17,388 research outputs found
Atlas of Structural Geology /
No full textAtlas of Structural Geology features a broad and inclusive range of high-quality meso- and micro-scale full-color photographs, descriptions, and captions related to the deformation of rocks and geologic structures. It is a multi-contributed, comprehensive reference that includes submissions from many of the world's leading structural geologists, making it the most thorough and comprehensive reference available to the scientific community. All types of structures are featured, including structures related to ductile and brittle shear zones, sigma- and delta-structures, mineral fish, duplexe.Includes bibliographical references and indexes.Vendor-supplied metadata.Front Cover; Atlas of Structural Geology; Copyright; Contents; List of Contributors; Preface; Acknowledgments; Chapter 1 -- Folds; REFERENCES; Chapter 2 -- Ductile Shear Zones; REFERENCES; Chapter 3 -- Brittle Faults; REFERENCES; Chapter 4 -- Boudins and Mullions; REFERENCES; Chapter 5 -- Veins; REFERENCES; Chapter 6 -- Various Structures; REFERENCES; Author Index; Subject Index.Atlas of Structural Geology features a broad and inclusive range of high-quality meso- and micro-scale full-color photographs, descriptions, and captions related to the deformation of rocks and geologic structures. It is a multi-contributed, comprehensive reference that includes submissions from many of the world's leading structural geologists, making it the most thorough and comprehensive reference available to the scientific community. All types of structures are featured, including structures related to ductile and brittle shear zones, sigma- and delta-structures, mineral fish, duplexe.Elsevie
The Central European, Tarim and Siberian Large Igneous Provinces, Late Palaeozoic orogeny and coeval metallogeny
No full textThe formation of the Central European and Tarim Large Igneous Provinces (LIPs) in the Early Permian coincided with the demise of the Variscan and the Southern Tianshan orogens, respectively. The Early Triassic Siberian LIP was formed in the wake of the Western Altaid orogeny in the Late Permian. These processes coincided with the development of the majority of known Late Palaeozoic and Early Mesozoic hydrothermal and magmatic ore deposits in the corresponding orogenic domains. Nickel-copper (-PGE) deposits followed directly from the evolution of the (ultra-)mafic melts which make up the LIPs. In Western Siberia, the diverse assemblage of associated noble and base metals in the Noril?sk-Talnakh Ni-Cu (-PGE) deposits suggests these metals also had their source in the mantle domain from which the (ultra-)mafic melts were generated. The same metals variably found their way into the hydrothermal ore deposits in the defunct Variscan and Southern Tianshan orogenic domains. These ore deposits have traditionally been viewed as a result of orogenic processes. However, their ages, together with the timing and nature of their by then intracontinental tectonic control cause uncertainty concerning the role of the orogens. In view of their mantle sources in their association with the Siberian LIP, the mantle contribution to these Late Palaeozoic hydrothermal ore deposits in the orogenic belts may have been more significant than previously thought. An orogenic contribution to melting of mantle complexes and to mineralisation may have resided in the earlier modification of subcontinental mantle domains by subduction of oceanic lithosphere. In all three cases, the controlling tectonic setting of orogenic cessation, LIP formation and mineralisation was dominated by translithospheric strikeslip deformation, possibly in combination with orogenic collapse and lithosphere delamination. In view of their recurrence, the orogen-lip sequences were probably not fortuitous. The controlling strike-slip faults were principal elements of the lithosphere-scale dynamic framework that led to the amalgamation of Pangaea. At this scale, the exceptionally large volume of the Siberian LIP may, in addition to the strike-slip dissection of the lithosphere, have been related to extension in the continental lithosphere of the margin of the Supercontinent (cf. Gutiérrez-Alonso et al. 2008). The peripheral extension was associated with compression in its centre. The explanation of these Large Igneous Provinces does not require the concept of an active mantle plume because deep-reaching strike-slip deformation, orogenic collapse and lithosphere delamination involved in the destruction of the orogenic edifices can have caused decompression melting in large domains of the subcontinental mantle
Quantifying reaction-induced stresses using high angular resolution electron backscatter diffraction (HR-EBSD): Implications for metamorphic hydration reactions
No full textHydration reactions are a fundamental metamorphic process and play a critical role in Earth’s tectonics and water budget. Petrological observations previously emphasized that volume expansion was accommodated by pressuresolution or tectonic extension. Hydration can also generate significant non-hydrostatic stresses. Resultant dilatant fracturing can increase permeability, driving reaction fronts forward, but constraints on reaction-induced stress magnitude and distribution and the contribution of thermal contraction to this stress remain to be set. The authors apply high-angular resolution electron backscatter diffraction (HR-EBSD) to the simple case of deformed calcite surrounding brucite after periclase. By cross-correlating regions of interest within diffraction patterns, HR-EBSD provides precise determination of lattice strains and residual stresses. Using finite element modelling we estimate the stresses induced by thermal contraction, indicating that the minimum reaction-induced residual stresses are roughly one gigapascal. The stress fields extend tens of micrometres away from hydration sites. High twin, fracture, and dislocation densities in calcite near brucite likely formed by relaxation of these stresses. HR-EBSD efficiently quantifies reaction-induced stresses. These strongly non-hydrostatic stresses are large enough to lead to deformation, possibly influence the far-field stress state and potentially affect local reaction thermodynamics
Tectono-stratigraphical evolution of the Çankırı basin (Central Anatolia, Turkey)
No full textThe Izmir-Ankara-Erzincan Suture Zone (IAESZ) demarcates the former position of the
northern Neotethys ocean. Along the IAESZ, the Rhodope-Pontide fragments and
Taurides collided and amalgamated in the Early Tertiary, leaving behind a number of
basins with a thick in-fill that was accumulated during the subduction and collision
processes. The <;:anklrl Basin is one of the largest of such Tertiary basins in Turkey and is
located within the IAESZ. It is a unique area to study the subduction and collisionary
processes and post-collisional history of central Anatolia, owing to a nearly complete
sedimentary record from Late Cretaceous to Recent.
This thesis presents an integrated stUdy concerning the Late Cretaceous to Recent
tectono-stratigraphical evolution of the <;:anklrl Basin using stratigraphical studies,
structural geology, kinematic analysis, paleomagnetic studies, 3D modeling, seismic
interpretation and gravimetric analysis
Geodynamic evolution of the Pan-African lower crust in Sri Lanka : structural and petrological investigations into a high-grade gneiss terrain
No full textSome main objectives of present-day geological research are to assess the role of the lower
crust in collision and extensional tectonics and to unravel the mechanism and timing of crustal
growth. Both objectives require input from the study of high-grade gneiss terrains, notably data
concerning their composition and structure and pressure-temperature-time evolution.
The high-grade gneiss terrain of Sri Lanka is a suitable area to study deep-<:rustal processes
because of good access, high outcrop density and large variation in rock composition. It
comprises three provinces: the Highland Complex (HC) flanked by the Wanni and
Kadugannawa Complexes (WKC) to the W and the Vijayan Complex (YC) to the E. The WKC
lies on top of the HC, which tectonically overlies the Vc. The VC is dominated by amphibolite
facies orthogneisses, while the other units contain granulite facies gneisses of meta-igneous and
metasedimentary parentage. Peak metamorphism occurred between -610 and -550 Ma (HOIzI et
aI., 1991) and KrOner (1991) therefore proposed a link with the Pan-African Mozambique Belt.
This thesis discusses the geodynamic evolution of the Sri Lankan basement on the basis of
new structural and petrological data and a review of earlier work. The petrological part of the
thesis starts with a description of mineral reactions in sapphirine-bearing assemblages from the
HC, which can be modelled in the FMAS system. Thermobarometry on critical assemblages
indicates peak metamorphism at about 9 kbar and 830 oC, followed by isothermal
decompression to -7.5 kbar
Gravity tectonics in Eastern Cadore and Western Carnia, (respectively provinces of Belluno and Udine), NE Italy : (with additional notes on the geochemistry of lead)
No full textIn this thesis the results are discussed of five summers
of fieldwork, (1963-1967), carried out by the
author in the areas of Eastern Cadore, (Prov. of
Belluno) and Western Carnia (Prov. of Udine), NE
Italy.
During the first and the second summer the research
was made with the aid of some B.Sc.'s in geology of
the University of Utrecht.
The purpose of this study was to give a tectonic interpretation
of this area in the Southeastern Alp
The Friningen Garnet Peridotite (central Swedish Caledonides). A good example of the characteristic PTt path of a cold mantle wedge garnet peridotite
Full text linkWe present pseudosections of Cr-bearing garnet peridotite that together with new mineral–chemical data allow quantification of the early PT conditions of the original lithospheric mantle assemblage (M1) of the Friningen Garnet Peridotite (FGP) located in the central/middle belt of the Seve Nappe Complex in central Sweden. Results indicate that the early, coarse grained, olivine + orthopyroxene + clinopyroxene + “high Cr” garnet assemblage (M1a) was formed at 1100 ± 100 °C and 5.0 ± 0.5 GPa. These metamorphic conditions were followed by an inferred late Proterozoic exhumation event down to 850–900 °C and 1.5 GPa (M1b). The latter PT estimate is based on the breakdown of high-Cr M1a garnet (Cr# = 0.065) + olivine into an orthopyroxene + clinopyroxene + spinel (Cr# = 0.15–0.25) ± pargasite kelyphite (M1b) and the exsolution of garnet from Al-rich orthopyroxene and clinopyroxene. The M1b kelyphite is overprinted by an early-Caledonian UHPM mineral assemblage (M2; T = 800 °C and P = 3.0 GPa), equivalent to the earlier discovered UHP assemblage within an eclogitic dyke that cross-cuts FGP. In the garnet peridotite M2 is displayed by low-Cr garnet (Cr# = 0.030) growing together with spinel (Cr# = 0.35–0.45), both these minerals form part of the olivine + orthopyroxene + clinopyroxene + garnet + spinel + pargasite M2 assemblage. The formation of plagioclase + diopside symplectites after omphacite and breakdown of kyanite to sapphirine + albite in internal eclogite and the breakdown of M2 olivine + garnet to amphibole + orthopyroxene + spinel assemblages (M3) in garnet peridotite indicate post-UHP isothermal decompression down to 750–800 °C and 0.8–1.0 GPa (= M3). Multiphase solid-and fluid inclusion assemblages composed of Sr-bearing magnesite, dolomite or carbon decorate linear defect structures within M1a–b minerals and/or form subordinate local assemblages together with M2 minerals. The latter are interpreted as evidence for infiltration of early-Caledonian COH-bearing subduction zone fluids. The well-defined PTt-deformation path of the FGP resembles that of a mantle wedge garnet peridotite. The M1 assemblage originates from the base of a cold, old and thick subcontinental lithospheric mantle that is inferred to extend asymmetrically leading to extreme exhumation of FGP down to lithospheric conditions around 1.5 GPa and 850–900 °C. After that the FGP became incorporated into the subducting continental crust of the SNC during “early-Caledonian” subduction (M2) down to UHPM conditions (800 °C/3.0 GPa), subsequently followed by eduction back to sub-crustal levels. As such, FGP is the first locality in the Swedish Caledonides from which two UHP metamorphic events are described, the first event can be related to the formation of an ancient (> 1.0 Ga) lithosphere underneath a craton (Rodinia) and the second is of early-Caledonian age
Three sets of crystallographic sub-planar structures in quartz formed by tectonic deformation
Full text linkIn quartz, multiple sets of fine planar deformation microstructures that have specific crystallographic orientations parallel to planes with low Miller-Bravais indices are commonly considered as shock-induced planar deformation features (PDFs). 1 diagnostic of shock metamorphism. Using polarized light microscopy, we demonstrate that up to three sets of tectonically induced sub-planar fine extinction bands (FEBs), sub-parallel to the basal, γ, ω, and π crystallographic planes, are common in vein quartz in low-grade tectonometamorphic settings. We conclude that the observation of multiple (2-3) sets of fine scale, closely spaced, crystallographically controlled, sub-planar microstructures is not sufficient to unambiguously distinguish PDFs from tectonic FEBs
Sulfide Mineralogy as a Tracer for Fluid-Rock Interaction in Serpentinites
No full textFluid-rock interaction in ultramafic rocks leads to considerable changes in the fluid redox conditions and the formation of highly reducing conditions. In this regard, serpentinization systems are some of the most reducing environments found on Earth allowing for the stabilization of native metals and metal alloys and thus affecting the petrophysical properties of the oceanic lithosphere. At the Chimaera hydrothermal field in Turkey highly methaneenriched fluids issue from an ultramafic basement that is undergoing continental serpentinization, though partial serpentinization already took place during mantle exposure along an oceanic spreading center. Here, we study the sulfur geochemistry and mineralogy of selected, highly serpentinized peridotites to track sulfur sources, mobilization mechanisms of sulfur and the evolution of the redox conditions during hydrothermal alteration of these rocks – from high-temperature oceanic to low temperature continental serpentinization. Sulfur isotope compositions document seafloor alteration with introduction of Cretaceous seawater and a mostly magmatic origin of the sulfide that mainly includes pentlandite. However, sulfide and metal mineral assemblages also document fluid-rock interaction processes; awaruite and native Cu reflect highly reducing fluid conditions whereas hematite and magnetite reflect oxidizing conditions suggesting secondary formation or alteration of primary formed pentlandite during fluid-rock interaction. Sulfide minerals show distinct decomposition features with formation of native metals (mostly native Cu) providing evidence for disequilibrium conditions. Furthermore, we find strong redox gradients on the micrometer scale indicating that late stage fluid infiltration – most likely during continental serpentinization and associated with highly reducing fluids – overprinted earlier sulfide and metal mineral assemblages from oceanic serpentinization. These observations provide evidence that redox conditions strongly vary during the evolution of peridotite-hosted hydrothermal systems
Low-temperature intracrystalline deformation microstructures in quartz
Full text linkA review of numerous genetic interpretations of the individual low-temperature intracrystalline deformation microstructures in quartz shows that there is no consensus concerning their formation mechanisms. Therefore, we introduce a new, purely descriptive terminology for the three categories of intracrystalline deformation microstructures formed in the low-quartz stability field: fine extinction bands (FEB), wide extinction bands (WEB) and localised extinction bands (LEB). The localised extinction bands are further subdivided into blocky (bLEB), straight (sLEB) and granular (gLEB) morphological types. A detailed polarised light microscopy study of vein-quartz from the low-grade metamorphic High-Ardenne slate belt (Belgium) further reveals a series of particular geometric relationships between these newly defined intracrystalline deformation microstructures. These geometric relationships are largely unrecognised or underemphasised in the literature and need to be taken into account in any future genetic interpretation. Based on our observations and a critical assessment of the current genetic models, we argue that the interpretation of the pertinent microstructures in terms of ambient conditions and deformation history should be made with care, as long as the genesis of these microstructures is not better confined
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