Rockburst is a typical rock failure which frequently threatens both human life and construction equipment during highly stressed underground excavation. Rock lithology is a control factor of ...rockburst. In this paper, rockburst tests were conducted on rectangular prismatic specimens of six types of intact hard brittle rocks, i.e. granodiorite, granite, marble, basalt, sandstone and limestone, under one-free-face true triaxial loading conditions. With the use of high-speed cameras, an acoustic emission (AE) system and a scanning electron microscope (SEM), rockburst of different rocks was investigated. The results show that the strainbursts of granodiorite, granite and marble were accompanied by tensile splitting near the free face, and consequently were relatively strong with a large amount of fragment ejection and kinetic energy release. For basalt, sandstone and limestone, failure was primarily dominated by shear rupture. The strainbursts of basalt and sandstone were relatively small with minor fragment ejection and kinetic energy release; while no burst failure occurred on limestone due to its relatively low peak strength. Rock strength, fracturing and fragmentation characteristics, and failure modes of different rocks can significantly affect rockburst proneness and magnitude. The AE evolution coupled with SEM analysis reveals that the differences in the inherent microstructures and fracture evolution under loading are the primary factors accounting for different rockbursts in various rock types.
In natural rock masses, joints or flaws usually occur in sets that are more or less parallel and regularly spaced. Many problems occurred in tunnel engineering mainly result from the failure of ...joints or faults because they are weaker compared with the rock matrix. Therefore, it is important to study the interaction of joints with the tunnel, as well as the interactions between themselves. In this research, rock-like specimens of non-persistent jointed rock masses containing a circular hole are prepared and tested under uniaxial compression. The test results show that the peak strength and elastic modulus of the non-persistent jointed rock specimens display a “U” type variation with respect to the joint inclination. The multiple joints can be simplified and regarded as a combination of three types of two-joints relative location, and the crack coalescence types and failure modes are in accordance with the classic crack coalescence types of the two joints. The crack coalescence between the joints and a circular hole can be categorized into three modes with respect to the joint inclination. The Discrete Element Method (DEM) model of the jointed rock specimen that contains a circular hole is established in particle flow code 2D (PFC2D). The simulation results show a good agreement with the experiment results. Furthermore, the displacement fields at the crack zones reveal that the coalescence of joints is mainly caused by tensile cracks and that shear slipping cracks easily occur at the sidewalls of the circular hole. By comparing the parallel-bond force fields in jointed models containing a circular hole with no a circular hole, it is shown that the circular hole can change the stress state at the top and bottom. The joints at a joint inclination of 90° have the smallest effect on the mechanical behavior of the rock specimen.
An integrated study on two subduction-related units (the Heilongjiang Complex and magmatic rocks in the Lesser Xing'an-Zhangguangcai Range) was carried out to explore the Paleozoic to early Mesozoic ...tectonic framework of the eastern Northeast China, with a focus on the Jiamusi block. The Heilongjiang Complex, which is considered as the suture between the Jiamusi and Songliao blocks, is composed of blueschist, amphibolite and ultramafic rocks. The blueschist from the Yilan area shows geochemical features similar to OIB and has a 206Pb/238U age of 288±2Ma, which is interpreted as the crystallization age of protolith formed in an ocean island setting. In contrast, amphibolite from the Xiachengzi area shows geochemical features similar to N-MORB. Zircons in this amphibolite show magmatic character and yield a 206Pb/238U age of 248±4Ma, which is interpreted as the protolith age. Calcic amphiboles in the amphibolite give a 40Ar/39Ar plateau age of 195±3Ma, which is interpreted as the metamorphic age of the Heilongjiang Complex. Magmatic rocks in the Lesser Xing'an-Zhangguangcai Range mostly belong to I-type granites that were formed in an active continental margin setting. Zircon U-Pb ages of these granites range from ~200Ma to ~174Ma with a westward younging trend shown as two groups of emplacing ages of ~200Ma in the east and ~180Ma in the west. Our new data support an early occurrence (likely since the early Permian) of a large ocean (namely the Mudanjiang Ocean) in the area, whose subduction resulted in the metamorphic unit (the Heilongjiang Complex) and the magmatic unit (the Lesser Xing'an-Zhangguangcai Range) in the Jurassic.
•The metamorphism of the Heilongjiang Complex likely occurred during the Early Jurassic.•The protoliths of metabasalts have affinities to OIB and N-MORB.•The Mudanjiang Ocean began to exist from early Permian and started to subduct in the Jurassic.
Six hydraulic fracturing (HF) experiments were conducted in situ at the Grimsel Test Site (GTS), Switzerland, using two boreholes drilled in sparsely fractured crystalline rock. High spatial and ...temporal resolution monitoring of fracture fluid pressure and strain improve our understanding of fracturing dynamics during and directly following high-pressure fluid injection. In three out of the six experiments, a shear-thinning fluid with an initial static viscosity approximately 30 times higher than water was used to understand the importance of fracture leak-off better. Diagnostic analyses of the shut-in phases were used to determine the minimum principal stress magnitude for the fracture closure cycles, yielding an estimate of the effective instantaneous shut-in pressure (effective ISIP) 4.49±0.22 MPa. The jacking pressure of the hydraulic fracture was measured during the pressure-controlled step-test. A new method was developed using the uniaxial Fibre-Bragg Grating strain signals to estimate the jacking pressure, which agrees with the traditional flow versus pressure method. The technique has the advantage of observing the behavior of natural fractures next to the injection interval. The experiments can be divided into two groups depending on the injection location (i.e., South or North to a brittle-ductile S3 shear zone). The experiments executed South of this zone have a jacking pressure above the effective ISIP. The proximity to the S3 shear zone and the complex geological structure led to near-wellbore tortuosity and heterogeneous stress effects masking the jacking pressure. In comparison, the experiments North of the S3 shear zone has a jacking pressure below the effective ISIP. This is an effect related to shear dislocation and fracture opening. Both processes can occur almost synchronously and provide new insights into the complicated mixed-mode deformation processes triggered by high-pressure injection.
Abyssal peridotites are ultramafic rocks collected from mid-ocean ridges that are the residues of adiabatic decompression melting. Their compositions provide information on the degree of melting and ...melt–rock interaction involved in the formation of oceanic lithosphere, as well as providing constraints on pre-existing mantle heterogeneities. This review presents a compilation of abyssal peridotite geochemical data (modes, mineral major elements, and clinopyroxene trace elements) for >1200 samples from 53 localities on 6 major ridge systems. On the basis of composition and petrography, peridotites are classified into one of five lithological groups: (1) residual peridotite, (2) dunite, (3) gabbro-veined and/or plagioclase-bearing peridotite, (4) pyroxenite-veined peridotite, and (5) other types of melt-added peridotite. Almost a third of abyssal peridotites are veined, indicating that the oceanic lithospheric mantle is more fertile, on average, than estimates based on residual peridotites alone imply. All veins appear to have formed recently during melt transport beneath the ridge, though some pyroxenites may be derived from melting of recycled oceanic crust.
A limited number of samples are available at intermediate and fast spreading rates, with samples from the East Pacific Rise indicating high degrees of melting. At slow and ultra-slow spreading rates, residual abyssal peridotites define a large (0–15% modal clinopyroxene and spinel Cr#=0.1–0.6) compositional range. These variations do not match the prediction for how degree of melting should vary as a function of spreading rate. Instead, the compositional ranges of residual peridotites are derived from a combination of melting, melt–rock interaction and pre-existing compositional variability, where melt–rock interaction is used here as a general term to refer to the wide range of processes that can occur during melt transport in the mantle. Globally, ~10% of abyssal peridotites are refractory (0% clinopyroxene, spinel Cr#>0.5, bulk Al2O3<1wt.%) and some ridge sections are dominated by harzburgites while lacking a significant basaltic crust. Abyssal ultramafic samples thus indicate that the mantle is multi-component, probably consisting of at least three components (lherzolite, harzburgite, and pyroxenite). Overall, the large compositional range among residual and melt-added peridotites implies that the oceanic lithospheric mantle is heterogeneous, which will lead to the generation of further heterogeneities upon subduction back into the mantle.
•A global database for >1200 abyssal peridotite compositions is presented.•Abyssal peridotites have large major and trace element compositional ranges.•Compositions reflect melting, melt–rock interaction and source heterogeneity.•Peridotites extend to refractory compositions at all spreading rates.•The mantle globally consists of fertile and refractory domains.
The deformation modulus of heavily jointed andesitic rock mass was investigated by using 41 Menard pressuremeter test results and geotechnical information obtained from seven geotechnical boreholes. ...The geotechnical borehole logs and laboratory test results provided by a mining company were used for the assessment of rock mass characterization. The log and the test results were taken into account in the rock mass classification work. The well-known empirical equations were employed to predict the deformation modulus of the rock mass. The predictions and the pressuremeter test results were compared and their performance indicators were presented. Non-linear multiple regression methods were used for predictive modelling of the deformation modulus of the rock mass by considering the available data. Rock Quality Designation (RQD), discontinuity condition rating (Dc) of the Rock Mass Rating (RMR) system and uniaxial compressive strength of the intact rock (σci) were taken into consideration as input parameters in four new prediction equations to be used for determination of deformation modulus. One more equation was proposed by the addition of the depth as a predictive parameter. The influence of the depth and vertical to horizontal stress ratio (k) on the deformation modulus was preliminarily examined by using finite element modelling. Initially, the rock mass was assumed to be an isotropic elastic-brittle-plastic medium. Later on, the rock mass was modelled as a discontinuum by imposing a discrete fracture network (DFN). Keeping all of the mechanical properties constant, different depth and k parameters were applied to the pressuremeter models. No influence of the depth and k on the deformation modulus was observed for the isotropic medium while the depth contributed to an increase in the modulus in the anisotropic discontinuum analysis. The numerical modelling findings constituted a basis for the inclusion of the depth parameter into the new predictions.
This open access volume explores the impact of globalization on the contemporary study of deep-time art. The volume explores how early rock art research’s Eurocentric biases have shifted with ...broadened global horizons to facilitate new conversations and discourses in new post-colonial realities. The book uses seven main themes to explore theoretical, methodological, ethical, and practical developments that are orienting the study of Pleistocene and Holocene arts in the age of globalization. Compiling studies as diverse as genetics, visualization, with the proliferation of increasingly sophisticated archaeological techniques, means that vast quantities of materials and techniques are now incorporated into the analysis of the world’s visual cultures. Deep-Time Images in the Age of Globalization aims to promote critical reflection on the multitude of positive – and negative – impacts that globalization has wrought in rock art research. The volume brings new theoretical frameworks as well as engagement with indigenous knowledge and perspectives from art history. It highlights technical, methodological and interpretive developments, and showcases rock art characteristics from previously unknown (in the global north) geographic areas. This book provides comparative approaches on rock art globally and scrutinises the impacts of globalization on research, preservation, and management of deep-time art. This book will appeal to archaeologists, social scientists and art historians working in the field as well as lovers of rock art.
We address in situ serpentinization and mineral carbonation processes in oceanic lithosphere using integrated field magnetic measurements, rock magnetic analyses, superconducting quantum interference ...device (SQUID) microscopy, microtextural observations, and energy dispersive spectroscopy phase mapping. A representative suite of ultramafic rock samples were collected, within the Atlin ophiolite, along a 100‐m long transect across a continuous outcrop of mantle harzburgite with several alteration fronts: serpentinite, soapstone (magnesite + talc), and listvenite (magnesite + quartz). Strong correlations between changes in magnetic signal strengths and amount of alteration are shown with distinctive contrasts between serpentinite, transitional soapstone, and listvenite that are linked to the formation and breakdown of magnetite. While previous observations of the Linnajavri ultramafic complex indicated that the breakdown of magnetite occurred during listvenite formation from the precursor soapstone (Tominaga et al., 2017, https://doi.org/10.1038/s41467-017-01610-4), results from our study suggest that magnetite destabilization already occurred during the replacement of serpentinite by soapstone (i.e., at lower fluid CO2 concentrations). This difference is attributed to fracture‐controlled flow of sulfur‐bearing alteration fluid at Atlin, causing reductive magnetite dissolution in thin soapstone zones separating serpentinite from sulfide‐mineralized listvenite. We argue that magnetite growth or breakdown in soapstone provides insight into the mode of fluid flow and the composition, which control the scale and extent of carbonation. This conclusion enables us to use magnetometry as a viable tool for monitoring the reaction progress from serpentinite to carbonate‐bearing assemblages in space and time with a caution that the three‐dimensionality of magnetic sources impacts the scalability of measurements.
Plain Language Summary
Magnetic remote sensing has been used in unlocking otherwise inaccessible information about geodynamic processes. Here, we expand and use magnetometry to monitor in situ mineral carbonation processes in mantle peridotite, one of the major rock formations that compose this planet Earth. We conducted integrative magnetometry‐geochemistry observations in the field and lab using magnetic measurements, rock magnetic analyses, superconducting quantum interference device microscopy, microtextural observations, and energy dispersive spectroscopy phase mapping. Based on results from this integrative approach, we observe a correlation between magnetic signal and in situ carbonation process. This observation supports the idea that magnetic measurements can delineate carbonation extent and degree in peridotite alteration processes. We also observe that fluid chemistry and flow mode impact the magnetic signal of incipient carbonation. Altogether, our study enables us to further use magnetometry results in monitoring in situ peridotite carbonation, and possibly, the mode of fluid flows during the chemical process.
Key Points
Magnetic measurements delineate carbonation processes and extent in peridotite
We observe a correlation between magnetic signal and in situ carbonation process
Fluid chemistry and flow mode impact magnetic signal of incipient carbonation
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