Kinematics of fault-related folding derived from a sandbox experiment

We analyze the kinematics of fault tip folding at the front of a fold-and-thrust wedge using a sandbox experiment. The analog model consists of sand layers intercalated with low-friction glass bead layers, deposited in a glass-sided experimental device and with a total thickness h = 4.8 cm. A computerized mobile backstop induces progressive horizontal shortening of the sand layers and therefore thrust fault propagation. Active deformation at the tip of the forward propagating basal décollement is monitored along the cross section with a high-resolution CCD camera, and the displacement field between pairs of images is measured from the optical flow technique. In the early stage, when cumulative shortening is less than about h/10, slip along the décollement tapers gradually to zero and the displacement gradient is absorbed by distributed deformation of the overlying medium. In this stage of detachment tip folding, horizontal displacements decrease linearly with distance toward the foreland. Vertical displacements reflect a nearly symmetrical mode of folding, with displacements varying linearly between relatively well defined axial surfaces. When the cumulative slip on the décollement exceeds about h/10, deformation tends to localize on a few discrete shear bands at the front of the system, until shortening exceeds h/8 and deformation gets fully localized on a single emergent frontal ramp. The fault geometry subsequently evolves to a sigmoid shape and the hanging wall deforms by simple shear as it overthrusts the flat ramp system. As long as strain localization is not fully established, the sand layers experience a combination of thickening and horizontal shortening, which induces gradual limb rotation. The observed kinematics can be reduced to simple analytical expressions that can be used to restore fault tip folds, relate finite deformation to incremental folding, and derive shortening rates from deformed geomorphic markers or growth strata

Investigating the kinematics of mountain building in Taiwan from the spatiotemporal evolution of the foreland basin and western foothills

The Taiwanese range has resulted from the collision between the Luzon volcanic arc and the Chinese continental margin, which started about 6.5 Myr ago in the north, and has since propagated southward. The building of the range has been recorded in the spatiotemporal evolution of the foreland basin. We analyze this sedimentary record to place some constraints on the kinematics of crustal deformation. The flexure of the foreland under the load of the growing wedge started with a 1.5 Myr long phase of rapid subsidence and sedimentation, which has migrated southward over the last 3.5 Myr at a rate of 31 +10/−5 mm/yr, reflecting the structural evolution of the range and the growth of the topography during the oblique collision. Isopachs from the Toukoshan (~0 to 1.1 Ma) and Cholan (~1.1 to 3.3 Ma) formations, as well as the sedimentation rates retrieved from a well on the Pakuashan anticline, indicate that the foreland basement has been moving toward the center of mass of the orogen by ~45–50 mm/yr during the development of the basin. From there, we estimate the long-term shortening rate across the range to 39.5–44.5 mm/yr. By considering available data on the thrust faults of the foothills of central Taiwan, we show that most (if not all) the shortening across the range is accommodated by the most frontal structures, with little if any internal shortening within the wedge. The range growth appears therefore to have been essentially sustained by underplating rather than by frontal accretion. In addition, only the upper ~7 to 9 km of the underthrusted crust participates to the growth of the orogen. This requires that a significant amount of the Chinese passive margin crust is subducted beneath the Philippine Sea plate

Mountain building in Taiwan: A thermokinematic model

The Taiwan mountain belt is classically viewed as a case example of a critical wedge growing essentially by frontal accretion and therefore submitted to distributed shortening. However, a number of observations call for a significant contribution of underplating to the growth of the orogenic wedge. We propose here a new thermokinematic model of the Taiwan mountain belt reconciling existing kinematic, thermometric and thermochronological constraints. In this model, shortening across the orogen is absorbed by slip on the most frontal faults of the foothills. Crustal thickening and exhumation are sustained by underplating beneath the easternmost portion of the wedge (Tananao Complex, TC), where the uplift rate is estimated to ~6.3 mm a^(−1), and beneath the westernmost internal region of the orogen (Hsueshan Range units, HR), where the uplift rate is estimated to ~4.2 mm a^(−1). Our model suggests that the TC units experienced a synchronous evolution along strike despite the southward propagation of the collision. It also indicates that they have reached a steady state in terms of cooling ages but not in terms of peak metamorphic temperatures. Exhumation of the HR units increases northward but has not yet reached an exhumational steady state. Presently, frontal accretion accounts for less than ~10% of the incoming flux of material into the orogen, although there is indication that it was contributing substantially more (~80%) before 4 Ma. The incoming flux of material accreted beneath the TC significantly increased 1.5 Ma ago. Our results also suggest that the flux of material accreted to the orogen corresponds to the top ~7 km of the upper crust of the underthrust Chinese margin. This indicates that a significant amount (~76%) of the underthrust material has been subducted into the mantle, probably because of the increase in density associated with metamorphism. We also show that the density distribution resulting from metamorphism within the orogenic wedge explains well the topography and the gravity field. By combining available geological data on the thermal and kinematic evolution of the wedge, our study sheds new light onto mountain building processes in Taiwan and allows for reappraising the initial structural architecture of the passive margin

Linking Taiwan's subcritical Hsuehshan Range topography and foreland basin architecture

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95204/1/tect2249.pd

Real and Imagined Women's Voices in Russian and Japanese Societies: Media, Self-Perceptions, and Everyday Language Practices

The complex relationship between gender and language has been studied from a diversity of perspectives, which have explored both the historical control of women’s language by men and the evolving interactions between genders that shape contemporary language use. To date, however, there is little cross-cultural work exploring the crucial role of the media in shaping the social norms that regulate the use of gendered language. Furthermore, few studies analyzed women’s discourses on their perceptions of normative and ideal femininities along with women’s real linguistic practices. This dissertation aims to fill this gap by conducting a cross-linguistic and cross-cultural study of women’s language in contemporary Japanese and Russian societies. The dissertation is three-fold: it investigates current gender ideologies in televised advertising, their manifestations in women’s narratives on their ideal selves, and women’s actual speech in spontaneous conversations in Japan and Russia. By juxtaposing women’s scripted speech in televised commercials, women’s beliefs in interviews and their actual language behavior, I examine how various social expectations suggested in media are evoked, asserted, and rejected in women’s perceptions of femininity and in their everyday life. Thus, this dissertation compares and contrasts women's self-articulated femininities with the normative portrayals dominant in media, exploring the ways in which women challenge and subvert social expectations.The results of this dissertation suggest that Japanese and Russian media frequently depicts women highlighting their femininity, which reflects a synthesis of current gender ideologies, traditional models and postfeminist ideas of ‘power femininity.’ Japanese and Russian women have rigid perceptions about the ideal femininity that in some ways echo the media representations. The corpus analysis of women’s conversations and blogs, however, demonstrates the large gap between these perceptions and women’s real practices. The dissertation findings add to our understanding of the constructed nature of femininity, its components, and its significance in both Japanese and Russian societies. The findings also highlight the culture-sensitive, nuanced creation of gender, and reveal the cultural inhomogeneity of its manifestations