from slight homogeneous pure shear strain to intense heterogeneous noncoaxial shear strain strain distribution within the lower crust is less well constrained by field observation however analogies between cocorp and ecors deep seismic reflection profiles give important constraints on crustal structure wide zones of highly subhorizontally layered lower crust and a flat high amplitude reflection moho characterize both evolved orogenic domains suggesting that major deformations and flow occur within the lower crust during extension a kinematic model involving heterogeneous crustal deformation and regional scale flow fits relatively well with late orogenic structures observed in continental domains a weak hot upper mantle allows large scale flow of lower crust material from zones of deep ductile extension to uplifted domains of upper crustal denudation heterogeneous strain is accommodated by low angle extensional shear zones from localized zones of extension in the brittle crust to ductile lower crust combined pure and simple shear occurs along localized shear zones whereas at the scale of the whole lithosphere deformation nearly corresponds to a vertical pure shear such deformation processes which affect a thick and hot crust seem to be common in both compared domains suggesting that late orogenic extensional processes are slightly dependent of the type of contractional tectonics thus as much in the andean type west american cordilleran belt as in the collision type variscan belt late orogenic processes produced similar extensional features

generation and expulsion of oils from permian coals of the sydney basin australia abstract organic geochemical and petrological assessment of coals coaly shales and fine grained sediments coupled with organic geochemical analyses of oil samples all from permo triassic sections of the southern sydney basin australia have enabled identification of the source for the widely distributed oil shows and oil seeps in this region the permian coals have higher hydrogen indices higher liptinite contents and much higher total organic matter extract yields than the fine grained sediments a variety of source specific parameters obtained from n alkanes regular isoprenoids terpanes steranes and diasteranes indicate that the oil shows and seeps were generated and expelled predominantly from higher plant derived organic matter deposited in oxic environments the source and maturity related biomarkers and aromatic hydrocarbon distributions of the oils are similar to those of the coals the oil coal relationship also is demonstrated by similarities in the carbon isotopic composition of the total oils coal extracts and their individual n alkanes extracts from the permo triassic fine grained sediments on the other hand have organic geochemical signatures indicative of mixed terrestrial and prokaryotic organic matter deposited in suboxic environments which are significantly different from both the oils and coal extracts the molecular signatures indicating the presence of prokaryotic organic matter in some of the coal extracts and oils may be due to thin sections of possibly calcareous lithologies interbedded within the coal measures the genetic relationship between the oils and coals provides new evidence for the generation and expulsion of oils from the permian coals and raises the possibility for commercial oil accumulations in the permian and early triassic sandstones potentially in the deeper offshore part of the sydney basin

injection veins of crushing originated pseudotachylyte and fault gouge formed during seismic faulting this paper describes the injection veins of crushing originated pseudotachylyte and fault gouge formed along the iida matsukawa fault in granitic cataclasite southern nagano prefecture central japan the pseudotachylyte which shows a dense and aphanitic appearances and fault gouge occur as simple veins fault vein along the main fault plane and as complex network veins injection vein in the neighboring cataclasite locally the injection veins of pseudotachylyte and fault gouge can be traced back to the fault veins powder x ray diffraction patterns and petrological analysis indicate that both of the pseudotachylyte and fault gouge consist entirely of fine grained angular clasts and that the pseudotachylytes and fault gouges have a similar x ray diffraction patterns with that of the host granite the similarity of chemical compositions and distribution patterns of grain size also show that the injection veins of pseudotachylyte and fault gouge have the same source material as that of fault veins field occurrences and petrological characteristics strongly suggest that the injection veins of pseudotachylyte and fault gouge formed during seismic faulting by a rapid intrusion and fluidization of crushed fine grained materials generated in the shear zone in a gas solid fluid system

hydrothermal brecciation due to fluid pressure fluctuations examples from the olary domain south australia abstract two breccias the doughboy and cathedral rock breccias hosted by the willyama supergroup in the olary domain northeastern south australia were mapped and described in this study mapping of the breccias has demonstrated that they are controlled by the regional deformational history of the area and they are intimately related to episodes of hydrothermal fluid flow and alteration the clast morphology particle size distribution dilation ratio structural position and contact relationships with the host rocks allow the degree of maturity and the nature of the fluid rock interactions for each breccia to be determined breccia clast size distribution and morphology were quantified using fractal analysis techniques textural analysis revealed significant differences in particle size distribution and clast morphology for the different breccias the results of the fractal analysis indicate that the doughboy breccia is the result of multiphase tectonic and fluid assisted failure on a fault plane whereas the cathedral rock breccia is the result of fluid assisted failure during fold related faulting due to the high fluid pressure constraints on reverse fault initiation large fluid pressure differentials are generated during the opening of dilatant sites it is the opening of these dilatant spaces which provides the room to accommodate and the mechanism for brecciation reverse faulting created dilatant spaces that due to the large pressure differential between the wall rock and the dilational space initiated failure of the wall rock whether this was a single event such as at cathedral rock or occurred during multiple events such as at doughboy can be deduced via the fractal characteristics collectively these observations shed light on the processes that occur during regional deformational events associated with multiple generations of hydrothermal activity the relationship between fluid pressure and brecciation may explain why they are the sites where the most intense effects of hydrothermal activity in the olary domain occur

modeling fluid transfer along california faults when integrating pressure solution crack sealing and compaction processes 1 several models pertaining to earthquake cycles imply intermittent fluid flow through fault during the interseismic period increase in fluid pressure from hydrostatic to lithostatic values is a crucial parameter in mechanisms leading to earthquakes to achieve such pressures geodynamic processes gouge compaction fluid flow and changes in permeability are required previous models have postulated that changes in permeability by self healing are faster than the effects of geodynamic processes we consider the different mechanisms and rates of crack sealing near active fault on the examples of uplifted californian faults we find that natural crack sealing is normally not achieved by a rapid self healing process pressure solution with mass transfer from solution cleavage to cracks appears to be a more important mechanism for crack sealing and creep during postseismic deformation the geometry of transfer path and experimental data have been used to model crack sealing rates by pressure solution which are estimated to be rather slow similar to the recurrence time of some earthquakes such slow changes in permeability may be crucial factors in controlling the increase in fluid pressure and consequently the mechanism of critical failure in faults then numerical modeling of fluid pressure and transfer around active faults has been performed integrating a slow change in permeability by crack sealing gouge compaction and fluid flow from depth this modeling shows various location and evolution of fluid overpressure during the interseismic period depending on these processes and allows one to estimate the amount of fluid transferred from depth during interseismic periods

permian and mesozoic extensional faulting within the caledonides of central south norway palaeomagnetic data from fault rocks along major faults in the laerdal gjende fault system cutting the caledonian structure in the jotunheimen area of central south norway reveals a multi component remanence pattern sample and site mean directions from the fault rocks obtained by thermal cleaning demonstrate a simple pattern of normal polarity low blocking components and reverse polarity high blocking directions the magnetic signature of the laerdal gjende fault system fault rocks is identical to that observed on breccias on late faults along the west coast of norway based on available palaeomagnetic reference data we assign ages of mid late permian and late jurassic early cretaceous for important phases of faulting and breccia formation along the laerdal gjende fault system in central south norway structural windows partly exposing basement along the axis of the caledonides in southern norway were exhumed by footwall uplift on major faults in the laerdal gjende fault system the consanguinity of fault rock data from the laerdal gjende fault system and fault rocks in western norway and comparison with displacement on the offshore continuation of the laerdal gjende fault system along the hardangerfjorden shear zone indicate that the main tectonic events responsible for the development of the north sea basin also significantly affected the geology of central south norway

paleoreconstruction by biological markers abstract during diagenesis and conversion of the original lipid fraction of biological systems to petroleum hydrocarbons the following four basic events needed for paleoreconstruction can be monitored by biological markets 1 sourcing 2 maturation 3 migration and 4 biodegradation actual cases of applying biological markers to petroleum exploration problems in different parts of the world are demonstrated cretaceous and phosphoria sourced oils in the wyoming thrust belt can clearly be distinguished from one another by high quality source fingerprinting of biomarker terpanes using gas chromatography mass spectrometry identification of recently discovered biological markers head to head isoprenoids allows subtle source differentiation between oils from sumatra the degree of crude oil maturation in basins from california alaska russia wyoming and louisiana can be assessed by specific novel biomarker ratios 20s 20r sterane epimers field evidence from such interpretation is confirmed by laboratory pyrolysis of the rock an example of immature sumatra rock is given extensive migration is documented by biomarkers in several oils the effect of biodegradation on biomarker steranes and terpanes is exemlified in a california basin all biological marker results are consistent with the geological setting and add a new dimension in assisting the petroleum explorationist toward paleo reconstruction

fracturing and hydrothermal alteration in normal fault zones large normal fault zones are characterized by intense fracturing and hydrothermal alteration displacement is localized in a slip zone of cataclasite breccia and phyllonite surrounding corrugated and striated fault surfaces slip zone rock grades into fractured but less comminuted and hydrothermally altered rock in the transition zone which in turn grades abruptly into the wall rock fracturing and fluid flow is episodic because permeability generated during earthquakes is destroyed by hydrothermal processes during the time between earthquakes

rheology and geodynamic modelling the next step forward the application of continuum mechanics and microstructural analysis to geological studies over the past 30 years has spurred earth scientists to reassess fundamental tectonic processes such as subduction collision and rifting in terms of dynamics armed with new analytical methods geologists have returned to the field to look at rock structures with more mechanistic eyes the advent of sophisticated computers programs and laboratory deformation equipment has facilitated the simulation of geodynamic processes that range in scale from the grain to the lithosphere the result has been specialization with the concomitant opening of communication gaps between geodynamicists field geologists and rock mechanicists partly these gaps reflect differences of perception and approach in order to bridge these gaps a workshop was organized after the drm conference to debate how field and laboratory studies of deformed rocks can improve our understanding of lithospheric rheology and in turn how this understanding can be used to refine dynamic models of orogenesis the workshop hosted participants with backgrounds in structural geology experimental rock mechanics metamorphic petrology and both numerical and analogue modelling this paper summarizes the main controversies and conclusions reached during the workshop for the sake of brevity referencing in this summary is restricted to literature referred to during the oral presentations and to comments made by speakers themselves names italicized

the age and tectonic significance of dolerite dykes in western norway coast parallel dykes in sw norway primarily of permo triassic age have been linked regionally to the early tectonic evolution of the norwegian continental shelf we demonstrate from palaeomagnetic data mean declination 206 1 inclination 30 1 a 95 11 8 that dolerite dykes in the coastal sunnfjord region of western norway and immediately west of the devonian basins are also of permian c 250 270 ma age and not lower or pre devonian as previously advocated the sunnfjord dykes appear to be contemporaneous with dykes from sw norway at sotra 262 6 ma and the oldest dykes from sunnhordland 260 280 ma and geochemical data attest to a transition from sub alkaline to alkaline magmatism at the dawn of the mesozoic the sunnfjord dykes are not simple records of e w extension and magma intrusion but instead represent significant mid late permian time markers within a complex zone of fault activation and rejuvenation late mesozoic cenozoic magnetic overprinting mean declination 348 6 inclination 68 9 a 95 12 and metamorphic alteration documented by these dykes are directly dependent upon proximity to major e w brittle faults south of the hornelen devonian basin hence some motion and related fluid activity do post date dyke intrusion the e w high angle normal or oblique slip faults can be regionally traced offshore to the oygarden fault zone onshore these faults truncate the hornelen low angle detachment which in turn cuts folded d evonian strata these observations along with evidence for permian and late jurassic cretaceous extension from the nearby dalsfjord region demonstrate important reactivation of a late to post caledonian detachment and high angle fault system in western norway

significance of coniferous rain forests and related organic matter in generating commercial quantities of oil gippsland basin australia contrary to the conventional belief that humic coal generates primarily gas 3 billion bbl of recoverable oil has been discovered in the humic coaly succession of the fluviodeltaic latrobe group upper cretaceous tertiary that serves as both the reservoir and the source for hydrocarbons in the offshore gippsland basin of southeastern australia evidence for generation of liquid hydrocarbons from the coaly succession includes 1 similarity of n alkane distribution in the oil and in the coal extracts 2 high wax content of oil up to 27 by weight 3 high ratio of pristane phytane in oil 5 6 and 4 dominance of c29 steranes in the oil in the gippsland basin coniferous rain forests dominated by kauri vegetation flourished in a raised bog setting present temperate climate and kauri vegetation of new zealand are considered to be the modern analog to the gippsland basin the coniferous vegetation provided large quantities of hydrogen rich exinite macerals such as cutinite and resinite with potential to generate oil high rainfall raised ground water level low oxygen high acidity and low nutrient conditions of a raised bog setting were suitable for preserving organic matter a comparison of gas chromatograms of oils in the gippsland basin with gas chromatograms of oils generated by hydrous pyrolysis in the laboratory from the immature source rocks suggests that the paraffinic fraction of the oil was derived from coal and the naphthenic fraction was derived chiefly from resin

combined isotopic and biomarker investigations of temperature and facies dependent variations in the kupferschiefer of the lower rhine basin northwestern germany abstract organic material in selected kupferschiefer samples from the lower rhine basin of nw germany has been studied using gas chromatography gc coupled gas chromatography mass spectrometry gc ms as well as c and h isotopic analyses of the organic matter o and c isotope compositions of carbonates have also been investigated the study area is located at the southwest shore of the ancient zechstein ocean the permian kupferschiefer was deposited here under anoxic lagoonal conditions five closely sampled profiles were analysed covering a total depth range of 350 760 m in order to detect temperature sensitive variations and compositional changes during kupferschiefer deposition variations in isotopic and molecular compositions of organic material as well as in calcite 13c within the kupferschiefer section in proximity of the basic intrusion that forms the krefeld high are the result of post sedimentary thermal degradation of organic matter variations in the 18o values of carbonates are governed primarily by the mineralogical composition cao mgo ratios outside this area the isotopic data point toward a slightly increasing salinity of the seawater during kupferschiefer sedimentation an input of terrigenous organic matter is indicated by the occurrence of the ring a degraded pentacyclic triterpenoid des a arborene the compound is thought to be generated from the related pentacyclic precursor by anaerobic bacteria the significant decrease of the compound towards the top of the kupferschiefer correlates with decreasing anoxic conditions during kupferschiefer sedimentation

multistage strain localisation and fluid assisted cataclasis in carbonate rocks during the seismic cycle insights from the belluno thrust eastern southern alps italy abstract strain localisation in carbonate rocks impacts upon the nucleation and development of structures within the shallow seismogenic crust studying deformed carbonate rocks is thus a key to the refined understanding of the mechanical behaviour of rock successions with high potential to fail coseismically in response to stress accumulation we studied deformation structures and mechanisms of the miocene belluno thrust from the seismically active eastern southern alps italy the thrust contains several structural facies and features pressure soluted and veined lithons cataclasites s c fabrics principal slip surface which make it possible to define a sequence of deformation events in space and through time during thrusting image analysis of cataclasite particle size distribution and morphology supported by cathodoluminescence imaging indicates corrosive wearing as the main comminuting mechanism during cataclasis and repeated ingress of overpressured aqueous fluids promoting carbonate clast dissolution we propose an evolutionary scenario of multiple episodes of fabric formation and rejuvenation that localised and accommodated increasing shear strain into a progressively narrowing fault core we propose that strain localisation in carbonate rocks can be greatly facilitated by cyclic fluctuations between strain hardening and softening conditions punctuated by transient spikes of coseismic failure accommodated by cataclasis during the ingress of overpressured chemically reactive fluids that control carbonate precipitation and dissolution

exhuming norwegian ultrahigh pressure rocks overprinting extensional structures and the role of the nordfjord sogn detachment zone 1 the nordfjord sogn detachment zone nsdz is widely cited as one of the primary structures responsible for the exhumation of norwegian ultra high pressure uhp rocks here we review data from the considerable volume of research describing this shear zone and compile a strikeparallel cross section along the nsdz from the solund basin in the south to the soroyane uhp domain in the north this cross section highlights several previously unrecognized patterns revealing a shear zone with top to the west asymmetric fabrics that 1 initiated at amphibolite facies 2 overprints metamorphic breaks and tectonostratigraphic contacts and 3 has a gradational continuum of muscovite cooling ages these patterns constrain the kinematic evolution of the nsdz and suggest a new three step model for the exhumation of norwegian u hp rocks the initial stages of exhumation were characterized by the rise of crustal rocks from u hp depths to the base of the crust by buoyancydriven mechanisms not specified in this paper mantle exhumation was followed by top to thewest normal sense displacement within a broad noncoaxial ductile shear zone near the base of the crust that overprinted tectonostratigraphic contacts formed previously during mantle exhumation in the final stages of crustal exhumation top w brittleductile detachments soled into and partially excised this ductile shear zone dropping the devonian basins into contact with rocks of varying tectonostratigraphic levels this new interpretation of the nsdz is significant as it accounts for the extreme crustal excision observed in western norway using three sequentially overprinting structures active at different stages of uhp rock exhumation citation johnston s m b r hacker and t b andersen 2007 exhuming norwegian ultrahigh pressure rocks overprinting extensional structures and the role of the nordfjord sogn detachment zone tectonics 26 tc5001

hydrocarbon source for oil and gas indication associated with gas hydrate and its significance in the qilian mountain permafrost qinghai northwest china abstract since gas hydrate was sampled by drilling in the qilian mountain permafrost in 2008 to investigate the source of the gas hydrate and the relationship between gas hydrate and the concomitant oil and gas indication ogi have become an important research focus the rocks bearing gas hydrate and ogi from the middle jurassic strata in the qilian mountain permafrost qinghai northwest china were extracted by organic solvent and thermally treated 300 c and 400 c in vacuum glass tubes the hydrocarbons from the extracts and cracked products of the rocks and the stable carbon isotope of the gas hydrocarbons were studied the results showed that the ogis can be classified into two types according to different biomarker characteristics the i type of ogis which suffered from the process of early biodegradation and later hydrocarbon input and featured high concentrations of 17 h diahopane and regular steranes mainly originated from the shallow source rocks of the middle jurassic strata while the ii type one with a series of long chain alkylnaphthalene may originate from the lower portion of middle jurassic or deeper source rocks than the middle jurassic strata the adsorbed gas 300 c of the middle jurassic rocks was very wet had a normal carbon isotope sequence and can be regarded as an organic thermogenic gas derived from middle jurassic source rocks comparing the adsorbed 300 c and cracked 400 c gases from the rocks with gases from the gas hydrate and drilling core we found they had similar stable carbon isotope distributions but different relative contents of methane c 1 ethane c 2 and propane c 3 the middle jurassic source rocks are mainly deposited in a freshwater paleo environment similar to the parent biomass of the gas hydrate and drilling core gas the difference of the relative concentrations of c 1 c 3 may result from different formation processes between the adsorbed and cracked gases and the gas hydrate and drilling core gas the ii type ogi which possibly originated from deeper strata than the middle jurassic were closely associated with the gas hydrate under the drilling well and had a similar parent biomass and depositional environment as the gas hydrate showing they have a closely correlated hydrocarbon origin

thermal structure of supra detachment basins a case study of the devonian basins of western norway we investigate the peak temperatures of the devonian hornelen kvamshesten and solund basins in sw norway to constrain their thermal history these basins are the three largest devonian units exposed in norway and were formed as supra detachment basins in the hangingwall of the nordfjord sogn detachment zone the peak temperatures of the basins were obtained using a geothermometer based on raman spectroscopy of carbonaceous material on detrital carbonaceous plant fossils the data confirm an anchizone to low greenschist facies metamorphism with temperatures 30 c of 284 301 c in the hornelen and solund basins and a significantly higher temperature 345 c in the kvamshesten basin the temperature increases toward the detachment fault and cannot be explained by ordinary burial alone in the kvamshesten basin this temperature increase is close to 100 c the new data demonstrate that exhumation of high grade rocks in the footwall in the nordfjord sogn detachment zone played an important role in controlling temperatures in the hangingwall we conclude that the dynamic evolution along large scale detachments may introduce heat at the base of the hangingwall and thereby control the thermal state of supra detachment basins formed during extension

shear zone evolution during core complex exhumation implications for continental detachments abstract the formation of low angle detachments involves exhumation of previously ductile material and fault zone weakening to better understand this relationship we studied a deeply eroded metamorphic core complex which formed in the core of the bergen arcs w norway during caledonian post orogenic collapse multi scale structural mapping in the oygarden complex constrains three structural levels characterized by localized shear upper unit distributed deformation middle unit and a migmatite double dome lower unit all levels show retrogressive e w stretching accompanied by extension parallel recumbent folding albeit with opposing shear senses at upper and middle lower levels the systematic comparison of 23 shear zones constrains the ductile to brittle structural evolution initially high temperatures and partial melting controlled pervasive deep crustal flow and ductile doming during retrogressive shearing lithological heterogeneity controlled strain localization and channelized fluid flow causing retrograde phyllosilicate growth this established a feedback loop of fluid flow fabric weakening and progressive shear localization the interconnection of inherited and newly formed weak phyllosilicate rich layers promoted the formation of bivergent detachments that rapidly exhumed a dome of previously ductile crust retrogressive weakening in a kilometer wide ductile to brittle processing zone may be essential for the formation of continental detachments

structural analysis of flow related textures in lavas abstract the textures of coherent volcanic rocks including lavas and volcanic intrusives commonly contain features that are attributed to flowage previous applications of structural analysis to volcanic rocks are expanded here to provide a framework for analysis textures defined as the crystallinity granularity and shapes and arrangements of the components crystals glass and voids of a rock together with structures defined as individual features composed of the disposition attitude arrangement or relative positions of the components of a rock are first described second the spatial fabrics shapes and arrangements of the components of a rock and the orientation of textures and structures are identified third textures structures and fabrics are placed in the spatial and temporal geological context finally detailed interpretations of the kinematics and rheology of structures and fabrics is made leading to an integrated flow history of the rock illustrative case studies include rhyolite from the basal part of the tertiary minyon falls dome northeastern new south wales australia which has a texture comprising planar domains of differing crystal abundance flow bands multiple folds of these domains relatively homogeneous crystal alignment parallel to the fold axes and microfolding of these domains in the zone of interaction between phenocrysts and matrix including retrorotation of phenocrysts on short limbs of inequant folds trachyte dykes on fraser island queensland australia have a texture comprising crystal alignment planar concentration domains banding two planar domains of crystal alignment interpreted to be conjugate shear zones phenocrysts influence the spacing and distribution of the domains and interacted with shear zones by undergoing small amounts of rotation the shear zones overprinted a homogeneous crystal alignment during the last stage of flow before solidification as a result of dilatant granular interactions lava from miocene submarine banded silicic mafic domes on katsurajima on the coast of the shimane peninsula southwestern japan has a texture comprising crystal alignment irregular domains interpreted as the result of quenching local internal deformation of crystals including brittle boudinage and elongate vesicles and amygdales dacite from the late stages of the 1991 1995 eruption of mount unzen in western kyushu japan has a texture comprising crystal alignment deformation of phenocrysts and their surrounding matrix producing voids by mechanical means with the possible involvement of vapour phases the pervasive mechanical failure of the flowing magma may have triggered frontal collapse and the ensuing pyroclastic eruptions a spectrum of increasingly intense flow related textures can be recognised from simple planar alignments of crystals and vesicles to overprinting effects and domainal textures such as banding and shear zones and deformed domains pervasive ductile tearing and ultimately brittle fracture record flow during the transition from ductile magma to brittle rock the development of these flow related textures is controlled by the interplay of driving forces magma pressure gravity and resisting forces viscosity where driving forces are strong flow related textures are well developed when viscous resistance exceeds the driving forces flow and the development of flow related textures ceases

the biomarker composition of some crude oils from sumatra abstract crude oils from the north central and south sumatra basins have been analysed using gc and gc ms techniques and the biomarker compositions of the crude oils have been used to classify the samples into three types one oil from the north sumatra basin contained 3 methylhexadecane 2 methylhexadecane pristane and phytane in similar abundances regular steranes and 24 n propylcholestanes indicative of an algal contribution a series of 30 norhopanes and an absence of plant derived pentacyclic triterpanes these features have been interpreted as indicating a marine carbonate depositional setting two crude oils from the central sumatra basin are waxy crudes with abundant botryococcane pristane phytane and abundant 4 methyl 24 ethylcholestanes relative to dinosteranes these features suggest a brackish lacustrine depositional setting one light oil from the north sumatra basin and two crude oils from the south sumatra basin have abundant pristane compared with n c 17 and a high pristane phytane value the saturated polycyclic compounds are dominated by bicadinanes and other pentacyclic triterpanes of land plant origin the presence of abundant oleananes in these samples has been interpreted as evidence for deltaic near shore depositional setting these results show that crude oils from the sumatran region have source rocks with a range of depositional environments however the major oil fields are associated with lacustrine source rocks

predictive permeability model of extensional faults in crystalline and metamorphic rocks verification by pre grouting in two sub sea tunnels norway abstract this paper link quantitative fault zone descriptions qualitative fracture and fault rock properties and engineering data in the study of the permeability structure of fault zones datasets include scan lines drill cores and cement pre grouting from two sub sea tunnels in gneissic and granitic rocks from which systematic pre grouting volumes can be used to analyse the in site relative permeability both in host rocks and fault zones major extensional faults intersected by the tunnels reveal common fault rocks surrounding intensively fractured rock lenses in the core fracture frequencies in these lenses can reach 100 fractures metre f m in the bounding damage zones networks of fracture sets make up an inner zone of fairly high frequency 20 30 f m of fault parallel long fractures connected by shorter fractures an outer zone has lower frequencies tunnel scale injection of cement reveals patterns that can be ascribed to the impact of faulting there is an increase in cement injection in fault zones compared to areas with background fracturing away from faults in detail there is an innate division of the rock volume into sub zones characterized by distinct structural style and permeability with a background level and three fault related sub zones fault core inner damage zone and outer damage zone injection data shows that the background sub zone commonly can be injected with less than 0 05 m3 cement per metre tunnel commonly not injected whereas the fault core has permeability characteristics nearly as low as the outer damage zone represented by 0 1 0 2 m3 cement per metre tunnel with occasional peaks towards 0 5 m3 the maximum of cement injection lies in the inner damage zone marginal to the fault core with 0 3 0 7 m3 cement per metre tunnel locally exceeding 1 m3 this gives a relative relationship for cement injection of approximately 1 2 1 between fault core inner damage zone and outer damage zone of extensional fault zones in crystalline and metamorphic rocks

the role of fault reactivation and growth in the uplift of western fennoscandia new structural data published aft data and topographic data suggest that the latest cretaceous cenozoic uplift of western norway was associated with normal reactivation of the more trondelag fault complex reactivation focused along the base of today9s topographic rise with maximum displacements in the order of 2 3 km structural and aft data indicate that reactivation occurred along a displacement gradient with least normal displacement in the ne and increasing displacements towards the sw reactivation commenced in connection with the triassic to earliest cretaceous phases of rifting on the norwegian margin and probably continued through most of the tertiary the late cretaceous to cenozoic topographic development of the scandes mountains followed structurally induced templates such as those described from other areas of active normal faulting a fault model for the cenozoic uplift of the norwegian mainland provides a framework for provenance erosion and transport of sediments eventually deposited in the offshore post rift basins in the latest cretaceous palaeogene and neogene the asymmetric topographic profile of fennoscandia is reflected in the aft data and suggests that lithospheric flexure places a first order control on the shape of the scandes mountains and the central fennoscandian craton

extensional faults in fine grained carbonates analysis of fault core lithology and thickness displacement relationships abstract a study of 103 extensional faults hosted by fine grained carbonates in western sinai svalbard and oman reveals that faults vary geometrically between simple cores and cores comprising fault splays lenses segment linkages and overlap structures fault core rocks are typically carbonate breccias carbonate and shale gouge shale smear secondary calcite cement and veins and host rock lenses there is a significant scatter in the core thickness for any given displacement but the overall pattern is that the thickness increases with displacement this increase best fits a power law function 0 29d 0 56 that describes a gradual decrease in the thickness displacement relationship for increasing slip along faults in more detail the general function can be seen as the sum of two power law trend lines the first representing thin localized fault cores with generally simple and planar geometry the second representing thicker fault cores with complex geometry of lenses and overlap structures and with fault rock membranes the studied faults show a significant change in composition and geometry from small 0 1 m to moderate 1 10 m and to large offset faults 10 400 m the overall pattern is that fault initiates as fractures filled with calcite veins and thin shear fractures that hosts gouge membranes with increased fault offset complexity increases with breakdown of veins more extensive fault rock membranes and a trend towards development of lenses when offset exceeds 100 m cores become complex with multiple slip zones cemented breccia and shale smear membranes and various types of lenses we envision that the fault development as reflected by offset is dominated by forces extension compression acting in the fault mechanical heterogeneity of wall rocks the core lithologies and their developing rheology and especially geometric effects arising from fault irregularities

development of phyllonite from granodiorite mechanisms of grain size reduction in the santa rosa mylonite zone california abstract field and laboratory investigations indicate that phyllonite within the santa rosa mylonite zone developed from granodiorite without hydrous alteration of the original mineral assemblage initial grain size reduction within zones of phyllonite was accomplished through whole rock cataclasis subsequent deformation occurred through ductile flow the original cataclastic failure is recorded by sharp boundaries with the surrounding rock which are retained through the ductile overprint biotite in phyllonite has a mean grain size of 3 m and exhibits straight boundaries and a strong crystallographic preferred orientation trace analyses of hvem images indicate that the largest biotite grains are most strongly oriented and the grains are elongate parallel to lineation tem observations indicate that typical grains have irregularly spaced stacking faults and twins evidence for intracrystalline folding and cataclasis present in protomylonite and mylonite is absent bending or kinking of grains is rare these observations suggest that biotite in phyllonite accommodated deformation through dynamic recrystallization in concert with intracrystalline slip and mechanical rotation grain size reduction to form phyllonite is accompanied by macroscopically and microscopically visible changes in the character of foliations in the rock we suggest that these changes are linked to the deformation mechanisms operating within the fine grained phyllonite

the proximal domain of the mid norwegian rifted margin the trondelag platform revisited abstract located along the coast of norway the trondelag platform area corresponds to the proximal domain of the mid norwegian voring rifted margin we investigated its architecture and structural evolution based on interpretation of a dense network of high resolution seismic reflection profiles supplemented by comparison with local onshore analogues the entire area is floored by ductile crustal shearing and regional scale core complexes that form a corrugated surface with basement culminations that are flanked and sometimes cut by detachment faults the detachments are segmented suggesting long lived and multiphase tectonic activity the observed geometries are directly comparable to the ones mapped onshore in and around devonian old red sandstone basins in western and south western norway and in the adjacent north sea the combination of intensively sheared basement core complexes flanking and cutting detachment faults is interpreted to represent the offshore record of the transition from orogenic collapse to the first phases of rifting the observations demand a revision of our conceptual approach of margins proximal domains geometries for rifted margins that develop on collapsed orogens

earthquakes and rock deformation in crustal fault zones the physical origin of earthquakes lies ultimately in the geological structure of fault zones and the deformation processes that occur therein in response to tectonic stress although the possibility now exists that the nucleation regions for large earthquakes at depths of 10 km may shortly become directly accessible by deep drilling our present knowledge of fault structure and the shallow earthquake source is derived largely from a variety of indirect sources these include seismological studies surface studies of fault zones and earthquake ruptures geodetic information on modes of fault slip geophysical constraints on fault zone structure and rheology and information garnered from materials science and experi mental rock deformation studies of fault zone structure and the rock products of faulting provide complementary information on deformation processes at depth in fault zones although descriptions of fault rocks are widespread in the geological literature e g spry 1969 higgins 1971 it is only in the past decade that they have begun to be interpreted in the context of the physical conditions and processes prevalent in seismically active fault zones at different crustal depths sibs on 1977 watts williams 1979 anderson et a11983 wise et ai 1984 such interpretations are still at an early stage but the deformation textures and structural associations of fault rocks have already been shown to have the potential to yield information on such diverse topics as shear stress levels power dissipation and seismic efficiency during earthquake faulting on fluid pressure levels and episodic fluid flow accompanying

absolute dating of brittle fault movements late permian and late jurassic extensional fault breccias in western norway 40ar 39ar geochronological and palaeomagnetic dating methods applied to fault breccias in western norway have isolated two brittle reactivation episodes of the syn post caledonian extensional nordfjord sogn detachment these events of latest permian and latest jurassic early cretaceous ages demonstrate temporal relationships between development of chemical remanent magnetism and partial resetting of ar isotopic systems during distinct breccia forming episodes a third event of carboniferous age was also identified in the breccias with the 40ar 39ar technique and is a relict unroofing signature inherited from the fault wall rocks these brittle faults are significant time markers and become relevant to interpretations of offshore seismic data which attempt to place ages on faults that have undergone multiple reactivation episodes

land offshore tectonic links in western norway and the northern north sea aeromagnetic and marine gravity data sets for the northern north sea and western norway have been interpreted in terms of land to offshore tectonic links the data allow identification of linking structures both in crystalline basement and overlying sedimentary rocks and consequently facilitate a more comprehensive interpretation of regional structural features and trends with the help of bathymetric data in the inshore region major fault structures can be traced between western norway and the offshore region west of the oygarden fault zone in this way spatial and chronological links have been established between tectonic events recognized on land and the development of the north sea basin an interpretation of basement geology is proposed for the region between western norway and the uer terrace this is complemented with a depth to top crystalline basement map covering the north sea basin between the uer terrace and the east shetland basin two regional nw se lineaments were recognized offshore western norway and given the names marflo lineament and troll lineament the marflo lineament is interpreted to be a caledonian or older zone of weakness that accommodated development of a 20 30 km offset in the jurassic viking graben axis the lineament can be traced into the north atlantic where it parallels oceanic fracture zones and transform faults the troll lineament relates to a deep geological discontinuity crossing the uer and lomre terraces a grouping of earthquake epicentres along part of the lineament suggests that the discontinuity is tectonically active

metamorphic core complexes windows into the mechanics and rheology of the crust metamorphic core complexes are products of normal fault displacements sufficient to exhume rocks from below the brittle ductile transition these faults detachments may initiate within the brittle crust at steep angles but they sole into the ductile middle crust and during displacement rotate to gentler dips due to hanging wall extension the exhumed footwall commonly adopts an arched or domed geometry owing to flexural isostatic readjustment and may be overlain by strongly extended upper crustal rocks that slipped on gently dipping low friction shallow segments of the detachment metamorphic rocks exhumed beneath the detachment record progressively increasing flow stress strain localization and strain rate with decreasing temperature providing a window into physical conditions and deformational processes in the mid crust the metamorphic and deformational history of the footwall rocks may reflect tectonic processes that predate formation of the detachment fault in addition to those accompanying exhumation these processes may include diapiric emplacement of gneiss domes or exhumation in a subduction channel and may not be directly related to formation of the core complex factors favouring core complex formation are high gravitational potential energy of the extending crust weak rheology and a change in the tectonic boundary conditions such as a cessation or slowing of plate convergence

deep crustal flow within postorogenic metamorphic core complexes insights from the southern western gneiss region of norway 2019 the authors this is an open access article under the terms of the creative commons attribution license which permits use distribution and reproduction in any medium provided the original work is properly cited

thermobarometry of metamorphosed pseudotachylyte and associated mylonite constraints on dynamic co seismic rupture depth attending caledonian extension north norway abstract the exhumed post caledonian eidsfjord and fiskfjord extensional shear zones of northern norway exhibit evidence of coseismic rupture propagating into the ductile crust as evidenced by the presence of mylonitic and metamorphosed pseudotachylyte geothermobarometric calculations on garnet bearing mineral assemblages in mylonitic gneisses associated with mylonitic pseudotachylyte and in metamorphosed pseudotachylyte permit determination of the depth and ambient temperature of seismogenic low angle ductile extension average pressures from eidsfjord 570 115 mpa at ca 650 c and fiskfjord 1120 220 mpa at ca 650 c correspond to faulting depths of 21 4 km and 41 9 km respectively the fiskfjord results agree with previous thermobarometric calculations on mylonitic cpx grt bearing pseudotachylyte at fiskfjord the calculated depths are 5 25 km below the depth of the standard seismogenic zone these results demonstrate that low angle normal faults may cut through a large portion of continental crust this occurrence of mylonitic pseudotachylyte in an extensional crustal setting is most easily explained by dynamic downward rupture into the ductile regime and or unusually high shear stresses to account for coseismic rupture at such depths implying a direct connection with a seismogenic normal fault in the upper crust

coeval formation of cataclasite and pseudotachylyte in a miocene forearc granodiorite southern kyushu japan abstract cataclastic rocks and pseudotachylytes are exposed along the uchinoura shear zone a normal fault zone cutting the middle miocene 14 ma osumi granodiorite in southern kyushu japan cataclastic rocks include non foliated clast supported to matrix supported cataclasite and foliated clast supported cataclastic granodiorite in these rocks fracturing and comminution played a major role but dissolution and recrystallization of quartz and plastic deformation of quartz and biotite were also active processes especially in foliated granodiorite two types of pseudotachylyte are distinguished a foliated type characterized by a planar arrangement of clasts and microlites and a spherulitic type characterized by clasts surrounded by microlite overgrowths both types are of melt origin as attested by the presence of microlites and rounded or embayed clasts and by the scarcity of biotite clasts unlike spherulitic type pseudotachylyte which solidified without being deformed the foliated type pseudotachylyte underwent flow before complete solidification this deformation is thought to reflect post seismic strain accommodation immediately following the main slip episode kinematic indicators which consist of riedel type secondary fractures branching on primary fractures shear bands offsetting the foliation of foliated granodiorite or asymmetrical porphyroclast systems within pseudotachylyte veins show that all fault rocks were generated during n s to nw se directed extensional deformation pseudotachylyte is closely associated both in time and space with cataclastic rocks thus indicating that the behaviour of the uchinoura fault zone alternated between comminution and frictional melting given the slow strain rates which characterize dissolution and recrystallization processes detected in cataclasites the juxtaposition of pseudotachylytes and foliated cataclasites provides an example of aseismic and seismic displacements within the same shear zone

the tectonic implications of solundian upper devonian magnetization of the devonian rocks of kvamshesten western norway the allochthonous old red sandstone of kvamshesten western norway records polyphase orogenic deformation and palaeomagnetic results from both the devonian sediments and mylonites associated with the basal thrust define a syn to post tectonic magnetization withd 218 i 3 and 95 9 7 the corresponding pole position lat 21 s long 324 e suggests a late devonian early carboniferous magnetization age solundian and probably dates the time of thrust movements

trimethylnaphthalenes in crude oils and sediments effects of source and maturity abstract three sedimentary sequences and a number of crude oils have been analysed for trimethylnaphthalenes tmns using gas chromatography the sediments were found to contain enhanced relative abundances of 1 2 5 tmn and 1 2 7 tmn in samples of cretaceous age and younger this was especially pronounced in lower maturity sediments containing type iii organic matter older samples containing type iii organic matter were found to contain enhanced relative abundances of 1 2 5 tmn and lower relative abundances of 1 2 7 tmn 1 2 7 tmn appears to be derived directly from the structural degradation of oleanane type triterpenoids present in angiosperms and as such is proposed as a marker for this class of plant and indirectly therefore also for samples deposited since the early cretaceous the crude oils have been classified according to their trimethylnaphthalene compositions this classification enables crudes of higher plant origin to be identified and to be further classified according to whether the organic matter pre dated or post dated the evolution of angiosperms

exhumation of ultrahigh pressure rocks beneath the hornelen segment of the nordfjord sogn detachment zone western norway the nordfjord sogn detachment zone of western norway represents an archetype for crustal scale normal faults that are typically cited as one of the primary mechanisms responsible for the exhumation of ultrahighpressure uhp terranes in this paper we investigate the role of normal sense shear zones with respect to uhp exhumation using structural geology thermobarometry and geochronology of the hornelen segment of the nordfjord sogn detachment zone the hornelen segment of the zone is a 2 6 km thick top w shear zone primarily developed within amphibolite grade allochthonous rocks that juxtaposes the uhp rocks of the western gneiss complex in its footwall with lower grade allochthons and carboniferous devonian basins in its hanging wall new thermobarometry and sm nd garnet geochronology show that these top w fabrics were initiated at lower crustal depths of 30 40 km between 410 ma and 400 ma structural geology and quartz petrofabrics indicate that top w shear was initially relatively evenly distributed across the shear zone and then overprinted by discrete ductile brittle detachment faults at slower strain rates during progressive deformation and exhumation these results require a three stage model for uhp exhumation in which normal sense shear zones exhumed uhp rocks from the base of the crust along initially broad ductile shear zones that were progressively overprinted by discrete ductile brittle structures

fault related rocks suggestions for terminology many traditional terms for fault related rocks have undergone recent dynamic metamorphism under high pressure discussions by various groups of specialists a generally acceptable simplified framework encompassing these and associated structural terms is now needed for many geologic engineering and legal purposes such a framework is proposed here focusing on a rate of strain versus rate of recovery diagram and relating this framework to the products of brittle and ductile deformation along faults

crustal exhumation of the western gneiss region uhp terrane norway 40 ar 39 ar thermochronology and fault slip analysis article i nfo ar 39 ar muscovite thermochronology 40 ar 39 ar k feldspar thermochronology fault slip analysis new 40 ar 39 ar muscovite and k feldspar thermochronology combined with existing data reveal the timing and patterns of late stage exhumation across the western gneiss region u hp terrane muscovite age contours show that exhumation into the mid upper crust progressed westward over a 20 myr period 400 380 ma this exhumation was caused by i e w stretching and eastward tilting north of nordfjord where muscovite ages decrease from the foreland allochthons westward into the uhp domains and ii differential exhumation south of nordfjord where muscovite ages depict a ne sw dome like pattern and the western gneiss region is bounded by overlying units little affected by the scandian metamorphism exhumation of the uhp domains into the mid upper crust by late folding continued through 374 ma the smooth gradient of fairly flat muscovite age spectra demonstrates minimal influence of excess ar which is relatively unusual for a u hp terrane 40 ar 39 ar spectra and modeled cooling histories from k feldspar combined with brittle ductile

s c cataclasite in granitic rock abstract foliated cataclasites in granitic rocks along the rokko awaji fault zone japan display s c fabrics similar to those of mylonites the s c cataclasites have s surfaces defined by shape preferred orientation of biotite fragments and aggregates of quartz and feldspar fragments and c surfaces defined by microshears all quartz and feldspar fragments show mainly brittle deformational microstructures the biotite fragments however have some fabric characteristics like those observed in s c mylonites such as biotite fish cleavage steps bending and folding these differences in microfabric between biotite quartz and feldspar suggest that there are marked differences in their deformational behavior under the same deformational conditions biotite deformed by a combination of brittle plastic shearing processes and quartz and feldspar were brittlely damaged one of the most significant microstructural differences between s c cataclasites and s c mylonites is the absence of dynamically recrystallized grains in the s c cataclasites the microstructural characteristics and the geological evidence suggest that the s c cataclasites in the rokko awaji fault zone formed at temperatures between 150 and 250 c corresponding to depths of 5 8 km at a continental geothermal gradient of 30 c km before being uplifted and exposed this study of cataclastically deformed rocks shows that the fault zone rheology of the upper 5 10 km of crust is greatly influenced by deformational processes in s c cataclasites

shear heating in extensional detachments implications for the thermal history of the devonian basins of w norway article i nfo the supra detachment basins in western norway were formed during lower to middle devonian in the hangingwall of the extensional system of detachments known as the nordfjord sogn detachment zone nsdz the basins experienced elevated peak temperatures up to 345 c adjacent to the main detachment fault during the terminal stages of the extension in this study we show that the heat generated by the de formation of the rocks within the shear zone of the detachment also known as shear heating played a role in the thermal evolution of the entire region during the extension and could have induced the elevated peak temperatures of the supra detachment basins we numerically analyse the influence of the rheology and the deformation style within the shear zone the rate of exhumation of the footwall and the thickness of the sedimentary accumulation on the top of the system the model reproduces the elevated temperatures recorded in the supra detachment basins where locally 100 c and 25 of the total heat budget can be attrib uted to shear heating we show that this additional heat source may increase the peak temperatures of the hangingwall as far as 5 km away from the detachment

deformation processes and weakening mechanisms within the frictional viscous transition zone of major crustal scale faults insights from the great glen fault zone scotland abstract the great glen fault zone ggfz scotland is a typical example of a crustal scale reactivated strike slip fault within the continental crust analysis of intensely strained fault rocks from the core of the ggfz near fort william provides a unique insight into the nature of deformation associated with the main phase of sinistral movements along the fault zone in this region an exhumed sequence of complex mid crustal deformation textures that developed in the region of the frictional viscous transition ca 8 15 km depth is preserved fault rock fabrics vary from mylonitic in quartzites to cataclastic in micaceous shear zones and feldspathic psammites protolith mineralogy exerted a strong control on the initial textural development and distribution of the fault rocks at lower strains crystal plastic deformation occurred in quartz dominated lithologies to produce mylonites simultaneously with widespread fracturing and cataclasis in feldspar and mica dominated rocks at higher strains shearing appears to increasingly localise into interconnected networks of cataclastic shear zones many of which are strongly foliated textures indicative of fluid assisted diffusive mass transfer mechanisms are widespread in such regions and suggest that a hydrous fluid assisted grainsize controlled switch in deformation behaviour followed the brittle comminution of grains the fault zone textural evolution implies that a strain induced fluid assisted shallowing and narrowing of the frictional viscous transition occurred with increasing strain it is proposed that this led to an overall weakening of the fault zone and that equivalent processes may occur along many other long lived crustal scale dislocations

the middle devonian basins of western norway sedimentary response to large scale transtensional tectonics abstract the devonian basins of western norway were formed during late to post orogenic extension of overthickened caledonian crust the basins are situated in the hanging wall of the extensional nordfjord sogn detachment zone nsdz and display extensional half graben geometries in sections parallel to the local direction of principal extension based on overall facies configurations paleocurrent patterns and intrabasinal structures we infer an anticlockwise rotation of the syndepositional extension direction from nw se in the south solund basin to wsw ene in the north hornelen basin the axes of folds that are roughly parallel to the local extension direction are rotated correspondingly the kvamshesten basin is located between the solund and hornelen basins sedimentological and structural data show evidence of an early southeastwards tilt direction followed by a more eastwards tilt and associated e w flowing paleodrainage correspondingly nw se trending folds and reverse faults are superposed by e w trending ones at low to intermediate stratigraphic levels the variations in apparent tilt direction for the basins together with variations in intrabasinal structure is interpreted to reflect an anticlockwise rotation of the regional syndepositional strain field the above observations and inferences indicate that the devonian basins in western norway formed in a strain field dominated by regional transtension accommodated by extension along the nsdz and sinistral strike slip along orogen parallel shear zones and faults to the north of the basins alternatively nw directed extension preceded the introduction of a sinistral strike slip component the models are in accordance with recent work carried out in the footwall of the nsdz and illustrates the tectono sedimentary response to a complex interplay between extension and strike slip that appears to have been fundamental in the late stage disintegration of the caledonian orogen

palaeomagnetic dating of fault rocks evidence for permian and mesozoic movements and brittle deformation along the extensional dalsfjord fault western norway summary palaeomagnetic and structural studies of the dalsfjord nappe western norway show that the basal ow angle detachment dalsfjord fault is a long lived fault zone and that the most important phase of faulting was of devonian extension probably nucleated on an earlier silurian scandian thrust fault rocks produced during subsequent movements indicate that the dalsfjord fault underwent periods of brittle low angle extensional reactivation during the permian 250 260 ma and upper jurassic lower cretaceous c 150 ma corresponding with stages of major extensional movements on the continental shelf palaeomagnetic studies may be of great importance for dating faults and major movement stages in long lived fault systems the particular importance of the results is that they show that low angle normal faults can operate in a brittle upper crustal regime

kinematics of post caledonian polyphase brittle faulting in the sunnfjord region western norway abstract structural studies in the sunnfjord region of western norway focused on faulting episodes that post date the major period of early devonian extension clarify the style and prolonged complex evolution of brittle faulting major brittle structures in the region can generally be divided into 1 e w faults and 2 n s fault joint zones with subordinate ne sw and nw se structures in close association with these large scale features four distinct groups populations of mesoscopic faults can be distinguished with basis in common characteristics spatial distribution orientation sense of slip and cross cutting relationships two reference areas the eastern parts of the kvamshesten and hornelen devonian basins feature clear cross cutting relationships of major faults and folds such relations and kinematic patterns of the distinct populations of mesoscopic faults and their relationship to dated fault rocks and dykes form the basis for a four stage history of post early devonian brittle faulting stage 1 is characterised by n s shortening expressed by thrusting and folding related to either late devonian carboniferous transpression or compression stage 2 is characterised by n s shortening and e w extension on conjugate strike slip faults and bisecting normal faults and is probably related to the regional e w folding during progressive shortening stage 3 is characterised by approximate e w extension and is manifested as low angle silicified fault breccias of possible permian age that mainly bound the eastern margin of the devonian basins stage 4 features n s extension on steep e w striking normal faults that possibly relates to a regional late jurassic early cretaceous extensional phase significant throw 500 1000 m on some of the faults emphasise the importance of late devonian and younger faulting indicating that these deformation episodes had a regional extent and therefore also occurred in the neighbouring offshore areas the established four stage fault evolution is examined in the light of known episodes of rejuvenation of faults on the nearby shelf and along the more trondelag fault zone emphasising the importance of movement on master faults with respect to local strain conditions in the sunnfjord region

extensional fault cores in micritic carbonate case studies from the gulf of corinth greece abstract the major pisia and doumena faults of the corinth rift greece are both hosted by micritic carbonate rock their common fault elements are principal slip surfaces layers of fault rocks fault rock and host rock lenses corrugations and smaller shear and tension fractures along planar fault segments a corrugated slip surface with an associated thin fault rock layer is formed well developed down dip corrugations indicate movement along the same surface over many fault increments bends jogs in the faults are sites of complex structural relations hosting frequent lenses more porous fault rocks and dense networks of fractures major jogs in the slip surfaces have both strike and dip oriented undulating curvature that are associated with higher order fracture networks as well as frequent lenses fault core lens shapes of the doumena fault show relationship of length vs width of 3 2 similarly principal slip surfaces of the two faults show undulations with aspect ratios of amplitude vs wavelength 1 19 and 1 14 in strike direction despite a prominent difference in down dip geometry the intrinsic deformation in fault cores of micritic carbonate supports a model in which fluids entered the core by damage zone fractures that are linked to the principal slip surface flow along the fault core was controlled by the fracture system of lenses and thereby lens connectivity but may have been hampered by flow retarding fault rocks the flow potential is especially well developed in fault bends and breached relays due to frequent lenses and well developed fracture networks