We present in situ secondary ion mass spectrometry (SIMS) and electron microprobe analyses of coexisting garnet, omphacite, phengite, amphibole, and apatite, combined with pyrohydrolysis bulk-rock ...analyses to constrain the distribution, abundance, and behavior of halogens (F and Cl) in six MORB-like eclogites from the Raspas Complex (Southern Ecuador). In all cases concerning lattice-hosted halogens, F compatibility decreases from apatite (1.47-3.25 wt%), to amphibole (563-4727 µg/g), phengite (610-1822 µg/g), omphacite (6.5-54.1 µg/g), and garnet (1.7-8.9 µg/g). The relative compatibility of Cl in the assemblage is greatest for apatite (192-515 µg/g), followed by amphibole (0.64-82.7 µg/g), phengite (1.2-2.1 µg/g), omphacite (<0.05-1.0 µg/g), and garnet (<0.05 µg/g). Congruence between SIMS-reconstructed F bulk abundances and yield-corrected bulk pyrohydrolysis analyses indicates that F is primarily hosted within the crystal lattice of eclogitic minerals. However, SIMS-reconstructed Cl abundances are a factor of five lower, on average, than pyrohydrolysis-derived bulk concentrations. This discrepancy results from the contribution of fluid inclusions, which may host at least 80% of the bulk rock Cl. The combination of SIMS and pyrohydrolysis is highly complementary. Whereas SIMS is well suited to determine bulk F abundances, pyrohydrolysis better quantifies bulk Cl concentrations, which include the contribution of fluid inclusion-hosted Cl. Raspas eclogites contain 145-258 µg/g F and at least 7-11 µg/g Cl. We estimate that ∼95% of F is retained in the slab through eclogitization and returned to the upper mantle during subduction, whereas at least 95% of subducted Cl is removed from the rock by the time the slab equilibrates at eclogite facies conditions. Our calculations provide further evidence for the fractionation of F from Cl during high-pressure metamorphism in subduction zones. Although the HIMU (high U/Pb) mantle source (dehydrated oceanic crust) is often associated with enrichments in Cl/K and F/Nd, Raspas eclogites show relatively low halogen ratios identical within uncertainty to depleted MORB mantle (DMM). Thus, the observed halogen enrichments in HIMU ocean island basalts require either further fractionation during mantle processing or recycling of a halogen-enriched carrier lithology such as serpentinite into the mantle.
There is a growing demand of knowledge on the behavior of rock masses after thermal treatment in both academic and practical aspects due to the high demand of construction of underground structures ...under the high-temperature environment. The peak shear strength of rock joints has a significant role in evaluating the stability problems of surrounding rocks. However, there is a lack of information about the temperature-dependent nature of the basic friction angle of rock joints, which serves as an essential parameter to evaluate the peak shear strength. The present study experimentally investigates the influences of temperature magnitude (20, 200, 400, 600, and 800 °C) on the basic friction angle of granite, marble, and red sandstone joints. The basic friction angles of the three kinds of rock joints exhibit linear trends with the increase in the treatment temperature. The basic friction angles of granite and red sandstone joints increase with the increase in the treatment temperature, while the values for marble joints continually decrease. The mechanisms for the thermally altered variations in the basic friction angle of rock joint are mainly related to dehydration process, uneven expansion of mineral grains, thermally weakened asperities distributed on the surfaces, and change in physical and mechanical properties of minerals. In addition, other test conditions, including tilting rate, specimen size, repetition number, and cooling rate, are also analyzed. The present study provides useful data in establishing a peak shear strength criterion for rock joints by considering the temperature effect.
The tectonic regime and melting conditions of adakitic tonalitic‐trondhjemitic leucosomes and tonalite plutons from the North Qaidam terrane are evaluated through petrology, whole‐rock major, trace ...element and Sr‐Nd isotopic data and zircon U‐Pb data. Zircons from leucosomes and metabasites preserve distinct U‐Pb age populations: early Ordovician inherited zircon cores record a protolith age of ~470 Ma, whereas zircon rims preserve subsequent HP granulite facies metamorphism, anatexis, and magmatism between 437 and 433 Ma. Whole‐rock geochemistry suggests that three types of leucosomes and tonalite plutons have geochemical features similar to adakites. Type 1 leucosomes record high Sr contents and positive Eu anomalies representing an earlier period of plagioclase accumulation. The flat fractionated rare earth element patterns of type 2 leucosomes correspond to residues of HP mafic granulites, and the steep fractionated rare earth element patterns of type 3 leucosomes correspond to garnet‐ and clinopyroxene‐rich residues. Petrological observations with P‐T paths and experimentally constrained melting curves together infer that melting of the metagabbro were triggered by the breakdown of amphibole ± zoisite under high‐pressure conditions. Therefore, tonalite, trondhjemite, and granodiorite (TTG)‐adakitic magmas in the North Qaidam terrane were produced through partial melting of newly emplaced gabbroic rocks with an arc affinity under high‐pressure, granulite facies conditions in a thickened lower crust during continental collision. This model explains the origin of TTG‐adakitic rocks and related continental growth and crustal differentiation genetically associated with continental collision.
Key Points
TTG‐like magmas in the North Qaidam were produced by partial melting of newly emplaced metagabbros under HP granulite facies conditions
Metagabbros possess a subduction‐related arc signature, whereas leucosomes and tonalite plutons record geochemical features similar to TTGs
TTG‐like rocks and related continental growth genetically are associated with continental collision zones
Discrete element simulation of rock cutting Rojek, Jerzy; Oñate, Eugenio; Labra, Carlos ...
International journal of rock mechanics and mining sciences,
09/2011, Volume:
48, Issue:
6
Journal Article
Peer reviewed
Open access
This paper presents numerical modelling of rock cutting processes. The model consists of a tool–rock system. The rock is modelled using the discrete element method, which is suitable to study ...problems of multiple material fracturing such as those involved in rock cutting. Both 2D and 3D models are considered in this work. The paper presents a brief overview of the theoretical formulation and calibration of the discrete element model by a methodology combining the dimensional analysis with simulation of the unconfined compressive strength (UCS) and indirect tension (Brazilian) tests. The rock cutting process with roadheader picks, which is typical for underground excavation, has been simulated. The results of the 2D and 3D analyses have been compared with one another, and numerical results have been compared with the available experimental data.
► Advanced modelling of a complex engineering problem using the discrete element model. ► Calibration of the discrete element model. ► Successful validation of the numerical model using experimental results of rock cutting.
Owing to the importance of serpentinites for planetary geochemical and geodynamic processes, there has been much work discerning the origins of their parent rocks, including distinguishing between ...serpentinites derived from a subducting plate versus overlying mantle in exhumed subduction complexes. The island of New Caledonia (SW Pacific Ocean) provides a rare window into Cenozoic Pacific subduction processes. The island is unique in exposing both an exceptionally preserved high‐pressure, low‐temperature subduction complex and one of the largest supra‐subduction zone ophiolites in the world. Previous studies disagree on the origin of serpentinites in the subduction complex. In this study, we analyze 23 serpentinites from this complex for whole‐rock major and trace element geochemistry and stable isotope (δD, δ18O) compositions. Our data reveal two distinct groups of serpentinites: Group I samples in the northern portion of the complex are pervasively serpentinized, and exhibit enriched heavy rare earth element (REE) compositions and δ18O values between +6.7‰ and +10.2‰. In contrast, Group II serpentinites in the south preserve relict orthopyroxene and olivine, and show depleted trace element compositions and comparatively lower δ18O values between +5.1‰ and +8.0‰. We interpret Group I serpentinites to derive from downgoing plate mantle, whereas Group II serpentinites derive from overlying mantle wedge, exhibiting remarkable similarity to the REE geochemistry of the structurally overlying New Caledonia ophiolite. Our results establish the subduction complex in New Caledonia as an unusual natural record of the entrainment and exhumation of mantle from both the overlying mantle wedge and the downgoing plate in an oceanic subduction zone.
Plain Language Summary
The hydration of Earth's mantle produces rocks called serpentinites that are important to chemical cycling within the Earth system. This process, a form of metamorphism, occurs in several types of tectonic settings on Earth. Serpentinites formed in these different settings are imparted with unique geochemical “fingerprints” due to different types of fluids and varied compositions of the original mantle material. In metamorphic complexes that preserve remnants of subduction zones, serpentinites can offer clues to the original tectonic setting and subsequent mechanics of subduction. We analyze stable isotope and whole‐rock compositions to determine the origin of the mantle that produced serpentinites found in the metamorphic complex preserved in New Caledonia (SW Pacific). We discover two distinct groups of serpentinites: one group in the northern portion of the complex likely formed on the ocean floor prior to subduction, and experienced high degrees of fluid alteration as it was metamorphosed. In contrast, a second group of serpentinites in the southern portion of the complex resembles material from the mantle overlying the subducting plate and is less altered. This locality represents an uncommon example, globally, where material from the overlying mantle was entrained and then preserved at the surface in an exhumed subduction complex.
Key Points
Two compositionally distinct types of serpentinites are identified in the New Caledonia subduction complex
Some serpentinites derive from the subducting plate, others from the overlying mantle wedge
New Caledonia preserves evidence for incorporation and exhumation of mantle hangingwall via the subduction channel
Constraining the source, genesis, and evolution of Archaean felsic crust is key to understanding the growth and stabilization of cratons. The Akia Terrane, part of the North Atlantic Craton, West ...Greenland, is comprised of Meso-to-Neoarchaean orthogneiss, with associated supracrustal rocks. We report zircon U–Pb and Lu–Hf isotope data, and whole-rock geochemistry, from samples of gneiss and supracrustals from the northern Akia Terrane, including from the Finnefjeld Orthogneiss Complex, which has recently been interpreted as an impact structure. Isotope data record two major episodes of continental crust production at ca. 3.2 and 3.0 Ga. Minor ca. 2.7 and 2.5 Ga magmatic events have more evolved εHf, interpreted as reworking of existing crust perhaps linked to terrane assembly. Felsic rocks from the Finnefjeld Orthogneiss Complex were derived from the same source at the same time as the surrounding tonalites, but from shallower melting, requiring any bolide-driven melting event to have occurred almost simultaneously alongside the production of the surrounding crust. A simpler alternative has the Finnefjeld Complex and surrounding tonalite representing the coeval genesis of evolved crust over a substantial lithospheric depth. Hafnium isotope data from the two major Mesoarchaean crust-forming episodes record a contribution from older mafic Eoarchaean crust. Invoking the involvement of an Eoarchaean root in the growth of younger Mesoarchaean crust puts important constraints on geodynamic models of the formation of the discrete terranes that ultimately assembled to form Earth’s cratons.
During underground mining, rock deformation may be time-dependent and is reflected in rheological behavior. These changes may be also accelerated by dynamic disturbances, such as rock blasting, which ...can trigger mining-induced hazards such as rockburst and a falling roof. A combined double-rock sample was analyzed to clarify the rockburst mechanism resulting from interaction between roof and pillar. In this work, a double-rock sample was subjected to a combined creep and dynamic loading condition. Based on the results, an ideal mechanical model was developed to describe the interaction between double rock samples loaded in series to simulate interaction between the pillar and roof. To test the model, a double-rock sample composed of granite and sandstone was loaded in series under creep and dynamic loading and the effect of dynamic disturbance on the creep process was quantified. Under the same creep stress, a higher impact dynamic disturbance resulted in shorter failure time. Under the same dynamic disturbance, the specimen failed faster with increased strain energy of rebound of the granite sample under increasing creep stress. The energy dissipation rate and energy transfer efficiency are defined to quantify the energy dissipation of double-rock sample and energy transfer between strong and weak sample. Based on the quantification of energy transfer efficient, it confirms that the ratio of stiffness of the double-rock sample should be a indicator for the energy transfer between strong and weak samples. The granite sample had higher uniaxial compressive strength, so it did not fail during the loading process. For the plaster-granite sample, the granite released most energy to accelerate the unstable failure of plaster. The granite-granite sample failed simultaneously and released most strain energy violently. The results can provide a reference to evaluate the delayed rockburst of rock subjected to creep stress.
Brian Eno Albiez, Sean; Pattie, David
2016, 2016-08-11
eBook
On the back of his published diary Brian Eno describes himself variously as: a mammal, a father, an artist, a celebrity, a pragmatist, a computer-user, an interviewee, and a 'drifting clarifier'. To ...this list we might add rock star (on the first two Roxy Music albums); the creator of lastingly influential music (Another Green World; Music for Airports); a trusted producer (for Talking Heads, U2, Coldplay and a host of other artists); the maker of large-scale video and installation artworks; a maker of apps and interactive software; and so on. He is one of the most feted and influential musical figures of the past forty years, even though he has described himself on more than one occasion as a non-musician. This volume examines Eno's work as a musician, as a theoretician, as a collaborator, and as a producer. Brian Eno is one of the most influential figures in popular music; an updated examination of his work on this scale is long overdue. - See more at: http://www.bloomsbury.com/uk/brian-eno-9781441129123/#sthash.CmHDQ6Xy.dpuf
Drop the record needle on any vinyl album in your collection, then read the first pages of that novel you've been meaning to pick up—the reverberations between them will be impossible to miss. Since ...Dylan went electric, listening to rock 'n' roll has often been a surprisingly literary experience, and contemporary literature is curiously attuned to the history and beat of popular music. In The Ink in the Grooves, Florence Dore brings together a remarkable array of acclaimed novelists, musicians, and music writers to explore the provocatively creative relationship between musical and literary inspiration: the vitality that writers draw from a three-minute blast of guitars and the poetic insights that musicians find in literary works from Shakespeare to Southern Gothic. Together, the essays and interviews in The Ink in the Groove s provide a backstage pass to the creative processes behind some of the most exciting and influential albums and novels of our time. Contributors: Laura Cantrell, Michael Chabon, Roddy Doyle, Bob Dylan, Steve Earle, William Ferris, Dom Flemons, Rhiannon Giddens, Dave Grohl, Peter Guralnick, Amy Helm, Randall Kenan, Jonathan Lethem, Greil Marcus, Rick Moody, Lorrie Moore, the John Prine band (Dave Jacques, Fats Kaplin, Pat McLaughlin, Jason Wilber), Dana Spiotta, John Jeremiah Sullivan, Richard Thompson, Scott Timberg, Daniel Wallace, Colson Whitehead, Lucinda Williams, Warren Zanes.
Rock failure phenomena, such as rockburst, slabbing (or spalling) and zonal disintegration, related to deep underground excavation of hard rocks are frequently reported and pose a great threat to ...deep mining. Currently, the explanation for these failure phenomena using existing dynamic or static rock mechanics theory is not straightforward. In this study, new theory and testing method for deep underground rock mass under coupled static-dynamic loading are introduced. Two types of coupled loading modes, i.e. “critical static stress t slight disturbance” and “elastic static stress t impact disturbance”, are proposed, and associated test devices are developed. Rockburst phenomena of hard rocks under coupled static-dynamic loading are successfully reproduced in the laboratory, and the rockburst mechanism and related criteria are demonstrated. The results of true triaxial unloading compression tests on granite and red sandstone indicate that the unloading can induce slabbing when the confining pressure exceeds a certain threshold, and the slabbing failure strength is lower than the shear failure strength according to the conventional Mohr-Column criterion. Numerical results indicate that the rock unloading failure response under different in situ stresses and unloading rates can be characterized by an equivalent strain energy density. In addition, we present a new microseismic source location method without premeasuring the sound wave velocity in rock mass, which can efficiently and accurately locate the rock failure in hard rock mines. Also, a new idea for deep hard rock mining using a non-explosive continuous mining method is briefly introduced.
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