technical innovations and optimizations for intermediate ice core drilling operations the british antarctic survey in collaboration with laboratoire de glaciologie et geophysique de l environnement has in recent years successfully drilled to bedrock on three remote sites around the antarctic peninsula based on the experience from the multi season project at berkner island 948m depth 2002 05 we optimized the drill set up to better suit two subsequent single season projects at james ross island 363m depth 2008 and fletcher promontory 654m depth 2012 the adaptations as well as the reasons for them are discussed in detail and include a drill tent set up without a trench drilling without a borehole casing with a relatively low fluid column height and using a shorter drill these optimizations were aimed at reducing cargo loads and installation time while maintaining good core quality productivity and a safe working environment in addition we introduce a number of innovations ranging from a new lightweight cable tensioning device and drill head design to core storage and protection trays to minimize the environmental impact all the drill fluid was successfully recovered at both sites and we describe and evaluate this operation

the electrical resistivity of canada s lithosphere and correlation with other parameters contributions from lithoprobe and other programmes over the last 30 years through lithoprobe and other programmes modern high quality magnetotelluric mt measurements probing deep into the lithosphere and underlying asthenosphere have been made at over 6000 sites across canada in all provinces and territories except nova scotia some regions are well covered particularly alberta southern british columbia and western ontario whereas others remain poorly covered such as quebec and large swaths of nunavut prior publications from individual studies have added significantly to the wealth of canada s geoscience knowledge and have demonstrated that mt can contribute significantly to understanding of the tectonic processes that have shaped canada however to date no continent scale maps of lithospheric electrical parameters have been constructed from the extensive mt database herein we review the contributions made by the mt components of lithoprobe and present new continental scale maps of various electrical parameters at crustal and upper mantle

imaging of deep fluids in archaean crust despite the importance of aqueous fluids in tectonic metamorphic and magmatic activity in the earth s crust few techniques are available for directly observing their distribution at depth even in stable continental crust such observations as have been made electromagnetic deep sounding which by inference1 2 images saline fluids and super deep drilling3 suggest that fluids are present in varying amounts throughout the crust in direct conflict4 with the normal petrological inference of a very dry deep crust here we report the results of an unusually high resolution electromagnetic sounding method to image the deep electrical conductivity structure below a 30 km profile in ontario which crosses archaean lower crustal material of high metamorphic grade exposed by a proterozoic thrust fault the ivanhoe lake cataclastic zone the electrical resistivity image obtained shows embedded in very resistive crystalline crust two nearly continuous sub horizontal zones of enhanced electrical conductivity at depths of 2 3 and 5 6 km below this the commonly observed2 5 7 mid crustal rise in conductivity is seen at depths of 15 20 km the image does not correlate well with the structure inferred from surface geology suggesting that the transport and distribution of fluids was not strongly controlled by lithological boundaries or the thrust fault itself

proterozoic geochronologic and isotopic boundary in nw arizona u pb ages determined from zircon sphene and apatite in conjunction with pb isotopic analyses of alkali feldspar establish a regional geochronological framework and constrain the location of a major north trending proterozoic crustal boundary in northwestern arizona two regions west of the boundary hualapai mountains and lost basin range garnet mountain are characterized by complex u pb zircon systematics evidence for inheritance of an older zircon component 1 8 2 3 ga and elevated sup 207 pb sup 204 pb from feldspars compared to the east although the discordia patterns are complex supracrustal rocks are interpreted to be ca 1 73 ga and are intruded by plutonic rocks ca 1 70 ga deformation is younger than ca 1 70 ga foliated granites and older than the 1 682 plus minus 4 ma garnet mt monzogranite the rocks in one area east of the boundary cottonwood cliffs are characterized by relatively simple u pb zircon systematics no evidence for inheritance of any older component and feldspar sup 207 sup 204 pb near model mantle values supracrustal rocks are older than 1 73 ga as they are intruded by a 1 730 plus minus 9 ma foliated granodiorite timing of deformation is constrained by the late syn kinematic valentine granite dated at 1 713 plus minus 12 ma mineral ages indicate thatmore the rocks on either side of the boundary had different cooling histories and inferentially different uplift histories west of the boundary the cooling history is inferred from minerals separated from an amphibolite metamorphic zircon is 1 687 13 minus 8 ma sphene is 1 660 plus minus 5 ma hornblende has a sup 40 ar sup 39 ar age of 1 552 plus minus 5 ma and apatite has a u pb age of 1 520 plus minus 45 ma east of the boundary an amphibolite has sphene with an age of 1 670 plus minus 11 ma and apatite with an age of 1 630 plus minus 8 ma less

the conductivity of the crust and mantle beneath the kapuskasing uplift electrical anisotropy in the upper mantle summary kapuskasing uplift has been interpreted as an oblique cross section of up to 25km of crust and thus provides the opportunity to examine the properties of exposed mid to lower crustal material a magnetotelluric mt survey mapped a remarkably uniform upper crust and provided no evidence for upper crustal conductive zones that could be related to the often observed increase in mid and lower crustal conductivity the only shallow conductive anomaly is related to the ivanhoe lake cataclastic zone but its electrical signature does not appear to extend more than one kilometer in depth a regional apparent resistivity curve was determined from mt data and confirmed by subsequent controlled source electromagnetic surveys regional curves are essential for proper structural interpretation but are often difficult to determine because of electric field distortions the data show a decrease in resistivity at depths below 15 km which is typical of continental crust in many areas of the world there is a clear difference in orthogonal apparent resistivity and phase curves at periods greater than 10s which is most pronounced in a n65 e and n25 w coordinate frame two different models are proposed to explain the data the first consists of a conducting 2 d slab of approximately 50 km width in the lower crust and striking n65 e the strike direction is consistent with a number of regional structural trends but there is no other direct supporting evidence for it the second model invokes either micro or macro electrical anisotropy in the upper mantle there is considerable evidence for seismic anisotropy in the region the electrical anisotropy could be the result of preferential conduction along the c axis of olivine crystals hydrogen dissolved in the olivine lattice with preferential conduction along the a axis or possible alignment of dykes joints and faults in the upper mantle if the anisotropy is related to strain induced orientations of crystals or fabric it will provide evidence for the motions of the mantle associated with plate tectonics

a summary of electromagnetic studies on the abitibi grenville transect electromagnetic surveys on the abitibi grenville lithoprobe transect have elucidated a number of conductivity signatures that can be genetically linked to precambrian tectonic processes some major fault zones are moderately conductive possibly signalling graphite deposition from a mantle co2 flux along crust penetrating fault systems however conductive graphitic metasedimentary rocks characteristic of foreland basins are apparently absent from the transect area a weak inverse correlation between metamorphic grade and electrical conductivity was observed by following rock units across the grenville front into high grade equivalents within the parautochthonous belt a uniformly conductive mid crustal layer extends across the grenville front apparently without change in character the existence of this ubiquitous mid crustal conductor has been interpreted to mean that electrical conductivity is controlled by the present day pressure temperature and fluid saturation of the lower crust independent o

a controlled source time domain electromagnetic survey over an upthrust section of archean crust in the kapuskasing structural zone summary a pilot controlled source electromagnetic survey was conducted in the kapuskasing structural zone to test the application of the utem technique for determining the electrical conductivity structure of the earth s crust to depths of up to 10 km in general the data are consistent with the results of an earlier broadband magnetotelluric mt survey and indicate a quasi layered earth below a variable overburden zone with conductances between 0 1 and 0 5 s at some depth below 10 km conductivity appears to increase in agreement with the mt interpretation and provides confidence that the static shift of the mt data was corrected a weakly conductive layer located at depths greater than 2 km is possibly associated with a feature of the ivanhoe lake cataclastic zone ilcz a major fault zone along which up to 30 km of the earth s crust has been thrust to the surface there was no clear evidence in the utem data for a conductive zone extending to the proposed surface strike location of the ilcz a conductive anomaly at depths of 1 2 km may extend east of the present survey area and suggested that a subsequent utem survey must expand the coverage to the east

geometry of the kapuskasing structure from a lithoprobe pilot reflection survey a short 10 km pilot seismic reflection profile recorded in the kapuskasing structural zone near foleyet ontario reveals reflections with travel times of at least 5 0 s about 16 km depth an event dipping west from about 1 7 to 3 4 s probably corresponds to the ivanhoe lake cataclastic zone the true geologic dip on this boundary is calculated to be about 35 38 west northwest and is consistent with interpretations of this zone as a west dipping crustal scale thrust fault east dipping reflections are observed with longer travel times than the fault zone arrival and are likely from within the greenstone terrane of the abitibi subprovince

archean crust as revealed in the kapuskasing uplift superior province canada in the central superior province of the canadian shield a 120 km wide transition from the low grade michipicoten greenstone belt to the high grade kapuskasing structural zone represents an oblique section through some 20 km of archean crust uplifted along a northwest dipping thrust fault the restored vertical section through the upper and middle crust consists of three megalayers with undulating boundaries 1 0 to 25 km a high grade heterogeneous gneissic assemblage in part older than the upper supracrustal succession

magnetotelluric interpretation of crustal and mantle structure in the grenville province summary accurate determinations of depths and conductivities of electrical structures in shield regions are often difficult because of the inhomogeneity of the uppermost crust a magnetotelluric mt station bat in the grenville province of the precambrian shield in eastern canada has been in operation since 1975 for time dependency studies of electrical resistivity changes related to earthquakes the mt response of the station displays low skew with small to moderate anisotropy one dimensional inversion of the apparent resistivity and phase reveals two well defined conductors in the crust one at 10 km and the second at the base of the crust the latter has a resistivity less than 50 m these results are substantiated by three additional mt stations located up to 40 km distant data from other new mt stations and from stations previously published in the literature are compared with two dimensional computer model results and with the three dimensional analogue scale model results of dosso et al while additional data for periods less than 100 s would be desirable the results from a number of the mt stations are not inconsistent with a widespread occurrence of a conducting zone at the base of the crust in the grenville the inversion analysis also indicates the existence of a conductor at some depth greater than 100 km with a resistivity less than 30 m this may coincide with a seismic low velocity zone observed in the mantle under the canadian shield

petrophysical model of deep electrical conductors graphite lining as a source and its disconnection due to uplift petrophysical information including stress release data recently made available for low porosity 0 1 0 4 crystalline rocks has been used to develop a broken conductor model that may explain the origin of enhanced electrical conductivity of the intermediate to lower continental crusts of shields and its disappearance when the rocks are uplifted average pore size and pore density of their fluid flow paths are 0 1 0 4 m and 1 400 m respectively the model assumes that these paths are filled or lined with interconnected electrical conducting minerals such as graphite resulting in the rocks having resistivities as low as 40 to 800 m in situ graphite film thicknesses required to produce these resistivities are 5 20 nm 50 200 a the model also assumes that electrical conducting paths break up during uplift due to stress release resulting in a poorly conducting rock petrophysical data of granites and observations from deep drill holes suggest a porosity increase of the order of 3 from an uplift of 10 km or more however the newly formed pore space would fill with deposits or intruded material so that surface rock porosities would not be much larger than at depth electrical resistivities of rock samples containing disconnected grain boundary graphite presently exposed by the kapuskasing uplift of the canadian shield are in the range of 3000 12000 m for the direction of foliation these values are 10 100 times larger than the estimates for similar rocks containing interconnected graphite but are 10 100 times smaller than usually observed in the canadian shield for similar rocks absent of grain boundary graphite these observations are in good agreement with the results predicted by the broken conductor model for an uplift of 10 km or more if a gross linear relationship is assumed between crack porosity and uplift for the upper 10 km of the crust

perspectives for development of ice core drilling technology a discussion abstract more than 170 years ago louis agassiz one of the creators of glacial theory made his firstattempt to drill into the bed of unteraargletscher swiss alps since that time various systems forthermal and mechanical drilling have been designed especially for boring into ice and someconventional drill rigs been adopted for ice coring although contemporary ice drilling knowledge andtechniques are now familiar there remain many problems to be solved by advanced moderntechnology specific challenges related to improving old drilling methods and developing new emergingtechnologies include 1 identification of depth limitation of dry drilling 2 improvement of casing 3 searching for the new environmentally friendly low temperature drilling fluids 4 reliableelimination of sticking drills 5 improvement of core quality in the brittle zone 6 additional coresampling from borehole walls after the core has been drilled 7 obtaining oriented core 8 designingautomation drilling systems 9 developing rapid access drills possible ways of solving these problemsare presented below keywords

a magnetotelluric survey over the east bull lake gabbro anorthosite complex tensor and scalar magnetotelluric and audiomagnetotelluric mt amt data have been acquired on a gabbro anorthosite pluton in northern ontario about 100 km west of sudbury the scalar data from 102 sites were used to map resistivity contrasts associated with near surface geology and overburden data from stations located away from possible geological inhomogeneities provided a structural interpretation which was subsequently confirmed by tensor mt soundings and by drilling the scalar data also provided a means of interpreting the bedrock structure associated with a major fault that bisects the pluton the apparent resistivity curves from the eight tensor stations ranged from nearly isotropic to strongly anisotropic with large shifts in apparent resistivity between the different locations however the measured impedances both modulus and phase strongly reflected the predominant northwest southeast trend of faulting and diabase dykes in the region modelling indicates the presence of an anisotropic subhorizontal conducting layer beginning at a depth of about 800 m the direction of fluid transport within this layer is expected to be parallel to the structural trends and to the e polarization axis of the impedance tensor the presence of this conductor has been confirmed by borehole resistivity measurements a conductive zone in the lower crust has also been detected commencing at a depth of about 18 km finally the tensor measurements at the longest periods are consistent with an increase in conductivity in the upper mantle suggesting the existence of an electrically conducting asthenosphere in this part of the canadian shield

reconnaissance electromagnetic induction study of the kapuskasing structural zone implications for lower crustal conductivity abstract a large scale electromagnetic induction study has been carried out over the kapuskasing structural zone ksz an upthrust section of lower crustal rocks in north central ontario the absence of an overall anomalous response from the ksz even though the lower crust in this region of the canadian shield is known to be anomalously conductive implies that enhanced lower crustal conductivity is related to intrinsic conditions at lower crustal depths and not to mineralogical composition

deep crustal structure and tectonic history of the northern kapuskasing uplift of ontario an integrated petrological geophysical study the northeast trending kapuskasing uplift transects the east west belts of the central superior province over a distance of some 500 km granulite to upper amphibolite facies rocks of the uplift form three distinct geological geophysical entities from south to north the chapleau groundhog river and fraserdale moosonee blocks uplift of the granulites along a moderately northwest dipping crustal scale thrust fault is attributed to an early proterozoic compressional event major northeast striking faults that bound the kapuskasing zone on the west were examined by modelling of geophysical anomalies to determine dip and by geobarometry of garnet orthopyroxene plagioclase quartz assemblages to determine vertical displacement granulites in the kapuskasing zone have 7 to 9 kbar signatures whereas those in the quetico belt to the west indicate metamorphic pressure of 4 6 kbar individual calibrations of the barometer yield consistent pressure differences of 2 3 kbar suggesting 7 10 km of west side down movement on the faults modelling of gravity and aeromagnetic gradients indicates westerly dips of 60 65 with west side down offset of up to 14 km these major normal faults probably formed as collapse structures in response to crustal thickening which occurred during the preceding compressional uplift stage differences in the configuration of individual blocks of the kapuskasing zone can be related to variable fault slip and intersection angles between normal and reverse faults thus the groundhog river and southern fraserdale moosonee blocks are perched thrust tips analogous to the sangre de cristo range of the laramide uplift province whereas the southern chapleau block is a tilted slab with similar configuration to the laramide wind river range pop up geometry deduced for the northern fraserdale moosonee block resembles the structure of the laramide uinta mountains a normal fault crosses the surface trace of the basal thrust fault between the groundhog river and fraserdale moosonee blocks and causes a 65 km gap without granulites this article contains supplementary material