• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 2
  • 1
  • 1
  • Tagged with
  • 8
  • 8
  • 3
  • 3
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 2
  • 1
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Cosmogenic dating of fluvial terraces in the Sorbas Basin, SE Spain

Ilott, Samantha January 2014 (has links)
Long term fluvial incision spanning the Late Cenozoic is recorded in many fluvial systems around the world by terrace landform sequences. The incision manifests itself as inset sequences of river terraces which form terrace staircases. The timing of the onset of incision and the rate incision then proceeds at is poorly constrained due to the difficulties in dating river terraces. This study applies the technique of cosmogenic exposure dating to a fluvial staircase, for the first time, in the Sorbas Basin, SE Spain. Cosmogenic exposure dating allows the timing of abandonment of the fluvial terraces to be calculated therefore recording periods of incision. Cosmogenic exposure dating and the profile method offer a viable way to date Early and Middle Pleistocene terrace deposits. Combined exposure and burial age’s approaches using paired isotopes allow for insights into terrace aggradation and fluvial incision timing. The fluvial deposits in the Sorbas Basin record 1.0 Ma of incision by the Río Aguas. The timing of aggradation and incision in the Sorbas basin has been linked to both tectonics and climate cycles. Terrace aggradation took place in glacial and interglacial periods. The abandonment of terrace surfaces occurred both at warming transitions and in interglacial periods. New uplift rates calculated for the Pleistocene fluvial system suggest that tectonic activity in the Sorbas Basin has been episodic. The south margin and centre of the Sorbas Basin has uplifted at a faster rate than the northern margin impacting on the rates of incision taking place in the fluvial systems. Overall tectonic uplift has increased the fluvial system sensitivity to climatic variations.
2

Quaternary Incision, Salt Tectonism, and Landscape Evolution of Moab-Spanish Valley, Utah

Mauch, James P. 01 May 2018 (has links)
To study the history of processes that shape the Earth’s surface, geologists look for markers in the landscape that they can date and use to measure change. Rivers leave such markers in their deposits and terrace landforms and in the overall shape of their elevation profile from head to toe. This thesis uses luminescence and cosmogenic methods to date the sediment in terraces to determine when the river deposited it. Field mapping and global positioning system (GPS) surveying are also used to measure the distance between terrace levels to quantify how much change has occurred. This study seeks to answer questions about when, how quickly, and why streams near Moab in Utah’s Canyonlands region have incised into bedrock. It seeks also to determine the history, rates, and patterns of the active and incremental sinking of Moab and Spanish valleys. The results from this work show that the incision of canyons along Mill and Pack creeks upstream from Moab accelerated around 200,000 years ago to between 0.44 and 0.62 millimeters per year (mm/yr). The sinking of Moab and Spanish valleys also appears to have quickened around the same time and has occurred at up to 1.35 mm/yr in Moab Valley and around 0.45 mm/yr in Spanish Valley over the last 100,000 years. The Kayenta Heights fault zone (KHFZ) accommodates part of the sinking of Moab Valley and has slipped at an average rate of 0.44 mm/yr in the last 100,000 years. This study’s mapping of the length and width of individual fault strands supports prior interpretations that the KHFZ does not pose an earthquake hazard, though it can still be expected to produce active rock fall and rupture the ground surface locally. That the sinking of Moab and Spanish valleys and the down-cutting of the upstream canyons has occurred at similar rates, and may indeed have sped up at a similar time in the past, indicates a linkage of the two processes. This is consistent with an existing hypothesis that Moab and Spanish valleys are sinking because groundwater is dissolving the buried salt deposits and transporting them out through the Colorado River. This process is able to continue because as the Colorado River and its tributaries incise lower into the landscape, groundwater follows and can reach greater depths in the salt deposits. The results of this study paint a picture of the recent and accelerated sinking of Moab and Spanish valleys, which has occurred jointly with incision of the regional drainage network. This acceleration of incision, which has been documented throughout the Canyonlands region, may relate to the Colorado River’s carving of Grand Canyon around 6 million years ago or may have come from a more recent and unknown downstream source.
3

Constraining Basin Geometry and Fault Kinematics on the Santo Tomás Segment of the Agua Blanca Fault Through a Combined Geophysical and Structural Study

Springer, Adam 01 January 2010 (has links)
The Agua Blanca fault is a major transverse structure of northern Baja California, extending more than 120km east from the Punta Banda ridge near the city of Ensenada to the San Matais Pass in central Baja. Through much of its eastern extent slip on this fault appears to be pure strike slip, however, at the Valle de Santo Tomás the fault makes a ~25°; change in orientation, which coincides with the formation of extensional basins on the fault. Recent evidence of the independent movement of the Baja Micro-plate relative to a stable Southern California Black leads to several possible hypotheses to explain this including: 1)That basins are localized structures, the result of a series of right steps or bends along the dextral Agua Blanca fault. 2)Basins are transtensional, possibly as a result of complexities associated with the northern boundary of the Baja Micro-plate . To test between these hypotheses it was necessary to constrain the fault kinematics on both basin bounding and in-basin faults, well as the basin geometry. This was accomplished through combined structural and geophysical surveys. Data collected suggest that the majority of dip-slip is confined to the Santo Tomás fault bounding the basin to the south, while the Agua Blanca fault bounding the basin to the north is primarily strike slip. This orientation typical in transtensional basins, suggesting that although Valle de Santo Tomás formed at a step over it is not a pull apart basin. Possible explanations for transtension in this area come from the orientation of the Agua Blanca fault in relation to the Baja Micro-plate. Where the fault is close to aligned with the relative motion of the plate there is little transtension, such as in Valle de Agua Blanca, however, where the fault makes a 25° change in orientation and becomes more oblique the motion of the Baja Micro-plate transtension is present.
4

New constraints on the late Cenozoic incision history of the New River, Virginia

Ward, Dylan J. 12 July 2004 (has links)
The New River crosses the core of the ancient, tectonically quiescent Appalachian orogen as it follows its course through North Carolina, Virginia, and West Virginia. It is ideally situated to record the changes in geomorphic process rates that occur in the Appalachians as a response to late Cenozoic climate variations. Active erosion features on resistant bedrock that floors the river at prominent knickpoints demonstrate that the river is currently incising toward base level. However, large packages of alluvial fill and fluvial terraces cut into this fill record an incision history for the river that includes several periods of stalled downcutting and aggradation. Cosmogenic 10-Be exposure dating, aided by mapping and sedimentological examination of terrace deposits, is used to constrain the timing of events in this history. Fill-cut and strath terraces at elevations 10, 20, and 50 m above the modern river yield cosmogenic exposure ages of approximately 130, 610, and 955 ka, respectively, but uncertainties on these ages are not well-constrained. This translates to a long-term average incision rate of 43 m/my, which is comparable to rates measured elsewhere in the Appalachians. During specific intervals over the last 1 Ma, however, the New River's incision rate reached 97 m/my. Fluctuations between aggradation and rapid incision appear to be related to late Cenozoic climate variations, though uncertainties in modeled ages preclude direct correlation of these fluctuations to specific climate change events. Erosion rates on higher alluvial deposits adjacent to the river are estimated from 10-Be concentrations; these rates are very low, about 2 m/my or less. This demonstrates a disequilibrium in the modern landscape, with river incision greatly outpacing erosion from nearby landforms. / Master of Science
5

Depósitos sedimentares Pleistocenos-Holocenos da zona de confluência dos rios Solimões e Purus, Amazônia Ocidental

Passos, Marcel Silva 15 April 2016 (has links)
Submitted by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2017-02-20T14:59:17Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertação - Marcel Silva Passos.pdf: 18087958 bytes, checksum: 7ce5b597a99561e6c73f24a81086a760 (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2017-02-20T14:59:32Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertação - Marcel Silva Passos.pdf: 18087958 bytes, checksum: 7ce5b597a99561e6c73f24a81086a760 (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2017-02-20T14:59:50Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertação - Marcel Silva Passos.pdf: 18087958 bytes, checksum: 7ce5b597a99561e6c73f24a81086a760 (MD5) / Made available in DSpace on 2017-02-20T14:59:50Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissertação - Marcel Silva Passos.pdf: 18087958 bytes, checksum: 7ce5b597a99561e6c73f24a81086a760 (MD5) Previous issue date: 2016-04-15 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The Solimões River, at the confluence zone with the Purus River (Western Amazonia) features 3 levels of Pleistocene-Holocenos river terraces, informally called Superior (TS), Intermediário (TI) and Inferior (TInf), defined in this study based in remote sensing data, sedimentology, stratigraphy and geochronology. In general, the terraces display symmetrical distribution, form parallel tracks to the river and extend for tens of kilometers. Located between the elevations 15-75 m, display aged 750-204,000 years BP and internally consist of interbedded sand and mud layers (silt and clay) forming pairs of Stratification Heterolytic Leaning (EHI). The TS (55,000 to 204,596 years BP) is characterized by raised ridges and depressions, showing dendritic drainage patterns to subdendritic and traces of old lines of lateral accretion. The terraces TI (28,400 to 37,240 years BP) and TInf (750-9315 years BP) are part of the active floodplain of the river, subject to seasonal flooding. TI provides relief plan with gentle undulations, displaying rows of lateral accretion and dozens of lakes with elongated shapes, rounded and curved, while the TInf is the closest unit to the main channels, making the marginal bars and islands, stands out for most density lines accretion and lakes. The symmetry of the levels of the terraces of the Solimões River, as well as the features of paleochannels and the presence of EHI, show your past meandering fluvial style that prevailed in the Late Pleistocene, leading to the conclusion that the migrated channel for tens of kilometers. However, recent data show that this river has a high degree of stability, defined primarily based on the channel low migration rate (around 0.32% / year), and by the presence of islands and marginal bars and muddy fitoestabilizadas that define the current anastomosing-anabranching style. The change of fluvial style in the Pleistocene-Holocene boundary can be mainly related to climatic variations, tectonics and glaciostatic. The rise in the sea to the current level, between 18,000 and 6,000 and years BP, blocked the mouth of Solimões-Amazonas river system, causing a decrease in slope and greater input of fine sediments, which in combination with the increased humidity (which allowed phytostabilization the islands and margins) made this system more stable and allowed the installation of the current anastomosing-anabranching style. The predominance of this style can be extended to the east, to the confluence region with the Madeira River. / O Rio Solimões, na zona de confluência com o Rio Purus (Amazônia Ocidental), apresenta 3 níveis de terraços fluviais pleistocenos-holocenos, denominados informalmente de Superior (TS), Intermediário (TI) e Inferior (TInf), definidos neste estudo com base em dados de sensores remotos, sedimentológicos, estratigráficos e geocronológicos. Em geral, os terraços exibem distribuição simétrica, formam faixas paralelas ao rio e se estendem por dezenas de quilômetros. Localizam entre as cotas de 15 a 75 m, exibem idades entre 750 a 204.000 anos AP e, internamente, são constituídos por intercalações de camadas de areia e lama (silte e argila), que formam os pares da Estratificação Heterolítica Inclinada (EHI). O TS (55.000 a 204.596 anos AP) é caracterizado pelo relevo de cristas e depressões, exibe padrões de drenagem dendrítico a subdendrítico e vestígios de antigas linhas de acreção lateral. Os terraços TI (28.400 a 37.240 anos AP) e TInf (750 a 9.315 anos AP) fazem parte da planície aluvial ativa deste rio, estando sujeitos às inundações sazonais. O TI apresenta relevo plano com suaves ondulações, exibindo linhas de acreção lateral e dezenas de lagos com formas alongadas, arredondadas e curvadas, enquanto o TInf é a unidade mais próxima aos canais principais, compondo as barras marginais e ilhas e, se destaca pela maior densidade de linhas de acreção e lagos. A simetria dos níveis dos terraços do Rio Solimões, bem como as feições de paleocanais e a presença da EHI, evidenciam o seu pretérito estilo fluvial meandrante que predominou no Pleistoceno Superior, permitindo inferir que o canal migrou por dezenas de quilômetros. Entretanto, os dados atuais mostram que este rio tem um elevado grau de estabilidade, definido principalmente com base na baixa taxa de migração dos canais (em torno de 0,32%/ano), bem como pela presença de ilhas e barras marginais lamosas e fitoestabilizadas que definem o atual estilo anastomosado-anabranching. A mudança do estilo fluvial no limite Pleistoceno-Holoceno pode ser relacionada principalmente as variações climáticas, tectônicas e glacioeustáticas. A subida do mar até o nível atual, entre 18.000 e 6.000 e anos AP, bloqueou a foz do sistema fluvial Solimões-Amazonas, provocando a diminuição da declividade e maior aporte de sedimentos finos, que em associação com o aumento da umidade (que permitiu a fitoestabilização das ilhas e margens) tornaram este sistema mais estável, e permitiu a instalação do atual estilo anastomosado-anabranching. A predominância deste estilo pode ser estendida a leste, até a região de confluência com o rio Madeira.
6

Terraços fluviais quaternários das regiões de Careiro-da-Várzea, Manaquiri, Careiro-Castanho e Autazes, Amazonia central

Gonçalves Júnior, Eliezer Senna 30 August 2013 (has links)
Submitted by Geyciane Santos (geyciane_thamires@hotmail.com) on 2015-10-21T15:22:02Z No. of bitstreams: 1 Dissertação - Eliezer Senna Gonçalves Júnior.pdf: 13704881 bytes, checksum: 1d71d2269743a9193eaff46fd6fd9f0b (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2015-10-21T15:42:49Z (GMT) No. of bitstreams: 1 Dissertação - Eliezer Senna Gonçalves Júnior.pdf: 13704881 bytes, checksum: 1d71d2269743a9193eaff46fd6fd9f0b (MD5) / Approved for entry into archive by Divisão de Documentação/BC Biblioteca Central (ddbc@ufam.edu.br) on 2015-10-21T18:26:04Z (GMT) No. of bitstreams: 1 Dissertação - Eliezer Senna Gonçalves Júnior.pdf: 13704881 bytes, checksum: 1d71d2269743a9193eaff46fd6fd9f0b (MD5) / Made available in DSpace on 2015-10-21T18:26:04Z (GMT). No. of bitstreams: 1 Dissertação - Eliezer Senna Gonçalves Júnior.pdf: 13704881 bytes, checksum: 1d71d2269743a9193eaff46fd6fd9f0b (MD5) Previous issue date: 2013-08-30 / OUTRAS / In Careiro-da-Várzea, Careiro-Castanho, Manaquiri and Autazes areas, near Manaus, three asymetric quaternary fluvial terraces levels overlains the Alter do Chão (Cretaceous) and Novo Remanso (Miocene) siliciclastic sediments. Locally, these geological basement outcrops as an elongated stripe about 150 kilometers length toward NE-SW, in heights between 100 and 50 meters sustained by three chemically distinct lateritic paleosoils levels. The quaternary fluvial terraces developed between 240.000 and 2.000 years BP extends more than 100 kilometers between 80 e 10 meters heights composing the Amazonas-Solimões Fluvial System alluvial plain on the studied reach. Generally, these deposits present scroll-bars morphology, with low drainages density, characterized by sparse plain secondary channels and rounded lakes. Internally, they are constituted by pairs of layers made of sand and mud (silt and clay) forming Inclined Heterolitic Stratification (IHS) within the meander point bars. The TS deposits presents pink to reddish colors and shows pedogenesis features, while the TI and TInf deposits tends to present brownish to greyish colors due the rich organic matter and bioturbation features. The TS deposits occupies de south-central portion of the study area extending around 100 kilometers being constituted mainly of mud deposits, commonly used by the locals to brick and tiles manufacture. The TI and TInf deposits occur as narrow and elongated stripes of maximum 30 kilometers width, composing the active floodplain of the actual Solimões-Amazonas system. The point bars with IHS deposits, the terraces asymmetric distribution and the register of paleochannels features near the mouth of Purus River, suggests the predominance of a meander pattern in the study area between 240.000 and 6.000 years BP. The Solimões-Amazonas Fluvial System developed the last 6.000 years to an anastomosed-anabranching stable river related to the rise of sea level during the Late Holocene and the climatic changes that boosted the development of the rainforest, furthering the stabilization of margins on this fluvial system. / Na região entre os municípios do Careiro-da-Várzea, Careiro-Castanho, Manaquiri e Autazes, ao sul de Manaus, ocorrem três níveis de terraços fluviais quaternários, de distribuição assimétrica, desenvolvidos sobre as rochas siliciclásticas (arenitos, pelitos e conglomerados) das formações Alter do Chão (Cretáceo) e Novo Remanso (Mioceno), que compõem o embasamento geológico desta região. Localmente, este embasamento aflora como uma faixa alongada de direção NE-SW, com cerca de 150 km de comprimento e 15 km de largura, entre cotas de 100 e 50 metros sustentadas por três níveis de paleossolos lateríticos quimicamente distintos. Os terraços fluviais desenvolvidos entre 240.000 e 2.000 anos AP, se estendem por mais de 100 km e situam-se em cotas variando entre 80 e 10 metros de altitude, constituindo as planícies aluviais do sistema fluvial Solimões-Amazonas, no trecho estudado. Em geral, apresentam morfologia deposicional de barras de acresção lateral, com baixa densidade de drenagem, caracterizada por esparsos canais secundários de planície, além de lagos de vários tamanhos e formas. Internamente, os depósitos são constituídos principalmente de areia e lama (silte e argila), em diferentes proporções, que compõem os pares de estratificação heterolítica inclinada (EHI) das barras em pontal. Os depósitos do Terraço Superior (TS) apresentam coloração rosada a avermelhada e exibem feições de pedogênese, enquanto os depósitos dos Terraços Intermediário (TI) e Inferior (TInf) apresentam coloração marrom a cinza médio, com feições de bioturbação, sendo ricos em matéria orgânica. O TS ocupa a porção centro-sul da área de estudo, com cerca de 100 km de extensão, sendo constituído principalmente por depósitos finos (silte e argila), usados na fabricação da cerâmica vermelha (tijolos e telhas) pelas comunidades locais. Os TI e TInf ocorrem como faixas estreitas e alongadas de até 30 km de extensão, que compõem a planície ativa do sistema fluvial Solimões-Amazonas, estando, portanto, sujeitos as inundações periódicas. As barras em pontal com EHI, a distribuição assimétrica dos terraços, o registro de paleocanais na planície aluvial na região da foz do Rio Purus são evidências da predominância do estilo fluvial meandrante, com migração geral para norte, entre 240.000 e 6.000 anos AP. No Holoceno Tardio o sistema fluvial Solimões-Amazonas evoluiu para um estilo anastomosado-anabranching relativamente estável em resposta ao aumento do nível do mar que barrou sua foz e ao aumento da umidade que proporcionou o desenvolvimento vegetal e subsequentemente a fitoestabilização das margens e aumento da carga de finos em suspensão.
7

Paleogeografický vývoj kenozoických říčních systémů ve středních a severních Čechách a jejich vztah ke klimatickým změnám a neotektonice / Paleogeographic development of the Cenozoic river systems in the central and northern Bohemia and its link to climatic changes and neotectonics

Štor, Tomáš January 2018 (has links)
The main aim of this thesis is to provide greater details on the timing of the fluvial river systems formation in the middle and the northern Bohemia. We focused on the Ploučnice River and Vltava River evolution. The river systems are very complex therefore we have used multiple approaches of the research with the disciplines range from geology, sedimentology, geomorphology, geochemistry, over different dating methods such as 10Be and 26Al isochron burial dating, optically stimulated luminescence dating and radiocarbon dating methods. Our results suggests that the terraces are significantly older than previously proposed. The fluvial style of the Ploučnice River system changes from high-energy braided to long-bend meandered river in the upper terrace levels (36 to 29 m above the modern river) and from high- to medium-energy braided river in the middle terrace levels (22-14 m). In the lower terrace levels (13 to 5 m) high-energy braided to long-bend meandered river environments were identified. Terraces were dating at 34 m, 29 m and 14 m above the modern floodplain with cosmogenic radionuclides while the 19 m, 12 m and 6 m above the modern floodplain terraces were dating with OSL. The time span represented by the river terraces remains unclear and varies from Eburonian to Eemian (1.68 to 0.056 Ma)....
8

Activité hors séquence des chevauchements dans la syntaxe nord-ouest himalayenne : apports de la modélisation analogique et quantification quaternaire par analyse morphotectonique / Out of sequence thrust activity in the northern western himalayan syntaxis : analogic models and quaternary quantification by morphotectonic analysis.

Vignon, Violaine 07 November 2011 (has links)
L’Himalaya est un prisme orogénique cylindrique, répondant dans son ensemble aux caractéristiques du prisme de Coulomb. Ainsi, la localisation de la déformation s’effectue principalement au front du prisme et les chevauchements transportés ne sont affectés que par de faibles réactivations hors séquence. Cependant, la terminaison ouest de la chaîne himalayenne, appelée syntaxe nord-ouest himalayenne, apparaît comme une singularité. Cette région correspond à une zone d’interaction entre différentes directions de déformation, avec, d’est en ouest, la chaîne du Pir Panjal au sud du bassin du Cachemire orientée NW-SE, la syntaxe d’Hazara-Kashmir et la chaîne des Salt Range orientée E-W, et la chaîne des Sulaiman Range orientée NE-SW. La séquence normale de déformation dans la syntaxe nord-ouest himalayenne n’est pas respectée : une activité hors séquence importante, caractérisée par une déformation accommodée sur des structures internes au front de la chaîne, a été mesurée dans la chaîne des Salt Range par l’étude structurale de la région. De plus, la chaîne du Pir Panjal présente une activité tectonique hors séquence à l’échelle du cycle sismique : le séisme du Kashmir de magnitude Mw = 7.6 du 8 octobre 2005 s’est produit sur la faille de Balakot-Bagh (extrémité nord-ouest du Medlicott Wadia Thrust, MWT) située à plus de 100 km du front de la chaîne. Ces observations posent deux interrogations : (i) la déformation hors séquence observée dans la syntaxe nord-ouest himalayenne à l’échelle du cycle sismique et à l’échelle long terme existe-t-elle à l’échelle intermédiaire ? (ii) la configuration géométrique de la syntaxe nord-ouest himalayenne favorise-t-elle la déformation hors séquence observée ? Pour répondre à ces questions nous avons entrepris une étude de terrain morphotectonique afin de caractériser la déformation dans la chaîne du Pir Panjal. Pour cela, nous avons cartographié le long de la rivière Chenab 7 niveaux de terrasses d’abrasion au toit du MWT, et trois événements d’aggradation régionaux que nous avons datés grâce à trois méthodes (53 échantillons 10Be, 6 OSL et 4 14C). Ces remplissages se terminent aux environs de 35 ka, 15 ka et 3.5 ka à la fin d’épisodes de moussons intenses. La topographie de ces terrasses a été mesurée grâce au GPS cinématique et une station totale, et leur déformation montre qu’il existe actuellement deux structures actives dans cette région : la structure frontale qui conduit au développement d’un anticlinal, et un grand chevauchement situé 20 km en position interne : le Riasi Thrust (portion du MWT). La majorité du raccourcissement, qui atteint 16 mm/an dans la région, est accommodée par le Riasi Thrust avec un déplacement sur la faille compris entre 10 et 14 mm/an. Le reste étant principalement accommodé sur la structure frontale. L’étude du chevauchement situé encore en position interne, le Main Boundary Thrust, a montré que cette structure n’est plus active depuis 15 ka. En parallèle, nous avons réalisé une série de 24 expériences analogiques en utilisant une boîte à sable dont la géométrie des bordures reproduit la partie externe de la syntaxe nord-ouest himalayenne et en faisant varier la rhéologie basale et les épaisseurs de matériaux. Ces expériences ont montré un important raccourcissement perpendiculaire à la direction de convergence, et une influence de cette géométrie des conditions aux limites sur la séquence de déformation : le pourcentage de déformation hors séquence est plus important dans ce cas que dans celui d’un prisme cylindrique. Notre étude montre donc que la déformation hors séquence dans la syntaxe nord-ouest himalayenne existe aussi sur une échelle de temps intermédiaire entre le cycle sismique et le long terme. Nous l’expliquons en partie comme une caractéristique de la déformation d’une forme en syntaxe. D’autres mécanismes tels que l’érosion due à de fortes précipitations locales et un héritage structural pourraient également être envisagés. / Himalaya is a mountain range that follows globally characteristics of the Coulomb prism. Upon them, the deformation is globally localized at the front of the range, and transported thrusts show few out of sequence activity. The northern western Himalayan syntax is different from the rest of the range. In this area, several ranges with different orientations interact; from east to west the Pir Panjal Range, orientated NW-SE, the Salt Range globally orientated E-W and the Sulaiman Range orientated NE-SW. The normal sequence of deformation in the syntax is not respected: an important out of sequence deformation has been measured in the Salt Range by structural studies. Moreover, Pir Panjal Range also presents out of sequence deformation as illustrated by the Mw 7.6 earthquake on 8th October 2005. It occurred on the Balakot-Bagh fault (northern extremity of the Medlicott Wadia Thrust, MWT), located more than 100 km from the front. These observations arise two questions: (i) does out of sequence deformation observed in the syntax at seismic and long term time scale exists at intermediate time scale? (ii) does the geometry of the syntax favor the observed out of sequence deformation? To address these questions we characterized the deformation in the Pir Panjal Range through a morphotectonic study. Along the Chenab River, we mapped 7 strath terraces at the hanging wall of the MWT, and dated 3 regional alluviation events using 3 methods (53 10Be samples, 6 OSL and 4 14C). These events correspond to the end of maximum monsoon phases. We measured the topography of alluvial terraces with kinematic GPS and total station and their deformation revealed that in the Pir Panjal Range deformation is localized along two structures: the frontal one that leads to a growing anticline, and a major thrust situated 20 km in internal position, called the Riasi Thrust (segment of the MWT). Most of the 16 mm/yr convergence in the area is absorbed by the Riasi Thrust which fault displacement rate is comprised between 10 and 14 mm/yr. The frontal structure absorbs the remaining part of the convergence. Also, we looked the more internal thrust called Main Boundary Thrust, and showed that this structure is not active since at least 15 kyr. In parallel, we designed a set of 24 analogic experiments using a sand box which borders geometry reproduced the external part of the northern western Himalayan syntax and changing the basal rheology and thickness of materials. These experiments showed an important shortening perpendicular to the convergence direction, and an influence of this geometry on the deformation sequence: the out of sequence deformation percentage is higher than in cylindrical prism. Our study shows that in the northern western Himalayan syntax, out of sequence deformation also exists at intermediate time scale between seismic cycle and long term time scale. It can be partly explained by the geometry of the syntax. Other mechanism such as erosion, due to intense local precipitations and structural heritage could also be considered.

Page generated in 0.0972 seconds