Lithosphere Dynamics And Evolution Of Continental Crust

Author : Brian Zurek
Publisher :
ISBN 13 : 9780549640660
Total Pages : 250 pages
Book Rating : 4.6/5 (46 download)

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Download or read book The Evolution and Modification of Continental Lithosphere, Dynamics of 'indentor Corners' and Imaging the Lithosphere Across the Eastern Syntaxis of Tibet written by Brian Zurek and published by . This book was released on 2008 with total page 250 pages. Available in PDF, EPUB and Kindle. Book excerpt: An important question in tectonics today is how the continental lithosphere evolves and is modified over time. At the Himalayan orogeny and Tibetan plateau, we have the opportunity to study the processes that deform and modify the crust and mantle lithosphere during a continent-continent collision in real-time. In this study the internal lithospheric architecture of the eastern syntaxis of Tibet is examined using broad-band seismology. For the first part of the study the thickness of the crust and the bulk Poisson's ratio of the crust are mapped using converted P- to S-waves. Across the study region, a strong correlation between Moho depth and surface topography exists. The prediction of crustal Airy isostasy is in agreement with the observed correlation between the Moho and surface topography. The Poisson's ratio indicates a crust that transitions from a felsic to mafic composition from the central plateau to the southeastern margin. For the second part of the study detailed 3-d receiver-function images are used in conjunction with finite-difference wave-form modeling to derive the velocity structure and geometry of the crust. Our two fundamental observations are a dramatic change in a high-velocity lower crust across the end of the collisional zone and an asymmetric step in the crust-mantle interface beneath the Namche Barwa/Gyala Peri massifs. The observed termination of the high velocity lower crust coincides with the transition from collisional tectonics of the central plateau to the escape tectonics of the east. This lower crustal layer is interpreted to be Indian lower crust that has subducted beneath Asian crust north of the Tsangpo suture and metamorphosed into the ecologite facies. For the third part of the study the focal depth distribution is examined from the local seismicity located on the Eastern Syntaxis Seismic Experiment and in the historical ISC/PDE catalogs for central and southeast Tibet. The primary findings are earthquakes systematically occur in both the lower crust and upper mantle, implying that in a region of ongoing active collision such as Tibet, lateral heterogeneities are going to provide localized conditions where brittle failure can occur in the lower crust and in the upper mantle.