double flood basalts and plume head separation at the 660 kilometer discontinuity several of the world s flood basalt provinces display two distinct times of major eruptions separated by between 20 million and 90 million years these double flood basalts may occur because a starting mantle plume head can separate from its trailing conduit upon passing the interface between the upper mantle and the lower mantle this detached plume head eventually triggers the first flood basalt event the remaining conduit forms a new plume head which causes the second eruptive event the second plume head is predicted to arrive at the lithosphere at least 10 million years after the first plume head in general agreement with observations regarding double flood basalts

promotion of graphite formation by tectonic stress a laboratory experiment summary graphitization of less ordered hexagonal carbon was studied under in situ pressure and temperature conditions on anthracite black shale and a synthetic calcite anthracite mixture at upper greenschist facies conditions anthracite exhibited a continuous loss of volatiles in the temperature range from 100 cu p to850 c 9 9 weight per cent at 450 c as detected by differential thermal analysis dta and thermo gravimetry tg energy dispersive x ray diffraction edx revealed a broad amorphous 002 graphite reflection while after p t treatment nearly perfect crystallized graphitic carbon was detected the electrical conductivity was measured at the same time in the frequency range from 0 7 up to 100 khz as a function of time the bulk resistivity was decreased by about three orders in magnitude at constant pressure and temperature conditions 0 7 gpa 450 c while the complex response exhibited a continuous decrease of the imaginary part of the impedance quasi metallic conduction now dominated the charge transport application of pressure strain temperature and time caused an increase in ordering and the degree of interconnection of the formerly randomly oriented carbon sheets the experimental results are an approach towards the explanation of the abundant occurrence of crystalline graphite observed in overthrusts and nappe structures which are distinguished by high conductivity structures

the limiting pressure on a circular pile loaded laterally in cohesive soil in the analysis of the undrained loading of laterally loaded piles an important quantity is the ultimate lateral resistance at depth to purely horizontal movement if the soil is modelled as a perfectly plastic cohesive material then the calculation of this quantity reduces to a plane strain problem in plasticity theory in which the load is calculated on a long cylinder which moves laterally through an infinite medium an exact calculation of the load on such a cylinder is presented if this load is non dimensionalized with respect to the soil strength and the diameter of the pile it is found that the load factor varies between for a perfectly smooth pile and for a perfectly rough pile this result is discussed in the context of previous calculations for the lateral load capacity of piles and is compared with approximate calculations using cavity expansion theory and a wedge failure near the soil surface la resistance laterale limite en profondeur au seul mouvement horizontal represente un parametre im

potbellies wasp waists and superparamagnetism in magnetic hysteresis because the response of a magnetic substance to an applied field depends strongly on the physical properties of the material much can be learned by monitoring that response through what is known as a magnetic hysteresis loop the measurements are rapid and quickly becoming part of the standard set of tools supporting paleomagnetic research yet the interpretation of hysteresis loops is not simple it has become apparent that although classic single domain pseudo single domain and multidomain loops described in textbooks occur in natural samples loops are frequently distorted having constricted middles wasp waisted loops or spreading middles and slouching shoulders potbellies such complicated loops are often interpreted in oversimplified ways leading to erroneous conclusions the physics of the problem have been understood for nearly half a century yet numerical simulations appropriate to geological materials are almost unavailable in this paper we discuss results of numerical simulations using the simplest of systems the single domain superparamagnetic sd sp system examination of the synthetic hysteresis loops leads to the following observations 1 wasp waisting and potbellies can easily be generated from populations of sd and sp grains 2 wasp waisting requires an sp contribution that saturates quickly resulting in a steep initial slope and potbellies require low initial slopes the sp contribution approaching saturation at higher fields the approach to saturation is dependent on volume hence the cube of grain diameter therefore there is a very strong dependence of hysteresis loop shape on the assumed threshold size 3 we were unable to generate potbellies using an sp sd threshold size as large as 30 nm and wasp waists cannot be generated using a threshold size as small as 8 nm the occurrence of both potbellies and wasp waists in natural samples is consistent with a room temperature threshold size of some 15 nm 5 4 simulations using a threshold size of 15 20 nm with populations dominated by sp grain sizes that is with a small number of sd grains produce synthetic hysteresis loops consistent with measured hysteresis loops and transmission electron microscopic observations from submarine basaltic glass 5 simulations and measurements using two populations with distinct coercivity spectra can also generate wasp waisted loops a relatively straightforward analysis of the resulting loops can distinguish the latter case from wasp waisting resulting from sp sd behavior

magnetic properties and ferromagnetic mineralogy of oceanic basalts summary rockmagnetic properties of a number of oceanic basalt samples collected by the dsdp odp drillings after leg 45 as well as one dredge haul were investigated in conjunction with palaeomagnetic characteristics of the same samples the electron probe micro analysis epma study indicated that chemical composition of the primary titanomagnetites has a variety particularly in minor constituent elements such as al2o3 mgo mno and v2o3 the variation in chemical composition in the primary phase of titanomagnetites seems to be controlled by changes in temperature oxygen fugacity and volatile pressure during the crystallization as well as chemistry of residual liquid hi magma general crystallization trend is found that is the later crystallized titanomagnetites have higher ulvospinel component higher titanium oxide and lower iron oxide due to decrease in temperature and oxygen fugacity it is established that minor constituent elements are good indicators of crystallization sequence of titanomagnetites in the contrast of variation in major constituent elements in the later stage al2o3 and mgo spinel component and v2o3 decrease whereas mno increases although there is a reversed crystallization trend with a few elements in several cases this reversed trend may suggest that there are discontinuous changes of environmental condition in magma to control titanomagnetite chemistry during a crystallization sequence the primary variation of chemistry shows different trends of the secondary variation due to oxidation oxidation process of titanomagnetites contained in oceanic basalts was examined in detail by means of an improved epma technique being able to directly determine the absolote contents of oxygen in materials the result of the quantitative oxygen measurement shows that the oxidation process of titanomagnetites is not a simple process by changes of ferrous ions to ferric ones with acrretion of oxygen but associated with migration of iron ions of the titanomagnetite lattice this is consistent with the results of recent studies on oxidation processes of titanomagnetites in oceanic basalts

thrust fault mechanics and origin of a frontal ramp several features of thrust sheets in nonmetamorphic and relatively low grade metamorphic terrains indicate that the modes of faulting included both gradual and stick slip types of motion a first order quantitative analysis is made of the mechanics of this type of faulting in the analysis part of a wedge shaped thrust belt slips forward over a fault area of length l and unit width w producing a strain concentration in subhorizontal strata at the front of the growing thrust where a frontal ramp develops by shear fracturing equations for net slip x and the conditions for ramping are evaluated with limit equilibrium principles and coupled oscillator theory the quantitative analysis takes into account anisotropy resulting from contrasts in competency and facies changes a special case solution for maximum net slip associated with stick slip is lw ki 1 cos ot o 12 1 cos 1t where is the stress drop ki are spring constants of the strata 0 and 1 are natural frequencies of the system and t evaluated from another equation is the time for net slip the spring constants and natural frequencies can be evaluated from seismic and stratigraphic data a preliminary solution for piggy back thrusting indicates that ramp spacing can be systematic and that it depends upon the thickness of the deforming package the elastic parameters of the deforming package the slope of the topographic surface and the stresses along the trailing edge of the package

experimental frictional heating of coal gouge at seismic slip rates evidence for devolatilization and thermal pressurization of gouge fluids high velocity 1 m s friction experiments on bituminous coal gouge display several earthquake related phenomena including devolatilization by frictional heating gas pressurization and slip weakening stage i is characterized by sample shortening and reduction in the coefficient of friction from 1 to 0 6 stage ii is characterized by high frequency 5 hz oscillations in stress and strain records and by gas emissions stage iii is marked by rapid weakening 0 1 to 0 35 and sample shortening together with continued gas emissions stage iv produces stable stress records and continued weakness 0 2 but without gas emission stage i shortening is due to compaction of the gouge and the weakening is attributed to mechanical or thermal effects stage ii behavior is interpreted as due to coal gasification and fluctuations in fluid pressure resulting in high frequency stick slip type behavior dramatic reduction in shear stress in stage iii is attributed to gas pressurization by pore collapse and corresponds to a frictional instability analogous to nucleation of an earthquake microstructural observations indicate the deformation was brittle during stages i and ii but ductile during stages iii and iv time dependent finite element frictional heat models indicate the center of the samples became hot 900 c during stage ii whereas the edge of samples remained relatively cold 300 c vitrinite reflectance of coal samples shows an increase in reflectance from 0 5 to 0 8 over the displacement interval 20 40 m 20 40 s indicating that the reflectance responds to frictional heating on a short time scale the energy expended per unit area in these low stress large displacement experiments is similar to that of higher stress 50 mpa short displacement 1 m earthquakes 107 j m2

upper bound and load displacement solutions for laterally loaded piles in clays based on energy minimisation introduction an important part of any foundation design procedure is the evaluation of the ultimate capacity and displacements under working loads the most widely used solution for ultimate loads of laterally loaded piles in clays is that of broms 1964 broms ignored the soil resistance down to a depth of one and a half diameters and used a constant resistance value of 9sud along the remainder of the pile where su is the undrained shear strength and d is the pile diameter while the value of 9sud closely corresponds to the bestknown lowerand upper bound solutions 9 14sud and 9 20sud respectively randolph houlsby 1984 martin randolph 2006 the omission of the upper soil resistance is somewhat arbitrary on the other hand associating a resistance value of 9sud with the upper soil would not be conservative as a wedge type mechanism will develop in that area murff hamilton 1993 reduction factors are therefore commonly applied to the ultimate soil resistance near the surface in p y curves e g matlock 1970 fleming et al 1992 murff hamilton 1993 dealt thoroughly with this problem by suggesting an upper bound failure mechanism comprising a conical wedge near the surface and a flowround plane strain mechanism below the wedge strictly speaking their upper bound solution is not rigorous since the transition from the wedge to the flow round mechanism is not continuous and the associated dissipation due to the abrupt change in the velocity field was not taken into account also energy dissipation due to relative shearing between the stratified flow round mechanisms was not considered in their solution in the present work a wedge type mechanism following the methodology of murff hamilton 1993 but eliminating the discontinuity at the outer boundary of the wedge is combined with the continuous flow round mechanism of klar osman 2008a to result in a fully compatible and continuous deformation field this deformation field allows rigorous calculations of upper bound values in addition since the mechanism is continuous with strain and strain rates defined everywhere the mobilisable strength design msd method bolton powrie 1988 osman bolton 2005 may be applied for estimation of displacements under working loads formulation figure 1 outlines the mechanism assumed for a long pile the pile rotates rigidly above a plastic hinge which develops at depth h a conical wedge type failure originating from depth z0 and extending to radial distance of rw develops near the surface below z0 a flow round mechanism prevails the parameters h rw and z0 are not known a priori and must be found by the upper bound minimisation process the suggested flow round mechanism corresponds to the solution of klar osman 2008a who utilised the airy stress function usually associated with elasticity to obtain a continuous kinematically admissible velocity field for the t bar problem the mechanism may be represented in a cylindrical coordination system r by the functions

major and minor structural features of a bedding shear zone along a coal seam and related gas outburst pingdingshan coalfield northern china abstract a fractured coal band traditionally called a soft coal band or structurally referred to as a bedding shear zone within the wu coal seam in the pingdingshan coalfield northern china was structurally studied based on field examination and observations by reflectance microscopy and scanning electron microscopy sem the bedding shear zone is not consistent with a simple bedding fault defined by pioneering geologists but rather a complexly deformed band locally overprinted by ductile shearing fabrics dominant small scale structures within the bedding shear zone are thrusts folds cleavage duplexes and related structures but local refolded folds kink bands and s c band structures also indicate ductile shear deformation typically developed in areas of steep dip such as within the limb of a subordinate fold bed parallel shearing within the coal seam has been considered a serious influence on gas outburst in underground mining production in addition to thickening the seam and reducing the quality of coal locally abnormal thickening of a shear zone and extensive compressive structures where ductile fabrics frequently occur are closely related with the site of an outburst thickening of a shear zone increases the capacity of methane storage and compressive structures within a shear zone may act as a tectonic screen blocking methane migration which can result in a pocket of high methane pressure a potential risk of outburst is indicated as a working face approaches an area of high methane pressure three abnormal phenomena encountered during a mining operation presage methane outburst for seams with a bedding shear zone

thermal considerations in inferring frictional heating from vitrinite reflectance and implications for shallow coseismic slip within the nankai subduction zone abstract frictional properties within the upper few kilometers of subduction zones are generally thought to inhibit rupture propagation understanding whether large rapid slip propagates to the surface during megathrust earthquakes is important for characterizing tsunami hazard recent vitrinite reflectance analysis by sakaguchi et al 2011 on cores from the nantroseize drilling transect at the nankai trough japan has been interpreted to suggest that these faults reached temperatures 380 c considerably larger than background temperature values implying they hosted coseismic slip at shallow depths analysis of other temperature proxies on the megasplay by hirono et al 2009 however suggests temperatures have not exceeded 300 c and is inconclusive as to whether the fault slipped at high velocity we evaluate the effects of frictional heat generation on the spatial distribution of vitrinite reflectance its sensitivity to slip zone thickness and slip duration and the cumulative effects of numerous events we build on the analysis of sakaguchi et al 2011 by estimating frictional heating scenarios that are consistent with both the peak and spatial extent of anomalous vitrinite reflectance data our results imply coseismic slip magnitudes of several 10s of meters peak temperature estimates from the vitrinite reflectance data can be reconciled with the other geochemical constraints only by assuming the vitrinite reflectance results from the cumulative effects of multiple earthquakes however this results in unrealistically large estimates of total displacement our results imply that current understanding of how vitrinite reflectance is affected by fault slip is incomplete

grain size dependence of the magnetic behavior of pyrrhotite during its low temperature transition at 34 k the grain size dependent behavior of pyrrhotite during a magnetic lt transition at 34 k is suitable for granulometric purposes cycling down to liquid helium temperature suppresses soft md jrs more than hard sd jrs so that it may be effective in removing soft secondary nrm components the domain structure of large pyrrhotite grains changes from md at room temperature to sd or psd below the lt transition

self reversed magnetization carried by titanomaghemite in oceanic basalts abstract self reversal the remarkable ability of some rocks to acquire a magnetization antiparallel to the earth s magnetic field was of great interest in the 1950s and 1960s but it was subsequently found to be rare limited to a few hemoilmenite bearing igneous rocks here we show through thermal demagnetization experiments that pillow basalts from the northwestern pacific ocean lacking hemoilmenite contain two nearly antiparallel components of natural remanent magnetization partial thermoremanent magnetization experiments indicate that the component isolated at lower temperatures is a self reversal of the primary magnetization the self reversal is carried by titanomaghemite formed by low temperature oxidation because maghemitization of oceanic crust is ubiquitous self reversals may be an important factor contributing to the decrease with age in marine magnetic anomaly amplitudes observed for crust formed during the last 30 million years

diagenesis to very low grade metamorphism in lower palaeozoic sediments a case study from deep borehole tobolka 1 the barrandian basin czech republic abstract the diagenetic grade of a 2 7 km thick sequence of lower palaeozoic marine sediments in the tobolka 1 deep exploration borehole was investigated by analysing organic and mineral components and fluid inclusions embedded in vein minerals the reflectance of organic matter r r increases down section from values of about 0 77 at the top of the devonian srbsko formation to values around 3 at the base of the ordovician letna formation in the devonian and silurian sediments the reflectance values of vitrinite like and graptolite fragments 0 77 1 13 r r and 1 09 1 46 r r respectively and the composition of fluid inclusions entrapped in vein minerals ch 4 co 2 complex saline solutions light gaseous hydrocarbons liquid petroleum t h 170 230 c collectively indicate organic maturation within the high temperature part of the oil window to the wet gas stage in the ordovician sediments below 1000 m chitinozoan reflectance values 1 38 3 03 r r and the ch 4 dominated composition of the fluid inclusions t h 250 310 c indicate a wet gas condensate stage to an advanced dry gas stage the clay mineral assemblage remains uniform throughout the whole succession and consists of illite mixed layered illite smectite is chlorite and kaolinite below 1400 m the illite content gradually increases down hole forming up to 45 55 of the clay fraction in the deeply buried ordovician sediments throughout the borehole the is displays uniformly low expandability 7 12 3 of smectite layers and an isii ordering the illite crystallinity broadly correlates with organic matter reflectance values and improves with depth from 1 1 to 0 54 2 according to the crystallinity index standard cis scale indicating high grade diagenesis to incipient anchimetamorphism the chlorite crystallinity chc index however shows no systematic correlations with depth the combined evidence from organic matter clay minerals and fluid inclusions points to maximum paleotemperatures of 100 230 c in the silurian devonian strata and up to 250 c or even higher in the ordovician strata apatite fission track analysis afta data suggests that maximum heating occurred between 340 and 380 ma i e during variscan orogenic deformations these paleotemperatures and the degree of diagenesis may have been produced by a post middle devonian burial or tectonic load that was subsequently eroded or by higher paleogeothermal gradients or by a combination of both

new paleomagnetic results from basaltic drill cores of the nauru basin western pacific tectonic and magnetostratigraphic implications abstract the voluminous volcanic eruptions in the nauru basin western pacific have long been regarded as important research targets for tectonic history of the pacific plate and for the widespread cretaceous volcanic activity in the western pacific the nauru basin volcanic rocks were recovered at site 462 by deep sea drilling project dsdp legs 61 and 89 where more than 600 m of lavas and sills were drilled thereby making it the deepest penetration into crust of cretaceous age in the pacific ocean for paleomagnetism this section represents a unique possibility for averaging out secular variation to obtain a reliable paleolatitude estimate however previous paleomagnetic studies have only been subjected to alternating field af demagnetization on several core samples thus unable to provide comprehensive understanding on the paleolatitude of the basin the work reported here aims to determine the cretaceous paleomagnetic paleolatitude for the pacific plate and define the magnetostratigraphy for the basaltic sections drilled in the nauru basin a total of 391 basaltic rock samples were carefully re sampled from dsdp sites 462 and 462a stepwise thermal and af demagnetizations have isolated characteristic components in the majority of the samples the most important findings from this study include 1 two normal and one reversed polarity intervals are identified in site 462 and six normal and six reversed polarity intervals are found in site 462a although possible erroneous markings of the opposite azimuth for some reversed polarity cores during the dsdp coring cannot be completely ruled out 2 based on previous radiometric ages the magnetostratigraphic correlations with the geomagnetic polarity time scale gpts indicate that the lower basaltic flow unit in site 462a began to erupt at least before 130 ma no correlation is available for the upper sill unit 3 paleosecular variation for the lower flow unit has been sufficiently averaged out whereas bias may exist for that of the upper sill unit 4 the calculated mean inclination of 50 for the lower flow unit yields a paleolatitude of 30 8 s for the nauru basin at the time of emplacement this value is well to the north of suggested location in plate reconstruction models suggesting that there has been a significant amount of apparent polar wander of the nauru basin and pacific plate since 130 ma in addition the paleolatitude for the nauru basin is 7 further south and the basin s age is more than 10 my older than those of the ontong java plateau ojp which suggest that the volcanic eruptions of the lower flows in the nauru basin are unlikely related to the emplacement of the ontong java plateau

the timing of coalification in relation to structural events in the grande cache area alberta canada lower cretaceous coals from the inner foothills of the rocky mountains were sampled for a study of the relationships between coal rank and folding and faulting the coals were collected from laterally continuous seams in a highly folded and faulted area near grande cache alberta rank of the coals as determined by measuring mean maximum vitrinite reflectances ranges from medium to low volatile bituminous the results indicate that the degree of coalification was established during burial from albian to late paleocene times before folding and faulting started isoreflectance lines run parallel to the bedding of the folded strata and there are no significant changes in reflectances in the same seam from one thrust sheet to the other however in the footwall of the mason thrust the mean maximum reflectances and bireflectances are locally increased above regional values regionally there appears to be a trend to slightly lower reflectances in the southeast of the study area it is suggested that the low

organic metamorphism in middle ordovician carbonates lebanon valley nappe pennsylvania abstract an assemblage of highly brecciated organic fragments at the contact of the middle ordovician annville and myerstown formations in the lebanon valley nappe lebanon county pennsylvania was found to have maximum reflectances generally exceeding 8 r with the highest values approaching 13 r such reflectance values are consistent with greenschist facies metamorphism the latter supported by metamorphic mineral assemblages brecciation and metamorphism of the organics probably occurred at the time of the emplacement of the nappe during the ordovician taconic orogeny

effect of loading direction on the ultimate lateral soil pressure of two piles in clay design equations are presented for the calculation of the ultimate lateral resistance of two pile groups in clay under a general loading direction analytical upper bound solutions numerical upper

recognition and implication of tectonic loading induced reheating in the northern variscan front belgium and northern france based on an illite kubler index and oxygen isotope study illite kubler index ki and oxygen isotope brachiopods and micrites investigations have been performed on more than 300 frasnian limestones sampled in one borehole and numerous outcrops in the dinant synclinorium belgium northern france of the northern variscan front the illite kubler index and 18o data of a 3 km thick tectonically repeated frasnian series from the focant borehole are compared with their surrounding surface correspondents and document in situ reheating induced by variscan tectonic loading which post dated sedimentary burial alteration the boundary between these two thermal processes sedimentary burial and tectonic loading on the focant profile corresponds to an important location where the heat induced by the tectonic loading was equivalent to that frasnian strata suffered during maximum sedimentary burial mainly based on this knowledge and on a former conodont colour alteration index study the thickness of the eroded thrust sheet in the focant area is estimated to be around 3 000 m oxygen isotopic exchange in these frasnian closed carbonate systems occurring under highest grade diagenesis and anchimetamorphism records two events brachiopods present a quite different and more homogeneous pattern due to their higher resistance to heat alteration these thermal events caused both 18o records to become increasingly lighter than the presumed original seawater signature the comparison between ki and 18o profiles indicates that illite ki analysis is more appropriate than 18o in highlighting the temperature variations in the burial metamorphism at the periphery of orogenic belts

organic maturity in the western canada sedimentary basin abstract organic maturity of strata in the western canada sedimentary basin has been investigated in numerous studies using petrological chemical and physical methods compilation of these data has facilitated a regional analysis of the maturity patterns and maturation history variation in maturity patterns can be divided into three levels basin wide 1st order regional 2nd order and local 3rd order first order variations are manifested by an overall increase in maturity of strata of the same age from east to west from the plains to the rocky mountain foothills and front ranges in response to progressively deeper burial and higher paleo geothermal gradients superimposed on this first order basinal scale variation in maturity are second and third order variations which reflect local differences in depth of burial conductive and advective heat transport or effects of thrust faulting maturity gradients in the axis of the basin are low averaging 0 10 log r omax km whereas in the front ranges and foothills the gradients are substantially greater average 0 25 log r omax km variations in maturity gradients reflect lower paleo geothermal gradients resulting from rapid sediment loading and subsequent unloading in the plains and higher conductive heat transport in the deformed belt the main component of maturity of most phanerozoic strata occurred during deep burial under upper cretaceous and or paleogene molasse in foredeeps developed in response to crustal loading during the easterly migration of the foreland fold and thrust belt as a result of the west to east propagation of deformation during the laramide orogeny deep burial maturation hydrocarbon generation and uplift occurred earlier in the foreland belt late cretaceous than in the plains to the east where the main component of maturity and hydrocarbon generation occurred as late as eocene in the plains because of the low maturity gradients a thick succession of strata currently is within the oil window in the deformed belt however higher maturity gradients have resulted in a thinner succession of strata within the oil window in response to higher paleo geothermal gradients strata in the deformed belt matured more quickly leading to more rapid hydrocarbon generation and migration than areas to the east in the southern part of the cordillera a significant component of maturation post dates structural deformation of the strata whereas in northeastern british columbia and adjacent parts of alberta maturity primarily pre dates structural deformation data from some deep bore holes and surface samples in the southern part of the cordillera provide evidence for maturity post dating or accompanying emplacement of major overthrust sheets tectonic burial in most areas however there is no clear evidence for the timing of maturity relative to faulting or evidence of frictional heating the maturity gradients and levels of maturity of surface and near surface strata in the western plains and rocky mountain foothills indicate that a succession several kilometres of paleogene strata were deposited in these regions foredeep and subsequently eroded in response to post laramide uplift

hot faults iridescent slip surfaces with metallic luster document high temperature ancient seismicity in the wasatch fault zone utah usa and localized iridescence in the footwall dam age zone of the wasatch fault utah usa and document elevated temperatures on these faults we propose that the formation of these iridescent slip surfaces requires frictional heat generated at geometric asperities at seismic slip rates wasatch fault zone abstract we document new geological indicators of ancient seismicity in the form of highly reflec tive iridescent hematite coated fault surfaces small faults that cut the paleoproterozoic farmington canyon complex in the footwall damage zone of the brigham city segment of the wasatch fault utah usa are smooth to striated surfaces tens of square centimeters to 30 m 2 in area the dull rusty to high metallic luster and moderate to high gloss surfaces exhibit multicolored elliptical iridescent patches 0 5 3 cm across preexisting hematite crystals were deformed during slip on 1 200 mm thick slip surfaces textural observations x ray diffraction x ray photoelectron spectroscopy electron backscattered diffraction analysis surface metrology and similarity to experimentally formed iridescent spots in rocks and metals indicate that iridescence is associated with high temperature 300 c reduction of iron fe 3 to fe 2 and associated conversion of hematite to magnetite we pro pose that the iridescent slip surfaces in the wasatch fault damage zone are the result of seismic slip and flash heating at asperities along the small faults the thousands of these sur faces represent coseismic or aftershock deformation down to magnitude 3 in the exhumed footwall damage zone of the wasatch fault

vitrinite reflectance and shear induced graphitization in orogenic belts a case study from the kandersteg area helvetic alps switzerland vitrinite reflectance vr is an important indicator of incipient metamorphism and it is generally assumed that temperature and to a lesser degree time are the two main variables the role of stress in vr is controversial and will be addressed in this study in the kandersteg area north of lake oeschinen four different helvetic tectonic units are present comprising mainly limestones marls and greywackes of mesozoic and lower tertiary age vr rr rmax rmin and illite crystallinity ic were determined from a very steep section at elevations between 1700 and 2900 m a s l in general rr rmax and ic increase from tectonically higher to lower units i e from upper diagenetic 2 3 to 4 5 rr to upper anchizonal conditions 3 4 to 5 6 rmax several samples contain in addition to coaly fragments abundant semigraphitized and graphitized particles that are believed to be of authigenic origin transitional matter showsrmax values ranging from 7 to about 11 and rmin of 1 3 3 4 optical graphite showsrmax of about 15 16 and rmin of 1 6 1 8 there is good textural evidence that tectonic deformation has played a major role in the development of these strongly coalified particles the first tiny needle like crystals of graphitic material occur within narrow shear zones transecting the rock matrix the beginning of graphite formation parallels the onset of plastic deformation and dynamic recrystallization of quartz elevated vitrinite reflectance rmax and bireflectance values are found near thrust planes where simple optical observation on quartz grain morphology indicates an increase in strain intensity it appears that frictional heating associated with thin shear zones may have been responsible for the formation of authigenic graphite in the kandersteg samples

extractable organic material in fault zones as a tool to investigate frictional stress abstract the detection of a frictional heating signature is an attractive but elusive way to measure frictional stress on exhumed faults with no evidence of melting we present a new paleothermometer for fault zones that utilizes the thermal maturity of extractable organic material to determine the maximum frictional heating experienced by the fault because there are no retrograde reactions in these organic systems maximum heating is preserved we investigate the punchbowl fault an ancient strand of the san andreas fault in southern california according to the methylphenanthrene index for thermal maturity there is no differential heating between the fault and off fault samples indicating that the fault did not get hotter than the surrounding rock during slip additionally the thermal maturity of the rocks falls within the range of heating expected from the bounds on burial depth and time and adds some constraint to the burial depth range simple heating models indicate that the fault must have had either 1 an extremely low shear stress during slip 2 an active slipping zone thicker than 1 mm or 3 earthquakes smaller than m6 to lack a differential heating signature after 44 km slip

late cretaceous paleolatitude of the hawaiian hot spot new paleomagnetic data from detroit seamount odp site 883 1 paleomagnetic data from detroit seamount of the emperor seamount chain northwestern pacific ocean provide a direct way to estimate the latitudinal position of the hawaiian hot spot in the late cretaceous 75 81 ma providing important constraints on geodynamic models for hawaiian plume motion crystalline basement of detroit seamount was sampled at four drill sites by ocean drilling program odp legs 145 sites 883 and 884 and 197 sites 1203 and 1204 here we report detailed thermal and alternating field af demagnetization data collected from basalt lava flows recovered at odp site 883 most samples showed two nearly antiparallel components of natural remanent magnetization nrm af demagnetization was often insufficient to separate the magnetization components therefore thermal demagnetization data were used to define their directions both magnetization components are chemical remanent magnetizations crms carried by single domain to pseudo single domain titanomaghemite produced by low temperature oxidation of titanomagnetite rock magnetic experiments suggest that the normal polarity component is a crm which pseudomorphs the primary thermal remanent magnetization trm of parental titanomagnetite in contrast the reversed polarity component is a crm self reversed with respect to a primary trm doubrovine and tarduno 2004 inclination data analysis of characteristic remanence normal polarity component results in the five distinct inclination groups and an average inclination of 57 7 13 8 12 3 95 confidence limits quoted the angular dispersion of paleomagnetic directions suggests that the site 883 basalts adequately average paleosecular variation and that the inclination average represents the time averaged geomagnetic field combining all available paleomagnetic data from the four sites on detroit seamount a revised paleolatitude of 34 4 5 8 3 2 was calculated this estimate is significantly north of the present latitude of the hawaiian hot spot 19 n suggesting that the hot spot moved southward from late cretaceous to paleogene times 81 47 ma at rates of 33 67 mm yr if the inclination results from odp site 883 represent the best estimate among the data available from detroit seamount rates at the higher range of values are favored because such rates are comparable to the velocities of lithospheric plates the new data from odp site 883 present a strikingly different view on hot spot stability

organic maturation in the french subalpine chains regional differences in burial history and the size of tectonic loads the french subalpine chains of southeastern france are the foreland fold thrust belt of the western alps formed in the mid to late tertiary as a result of the continental collision between the european and italian north african plates with the change from passive margin to destructive margin certain areas of the subalpine chains experienced enhanced temperatures through being buried to greater depths burial of these areas has been investigated using vitrinite reflectance r o levels of organic maturity of mesozoic and tertiary horizons have been established using vitrinite reflectance r o and spore fluorescence in the southwestern part of the chain values of r o for mesozoic units from the vercors and chartreuse massifs are generally low with all cretaceous units having values r o older jurassic horizons have higher values up to 1 25 for the mid jurassic oxfordian when compared to values from the same horizons and from younger tertiary units published data from the northeastern part of the chain it is clear that this part of the belt has encountered higher temperatures produced by greater depth of burial in the haut giffre and aravis massifs mesozoic units have r o values as high as 2 7 and in terms of hydrocarbon generation can be considered mature or overmature two causes of greater depth of burial of the northeastern part of the belt are indicated by field studies and by burial history modelling of specific localities of the subalpine chains first the earlier initiation of the tertiary foredeep in the northeast compared to the southwest and second differences in the size of tectonic loads emplaced onto the subalpine chains during the final stages of alpine compression with the greater structural deformation of the subalpine chains occurring in the northeast

alteration and self reversal in oceanic basalts 1 we report on magnetic properties and compositions of titanomaghemites from moderately to highly oxidized basalts recovered at nine drilling sites in the pacific ocean these new data together with similar data sets allow us to test compositional fields of titanomaghemite that could carry self reversed components of natural remanent magnetization above room temperature these compositions have been proposed on the basis of theoretical considerations of cation distributions during ionic reordering associated with low temperature oxidation maghemitization the data indicate that very high oxidation states z 0 9 and relatively high ti contents x 0 6 are needed to produce natural self reversed components this compositional range is much more limited than predicted the severe restrictions on compositions and oxidation state strongly suggest that self reversed magnetizations should not be a general feature of the magnetization carried by oceanic basalt instead the formation of self reversed components may signify unusual conditions such as extreme fluid flow and iron removal which could result in the required oxidation states while maintaining stability of the cation deficient titanomaghemite lattice structure

heating during thrust faulting in the rocky mountains friction or fiction abstract measurement of the levels of organic maturation below and within shear zones of thrust faults in the rocky mountains has revealed no general thermal metamorphism that can be attributed to faulting with the exception of very localized areas with few exceptions the vitrinite reflectance values obtained are in the range expected if the maximum level of organic maturation was produced as a result of increasing temperature during progressive burial accompanying sedimentation only at marias pass evidence has been found to suggest additional maturation as a result of post orogenic burial below the thrust sheets anomalously high vitrinite reflectances obtained from the lewis thrust mcconnell thrust coleman thrust and two unnamed thrusts are restricted to very narrow films immediatly adjacent to or within the shear zone which considering any reasonable thermal conductivity indicates elevated temperatures were very short lived the anomalously high vitrinite reflectances within these films when compared to laboratory heated coals suggest temperatures in the order of 350 650 c were locally generated during faulting such high temperatures are considered to have been generated during stick slip faulting at macro asperities or at ramps on the fault plane where local and possibly transient high frictional stresses existed the absence of evidence for extensive frictional heating supports previous arguments that stable sliding and or low frictional stress must exist during thrusting

possible mechanism of mud volcanism at the prism backstop contact in the western mediterranean ridge accretionary complex abstract the eastern mediterranean seafloor has numerous mud volcanoes most of which form a well defined belt within the mediterranean ridge medridge accretionary complex however mud volcano fields in the western medridge are less well known as those in the central and eastern medridge this study investigates material cycling and fluid migration within the western medridge we propose a possible ascent style of the ejecta forming the medee hakuho mud volcano mhmv in the western medridge by applying the vitrinite reflectance technique to ejecta samples first we model the 2 d thermal structure in the western medridge taking into account frictional heating on the plate interface to help estimate the source depth of the mhmv ejecta the result suggests an effective coefficient of friction of around 0 01 and a temperature of about 160 15 c along the plate interface at a distance of 180 km from the deformation front the location of the seaward toe of the aegean backstop second we evaluate the source depth of the mhmv ejecta using vitrinite reflectance in conjunction with the modeled thermal structure the results suggest that the ejecta matrix showing vitrinite reflectance values of 0 6 was subjected to a temperature of around 85 c corresponding to a depth of approximately 5 km below the seafloor kmbsf whereas older clasts of aptian or earlier age with vitrinite reflectance values of 0 6 1 0 are derived from much deeper depths most of the clasts are considered to have been lifted to the depth of 5 kmbsf as a result of underplating at the toe of a rigid backstop that had developed below mhmv after underthrusting related to plate subduction at that depth fluid pressures that are dramatically increased because of underplating promote the ascent of fluid rich sediments and entrain clasts along an existing fault in the accretionary wedge

low temperature oxidation in morb of titanomagnetite to titanomaghemite a gradual process with implications for marine magnetic anomaly amplitudes mid ocean ridge basalt morb samples varying in age from recent to jurassic were selected for electron microscopic and rock magnetic studies our observations indicate that the degree of oxidation of titanomagnetite in morb increases only gradually with sample age the titanomagnetite in recent morb 100 ka both electron microscopic observations and rock magnetic data support the notion that low temperature oxidation of titanomagnetite to titanomaghemite in morb is a gradual process moreover the rate of maghemitization is controlled by many factors on both macroscopic and microscopic scales including regional oceanic crustal structures lithological features grain size and surrounding matrices pillow lavas and the tops of massive flows tend to have higher degrees of oxidation than the interiors of massive flows owing to higher porosity and permeability of the former in contrast interstitial glass can protect fine titanomagnetite grains from alteration the natural remanent magnetization nrm intensity of morb varies as a function of age magnetic granulometry concentration of magnetic materials and the degree of alteration fine grained morb samples typically have higher nrm intensity the nrm intensity appears to decrease substantially with increasing degree of maghemitization and hence with age the envelope of the smoothed magnetic anomaly amplitudes resembles the change in nrm intensity for morb samples of the last 30 million years but the underlying assumption that the highest degree of maghemitization observed in the samples of a given age is entirely responsible for these intensity changes is not supported maghemitization of the micrometer sized and larger grains is probably only partly responsible whereas a significant contribution to nrm intensities is inferred from those submicrometer sized titanomagnetite grains that remained protected from oxidation by the surrounding matrix of interstitial glass

on the magnetostratigraphic age of nauru basin basalts of the western pacific ocean and timing of ontong java volcanism abstract cretaceous lava flows overlie jurassic to early cretaceous oceanic crust in the nauru basin of the western equatorial pacific but their exact age and origin is controversial in one model they are generically related to volcanism forming the ontong java plateau however paleomagnetic data from basalts recovered by ocean drilling in the nauru basin have been interpreted as recording numerous geomagnetic reversals suggesting the nauru basin basalts are older than the early aptian flows on the ontong java plateau and the correlative volcanism seen in the western equatorial and southwestern pacific ocean basin here we examine the magnetic fidelity of the nauru basin basalts through rock magnetic and paleomagnetic approaches we find the magnetic carriers in the lavas are unlike most basaltic units recovered by oceanic drilling in that they are magnetically soft this quality makes the rocks especially prone to the acquisition of secondary magnetic components induced during drilling we demonstrate that the reversed polarity intervals are illusory and instead record subtle changes in magnetic hardness that result in partial and complete overprinting by the magnetic field associated with the drill string e g the core barrel drill pipe and bit the recognition of these magnetic overprints the identification of only normal polarity in the nauru basin basalts and a critical consideration of the available radiometric and biostratigraphic age data lead us to conclude that coeval formation of the nauru basin basalts and ontong java plateau in aptian times remains a viable hypothesis

impact origin for the greater ontong java plateau abstract the 120 ma ontong java plateau and neighboring contemporaneous nauru east mariana and probably pigafetta basin flood basalts in the western equatorial pacific ocean comprise the earth s largest flood basalt province geophysical geochemical and geodynamic evidence from the province are difficult to reconcile with mantle plume models absence of an obvious hotspot source or track minor crustal uplift associated with emplacement minor total subsidence compared with normal oceanic crust or other oceanic plateaus and submarine ridges high degrees of melting at shallow upper mantle depths low water contents of basalts enrichment of platinum group elements in basalts and a 300 km deep seismically slow mantle root are more consistent with the consequences of an impacting bolide an object 20 km in diameter impacting relatively young 20 myr pacific lithosphere and penetrating into the uppermost asthenosphere would have initiated massive decompression melting in the upper mantle and may have resulted in emplacement of the greater ontong java plateau

regional coalification pattern of lower cretaceous coal bearing strata rocky mountain foothills and foreland canada implications for future exploration abstract the regional coalification pattern of lower cretaceous strata in parts of the canadian foothills belt and adjacent foreland has been determined by vitrinite reflectance measurements the present study focusses on two coal bearing sequences bluesky gething and gates formation both of which contain coal resources of economic interest the vitrinite reflectances r max in the bluesky gething formation range from 0 76 high volatile a bituminous to 2 55 semianthracite rank changes from top to the base of bluesky gething formation follow 1st order regression lines factors influencing the rate of increase of r max per depth interval coalification gradient include paleogeothermal gradients the rank level under investigation conductivities of host rocks and thicknesses of coal seams time depth burial curves for the lower cretaceous bluesky gething formation suggest that the regional coalification pattern for the top of the formation results largerly from variations in the depth and or duration of burial beneath maastrichtian tertiary foredeep deposits coalification largerly predates deformation the coalification pattern is more complicated for the base of the bluesky gething formation because thickness changes in the lower cretaceous bluesky gething interval locally have a greater effect on the rank than does the regional change in the thickness of maastrichtian tertiary sedimentary wedge detailed rank studies on laterally continuous coal seams of the gates formation showed that coalification levels were largerly established before folding and thrusting started isoreflectance lines of the beds run parallel to the bedding of the folded strata seams collected from various thrust sheets exposed at surface do not in general show significant changes in vitrinite reflectances from one thrust sheet to another many of the coals of the gates formation were found to have biaxial negative reflectance in dicatrices orientation of r max is in all cases parallel of subparallel to the mactroscopic fold axes indicating preferential orientation of the aromatic lamellae in the coals in the direction of minimum compressive stress it is suggested that the occurrence of biaxial negative coals is related to a tectonic stress field that existed during the later stages of burial and subsequent deformation

influence of igneous intrusions on thermal maturity and optical texture comparison between a bituminous marl and a coal seam of the same maturity abstract the impact of a 120 cm thick dike on dispersed organic matter in the triassic marry harbour mh bituminous marl in the raanes peninsula ellesmere island arctic canada was studied using reflected light microscopy and rock eval pyrolysis results were compared to a coal seam of similar maturity that was thermally altered by an igneous intrusion the mh bituminous marl is mature and within the oil window ro 0 94 whereas the coal is high volatile b bituminous rank ro 0 80 thermal alteration impacted differently the organic rich marl than the coal seam most of the heat generated by the intrusive emplacement in contact with coal is spent transforming coal to coke in the plastic layer zone similar to the process that coal undergoes in industrial coking operations in contrast the thermal alteration of sedimentary rocks occurs over longer distances as a result of the absence of a plastic layer zone the impact zone of the 120 cm thick igneous intrusion was greater in the mh bituminous marl which became thermally altered ro 2 34 at 190 cm from the contact with the dike on the contrary the coal became thermally altered ro 5 0 by a 240 cm alkali basalt intrusion twice the thickness of the mh dike and its impact zone was only 65 cm heat and hot volatile matter produced by the thermal decomposition of organic matter and minerals carbonate dehydration of clay minerals in contact with the igneous intrusion body is transferred through the sedimentary rock matrix by convection through fractures this transformation is evident by the occurrence of the pyrolytic carbon at various distances in the fractured mh marl from contact the hydrogen index hi shows a similar trend to that of the remaining source potential s2 both parameters decrease systematically toward the dike and go through a minimum at 20 cm from the dike contact as the indigenous organic matter is converted to hydrocarbons or devolatilized at the dike contact both s2 and hi have higher values these trends are similar to those of the volatile elements h and cl in the intruded coal seam the free hydrocarbons s1 showed a slightly different trend than s2 and hi it increased initially from 300 cm and reached a maximum at about 190 cm from the dike contact before decreasing continually and reaching a minimum at 20 cm from the contact at the dike contact the s1 increased slightly similar to the hi and s2 the presence of oil droplets trapped in carbonate concretions in combination with the highest value of oil expelled from the source rock based on s1 toc at distance of 190 cm from dike is an indication of the influence of contact metamorphism on oil generation locally furthermore it indicates that intrusion of igneous dikes into the bituminous mh marl resulted in an increase of organic matter maturation locally and in hydrocarbon generation

application of organic matter and clay mineral studies to the tectonic history of the abruzzo molise sannio area central appenines italy abstract the abruzzo molise sannio region is part of the central apennines foreland fold and thrust belt a structure that formed during the neogene as a result of the continental collision between the european and adria plates certain areas of this crust experienced anomalously high temperatures due to deep burial while others did not this burial has been investigated using optical indicators of organic matter om maturity and clay mineralogy the maximum depths of burial of tertiary surface sequences have been established based on the vitrinite reflectance ro and thermal alteration index tai of om dispersed in synorogenic sediments and from clay mineralogy of pre thrusting clayey deposits the synorogenic deposits show low levels of organic maturity having ro values less than 0 6 indicating early mature to mid mature hydrocarbon generation the pre thrusting deposits are shales characterised by a very high percentage of clay minerals with lesser amounts of quartz k feldspar plagioclase and calcite the dominant minerals are highly smectitic interstratified illite smectite ris both ro and i s ratios were used to calibrate burial and thermal evolution of this chain sector by numerical modelling the results indicate that the structural units which outcrop in the study area particularly the molise unit were never overthrust by significant thicknesses of rocks during mountain building at least before pliocene times the hypothesis that more internal units overthrust the presently exposed units also seems to be unlikely

optical properties of organic matter in relation to thermal gradients and structural deformation the general response of macerals to the coalification process the effectiveness of organic geochemical and petrological parameters as estimators of coalification and the applicability of different microscopical parameters in the assessment of rank are reviewed the central role of vitrinite reflectance as the most widely used estimator of coalification from brown coals to the low grade metamorphic zone is established on the basis of its relatively uniform variation with rank specificity ease and rapidity of measurement and cheapness factors influencing the optical properties ofvitrinites are considered temperature has the dominant influence in modifying optical properties with rank but time static pressure and stress can all have significant influences upon the course of optical properties depending upon particular geological conditions static pressure has a retarding effect on the coalification process but it is also responsible for creating increasing anisotropy within the condensing aromatic structures as rank rises hydrostatic pressures and pore pressures can contribute to the overpressuring of sediments thus affecting their thermal conductivities and consequently the rate of coalification stress is responsible for the development of biaxicity in the reflectance indicatrix fast and high levels of heating from igneous bodies cause textural effects on vitrinites as a result of carbonization that are quite different from those of coalification recognizing these different influences upon the optical properties of vitrinites examples are given of the use and application of vitrinite reflectance in the preparation of rank maps in the burial histories of basins in the timing of coalification in relation to orogenesis and igneous activity and in the zones of anchimetamorphism and low grade metamorphism consideration is also given to the problem of provincialism in correlations between chemical and physical parameters and to the future development of optical studies in organic petrology and their relation to organic geochemical investigations

mechanisms of coal metamorphism case studies from paleozoic coalfields controls on coal metamorphism can be complex in this paper we examine four paleozoic coalfields the western kentucky portion of the illinois basin the pennsylvania anthracite fields the south wales coalfield and the bowen basin an increase in temperature with depth of burial is certainly a factor in coal metamorphism in many coalfields however including the coalfields reviewed here it has become apparent that such a simple mechanism does not explain the coal rank patterns observed the flow of hydrothermal fluids through the coals has been proposed as a cause of coal metamorphism evidence includes inverted rank gradients elevated cfl as an indicator of brine fluids isotopic evidence for hydrothermal fluids and vein and cleat mineral assemblages in any case multiple hypotheses must often be evaluated in the examination of any coalfield since the simple paradigm of coal rank increases with a simple increase in temperature with increasing depth does not fit the evidence observed in many cases

determination of lattice parameter oxidation state and composition of individual titanomagnetite titanomaghemite grains by transmission electron microscopy a transmission electron microscopy tem method higher order laue zone holz diffraction has been applied to measurement of accurate lattice parameters of individual titanomagnetite and titanomaghemite grains lattice parameters and cation composition data are obtained with tem analytical electron microscopy aem for individual grains smaller than 0 1 m in diameter a suite of ocean drilling program deep sea drilling project ocean floor basalts containing titanomagnetite titanomaghemite with a wide range of oxidation degree z were employed to establish the relationship between lattice parameter a z and ti content x for naturally occurring samples standardization was accomplished with measurements on grains sufficiently large to allow the determination of absolute oxygen contents by electron microprobe analyses which directly yielded z values the probe data confirm that the maghemitization process in ocean floor basalts is one involving loss of iron and indicate a nearly linear relationship between lattice parameters and oxidation degrees for a given x value except for the smallest and largest values of z the standardized relation permits determination of z for individual submicrometer sized grains using only measured a values and cation compositions as determined by holz diffraction and aem

anisotropic fragments in strongly folded and faulted coals from the rocky mountain area of southeast british columbia the mammoth coal seam in southeastern british columbia canada was structurally thickened to 100 m as a result of laramide folding and faulting samples from the coal seam examined using reflected light microscopy include thermally altered coal macerals their by products e g pyrolytic carbon and in addition heat affected preoxidized coke the heat affected residues are composed of material formed by friction produced from faulting of the coal bearing strata the pyrolytic carbon was formed from the distillation of coal and from coal tar pitch the occurrence of preoxidized heat affected vitrinite suggests that the mammoth coal seam was oxidized before faulting

thermal histories and overthrusting application of numerical simulation technique abstract overthrust belts frequently contain potential exploration targets and an assessment of the effects of overthrusting on temperature histories and hydrocarbon hc generation can reduce exploration costs however many models oversimplify the problem for example by neglecting the physical and thermal characteristics of lithologies or by using instantaneous thrust sheet emplacement rates the adaptation of numerical simulation techniques to handle overthrusting in a two dimensional simulation enables the emplacement of a previously deposited and therefore physically and thermally well defined sedimentary sequence over a sequence or partial sequence of previously deposited units the combined effects of factors such as complex lateral and vertical lithological variations thrust sheet thicknesses movement rates compaction and forced fluid flow can be taken into account the method is demonstrated by its application to a schematic model the following variables are tested thrust sheet emplacement rates thermal conductivities and heat flow a thickness of 5 km is used in order to limit the total amount of variables the results show that simple one dimensional models can considerably overestimate temperature differences and effects across thrust sheet planes through time this can lead to incorrect conclusions on the establishment of a temperature equilibrium in the thrusted sequence and on hc generation timing

effects of frictional heating on the thermal hydrologic and mechanical response of a fault the mechanical response of a fault zone during an earthquake may be controlled by the diffusion of excess heat and fluid pressures generated by frictional heating in this study we formulate a fault model which incorporates the effects of frictional heating on the thermal hydrologic and mechanical response of a small patch of the failure surface this model is used to examine the parameters that control the fault response and to determine their critical range of values where thermal pressurization is significant the problem has two time scales a characteristic slip duration and a characteristic time for thermal pressurization the slip duration is set by the fault geometry the characteristic time for thermal pressurization is set by the slip rate the friction coefficient and the thermal and hydraulic characteristics of the medium the response of the fault depends on the relative magnitude of these two times results suggest that the fault width and hydraulic characteristics of the fault zone and adjacent medium are the primary parameters controlling the mechanical response for earthquakes occurring across zones of low porous medium compressibility 10 9 pa 1 and permeability 10 18 m2 the characteristic time for thermal pressurization is small in this case frictional heating can cause fluid pressures to approach lithostatic values the shear strength to approach zero and the temperature rise to stabilize at a maximum value dependent on the pore dilatational and transport properties of the porous medium whether the patch acts as a barrier to slip or exhibits substantial strain weakening is dependent on the shear strain across the fault moderate slip events where shear strains exceed two cause substantial strain weakening and consequently large stress drops accelerations and displacements thus it is possible for the patch to act as a barrier for small earthquakes but not for large ones both the dynamic stress drop and total displacement decrease for zones with larger compressibility permeability or width if the compressibility or permeability exceeds 10 8 pa 1 or 10 14 m2 or the shear strain is less than one then the effects of frictional heating may be negligible and the fault will exhibit no strain weakening characteristics consequently the patch acts as barrier that halts or resists further fault motion extrapolation of these results suggests that spatial variations in fault width and hydraulic characteristics will cause a heterogeneous stress drop and fault slip over the failure surface explaining many of the features of active faulting e g barriers nonuniform slip rupture stoppage random ground accelerations strong motions and frequency magnitude relations

isotopic evidence for the origin of the manihiki and ontong java oceanic plateaus abstract pb nd and sr isotopic results for lavas of the cretaceous ontong java and manihiki oceanic plateaus fall well within the modern day oceanic island or hotspot field the data provide no evidence of old continental basements but indicate a major involvement of kerguelen type or em i like mantle in the sources of both plateaus which appear to have probably been formed at least in part by hotspots however the presently active hotspots that pacific plate reconstructions suggest might have been possible plateau sources lack kerguelen type isotopic compositions either these hotspots did not participate in the formation of the two plateaus or if they did kerguelen type material must have been volumetrically much more important early in their existence two hypotheses for the origins of these plateaus which involve hotspot sources are consistent with the sparse available geochemical geochronological and geophysical data the first holds that the plateaus formed cataclysmically in association with surfacing plume heads the second posits a relatively steady but robust hotspot at or near a ridge crest and requires a much longer period of formation a near ridge origin appears to be indicated by evidence that most of the pacific plateaus were built largely on relatively young ocean crust however we suggest that a near ridge origin is also compatible with the plume head concept in that plume heads appear very likely to become associated with spreading axes through their influence on rift propagation which should be substantially greater than for ordinary hotspots in either case the lack of hotspot tracks seamount chains attached to the two plateaus would be a consequence of ridge migration or rift propagation in a near ridge setting

polar standstill of the mid cretaceous pacific plate and its geodynamic implications paleomagnetic data from the mid cretaceous mountains suggest that pacific plate motion during the early to mid cretaceous was slow less than 0 3 degree per year resembling the polar standstill observed in coeval rocks of eurasia and north america there is little evidence for a change in plate motion that could have precipitated the major volcanic episode of the early aptian that is marked by the formation of the ontong java plateau during the volcanism oceanic plates bordering the pacific plate moved rapidly large scale northward motion of the pacific plate began after volcanism ceased this pattern suggests that mantle plume volcanism exerted control on plate tectonics in the cretaceous pacific basin

onset of the mid cretaceous greenhouse in the barremian aptian igneous events and the biological sedimentary and geochemical responses basalts and biostratigraphy dated at 125 120 ma from the ontong java and manihiki plateaus in the western pacific evidence the largest volcanic event in earth history in at least the past 160 m y the intervening nova canton trough rifted at about 121 118 ma and a number of guyots and seamounts formed concurrently or slightly later geological events that probably were responses to these volcanic tectonic events occurred in the following chronostratigraphic order biotic fluctuations began at about 122 5 ma at about 122 0 ma 87sr 86sr began to decline slowly metal concentrations of co mn pb yb and cu in sediments peaked at about 121 5 121 2 ma changes in planktonic communities and sedimentation culminated in a nannoconid crisis just prior to 120 5 ma and in the selli black shale oae la at about 120 5 119 5 ma a sharp drop in 13c occurred at the beginning of the selli event and rebounded into a longer positive excursion that reached a peak after the selli event at about 119 5 118 5 ma at 120 5 ma 87sr 86sr declined rapidly and reached a minimum at about 116 113 ma we speculate that the intensity of these latter responses suggests a corresponding peak in volcanic tectonic activity at about 121 119 ma

timing of organic maturation coalification relative to thrust faulting in the southeastern canadian cordillera abstract in order to access the effects if any of overthrusting tectonic burial on levels of organic maturation coalification detailed vitrinite reflectance profiles were constructed for 11 deep boreholes that penetrated stacked thrust sheets of mesozoic and paleozoic strata in the southeastern canadian cordillera recognition of the timing and degree of maturation resulting from emplacement of thrust sheets is largely dependent on the accuracy with which the preorogenic level of maturation of the strata is known the vitrinite reflectance profiles of several boreholes suggest that a significant component of organic maturation coalification postdates emplacement of overthrust sheets and have resulted from tectonic burial for other boreholes however the maturation profiles are ambiguous and suggest that postorogenic maturation if any was insufficient to overprint preorogenic levels of maturity maturity levels and reflectance gradients of mesozoic strata in general are lower in the southern part of the southeastern cordillera than in the northern part which imply higher paleoheat flow in the north

paleo stress estimates on ancient seismogenic faults based on frictional heating of coal 1 faulted coals from eastern kentucky and montana usa and the south wales coalfield uk show fault related vitrinite reflectance anomalies interpreted as due to frictional heating during seismic slip the vitrinite reflectance anomalies are converted to temperature using kinetic based software easy r for post seismic cooling rates shear stresses are calculated using lachenbruch s 1986 piezometer which depends only on the area under the thermal anomaly and fault displacement for maximum displacements of 1 3 meters the minimum shear stresses are 13 64 mpa and overlap with seismological estimates of stress drops during modern earthquakes the calculated local mean normal stress is 100 mpa resulting in coefficients of friction of 0 1 0 6 thrust and 0 2 0 4 normal faults which are lower than laboratory based values

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

m sequence reversals recorded in dsdp sediment cores from the western mid pacific mountains and magellan rise new paleomagnetic and paleontologic data from pacific dsdp sites 463 and 167 define the magnetic reversals that predate the cretaceous normal polarity superchron k n data from mid pacific mountain site 463 provide the first definition of polarity chron m0 in the pacific deep sea sedimentary record foraminiferal biostratigraphy suggests that polarity chron m0 is contained entirely within the lower aptian hedbergella similis zone in agreement with foraminiferal data from the italian southern alps and atlantic ocean nannofossil assemblages also suggest an early aptian age for polarity chron m0 contrary to results from the italian umbrian apennines and southern alps which place polarity chron m0 on the barremian aptian boundary biostratigraphic dating discrepancies caused by the time transgressive preservational or provincial nature of paleontological species might be reconciled by the use of magnetostratigraphy specifically polarity chron m0 which lies close to the barremian aptian boundary at magellan rise site 167 five reversed polarity zones are recorded in hauterivian to aptian sediments correlation with m anomalies is complicated by synsedimentary and postsedimentary sliding about 25 m y after basement formation producing gaps in and duplications of the stratigraphic sequence the magnitude and timing of such sliding must be addressed when evaluating the stratigraphy of these oceanic rise environments

the association between tectonic deformation inorganic composition and coal rank in the bituminous coals from the south wales coalfield united kingdom analysis of vertical distribution of coal rank in three collieries and one opencast mine in the se of the south wales coalfield has revealed deviations from hilt s law in both proximate analyses and in vitrinite reflectance the variations in rank parameters studied are closely correlated with variations in the intensity of tectonic deformation measured using a numerical deformation index ndi three seams in the sequence were also analysed for major and trace element geochemistry and rock eval pyrolysis variations in these parameters are related to thrust inclusion of floor and or roof mudrocks into the seams a detailed conceptual model of a major thrust and associated in seam thrust detachments and lag faults is developed to explain the vertical rank profile by post coalification faulting it is concluded that although the model can explain the vertical pattern of rank the complexity of the required faults render the model improbable the alternative mechanisms for enhancement of the rank parameters associated with tectonic deformation including shear stress control frictional heating and localised fluid flow are discussed and are thought more likely to be responsible for the deviations from hilt s law in the vertical rank profile rank suppression shown by three seams two of which are overlain by marine bands is thought to be related to biochemical activity in the peat environment resulting from the influx of saline waters

deformation metamorphism of bituminous and anthracite coals from china abstract tectonic displacement of coal seams in china has resulted in faulting parallel to coal bedding displacement along these faults caused significant comminution of the coal on the footwall contributing to various mining problems the worst of which is catastrophic failure or outbursting of the working face during mining the granular texture and mostly unconsolidated nature of the coal suggests that faulting occurred relatively late in the coalification sequence at a time of maximum tectonic stress coal samples taken on either side of the fault plane normal and deformed coal layers were obtained in an effort to establish what influence these tectonic stresses might have had on coal properties as well as what they might reveal about the influence of tectonic pressure on organic maturity sample sets were collected within coal beds from undisturbed and adjacent deformed layers including 21 bituminous samples from the pingdingshan coal field and nine anthracite samples from the jiaozuo coal field the tieshenggou coal mine of the yuxi coal field in henan province the beijing xishan coal field the baijiao mine of the furong coal field in sichuang province and the baisha coal field in hunan province china results from vitrinite reflectance proximate and ultimate analyses show some differences in reflectance hydrogen content and nitrogen content of anthracite coal no significant difference was found between volatile matter yields of normal and deformed coal specimens gc measurements of the saturated hydrocarbon fraction of chloroform extracts from bituminous coals showed that lower molecular weight carbon fragments were concentrated in the deformed samples therefore although changes in the gross chemical properties of the deformed coal were insignificant some modification of the chemical structure is seen to have occurred as a result of exposure to tectonic pressure

paleomagnetic paleolatitude of early cretaceous ontong java plateau basalts implications for pacific apparent and true polar wander abstract we present paleomagnetic data from basaltic pillow and lava flows drilled at four ocean drilling program odp leg 192 sites through the early cretaceous 120 ma ontong java plateau ojp altogether 270 samples out of 331 yielded well defined characteristic remanent magnetization components all of which have negative inclinations i e normal polarity dividing data into inclination groups we obtain 5 7 14 and 15 independent inclination estimates for the four sites statistical analysis suggests that paleosecular variation has been sufficiently sampled and site mean inclinations therefore represent time averaged fields of particular importance is the finding that all four site mean inclinations are statistically indistinguishable strongly supporting indirect seismic observation from the flat lying sediments blanketing the ojp that the studied basalts have suffered little or no tectonic disturbance since their emplacement moreover the corresponding paleomagnetic paleolatitudes agree excellently with paleomagnetic data from a previous odp site site 807 drilled into the northern portion of the ojp two important conclusions can be drawn based on the presented dataset i the leg 192 combined mean inclination inc 41 4 n 41 k 66 0 95 2 6 is inconsistent with the early cretaceous part of the pacific apparent polar wander path indicating that previous paleomagnetic poles derived mainly from seamount magnetic anomaly modeling must be used with care ii the leg 192 paleomagnetic paleolatitude for the central ojp is 20 north of the paleogeographic location calculated from pacific hotspot tracks assuming the hotspots have remained fixed the difference between paleomagnetic and hotspot calculated paleolatitudes cannot be explained by true polar wander estimates derived from other lithospheric plates and our results are therefore consistent with and extend recent paleomagnetic studies of younger hotspot features in the northern pacific ocean that suggest late cretaceous to eocene motion of pacific hotspots

investigation of the records of earthquake slip in carbonaceous materials from the taiwan chelungpu fault by means of infrared and raman spectroscopies this research was supported by a grant in aid for young scientists a from the japan ministry of education science sports and culture 23684039 2013

optical parameters of maturity of organic matter dispersed in sediments first results from the central apennines italy levels of organic maturity of mesozoic and tertiary sequences outcropping in the central apennines have been established using vitrinite reflectance techniques the thermal alteration index and fluorescence colours of organic matter dispersed in sediments these results provide new constraints throughout the meso cenozoic evolution of this crustal sector in exploration geology vitrinite reflectance provides data on hydrocarbon maturation by constraining organic matter maturity in sedimentary basin modelling it is adopted to define the palaeothermal regime vitrinite reflectance ro also provides information on the burial history of sedimentary basins and may be employed to estimate tectonic uplift and erosion rates thermal alteration index tai and fluorescence colour values can be correlated with ro and may be used to estimate the degree of maturation when vitrinite is absent samples derived from the sabini and tiburtini mts in slope facies between the latium abruzzi carbonate platform and the umbria marche pelagic basin from the simbruini and ernici mts in carbonate platform facies and from upper miocene turbiditic deposits outcropping between the olevano antrodoco une towards the west and the marsica slope facies towards the east both the pre terrigenous meso cenozoic sequences show a low grade of organic maturity the sabini and tiburtini mts show ro values that are less than 0 4 and the simbruini ernici range show ro values that range between 0 5 and 0 65 field analysis indicates that the cause of these low maturity levels is that thick sequences of turbidites were never deposited during the neogene evolution of the apennine thrust belt moreover upper miocene turbiditic deposits also show low maturity levels with ro values that are less than 0 5 indicating that these deposits were never overthrusted by huge volumes of rocks during the chain building the slight increase in the maturity level recorded in the marsica area may be related to local heating along shear zones in areas of strike slip tectonics

thermal maturity of a fold thrust belt based on vitrinite reflectance analysis in the western foothills complex western taiwan abstract burial depth cumulative displacement and peak temperature of frictional heat of a fault system are estimated by thermal analysis in the fold thrust belt of the western foothills complex western taiwan based on the vitrinite reflectance technique the regional thermal structure across the complex reveals that the rocks were exposed to maximum temperatures ranging from 100 c to 180 c which corresponds to a burial depth of 3 7 6 7 km a large thermal difference of 90 c were observed at the shuilikeng fault which make the eastern boundary of the fold thrust belt where it is in contact with metamorphic rock of hsuehshan range the large thermal difference corresponds to cumulative displacements on the shuilikeng fault estimated to be in the range of 5 2 6 9 km however thermal differences in across the shuangtung and chelungpu faults cannot be determined apparently due to small vertical offsets the large displacement observed across the shuilikeng fault is absent at the other faults which are interpreted to be younger faults within the piggyback thrust system localized high temperatures adjacent to fault zones were observed in core samples penetrating the chelungpu fault three major fracture zones were observed at core lengths of 225 m 330 m and 405 m and the two lower zones which comprise dark gray narrow shear zones a value of vitrinite reflectance of 1 8 higher than the background value of 0 8 is limited at a narrow shear zone of 1 cm thickness at the fracture zone at 330 m the estimated peak temperature in the range of 550 680 c in the shear zone is far higher than the background temperature of 130 c and it is interpreted as due to frictional heating during seismic faulting

thickness of the seismic slip zone this article reviews geologic and other evidence constraining the thickness of the principal slip zone psz that accommodates the bulk of coseismic shear displacement during an individual rupture event surface deformation from rupturing may occupy swaths tens of meters or more in width but trenches across active faults generally reveal that incremental slip is accommodated by a psz that is tens of centimeters or less in thickness geomorphic evidence coupled with the observations from trenching suggest a psz may stay well localized for distances of several kilometers through many rupture episodes mine exposures and exhumed fault zones demonstrate that pszs separating different lithologies within the fault core although contained within damage zones of variably fractured rock ranging up to hundreds of meters in thickness often comprise just a few centimeters of gouge ultracataclasite that have accommodated large finite displacements 1 km microstructural studies demonstrate incremental slip localized still further down to 1 10 mm as do other fault rock assemblages slickensides and slickenfibers fault veins of pseudotachylyte friction melt intravein septa in hydrothermal fault infills the accumulated evidence indicates that localization of coseismic shearing to less than 10 cm on planar faults is widespread throughout the crustal seismogenic zone with extreme localization to less than 1 cm not uncommon however some distributed coseismic shear may also develop especially at rupture irregularities coseismic reduction of shear resistance from friction melting t 1000 c or from transient thermal pressurization of aqueous fluids t 100 c requires slip during moderate to large earthquakes u 1 m to be restricted to narrow zones respectively a few centimeters or tens of centimeters in thickness given the evidence for slip localization the apparent scarcity of pseudotachylyte suggests either that seismic friction melting is a rare phenomenon or that pseudotachylyte is only rarely preserved in recognizable form within mature hydrated fault zones

metamorphic evolution of a very low to low grade metamorphic core complex danubian window in the south carpathians the danubian window characterized by diagenetic to low greenschist facies conditions at a high thermal gradient is evidently of great interest for methodological studies because high metamorphic thermal gradient conditions during low grade metamorphism have received little attention so far the general increase in metamorphic grade from sw to ne in the danubian window is indicated by mineral parageneses studies as well as by illite kubler index ki measurements and organic matter reflectance omr for the first time this study distinguishes between metamorphic conditions related to jurassic ocean floor cretaceous nappe stacking post collisional accommodation and syn kinematic getic detachment metamorphism and cooling after oligocene exhumation the occurrence of the prehnite pumpellyite facies in the severin cosustea units in the southeastern area is the result of cretaceous metamorphism remnants of ocean floor metamorphism prevailed the highest pressure is constrained by the upper stability limit of prehnite to be at around 4 0 kbar the danubian units situated within the diagenetic zone were not below 200 8c due to epidote formation the ki omr and mineral data indicate diagenetic conditions assuming temperatures between 200 and 250 8c pressures between 1 8 and 2 6 kbar were calculated using kinetic and numerical maturity models orogenic collisional cretaceous peak pressure conditions of 4 0 1 0 kbar are found in the danubian nappes not altered by a subsequent syn detachment metamorphic overprint highest temperatures in chloritoid schists and epidote hornblende bearing mylonites have been inferred for samples from the northern border of the danubian window between 300 and 400 8c along a synto post detachment retrograde pressure path post dating the chloritoid formation the occurrence of clinozoisite chlorite quartz suggests temperatures 300 8c in the northwest while the association andalusite quartz and biotite muscovite indicates temperatures between 370 and 400 8c at 3 5 kbar in the northeast it is demonstrated that the slope of the regression lines between ki and omr data gives valuable qualitative information about the relative magnitudes of p and t the slope of the regression line for the danubian window samples indicates normal heat flow conditions during nappe stacking and hyperthermal conditions during the formation of the getic detachment high thermal gradient conditions can easily be explained by partly isothermal decompression during the getic detachment event the elevation of the geotherm being caused by crustal thinning and rapid exhumation of the danubian units probably also a higher heat flux prevailed at the end of the getic detachment at a time when the retrograde chloritoid decomposition reactions took place documenting late stage ht greenschist facies metamorphism from siegesmund s fugenschuh b froitzheim n eds tectonic aspects of the alpine dinaridecarpathian system geological society london special publications 298 281 315 doi 10 1144 sp298 14 0305 8719 08 15 00 the geological society of london 2008 location of the study area and

on the compositional field of self reversing titanomaghemite constraints from deep sea drilling project site 307 1 in 1956 verhoogen proposed that ionic reordering during low temperature oxidation of titanomagnetite could result in self reversal of natural remanent magnetization later in 1966 o reilly and banerjee concluded that 1 the compositional field of self reversing titanomaghemite was restricted to very high oxidation states and 2 that high oxidation temperature 250 c would be required to reach these oxidation levels which would in turn be inconsistent with stability of the cation deficient structure of titanomaghemite in nature however an example of the process has been reported in some altered pillow basalt lavas of late cretaceous age from detroit seamount ocean drilling program odp sites 883 1203 and 1204 in the northwestern pacific ocean here we present new paleomagnetic rock magnetic and compositional data from mid ocean ridge tholeiitic basalts of late jurassic age collected at deep sea drilling project dsdp site 307 although severely oxidized the dsdp site 307 basalt samples lack the clear self reversed magnetizations seen in some samples from detroit seamount these data constrain the compositional field of self reversing titanomaghemite to extremely high oxidation states z 0 95 consistent with the first conclusion of o reilly and banerjee the comparison of results from odp sites 883 1203 and 1204 on detroit seamount and those from the dsdp site 307 basalts suggests that the presence of self reversed magnetizations may signify unusually vigorous and sustained fluid flow that resulted in very efficient removal of fe from titanomaghemite producing the extremely high oxidation states required for self reversal

contrasts in thermal maturity within terranes and across terrane boundaries of the franciscan complex northern california the franciscan subduction complex of northern california includes several tectonostratigraphic units we have used the technique of vitrinite reflectance to document levels of thermal maturity for the central belt and the yager coastal and king range terranes spatial variations in thermal maturity help define the thermal structure of each franciscan terrane and each terrane displays a different geometry of thermal structure these differences are controlled by the style of structural deformation the overprinting effects of deformation following metamorphism and thermal overprinting caused by hydrothermal circulation anomalies along and contrasts across terrane boundaries help establish the relative timing and the structural mechanisms of terrane amalgamation for example localized anomalies are evident along the eel river fault central yager boundary and these increases in thermal maturity may be due to shear heating hydrothermal discharge or conductive heat transfer across the fault cross c

basalt core paleomagnetic data from ocean drilling program site 883 on detroit seamount northern emperor seamount chain and implications for the paleolatitude of the hawaiian hotspot abstract paleomagnetic data were measured from basaltic flows cored by the ocean drilling program odp at site 883 on the summit of detroit seamount located in the northernmost emperor seamounts these data are important because they reflect the paleolatitude of hawaiian volcanism for the late cretaceous and bear upon geodynamic models of hotspot drift a total of 143 samples were measured from cores acquired at two holes 20 30 m apart most samples gave apparently reliable magnetic directions that were analyzed in a tiered fashion to compute a composite inclination vs depth curve one hole gave 13 distinct inclination groups the other 10 and the two were combined into nine groups thought to represent independent measurements of paleofield direction these data indicate normal magnetic polarity and give a mean inclination of 61 5 10 6 6 4 and paleolatitude of 42 8 13 2 7 6 95 confidence limits this paleolatitude is 6 2 higher than results from another odp site 884 drilled on the lower flank of the same seamount the difference is thought to result partly from an age difference 1 3 myr and partly from incomplete averaging of paleosecular variation at both drill sites together the data from the two sites reinforce the conclusion that the northern emperor seamounts were formed far north of the present day hotspot latitude 19 5 n and suggest prior estimates of the amount and rate of southward drift may have been low this analysis also illustrates uncertainties in determining paleolatitude from a small number of lava flow units from a single drill site

the role of veining and dissolution in the evolution of fine grained mylonites the mcconnell thrust alberta microstructural observations of the mcconnell thrust fault rocks demonstrate the importance of vein formation and calcite dissolution in the evolution of the mcconnell thrust limestone mylonites the protolith to the mylonite is a micritic limestone the mylonite contains numerous discontinuous bedding parallel calcite veins that range from relatively undeformed except for twinning and undulose extinction to highly sheared the highly sheared veins show evidence for dynamic recrystallization and grain size reduction along grain and twin boundaries that can lead to complete recrystallization to a grain size of approximately 1 3 m the bulk of the calcite matrix within the mcconnell thrust mylonite is interpreted to have formed by dynamical recrystallization of veins the emplacement of relatively coarse grained veins promoted the activation of dislocation creep within the fault rocks of the thrust in the absence of the increase in grain size afforded by vein emplacement it is anticipated that the fine grained protolith would have deformed predominantly by solution transfer with grain boundary sliding and localized brittle shearing the layer parallel calcite veins are found in close proximity to sheared clay seams which are interpreted to represent the insoluble residue left behind after dissolution of calcite these clay seams may have contributed to the build up of high pore fluid pressures which if intermittently reaching lithostatic conditions during displacement would result in transient brittle failure and thrust surface parallel vein emplacement in an otherwise ductilely deforming rock

incrementally developed slickenfibers geological record of repeating low stress drop seismic events an accretionary melange of triassic age ocean floor sediments exposed in the chrystalls beach complex south island new zealand comprises competent sandstone and chert phacoids set in a cleaved mudstone matrix deformed in a continuous discontinuous style at subgreenschist conditions deformation structures include a pervasive anastomosing fault fracture mesh of multiple shearing surfaces subparallel to cleavage coated with incrementally developed quartz calcite slickenfibers microstructural observations reveal slickenfiber growth by crack seal shear slip increments of 10 100 m with incremental slip transfer of the same order accommodated by opening of extension fractures that link en echelon slip surfaces individual slip surfaces can be traced for meters to tens of meters so that the ratio of average slip u to potential rupture length l predominantly lies within the range 10 6 u l 10 5 characteristic of microearthquakes obeying constant stress drop scaling with a low stress drop 30 kpa typical of low frequency earthquakes the host rock assemblage metamorphic environment inference of near lithostatic fluid overpressures low stress drop and mixed continuous discontinuous shearing resemble conditions and characteristics of low frequency earthquakes as identified within the seismic signals recorded during episodic tremor and slow slip events at the downdip end of the seismogenic subduction thrust interface and within accretionary prisms

recent advances in coalification studies and their application to geology abstract recent advances in coalification studies since 1970 are reported concerning microscopic methods causes of coalification the coalification process as such and application to geology the degree of coalification rank is mostly determined on the basis of vitrinite reflectance measured on finely dispersed material in rocks for rocks bare of vitrinite other microscopic methods are used such as fluorescence properties of liptinites and graptolite reflectance under incident light or coloration of microfossils like palynomorphs and conodonts in transmitted light the validity of the various methods is discussed maximum rock temperature and its duration are the main causes of chemical coalification reactions heating rates during subsidence influence the attainment of rank equilibrium contact metamorphic coals and natural cokes formed from bituminous coals are characterized by a relatively high reflectance and anisotropy strong frictional heat may cause local increase of rank adjacent to thrust planes graphitization is thermodynamically not possible in nature without pressure and shearing confining pressure retards the chemical coalification reactions tectonic stress especially shearing promotes the increase of maximum reflectance and of anisotropy it commonly leads to bi axial optical properties instead of the more typical uni axial negative geometry of vitrinite in undisturbed coal seams bi axial optical properties are common for vitrinite inclusions in clastic rocks on the basis of combined fluorescence microscopical and geochemical studies bituminization has been recognized as the characteristic part of coalification in the range between sub bituminous and bituminous coal it is characterized by the generation of petroleum like substances which enable the coal to soften and to agglomerate during carbonization hydrogenation properties are favoured by the bituminization process the different liptinite macerals behave differently during coalification and pass coalification jumps at different rank stages a considerable part of total inertinites is formed during early coalification brown coal to sub bituminous coal stage as rank inertinite this new knowledge appears to become important in relation to hydrocarbon exploration diagenetic methane some examples for the application of coalification studies to geology refer to vitrinite reflectance as an indicator of rock diagenesis and metamorphism palaeogeographical and structural history palaeogeothermics and hydrocarbon exploration large scale areal coalification studies in foredeeps and backdeeps of ancient and recent orogens suggest estimations of crustal thicknesses and relations to plate tectonics

petrography and metamorphism of the lower gondwana permian coal of rangit valley eastern himalays india abstract a triangular outlier of coal bearing lower gondwana rocks comprises a tectonic window within the precambrian metamorphic terrain of the rangit valley in the eastern himalays of india due to a series of tectonic events which took place during the mesozoic and tertiary the succession has become reversed and the coal has undergone severe physical chemical microstructural and optical changes studies reveal that 1 the rank of the coal prior to tectonism was low 2 the coal underwent oxidation in the peat forming stage and during subsequent orogenic stages but effect of oxidation on the properties of coal was insignificant 3 the coal reached its present abnormally high rank mainly due to heating under tectonic pressure and 4 the heat which was generated due to tectonic pressure affected all the coal seams of this belt