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Late miocene/pliocene origin of the inverted metamorphism of the Central Himalaya

Description: The spatial association of intracontinental thrusting and inverted metamorphism, recognized in the Himalaya more than a century ago, has inspired continuing efforts to identify their causal relationship. Perhaps the best known sequence of inverted metamorphism is that found immediately beneath the Himalayan Main Central Thrust (MCT), generally thought to have been active during the Early Miocene. It has been widely assumed that the pattern of inverted metamorphism also developed at that time. Using a new approach, in situ Th-Pb dating of monazite included in garnet, we have discovered that the peak metamorphic recrystallization recorded in the footwall of the MCT fault occurred at ca. 5 Ma. The apparent inverted metamorphism resulted from activation of a broad shear zone beneath the MCT zone which juxtaposed two right-way-up metamorphic sequences. Recognition of this remarkably youthful phase of metamorphism resolves outstanding problems in Himalayan tectonics, such as why the MCT (and not the more recently initiated thrusts) marks the break in slope of the present day mountain range, and transcends others, such as the need for exceptional conditions to explain Himalayan anatexis.
Date: January 1, 1997
Creator: Harrison, T.M.; Ryerson, F.J.; LeFort, P. & Yin, A. Lovera, O.M.
Partner: UNT Libraries Government Documents Department

Applications of Morphochronology to the Active Tectonics of Tibet

Description: The Himalayas and the Tibetan Plateau were formed as a result of the collision of India and Asia, and provide an excellent opportunity to study the mechanical response of the continental lithosphere to tectonic stress. Geophysicists are divided in their views on the nature of this response advocating either (1) homogeneously distributed deformation with the lithosphere deforming as a fluid continuum or (2) deformation is highly localized with the lithosphere that deforms as a system of blocks. The resolution of this issue has broad implications for understanding the tectonic response of continental lithosphere in general. Homogeneous deformation is supported by relatively low decadal, geodetic slip-rate estimates for the Altyn Tagh and Karakorum Faults. Localized deformation is supported by high millennial, geomorphic slip-rates constrained by both cosmogenic and radiocarbon dating on these faults. Based upon the agreement of rates determined by radiocarbon and cosmogenic dating, the overall linearity of offset versus age correlations, and on the plateau-wide correlation of landscape evolution and climate history, the disparity between geomorphic and geodetic slip-rate determinations is unlikely to be due to the effects of surface erosion on the cosmogenic age determinations. Similarly, based upon the consistency of slip-rates over various observation intervals, secular variations in slip-rate appear to persist no longer than 2000 years and are unlikely to provide reconciliation. Conversely, geodetic and geomorphic slip-rate estimates on the Kunlun fault, which does not have significant splays or associated thrust faults, are in good agreement, indicating that there is no fundamental reason why these complementary geodetic and geomorphic methods should disagree. Similarly, the geodetic and geomorphic estimates of shortening rates across the northeastern edge of the plateau are in reasonable agreement, and the geomorphic rates on individual thrust faults demonstrate a significant eastward decrease in the shortening rate. This rate decrease is consistent with the ...
Date: January 28, 2005
Creator: Ryerson, F J; Tapponnier, P; Finkel, R C; Meriaux, A; der Woerd, J V; Lasserre, C et al.
Partner: UNT Libraries Government Documents Department

Report of Planning Workshop on MAIRS Mountain Zone Implementation

Description: Monsoon Asia Integrated Regional Study (MAIRS) is an IRS research program over monsoon Asia under START and the Earth System Science Partnership (ESSP). It was established to address questions about the coupled human and environment system in the monsoon Asia region. The vision of MAIRS is to significantly advance understanding of the interactions between the human and natural components of the overall environment in the monsoon Asian region and implications for the global earth system, in order to support strategies for sustainable development. Regional-scale studies of global change provide the knowledge base for undertaking vulnerability analyses, identification of hotspots of risk and studies of environmental degradation which are crucial for the sustainable development. Regions may manifest significantly different environmental dynamics, and changes in regional biophysical, biogeochemical and anthropogenic components may produce considerably different consequences for the earth system at the global scale. Regions are not closed systems and thus the linkages between regional changes and the global earth system are crucial. This specific report focuses on Planning Workshop on MAIRS Mountain Zone Implementation that held in China. Integrated Regional Studies (IRSs) should have relevance for people living in the regions and should provide a sound scientific basis for the sustainable development of the countries in the regions, and IRSs are also important from an earth system science perspective.
Date: June 2007
Creator: Manton, Michael & Ailikun
Partner: UNT Libraries