Fractures occur in nearly all rocks at the Earth’s surface and exert essential control on the mechanical strengths of rock masses and permeability.The fractures strongly impact the stability of geological or man-made...Fractures occur in nearly all rocks at the Earth’s surface and exert essential control on the mechanical strengths of rock masses and permeability.The fractures strongly impact the stability of geological or man-made structures and flow of water and hydrocarbons,CO_(2) and storing waste.For this,the dependence of opening mode fracture spacing(s)on bed thickness(t)in sedimentary basins(reservoirs)is studied in this context.This paper shows that the MichaeliseMenten equation can provide an algebraic expression for the nonlinear s-t relationship.The two parameters have clear geological meanings:a is the maximum fracture spacing which can no longer increase with increasing t,and b is the characteristic bed thickness when s=0.5a.The tensile fracture strength(C)of the brittle beds during the formation of tensile fractures can be estimated from the two parameters.For sandstones of 16 areas reported in the literature,C ranges from 2.7 MPa to 15.7 MPa with a mean value of 8 MPa,which lies reasonably within the range of tensile strengths determined experimentally.This field-based approach by means of MichaeliseMenten equation provides a new method for estimating the tensile fracture strength of rock layers under natural conditions.展开更多
Vertical orthogonal joints are a common feature in shallow crustal rocks.There are several competing theories for their formation despite the ubiquity.We examined the exceptional exposures of orthogonal joints in flat...Vertical orthogonal joints are a common feature in shallow crustal rocks.There are several competing theories for their formation despite the ubiquity.We examined the exceptional exposures of orthogonal joints in flat-lying Ordovician limestone beds from the Havre-Saint-Pierre Region in Quebec,Canada(north shore of Saint-Lawrence River)to test conceptual models of joint formation in a natural setting.In the region,the spacing of cross-joints is consistently larger than the spacing of systematic joints by a factor of 1.5 approximately.The joint-spacing-to-bed-thickness ratios(s/t)are much larger in these beds(s/t=4.3 for systematic joints,and 6.4 for cross-joints)than those in higher strained strata along the south shore of the Saint-Lawrence River(s/t=1),highlighting the effect of tectonic strain in decreasing fracture spacing and block size.The high values of s/t indicate that cross-joint formation was unlikely caused by a switch from compression to tension once a critical s/t ratio for systematic joints was reached(as hypothesized in previous studies).We proposed a new model for the formation of orthogonal joint systems where the principal stress axes locally switch during the formation of systematic fractures.The presence of ladder-shaped orthogonal joints suggests a state of effective stress withσ_(1)^(∗)≫0>σ_(2)^(∗)>σ_(3)^(∗)and whereσ_(2)^(∗)-σ_(3)^(∗)is within the range of fracture strength variability at the time of fracture.This research provides a new mechanical model for the formation of orthogonal joint systems and cuboidal blocks.展开更多
Two vertical and orthogonal systematic joint sets are generally arrayed in a grid pattern on the bedding surface,which are the significant features of flat-lying sandstone terrains.Although extensive researches are re...Two vertical and orthogonal systematic joint sets are generally arrayed in a grid pattern on the bedding surface,which are the significant features of flat-lying sandstone terrains.Although extensive researches are reported on this topic,many fundamental problems have still not been solved.Such mutually perpendicular opening-mode fractures are an obvious manifestation of effective tensile stresses in two orthogonal directions in the horizontal bedding plane.A good understanding of these orthogonal joint systems is a key to structural analysis,landscape interpretation,and guidance of resolving a number of very practical problems in engineering,mining and hydrologic projects.Based on an anatomic investigation on the orthogonal joints in the Potsdam sandstone of Cambrian age at Ausable Chasm(New York State,USA)and Beauharnois(Quebec,Canada),we proposed that the orthogonal joints may result from the auxetic effects of quartz-rich sandstone rather than local or regional rotation of the maximum tensile stress(σ_(3))direction by about 90°.The sandstone beds with negative Poisson's ratios are so fascinating that,when placed under vertical burial compression and layer-parallel extension in one direction(σ_(3)),it becomes stretched in the transverse direction(σ_(2)),producing two orthogonal sets of mutual abutting and intersecting joints(J1 and J2 normal toσ_(3) andσ_(2),respectively),and both are normal to the bedding surface.Joint set J1 is more closely-spaced than J2 by a factor of∼3.3,which is correlated with an average Poisson's ratio of−0.3 for the Potsdam sandstone at the time of joint formation.展开更多
Although the Indus-Tsangpo Suture(ITS) is the most spectacular thrust system of continent-continent collision in the world, fundamental questions about its strength evolution and deformation behavior transition remain...Although the Indus-Tsangpo Suture(ITS) is the most spectacular thrust system of continent-continent collision in the world, fundamental questions about its strength evolution and deformation behavior transition remain unanswered. Here we reported, for the first time, frictional melting-induced pseudotachylytes in the intensively deformed felsic rocks along the ITS zone in southern Tibet. This study reveals that pseudotachylytes induced profound weakness of the boundary fault between Indian and Asian plates. The intrinsically low strength of the foliated microlites crystallized from frictional melt or glass(i.e., pseudotachylyte) at seismogenic depths compared with the surrounding coarse-grained quartzofeldspathic rocks in the brittle and semi-brittle regime is sufficient to explain the localization of shear strain, the development of ductile shear zones embedded in strong wall rocks, and the transition from the strong to weak fault behaviors without invoking the presence of high fluid pressure or low friction coefficient metasomatic materials(e.g., smectite or lizardite) within the faults.展开更多
In this contribution,we analyzed a pair of mafic samples collected from a recently identified shear zone and its proximal footwall from the Manicouagan Imbricate Zone(MIZ)of the central Grenville Province,Québec,...In this contribution,we analyzed a pair of mafic samples collected from a recently identified shear zone and its proximal footwall from the Manicouagan Imbricate Zone(MIZ)of the central Grenville Province,Québec,Canada.Titanite petrochronology,metamorphic phase equilibria modelling,trace element thermometry,and electron backscattered diffraction data were used to define a Pressure-Temperature-timeDeformation path for the two samples.An interconnected dislocation network within titanite grains,as outlined with Kerneled Average Misorientation maps,are spatially correlated with variation in the U-Pb system but not with that observed for trace element These results suggest that the U-Pb system was decoupled from trace and rare earth elements and that deformation,rather than interface-coupled dissolution-precipitation reactions or re-crystallisation,was the main driver for this decoupling.In addition to highlighting a potential pitfall of titanite petrochronology,our P-T-t-D path reveals that ductile shear zones were active later than previously suggested within the MIZ.展开更多
The generalized mixture rule(GMR) is used to provide a unified framework for describing Young’s(E),shear(G) and bulk(K) moduli, Lame parameter(l), and P- and S-wave velocities(Vpand Vs) as a function of porosity in v...The generalized mixture rule(GMR) is used to provide a unified framework for describing Young’s(E),shear(G) and bulk(K) moduli, Lame parameter(l), and P- and S-wave velocities(Vpand Vs) as a function of porosity in various isotropic materials such as metals, ceramics and rocks. The characteristic J values of the GMR for E, G, K and l of each material are systematically different and display consistent correlations with the Poisson’s ratio of the nonporous material(v0). For the materials dominated by corner-shaped pores, the fixed point at which the effective Poisson’s ratio(n) remains constant is at v0=0.2, and J(G) > J(E) > J(K) > J(l) and J(G) < J(E) < J(K) < J(l) for materials with v0> 0.2 and v0< 0.2, respectively.J(Vs) > J(Vp) and J(Vs) < J(Vp) for the materials with v0> 0.2 and v0< 0.2, respectively. The effective n increases, decreases and remains unchanged with increasing porosity for the materials with v0< 0.2,v0> 0.2 and v0=0.2, respectively. For natural rocks containing thin-disk-shaped pores parallel to mineral cleavages, grain boundaries and foliation, however, the n fixed point decreases nonlinearly with decreasing pore aspect ratio(a: width/length). With increasing depth or pressure, cracks with smaller a values are progressively closed, making the n fixed point rise and finally reach to the point at v0=0.2.展开更多
Detection of SARS-CoV-2 RNA in wastewater is a promising tool for informing public health decisions during the COVID-19 pandemic.However,approaches for its analysis by use of reverse transcription quantitative polymer...Detection of SARS-CoV-2 RNA in wastewater is a promising tool for informing public health decisions during the COVID-19 pandemic.However,approaches for its analysis by use of reverse transcription quantitative polymerase chain reaction(RT-q PCR)are still far from standardized globally.To characterize inter-and intra-laboratory variability among results when using various methods deployed across Canada,aliquots from a real wastewater sample were spiked with surrogates of SARS-CoV-2(gamma-radiation inactivated SARS-CoV-2 and human coronavirus strain 229E[HCoV-229E])at low and high levels then provided"blind"to eight laboratories.Concentration estimates reported by individual laboratories were consistently within a 1.0-log_(10) range for aliquots of the same spiked condition.All laboratories distinguished between low-and high-spikes for both surrogates.As expected,greater variability was observed in the results amongst laboratories than within individual laboratories,but SARS-CoV-2 RNA concentration estimates for each spiked condition remained mostly within 1.0-log_(10) ranges.The no-spike wastewater aliquots provided yielded non-detects or trace levels(<20 gene copies/mL)of SARS-CoV-2 RNA.Detections appear linked to methods that included or focused on the solids fraction of the wastewater matrix and might represent in-situ SARS-CoV-2 to the wastewater sample.HCoV-229E RNA was not detected in the no-spike aliquots.Overall,all methods yielded comparable results at the conditions tested.Partitioning behavior of SARS-CoV-2 and spiked surrogates in wastewater should be considered to evaluate method effectiveness.A consistent method and laboratory to explore wastewater SARS-CoV-2 temporal trends for a given system,with appropriate quality control protocols and documented in adequate detail should succeed.展开更多
基金The author thanks the Natural Sciences and Engineering Research Council of Canada for a discovery grant(Grant No.06408),Dr.Le Li for drawing the figures,and Dr.A.I.Chemenda for discussion.Three anonymous reviewers and the editors are sincerely thanked for their critical comments and helpful suggestions.
文摘Fractures occur in nearly all rocks at the Earth’s surface and exert essential control on the mechanical strengths of rock masses and permeability.The fractures strongly impact the stability of geological or man-made structures and flow of water and hydrocarbons,CO_(2) and storing waste.For this,the dependence of opening mode fracture spacing(s)on bed thickness(t)in sedimentary basins(reservoirs)is studied in this context.This paper shows that the MichaeliseMenten equation can provide an algebraic expression for the nonlinear s-t relationship.The two parameters have clear geological meanings:a is the maximum fracture spacing which can no longer increase with increasing t,and b is the characteristic bed thickness when s=0.5a.The tensile fracture strength(C)of the brittle beds during the formation of tensile fractures can be estimated from the two parameters.For sandstones of 16 areas reported in the literature,C ranges from 2.7 MPa to 15.7 MPa with a mean value of 8 MPa,which lies reasonably within the range of tensile strengths determined experimentally.This field-based approach by means of MichaeliseMenten equation provides a new method for estimating the tensile fracture strength of rock layers under natural conditions.
基金The authors express their gratitude to the Natural Sciences and Engineering Research Council of Canada for financial support through a Discovery Grant(Grant No.06408).
文摘Vertical orthogonal joints are a common feature in shallow crustal rocks.There are several competing theories for their formation despite the ubiquity.We examined the exceptional exposures of orthogonal joints in flat-lying Ordovician limestone beds from the Havre-Saint-Pierre Region in Quebec,Canada(north shore of Saint-Lawrence River)to test conceptual models of joint formation in a natural setting.In the region,the spacing of cross-joints is consistently larger than the spacing of systematic joints by a factor of 1.5 approximately.The joint-spacing-to-bed-thickness ratios(s/t)are much larger in these beds(s/t=4.3 for systematic joints,and 6.4 for cross-joints)than those in higher strained strata along the south shore of the Saint-Lawrence River(s/t=1),highlighting the effect of tectonic strain in decreasing fracture spacing and block size.The high values of s/t indicate that cross-joint formation was unlikely caused by a switch from compression to tension once a critical s/t ratio for systematic joints was reached(as hypothesized in previous studies).We proposed a new model for the formation of orthogonal joint systems where the principal stress axes locally switch during the formation of systematic fractures.The presence of ladder-shaped orthogonal joints suggests a state of effective stress withσ_(1)^(∗)≫0>σ_(2)^(∗)>σ_(3)^(∗)and whereσ_(2)^(∗)-σ_(3)^(∗)is within the range of fracture strength variability at the time of fracture.This research provides a new mechanical model for the formation of orthogonal joint systems and cuboidal blocks.
基金Shaocheng Ji thanks the Natural Sciences and Engineering Research Council of Canada for a discovery grant,and Dr.Terry Engelder for helpful discussion.
文摘Two vertical and orthogonal systematic joint sets are generally arrayed in a grid pattern on the bedding surface,which are the significant features of flat-lying sandstone terrains.Although extensive researches are reported on this topic,many fundamental problems have still not been solved.Such mutually perpendicular opening-mode fractures are an obvious manifestation of effective tensile stresses in two orthogonal directions in the horizontal bedding plane.A good understanding of these orthogonal joint systems is a key to structural analysis,landscape interpretation,and guidance of resolving a number of very practical problems in engineering,mining and hydrologic projects.Based on an anatomic investigation on the orthogonal joints in the Potsdam sandstone of Cambrian age at Ausable Chasm(New York State,USA)and Beauharnois(Quebec,Canada),we proposed that the orthogonal joints may result from the auxetic effects of quartz-rich sandstone rather than local or regional rotation of the maximum tensile stress(σ_(3))direction by about 90°.The sandstone beds with negative Poisson's ratios are so fascinating that,when placed under vertical burial compression and layer-parallel extension in one direction(σ_(3)),it becomes stretched in the transverse direction(σ_(2)),producing two orthogonal sets of mutual abutting and intersecting joints(J1 and J2 normal toσ_(3) andσ_(2),respectively),and both are normal to the bedding surface.Joint set J1 is more closely-spaced than J2 by a factor of∼3.3,which is correlated with an average Poisson's ratio of−0.3 for the Potsdam sandstone at the time of joint formation.
基金supported by the National Natural Science Foundation of China(No.40921001 and No.40921001)the Geological Survey of China(No.1212010818094)to Xuthe Natural Sciences and Engineering Research Council of Canada to Ji
文摘Although the Indus-Tsangpo Suture(ITS) is the most spectacular thrust system of continent-continent collision in the world, fundamental questions about its strength evolution and deformation behavior transition remain unanswered. Here we reported, for the first time, frictional melting-induced pseudotachylytes in the intensively deformed felsic rocks along the ITS zone in southern Tibet. This study reveals that pseudotachylytes induced profound weakness of the boundary fault between Indian and Asian plates. The intrinsically low strength of the foliated microlites crystallized from frictional melt or glass(i.e., pseudotachylyte) at seismogenic depths compared with the surrounding coarse-grained quartzofeldspathic rocks in the brittle and semi-brittle regime is sufficient to explain the localization of shear strain, the development of ductile shear zones embedded in strong wall rocks, and the transition from the strong to weak fault behaviors without invoking the presence of high fluid pressure or low friction coefficient metasomatic materials(e.g., smectite or lizardite) within the faults.
基金funded in part by the Ministère des Ressources naturelles du Québec contribution no.8449–2021-2022–04 under the supervision of AMoukhsil and partially funded by an NSERC-Discovery grant RGPIN-2014-04593 hosted by F.Gervais.
文摘In this contribution,we analyzed a pair of mafic samples collected from a recently identified shear zone and its proximal footwall from the Manicouagan Imbricate Zone(MIZ)of the central Grenville Province,Québec,Canada.Titanite petrochronology,metamorphic phase equilibria modelling,trace element thermometry,and electron backscattered diffraction data were used to define a Pressure-Temperature-timeDeformation path for the two samples.An interconnected dislocation network within titanite grains,as outlined with Kerneled Average Misorientation maps,are spatially correlated with variation in the U-Pb system but not with that observed for trace element These results suggest that the U-Pb system was decoupled from trace and rare earth elements and that deformation,rather than interface-coupled dissolution-precipitation reactions or re-crystallisation,was the main driver for this decoupling.In addition to highlighting a potential pitfall of titanite petrochronology,our P-T-t-D path reveals that ductile shear zones were active later than previously suggested within the MIZ.
文摘The generalized mixture rule(GMR) is used to provide a unified framework for describing Young’s(E),shear(G) and bulk(K) moduli, Lame parameter(l), and P- and S-wave velocities(Vpand Vs) as a function of porosity in various isotropic materials such as metals, ceramics and rocks. The characteristic J values of the GMR for E, G, K and l of each material are systematically different and display consistent correlations with the Poisson’s ratio of the nonporous material(v0). For the materials dominated by corner-shaped pores, the fixed point at which the effective Poisson’s ratio(n) remains constant is at v0=0.2, and J(G) > J(E) > J(K) > J(l) and J(G) < J(E) < J(K) < J(l) for materials with v0> 0.2 and v0< 0.2, respectively.J(Vs) > J(Vp) and J(Vs) < J(Vp) for the materials with v0> 0.2 and v0< 0.2, respectively. The effective n increases, decreases and remains unchanged with increasing porosity for the materials with v0< 0.2,v0> 0.2 and v0=0.2, respectively. For natural rocks containing thin-disk-shaped pores parallel to mineral cleavages, grain boundaries and foliation, however, the n fixed point decreases nonlinearly with decreasing pore aspect ratio(a: width/length). With increasing depth or pressure, cracks with smaller a values are progressively closed, making the n fixed point rise and finally reach to the point at v0=0.2.
基金supported by a CHEO (Children’s Hospital of Eastern Ontario) CHAMO (Children’s Hospital Academic Medical Organization) grant, awarded to Dr.Alex E.Mac Kenziesupported by the “Next generation solutions to ensure healthy water resources for future generations” funded by the Global Water Futures program, Canada First Research Excellence Fund (#419205)+7 种基金supported by the Canada Research Chairs Program of the Natural Sciences and Engineering Research Council of Canada (NSERC)supported by funding from NSERC Discovery and Strategic Grant Programssupported by funding from an NSERC Discovery Grantsupported by the NSERC Alliance COVID-19 Grantby Mitacs through the Mitacs Accelerate programsupported by Canadian Institutes of Health Research (CIHR), Alberta Innovates, Alberta Health-Water for Life Strategysupported by the BC center for Disease Control, BC center for Disease Control Foundation for Public Health and Metro Vancouversupported by the Canada Research Chairs Program of NSERC。
文摘Detection of SARS-CoV-2 RNA in wastewater is a promising tool for informing public health decisions during the COVID-19 pandemic.However,approaches for its analysis by use of reverse transcription quantitative polymerase chain reaction(RT-q PCR)are still far from standardized globally.To characterize inter-and intra-laboratory variability among results when using various methods deployed across Canada,aliquots from a real wastewater sample were spiked with surrogates of SARS-CoV-2(gamma-radiation inactivated SARS-CoV-2 and human coronavirus strain 229E[HCoV-229E])at low and high levels then provided"blind"to eight laboratories.Concentration estimates reported by individual laboratories were consistently within a 1.0-log_(10) range for aliquots of the same spiked condition.All laboratories distinguished between low-and high-spikes for both surrogates.As expected,greater variability was observed in the results amongst laboratories than within individual laboratories,but SARS-CoV-2 RNA concentration estimates for each spiked condition remained mostly within 1.0-log_(10) ranges.The no-spike wastewater aliquots provided yielded non-detects or trace levels(<20 gene copies/mL)of SARS-CoV-2 RNA.Detections appear linked to methods that included or focused on the solids fraction of the wastewater matrix and might represent in-situ SARS-CoV-2 to the wastewater sample.HCoV-229E RNA was not detected in the no-spike aliquots.Overall,all methods yielded comparable results at the conditions tested.Partitioning behavior of SARS-CoV-2 and spiked surrogates in wastewater should be considered to evaluate method effectiveness.A consistent method and laboratory to explore wastewater SARS-CoV-2 temporal trends for a given system,with appropriate quality control protocols and documented in adequate detail should succeed.
