Late Paleozoic and Mesozoic deformations in the southwestern Primorye region

Two types of tectonic deformations indicating different geodynamic settings are defined in the southwestern Primorye region. Near-latitudinal compression forces were responsible for the oldest, Late Paleozoic deformations. The Permian stratified complexes host a near-meridional system of folds and zones of dynamothermal metamorphism, cleavage, and foliation oriented orthogonally relative to the compression. Late Proterozoic (?) mafic-ultramafic rocks are characterized by similar deformations. In the Late Permian, the deformations were accompanied by granitoid magmatism controlled by fold and cleavage structures. The younger, Mesozoic deformations produced by near-meridional compression are represented by NE-trending sinistral strike-slip faults and their structural parageneses: an ENE-trending system of folds and downdip-thrusts both superimposed on Paleozoic protostructures and manifested in Mesozoic and Cenozoic sequences. It is inferred that, at the Paleozoic-Mesozoic boundary, near-latitudinal compression was replaced by near-meridional compression, probably, in response to the corresponding change in direction of the lateral displacement of the interacting Asian continent and (or) Pacific Plate.     

Extensive deformations of rock slopes in southern Coast Mountains, southwest British Columbia, Canada

Extensive deformations of mountain slopes occur in crystalline intrusive rocks in the southern Coast Mountains of British Columbia. Typical morphological evidence of slope movement includes extensive systems of tension cracks, grabens, and antislope scarps (collectively referred to here as linears). These landforms involve displacements along penetrative joints observed in surface exposures. Kinematic tests on rock-structural data indicate that the observed patterns of linears are generally consistent with the feasible gravitational movements along the dominant discontinuities. Most sites indicate sliding as the most likely initial mode of movement, followed by or accompanied by toppling and toppling-induced sliding movements, and do not support the view that linears are the traces of active faults.     

山东仰口地区超高压变质岩混杂带的组成及其构造变形

从构造岩石角度将山东青岛仰口地区发育的超高压变质岩混杂带划分为构造整合单元和构造混杂单元两个组成部分，对不同单元的岩性组成及其超高压变质特征进行了描述。着重对不同构造单元中的构造变形期次进行了划分。总结了不同期次构造变形的宏观及微观特征。结合苏鲁超高压变质带在区域上构造变形期次的研究情况，初步提出形成仰口地区超高压变质岩中各种构造形迹的构造模式，并对它们所反映的仰口超高压带形成和折返的构造意义进行了探讨。     

Elasto-plastic Behavior of Raghadan Tunnel Based on RMR and Hoek–Brown Classifications

Lining contact pressure and ground deformation of Raghadan transportation tunnel (Amman, Jordan) were investigated. The tunnel is 1.1 km in length and 13.5 m in diameter. This study was intended to integrate useful relations among the widely used rock classification system (RMR: rock mass rating), Hoek–Brown classification, and lining-ground interaction. The materials encountered along the tunnel alignment were limestone, dolomatic limestone, marly limestone, dolomite, and sillicified limestone. The ground conditions along the tunnel alignment including bedding planes, joint sets and joint conditions, rock quality, water flow, and rock strength were evaluated based on the drilled boreholes and rock exposures. Elasto-plastic finite element analyses were conducted to study the effect of rock mass conditions and tunnel face advance on the behavior of lining-ground interaction. The results of the analyses showed that lining contact pressure decreases linearly with the increase in RMR value. Also the results showed that tunnel lining contact pressure and crown inward displacement decreases with the increase in the unsupported distance (distance between tunnel face and the end of the erected lining). Ground displacement above the tunnel crown was found to be increases in an increasing rate with the decrease in the depth above the crown. This displacement was also found to be affected by the RMR value and the unsupported distance.     

Diatom taxonomic and morphological changes as indicators of metal pollution and recovery in Lac Dufault (Québec, Canada)

We studied diatom taxonomic composition and the presence of morphological alterations (size and deformations) along a sediment core collected in Lac Dufault, Abitibi, whose watershed has a long history of mining pollution presently undergoing mitigation. According to sediment dating with ²¹⁰Pb and metal profiles along the core, we could identify four periods in the contamination history of the lake, which were characterized by different diatoms. Tabellaria flocculosa was dominant in the pre-mining period but was drastically reduced at the onset of pollution when Fragilaria cf. tenera became important. This diatom, together with other Fragilaria species and cysts of Chaetoceros muelleri, typified the transition period in which Cu reached its maximum value and other metals started to increase. During the period of maximum contamination with Zn, Cd, and Fe accompanied by acid mine drainage, Achnanthes minutissima and Brachysira vitrea were dominant. These taxa started to wane in the most recent sediments representing a partial chemical recovery. Asterionella formosa, which almost vanished at mining onset, reappeared with high abundance in these superficial sections. Beside these taxonomical shifts, we observed during the contamination period significant reduction in valve length together with increased percentages of valve deformations. Because available data on water chemistry and a diatom-based pH reconstruction suggest that Lac Dufault escaped severe acidification, diatom patterns observed in the core can be mostly ascribed to metal contamination. Individual diatom abundance and valve length had strong statistical relationships with the different metals identified in the core. Diatom changes both taxonomic and morphological can be excellent specific indicator of metal contamination and early recovery.     

Structure of the Transkei Basin and Natal Valley, Southwest Indian Ocean, from seismic reflection and potential field data

Marine geophysical data from the southern Natal Valley and northern Transkei Basin, offshore southeast Africa, were used to study the structure of the crust and sedimentary cover in the area. The data includes seismic reflection, gravity and magnetics and provides information on the acoustic basement geometry (where available), features of the sedimentary cover and the basin's development. Previously mapped Mesozoic magnetic anomalies over a part of the basin are now recognized over wider areas of the basin. The ability to extend the correlation to the southeast within the Natal Valley further confirms an oceanic origin for this region and provides an opportunity to amplify the existing plate boundary reconstructions.The stratigraphic structure of the southern Natal Valley and the northern Transkei Basin reflects processes of the ocean crust formation and subsequent evolution. The highly variable relief of the acoustic basement may relate to the crust formation in the immediate vicinity of the continental transform margin. Renewed submarine seismicity and neotectonic activity in the area is probably related to the diffuse boundary between the Nubia and Somalia plates.2.5-D crustal models show that a 1.7–3.2-km-thick sediment sequence overlies a 6.3±1.2-km-thick normal oceanic crust in the deep southern Natal Valley and Transkei Basin. The oceanic crust in the study area is heterogeneous, made up of blocks of laterally varying remanent magnetization (0.5–3.5 A/m) and density (2850–2900 kg/m³). Strong modifications of accretionary processes near ridge/fracture zone intersections may be a reason of such heterogeneity.