Linking stress field deflection to basement structures in southern Ontario: Results from numerical modelling

Analysis of stress measurement data from the near-surface to crustal depths in southern Ontario show a misalignment between the direction of tectonic loading and the orientation of the major horizontal principal stress. The compressive stress field instead appears to be oriented sub-parallel to the major terrane boundaries such as the Grenville Front, the Central Metasedimentary Belt boundary zone and the Elzevir Frontenac boundary zone. This suggests that the stress field has been modified by these deep crustal scale deformation zones. In order to test this hypothesis, a geomechanical model was constructed using the three-dimensional discontinuum stress analysis code 3DEC. The model consists of a 45 km thick crust of southern Ontario in which the major crustal scale deformation zones are represented as discrete faults. Lateral velocity boundary conditions were applied to the sides of the model in the direction of tectonic loading in order to generate the horizontal compressive stress field. Modelling results show that for low strength (low friction angle and cohesion), fault slip causes the stress field to rotate toward the strike of the faults, consistent with the observed direction of misalignment with the tectonic loading direction. Observed distortions to the regional stress field may be explained by this relatively simple mechanism of slip on deep first-order structures in response to the neotectonic driving forces.     

Tectonothermal evolution of high-alumina rocks within the Protogine Zone, southern Sweden

Abstract The Protogine Zone comprises a system of anastomosing deformation zones which approximately parallel the eastern boundary of the Sveconorwegian (1200–900 Ma) province in south-west Sweden. Ages of granulite facies metamorphism in the Sveconorwegian province require exhumation from c . 30 to 35 km crustal depths after 920–880 Ma. ⁴⁰Ar/³⁹ Ar cooling ages are presented for muscovite from high-alumina rocks formed by hydrothermal leaching associated with the Protogine Zone. Growth of fabric-defining minerals was associated with a ductile deformational event; muscovite from these rocks cooled below argon retention temperatures ( c . 375 ± 25° C) at c . 965–955 Ma. Muscovite from granofels in zones of intense alteration indicates that temperatures > 375 ± 25° C were maintained until c . 940 Ma. Textural relations of Al₂SiO₅ polymorphs and chloritoid suggest that dated fabrics formed during exhumation. The process of exhumation, brittle overprint on ductile structures and hydrothermal activity along faults within the Protogine Zone tentatively are interpreted as the peripheral effects of initial Neoproterozoic exhumation of the granulite region of south-western Sweden.
Muscovite in phyllonites associated with the 'Sveconorwegian thrust system'cooled below argon retention temperatures at c . 927 Ma. Exhumation associated with this cooling could have been related to extension and onset of brittle-ductile deformation superimposed on Sveconorwegian contraction.     

Hydrothermal alteration of plagioclase in granitic rocks from Proterozoic basement of SE Sweden

Petrographic examinations and electron microprobe analyses of Proterozoic granitic rocks, SE Sweden aimed to characterize and unravel the mechanisms and conditions of plagioclase alterations. These alterations include saussuritization, albitization and replacement of plagioclase by K‐feldspar. The hydrothermal alterations, which are inferred to have occurred at ca. 250–400°C, resulted in concomitant formation of Al‐rich titanite, epidote, calcite, pumpellyite, prehnite and iron oxides. Replacement of plagioclase by K‐feldspar occurs in red‐stained zones, which have developed close to thin fractures owing to the precipitation of tiny Fe‐oxide pigment particles within the altered plagioclase, whereas saussuritized plagioclase has less systematic spatial relationships to these fractures. Albitization of plagioclase occurred in rocks that are poor in biotite compared to rocks that suffered extensive saussuritization. The chemical and textural characterization of various types of plagioclase alterations allows elucidation of the granitic hydrothermal systems. Features of feldspar alteration in the granitic rocks are similar to those encountered in feldspathic sandstones and should hence be considered in studies on diagenetic changes of siliciclastic successions during basin evolution. Copyright © 2009 John Wiley & Sons, Ltd.     

Regional stress field as determined from electromagnetic radiation in a tunnel

The paper presents the results of electromagnetic radiation (EMR) measurements in the Feuerberg tunnel in southwest Germany. EMR is associated with small scale fracturing processes. The measured numbers of EMR impulses are shown to be proportional to shear stresses. From the correlation of EMR and shear stresses along the long axis of the tunnel, orientations and magnitudes of the horizontal principal stresses are determined. The major horizontal principal stress is 3.6±0.3 MPa and has an azimuth of 143±6°. The minor principal horizontal stress is 2.1±0.3 MPa. Zones in the tunnel are located where low shear stresses occur because vertical overburden and horizontal stresses are equal. In these zones also minimum radiation was detected. A possible stress accumulation close to a fault is suggested by higher EMR values in a part of the tunnel. Orientations and magnitudes of the horizontal principal stresses, which are derived from the measurements of EMR, correlate well with conventional stress measurements. It is suggested that the cross-section measuring method described in the study is used to determine regional stress fields as well as to investigate endangered zones with high stresses in underground facilities, which may be critical with regard to stability.     

Isotopic connections between basement rocks exposed in the St. Francois Mountains and the Arbuckle Mountains,southern mid-continent,North America

Two distinct crustal provinces have been identified in the southern mid-continent based on U–Pb crystallization ages. Both contain large volumes of undeformed granite and rhyolite, with minor amounts of metamorphic rock and mafic intrusions. The Eastern Granite-Rhyolite province is characterized by felsic rocks with crystallization ages of 1,470 ± 30 Ma and exposures are restricted to the St. Francois Mountains in southeastern Missouri. Similarly, the Southern Granite-Rhyolite (SGR) province is characterized by felsic units with ages of 1,370 ± 30 Ma with primary exposures in the eastern Arbuckle Mountains of southern Oklahoma. Within the SGR province three magmatic pulses can be identified starting at 1,400, 1,370, and 1,340 Ma. Although the crystallization ages are different, the Sm–Nd isotopic signatures are similar for the units exposed in these areas as well as the buried basement in between. Depleted mantle model ages for rocks within the Arbuckle Mountains range from 1,530 to 1,430 Ma with ɛ_Nd(t) values of +3.2 to +4.1 while units of the St. Francois Mountains range from 1,550 to 1,430 Ma and +4.5 to +4.7. Comparison of Sm–Nd isotopic data also indicate similarities between the ¹⁴⁷Sm/¹⁴⁴Nd and ¹⁴³Nd/¹⁴⁴Nd ratios for the rock units in these areas suggesting a common source.     

Influence of differential basement mobility on contrasting structural styles in the cover rocks: An example from Early Precambrian rocks east of Udaipur,Rajasthan

Detailed structural and lithological mapping of the Aravalli rocks overlying the Mewar Gneiss in the area east of Udaipur, Rajasthan, suggests presence of blocks bounded by faults, showing a contrasting structural pattern. The contrast is reflected in the differential development and in the orientation of AF1, AF2 and AF4 folds in different blocks. In the central Umra block, the rocks constitute a virtually homoclinal sequence showing one dominant orientation of bedding and axial planar schistosity. Fold axes, lineations andβ orientations indicate presence of reclined folds of AF1 generation. AF2 folds are either absent or have developed only locally. The two other blocks which border the Umra block show development of large AF2 synforms and local minor antiforms having N-S or NNE-SSW trend. The folds interfere with AF4 folds producing irregular domes and basins in the western Kanpur-Kalarwas Block and minor plunge reversals in Bagdara-Dhamdhar Block. It is argued that the constituents of the different blocks which formed a collage of rift basins and horsts during sedimentation, responded differentially to deforming forces because of differential mobility of the underlying basement.     

Accuracy of CFC groundwater dating in a crystalline bedrock aquifer: Data from a site in southern Sweden

The concentrations of chlorofluorocarbons (CFC-11, CFC-12, and CFC-113) and tritium were determined in groundwater in fractured crystalline bedrock at Finnsjön, Sweden. The specific goal was to investigate the accuracy of CFC dating in such an environment, taking potential degradation and mixing of water into consideration. The water was sampled to a depth of 42 m in three boreholes along an 800-m transect, from a recharge area to a local discharge area. The CFC-113 concentration was at the detection limit in most samples. The apparent recharge date obtained from CFC-11 was earlier than from CFC-12 for all samples, with a difference of over 20 years for some samples. The difference was probably caused by degradation of CFC-11. The CFC-12 dating of the samples ranged from before 1945 to 1975, with the exception of a sample from the water table, which had a present-day concentration. Conclusions about flow paths or groundwater velocity could not be drawn from the CFCs. The comparison between CFC-12 and tritium concentrations showed that most samples could be unmixed or mixtures of waters with different ages, and the binary mixtures that matched the measured concentrations were determined. The mixing model approach can be extended with additional tracers.

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Resumen Precisión en la datación de aguas subterráneas utilizando CFC en un acuífero de rocas cristalinas: datos provenientes de un sitio al sur de Suecia.Se determinaron las concentraciones de clorofluorucarbonos (CFC-11, CFC-12, y CFC-113) y de tritio en aguas subterráneas alojadas en rocas cristalinas fracturadas de Finnsjön, Suecia. El objetivo específico consistió en investigar la precisión de la datación de aguas subterráneas con CFC en este tipo de ambiente, tomando en consideración la degradación potencial y la mezcla de agua. Las muestras de agua se tomaron a una profundidad de 42 m en tres pozos ubicados a lo largo de una línea de 800 m transversal a una zona de recarga y de zona de descarga local. En la mayoría de las muestras se encontró que la concentración de CFC-113 estuvo en el límite de detección. La edad que se estimó en todas las muestras para la recarga aparente en base a CFC-11 fue más joven que la edad proveniente de CFC-12, con una diferencia de más de 20 años para algunas muestras. Esta diferencia fue causada probablemente por la degradación del CFC-11. La datación CFC-12 de las muestras varió de antes de 1945 a 1975, con la excepción de una muestra tomada en el nivel freático, la cual presentó concentración actual. No fue posible obtener conclusiones acerca de las trayectorias de flujo o la velocidad de agua subterránea a partir de los CFCs. La comparación entre las concentraciones de CFC-12 y tritio mostró que la mayoría de las muestras pueden tener composición sencilla o bien consistir de mezclas de aguas de diferentes edades. Esta comparación también permitió determinar las mezclas binarias que corresponden a las concentraciones medidas. Pueden utilizarse trazadores adicionales para ampliar el modelo de mezclas propuesto.

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Résumé Précision de la datation au CFC dans un aquifère rocheux-fracturé: données dun site du sud de la Suède.Les concentrations en chlorofluorocarbones (CFC-11, CFC-12, CFC-113) et entritium ont été déterminées dans leau souterraine dun massif fracturé à Finnsjön en Suède. Le but de cette étude est de mieux cerner la précision de la méthode de datation au CFC dans ce type denvironnement hydrogéologique, tout en considérant déventuels phénomènes de dégradation et de mélange deaux. Leau a été échantillonnée à une profondeur de 42 mètres dans trois forages alignés sur 800 mètres entre une zone de recharge et une zone de déversement. Les concentrations en CFC-113 sont dans la plupart des échantillons à la limite de détection. Pour tous les échantillons, la date de la recharge établie avec le CFC-11 est antérieure à la date établie avec le CFC-12. La différence entre les deux dates peut dépasser 20 ans et sexplique—probablement—par la dégradation du CFC-11. Les dates de recharge de la nappe mesurées au CFC-12 sont comprises entre 1945 et 1975, excepté pour un échantillon qui possède une concentration actuelle. Il nest pas possible de tirer des conclusions concernant la direction des écoulements et la vitesse de leau souterraine. La comparaison entre CFC-12 et tritium montre que des échantillons pourraient être soit le résultat du mélange deaux dâges différents, soit des échantillons non-mélangés. Dans le cas dun mélange binaire, les rapports du mélange composant la concentration mesurée sont déterminés. Lapproche par modèle de mélange peut être étendue à des traceurs additionnels.

     

华北克拉通南部早前寒武纪基底形成与演化

简要总结了华北克拉通南部鲁山地区、小秦岭地区、登封及中条山地区的早前寒武纪地质事件序列及其地质意义,并对各地区地质特征和变质演化特点进行对比。结合前人研究工作,初步探讨了华北克拉通南部早前寒武纪基底的演化特点、陆壳形成的主要时期和华北南部基底的构造区划等问题,提出几点认识:1)华北克拉通南部鲁山、中条山、小秦岭等地区均有2.7~2.9Ga岩石记录,以英云闪长质-奥长花岗质-花岗闪长质(TTG)岩石为主,它们共同构成华北南缘的古老结晶基底,并经历了新太古代晚期~2.5Ga构造-热事件,标志着华北克拉通南部在新太古代末期可能已经形成统一基底;2)华北克拉通南部主要的陆壳形成时期为中太古代晚期-新太古代,与全球其他主要克拉通一致,而古元古代早-中期则以地壳再循环为主;3)综合地质、地球化学等特点,将华北南部鲁山-小秦岭地区和中条山等地区划归为"南部古陆块",并提出该陆块呈现为一个大型的倾伏向斜构造,可能在新太古代晚期已经形成,其枢纽向南东倾斜。"南部古陆块"在新太古代末期与其它微陆块拼合,并发生了变质作用和陆壳的活化与再循环,共同指示新太古代晚期华北克拉通统一基底的形成。     

藏北羌塘盆地基底变质岩的锆石SHRIMP年龄及其地质意义

羌塘盆地经受了青藏高原隆升事件等强烈的构造作用,盆地是否具有刚性结晶基底,对于油气的保存至关重要。长期以来对于该盆地是否具有前古生代的结晶基底,分歧较大。笔者新近在羌塘盆地中央隆起带北缘俄久卖发现的含夕线石和蓝晶石的片麻岩以及其附近发现的极浅变质的奥陶系地层,证实羌塘盆地具有变质结晶基底。本文进一步开展了片麻岩中锆石的SHRIMP年龄分析,获得了7组锆石年龄：2498~2374Ma 、1780 ~1666Ma、645~522Ma、465~420Ma、402~369Ma、270~233Ma和223~198Ma。通过CL图象对各组年龄锆石进行成因分析,并结合区域地质特征,认为1780 ~1666Ma为该片麻岩的主期变质年龄,羌塘盆地具有前寒武纪结晶基底,并对其余年龄组反映的构造热事件及其地质意义进行了讨论。     

Thermotectonic evolution of Precambrian basement rocks of the Kuruktag uplift,NE Tarim craton,China: evidence from apatite fission-track data

The Kuruktag uplift is located directly northeast of the Tarim craton in northwestern China. Neoarchaean-to-Neoproterozoic metamorphic rocks and intrusive rocks crop out widely in the uplift; thus, it is especially suited for a more complete understanding of the thermal evolution of the Tarim craton. Apatite fission-track (AFT) methods were used to study the exhumation history and cooling of these Precambrian crystalline rocks. Nine apatite-bearing samples were collected from both sides of the Xingdi fault transecting the Kuruktag uplift. Pooled ages range from 146.0 ± 13.4 to 67.6 ± 6.7 Ma, with mean track lengths between 11.79 ± 0.14 and 12.48 ± 0.10 μm. These samples can be divided into three groups based on age and structural position. Group A consists of five samples with AFT apparent ages of about 100–110 Ma and is generally associated with undeformed areas. Group B comprises three specimens with AFT apparent ages lower than 80 Ma and is mostly associated with hanging wall environments close to faults. Group C is a single apatite sample with the oldest relative apparent age, 146.0 ± 13.4 Ma. The modelled thermal history indicates four periods of exhumation in the Kuruktag uplift: late-Early Jurassic (180 Ma); Late Jurassic–Early Cretaceous (144–118 Ma); early-Late Cretaceous (94–82 Ma); and late Cenozoic (about 10 Ma). These cooling events, identified by AFT data, are assumed to reflect far-field effects from multi-stage collisions and accretions of terranes along the south Asian continental margin.     

Petrology and geochemical characteristics of Precambrian granitic basement complex rocks in the southernmost part of North-Central Nigeria

The Precambrian basement complex in the southernmost part of North-Central Nigeria is underlain by migmatitic banded gneisses, granitic intrusions and dykes of dolerite, rhyolite porphyry and pegmatite. The rocks are generally felsic, containing modal and normative hypersthene, as well as normative corundum. The basement complex has experienced high-grade regional metamorphism as indicated by the presence of hypersthene and plagioclase of andesine composition. Anatectic melting is suggested by the occurrence of ptygmatic folds, folded gneissose foliation, numerous quartzo-feldspathic veins and lenses of dark-colured, micaceous schistose rocks. Geochemically, the rocks have magnesian, calc-alkalic and strongly peraluminous characteristics. Their overall characteristics suggest derivation from progressive (fractional) partial melting of pelitic rocks during high-grade regional metamorphism, possibly associated with intense hydrothermal activities. The magnesian characteristics reflect close affinity to relatively hydrous, oxidizing melts and source regions in settings broadly related to subduction.     

北京昌平地区基底片麻岩和中-新元古代盖层锆石U-Pb年龄和Hf同位素研究及其地质意义

本文通过对北京昌平地区燕辽裂陷槽内出露的基底密云群片麻岩及其上覆沉积盖层底部长城系常州沟组和顶部青白口系长龙山组砂岩的锆石LA-ICP-MS U-Pb年龄和Hf同位素组成的研究,对华北克拉通新太古代-元古宙期间的沉积与地壳演化进行探讨.锆石的LA-ICP-MS U-Pb年代学研究表明,密云群含辉石角闪斜长片麻岩的原岩形...     

东昆仑前寒武纪基底变质岩系的锆石SHRIMP年龄及其构造意义

东昆仑地区有一系列前寒武纪变质基底岩系出露 ,这些基底岩块可以划分为两类 :北部基底以太古宙—古元古代的白沙河岩群和中元古代的小庙岩群为代表 ,南部基底以古、中元古代苦海杂岩为代表。对北部基底岩系小庙岩群变质碎屑岩系的锆石U PbSHRIMP年龄分析结果显示小庙岩群(Pt2 x)碎屑物源区是年龄大于 2 4亿年的岩石 ,2 4～ 2 5亿年的碎屑锆石的群组年龄很可能反映了小庙岩群源区的一期变质作用时间。个别 32亿年的碎屑锆石年龄指示源区存在古太古代的陆核。变质锆石及深熔成因的锆石给出的 10 35～ 10 74Ma群组年龄是小庙岩群的主期构造热事件时间 ,反映以清水泉蛇绿岩为代表的中元古代洋盆的闭合和南北不同基底块体的愈合 ,是Rodinia大陆聚合事件在东昆仑地区的表现。     

Late Cretaceous scleractinian corals from the rocky shore of Ivö Klack, southern Sweden, including some of the northernmost zooxanthellate corals

A relatively low diversity coral fauna comprising eight zooxanthellate, three azooxanthellate, and one unidentified species is described from a Late Cretaceous rocky shore at Ivö Klack, southern Sweden. All species, except the solitary azooxanthellate Paracyathus? sp., are represented by one or two specimens only, indicating low preservation potential similar to the aragonite-shelled gastropod fauna from the same locality. The fauna comprises one out of two northernmost zooxanthellate forms known and adds important environmental information to the fauna and depositional conditions of the rocky shore at Ivö Klack.     

The REVEALS model,a new tool to estimate past regional plant abundance from pollen data in large lakes: validation in southern Sweden

The REVEALS model was developed to reconstruct quantitatively regional vegetation abundance (in a 10⁴–10⁵ km² area) from pollen assemblages in large lakes (≥100–500 ha). This model corrects for biases in pollen percentages caused by inter‐taxonomic differences in pollen productivity and dispersal. This paper presents the first case study to validate REVEALS, using empirical data from southern Sweden. Percentage cover of modern regional vegetation in Skåne and Småland, two contrasting vegetation regions, was predicted with REVEALS for 26 key taxa, using pollen assemblages from surface sediments in 10 large lakes, and compared to the actual vegetation within 10⁴ km² compiled from satellite data, forestry inventories, crop statistics, aerial photographs, and vegetation inventories. REVEALS works well in predicting the percentage cover of large vegetation units such as total trees (wooded land), total herbs (open land), total conifers and total broad‐leaved trees, and it provides reasonable estimates for individual taxa, including Pinus, Picea, Betula, Corylus, Alnus, Tilia, Salix spp., Juniperus, Poaceae, Cyperaceae, Cerealia and Secale. The results show great potential for REVEALS applications, including (1) quantitative reconstructions of past regional land cover important for palaeoclimatology and nature conservation, and (2) local‐scale reconstruction of vegetation (<1 km² up to ～ 5 km² area) relevant for palaeoecology and archaeology. Copyright © 2007 John Wiley & Sons, Ltd.     

Prediction of fracture trajectory in anisotropic rocks using modified maximum tangential stress criterion

A new criterion to predict crack propagation trajectory in anisotropic rocks with incorporating the concept of T-stress in formulating stress field near the crack tip was developed. The developed criterion along with enrichment functions and interaction integral in the extended finite element method (XFEM) framework made a sophisticated tool in modeling fracturing process in anisotropic media. Numerical results indicated that stress intensity factors considerably depend on orientation of anisotropy axes and ratio of the elastic modulus. The proposed formulation for anisotropic media provides a more accurate prediction of crack propagation trajectory compared with conventional methods, especially in mixed mode conditions.     

The role of climate variability and fire in early and mid Holocene forest dynamics of southern Sweden

The objective of this study was to investigate the possible links between regional climate, fire and vegetation at the small spatial scale during the early and mid Holocene in southern Sweden using pollen, plant macrofossil and charcoal records from a small bog. The fire history was compared with climate reconstructions inferred from various proxy records in the study region. High fire activity is related to dry and warm climate around 8550, 7600, 5500–5100 and 4500 cal. a BC. Low fire activity ca. 6500–6000 and 4750 BC may correspond to the widespread ‘8.2 k event’ (ca. 6200 BC) recorded across the North Atlantic region, and a later, brief period of increased precipitation, respectively. The decrease in broadleaved trees culminating ca. 6500–6000 BC correlates with the ‘8.2 k event’. A long mid Holocene period with low fire activity (ca. 4350–1000 BC) agrees with the pattern emerging for Europe from the global charcoal database, and may correspond to generally wetter and cooler conditions. High fire activity ca. 8550 BC probably triggered the local establishment of Corylus. Warmer and drier conditions (and high fire activity) ca. 7600 BC might have favoured the establishment of Alnus, Quercus and Tilia. The fire‐adapted Pinus maintained important populations throughout the early and mid Holocene. Copyright © 2008 John Wiley & Sons, Ltd.     

云开地区加里东期花岗岩锆石U-Pb年龄及其地质意义

对云开地区1∶25万区调中划归前寒武纪或新元古代的(片麻状)花岗岩进行了锆石LA-ICP-MS U-Pb定年,获得的年龄分别为(443.3±2.6)Ma(样品1009,陆川县陆透水库东南)、(445.7±2.3)Ma(样品1010,陆川县月垌村)、(441.1±2.0) Ma(样品1012,高州市谢鸡镇)和(443.7±1.7)Ma(样品10108,信宜市朱砂镇),表明它们属于加里东期的产物而不是以往认为的前寒武纪基底或新元古代岩石.结合前人的研究表明,这些花岗岩主要由元古宙基底岩石发生深熔作用而成,是华南地区加里东期陆内造山作用的响应.随着云开地区前寒武纪基底中大量加里东期年龄的发现,说明加里东运动对该区的影响非常强烈,1∶25万区调中划归前寒武纪基底或新元古代的部分片麻状花岗岩应归属加里东期.云开地区前寒武纪基底主要是以片麻岩类为代表的高州杂岩和以变沉积岩类为代表的云开群,高州杂岩形成时代为中新元古代,云开群形成时代可能为新元古代.从整个华夏地块来看,存在古-中元古代结晶基底,但出露可能并不像以往认为的那么广泛.     

Basement-controlled faulting of Paleozoic strata in southern Ontario, Canada: new evidence from geophysical lineament mapping

Basement fault reactivation is now recognized as an important control on sedimentation and fault propagation in intracratonic basins. In southern Ontario, the basement consists of complexly structured mid-Proterozoic (ca. 1.2 Ga) crystalline rocks and metasedimentary rocks that are overlain by up to 1500 m of Paleozoic sedimentary strata. Reactivation of basement structures is suspected to control the location of Paleozoic fault and fracture systems, but evaluation has been hindered by a limited understanding of the regional structural characteristics of the buried basement. New aeromagnetic- and gravimetric-lineament mapping presented in this paper better resolves the location of basement discontinuities and provides further evidence for basement controls on the distribution of Paleozoic fault and fracture systems. Lineament mapping was facilitated by reprocessing and digital image enhancement (micro-levelling, regional residual separation, derivative filtering) of existing regional gravity and aeromagnetic datasets. Reprocessed images identify new details of the structural fabric of the basement below southern Ontario and delineate several previously unrecognized aeromagnetic and gravity lineaments and linear zones. Linear zones parallel the projected trends of mid-Proterozoic terrane boundaries identified by field mapping on the exposed shield to the north of the study area, and are interpreted as zones of shearing and basement faulting. Mapped aeromagnetic and gravity lineaments show similar trends to Paleozoic faults and fracture networks and broad zones of seismicity in southern Ontario. These new data support an ‘inheritance model’ for Paleozoic faulting, involving repeated reactivation and upward propagation of basement faults and fractures into overlying cover strata.     

Numerical modeling of stress effects on solute transport in fractured rocks

The effects of stress/deformation on fluid flow and contaminant transport in fractured rocks is one of the major concerns for performance and safety assessments of many subsurface engineering problems, especially radioactive waste disposal and oil/gas reservoir fields. However, very little progress has been made to study this issue due to difficulties in both experiments and numerical modeling. The objective of this study is to systematically investigate the influence of stress on solute transport in fractured rocks for the first time, considering different stress and hydraulic pressure conditions. A hybrid approach combining discrete element method (DEM) for stress-flow simulations and a particle tracking algorithm is developed. The impact of matrix diffusion (diffusion of molecular size solutes in and out of the rock matrix, and sorption onto the surface of micropores in rock matrix) is also included. The numerical results show that stress not only significantly changes the solute residence time through the fracture networks, but also changes the solute travel paths. Matrix diffusion plays a dominant role in solute transport when the hydraulic gradient is small, which is often encountered in practice.