uncertainties in the relative positions of the australia antarctica lord howe and pacific plates since the late cretaceous we determined parameters that describe finite rotations and their uncertainty regions for relative plate motion at the spreading centers between the pacific and antarctica plates between australia and antarctica and between the lord howe rise and australia we combined these to yield a range of possible finite rotations describing the relative positions of the pacific australia antarctica and lord howe plates since the late cretaceous if the pacific australia plate boundary has had its present trend since anomaly 18 time reconstructions show 330 110 km of motion of the pacific plate relative to the lord howe rise since anomaly 5 time 9 8 m y 420 110 km since anomaly 6 time 19 5 m y 770 330 km since anomaly 13 time 35 6 m y and 820 260 km since anomaly 18 time 43 0 m y we examined two cases for times prior to anomaly 18 assuming a late cretaceous age of australia antarctica separation if a plate boundary existed between the lord howe rise and pacific plates since the late cretaceous with no plate boundary in antarctica reconstructions with the lord howe rise fixed predict 610 200 km of westward motion of the pacific plate between the times of anomalies 31 and 22 followed by 260 100 km of northward motion between the times of anomalies 22 and 18 if the lord howe rise was fixed to the pacific plate until the eocene but a plate boundary existed between east and west antarctica reconstructions show very little motion across this boundary between the times of anomalies 31 and 22 followed by convergence between the times of anomalies 22 and 18 this second case also brings 70 80 m y paleomagnetic poles from the pacific and east antarctica plates into better agreement than the first case but large uncertainties in the reconstructions do not allow the first case to be conclusively eliminated

strain partitioning in the transition area between oblique subduction and continental collision hikurangi margin new zealand spatial differences in late quaternary structural style and deformation rates indicate a complex pattern of strain partitioning within the transition area from oblique subduction beneath southern north island to oblique continental collision in northern south island new zealand the late quaternary structure of the offshore southern hikurangi margin is determined here using seismic reflection profiles mr1 side scan sonar swath images em12dual multibeam swath bathymetry and backscatter images and sediment core and dredge samples where oblique 50 subduction of the oceanic hikurangi plateau is occurring beneath southern wairarapa region the steep dissected upper margin consists of a wedge of rocks that are being deformed by strike slip and reverse faults beneath the lower margin an accretionary wedge of quaternary age has developed rapidly by frontal accretion of a thick succession of turbidites on the pacific plate estimates of late quaternary geological strain rates have been made on two margin perpendicular transects across southern north island and the offshore margin to budget the predicted nuvel 1a plate motion more than 33 55 of the total plate motion is expressed in the offshore part of the upper plate above the subduction detachment in the central hikurangi margin between 40 s and 41 s this offshore deformation could potentially include margin parallel fault slip of up to 14 15 mm yr across the upper plate strain is partitioned into zones of folding and thrust faulting and possibly more than one zone of strike slip faulting but the partitioning may be incomplete with oblique slip thrusting an important component of the deformation the wide distribution of deformation within the upper plate partially reflects strong coupling between the subducting oceanic plateau and the leading edge of the overriding plate this coupling increases toward the southwest where the continental part of the subduction zone beneath marlborough may now be inactive or very strongly coupled toward the southwest the transpressive deformation style of the upper wairarapa margin continues into the upper marlborough margin and onshore into the strike slip marlborough fault system of northern south island in contrast the accretionary wedge narrows to the southwest and terminates in southeastern cook strait approximately above the transition from subducted oceanic crust to subducted continental crust of the pacific plate farther southwest beneath the lower marlborough margin low strain folding and thrust faulting is occurring but the style of deformation is not typical of the accretionary wedge this shortening results either from a small amount of subduction slip beneath marlborough and or from contractional strain partitioned to the southeast of the continental transpression zone whereas the initial onset of continental collision occurs in marlborough the surface expression of deformation of the pacific plate occurs south of 42 30 s normal faulting of the northwestern margin of the continental chatham rise possibly reflects flexural extension of the pacific plate crust at the southern end of the subduction zone whereas folding and thrust faulting of the north canterbury coastal region results from nw se contraction of the delaminated upper crust entering the southern alps collision zone

tectonic setting of synorogenic gold deposits of the pacific rim abstract more than 420 million oz of gold were concentrated in circum pacific synorogenic quartz lodes mainly during two periods of continental growth one along the gondwanan margin in the palaeozoic and the other in the northern pacific basin between 170 and 50 ma these ores have many features in common and can be grouped into a single type of lode gold deposit widespread throughout clastic sedimentary rock dominant terranes the auriferous veins contain only a few percent sulphide minerals have gold silver ratios typically greater than 1 1 show a distinct association with medium grade metamorphic rocks and may be associated with large scale fault zones ore fluids are consistently of low salinity and are co2 rich in the early and middle palaeozoic in the southern pacific basin a single immense turbidite sequence was added to the eastern margin of gondwanaland deformation of these rocks in southeastern australia was accompanied by deposition of at least 80 million oz of gold in the victorian sector of the lachlan fold belt mainly during the middle and late devonian lesser devonian gold accumulations characterized the more northerly parts of the gondwanan margin within the hodgkinson broken river and thomson fold belts additional lodes were emplaced in this flyschoid sequence in devonian or earlier palaeozoic times in what is now the buller terrane westland new zealand minor post devonian growth of gondwanaland included terrane collision and formation of gold bearing veins in the permian in australia s new england fold belt and in the jurassic early cretaceous in new zealand s otago schists collision and accretion of dozens of terranes for a 100 m y long period against the western margin of north america and eastern margin of eurasia led to widespread latest jurassic to eocene gold veining in the northern pacific basin in the former location late jurassic and early cretaceous veins and related placer deposits along the western margin of the sierra nevada batholith have yielded more than 100 million oz of gold additional significant ore forming events during the development of north america s cordilleran orogen included those in the klamath mountains region california in the late jurassic and early cretaceous the klondike district yukon by the early cretaceous the nome and fairbanks districts alaska and the bridge river district british columbia in the middle cretaceous and the juneau gold belt alaska in the eocene gold bearing veins deposited during the late jurassic and early cretaceous terrane collision that formed the present day russian far east have been the source for more than 130 million oz of placer gold the abundance of gold bearing quartz carbonate veins throughout the gondwanan north american and eurasian continental margins suggests the migration and concentration of large fluid volumes during continental growth such volumes could be released during orogenic heating of hydrous silicate mineral phases within accreted marine strata the common temporal association between gold veining and magmatism around the pacific rim reflects these thermal episodes melting of the lower thickened crust during arc formation slab rollback and extensional tectonism and subduction of a slab window beneath the seaward part of the forearc region can all provide the required heat for initiation of the ore forming processes

thermochronology of the south cyclades shear zone ios greece effects of ductile shear in the argon partial retention zone micas and potassium feldspars from the south cyclades shear zone ios cyclades greece yield varied and complex 40ar 39ar apparent age spectra a correlation exists between 40ar 39ar apparent ages and the relative timing of different episodes of recrystallization and grain growth as indicated by fabric and microstructural analysis the 40ar 39ar apparent age spectra record the effects of variation in the degree of recrystallization and grain growth and partial to complete resetting of argon systematics in potassium bearing minerals during hercynian m0 alpine m1 and late oligocene early miocene m2 metamorphism deformation was strongly partitioned within the shear zone and this led to localized recrystallization and heterogeneous resetting of argon systematics within preexisting minerals modeling suggests the oligo miocene thermal events were of insufficient magnitude and or duration to completely reset the isotopic systematics in these samples our data lead to the concept of the argon partial retention and resetting zone prz defined as that portion of the crust where temperatures are insufficient to completely reset argon systematics within preexisting potassium bearing minerals within the prz some radiogenic argon in preexisting potassium bearing minerals will be outgassed and only partially retained tectonic exhumation of the prz involves movement on crustal scale ductile shear zones accompanied by strongly partitioned deformation and localized recrystallization recrystallization leads to resetting of argon systematics and thus will result in heterogeneous 40ar 39ar age distributions within these ductile shear zones e g in the south cyclades shear zone

discharge of debris from ice at the margin of the greenland ice sheet sediment production at a terrestrial section of the ice sheet margin in west greenland is dominated by debris released through the basal ice layer the debris flux through the basal ice at the margin is estimated to be 12 45 m 3 m 1 a 1 this is three orders of magnitude higher than that previously reported for east antarctica an order of magnitude higher than sites reported from in norway iceland and switzerland but an order of magnitude lower than values previously reported from tidewater glaciers in alaska and other high rate environments such as surging glaciers at our site only negligible amounts of debris are released through englacial supraglacial or subglacial sediment transfer glaciofluvial sediment production is highly localized and long sections of the ice sheet margin receive no sediment from glaciofluvial sources these findings differ from those of studies at more temperate glacial settings where glaciofluvial routes are dominant and basal ice contributes only a minor percentage of the debris released at the margin these data on debris flux through the terrestrial margin of an outlet glacier contribute to our limited knowledge of debris production from the greenland ice sheet

rethinking conditions necessary for pseudotachylyte formation observations from the otago schists south island new zealand abstract pseudotachylytes and two distinct types of cataclasite in the otago schist at tucker hill south island new zealand provide evidence for both seismic slip and aseismic creep on a normal fault zone during regional crustal extension in late cretaceous time regional geologic evidence suggests that the fault had its present low angle dip ca 10 at the time it was active type a cataclasites presumably aseismic can be recognized by bi fractal grain size distributions monomict composition angular clasts of uniform textural maturity and a crude fabric defined by oriented grains and transgranular fractures type b cataclasites possibly cosesimic have characteristics consistent with fluidized grain flow including heterogeneous clast shapes and types a bimodal grain size distribution intrusive relationships with other rocks and the absence of any fabric or transecting fractures pseudotachylyte which occurs as fault veins injection veins and more complex types of intrusive structures consistently cuts across and invades type a cataclasites but is both intrusive into and included as clasts in type b cataclasites these relationships are consistent with a fault evolution model in which the development of a damage zone through aseismic cataclasis type a facilitates the formation of pseudotachylyte in a subsequent seismic event by providing a permeable matrix through which fluids can drain in the early stages of slip thereby maintaining frictional contact between rock surfaces the formation of pseudotachylyte in turn may seal the fault zone and lead to thermal pressurization in a later seismic cycle forming fluidized type b cataclasites seismic slip on the low angle normal fault zone at tucker hill may have occurred by two distinct modes of dynamic weakening melt lubrication and thermal pressurization in successive seismic events although there is a perception among geologists that pseudotachylyte is most likely to form in intact crystalline rocks geophysical models of fault zones clearly demonstrate that pseudotachylyte formation is actually suppressed in low permeability rock because any fluids present would be unable to escape the fault zone and thermal pressurization would rapidly reduce frictional resistance the paradigmatic occurrences of pseudotachylyte in otherwise pristine crystalline rocks probably represent somewhat exceptional circumstances single rupture events at very high effective stress in dry rock coseismic frictional melts may actually be more common in hydrated rocks like the schist at tucker hill but harder to recognize and also vulnerable to overprinting as a fault zone matures in such rocks pseudotachylyte may represent an intermediate stage in the evolution of a fault zone the period between the formation of a high permeability damage zone and the development of a low permeability fault core

fission track analysis reveals character of collisional tectonics in new zealand during the late cenozoic the pacific plate has been obliquely converging with the australia plate in south island new zealand this has resulted in westward obduction of continental crust of the pacific plate and consequently a major mountain range the southern alps has formed east of the alpine fault and within the leading edge of the pacific plate we have applied the apatite and zircon fission track dating technique to a suite of outcrop samples from three transects across the southern alps starting at the alpine fault to better understand the uplift age and structure of the continental collision the results show the following 1 uplift was underway at 7 ma in the south at haast pass and by 5 ma in the north at arthur s pass 2 profiles of the total amount of late cenozoic uplift show an exponential increase toward the alpine fault adjacent to the alpine fault there has been 14 5 to 21 5 km of uplift in the vicinity of haast pass 14 5 to 21 km near mt cook and 12 5 to 15 5 km in the arthur s pass transect adjacent to the alpine fault in the mount cook region the average uplift rate from 5 5 ma to 1 ma was 2 3 to 2 5 mm yr between 1 ma and the present it has averaged 6 2 mm yr the strongly asymmetric uplift pattern is responsible for the exposure of a 13 25 km wide belt of greenschist to midamphibolite facies rocks immediately east of the alpine fault known as the alpine schists 3 late cenozoic uplift of torlesse greywackes and alpine schists was preceeded during the jurassic early cretaceous by 5 8 km of uplift the otago schist belt to the south was uplifted much more during this interval and in addition western parts of the otago schists were uplifted 5 6 km during the late cretaceous 4 the fission track data do not support the notion of significant late cenozoic shear heating about the alpine fault as previously suggested from spatial variations in k ar ages of the otago and alpine schists

rheology of ice at the bed of engabreen norway a three dimensional finite element model is used to analyze field data collected as dirty basal ice flowed past an instrumented obstacle at the bed of engabreen a temperate glacier in northern norway the ice is modeled as an incompressible power law fluid with viscosity b 2 1 n 2n d where d is the second invariant of the stretching tensor and b and n are two parameters using measurements obtained in 1996 and 1997 two values of b are obtained one using the measured normal stress difference across the obstacle and the other using the measured bed parallel force over the instrument these two values are not equal probably owing to small frictional forces at the bed unaccounted for in the numerical model hence b ranges between 1 9 10 7 and 3 2 10 7 pa s 1 3 in 1996 and between 2 2 10 7 and 4 1 10 7 pa s 1 3 in 1997 these values are smaller than measured elsewhere for clean glacier or laboratory ice field measurements of water content fabric and texture of the basal ice suggest that unbound water between thin sediment layers and lamellae of clean ice may act as a lubricant and significantly weaken the ice near isotropic fabrics indicate that preferred fabric orientation does not enhance the deformation

cooling and uplift patterns in the lepontine alps south central switzerland and an age of vertical movement on the insubric fault line 96 new fission track ft apatite and zircon k ar and rb sr biotite and muscovite ages are presented for 19 samples mainly acid gneisses from a 40 km traverse through the lepontine alps in the maggia valley south central switzerland plotting measured mineral ages against assumed system closure temperatures yields cooling rates for each sample the entire profile shows a fairly uniform late neogene recent mean uplift rate of 0 5 mm a confirmed by a gradient of ft apatite age with elevation cooling from higher temperatures occurred earlier in the south where uplift rates of 2 2 mm a in the steep belt root zone indicate 9 km early miocene uplift of the northern pennine block this uplift started before 23 ma and is interpreted as resulting from a major phase of backthrusting along the insubric line and as dating the formation of the mylonite belt estimated cooling rates constrain the timing of lepontine mid tertiary metamorphism 3 schematic models are proposed which also consider published rb sr k ar mica and hornblende and u pb monazite ages slow cooling differential initial heating and subsequent cooling of different parts of the central alps and post 38 ma cooling with syntectonic metamorphism at 27 ma are postulated as alternative interpretations of isotopic data and geologic evidence from extrapolation between k ar and rb sr mica ages and apatite ft ages 240 50 c is proposed as the closure temperature for the retention of fission tracks in zircon

slab derived fluids and quartz vein formation in an accretionary prism otago schist new zealand regional quartz vein formation and the fluxes flow paths and sources of metamorphic fluids were investigated in the mesozoic accretionary prism of new zealand by using a new chemical mass balance analysis of outcrops samples were collected at meter or submeter intervals along outcrop length traverses and combined to obtain average chemical compositions of whole outcrops mass balance analysis used zr as an immobile reference frame and as a monitor of sedimentary sorting processes sio2 zr systematics produced by sedimentary processes differ greatly from those caused by metasomatic mass transfer of silica allowing evaluation of vein formation mechanisms relatively undeformed metasedimentary outcrops of low metamorphic grade mostly prehnite pumpellyite facies are nearly unveined and characterized by sedimentary compositional trends more deformed outcrops of higher metamorphic grade mostly greenschist facies contain 10 30 vol quartz veins these outcrops underwent mass addition of externally derived silica into quartz veins accompanied by addition of na and removal of k and w average silica additions suggest a time integrated fluid flux of 104 105 batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document m 3 fluid end document batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document m 2 rock end document for fluids ascending through the prism dehydration of spilitized oceanic crust subducting beneath the prism is the most probable source for this large fluid flux and could also have caused the na k metasomatism the w removed from deep levels of the prism may have been deposited in focused retrograde au w quartz veins at shallow levels by ascending fluids transfer of sio2 from subducting slabs into accretionary prisms is a plausible mechanism for long term bulk silica enrichment of the continents beyond that possible by magmatic differentiation

fission track lengths in the apatite annealing zone and the interpretation of mixed ages abstract measurements of confined fission tracks in apatites from deep boreholes show that their mean length is reduced and the length distribution becomes progressively broader through the fission track annealing zone at subsurface temperatures of around 100 c and above the length distribution characteristically becomes very broad without a pronounced peak the lengths of the longest tracks remain essentially constant at all stages of natural annealing observed in the boreholes this pattern is similar to that found in laboratory annealing of spontaneous fission tracks in apatite from an outcrop sample of the same formation these observations show that confined track lengths can be used as important indicators of the type of thermal history that a sample has experienced in the temperature zone of increasing track stability the length distributions reported here provide a basis for interpretation of fission track ages that might otherwise be ambiguous an apatite age which results from a uniform slow cooling history will have a broad negatively skewed length distribution while a bimodal distribution provides clear evidence of a two stage history involving partial annealing by a discrete thermal event the apparent fission track age associated with a bimodal length distribution will be a mixed age intermediate between the original age and that of the later event

deformation processes in an accretionary prism a study from the torlesse terrane of new zealand abstract the style of deformation observed in rocks of the torlesse pahau terrane exposed in the aorangi range of the north island records accretion of thick trench fill by offscraping at the toe of a growing accretionary prism during the early cretaceous the relatively coherent nature of the aorangi range rocks enables detailed study of the deformation processes produced by offscraping and subsequently within the prism and many of the structures observed in these rocks are consistent with those described from both modern accreting margins and other ancient accretionary terranes overprinting relationships indicate three phases of folding and multiple faulting events early deformation involved large scale sheath like folding oblique to the overall trend of the margin and development of an anastomosing axial planar cleavage folding of the sediments promoted dewatering the subsequent disruption of strata by shearing parallel to bedding and low angle to bedding faulting records the transition to more brittle responses to the deformation the most widespread folding phase d 2 produced numerous upright typically isoclinal folds with local development of an axial planar s 2 cleavage in macroscopic and some mesascopic fold hinges the variable plunge of the fold axes to the nne and ssw within the axial surface indicates progressive rotation of the fold axes after formation mesozoic strike slip faulting most likely produced the open e w trending folds and warps of the third folding phase d 3 in bedding already rotated to moderate dips faults which overprint the mesozoic deformation were formed in response to renewed subduction along the eastern coast of the north island during the cenozoic

evidence for two zones of debris entrainment beneath the greenland ice sheet investigation of the ice debris and stable isotope characteristics of basal ice exposed at the margin of the greenland ice sheet provides a means of testing and refining models of ice sheet erosion and deposition the basal ice exposed at the ice sheet margin gives evidence of the processes operating at the bed at different locations which can be used to constrain theoretical models predicting varying basal conditions1 2 improved understanding of the effects of isotope fractionation in hydrogen and oxygen caused by freezing processes at the bed which modify the isotope characteristics of the basal ice layers enables us to report evidence of two separate zones of debris entrainment beneath the ice sheet

short paper a note on rb sr whole rock ages from cleaved mudrocks in the welsh basin two cleaved epizone grade palaeozoic mudrock suites from snowdonia yield a mean rb sr whole rock age of 409 11 ma this is consistent with resetting of the rb sr whole rock isotope systems of the mudrocks during cleavage development in end silurian early devonian acadian deformation in contrast cleaved palaeozoic anchizone mudrocks from north and central wales give a silurian mean age of 430 9 ma this dates either a pre tectonic isotopic event preserved through acadian anchizone metamorphism or mid silurian deformation and metamorphism at anchizone grade unaffected by the acadian event the precise timing of the main caledonian deformation in wales has never been established firmly powell phillips 1985 suggest that it occurred in north and south wales in latest silurian time whereas ashgill and end llandovery tectonic events were dominant in central wales see also george 1963 however woodcock 1984 1987 and soper et al 1987 have argued in favour of a single tectonic event of early to middle devonian age this chronological study was undertaken to address this controversy the only previous attempt to define precisely the timing of cleavage development in wales was the k ar dating of cleavage parallel chlorite from a volcanic greywacke from north wales fitch et al 1969 when recalculated using modern decay constants these data give an age of 399 10 ma bath 1974 demonstrated the feasibility of obtaining rb sr ages from cleaved mudrocks of the welsh caledonides and this work produced caledonian ages of 409 20ma and 393 22ma from north wales and late

fission track analysis of the late cenozoic vertical kinematics of continental pacific crust south island new zealand during the late cenozoic the pacific plate has been converging obliquely with the australia plate in south island new zealand a result of this convergence has been the growth of a major mountain range the southern alps at the leading edge of the pacific plate the results of fission track analysis of 140 samples from 13 transects across the alps reported here establish the late cenozoic vertical kinematics amount age and rate of rock uplift of the pacific crust underlying the alps the late cenozoic rock uplift of the pacific crust is asymmetrical with respect to the alpine fault being a maximum 19 km immediately east of the central part of the fault with lesser values at the eastern 3 km northern 10 km and southern 8 km extremities of the alps the age of the start of rock uplift varies spatially across the southern alps the earliest indications from fission track analysis being at 8 ma at the southern end of the alps decreasing to 5 ma at the northern end and 3 ma along the southeastern margin this age variation reflects the longer time over which the southern parts of the alps have been in collision the rate of propagation of rock uplift southeastward into the pacific plate has been 30 mm yr nearly 4 times the late cenozoic average rate of convergence normal to the plate boundary late cenozoic mean rock uplift rates range from a maximum of 2 8 mm yr at the alpine fault to a minimum of 1 0 mm yr in the east and have been sustained for periods of 3 8 m y accompanying denudation has exhumed amphibolite grade rocks immediately east of the alpine fault the rock uplift has been controlled by oblique slip displacement on the alpine fault a continental crustal section at least 19 km thick has been uplifted on the alpine fault comparison of the late cenozoic mean rock uplift rates with uplift rates derived from reset zircon data 2 10 mm yr near the alpine fault shows that uplift has accelerated over time but only significantly since 1 3 0 3 ma the amount of mesozoic uplift ranged from minimal amounts north of arthur s pass to 3 km near mount cook to 10 km in the south at lake wanaka

a provisional structural thickness map of the otago schist new zealand metamorphic zones terranes and lithologic associations provide a subdivision of the lithologically monotonous otago schist on a 10 to 50 kilometer scale in this study form line maps of schist foliation have been used to construct a provisional structural thickness map of the otago schist that allows a more detailed 1 5 km scale subdivision of the entire schist the map shows the macroscopic thickness of schist measured orthogonal to dominant foliation relative to the datum of the caples rakaia terrane boundary the structural thickness map provides a new spatial reference frame for the otago schist that depicts the differing levels of exhumation of penetratively deformed metamorphic rocks the structural thickness parameter shows a good correlation with metamorphic grade white mica grain size and k ar and ar ar ages thus justifying the simplifying assumptions behind the map s construction the map reveals several hitherto little highlighted features including along and across strike correlations interference patterns between mesozoic and cenozoic macroscopic folds net displacement across known and inferred major faults and relative structural position of mesothermal gold deposits

origin of the torlesse terrane and coeval rocks south island new zealand the carboniferous to lower cretaceous torlesse terrane and haast schist derivatives constitute the major part of the complexly deformed facies of the eastern province of new zealand strata consist mainly of quartzofeldspathic graywacke and mudstone intercalated with minor but widely distributed conglomerate and volcanics with associated chert and limestone clastic rocks were deposited largely by sediment gravity flow mechanisms in a deep marine environment also present are a few highly fossiliferous shallow marine and terrestrial deposits of limited areal extent which rest unconformably on or in fault contact with torlesse flysch several periods of deformation are recognized and melange is present on both local and regional scales metamorphism ranges from zeolite to greenschist facies the bulk of the rocks fall into five areally extensive and mutually exclusive fossil zones of the following ages permian atomodesma middle triassic early late triassic torlessia late triassic monotis and late jurassic early cretaceous contacts between major fossil zones are mainly tectonic petrographic analysis permits subdivision of torlesse sandstones into five major petrofacies that correspond in age to the five major fossil zones the sandstone petrofacies mainly arkosic together with the composition of conglomerate clasts mainly indurated torlesse rocks indicate that the source terrane was a continental volcano plutonic arc probably part of gondwanaland coupled with autocannibalistic reworking of older uplifted torlesse rocks in contrast to the quartzofeldspathic nature of the torlesse coeval sedimentary rocks of the eastern province are volcanogenic they are thought to represent related forearc basin maitai murihiku terranes and trench complex caples terrane deposits derived from a volcanic island arc brook street terrane three petrofacies are established for maitai murihiku and caples sandstones the petrofacies indicate a common evolving immature to submature volcanic island arc source for these terranes a reconstruction of new zealand s eastern and western provinces is proposed in permian and triassic times the torlesse was deposited in trench slope or borderland basins along a trench transform margin fronting a continental volcano plutonic arc source western province gondwanaland deposition was spasmodic but voluminous and was accompanied by concurrent deformation and accretion resulting in parallel belts of torlesse rock younging outward from the gondwanaland margin at the same time the brook street terrane volcanic arc and associated terranes were forming to the west of the torlesse site separated from gondwanaland by a marginal sea in latest triassic or early jurassic times the torlesse was rafted into the volcanic arc system via transform faulting approximately parallel to the gondwana margin the collision event resulted in tectonic thickening of torlesse and caples rocks at the plate interface and metamorphism to haast schist the source was then dominated by older partly metamorphosed torlesse terrane newly uplifted along the collision front closing of the marginal sea behind the brook street terrane in late jurassic early cretaceous times resulted in juxtapositioning with the western province gondwanaland along the median tectonic line

continuous metamorphic gradient documented by graphitization and k ar age southeast otago new zealand the chrystalls beach brighton coastal section southwest of dunedin new zealand exposes otago schist including the weakly metamorphosed triassic accretionary melange of the chrystalls beach complex and higher grade rocks of a largely felsic arc derived provenance melange zones contain pelagic sediments some of which are manganiferous and metabasites the grade of metamorphism increases progressively from southwest to northeast four mineral zones are recognized largely on the basis of mineral assemblages in psammitic and semipelitic rocks pumpellyite chlorite pumpellyite actinolite epidote actinolite and biotite d 002 data for carbonaceous material b 0 values for phengite and metamorphic phengite k ar ages are reported for 32 pelitic and semipelitic samples remarkably tight correlations are revealed between d 002 for progressively graphitized carbonaceous material k ar ages that range from 184 6 to 138 7 ma and linear distance along the section both the d 002 values and the k ar ages decrease progressively toward the northeast through the four mineral zones and with progressive textural changes all rocks cropping out in the section have undergone a coherent episode of progressive metamorphism associated with terrane collision and have not been disturbed by any later major displacements a convex trend for phengite b 0 values plotted against advancing graphitization suggests p t conditions during metamorphism as in the high pressure intermediate facies series the age of the metamorphic peak is inferred to be 175 155 ma middle to late jurassic with cooling to the mica closure temperature at 155 135 ma late jurassic to early cretaceous unloading denudation and cooling were accompanied by localized hydrothermal events the oldest covering strata were deposited at ca 100 ma and denudation was completed by ca 75 80 ma middle triassic radiolarian nodules in melange zones are dated as preceding the metamorphic peak by about 65 ma associated turbidites contain suspected late middle to early late triassic tube fossils

direct measurement of basal motion at a hard bedded temperate glacier glacier de tsanfleuron switzerland hubbard b 2002 direct measurement of basal motion at a hard bedded temperate glacier glacier de tsanfleuron switzerland journal of glaciology 48 160 pp 1 8 rae2008

natural long term annealing of the zircon fission track system in vienna basin deep borehole samples constraints upon the partial annealing zone and closure temperature abstract fission track ft analysis of zircon from cretaceous and tertiary sandstone samples in vienna basin boreholes has provided constraints for the thermal stability of the zircon ft system over a geological timescale confined track lengths and ages were measured for samples from depths of 1 5 7 5 km the deepest with a present environmental temperature of 200 c mean track lengths range from 10 3 to 10 8 m indistinguishable within error from the unannealed reference length of 10 7 0 1 m 1 standard error thus showing no sign of systematic downhole reduction central zircon ages are consistently older than stratigraphic ages of parent rocks with no single grain ages significantly younger than their respective stratigraphic ages such ft age and length evidence strongly suggests that the tracks have not been significantly annealed since sediment deposition because the present geothermal regime as well as sample burial depths have been near constant for at least the past 5 m y the lower temperature limit of the zircon ft partial annealing zone is 200 c for a heating duration of the order of 5 10 m y such evidence from long term natural annealing is compatible with a zircon ft partial annealing zone cf 200 350 c derived by the extrapolation of laboratory annealing results based on onfined track length measurements but cannot alone discriminate between different annealing models for the zircon ft closure temperature a perhaps over simplified concept these results are consistent with the oft quoted temperature of 250 c for cooling rates of 10 100 c m y

deposition and deformation of an early cretaceous trench slope basin deposit torlesse terrane new zealand studies of modern convergent margins have highlighted the variety of depositional environments and deformational processes that occur in this tectonic setting and provide analogues by which ancient uplifted sequences can be interpreted the whatarangi formation is an early cretaceous trench slope basin deposit preserved within accretionary prism rocks of the pahau torlesse terrane of new zealand and is distinguished from the underlying accreted rocks by its younger age different depositional history structural style and metamorphic grade and lack of oceanic volcanic outcrops furthermore the whatarangi formation records the types of processes inferred to occur in modern slope basins sediments were derived from sources on the western side of the basin and were deposited mainly by gravity flows on channelized base of slope aprons the narrow elongate shape of the basin resulted in restricted longitudinal flow of the sandy turbidity currents and deposition of finer sediment farther down the inner trench slope or in the trench deformation of the turbidites produced open to tight asymmetric folds that are concentrated along the western margin and lower half of the formation the folds are best described by a model of simple shear and formed in response to active west over east thrusting in the underlying prism cleavage was initiated prior to folding in response to overall shortening of the basin with subsequent development of an axial planar cleavage in the tightest folds the compositional similarity between the slope basin strata and accreted sedimentary rocks of the aorangi range has important implications for the early cretaceous tectonic history of the torlesse terrane the sediments were eroded from an uplifted accretionary prism and an acid igneous source and the deposition of these sediments in upslope basins and the trench suggests that all the pahau sediments could have been transported from these transversely located sources

thermochronological analysis of the dynamics of the southern alps new zealand the isotopic ages of material exposed close to the alpine fault in the southern alps new zealand vary in a consistent fashion along the orogen for the k ar system muscovite and biotite ages display two distinct spatial trends that meet in the area of fox glacier where a strong relationship is observed between k ar age and altitude excess argon is present in samples between mount kinnaird and haast pass in the southwest of the southern alps giving unrealistically old inconsistent k ar ages across this region incorporation of excess argon appears to be highly variable however and minimization of its influence on dynamical interpretations of thermochronology is possible through considering only the youngest age from a given area such treatment indicates that excess argon contamination does not play an important role in the systematic k ar age variation identified along the southern alps the observed age distribution is consistent with estimates of the modern rapid uplift and exhumation of the southern alps beginning ca 5 ma k ar mica ages older than this south of the copland valley indicate that substantial late cenozoic exhumation occurred along the southern alps prior to the development of the modern tectonic regime but at rates lower than at present total exhumation during the current phase of tectonism in the southern alps decreases from the whataroa river southward north of fox glacier the southern alps have attained a dynamical steady state such that the observed distribution of exhumation will not change significantly with further deformation and denudation under current conditions

tectonic significance of ductile deformation in low grade sandstones in the mesozoic otago subduction wedge new zealand this study demonstrates how ductile strain measurements can determine the tectonic evolution of a large and long lived subduction wedge we provide a synthesis of the geology of the south island of new zealand with an emphasis on a wedge tectonics perspective that contrasts with a traditional view that interprets new zealand geology in the context of terrane collision and accretion we argue that the otago subduction wedge evolved in a steady fashion throughout its 290 to 105 ma history in response to accretion of trench fill and abyssal plain sediments and slow erosion of a subaerially exposed forearc high maximum temperatures for rocks in the flanks of the forearc high were no greater than 150 to 300 c with solution mass transfer active as the dominant ductile mechanism the 54 studied samples provide information about the absolute ductile strains acquired all along their flow path from the site of accretion to exhumation in the forearc high we use tensor averages to estimate strain at a regional scale these show plane strain uniaxial flattening given that the tensor averages for sy and sx are close to one on average sz is approximately 0 77 and this is balanced by a mass loss of about 23 percent the average z direction is sub horizontal in the prowedge and moderately plunging in the retrowedge a difference attributed to spatial variations in the mode of accretion we infer that rocks presently in the pro side of the otago high were sourced by frontal accretion and those in the retro side were underplated this result highlights the important role of accretion in determining the style of within wedge deformation and also demonstrates the benefit of using a tensor averaging approach to examine regional strain

a mesozoic time scale we present an integrated geomagnetic polarity and stratigraphic time scale for the triassic jurassic and cretaceous periods of the mesozoic era with age estimates and uncertainty limits for stage boundaries the time scale uses a suite of 324 radiomenc dates including high resolution 40 ar 39 ar age estimates this framework involves the observed ties between 1 radiometric dates biozones and stage boundaries and 2 between biozones and magnetic reversals on the seafloor and in sediments interpolation techniques include maximum likelihood estimation smoothing cubic spline fitting and magnetochronology

potassium argon age studies of a low grade progressively metamorphosed greywacke sequence dansey pass south island new zealand 39 potassium argon age determinations from a progressively metamorphosed greywacke schist sequence in southern new zealand prehnite pumpellyite to greenschist facies range from 199 to 154 ma early to late jurassic they show an inverse correlation of age with metamorphic grade concordant ages from varied lithologies at all metamorphic grades show that degassing of detrital potassium bearing minerals was completed during metamorphism the lowest grade metamorphic rocks which yield the oldest ages about 200 ma have only just exceeded the argon closure temperature and hence their ages date closely their time of metamorphism in the earliest jurassic thus it is shown that the jurassic cretaceous rangitata orogeny in new zealand commenced earlier is more complex and of longer duration than previously supposed the remaining ages from pumpellyite actinolite and lower greenschist rocks range uniformly through the jurassic and are interpreted as cooling ages from these data a long term uplift rate of 0 23 mm yr is calculated for the jurassic cretaceous

thermochronology of northern murihiku terrane new zealand derived from apatite ft analysis murihiku terrane is the least deformed of a series of tectonostratigraphic terranes that have been amalgamated to form the basement underlying new zealand apatite fission track ft thermochronology has been applied to the youngest beds late jurassic hettangian tithonian stages of this terrane located at port waikato in western north island which are broadly folded the apatite ft ages are partially annealed are younger than their stratigraphic ages and remarkably decrease in age upsection interpretation and modelling of the maximum palaeotemperatures experienced by the sample horizons and the timing of cooling requires a wedge of cretaceous sedimentary rocks to have accumulated within the axis of the major fold kawhia syncline deposition of murihiku terrane sequences continued therefore into the cretaceous and probably until c 100 ma deposition may have ended as late as 85 10 ma when cooling via denudation started the upper parts of the former succession probably accumulated during folding in addition interpretation of the ft data require a marked increase in palaeogeothermal gradient from a subnormal value of 15 c km 1 during the late jurassic up to c 30 c km 1 at 85 10 ma this is attributed to the termination of subduction along the pacific margin of gondwanaland and a transition to a rift transform tectonic setting in western new zealand during tasman sea spreading the latest cretaceous palaeocene eastward tilting of the murihiku basement at port waikato may have been accommodated on the taranaki fault or another coast parallel fault the waikato fault probably acted as a transfer fault at that time accumulating a significant amount of throw

structure of a growing accretionary prism hikurangi margin new zealand the hikurangi margin of eastern north island new zealand represents the feather edge of the indian plate at its convergent boundary with the subducting pacific plate a migrated seismic reflection profile across this margin clearly displays the structural evolution of an accretionary prism a 25 km wide band of protothrusts is delineated between the toe of the slope and a converging seamount this illustrates an early stage in the seaward propagation of a deformation front landward tilted trench slope basins are separated by ridges that have clearly defined thrusts which appear to sole out at a decollement the decollement continues at an angle of only 3 beneath the 150 km wide margin to a depth of 14 km near the coast where it coincides with an onshore zone of high seismicity

the influence of tectonic deformation on facies variability in stratified debris rich basal ice facies variability displayed within basal ice has hitherto been widely interpreted as a re ection of spatial variation in the processes of ice formation the basal boundary conditions or a combination of both recent literature has consequently been characterised by attempts to derive a genetic classi cation of basal ice facies applicable to di erent types of glacier we present new observations made at the russell glacier greenland which suggest that any such genetic classi cation must take account of post formational deformation occurring within basal ice all the ice sub facies occurring within the strati ed basal ice are explained in terms of two sets of processes the initial entrainment of a debris rich basal layer and subsequent ow related tectonic deformation of that layer to produce distinctive tectonically derived sub facies the evolution appearance and composition of some elements of the basal ice layer are therefore argued to be controlled primarily by post formational ow related deformation any useful genetic classi cation of basal ice facies must therefore include criteria able to distinguish between characteristics derived from the mechanism of ice formation and those that are tectonically derived 2000 elsevier science ltd all rights reserved

constraining coalbed methane reservoir petrophysical and mechanical properties through a new coal structure index in the southern qinshui basin northern china implications for hydraulic fracturing structurally deformed coal sdc influences not only gas outbursts during coal mining but also coalbed methane cbm production different sdcs have different mechanical strengths and physical properties the structurally constrained petrophysical and mechanical properties of a cbm reservoir from the southern qinshui basin sqb northern china have been investigated by using a coal structure index csi the csi was established as a quantitative criterion for the deformation of sdcs based on surface conditions and blockiness using the data of 783 coring samples from 109 cbm wells the results show that undeformed coal and slight brittle sdcs are dominant in the sqb with ductile sdcs distributed locally both compressive strength and tensile strength decline exponentially with increasing csi average avg coal structure is a crucial factor for coal seam fracturing with an increasing csi avg the major fracture length will first increase to the maximum of 266 m at a csi avg of 45 and then decrease rapidly however branch fractures are independent of the csi avg the major fracture height attained a minimum of 4 39 m at a csi avg of 40 and then slowly increased therefore slightly brittle sdcs should be beneficial for fracturing at least for high rank coals the presence of variable sdcs can have a considerable impact on cbm reservoir petrophysical and mechanical properties finally a csi model that strives to establish the relation between structure deformation and cbm reservoir physical and mechanical properties in coal is expected to effectively guide hydraulic fracturing

structural boundaries and biotite and garnet isograds in the otago and alpine schists new zealand the otago and alpine schist belts of southern new zealand have traditionally been treated as structurally continuous metamorphic belts with minor modification by brittle faulting mapping of biotite and garnet isograds has been hindered by rock types unfavourable for index mineral growth closer examination of well exposed boundaries between metamorphic zones shows that they juxtapose rocks of different type and structural history apparent structural continuity across these zones is due to development of a locally pervasive boundary parallel foliation on both sides of the boundary in a broad boundary zone up to 2 km wide this feature has implications for mapping and metamorphic petrology in other metamorphic belts where structural continuity has traditionally been assumed true metamorphic isograds may be rare and metamorphic zones may more commonly represent structural slices of complex tectonically disrupted metamorphic piles

evidence from u pb zircon and 40ar 39ar muscovite detrital mineral ages in metasandstones for movement of the torlesse suspect terrane around the eastern margin of gondwanaland new u pb detrital zircon ages from triassic metasandstones of the torlesse terrane in new zealand are compared with 40ar 39ar muscovite data and together reveal four main source components i major triassic permian 210 270 myr old and ii minor permian carboniferous 280 350 myr old granitoids recorded in zircon and muscovite data iii minor early middle palaeozoic metamorphic rocks recorded mainly by muscovite 420 460 myr old and iv minor late precambrian cambrian igneous and metamorphic complexes 480 570 myr old recorded by zircon only there are also proterozoic zircon ages with no clear grouping 580 1270 myr the relative absence of late palaeozoic 350 420 myr old components excludes granitoid terranes in the southern lachlan fold belt australia and its continuation into north victoria land east antarctica and marie byrd land west antarctica as a potential source for the torlesse the age data are compatible with derivation from granitoid terranes of the northern new england orogen and hinterland in ne australia this confirms that the torlesse terrane of new zealand is a suspect terrane that probably originated at the ne australian permian triassic gondwanaland margin and then 200 120 ma moved 2500 km southwards to its present new zealand position by the late cretaceous 90 ma this sense of movement is analogous to that suggested for palaeozoic mesozoic terranes at the north american pacific margin

stick slip behavior of ice streams modeling investigations a puzzling phenomenon of ice stream flow is the stick slip motion displayed by whillans ice stream wis west antarctica in this study we test the hypothesis that the wis stick slip motion has features similar to those of other known stick slip systems and thus might be of the same origin to do so we adapt a simple mechanical model widely used in seismology to study classic stick slip behavior observed in tectonic faults in which the difference between static and dynamic friction allows for the generation and spatial propagation of abrupt slip events we show how spatial variability in friction properties as well as a periodic forcing intended to mimic the effect of tides can reproduce the observed duration and periodicity of stick slip motion in an ice stream an intriguing aspect of the association of wis with mechanical stick slip oscillators is that the onset of stick slip cycling from a condition of permanent slip appears to be associated with the reduction in overall speed of wis if this association is true then stick slip behavior of wis is a transitional phase of behavior associated with the ice stream s recent deceleration

fluid evolution fluid immiscibility and gold deposition during cretaceous recent tectonics and uplift of the otago and alpine schist new zealand abstract the otago and alpine schist metamorphic belts have been uplifted and experienced collisional extensional transcurrent and then renewed collisional tectonics over the past 120 ma au bearing veins have been deposited in greenschist facies rocks at many different structural levels from 10 km depth to within a few hundred metres of the surface in many structural settings during this long uplift history fluids which deposited these veins have had a remarkably similar composition throughout the tectonic history veins formed near to the brittle ductile transition and in the lower parts of the brittle region were deposited by water with

a new perspective for the directivity of rock quality designation rqd and an anisotropy index of jointing degree for rock masses abstract the rock quality designation rqd index is defined as the percentage of the borehole core or scanline that consists of intact lengths 0 1 m and has been widely used as an engineering measure of the jointing degree of a rock mass the directivity of rqd which means the value of the rqd obtained from drilling cores or scanlines with different orientations can be different for a given site is usually regarded as a drawback by researchers and engineers this study presents a new perspective for the directivity of rqd the directivity of rqd should be regarded as an advantage of the index because it essentially reflects the anisotropy of rock masses because a smaller value of the rqd index implies a better reproduction of the different jointing degrees of different rock masses its minimum value is selected as the representative rqd rqdr and its corresponding direction is called as the representative direction of rqd in this study to obtain the rqdr and its representative direction theoretical formulas are derived to calculate the rqd in any direction based on some known rqds in different directions the proposed formulas consider the variance of the discontinuity orientations and sizes for a discontinuity set use the traditional concept of rqd and possess the associated simplicity they only require sampling a few additional discontinuity orientations therefore the proposed approach is easy to understand and apply in engineering practices an anisotropy index of jointing degree aijd is defined to quantitatively describe the anisotropy of jointing degree for rock masses the range of aijd is from 0 to 100 and the larger value of aijd reflects stronger anisotropy of jointing degree of a rock mass in this study a hypothetical three dimensional discontinuity network is constructed by performing monte carlo simulations based on which the generated data are analyzed to validate the proposed method the comparison between the calculated and actual values of the rqd shows that a the difference between the calculated and actual values of the rqd is 86 0 of the 1368 scanlines examined with respect to 12 scanline groups except sg4 1 group for which the proportion is 66 2 b the difference between the calculated and actual values of the rqd is 96 2 of the 1368 scanlines examined with respect to 12 scanline groups except sg4 1 for which the proportion is 86 7 and c the proposed method of calculating the rqd in any direction based on some known rqds in different directions is satisfactory in addition the comparisons show that the calculated rqdr and representative direction exhibit a good agreement with the actual results and hence the proposed method for this purpose is satisfactory moreover an actual rock mass of a slope around the qingshan lake national forest park in china is investigated and the results show that the proposed method is valid for that rock mass

seismicity structure and tectonics of the wellington region new zealand summary the wellington region lies on the border between the pacific and australian plates the former being subducted the plate interface lies at shallow depth under the region 10 60 km so that detailed and long term monitoring of the seismicity of the zone where large thrust earthquakes are expected to occur is possible hypocentres for events recorded by a 12 station seismic network for the period 1978 1982 7231 events have been refined by the use of a threedimensional velocity model derived from a simultaneous inversion of arrival time data from 129 local events for both hypocentres and velocity the hypocentres show that the subducting pacific plate is defined by a nw dipping zone of relatively intense activity the plate interface as given by the upper envelope of this activity is offset vertically by 7 km on average along a nw se line through cook strait parallel to the direction of absolute motion of the pacific plate rather than to the direction of convergence the strike of the interface at deeper levels also changes across this line this distortion may partly reflect effects of the transition to continent continent type convergence further south within the subducting pacific plate the seismic activity defines two parallel zones separated by about 20 km the lower zone being much less active and perhaps merging with the upper zone at a depth of 80 90 km composite focal mechanisms of events in the upper zone imply predominantly down dip tension with a compression axis perpendicular to the plate interface the mechanism in the lower zone also implies down dip tension but the compression axis has rotated to be horizontal and along strike indicating a component of lateral shearing within the plate these two types of mechanism correlate well with those found previously for events at depths of 150 km or more thus it seems that the large negative buoyancy of the subducted lithosphere dominates the internal stress field throughout the length of the seismically active region the lithosphere acting as a stress guide there is no evidence for a significant number of events with mechanisms indicating thrusting along the plate interface the seismic velocity in the region corresponding to the upper seismic band is close to that typical for oceanic crust which here is probably considerably thicker than normal there is no evidence for a substantial increase in velocity down

tracking crustal processes by ft thermochronology in a forearc high hikurangi margin new zealand involving cretaceous subduction termination and mid cenozoic subduction initiation abstract raukumara peninsula is a forearc high on the pacific margin of new zealand its basement comprises two sedimentary terranes that formed in subduction prisms during the late jurassic mid cretaceous marking the end of subduction along the pacific margin of eastern gondwanaland the cover includes allochthonous late cretaceous oligocene passive margin slope to basin facies emplaced into the forearc during the early miocene initiation of the current subduction regime as well as autochthonous neogene sediments apatite and zircon fission track ft data are reported and interpreted for the basement and cover sediments the detrital zircon ft ages constrain the maximum depositional ages of the low grade zeolite and pumpellyite facies basement pahau terrane is no older than 152 13 ma this zircon ft mode and older ones 198 8 ma 232 58 ma recording cooling denudation in the source areas probably including rakaia terrane waioeka terrane located oceanward of pahau terrane is no older than 125 2 ma being the age of volcanic derived zircons and supports early cretaceous dinoflagellate ages reported previously omaio petrofacies comprises the youngest part of the waioeka terrane and has a zircon ft age of 108 6 3 ma this indicates that basement sequences accumulated in the northeast contemporaneously with cover sequences koranga fm in the southwestern part of the peninsula these zircon ft ages together with the results of thermal history modelling of certain waioeka terrane samples are consistent with migration of a thrust system in a subduction prism environment during the late jurassic cretaceous until about 85 ma as proposed earlier when mesozoic subduction terminated apatite ft data indicate for all basement samples a phase of neogene heating and cooling associated with basin formation sediment accumulation and subsequent uplift and erosion resulting in almost complete removal of the neogene stratigraphic record over western parts of the peninsula forward modelling of the data imply rapid earliest miocene downwarping of the crust in bay of plenty coinciding with initiation of subduction of pacific plate followed by emplacement of a 1 5 2 0 km thick wedge of east coast allochthon from the northeast early miocene sediments accumulated in a foredeep along the front sw margin of the allochthon probably sourced from a block of pahau basement west of whakatane fault which was exhumed and denuded by 4 km contemporaneously during the late early to middle miocene the basin depocentre migrated further to the southwest while areas previously downwarped northeast were uplifted and eroded the depocentre migration and subsequent inversion is a pattern that affected most of north island and is related to mechanical or dynamical interaction of the two plates as the slab of pacific oceanic lithosphere was emplaced beneath north island this may be a general feature of young subduction zones

jurassic tectonic history of the otago schist new zealand a regional reanalysis of the otago schist shows that ductile mesoscopic structures can be interpreted as elements of a single progressive heterogeneous noncoaxial jurassic deformation related to juxtaposition of the caples and torlesse terranes stretching lineations are parallel oblique and perpendicular to the orogen in various parts of otago but changes in trend are generally unrelated to the terrane boundary structural geometry and rare shear criteria indicate that the caples terrane overthrust the torlesse terrane from the south and west but precise transport directions are not known being model dependent macroscopic recumbent folds may be present in the schist but mainly in the form of partially developed nappe structures truncated by zones of retransposed foliation and or high strain

quantifying the basal conditions of a mountain glacier using a targeted full waveform inversion bench glacier alaska usa glacier dynamics are inextricably linked to the basal conditions of glaciers seismic reflection methods can image the glacier bed under certain conditions however where a seismically thin layer of material is present at the bed traditional analyses may fail to fully characterize bed properties we use a targeted full waveform inversion algorithm to quantify the basal layer parameters of a mountain glacier thickness d p wave velocity and density we simultaneously invert for the seismic quality factor q of the bulk glacier ice the inversion seeks to minimize the difference between the data and a one dimensional reflectivity algorithm using a gradient based search with starting values initialized from a monte carlo scheme we test the inversion algorithm on four basal layer synthetic data traces with 5 added gaussian noise the inversion retrieved thin layer parameters within 10 of synthetic test parameters with the exception of seismic q for the seismic dataset from bench glacier alaska usa inversion results indicate a thin basal layer of debris rich ice within the study area having mean velocity 4000 700ms 1 density 1900 200kgm 3 and thickness 6 1 5m

critical wedge theory and the mesozoic accretionary wedge of new zealand abstract we apply principles of critical wedge theory to explain the jurassic and early cretaceous tectonic development of the mesozoic accretionary wedge of new zealand one of the best exposed subduction complexes on earth by summarizing factors that can lead to drastic changes in wedge balance the wedge has a carboniferous to cretaceous 330 110 ma stratigraphic record with an early cretaceous 145 130 ma hiatus in clastic deposition across the esk head melange near the front of the wedge in the rear of the wedge the age of moderately high pressure metamorphism of the otago schist which represents the forearc high of the wedge occurred near the end of this stratigraphic hiatus the otago schist has a subhorizontal foliation indicative of underplating as the mode of accretion the outer frontal part of the wedge has a subvertical foliation indicative of frontal accretion we propose that in the jurassic and earliest cretaceous the wedge grew by frontal accretion by 135 ma the wedge became too long and was subcritical this resulted in tectonic erosion of the front of the wedge the tectonically eroded material was underthrust underplated beneath the rear of the wedge to form the subhorizontally foliated otago schist colliding seamounts and or oceanic plateaux preserved in the esk head melange may have aided wedge instability the proposed wedge instability and increased horizontal shortening was largely coeval with major changes in the chemistry of subduction related arc magmatism and a phase of shortening and high pressure metamorphism in the arc our model provides a holistic and coherent interpretation explaining the major tectonic features of the long lived new zealand part of the east gondwana subduction zone

estimation of rock mass deformation modulus using variations in transmissivity and rqd with depth discontinuity normal stiffness and deformation modulus of large scale rock masses are very difficult to determine a method for estimation of discontinuity normal stiffness based on the decrease in transmissivity with depth has been proposed by the authors in a former paper in the current study the method is further developed by accounting for the changes in both discontinuity aperture and frequency with depth which are key factors that cause the transmissivity to decrease with depth the discontinuity frequency can be estimated from rqd measurements which are readily available in most geotechnical investigations the transmissivity data from packer tests are usually available in geotechnical investigations for hydropower plants for a rock mass in a dam site mainly controlled by lithostatic stress based on transmissivity and rqd data at different depths the change in discontinuity aperture with depth can be linked to the change in aperture with stress which defines the normal stiffness of discontinuities in the case study the discontinuity normal stiffness is successfully estimated by using transmissivity and rqd data and the result shows that the normal stiffness increases with stress depth and the rate of normal stiffness versus stress depth decreases with stress depth which is consistent with experimental studies the estimated normal stiffness has been utilized to calculate the rock mass deformation modulus using an equivalent model the result of deformation modulus by the proposed method is close to that obtained by using in situ measurements as well as by using empirical models relating rqd to deformation modulus

thermochronology of the torlesse accretionary complex wellington region new zealand the torlesse complex comprises several mesozoic accretionary prism complexes together forming continental basement over large parts of new zealand this study focuses on the thermal history of relatively low grade graywacke rocks exposed in a transect in southern north island that crosses the structural grain of the torlesse complex including its older and younger parts zircon fission track ft ages for the late triassic rakaia terrane which is the most inboard of the accretionary complexes are partially annealed some possibly reset and may indicate early cretaceous 134 10 ma cooling from maximum temperatures tmax probably related to imbrication of younger complexes of the pahau terrane numerical modeling of the zircon ft ages and published 40ara 39ar muscovite and biotite ages for the rakaia terrane suggest tmax values of 265 310 c and exhumation from depths of 10 12 km the rocks underlying the aorangi range and involving the youngest accretionary complex have experienced much lower tmax values of 210 and 110 c bracketed by reset apatite ft ages and detrital zircon ft ages the occurrence of a circa 100 ma component of zircon ft ages in both the weakly and highly indurated rocks beneath the aorangi range as well as in remnants of an overlying albian accretionary slope basin whatarangi formation imply multistorey accretion and incorporation of sediment into the youngest prism this circa 100 ma zircon ft age component also places a maximum age on the termination of mesozoic subduction beneath the new zealand region the occurrence of reset apatite ft ages across the whole of the wellington transect indicates that at least 4 km of exhumation occurred during the late miocene

rb sr resetting ages and chemical characterization of turbidites in an accretionary wedge torlesse complex otaki gorge new zealand whole rock geochemical and rb sr isotopic analyses have been undertaken on turbidites from three discrete localities each about 2 km apart across strike within the torlesse complex a permian cretaceous accretionary wedge in new zealand overall the three suites show similar petrographic and geochemical compositions to turbidites from elsewhere in the torlesse complex but between the suites there are detectable differences for most major and trace elements particularly sr mgo and na 2 o the individual suites define three parallel rb sr whole rock isochrons with identical dates of about 205 ma the presence of monotis bivalves provides a depositional age of norian 219 225 ma hence the isochrons suggest that the rb sr clock was reset some 15 20 m y after deposition during low grade metamorphism associated with accretion and deformation of the sediment pile there is a wide variation in the initial 87 sr 86 sr ratios from 0 70683 to 0 70955 which is best explained by changes in the composition of the detritus being provided from the source area as detected by the chemical differences sea water is not considered to have played a significant role in contributing to the initial ratios the failure of some samples collected away from the main sample localities to plot on their respective isochrons suggests that domains of sr isotopic equilibration are small in the order of a few cubic meters as a result of this study we have extended the rb sr whole rock dating method of sediments now widely applied to shales and cherts to the more complex turbidite sequences from accretionary wedges and have shown that meaningful dates can be obtained this should provide an invaluable method of dating these sparsely fossiliferous terranes

provenance of the detrital component of deep sea sediments from the sw pacific ocean based on mineralogy geochemistry and sr isotopic composition abstract clay mineralogy and chemical and strontium isotope compositions have been used to determine the detrital components of deep sea sediments from the sw pacific ocean continental detritus derived mainly from the new zealand landmass is characterised by high illite and chlorite contents and 87 sr 86 sr ratios close to 0 7110 this material eroded from the eastern margin of both islands is transported into deeper water by turbidity currents and hemipelagic processes and is carried northwards by the strong western boundary current as far north as the samoan basin due to the great distance from source and unfavourable prevailing winds the contribution of aeolian dust from the australian deserts to the sediment appears to be relatively small particularly in the northernmost part of the region in the vicinity of the oceanic volcanic islands of tonga samoa and the cook islands volcaniclastic material including heavy minerals pyroxene and magnetite pumice glass shards proximally and smectite clays distally is dispersed into the sediments by turbidity currents and airfall in areas of very low sedimentation distant from landmasses the sediments contain significant amounts of authigenic material rsos characterised by high concentrations of transition metals and rare earth elements strontium isotopes together with trace element compositions have proved particularly useful in determining the relative proportions of the detrital types the contrasting 87 sr 86 sr ratios and sr contents of the various source rocks permit the use of binary mixing relationships whch indicate that sediments less than 35 km from the cook islands contain 80 volcanic detritus and those more than 1200 km away contain up to 20 volcanic detritus

constraints on the tectonics of the mule mountains thrust system southeast california and southwest arizona the mule mountains thrust system crops out discontinuously over a 100 km strike length in the blythe quartzsite region of southeast california and southwest arizona along the thrust system middle and upper crustal metamorphic and plutonic rocks of proterozoic and mesozoic age are thrust north northeastward 015 degree to 035 degree over a lower plate metamorphic terrane that formed part of the proterozoic north american craton its paleozoic sedimentary rock cover overlying mesozoic volcanic and sedimentary rocks and the intruding jurassic and cretaceous granitic rocks stratigraphic petrologic and pb isotopic ties for jurassic granitoids and for jurassic and cretaceous sedimentary rocks across the various parts of the thrust system indicate that related crustal blocks are superposed and preclude it from having large displacements the thick skinned thrust system is structurally symmetrical along its length with a central domain of synmetamorphic thrust faults that are flanked by western and eastern domains where lower plate domains where lower plate synclines underlie the thrusts deformation occurred under low greenschist facies metamorphic conditions in the upper crust movement along the thrust system was probably limited to no more than a few tens of kilometers and occurred between 79 plus minus 2 ma and 70 plus minus 4 ma the superposition of related rocks andmore the geometry of the thrust system preclude it from being a major tectonic boundary of post middle jurassic age as has been previously proposed rather the thrust system forms the southern boundary of the narrow zone of cretaceous intracratonic deformation and it is one of the last tectonic events in the zone prior to regional cooling less

kar and rbsr age studies of the metamorphism and quartz vein au mineralisation on terawhiti hill near wellington new zealand abstract k ar and rb sr ages have been determined for low grade torlesse terrane metagreywacke sequences wellington greywackes at terawhiti hill near wellington and the more schistose rocks in a narrow sheared zone containing aubearing quartz reefs a rb sr whole rock isochron age of 200 7 ma provides the best age estimate late triassic or earliest jurassic for regional metamorphism of the wellington greywackes and their initial 87 sr 86 sr ratio at this time 0 70690 0 00009 is characteristic of the extensive torlesse terrane elsewhere that is derived from a silicic continental source both k ar and rb sr ages indicate a local but intense shearing event at terawhiti hill at 125 130 ma early cretaceous after earlier metamorphism and uplift of the greywackes and possibly during imbrication of torlesse rocks on a regional scale formation of quartz veins and some deposition of au in schists and cataclastic rocks is possibly synchronous with this event but au is more importantly associated with isolated and rare later quartz reefs formed at 100 110 ma from sr isotope evidence the earlier quartz veins have a local in situ origin but the younger veins have an extraneous possibly deeper source

internal structural architecture of a soft linkage transfer zone using outcrop and dc resistivity data implications for preliminary engineering assessment abstract the current study presents a new integrative approach for detailed structural mapping of a soft linkage transfer zone using outcrop boreholes and dcr data in the form of soundings and 2d electrical resistivity tomography 2d ert as a case study the present approach is implied for studying the geo engineering conditions of a highly deformed desert land entry to reclaim at cairo suez district egypt the approach has led to the spatial understanding of the subsurface heterogeneity and complex structures at a level of accuracy unattainable with traditional surface structural mapping alone for preliminary geotechnical assessment some physical and geotechnical properties are characterized by field and laboratory measurements for collected soil samples moreover the inverted dcr data are used to predict the rqd values using a polynomial relationship between rqd and the intrinsic resistivity notably the calculated and actual values of rqd are in general in the same order considering the error factor value and hence the derived equation for rqd prediction is satisfactory therefore the proposed approach reduces the uncertainty of the constructed structural model for engineering design in addition merging outcrop with dcr data allows us with a limited frame of time to partially mitigate disasters to civilization by better i potential location understanding and ii remediation plans tuning for a complex structured site

provenance of permian triassic and ordovician metagraywacke terranes in new zealand evidence from 40ar 39ar dating of detrital micas single crystal 40 ar 39 ar ages of detrital micas from greenland group ordovician low grade metagraywackes of the west coast south island new zealand indicate a source area having muscovite age patterns of 490 515 ma the detrital muscovite ages are characteristic of granitoid and gneiss terranes of the ross adelaide fold belt of antarctica therefore the source area for the greenland group sedimentary rocks was the immediately adjacent pacific margin of gondwana similar age determinations for rakaia terrane permian triassic torlesse supergroup metagraywackes of the wellington and canterbury regions of new zealand indicate that their source area included rocks having prominent muscovite cooling ages populations of 210 290 ma 80 and 410 460 ma 15 the torlesse detrital muscovite age data thus suggest that the source area of the metagraywackes was not within the lachlan fold belt of southeast australia and analogues in antarctica nor in the adjacent ross adelaide fold belt rather the rakaia terrane of the torlesse metagraywackes is a true suspect terrane derived from a source area within the hunter bowen fold belt of northeast australia and the immediately adjacent older orogens of eastern queensland

an integrated structure from motion and time lapse technique for quantifying ice margin dynamics fine resolution topographic data derived from methods such as structure from motion sfm and multi view stereo mvs have the potential to provide detailed observations of geomorphological change but have thus far been limited by the logistical constraints of conducting repeat surveys in the field here we present the results from an automated time lapse camera array deployed around an ice marginal lake on the western margin of the greenland ice sheet fifteen cameras acquired imagery three times per day over a 426 day period yielding a dataset of 19 000 images from these data we derived 18 point clouds of the ice margin across a range of seasons and successfully identified calving events ranging from 234 to 1475 m2 in area and 815 8725 m3 in volume induced by ice cliff undercutting at the waterline and the collapse of spalling flakes low ambient light levels locally reflective surfaces and the large survey range hindered analysis of smaller scale ice margin dynamics nevertheless this study demonstrates that an integrated sfm mvs and time lapse approach can be employed to generate long term 3 d topographic datasets and thus quantify ice margin dynamics at a fine spatio temporal scale this approach provides a template for future studies of geomorphological change

40ar 39ar thermochronologic constraints on deformation metamorphism and cooling exhumation of a mesozoic accretionary wedge otago schist new zealand abstract structural thickening of the torlesse accretionary wedge via juxtaposition of arc derived greywackes caples terrane and quartzo feldspathic greywackes torlesse terrane at 120 ma formed a belt of schist otago schist with distinct mica fabrics defining i schistosity ii transposition layering and iii crenulation cleavage thirty five 40ar 39ar step heating experiments on these micas and whole rock micaceous fabrics from the otago schist have shown that the main metamorphism and deformation occurred between 160 and 140 ma recorded in the low grade flanks through 120 ma shear zone deformation this was followed either by very gradual cooling or no cooling until about 110 ma with some form of extensional tectonic exhumation and cooling of the high grade metamorphic core between 109 and 100 ma major shear zones separating the low grade and high grade parts of the schist define regions of separate and distinct apparent age groupings that underwent different thermo tectonic histories apparent ages on the low grade north flank hanging wall to the hyde macraes and rise and shine shear zones range from 145 to 159 ma n 8 whereas on the low grade south flank hanging wall to the remarkables shear zone or caples terrane range from 144 to 156 ma n 5 most of these samples show complex age spectra caused by mixing between radiogenic argon released from neocrystalline metamorphic mica and lesser detrital mica several of the hanging wall samples with ages of 144 147 ma show no evidence for detrital contamination in thin section or in the form of the age spectra apparent ages from the high grade metamorphic core garnet biotite albite zone range from 131 to 106 ma n 13 with a strong grouping 113 109 ma n 7 in the immediate footwall to the major remarkables shear zone most of the age spectra from within the core of the schist belt yield complex age spectra that we interpret to be the result of prolonged residence within the argon partial retention interval for white mica 430 330 c samples with apparent ages of about 110 109 ma tend to give concordant plateaux suggesting more rapid cooling the youngest and most disturbed age spectra come from within the alpine chlorite overprint zone where samples with strong development of crenulation cleavage gave ages 85 107 and 101 ma due to partial resetting during retrogression the bounding remarkables shear zone shows resetting effects due to dynamic recrystallization with apparent ages of 127 122 ma whereas overprinting shear zones within the core of the schist show apparent ages of 112 109 and 106 ma these data when linked with extensional exhumation of high grade rocks in other parts of new zealand indicate that the east gondwana margin underwent significant extension in the 110 90 ma period

stick slip motion of an antarctic ice stream the effects of viscoelasticity stick slip behavior is a distinguishing characteristic of the flow of whillans ice stream siple coast antarctica distinct from stick slip on northern hemisphere glaciers which is generally attributed to supraglacial melt the behavior is thought be controlled by basal processes and by tidally induced stress however the connection between stick slip behavior and flow of the ice stream on long time scales if any is not clear to address this question we develop a new ice flow model capable of reproducing stick slip cycles similar to ones observed on the whillans ice plain the model treats ice as a viscoelastic material and emulates the weakening and healing that are suggested to take place at the ice till interface the model results suggest the long term ice stream flow that controls ice discharge to surrounding oceans is somewhat insensitive to certain aspects of stick slip behavior such as velocity magnitude during the slip phase and factors that regulate it e g elastic modulus furthermore it is found that factors controlling purely viscous flow such as temperature influence stick slip contribution to long term flow in much the same way additionally we show that viscous ice deformation traditionally disregarded in analysis of stick slip behavior has a strong effect on the timing of slip events and therefore should not be ignored in efforts to deduce bed properties from stick slip observations

a new determination method for the permeability tensor of fractured rock masses abstract hydraulic characteristics are important fundamental properties of fractured rock masses and involve various geoscience and engineering disciplines the determination of the permeability tensor is the basic input of the equivalent continuum ec model for hydraulic behavior analysis an analytical method to determine the permeability tensor of fractured rock masses is developed based on the orientation and linear frequency of fractures along with a value of the permeability in any direction the orientation and linear frequency of fractures can be easily sampled in practice and the value of the permeability in some direction can be tested by a relatively cheap single well pumping test the key step of this method is to derive the theoretical relationship between the permeabilities in two different directions in addition an anisotropy index of permeability aip is defined to quantitatively describe the permeability anisotropy some numerical experiments were conducted with the universal distinct element code udec to validate the developed method the results show that a the predicted values are very close to the real ones b for all cases of rock masses with equal aperture fracture sets the mean error rate of the permeabilities in 23 different directions is approximately 10 c for rock masses with different aperture fracture sets the mean error rate increases from 8 6 to 28 9 as the aperture ratio increases from 1 to 4 and d therefore the estimation method for directional permeability proposed in this study is valid especially for those rock masses in which the aperture ratios of the fracture sets are small e g less than 3

engineering characterization of hydraulic properties in a pilot rock cavern for underground lng storage abstract feasibility of storing lng in a lined rock cavern was evaluated using a pilot cryogenic rock cavern constructed in daejeon korea the pilot program included hydrogeological and engineering characterization of the rock mass around the cavern design and construction of a drainage system and pilot operation of the cryogenic cavern an appropriate drainage system is most important to protect the containment system of lng from thermal shocks due to ice lenses and hydrostatic pressure of groundwater as a part of the pilot program this study focused on the evaluation of hydraulic and engineering properties of the rock mass around the cavern for this purpose engineering logging of the rock cores single and cross hole hydraulic tests and recharge drainage tests were performed using seven drilled holes with different trends and plunges three main joint sets were found from the logging of the rock cores acoustic borehole televiewer and window mapping the orientations of the three major joint sets were 60 209 40 171 and 29 331 which can provide the main groundwater flow paths mean rqd values ranged from 56 to 88 which were classified as fair and good although varying with depth along single boreholes hydraulic conductivity from the single and cross hole hydraulic tests estimated in the order of 10 6 or 10 7 m s and corresponding transmissivity ranged between 10 5 and 10 6 m2 s permeable intervals identified from the hydraulic tests were mostly located above the cavern roof below the roof the permeable zone was difficult to observe according to the hydraulic communication tests performed for some designated intervals hydraulic connection between boreholes was highly varied with depth or location which indicated a very different distribution of water conducting joint sets along the boreholes when water was injected at r1 with constant or varying flow rates monotonous and stable seepage was observed at observation boreholes from this some stable drainage was expected even in relatively heavy rainfalls when designing the drainage system of the cavern the drainage holes should be orientated to maximize frequency of encountering the major joint sets and the permeable intervals identified from this study

duplex arrays and thickening of accretionary prisms an example from boso peninsula japan part of the emi group a miocene accretionary prism in the boso peninsula japan displays an extensive west trending duplex array the intense faulting there is divided into five stages the first stage involving layer parallel to subparallel faulting is primarily responsible for thickening and horizontal shortening of the strata this stage thickened the sequence by a factor of 3 5 duplex formation is here interpreted to be essential to thicken trench turbidites at a relatively early stage of deformation just after sedimentation even in shallow levels of accretionary prisms the east to west vergence of duplex formation might be attributed to the unique tectonics around the boso trench trench trench type triple junction

a discussion on the adjustment parameters of the slope mass rating smr system for rock slopes abstract rock mass classification systems are common tools used in the design and construction of rock engineering numerous classification systems have been developed for rock slopes of which the slope mass rating smr system is the most popular consequently many rock slope classification systems have been derived from the smr system however these systems are not good at determining the values of the two adjustment parameters f 1 and f 3 implying that the original smr system may contain theory defects in this paper we propose some corrected methods for determining f 1 and f 3 and perform a series of analyses considering the three failure modes of rock slopes plane wedge and toppling failures the results of the discrepancy analysis from f 1 illustrate that with respect to each of the aforementioned three failure modes the calculated original smr index is larger than or equal to the real value and the designed slope is possibly in danger the results of the discrepancy caused by the f 3 illustrate that for each of the aforementioned three failure modes the calculated original smr index is smaller than or equal to the real value and the designed slope might be conservative and not economical

zoned cretaceous and cenozoic garnet and the timing of high grade metamorphism southern alps new zealand new garnet sm nd and lu hf and existing rb sr 40ar 39ar u pb and sm nd ages and data on deformational fabrics and mineral compositions show for the first time that the garnet growth and ductile deformation in the alpine schist belt and southern alps orogen new zealand are diachronous and partly cenozoic in age the dominant metamorphic isograds in the alpine schist formed during crustal thickening at a previously unsuspected time at c 86 ma immediately prior to the opening of the tasman sea at c 84 82 ma obvious changes in the textures and compositional zoning patterns of garnet are not always reliable indicators of polymetamorphism and fabric elements can be highly diachronous a detailed timing history for the growth of a single garnet is recorded by a sm nd garnet whole rock age of 97 8 8 1 ma for the inmost garnet core zone 1 lu hf ages of 86 2 0 2 ma and 86 3 0 2 ma for overgrowth zones 2 and 3 a step leach sm nd age of 12 37 ma for zone 4 and growth of the garnet rim zone 5 over the alpine fault mylonite foliation during the modern phase of oblique collision that began at c 5 6 ma plate convergence along the new zealand portion of the gondwana margin continued after c 105 ma almost certainly culminating in the oblique collision of a large oceanic plateau hikurangi plateau the metamorphism of the alpine schist at c 86 ma is evidence of that hit the mid to late cretaceous extension that is widespread elsewhere in the new zealand region is attributed to upper plate extension and slab roll back the effects of the collision with the hikurangi plateau may have contributed to the changing plate motions in the region leading up to the opening of the tasman sea at c 82 ma

limestone and chert in tectonic blocks from the esk head subterrane south island new zealand the esk head subterrane is a continuous belt generally 10 20 km wide of tectonic melange and broken formation on the south island of new zealand this subterrane separates older and younger parts of the torlesse terrane which is an extensive accretionary prism composed mostly of quartzo feldspathic submarine fan deposits ranging from permian to early cretaceous in age the torlesse is the most pacific ward of several permian and mesozoic accreted terranes in new zealand that record tectonic amalgamation and ultimate accretion against the pacific facing gondwana margin the esk head subterrane of the torlesse is especially informative because it includes within it conspicuous tectonic blocks of submarine basalt and a variety of basalt associated seamount and sea floor limestones and cherty rocks thought to be representative of the subducted plate limestones in tectonic blocks are of late triassic and probably jurassic ages and include 1 submarine cemented pelagic bivalve geopetal packstone grainstone 2 brachiopod bryozoan encrinite and 3 radiolarian pelagic lime mudstone most of the triassic blocks have been dated using conodonts which have remarkably low color alteration index cai values paleogeographic inferences drawn from megafossils bioclasts and radiolarians as well as from carbonate cements indicate deposition of the oceanic sedimentary rocks at paleolatitudes somewhat lower than that of the new zealand part of the gondwana margin but higher than paleoequatorial latitudes these oceanic sediments and their basaltic substrates were evidently emplaced in the torlesse accretionary prism following off scraping from an extensive subducting oceanic plate probably the phoenix plate which was obliquely convergent with the northwest trending gondwana margin during late jurassic and or early cretaceous time

variation of rock quality designation rqd with scanline orientation and length a case study in korea abstract rock quality designation rqd has been widely used to evaluate the degree of fracturing of rock masses although it has been frequently pointed out that rqd is dependent on the orientation of measurement and on the scanline length these effects have not been considered in site investigation for tunneling in korea therefore a series of practical examinations using in situ data collected from recent tunneling sites in korea has been conducted variation of rqd with scanline orientation was observed to be as high as 24 in the sub horizontal tunneling where the design was based on the results of rqd from vertical drill core logging in addition the range of possible variation of rqd with scanline length was analyzed with four different models including two new models introduced in this case study for the first time it is shown that at least 4 m of scanline length is required to maintain a reliable value for the rqd in the three models the simulation from the so called a a s model showed that it is possible to maintain the same reliability of the rqd in a situation where only a much smaller extent i e 0 4 m of rock exposure is available in the field it is hoped that the results of this case study will provide the tunnel engineer with an enhanced understanding of the variation of rqd with measurement method

resolution of the age structure of the detrital zircon populations of two lower cretaceous sandstones from the weald of england by fission track dating modes in the frequency of distribution of fission track ages obtained from detrital zircon grains may prove characteristic of individual sandstone bodies supporting the identification of the sources from which a particular flow of sedimentary detritus was derived and thus allowing new inferences to be made concerning palaeogeography a computer program has been written and used to identify modes in the zircon fission track age distribution within two lower cretaceous sandstone samples from the weald of southern england pronounced modes appear in one rock around 119 ma 160 ma 243 ma and 309 ma and in the other around 141 ma 175 ma 257 to 277 ma and 394 to 453 ma the geological implications of these quite dissimilar zircon age spectra are discussed it is concluded that they support the palaeogeographical models of allen 1981 and indicate that the provenance of the first sample from the top ashdown sandstone member at dallington in east sussex was almost entirely southerly while that of the second from the netherside sand member at northchapel in west sussex was more varied but predominantly westerly and northerly

the basal ice layer of glaciers and ice sheets abstract in many glaciers and ice sheets there is a basal ice layer bil in which the ice is conditioned primarily by processes operating at the bed the bil is chemically and physically distinctive and is characterised by a component of basally derived sediment the bil is a rheological control on ice sheet dynamics an indicator of subglacial conditions and processes an agent of subglacial geologic processes the source of a substantial proportion of glacial sediments a limit to the downward extension of the climate record from deep ice cores if debris characteristics of the bil are preserved in glacial sediments former glacier conditions can be inferred analysis of stable isotopes gas and cation composition ice crystallography debris composition and structural glaciology has elucidated many mechanisms for bil formation common elements can be identified from a range of locations key issues are entrainment of ice and debris from the bed formation of new ice metamorphism of existing ice in the bil and thickening of the bil by deformation a distinction can be made between basal ice formed by accretion of material from the bed stratified facies and basal ice formed by metamorphic processes within the ice close to the bed dispersed facies

modified rock mass classification system by continuous rating it is not the purpose of this paper to propose a new rock mass classification system but rather to improve the existing ones by incorporating some simple quantitative interpretations the geomechanics classification system of naturally fractured rock masses is modified to decrease personal judgement involved in its calculation instead of six parameters in the classical rock mass rating rmr system only five basic parameters are considered in the proposed system which are namely rock quality designation rqd value with the underlying frequency distribution function of intact lengths uniaxial or point load strength of intact rock material conditions of the most unfavorable joints groundwater condition and joint orientation classical lump rating system is replaced by continuous grading system which leaves no ambiguity for an inexperienced engineer in allocating grades based on quantitative field or laboratory measurements finally necessary charts are presented for obtaining straightforward design values concerning average stand up time and corresponding unsupported span of excavations in fractured rock mass cohesion as well as friction angle of the rock mass the continuous rmr system is very convenient for calculators or in writing computer software the proposed methodology reduces the scale of subjectivity and leads to a unique rock mass design value

comparison of quantified and chart gsi for four rock masses abstract this paper discusses the geological strength index gsi it provides data from four different rock masses to extend the case history offered by hoek et al 2013 in their paper that proposes to quantify gsi with rqd and the joint condition rating of rmr the correlation between the gsi assessed from its chart and the quantified gsi was found to be fair for the datasets from the four rock masses the hawkesbury sandstone and ashfield shale of sydney the greenland group greywacke and argillite of south island new zealand and the otago schist of south island new zealand the two methods produce data points that are generally within 10 of each other the exceptions are rock masses whose blockiness may not be captured well by rqd it is recommended that the quantified gsi approach be used to supplement and check the visually assessed chart gsi the authors also suggest different gsi values that may be needed to cater for different numerical methods

metamorphism and uplift of alpine schist in the franz josef fox glacier area of the southern alps new zealand geothermometry and geobarometry of 10 garnet oligoclase zone schists in the franz josef fox glacier area southern alps new zealand give temperatures ranging from 415 to 625 c and pressures from 5 2 to 9 2 kbar indicating a t p array of about 50 c kbar and inferred peak temperature conditions over a c 15 km thick section at depths between c 20 and 34 km the present day distribution of the schist samples implies that only about one third of the original crustal section is now exposed the garnet oligoclase zone schists represent the deeper part of a metamorphosed and deformed accretionary complex that was associated with late palaeozoic early mesozoic subduction along the gondwana continental margin partial uplift c 0 2 m ma and erosion of the complex during jurassic cretaceous times rangitata uplift was synchronous with d2 deformation and recrystallization as recorded by the p t array cenozoic kaikoura uplift and exhumation of the schist since c 30 ma to form the southern alps was associated with oblique slip movement on the alpine fault the present day position and steep eastward dip of isograds and d2 structures suggest considerable clockwise rotation during uplift associated with ductile attenuation and tectonic thinning by over two thirds of the original schist sequence largely due to simple shear along schistosity planes as the schist generally shows only incipient greenschist facies retrograde recrystallization an apparently complete although contracted prograde mineral sequence has been preserved by rapid uplift 5 km ma of hot rock and the effects of limited shear heating near the alpine fault

modelling the effect of arbitrary p t t histories on argon diffusion in minerals using the macargon program for the apple macintosh argon diffusion in mineral grains has been numerically modelled using p t t histories that may be relevant to multiply metamorphosed orogenic terranes and for rocks that have resided at high ambient temperatures in the earth s crust for long durations the macargon program1 generates argon concentration profiles in minerals assuming argon loss occurs via volume diffusion it can be run on an apple macintosh computer with arbitrary p t t histories used as input finite difference equations are used in the calculation of 40ar concentration profiles across individual diffusion domains the associated macspectrometer generates model spectra after a p t t history has been specified the form of model 40ar39ar apparent age spectra suggests that considerable caution needs to be exercised in the use of the closure temperature concept and in the interpretation of the significance of plateaux observed in many 40ar39ar apparent age spectra particularly in cases involving metamorphic rocks where complex p t t histories might apply although modelled spectra cannot be directly compared to experimentally determined 40ar39ar age spectra especially when hydrous phases are involved or in cases where loss of argon has not occurred via volume diffusion they do provide insight into theoretically expected age spectra for samples that have experienced complex p t t histories

using geochemical fingerprinting to determine transpressive fault movement history application to the new zealand alpine fault 1 geochemical fingerprinting of conglomerate clasts from depocenters adjacent to a strike slip fault and of source areas on the opposite side of the fault provides a method of determining fault movement history in instances where potential piercing points have been removed by erosion or buried in pull apart or down warp basins our example demonstrating this method is the neogene maruia basin adjacent to the new zealand alpine fault the on land australian pacific plate boundary which shows permian pelorus caples terrane offset by 480 km twenty six sandstone and schist conglomerate clasts from the maruia basin rappahannock group were analyzed for major elements and 18 trace elements by x ray fluorescence and compared to similar analyses from potential regional source areas significant source terranes the caples group and the torlesse terrane were identified both located southeast of the fault dextral movement on the fault provided a conveyor belt of material to the maruia basin first supplying at 11 5 ma caples sandstone then caples schist followed by torlesse schist from 9 5 ma which translates to an average neogene movement rate of 36 37 mm yr 1 the increase in metamorphic grade reflects accelerated exhumation of source rocks as they passed through a restraining bend adjacent to the maruia basin and from later regional uplift from a change in the australian pacific plate motion vector and more transpressive movement from 5 ma this robust method of geochemical fingerprinting could be readily applied to determining movement history of transpressive faults of other regions

a users guide to fission track dating calibration abstract misconceptions regarding the fission track dating method prompt the description of five handling procedures and the derivation of commonly used system calibrations problems of registration geometry inhomogeneous uranium distribution accumulated radiation damage and anisotropic etching largely invalidate all but the population and external detector methods and impose strict limitations upon even their routine application complexities of unique absolute thermal neutron dosimetry are illustrated by the calibration and use of the nbs pre irradiated glass srm 962 the 20 disparity in measured f decay constant values cannot be isolated from neutron fluence measurement and calibration frequently a calibration ratio f is evaluated against an age standard and then split into its component parts to illustrate this interdependence of f and zircon fission track ages in agreement with independent k ar ages are obtained by calculating the same track count data with each of the preferred values of f f 7 03 10 17 yr 1 and8 46 10 17 yr 1 together with appropriate selected neutron dosimetry schemes an alternative approach is presented formally relating unknown ages of samples to known ages of standards either by direct comparison of standard and sample track densities or by the repeated calibration of a glass against age standards practical recommendations are given for the reporting and critical assessment of fission track data

estimating the intensity of rock discontinuities this paper presents an approach for estimating the intensity of discontinuities and formulating intensity and orientation as a fracture tensor specifically the size distribution and the number of discontinuities are estimated first from which the fracture tensor is then derived discontinuity size distribution is inferred from the trace data sampled in circular windows by using a general stereological relationship between the true trace length distribution and the discontinuity diameter distribution assuming circular shaped discontinuities because the measured trace lengths are biased a method is proposed to estimate the true trace length distribution for circular window sampling circular window sampling has the advantage of automatically eliminating the orientation bias when estimating the true trace lengths a method is then presented with which the total number of discontinuities in an objective volume can be estimated from the number of discontinuities observed in normal size boreholes and using the inferred discontinuity diameter from the circular window sampling on the rock surface with the derived size distribution and number of discontinuities the intensity of discontinuities which is the total surface area of discontinuities per unit volume can then be calculated and included in a new definition of a fracture tensor an application of the approach to analyze simulated discontinuities produces satisfactory results