scholarly journals Growing topography due to contrasting rock types in a tectonically dead landscape

2021 ◽  
Vol 9 (2) ◽  
pp. 167-181
Author(s):  
Daniel Peifer ◽  
Cristina Persano ◽  
Martin D. Hurst ◽  
Paul Bishop ◽  
Derek Fabel
Keyword(s):  
Active Tectonics ◽  
Landscape Dynamics ◽  
Granitic Rocks ◽  
Tectonic Activity ◽  
Mean Values ◽  
Rock Types ◽  
Denudation Rates ◽  
Spatial Differences ◽  
Long Timescales ◽  
Topographic Relief

Abstract. Many mountain ranges survive in a phase of erosional decay for millions of years following the cessation of tectonic activity. Landscape dynamics in these post-orogenic settings have long puzzled geologists due to the expectation that topographic relief should decline with time. Our understanding of how denudation rates, crustal dynamics, bedrock erodibility, climate, and mantle-driven processes interact to dictate the persistence of relief in the absence of ongoing tectonics is incomplete. Here we explore how lateral variations in rock type, ranging from resistant quartzites to less resistant schists and phyllites, and up to the least resistant gneisses and granitic rocks, have affected rates and patterns of denudation and topographic forms in a humid subtropical, high-relief post-orogenic landscape in Brazil where active tectonics ended hundreds of millions of years ago. We show that catchment-averaged denudation rates are negatively correlated with mean values of topographic relief, channel steepness and modern precipitation rates. Denudation instead correlates with inferred bedrock strength, with resistant rocks denuding more slowly relative to more erodible rock units, and the efficiency of fluvial erosion varies primarily due to these bedrock differences. Variations in erodibility continue to drive contrasts in rates of denudation in a tectonically inactive landscape evolving for hundreds of millions of years, suggesting that equilibrium is not a natural attractor state and that relief continues to grow through time. Over the long timescales of post-orogenic development, exposure at the surface of rock types with differential erodibility can become a dominant control on landscape dynamics by producing spatial variations in geomorphic processes and rates, promoting the survival of relief and determining spatial differences in erosional response timescales long after cessation of mountain building.

scholarly journals Growing topography due to contrasting rock types in a tectonically dead landscape

2020 ◽  
Author(s):  
Daniel Peifer ◽  
Cristina Persano ◽  
Martin D. Hurst ◽  
Paul Bishop ◽  
Derek Fabel
Keyword(s):  
Active Tectonics ◽  
Landscape Dynamics ◽  
Granitic Rocks ◽  
Tectonic Activity ◽  
Mountain Ranges ◽  
Rock Types ◽  
Denudation Rates ◽  
Spatial Differences ◽  
Long Timescales ◽  
Topographic Relief

Abstract. Many mountain ranges survive in a phase of erosional decay for millions of years (Myr) following the cessation of tectonic activity. Landscape dynamics in these post-orogenic settings have long puzzled geologists due to the expectation that topographic relief should decline with time. Our understanding of how denudation rates, crustal dynamics, bedrock erodibility, climate, and mantle-driven processes interact to dictate the persistence of relief in the absence of ongoing tectonics is incomplete. Here we explore how lateral variations in rock type, ranging from resistant quartzites to less-resistant schists and phyllites and up to the least-resistant gneisses and granitic rocks, have affected rates and patterns of denudation and topographic forms in a humid semitropical, high-relief, post-orogenic landscape in Brazil where active tectonics ended hundreds of Myr ago. We show that denudation rates are negatively correlated to topographic relief, channel steepness and modern precipitation rates. Denudation instead correlates with inferred bedrock strength, with resistant rocks denuding more slowly relative to more erodible rock units, and suggest that the efficiency of fluvial erosion varies primarily due to these bedrock differences. Variations in erodibility continue to drive contrasts in rates of denudation in a tectonically inactive landscape evolving for hundreds of Myr, suggesting that equilibrium is not a natural attractor state and that relief continues to grow through time. Over the long timescales of post-orogenic development, exposure at the surface of rock types with differential erodibility can become a dominant control on landscape dynamics by producing spatial variations in geomorphic processes and rates, promoting the survival of relief, and determining spatial differences in erosional response timescales long after cessation of mountain building.

scholarly journals Evaluation of active tectonics using geomorphic indices in a mountainous basin of Iran

2020 ◽  
Vol 111 (2) ◽  
pp. 109-117
Author(s):  
Siamak BAHARVAND ◽  
Biswajeet PARDHAN ◽  
Salman SOORI
Keyword(s):  
Great Basin ◽  
Active Tectonics ◽  
Geographical Information ◽  
Tectonic Activity ◽  
Stream Length ◽  
Mean Values ◽  
Geomorphic Indices ◽  
Hypsometric Integral ◽  
The Mean ◽  
Very High

ABSTRACTThis study aims to evaluate the tectonic activities of the Vark basin, located in the great basin of Dez River in northwestern Iran, using geomorphologic indices combined with the geographical information system technique. Some geomorphic indices were used to achieve this aim. In this regard, the indices of stream length (SL), drainage asymmetry (Af), hypsometric integral (Hi), valley floor ratio (Vf), basin shape (Bs), and mountain sinuosity (Smf) were estimated to reach an average index of relative tectonics (Iat), indicating the intensity classes of tectonic activity. The mean SL, Hi, Vf, and Bs values were estimated as 2273, 0.55, 0.45, and 1.75, respectively, regarding the active class of tectonic activity. Therefore, considering the Af and Smf indices with values of 27 and 1.14, the basin was categorised as having semi-active conditions. The overall Iat, with a value of 1.33, represented the very high class (1.0 < Iat < 1.5) of tectonic activity. Hence, by calculating the index of relative active tectonics, the study area is observed as the intensive class concerning tectonic movements. Overall, the mean values of the Iat for all sub-basins were calculated as 1.50, 1.17, and 1.83, revealing the very high and high classes of active tectonics in the basin. The results obtained on tectonic activity were further confirmed during field observations by examining the structurally complex joints, folds, slips, faults, and fractures of the area, which reflect the dynamic nature of the regional tectonics.

Layered Granitic Rocks at Chebucto Head, Halifax County, Nova Scotia

1975 ◽  
Vol 12 (3) ◽  
pp. 456-463 ◽  
Author(s):  
T. E. Smith
Keyword(s):  
Grain Size ◽  
Nova Scotia ◽  
Granitic Rocks ◽  
Textural Characteristics ◽  
Rock Types ◽  
Flow Sorting

Structural, mineralogical and textural characteristics of some layered granitic rocks are described. The layers result from the segregation of minerals into bands and lenses of contrasting color and grain size. They were formed near the roof of the pluton prior to final crystallization by flow sorting during episodic shearing generated during intrusion. Comparison of the mineralogy and textures of the layered rocks with those of the main rock types of the pluton shows that the differentiation of the pluton as a whole took place after the formation of the layers by interaction of felsic components concentrated in residual liquids with earlier formed crystals.

scholarly journals Active tectonics around the Mediterranean region: site studies and application of new methodologies

2013 ◽  
Vol 55 (5) ◽  
Author(s):  
Luigi Cucci ◽  
Paolo Marco De Martini ◽  
Eulalia Masana ◽  
Kris Vanneste
Keyword(s):  
Urban Areas ◽  
Active Tectonics ◽  
National Research Council ◽  
Time Span ◽  
Point Of View ◽  
Tectonic Activity ◽  
Tectonic Processes ◽  
Critical Facilities ◽  
Basic Studies ◽  
Tectonic Movements

<p>More than 25 years have passed since the definition of Active Tectonics as "tectonic movements that are expected to occur within a future time span of concern to society", formulated in a milestone book by the National Research Council on this topic (Studies in Geophysics, Active Tectonics, National Academy Press, Washington, D.C. 1986), and those words have still to be considered the most suitable and exhaustive way to explain this branch of the Earth Sciences. Indeed only bridging together basic studies ("tectonic movements"), rates of occurrence ("time span") and hazard assessment ("society") can we fully evaluate ongoing tectonic activity and its associated hazards. The broad Mediterranean Sea region is a paradigmatic area from this point of view, as on one hand this region displays in a relatively limited geographic extent a great variety of tectonic processes such as plate collision, subduction, volcanic activity, large-magnitude earthquakes, active folding and faulting, vertical uplift and/or subsidence. On the other hand, all the above mentioned tectonic processes can potentially affect a total population of about 450 million, mostly concentrated in fast-growing urban areas and/or close to industrial compounds and critical facilities often located nearby hazard sources. […]</p>

scholarly journals MORPHOTECTONIC EVALUATION OF SIRCH MOUNTAINS USING WATER BASIN GEOMORPHIC INDICES

2021 ◽  
Vol 13 (2) ◽  
pp. 208-214
Author(s):  
Nafise HOSEINI ◽  
◽  
Shahram BAFTI ◽  
Reza DERAKHSHANI ◽  
Mohammad GHANBARIAN ◽  
...  
Keyword(s):  
Information System ◽  
Form Factor ◽  
Geographical Information System ◽  
Active Tectonics ◽  
Geographical Information ◽  
Tectonic Activity ◽  
Mountainous Region ◽  
Large Area ◽  
Active Tectonic ◽  
Morphotectonic Indices

Morphotectonic indices are useful instruments for investigating the effect of tectonic activity in a certain region. Calculation of these indicators using the advantages of Geographical Information System, GIS, in a large area is useful for detecting potential disorders related to active tectonics. This method is useful in regions on which few morphotectonic studies have been conducted. An example of such areas can be the watersheds of the Sirch mountainous region. The watersheds of the Sirch region located in Central Iran’s zone in the southeast of Iran are a very ideal zone to evaluate the concepts of these indicators in the prediction of the relative tectonic activity according to the investigation of drainage systems or mountain fronts. Based on the values of the calculated indices including Form Factor (FF), Compaction Coefficient (CC), Ratio of Circularity (RC), Ratio of Elongation (RE), relative Basin Height (BH), and Ruggedness Number (RN), a final indicator called Active Tectonic Indicator (ATI) is obtained. The latter is a combination of the abovementioned indicators and evaluates the morphotectonic activity based on the shape of the watersheds. By measuring and combining these indicators, the tectonic activity stage of the Sirch region was determined by analyzing the watersheds of this region.

La viabilité des bétons du Québec: le rôle des granulats

1986 ◽  
Vol 13 (1) ◽  
pp. 12-24 ◽  
Author(s):  
Jean Bérard ◽  
Richard Roux
Keyword(s):  
Key Words ◽  
Silica Gel ◽  
Cement Paste ◽  
Chemical Reactions ◽  
Mechanical Deformation ◽  
Granitic Rocks ◽  
Concrete Aggregate ◽  
Coarse Aggregates ◽  
Rock Types ◽  
Petrographic Study

The petrographic study of numerous concrete structures in Quebec has revealed the extent of postconstruction chemical reactions. Those reactions between the aggregates, which form 70% of the volume of the concrete, and the cement paste result in early deterioration and undesirable mechanical deformation of the structures. From this study, it appears that the coarse aggregates can react in three different ways: (a) by peripheral reaction, which is the case for massive granitic rocks, (b) by bulk swelling, as illustrated by the Potsdam orthoquartzite, and (c) by formation of silica gel veinules within the aggregate, as shown by some Trenton limestone. Considering these three mechanisms, it is easy to understand why certain aggregates react rapidly, that is within a few months, whereas others show signs of distress only after scores of years. Using the three rock types cited above, we have also tried to evaluate existing concrete standards and their capability to detect the most important pathologies encountered in concrete. Key words: concrete, aggregate, alkalis, disintegration, expansion, testing, durability.

The oxygen isotope composition of the surface crystalline rocks of the Canadian Shield

1978 ◽  
Vol 15 (11) ◽  
pp. 1773-1782 ◽  
Author(s):  
Yuch-Ning Shieh ◽  
Henry P. Schwarcz
Keyword(s):  
Isotope Composition ◽  
Crystalline Rocks ◽  
Canadian Shield ◽  
Granitic Rocks ◽  
Baffin Island ◽  
Grenville Province ◽  
Metasedimentary Rocks ◽  
Rock Types ◽  
Northern District ◽  
Basic Rocks

The average 18O/16O ratios of the major rock types of the surface crystalline rocks in different parts of the Canadian Precambrian Shield have been determined, using 47 composite samples prepared from 2221 individual rock specimens. The sampling areas include Baffin Island, northern and southwestern Quebec, Battle Harbour – Cartwright, northern District of Keewatin, Fort Enterprise, Snowbird Lake, Kasmere Lake, and Saskatchewan, covering approximately 1 400 000 km2. The granitic rocks from the Superior, Slave, and Churchill Provinces vary only slightly from region to region (δ18O = 6.9–8.4‰) and are significantly lower in 18O than similar rock types from the younger Grenville Province (δ = 9.2–10.0‰). The sedimentary and metasedimentary rocks have δ18O = 9.0–11.7‰ and hence are considerably lower than their Phanerozoic equivalents, possibly reflecting the presence of a high percentage of little-altered igneous rock detritus in the original sediments. The basic rocks in most regions fall within a δ18O range of 6.8–7.6‰, except in northern and southwestern Quebec where the δ-values are abnormally high (8.5–8.9‰). The overall average 18O/16O ratio of the surface crystalline rocks of the Canadian Shield is estimated to be 8.0‰, which represents an enrichment with respect to probable mantle derived starting materials by about 2‰.

Topographic disequilibrium, landscape dynamics and active tectonics: an example from the Bhutan Himalayas

2021 ◽  
Author(s):  
Martine Simoes ◽  
Timothée Sassolas-Serrayet ◽  
Rodolphe Cattin ◽  
Romain Le Roux-Mallouf ◽  
Matthieu Ferry ◽  
...  
Keyword(s):  
Spatial Organization ◽  
Spatial Scales ◽  
Active Tectonics ◽  
Recent Change ◽  
Climatic Conditions ◽  
Landscape Dynamics ◽  
Drainage Basins ◽  
Equilibrium Conditions ◽  
Longitudinal Band ◽  
Active Tectonic

&lt;p&gt;The quantification of active tectonics from geomorphological and morphometric approaches most often implies that erosion and tectonics have reached a certain balance. Such equilibrium conditions may however be seldom found in nature, in particular because drainage basins may be quite dynamic even though tectonic and climatic conditions remain constant. Here, we document this drainage dynamics from the particular case example of the Bhutan Himalayas. Evidence for out-of-equilibrium morphologies have for long been noticed in Bhutan, from major (&gt; 1 km high) river knickpoints and from the existence of high-altitude low-relief regions within the mountain hinterland. These peculiar morphologies were generally interpreted as representing a recent change in climatic and/or tectonic conditions. To further characterize these morphologies and their dynamics, and from there discuss their origin and meaning, we perform field observations and a detailed quantitative morphometric analysis using Chi plots and Gilbert metrics of drainages over various spatial scales, from major Himalayan rivers to local streams draining the low-relief regions. We first find that the river network is highly dynamic and unstable. Our results emphasize that the morphology of Bhutan does not result from a general wave of incision propagating upstream, as expected from most previous interpretations. Also, the specific spatial organization in which all major knickpoints and low-relief regions are located along a longitudinal band in the Bhutan hinterland, whatever their spatial scale and the dimensions of the associated drainage basins, calls for a common local supporting mechanism most probably related to active tectonic uplift. Our results emphasize the need for a precise documentation of landscape dynamics and disequilibrium over various spatial scales as a first-order step in morpho-tectonic studies of active landscapes.&lt;/p&gt;

Sur quelques aspects de la zoneographie alpine dans les Alpes cottiennes meridionales

1962 ◽  
Vol S7-IV (4) ◽  
pp. 477-491
Author(s):  
Andre Michard
Keyword(s):  
Tectonic Activity ◽  
Structural Units ◽  
Zonal Distribution ◽  
Rock Types ◽  
Metamorphic Mineral ◽  
Mineral Assemblages ◽  
Alpine Metamorphism

Abstract A Permo-Carboniferous series and a polymetamorphic series are distinguished in the rocks of the southern Cottian Alps, Italy. The metamorphic mineral assemblages and facies of the principal rock types represented in each series and their zonal distribution are discussed. Alpine metamorphism is considered to have occurred after the tectonic activity responsible for superposition of the three structural units recognized in the region between Varaita and Stura.

Determination of the characteristics of crystalline rocks by field experiments: a review

1986 ◽  
Vol 319 (1545) ◽  
pp. 139-156 ◽  
Keyword(s):  
Radioactive Waste ◽  
Field Experiments ◽  
The United States ◽  
Crystalline Rocks ◽  
Granitic Rocks ◽  
Rock Types ◽  
Basement Rocks ◽  
Deep Boreholes ◽  
High Level ◽  
Underground Research Laboratory

Crystalline rocks, particularly granitic rocks and basalts, are one of the principal rock types under consideration as a potential host rock for a high-level radioactive waste repository. Permeability in such rocks is related to discontinuities of various scales, and the quantification and prediction of groundwater flow within both the fractures and the intact rock between the fractures is the major goal of field experiments. The Canadian Underground Research Laboratory is unique in that the hydrogeological conditions within a large volume of rock surrounding the experimental shaft are being monitored before, during and after excavation and the results compared with model predictions. In Switzerland twelve deep boreholes are being drilled to over 1000 m to investigate crystalline basement rocks beneath a cover of sediments. The Stripa Mine in Sweden has hosted a major experimental programme including heater tests to stimulate the thermal effect of radioactive waste and hydrogeological tests at various scales down to individual fractures. The United States of America, the United Kingdom, France and Finland have also embarked on major experimental programmes. Continuing research is needed, with an emphasis on field experiments and research in underground rooms, to provide the data on which detailed risk assessments can be based.

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