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Plate tectonics /
No full textDevelopments in Geotectonics, 6: Plate Tectonics focuses on the exposition of the plate-tectonics hypothesis, as well as plate boundaries, stratification, and kinematics. The book first offers information on the rheological stratification of the mantle and kinematics of relative movements. Topics include lithosphere, asthenosphere, kinematics of finite motions, measurements of instantaneous movements, and worldwide kinematic pattern. The text then ponders on movements relative to a frame external to the plates and processes at accreting plate boundaries. Discussions focus on reference frames,Includes bibliographical references (pages 279-300).Electronic reproduction.Master and use copy. Digital master created according to Benchmark for Faithful Digital Reproductions of Monographs and Serials, Version 1. Digital Library Federation, December 2002.digitizedPrint version record.Front Cover; Plate Tectonics; Copyright Page; Foreword; Preface; Tabel of Contents; CHAPTER 1. Introduction; CHAPTER 2. Definition; CONSEQUENCES; LIMITATIONS; CHAPTER 3. Rheological stratification of the mantle; LITHOSPHERE; ASTHENOSPHERE; THE LITHOSPHERE AS A STRESS-GUIDE; THE DRIVING MECHANISM; CHAPTER 4. Kinematics of relative movements; INTRODUCTION; INSTANTANEOUS MOVEMENTS; KINEMATICS OF FINITE MOTIONS; MEASUREMENTS OF INSTANTANEOUS MOVEMENTS; PRESENT WORLDWIDE KINEMATIC PATTERN; MEASUREMENTS OF FINITE MOVEMENTS; CHAPTER 5. Movements relative to a frame external to the platesINTRODUCTIONREFERENCE FRAMES; ""ABSOLUTE"" MOVEMENT DETERMINATION; PALEOMAGNETIC SYNTHESIS; CHAPTER 6. Processes at accreting plate boundaries; INTRODUCTION; THE CREATION OF THE OCEANIC CRUST; CONTINENTAL RIFTS; CONTINENTAL MARGINS; CHAPTER 7. Processes at consuming plate boundaries; INTRODUCTION; SINKING PLATE MODEL; STRUCTURE OF TRENCHES AND ASSOCIATED ISLAND ARCS AND CORDILLERAS; CONSUMPTION OF CONTINENT-BEARING LITHOSPHERE; PLATE TECTONICS AND GEOLOGY; Appendix; ReferencesDevelopments in Geotectonics, 6: Plate Tectonics focuses on the exposition of the plate-tectonics hypothesis, as well as plate boundaries, stratification, and kinematics. The book first offers information on the rheological stratification of the mantle and kinematics of relative movements. Topics include lithosphere, asthenosphere, kinematics of finite motions, measurements of instantaneous movements, and worldwide kinematic pattern. The text then ponders on movements relative to a frame external to the plates and processes at accreting plate boundaries. Discussions focus on reference frames,Elsevie
Digital Tectonics as a Morphogenetic Process
Full text linkp. 938-948Tectonics is a seminal concept that defines the nature of the relationship between
architecture and its structural properties. The changing definition of the symbiotic
relationship between structural engineering and architectural design may be considered one of the formative influences on the conceptual evolution of tectonics in different historical periods. Recent developments in the field of morphogenesis, digital media, theories techniques and methods of digital design have contributed a new models of integration between structure, material and form in digital tectonics.
The objective of this paper is to propose and define tectonics as a model of morphogenetic process. The paper identifies and presents the manner in which theory and emerging concepts of morphogenesis as well as digital models of design are contributing to this new model. The paper first analyzes the historical evolution of tectonics as a concept and characterizes the emergence of theoretical framework reflected in concepts and terms related to morphogenesis.Oxman, R. (2010). Digital Tectonics as a Morphogenetic Process. Editorial Universitat Politècnica de València. https://riunet.upv.es/handle/10251/695
Tectonic significance of changes in post-subduction Pliocene-Quaternary magmatism in the south east part of the Carpathian-Pannonian Region
Full text linkThe south-eastern part of the Carpathian–Pannonian region records the cessation of convergence between the European platform/Moesia and the Tisza–Dacia microplate. Plio-Quaternary magmatic activity in this area, in close proximity to the ‘Vrancea zone’, shows a shift from normal calc-alkaline to much more diverse compositions (adakite-like calc-alkaline, K-alkalic, mafic Na-alkalic and ultrapotassic), suggesting a significant change in geodynamic processes at approximately 3 Ma. We review the tectonic setting, timing, petrology and geochemistry of the post-collisional volcanism to constrain the role of orogenic building processes such as subduction or collision on melt production and migration. The calc-alkaline volcanism (5.3–3.9 Ma) marks the end of normal subduction-related magmatism along the post-collisional Călimani–Gurghiu–Harghita volcanic chain in front of the European convergent plate margin. At ca. 3 Ma in South Harghita magma compositions changed to adakite-like calc-alkaline and continued until recent times (< 0.03 Ma) interrupted at 1.6–1.2 Ma by generation of Na and K-alkalic magmas, signifying changes in the source and melting mechanism. We attribute the changes in magma composition in front of the Moesian platform to two main geodynamic events: (1) slab-pull and steepening with opening of a tear window (adakite-like calc-alkaline magmas) and (2) renewed contraction associated with deep mantle processes such as slab steepening during post-collisional times (Na and K-alkalic magmas). Contemporaneous post-collisional volcanism at the eastern edge of the Pannonian Basin at 2.6–1.3 Ma was dominated by Na-alkalic and ultrapotassic magmas, suggesting a close relationship with thermal asthenospheric doming and strain partitioning related to the Adriatic indentation. Similar timing, magma chamber processes and volume for K-alkalic (shoshonitic) magmas in the South Apuseni Mountains (1.6 Ma) and South Harghita area at a distance of ca. 200 km imply a regional connection with the inversion tectonics
Tectonics of the crystalline Basement of the Dolomites in North Italy
No full textThe present thesis deals with a number of
crystalline regions around the Dolomites in North
Italy. The geographic position is shown on sheet
I, which is depicted in fig. 105. The Dolomites
proper consist mainly of Permotriassic, overlying
a transgression plane, which cuts off the studied
crystalline rocks. The tectonics of this crystalline
basement have been scarcely studied hitherto,
in contradistinction with the overlying sediments,
the Alpine tectonics of which are rather wellknown.
The complexity of the geometry of the
crystalline basement, which may have caused this
apparent lack of interest, is due to several factors.
In the first place, a general stratigraphy of these
uniform and for the greater part mesozonal
micaschists has not been established. Therefore, it
is necessary to base the tectonic interpretation almost
entirely on the schistosity and the generally
present minor folds. The age of these tectonical
elements is generally pre-Permian. It can be proved
that originally subhorizontal schistOsity-planes
have been folded twice during the Hercynian orogenesis.
In the second place, this Hercynian folded
basement was deformed intensively during the
Alpine orogenesis. A clear distinction between
Hercynian and Alpine orogenesis is possible only
by studying the pure Alpine tectonics of the adjacent
Permotriassic sediments. For this reason,
and because the existing geologic maps appeared
to be inadequate, certain parts of these sediments
have been mapped again.
The fundamental tectonical values are scattered
around the mean of the group to which they
belong. Only the mean of a number of single
values is a basis for regional tectonics. The means
vary from place to place. Many measurements
had to be made to determine the geometry of the
means. A methodology had to be developed for
calculating the means and for constructing the
structure maps
Interactions between thin- and thick-skinned tectonics at the northwestern front of the Jura fold-and-thrust belt (eastern France)
Full text linkInternational audienceThis study investigates spatial and temporal interactions of thin- and thick-skinned tectonics in a classical foreland setting located at the front of the Jura fold-and-thrust belt in eastern France. The working area coincides with the intracontinental Rhine-Bresse Transfer Zone and represents the most external front of the deformed Alpine foreland. The investigation combines analyses of largely unpublished and newly available subsurface information with our own structural data, including an exhaustive paleostress analysis and geomorphologic observations. Results are provided in the form of a new tectonic map and a series of regional cross sections through the study area. The Besançon Zone, forming the most external part of the thin-skinned fold-and-thrust belt, encroached onto the Eo-Oligocene Rhine-Bresse Transfer Fault System until early Pliocene times. Thrust propagation was largely controlled by the Late Paleozoic to Paleogene preexisting fault pattern that characterizes the Rhine-Bresse Transfer Zone. Thick-skinned deformation, dominant throughout the Avant-Monts Zone located farther to the west, was associated with compressional to transpressional reactivation of such faults. Overprinting and crosscutting criteria of fault slip data allow distinguishing between systematically fanning maximum horizontal stress axes that define the front of the thin-skinned Jura fold-and-thrust belt and consistently NW–SE directed maximum horizontal stress axes that characterize deformation of the autochthonous cover of the foreland, which is affected by thick-skinned tectonics. Tectonic and geomorphic analyses indicate that thick-skinned tectonics started at a very late stage of foreland deformation (post-early Pliocene). Geomorphic observations imply that deformation between Mesozoic cover and basement is locally still decoupled. However, overprinting relationships and recent seismicity suggest that present-day tectonic activity is thick skinned, which probably reflects ongoing tectonic underplating in the Alpine foreland
Gravity tectonics in the Northwestern Dolomites (N. Italy)
No full textThe NW Dolomites (see fig. 1 and 2) have an
area of approximately 1500 sq. km and are situated
on the southern flank of the east alpine mountain
range. The region consists mainly of permo-triassic
and some younger mesozoic strata with a maximal
thickness of about 3000 m. This sedimentary series
was deposited unconformably on the basement of
quartz phyllites, which had been metamorphosed
during the hercynian orogenesis.
This thesis deals especially with the tectonic evolution
of the area. The greater part of the tectonic
structures of the permo-triassic strata have previously
been explained by most authors, excepting Diener,
Accordi and Signorini, as a result of regional,
tangential compression related to the alpine orogenesis.
But a study of the crucial points of the tectonics
showed that an explanation of the structural
evolution by means of more locally restricted gravity
tectonics should be preferred.
The more general principles of the tectonic evolution
of the eastern Alps, as expounded by Van
Bemmelen (1960 a and b), are accepted as the
tectonic setting for the structural evolution of the
NW Dolomites in cenozoic time.
The NW Dolomites are the northwestern corner
of the larger unit of the Dolomites. The latter unit
of the southeastern Alps lagged behind during the
rise of the east alpine geanticline in tertiary time.
This Dolomites-block has been separated from the
more elevated, central parts of the geanticline by
the large Judicaria and Pusteria faults (with a
vertical throw of at least 5 km). Between this fault
system and the area of the Dolomites a zone of
relative subsidence is intercalated, which has a
graben-like or synclinal character (Brenta Alps, Val
di Non area, Sarntal Alps, Pusteria Valley). From
San Candido this zone extends SE-ward to San
Stefano di Cadore, this tract (Valle di Sesto) separates
the Dolomites from the Carnian Alps.
Parts of this depressed zone have been compressed
subsequently by the gravitative spreading of the
adjacent higher areas to the NW, N, and NE.
(Dietzel, 1960; Van Hilten, 1960; Agterberg 1961).
These authors have shown that this marginal belt
along its NW, N, and NE side has been subjected
to tectogenesis as a result of gravitational reactions
to the rise of the east alpine geanticline.
The central part of the NW Dolomites, however,
has been more or less shielded from this gravitational
stress field radiating from the central alpine
uplift, by the deformations of this marginal belt.
In this central part of the NW Dolomites the tectonic
deformations of the sedimentary cover are
merely an indirect result of the alpine orogeny. The
tertiary uplift of the area caused a strong erosion.
This erosion created a considerable relief with more
local stress fields due to relief energy. The complicated
tectonic structures of the NW Dolomites appear
to be almost entirely the result of the local
relief-energy produced by differential erosion in the
course of the cenozoic time (such as the removal of
the soft La Valle and San Cassiano strata between
the ladino-carnian reef masses)
Low-temperature thermochronology and thermokinematic modeling of deformation, exhumation, and development of topography in the central Southern Alps, New Zealand
No full textApatite and zircon (U-Th)/He and fission track ages were obtained from ridge transects across the central Southern Alps, New Zealand. Interpretation of local profiles is difficult because relationships between ages and topography or local faults are complex and the data contain large uncertainties, with poor reproducibility between sample duplicates. Data do form regional patterns, however, consistent with theoretical systematics and corroborating previous observations: young Neogene ages occur immediately southeast of the Alpine Fault (the main plate boundary structure on which rocks are exhumed); partially reset ages occur in the central Southern Alps; and older Mesozoic ages occur further toward the southeast. Zircon apparent ages are older than apatite apparent ages for the equivalent method. Three-dimensional thermokinematic modeling of plate convergence incorporates advection of the upper Pacific plate along a low-angle detachment then up an Alpine Fault ramp, adopting a generally accepted tectonic scenario for the Southern Alps. The modeling incorporates heat flow, evolving topography, and the detailed kinetics of different thermochronometric systems and explains both complex local variations and regional patterns. Inclusion of the effects of radiation damage on He diffusion in detrital apatite is shown to have dramatic effects on results. Geometric and velocity parameters are tuned to fit model ages to observed data. Best fit is achieved at 9 mm a−1 plate convergence, with Pacific plate delamination on a gentle 10°SE dipping detachment and more rapid uplift on a 45–60° dipping Alpine Fault ramp from 15 km depth. Thermokinematic modeling suggests dip-slip motion on reverse faults within the Southern Alps should be highest ∼22 km from the Alpine Fault and much lower toward the southeast
The Heart of China revisited: II Early Paleozoic (ultra)high-pressure and (ultra)high-temperature metamorphic Qinling orogenic collage
No full textOrogens with multiple (ultra)high-pressure ((U)HP) and (ultra)high- temperature ((U)HT) metamorphic events provide a complex but telling record of oceanic and continental interaction. The Early Paleozoic history of the "Heart of China," the Qinling orogenic collage, offers snapshots of at least three (U)HP and two (U)HT metamorphic events. The preservation of remnants of both oceanic and continental domains together with a ≥110 Myr record of magmatism allows the reconstruction of the processes that resulted in this disparate metamorphism. Herein, we first illuminate the pressure-temperature-time (P-T-t) evolution of the Early Paleozoic (U)HP and (U)HT events by refining the petrographic descriptions and P-T estimates, assess published, and employ new U/Th-Pb zircon, monazite, and titanite, and 40Ar-39Ar phengite geochronology to date the magmatic and metamorphic events. Then we explore how the metamorphic and magmatic events are related tectonically and how they elucidate the affinities among the various complexes in the Qinling orogenic collage. We argue that a Meso-Neoproterozoic crustal fragment - the Qinling complex - localized subduction-accretion events that involved subduction, oceanic-arc formation, and back-arc spreading along its northern margin, and mtantle-wedge exhumation and spreading-ridge subduction along its southern margin. ©2013. American Geophysical Union. All Rights Reserved.link_to_subscribed_fulltex
Inherited landscapes and sea level change
Full text linkEnabled by recently gained understanding of deep-seated and surficial Earth processes, a convergence of views between geophysics and sedimentary geology has been quietly taking place over the past several decades. Surface topography resulting from lithospheric memory, retained at various temporal and spatial scales, has become the connective link between these two methodologically diverse geoscience disciplines. Ideas leading to the hypothesis of plate tectonics originated largely with an oceanic focus, where dynamic and mostly horizontal movements of the crust could be envisioned. But when these notions were applied to the landscapes of the supposedly rigid plate interiors, there was less success in explaining the observed anomalies in terrestrial topography. Solid-Earth geophysics has now reached a developmental stage where vertical movements can be measured and modeled at meaningful scales and the deep-seated structures can be imaged with increasing resolution. Concurrently, there have been advances in quantifying mechanical properties of the lithosphere (the solid outer skin of Earth, usually defined to include both the crust and the solid but elastic upper mantle above the asthenosphere). The lithosphere acts as the intermediary that transfers the effects of mantle dynamics to the surface. These developments have allowed us to better understand the previously puzzling topographic features of plate interiors and continental margins. On the sedimentary geology side, new quantitative modeling techniques and holistic approaches to integrating source-to-sink sedimentary systems have led to clearer understanding of basin evolution and sediment budgets that allow the reconstruction of missing sedimentary records and past geological landscapes
Seismicity and regional tectonics of the Estremadura, Southwestern Portugal
Full text linkThe RESTE Project was an integrated geophysical-geological study of the Estremadura, southwestern Portugal. The core of the programme consisted of the acquisition and analysis of microearthquake data. This was complemented by an investigation of the structural evolution of the sedimentary basins of the Estremadura. The geological evolution of the Lusitanian Basin was strongly marked by the reactivation of Palaeozoic basement faults, in response to a sequence of tectonic events: opening of the Central Atlantic, opening of the North Atlantic and Alpine convergence between Africa and Eurasia. The current tectonics are regarded as a subdued continuation of the Miocene deformation (Betic Orogeny), and the "tectonic memory" revealed by the Lusitanian and Lower Tagus Basins is explored to characterize the current tectonic processes. Strike-slip tectonics are identified as a dominant feature of several stages of the evolution of the basins, with particular relevance during the Miocene. The technique of "backstripping" is applied to well data, to constrain the history of vertical movement in the basins. This analysis highlighted the pre mature truncation, in the Late Jurassic, of a normal passive-margin evolution. Tectonic unstability caused the structural inversion of areas within the basins, and seems to have inhibited the predictable thermal subsidence. The rifting process, initially taking place at the Lusitanian Basin, jumped westwards in the Late Jurassic. Crustal underplating and the activity of transfer faults are in-voked as possible explanations for the subsequent deformation of the aborted rift. An upper-plate margin configuration is in good agreement with several observations. The tendency for structural inversion continued throughout theCretaceous, and with the onset of the Alpine convergence in the Turonian the control of the tectonic activity seems to have switched from the Atlantic to the Mediterranean. This reinforced the tectonic unstability, marked by magmatic activity and by a regional upwarp that was to last until the Eocene. Of particular interest was the behaviour, during the Late Cretaceous, of the Setúbal Peninsula sub-basin, which seems to have tilted towards the NW as a block, with a hinge line along the present Lower Tagus Valley. When sedimentation was resumed in the Eocene, a pattern of differential vertical movement was established, with some areas continuing to undergo inversion while nearby areas subsided. This pattern characterized the Cainozoic evolution of the basins, and probably still applies to the neotectonic deformation. The activity of strike-slip basement faults, reactivated under the compressive regime caused by the Afro-Eurasian conver-gence, is proposed as the best explanation for the Miocene deformation, with particular relevance for the Lower Tagus Valley. The RESTE Microearthquake Survey is described, and the data acquired with the RESTE network are analysed. The local earthquakes are accurately located, and focal mechanism solutions are obtained for some of them. This information is used to discuss a neotectonic model for the Lower Tagus Valley. In view of their small magnitudes (l.1< M(_L) < 3.8), the focal mechanisms of these events cannot be interpreted directly in terms of the current tectonics. Such small events are usually local readjustments to previous episodes of deformation. However, such features as the along-strike reversal of the polarity of vertical motion or the coexistence at the same region of different types of source mechanism are diagnostic of strike-slip deformation. This model was supported by the occurrence of a macroearthquake (M(_D)=3.8) with an interpreted source mechanism of sinistral strike-slip. The alignment of four hypocentres along the direction of the Lower Tagus Valley, with a compatible orientation of the interpreted nodal planes, supports the existence of a crustal fracture associated with the Valley. The hypocentral depths of the recorded events reach 20 km, showing that the basement faults responsible for the seismicity affect at least the entire upper crust. Since the limited existing data suggest a high level of heat flow in the Lusitanian Basin, the depths reached by the microearthquakes may indicate an abnormally thick seismogenic layer. An investigation of the broad velocity structure of the lithosphere underneath the RESTE Network using the technique of teleseismic tomographic inversion suggested a correlation between Moho undulations and the inversion of areas of the Lusitanian Basin, and this may indicate that the controlling faults cut the entire crust. In order to provide a rationale for the intraplate seismicity of western Portugal, the neotectonics of Iberia are discussed, and a new kinematic model, centred on the idea of continental extrusion, is proposed. According to the model, a continental block formed by Iberia and northern Morocco is being pushed west wards by the convergence between Africa and Eurasia. The resistance offered by the oceanic parts of the plates varies across the East Azores Transform, leading to dextral shear in the Betic Range. The regional stress field induced by the continental convergence can explain the reactivation, in a simple-shear regime, of basement faults of Hercynian orientation, in particular that proposed for the Lower Tagus Valley
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