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.
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.
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.
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
This paper aims to investigate the water saturation effects on the thermal infrared radiation (IRR) characteristics of rock materials during deformation and fracturing processes. Three kinds of ...rocks, namely sandstone, granite, and marble, were adopted for tests. Uniaxial compression tests were carried out on oven-dried and water-saturated rock samples. The evolution of IRR temperature on rock surface was monitored and recorded with the aid of an infrared thermographic camera. Test results show that the IRR temperature of saturated samples is apparently higher than that of dry ones subjected to the same axial stress. After water saturation, the heating rate in elastic deformation phase, the IRR temperature increment at peak stress, and the IRR temperature on the new-formed fracture surface have a significant growth compared to dry condition. These indicate that the presence of water facilitates the release of thermal energy. The sensitivities of the heating rates in elastic deformation phase to water saturation are very distinct for the three rocks. This is possibly resulted from the mineral composition of rock types, especially the proportion of calcite and swelling clay minerals. The IRR temperature increment at peak stress for rock not only depends on the moisture condition, but is also relevant to the uniaxial compressive strength.
Contamination is a common scenario of intracrustal magmatic processes that may significantly change the compositions of involved anatectic melts. Here, we present major element and B isotope analyses ...on tourmalines from the Guowu leucogranite and their host rocks, which allow us to unravel the potential contaminations of the Himalayan leucogranites by metapelite host rocks. Three types of tourmaline have been identified in our samples. Tur-M in the host schist has the highest Mg/(Mg+Fe) ratio (0.52-0.62) and low Al content, suggesting its metamorphic character. Tourmalines in the leucogranite (Tur-L) and in the contact zone between leucogranite and schist (Tur-C) have an identical core-rim texture, and their cores are characterized by the lowest Mg/(Mg+Fe) ratio (0.13-0.18) and high Al content, which are consistent with the composition of magmatic tourmaline in the Himalayan leucogranites. The rims of Tur-L show higher Mg/(Mg + Fe) ratio (0.32-0.45) and moderate Ca, Ti, F contents, reflecting the contribution of the host schist via contamination. The composition of Tur-C rims is similar to that of Tur-M, suggesting a more significant contribution from contaminated schist than that for Tur-L. The different types of tourmaline share consistent B isotope compositions with δ
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B ranging from −14 to −12‰. The compositional characteristics of the contaminated tourmaline and the mineral assemblage in the contaminated zone suggest that the involved components derived from the host schist, probably produced by the decomposition of tourmaline, biotite, plagioclase, primarily include Ca, K, Mg, Ti, B and F. In addition, contamination by tourmaline-bearing metapelite may be an alternative interpretation responsible for the peraluminous character of the Himalayan leucogranites. The occurrence of contaminated tourmaline in leucogranites suggests that contamination of host rocks is a possible way promoting the formation of tourmaline in the Himalayan leucogranites, and tourmaline is useful for deciphering the related contamination processes.
The acoustic emission (AE) signals generated during direct shear test were evaluated on different types of joints (rock–rock, rock–concrete and concrete–concrete). Several boreholes were cored from a ...dam body, rock mass and interface between dam and rock mass, and the samples were prepared and tested under direct shear test. A laser profilometer scanner was used for scanning the joint surfaces in order to assess surface roughness. By correlating the AE signals with the shear graphs one can predict the starting point of shearing during direct shear test. Count and energy parameters were analyzed in two different methods to monitor the shear behavior of the joints: a graph of the count and energy rates, and a graph of cumulative count and energy. Four separated periods were observed for bonded and non-bonded joints: linear pre-peak period, non-linear pre-peak period, post peak period and residual period. This study showed that AE has enough accuracy to monitor the shear behavior of the joints and it can be used in site confidently.
During the mining process of deep mines, the instability of surrounding rock caused by rock creep has occurred from time to time. However, it is difficult to study the accelerating creep phase of ...rock with the classical Nishihara model. Due to the influence of water seepage and different stress, rock creep exhibits non-linear characteristics. For this reason, on the basis of the Nishihara model, the dashpot in the Kelvin model was replaced by the Abel dashpot, and the dashpot in the plastomer model was modified to non-linear dashpot, and the modified Nishihara model and its constitutive equation were established. Based on the creep experimental data of granite, the experimental results of granite under different stress and different osmotic pressures were analyzed. The typical experimental data were fitted by using MATLAB software, and the fitting results showed that the modified Nishihara model was verified. The model can better describe the whole process (decelerating creep phase, stable creep phase, accelerating creep phase) and non-linear characteristics of rock creep. Especially when the load on the rock is greater than the long-term strength, the accelerating creep phase of rock is more obvious. The modified Nishihara model has five parameters, and the method for determining each parameter is simple and has wide applicability. It better reflects the damage and failure process of the surrounding rock subjected to stable creep phase and accelerating creep phase after excavation, which can provide theoretical basis for further revealing the objective law of rock creep.
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