Дисертації з теми "Himalaya Mountains Region – History"

Thesis (Ph.D.)--George Mason University, 2008.
Vita: p. 167. Thesis director: Menas Kafatos. Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Earth Systems an GeoInformation Sciences. Title from PDF t.p. (viewed Jan. 11, 2009). Includes bibliographical references (p. 156-166). Also issued in print.

Rocks west of the Coast Mountains batholith in central southeastern Alaska include the Alexander terrane, Gravina belt, Taku terrane, and newly defined Ruth assemblage. Geologic, geochronologic and thermobarometric studies of these rocks in the Petersburg region provide new constraints on the accretionary history of the Alexander terrane and structural evolution of the Coast Mountains batholith. Paleozoic and Upper Triassic strata of the Alexander terrane were deformed within the Duncan Canal shear zone. Dextral shear in this zone during Early or Middle Jurassic time is inferred to reflect deformation along the eastern margin of the Alexander terrane and record the juxtaposition of the Alexander terrane with the North American margin. Deposition of the Upper Jurassic-Lower Cretaceous Gravina belt occurred within a transtensional back-arc to intra-arc basin that evolved during the northward translation of the Alexander terrane. The Ruth assemblage and Taku terrane were structurally emplaced over the Gravina belt and Alexander terrane along the Sumdum-Fanshaw fault system during mid-Cretaceous time. West-vergent thrusting of the Ruth assemblage was accompanied by metamorphic P,T conditions of 6.8 kb, < 450°C in the Gravina belt and 6.9 to > 7.4 kb, > 550°C in the Ruth assemblage. The age of deformation is constrained by syntectonic and post tectonic intrusive bodies that yield U-Pb lower intercept apparent ages of 92.3 ± 3 Ma and 91.3 ± 6.3 Ma, respectively. Late Devonian-Mississippian orthogneiss and felsic metavolcanic rocks in the Ruth assemblage suggest correlation of the assemblage with continental margin rocks of the Yukon-Tanana and Nisling terranes east of the Coast Mountains batholith. Thus the mid-Cretaceous Sumdum-Fanshow fault system marks the fundamental boundary between the Alexander terrane and inboard fragments. This deformation records the final structural accretion of the Alexander, Wrangellia, and Peninsular terranes to the western margin of North America. The mid-Cretaceous thrust system is truncated to the east by the LeConte Bay shear zone: a complex zone of Late Cretaceous-early Tertiary fabrics that occur within and west of the Coast Mountains batholith. This zone has apparently accommodated both west-side-up and east-side-up displacement during the collapse of the overthickened crust developed during mid-Cretaceous time.

Kyoto University (京都大学)
0048
新制・課程博士
博士(理学)
甲第12122号
理博第3016号
新制||理||1450(附属図書館)
23958
UT51-2006-J117
京都大学大学院理学研究科地球惑星科学専攻
(主査)助教授 田上 高広, 教授 嶋本 利彦, 教授 小畑 正明
学位規則第4条第1項該当

The period between the 1750s and 1830s witnessed a major change in travel practices in Europe, moving away from the traditional Grand Tour and focusing more on natural places, their visual power, and their influence on individual emotions. Such changes meant that the Alps ceased to be seen as a natural obstacle that had to be crossed in order to access Italy, and became a place to explore and a mountainous space par excellence. This thesis addresses the importance of mental mapping in travel literature and its impact on the construction of the Alps as a transnational space, which eventually facilitated the creation of a viable touristic market in the Alps as we know it today. The first part of the thesis analyses the transformation of the Alps from a natural frontier to a border region explored by travellers and their networks. The second part discusses the consequences of these changes on mental mapping and spatial representations of the Alps by travellers: it highlights the way external visitors often had very subjective interpretations of what the Alps meant as a term and a place, and conveyed those to other travellers through travel writing. Finally, the third part of this work investigates the development of an Alpine myth as a product of these shifting mental representations: the Alps became a set of expectations, typical images, and encounters to be expected.

Estudando uma comunidade de serpentes da Serra da Mantiqueira, foram encontradas 11 espécies de serpentes, e constatada a superioridade numérica de indivíduos da família Viperidae. As áreas abertas foram as mais freqüentadas, além de mostrar maior riqueza de espécies. A maioria das espécies encontradas apresenta a viviparidade como modo reprodutivo. A altitude mostrou influenciar a distribuição e abundância das espécies. As três espécies mais abundantes foram B. neuwiedi, B. jararaca e C. durissus, e são apresentadas informações de sua história natural. As fêmeas são maiores e mais robustas do que os machos. Entre filhotes, o dimorfismo sexual não ocorre ou é restrito. Fêmeas são mais ativas na primavera e no verão, e machos no outono. As fêmeas parecem ser mais agressivas. As três espécies alimentam-se preferencialmente de pequenos mamíferos. A espermatogênese e a vitelogênese são sazonais, e machos e fêmeas estocam espermatozóides no trato genital a fim de harmonizarem seus ciclos. O nascimento dos filhotes ocorre no verão.
This study was conducted in the Serra da Mantiqueira, and show biological and ecological aspects within a community of snakes. Eleven species were found. The snakes was mostly found in open areas, and open areas also showed a greater richness of species. A significant percentage of the species reproduced by viviparity. Altitude influenced the abundance and distribution of the species. The three dominant species of snakes was B. neuwiedi, B jararaca and C. durissus. Females are bigger and stronger then the males. Among the young, sexual dimorphism does not happen or it is restricted. Females also showed increased activity during the spring and summer, whiles males had increased activity levels during the autumn months. Females were more aggressive. These three species feed primarily on small mammals. Spermatogenesis and vitellogenesis are seasonal, and males and females show sperm storage in the genital tract so their cycles are harmonized. B. jararaca is bigger and stronger than B. neuwiedi, and female B. jararaca have larger and heavier litters.

This study contributes to the understanding of major river evolution in Southeast Asia during the Cenozoic. In order to trace the evolution of a hypothesized palaeo-Yarlung Tsangpo-Irrawaddy River, this work undertakes the first systematic provenance study of detrital minerals from Cenozoic synorogenic fluvial and deltaic sedimentary rocks of the Central Burma Basin, employing a combination of high precision geochronology, thermochronology, and geochemistry analytical techniques on single grain detrital zircon and white mica. The dataset is compared to published isotopic data from potential source terranes in order to determine source provenance and exhumation history from source to sink. A Yarlung Tsangpo-Irrawaddy connection existed as far back as ca. 42 Ma and disconnection occurred at 18–20 Ma, based on provenance changes detected using a combination of U-Pb ages and εHf(t) values on detrital zircons, and ⁴ºAr/³⁹Ar dating on detrital micas. During the Eocene and Oligocene, units are dominated by U-Pb age and high positive εHf(t) values, characteristic of a southern Lhasa Gangdese magmatic arc source. An antecedent Yarlung Tsangpo-Irrawaddy River system formed the major river draining the eastern Himalaya at this time. A significant change in provenance is seen in the early Miocene, where detritus is predominantly derived from bedrock of the eastern Himalayan syntaxis, western Yunnan and Burma, a region drained by the modern Irrawaddy-Chindwin river system characterized by Cenozoic U-Pb ages and negative εHf(t) values. This is attributed to the disconnection of the Yarlung-Irrawaddy River and capture by the proto-Brahmaputra River, re-routing Tibetan Transhimalayan detritus to the eastern Himalayan foreland basin. Re-set zircon fission track ages of 14-8 Ma present in all units is used to infer post-depositional basin evolution related to changes in the stress regime accommodating the continued northward migration of India. The early Miocene initiation of the Jiali-Parlung-Gaoligong-Sagaing dextral shear zone and the continued northward movement of the coupled India-Burma plate aided in focusing deformation inside the syntaxis contributing to the disconnection of the Yarlung Tsangpo-Irrawaddy system, linking surface deformation and denudation with processes occurring at deeper crustal levels.

The Himalaya is an orogenic welt within the Alpine-Tethyan mountain chain. The extant tectonic model for the Himalayan terrane stack entails continuous post-collisional convergence and persistent heating during burial and subsequent exhumation. An alternative hypothesis to this "continuous evolution" scenario involves episodic tectonic mode switching, a concept that has been documented in other orogens along the Alpine-Tethyan belt. This thesis therefore tests the possibility that there is episodic mode switching in respect to the evolution of the Greater Himalaya in its topographically high crystalline core, in Himachal Pradesh, NW India. The approach adopted employs microstructurally-focused 40Ar/39Ar geochronology, across key tectonic contacts and geological terranes of the Greater Himalaya, to constrain the timing and temperature evolution of individual deformation and metamorphic events. In the leading edge of the Greater Himalaya, geological structures in the Shimla klippe and Narkanda syncline were examined with the intent of structurally and geochronologically characterising the Main Central Thrust (MCT). However, argon geochronology of fabrics structurally above and below the tectonic contact revealed that these fabrics formed in the Eocene period or earlier, during the Mesozoic. Therefore, these shear zones, although they had previously been intimately linked with the MCT, are in fact significantly older structures. In the root zone of the Phojal fold nappe, microstructural analysis revealed the influence of two distinct thermal excursions at upper greenschist grade that occurred towards the cessation of spatially associated ductile shearing events. Mica samples from the recumbently folded fabric of the supposed 'nappe' yield complex argon apparent age spectra, from which it can be inferred that: i) there were two distinct extensional shearing events that had terminated respectively by ~35 Ma and ~24-21 Ma; ii) the Phojal fold appears to have developed some time in the Oligocene, and not in the Miocene as is now supposed; iii) the fold recumbently folded the first Eocene-Oligocene ductile shear zone before itself being overprinted and attenuated in the Miocene by extensional ductile shear zones; iv) tectonic sequence diagrams inferred from those rocks are incompatible with a structural location in the hanging wall close to a thrust. Consequently the MCT as described today was not evident as a thrust in the Kullu region during the formation of the Phojal fold. From the character and timing of tectonic sequences, it is inferred that the fold geometry developed as a result of tectonic mode switching. Argon diffusion modelling supports the conclusion based on microstructures that the M1 and M2 metamorphic events cannot have occurred as part of a single protracted heating event. There must have been cooling (and possible exhumation) in between. The research in this thesis demonstrates that the tectonic evolution of the Greater Himalaya is consistent with multiple episodes of crustal shortening followed by regional extension events. The timing of the tectonic mode switches is broadly compatible with mode switches as observed in orogens elsewhere along the Alpine-Tethyan chain.

Many ideas about the tectonic history of the Himalayan orogen hinge on the arguments about the timing of collision (~70 Ma, ~50 Ma or ~34 Ma). One of these is whether the tectono-thermal evolution of the Himalaya involved dominantly episodic processes or continuous protracted deformation/heating. This thesis reviews the definitions proposed for the India-Asia collision and investigates whether the evolution of the Himalayan orogen involved episodic or continuous tectonic processes. This study used SHRIMP U/Pb geochronology to determine if the granitoids of the Ladakh and Karakorum batholiths of NW India were emplaced episodically or continuously during the Himalayan orogeny. The SHRIMP results indicate that magmatism was episodic. However, we also found that zircons with high-uranium concentrations produce older apparent ages when analysed with SHRIMP. This presented a problem when interpreting the age of particular granitoid samples. We therefore investigated the cause of this problem and found that older apparent ages were related to matrix effects associated with radiation damage in the zircon. One of the most widely used definitions to determine the timing of India-Asia collision suggests that this event is marked by a switch from 1- to S-type magmatism in the Trans-Himalayan batholith. Many consider this to occur at ~50 Ma. However, the work that is presented here suggests there was no switch from 1- to S-type magmatism where it is proposed to occur in NW India. However, U/ Pb SHRIMP and petrological data suggest there is potentially a switch from 1- to S-type magmatism in the Karakorum Batholith between 32 Ma and 18 Ma. This indicates that India-Asia collision occurred much later than many consider, or the I-S classification scheme should not be used to define the timing of collision. This thesis also reviews the published rotation data for the India-Eurasia plate circuit and presents a new methodology for presenting the data and decisions that are adopted in plate reconstructions. The review shows the problems associated with existing plate reconstructions of the Indian plate, and highlights the need to ensure the highest resolution data is used in a given plate reconstruction. The most appropriate rotation data was compiled to build a new plate reconstruction of India's motion relative to Eurasia. This reconstruction implies the velocity of the Indian plate was episodic over the past 100 Ma. The episodes of plate acceleration and deceleration correspond with the timing of many tectonic events recognised along the Alpine-Tethyan orogen. However, the changes in plate velocity are not necessarily related to the India-Asia collision as other geodynamic scenarios explain these changes in velocity. This thesis also questions the use of inherited/detrital age spectra of zircon to define the location of plate boundaries. New U/Pb data from the Karakorum Terrane suggests that it has a similar age spectra to the Himalayan Terrane to the south and the Pamir to the north. These results indicate that the Karakorum Terrane was once a component of Gondwana (or derived from Gondwanan material) and highlights the problems associated with using age spectra to "fingerprint" terranes. A synthesis of all of the results indicates that the Himalayan orogen involved multiple accretion events, not just one collision between India and Asia. Its evolution is therefore analogous to a multi-vehicle freeway pile-up, rather than a head-on collision between two vehicles.

From 1981 to 2010 flooding claimed an average of 92 lives each year in the United States. According to the National Oceanic and Atmospheric Administration National Weather Service, in 2010 the number of flood-related fatalities (103) was second only to heat (138). Flash flooding is especially dangerous as sudden, torrential downpours from thunderstorms can cause gullies, streams, and creeks to rise quickly and become an immediate risk to life and property. Across the southern Appalachian Mountains this threat is aggravated by steep terrain and the rapid accumulation of rainfall in narrow valleys and gorges. Severe storm reports were gathered from the National Climatic Data Center from 1996 to 2010. An emphasis was placed on flash flood events collected after the modernization of the National Weather Service in the mid-1990s when verification of storm reports became mandatory. Using a Geographic Information System, an abbreviated climatology of flash flood events was constructed to better understand the frequency and distribution of such events over the extent of the southern Appalachians. Additionally, forecasters and hydrologists provided insight on where flash floods occur most frequently across their County Warning Areas. In total, there were 4,938 flash flood reports across the southern Appalachian Mountains from 1996 to 2010. Of those reports there were 71 fatalities and 64 injuries, many of which occurred during the evening and overnight hours. Nearly 33 percent of all fatalities were associated with a vehicle and another 38 percent occurred when residents were swept away while traversing swollen creeks and streams. The information presented herein will assist meteorologists and hydrologists as well as those who would like to gain additional knowledge about flash flood climatology across the southern Appalachians.
Review of relevant literature -- Data and methodology -- Results, part I : an abbreviated climatology -- Results, part II : National Weather Service WFO discussions.
Department of Geography

韓朝建.
Thesis (Ph.D.)--Chinese University of Hong Kong, 2011.
Includes bibliographical references (leaves 181-192)
Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.
Abstracts in Chinese and English.
Han Chaojian.