Missing lawsonite found ! Resolving paradoxes of the metamorphic structure of the Western Alps

2021 ◽  
Author(s):  
Paola Manzotti ◽  
Michel Ballèvre ◽  
Pavel Pitra ◽  
Federica Schiavi
Keyword(s):  
Subduction Zones ◽  
Large Scale ◽  
Carbonaceous Material ◽  
Western Alps ◽  
Material Point ◽  
Ductile Deformation ◽  
Lower Grade ◽  
External Domain ◽  
Zone Field ◽  
Low X

<p>Lawsonite is a strongly hydrated (12 weight % H<sub>2</sub>O) Ca- and Al-rich silicate, exclusively stable along low P/T gradients, typical of subduction zones. The distribution and preservation of lawsonite at the scale of a subduction/collision belt reflect the occurrence of rocks with favourable chemical composition (mainly hydrothermally altered metabasalts and marly limestones (i.e. calcschists), two lithologies especially common in the oceanic units) and their pressure-temperature-fluid history (with preservation favoured by decreasing T during decompression).</p><p>The distribution of lawsonite in the Western Alps has been investigated since several decades. In the blueschist-facies units from the South-Western Alps (Queyras, Ubaye), lawsonite is well preserved in the external domain, at the contact with the Briançonnais domain, but is largely pseudomorphed in the more internal domain, at the contact with the Viso Unit. Further North, neither lawsonite nor lawsonite pseudomorphs have been reported in the supposedly blueschist-facies Combin Zone, taken by most studies as an equivalent of the Queyras-Ubaye units. This constitutes a paradox with respect to the overall metamorphic structure of the Alpine belt.</p><p>This study documents for the first time several occurrences of lawsonite and garnet in the calcschists from the Combin Zone. Field and metamorphic data (thermodynamic modelling and Raman spectroscopy on carbonaceous material) point to the occurrence of two tectonometamorphic units within the Combin Zone, characterised by distinct geometry, lithological content and Alpine P-T conditions.</p><p>In the higher grade unit, lawsonite and garnet were stable at peak P-T conditions (~14-16 kbar and ~460-490 °C) at very low X(CO<sub>2</sub>) values. Although lawsonite is systematically pseudomorphed, we have been able to recognize hourglass zoning in lawsonite or preservation of an internal fabric associated with the prograde ductile deformation.</p><p>The lower grade unit (~8 ± 1 kbar ~370-400 °C) is discontinuously exposed along the western base of the Dent Blanche nappe and records Alpine P-T conditions similar to those reached by the Dent Blanche nappe (Manzotti et al. 2020).</p><p>Our data show that lawsonite is not missing in the Combin Zone, and resolve a paradox about the large-scale metamorphic structure of the Alps.</p><p> </p><p>Manzotti, P., Ballèvre, M., Pitra, P., Müntener, O., Putlitz, B., Robyr, M. (2020). Journal of Petrology, egaa044, https://doi.org/10.1093/petrology/egaa044.</p>

scholarly journals Missing lawsonite and aragonite found: P–T and fluid composition in meta-marls from the Combin Zone (Western Alps)

2021 ◽  
Vol 176 (8) ◽  
Author(s):  
Paola Manzotti ◽  
Michel Ballèvre ◽  
Pavel Pitra ◽  
Federica Schiavi
Keyword(s):  
Raman Spectroscopy ◽  
Large Scale ◽  
Carbonaceous Material ◽  
Western Alps ◽  
Thermodynamic Modelling ◽  
The Other ◽  
Ductile Deformation ◽  
Fluid Composition ◽  
Lower Grade ◽  
The One

AbstractWe report the first findings of several occurrences of lawsonite and metamorphic aragonite in the meta-sediments from the Combin Zone (Piemonte–Liguria ocean, Western Alps), where the early blueschist-facies episode is poorly documented. New field and metamorphic data (thermodynamic modelling and Raman spectroscopy on carbonaceous material) are used to elucidate the P–T evolution and fluid composition of the Combin Zone and investigate the lawsonite growth and breakdown reactions. Two tectonometamorphic units have been identified within the Combin Zone with distinct geometry, lithological content and P–T conditions. In the higher grade unit, metamorphic aragonite occurs as inclusions in titanite. Lawsonite and garnet were stable at peak P–T conditions (~ 16–17 kbar and 460–480 °C) at very low X(CO2) values. Lawsonite is systematically pseudomorphed, but preserves hourglass zoning or internal fabric associated with the prograde ductile deformation. The lower grade unit (~ 8 ± 1 kbar ~ 370–400 °C) is discontinuously exposed along the western base of the continental Dent Blanche nappe and records P–T conditions similar to those recorded by the Dent Blanche nappe. A metamorphic discontinuity is, therefore, documented between the largest part of the Combin Zone on the one hand, and the Dent Blanche nappe on the other hand. The discovery of lawsonite and metamorphic aragonite allows a better understanding of the large-scale metamorphic structure of the Western Alps.

Structural and metamorphic evolution of the Ambin massif (western Alps): toward a new alternative exhumation model for the Briançonnais domain

2007 ◽  
Vol 178 (6) ◽  
pp. 437-458 ◽  
Author(s):  
Jerome Ganne ◽  
Jean-Michel Bertrand ◽  
Serge Fudral ◽  
Didier Marquer ◽  
Olivier Vidal
Keyword(s):  
Tectonic Evolution ◽  
Large Scale ◽  
Regional Scale ◽  
Shear Bands ◽  
Shear Zones ◽  
Western Alps ◽  
Ductile Deformation ◽  
Movement Direction ◽  
Lower Grade ◽  
Structural Investigations

Abstract The basement domes of the central part of western Alps may result either from a multistage tectonic evolution with a dominant horizontal shortening component, an extensional behaviour, or both. The Ambin massif belongs to the “Briançonnais” domain and is located within the HP metamorphic zone. It was chosen for a reappraisal of the tectonic evolution of the Internal Alps in its western segment. Structural investigations have shown that Alpine HP rocks were exhumed in three successive stages. The D1 stage was roughly coeval with the observed peak metamorphic conditions and corresponds to a non-coaxial regime with dominant horizontal shortening and north movement direction. Petrological observations and P-T estimates show that the exhumation process was initiated during D1, the corresponding mechanism being still poorly understood. The D2 stage took place under low-blueschist facies conditions and culminated under greenschist facies conditions. It developed a retrogressive foliation and pervasive shear-zones at all scales that locally define major tectonic contacts. D2 shear zones show a top-to-east movement direction and correspond actually to large-scale detachment faults responsible for the juxtaposition of less metamorphic units above the Ambin basement and thus to a large part of the exhumation of HP rocks toward the surface. D2 shear zones were subsequently deformed by D3 open folds, large antiforms (e.g. the Ambin dome) and associated brittle-ductile D3 shear-bands. The D1 to D3 P-T conditions and P-T path of the blueschists occurring in the deepest part of the Ambin dome, was estimated by using the multi-equilibrium thermobarometric method of the Tweeq and Thermocalc softwares. Peak pressure conditions, estimated at about 14–16 Kb, 500oC, are followed by a nearly-isothermal decompression that occurred concurrently with the major D1–D2 change in the ductile deformation regime. Eastwards, the Schistes Lustrés units exhibit a similar geometry on top of the Gran Paradiso dome but exhibit opposite D2 movement direction. Lower-grade units are lying above higher-grade units, the shear zones occurring in between being similar to Ambin’s D2 detachments. Thus at regional scale, the D2 detachments seem to form together with the Ambin shear-zones, a network of conjugate detachments. Such a pattern suggests that the exhumation history is mostly controlled by a D2+D3 crustal-scale vertical shortening resulting in the thinning of the previous tectonic pile formed during D1. The slab-break off hypothesis may explain such an extensional behaviour within the western Pennine domain. It is suggested that the thermo-mechanical rebound of the residual European slab initiated between 35 and 32 Ma the fast exhumation of the previously thickened orogenic wedge (stack of D1 HP slices). It was immediately followed by a collapse of the wedge that may correspond to the E-W Oligocene extensional event responsible for the opening of rifts in the West European platform.

Magnetite (U-Th-Sm)/He dating: analytical challenges and application

2021 ◽  
Author(s):  
Marianna Corre ◽  
Martine Lanson ◽  
Arnaud Agranier ◽  
Stephane Schwartz ◽  
Fabrice Brunet ◽  
...  
Keyword(s):  
Laser Ablation ◽  
Subduction Zones ◽  
Major Elements ◽  
Western Alps ◽  
Planetary Science ◽  
Mantle Xenoliths ◽  
Transform Faults ◽  
Geological Processes ◽  
History Of ◽  
Geochronological Constraints

<p>Magnetite (U-Th-Sm)/He dating method has a strong geodynamic significance, since it provides geochronological constraints on serpentinization episodes, which are associated to important geological processes such as ophiolite obductions, subduction zones, transform faults and fluid circulations. Although helium content that range from 0.1 pmol/g to 20 pmol/g can routinely be measured, the application of this dating technique however is still limited due to major analytical obstacles. The dissolution of a single magnetite crystal and the measurement of the U, Th and Sm present at the ppb level in the corresponding solution, remains highly challenging, especially because of the absence of magnetite standard. In order to overcome these analytical issues, two strategies have been followed, and tested on magnetite from high-pressure rocks from the Western Alps (Schwartz et al., 2020). Firstly, we purified U, Th and Sm (removing Fe and other major elements) using ion exchange columns in order to analyze samples, using smaller dilution. Secondly, we performed in-situ analyzes by laser-ablation-ICPMS. Since no solid magnetite certified standard is yet available, we synthetized our own by precipitating magnetite nanocrystals. The first quantitative results obtained by LA-ICP-MS using this synthetic material along with international glass standards, are promising. The laser-ablation technique overcomes the analytical difficulties related to sample dissolution and purification. It thus opens the path to the dating of magnetite (and also spinels) in various ultramafic rocks such as mantle xenoliths or serpentinized peridotites in ophiolites.</p><p>Schwartz S., Gautheron C., Ketcham R.A., Brunet F., Corre M., Agranier A., Pinna-Jamme R., Haurine F., Monvoin G., Riel N., 2020, Unraveling the exhumation history of high-press ure ophiolites using magnetite (U-Th-Sm)/He thermochronometry. Earth and Planetary Science Letters 543 (2020) 116359.</p>

3-D Qp and Qs Seismic Attenuation for the Central Alps and their Foreland

2021 ◽  
Author(s):  
Federica Lanza ◽  
Tobias Diehl ◽  
Donna Eberhart-Phillips ◽  
Marco Herwegh ◽  
Donat Fäh ◽  
...  
Keyword(s):  
Large Scale ◽  
Hot Springs ◽  
Western Alps ◽  
Seismic Attenuation ◽  
Upper Crust ◽  
Central Alps ◽  
Northern Switzerland ◽  
High Q ◽  
Velocity Models ◽  
Q Model

<p>In the framework of the SeismoTeCH project, which aims at advancing our understanding of seismotectonic processes in Switzerland, we present the first 3-D attenuation model of the upper crust for the Central Alps and their northern foreland. The 3-D inversions derive the quality factor Q (1/attenuation) using path attenuation t<sup>∗</sup> observations for 4,192 distributed earthquakes recorded on permanent and temporary stations, including both velocity and acceleration records for the period 2002-2019. We followed a procedure of gradational inversions, in which a series of inversions with increasingly grid complexity are performed, with the goal of obtaining a useful Q model everywhere despite the varied data distribution. The Qs and Qp results show large-scale features in the upper crust, which are consistent with a recently improved high-resolution velocity models of the same region and serve to refine the interpretations of crustal structures from Vp and Vp/Vs. For example, the foreland region of southern Germany and northern Switzerland show a low Q crustal block bounded by high Q regions in the uppermost layer between -2.5 and 2.0 km depth. This markedly correlates with the overlying surface geology, where low Q areas coincide with the Molasse Basin, and the transition between low and high Q regions outline the geological boundary between the Molasse and the Mesozoic sediments towards north and the Alpine front to the south. At depths ranging between 2.0 - 6.5 km, low Q is imaged along the Rhone valley in the Valais in southwest Switzerland. This region presents the transition between the Centrals and Western Alps and hosts the presently seismically most active fault zones. As the attenuation of fractured areas is enhanced by fluids, low Q values may relate here to distributed microfractures that produce greater fracture connectivity and permeability in a relatively higher strain-rate zone. These geophysical constraints seem to support crustal scale fluid flow along fracture networks as manifest by the prominent occurrence of hot springs in this area. On the other hand, the moderate-to-high Qs and Qp (400-800) along with low Vp/Vs ratio and high Vs observed in the external Aar Massif could be indicative of metamorphic processes leading to different Vp/Vs ratios compared to the basement in the northern foreland (Black Forest Massif), and possibly image the continuation of the massif 20-30 km further to the northeast. In combination with recently developed Vp and Vs velocity models, the developed 3-D attenuation models provide additional constraints in terms of composition and physical properties of the uppermost crust of the central Alps as well as crucial input for next generation seismic hazard models of Switzerland, allowing for a more realistic prediction of earthquake related ground motions.</p>

scholarly journals A fast and efficient MATLAB-based MPM solver: fMPMM-solver v1.1

2020 ◽  
Vol 13 (12) ◽  
pp. 6265-6284
Author(s):  
Emmanuel Wyser ◽  
Yury Alkhimenkov ◽  
Michel Jaboyedoff ◽  
Yury Y. Podladchikov
Keyword(s):  
Cantilever Beam ◽  
Large Scale ◽  
Solid Mechanics ◽  
Large Deformations ◽  
Material Point ◽  
Snow Avalanches ◽  
High Level Language ◽  
Numerical Accuracy ◽  
Computational Performance ◽  
High Level

Abstract. We present an efficient MATLAB-based implementation of the material point method (MPM) and its most recent variants. MPM has gained popularity over the last decade, especially for problems in solid mechanics in which large deformations are involved, such as cantilever beam problems, granular collapses and even large-scale snow avalanches. Although its numerical accuracy is lower than that of the widely accepted finite element method (FEM), MPM has proven useful for overcoming some of the limitations of FEM, such as excessive mesh distortions. We demonstrate that MATLAB is an efficient high-level language for MPM implementations that solve elasto-dynamic and elasto-plastic problems. We accelerate the MATLAB-based implementation of the MPM method by using the numerical techniques recently developed for FEM optimization in MATLAB. These techniques include vectorization, the use of native MATLAB functions and the maintenance of optimal RAM-to-cache communication, among others. We validate our in-house code with classical MPM benchmarks including (i) the elastic collapse of a column under its own weight; (ii) the elastic cantilever beam problem; and (iii) existing experimental and numerical results, i.e. granular collapses and slumping mechanics respectively. We report an improvement in performance by a factor of 28 for a vectorized code compared with a classical iterative version. The computational performance of the solver is at least 2.8 times greater than those of previously reported MPM implementations in Julia under a similar computational architecture.

3D linked megathrust, dynamic rupture and  tsunami propagation and inundation modeling:  Dynamic effects of supershear and tsunami earthquakes 

2021 ◽  
Author(s):  
Sara Aniko Wirp ◽  
Alice-Agnes Gabriel ◽  
Elizabeth H. Madden ◽  
Maximilian Schmeller ◽  
Iris van Zelst ◽  
...  
Keyword(s):  
Subduction Zones ◽  
Large Scale ◽  
Dynamic Models ◽  
Initial Conditions ◽  
Poisson Ratio ◽  
Fault Slip ◽  
Moment Magnitude ◽  
Dynamic Rupture ◽  
S Wave ◽  
Tsunami Propagation

<p>Earthquake rupture dynamic models capture the variability of slip in space and time while accounting for the structural complexity which is characteristic for subduction zones. The use of a geodynamic subduction and seismic cycling (SC) model to initialize dynamic rupture (DR) ensures that initial conditions are self-consistent and reflect long-term behavior. We extend the 2D geodynamical subduction and SC model of van Zelst et al. (2019) and use it as input for realistic 3-dimensional DR megathrust earthquake models. We follow the subduction to tsunami run-up linking approach described in Madden et al. (2020), including a complex subduction setup along with their resulting tsunamis. The distinct variation of shear traction and friction coefficients with depth lead to realistic average rupture speeds and dynamic stress drop as well as efficient tsunami generation. </p><p>We here analyze a total of 14 subduction-initialized 3D dynamic rupture-tsunami scenarios. By varying the hypocentral location along arc and depth, we generate 12 distinct unilateral and bilateral earthquakes with depth-variable slip distribution and directivity, bimaterial, and geometrical effects in the dynamic slip evolutions. While depth variations of the hypocenters barely influence the tsunami behavior, lateral varying nucleation locations lead to a shift in the on-fault slip which causes time delays of the wave arrival at the coast. The fault geometry of our DR model that arises during the SC model is non-planar and includes large-scale roughness. These features (topographic highs) trigger supershear rupture propagation in up-dip or down-dip direction, depending on the hypocentral depth.</p><p>In two additional scenarios, we analyze variations in the energy budget of the DR scenarios. In the SC model, an incompressible medium is assumed (ν=0.5) which is valid only for small changes in pressure and temperature. Unlike in the DR model where the material is compressible and a different Poisson’s ratio (ν=0.25) has to be assigned. Poisson’s ratios between 0.1 and 0.4 stand for various compressible materials. To achieve a lower shear strength of all material on and off the megathrust fault and to facilitate slip, we increase the Poisson ratio in the DR model to ν=0.3 which is consistent with basaltic rocks. As a result, larger fault slip is concentrated at shallower depths and generates higher vertical seafloor displacement and earthquake moment magnitude respectively. Even though the tsunami amplitudes are much higher, the same dynamic behavior as in the twelve hypocenter-variable models can be observed. Lastly, we increase fracture energy by changing the critical slip distance in the linear slip-weakening frictional parameterization. This generates a tsunami earthquake (Kanamori, 1972) characterized by low rupture velocity (on average half the amount of s-wave speed) and low peak slip rate, but at the same time large shallow fault slip and moment magnitude. The shallow fault slip of this event causes the highest vertical seafloor uplift compared to all other simulations. This leads to the highest tsunami amplitude and inundation area while the wavefront hits the coast delayed compared to the other scenarios.</p>

scholarly journals Crustal reworking and hydration: insights from element zoning and oxygen isotopes of garnet in high-pressure rocks (Sesia Zone, Western Alps)

2020 ◽  
Vol 175 (11) ◽  
Author(s):  
Vho Alice ◽  
Rubatto Daniela ◽  
Lanari Pierre ◽  
Giuntoli Francesco ◽  
Regis Daniele ◽  
...  
Keyword(s):  
Oxygen Isotopes ◽  
Subduction Zones ◽  
Sea Water ◽  
Fluid Flows ◽  
Western Alps ◽  
Garnet Growth ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
Chemical Zoning ◽  
Dehydration Reactions

Abstract Subduction zones represent one of the most critical settings for fluid recycling as a consequence of dehydration of the subducting lithosphere. A better understanding of fluid flows within and out of the subducting slab is fundamental to unravel the role of fluids during burial. In this study, major and trace element geochemistry combined with oxygen isotopes were used to investigate metasediments and eclogites from the Sesia Zone in order to reconstruct the effect of internal and external fluid pulses in a subducted continental margin. Garnet shows a variety of textures requiring dissolution–precipitation processes in presence of fluids. In polycyclic metasediments, garnet preserves a partly resorbed core, related to pre-Alpine high-temperature/low-pressure metamorphism, and one or multiple rim generations, associated with Alpine subduction metamorphism. In eclogites, garnet chemical zoning indicates monocyclic growth with no shift in oxygen isotopes from core to rim. In metasediments, pre-Alpine garnet relics show δ18O values up to 5.3 ‰ higher than the Alpine rims, while no significant variation is observed among different Alpine garnet generations within each sample. This suggests that an extensive re-equilibration with an externally-derived fluid of distinct lower δ18O occurred before, or in correspondence to, the first Alpine garnet growth, while subsequent influxes of fluid had δ18O close to equilibrium. The observed shift in garnet δ18O is attributed to a possible combination of (1) interaction with sea-water derived fluids during pre-Alpine crustal extension and (2) fluids from dehydration reactions occurring during subduction of previously hydrated rocks, such as the serpentinised lithospheric mantle or hydrated portions of the basement.

Geometry of the allochthonous Daly Bay Complex, Northwest Territories: a model constrained by geology and a three-dimensional gravity interpretation

1995 ◽  
Vol 32 (9) ◽  
pp. 1292-1302
Author(s):  
Terence M. Gordon ◽  
Donald C. Lawton
Keyword(s):  
Three Dimensional ◽  
Outer Part ◽  
Complex Form ◽  
Granulite Facies ◽  
Ductile Deformation ◽  
Lower Grade ◽  
Crustal Material ◽  
Tectonic Event ◽  
Granulite Facies Metamorphism ◽  
Dimensional Gravity

The Daly Bay Complex is one of several metamorphic complexes making up the Aqxarneq gneisses north of Chesterfield Inlet in central District of Keewatin. Granulite-facies metamorphism (0.55 GPa, 750 °C) and ductile deformation have affected all of the rocks in the complex. A 1–15 km wide, inward-dipping, ductile shear zone forms the outer part of the complex and contains strongly deformed equivalents of rocks in the core. Mesoscopic structures and metamorphic mineralogy suggest the Daly Bay Complex was emplaced into the surrounding lower grade rocks by northward-directed thrusting. A three-dimensional gravity model, constrained by structural observations and 1091 surface density measurements, shows that the relatively dense rocks of the complex form a spoon-shaped structure with a long axis trending northwest–southeast. It is approximately 50 km by 120 km in lateral extent and reaches a maximum depth of about 9 km. The thin-skinned geometry of the Daly Bay Complex supports the notion that the crust in central Keewatin between the Daly Bay Complex and Baker Lake comprises a series of undulating imbricated gneiss sheets of middle and lower crustal material, which were juxtaposed by a major tectonic event sometime between 2.5 and 1.9 Ga. The interpreted basal décollement is comparable to seismic features in many orogens, and a predictable consequence of increased ductility with depth in the crust.

A Brief Review of Abrasive Wear Modelling Using a Numerical-Experimental Approach

2019 ◽  
Vol 799 ◽  
pp. 83-88
Author(s):  
Ewald Badisch ◽  
Markus Varga ◽  
Stefan J. Eder
Keyword(s):  
Abrasive Wear ◽  
Wear Mechanisms ◽  
Large Scale ◽  
Scratch Test ◽  
Industrial Applications ◽  
Material Point ◽  
Field Application ◽  
Wear Rates ◽  
Wear Modelling ◽  
Free Material

Abrasive wear limits the lifetime of key components and wear parts used in various applications. Damage is caused by indentation of harder particles into the wearing materials and subsequent relative motion resulting in ploughing, cutting, and fracture phenomena. The wear mechanisms depend mainly on the applied materials, loading conditions, and abrasives present in the tribosystem, hence material choice is often a difficult task and requires careful evaluation. For this, a variety of laboratory abrasion tests are available of which the scratch test is discussed in this work as the most fundamental abrasive interaction. For further insight into the acting wear mechanisms and microstructural effects, large-scale molecular dynamics simulations were carried out as well as meso-/macroscopic scratch simulations with the mesh-free Material Point Method. The prediction of abrasive wear is of high relevance for industrial applications. Up to now, no general one-to-one match between field application and lab system is known. Here, a simulation-based transfer of experimentally determined wear rates via a lab-2-field approach enables the prediction of wear rates in real applications.

scholarly journals Triaxial experiments on iceberg and glacier ice

1995 ◽  
Vol 41 (139) ◽  
pp. 528-540 ◽  
Author(s):  
R. E. Gagnon ◽  
P. H. Gammon
Keyword(s):  
Large Scale ◽  
Freezing Point ◽  
Shear Plane ◽  
Confining Pressure ◽  
Ductile Deformation ◽  
Dominant Factor ◽  
Stick Slip ◽  
Glacier Ice ◽  
Confining Pressures ◽  
The Mean

Abstract Triaxial experiments, at confining pressures in the range 0–13.79 MPa, have been performed on glacial ice collected from four icebergs and one glacier. Tests were conducted at strain rates in the range of 5 × 10−5 to 5 × 10−5s−1 and at four temperatures in the range of −1° to −16°C. Depending on test conditions, the ice failed by one of four possible modes ductile deformation, due to extensive non-interacting microcracks; fracture along a shear plane followed by continuous or stick-slip sliding; large-scale brittle fracture; and combined ductile and shear-plane fracture and slip The strength Increased with decreasing temperature, increasing strain rate up to 5 × 10−3s−1 and increasing confining pressure at the lower temperatures. The strength at 5 × 10−2s−1 was lower than at 5 × 10−3s−1 probably because extension and interaction of microcracks is enhanced at the higher rate. For higher confining pressures at −1°C, the strength decreased due to freezing-point depression. The ice from the different sources exhibited different mean uniaxial compressive strengths. The mean number of air bubbles per unit volume correlated with the mean uniaxial compressive strengths and this may be the dominant factor distinguishing the strengths of the various ice types.

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