Age, Depth, and Residual Depth Anomalies in the North Pacific: Implications for Thermal Models of the Lithosphere and Upper Mantle

We present an empirical basement depth versus age relation for the North Pacific Ocean, based on the statistical treatment of an ocean-wide gridded data set. The SYNBAPS bathymetry was averaged into half-degree intervals and corrected for the effects of sediment loading. The resulting basement depths were plotted against ages determined from a revised isochron chart based on a recent compilation of magnetic lineations and various published plate reconstructions. On crust older than 80 Ma, the depths are skewed to the shallow side of the depth versus age distribution by large numbers of seamounts. Therefore the mean and standard deviations are not useful representations of the data. A more appropriate representation is the mode (or greatest concentration of points) and contours around the mode. The contours around the mode show that most ocean floor increases in depth with the square root of age out to crust of 80 Ma. Beyond this the majority of the data oscillates about a line that remains essentially constant as the age in-creases. Approximately 56% of all the data points lie within a + 300m band about the mode. If the sediment thickness data in the older basins of the western North Pacific is correct then the flattening of the depths favor a model in which extra heat is supplied to the base of the lithosphere on older ocean floor. Residual depth anomalies were calculated by removing the depths predicted by such a model. These anomalies correlate with bathymetric features and occur predominantly on crust of 120 and 160 Ma. They account for the rises in the mode at these two ages. The overall subsidence of the ocean floor can be accounted for by the cooling of a thermo-mechanical boundary layer. Correlations between geoid height and depth are evidence that many of the residual depth anomalies result from convective plumes which reset the thermal structure of the lithosphere. It is possible that this process observed at different times after the initial resetting of the isotherms may account for many of the depth anomalies in the western North Pacific.Institute for Geophysic

Analysis of the Importance of Extension in Accounting for the Post-Carboniferous Subsidence of the North Sea Basin

Post Carboniferous sedimentary deposition in the Central North Sea basins can be separated into three major periods: Permian, Triassic and mid-Jurassic through present. Most efforts to explain the basin within an extensional framework have concentrated on the post mid-Jurassic subsidence. These efforts have ignored the large amount of prior extension required to account for the observed crustal thinning and the substantial Permian and Triassic sediment fill. In addition the models predict a mid-Jurassic through early Cretaceous extension that significantly exceeds estimates of the horizontal displacement observed on high angle faults on multichannel seismic lines. We show in areas of minimal pre-Permian subsidence that adding two earlier phase extensions, one in the late Carboniferous through early Permian and the other in the Triassic produces a nearly horizontal late Carboniferous crustal thickness. The time-dependent extensional model required to account for the three periods of sediment deposition gives an excellent match to the observed subsidence history of the basement. We present an analysis of a recent seismic reflection line nm across the Central Graben in the vicinity of published refraction and well data. We show that the extension required in the third phase of the three phase model is compatible with the observed displacement on the high angle mid-Jurassic through early Cretaceous faults. However, we find no evidence for major extension either in the Triassic or late Carboniferous through early Permian.Institute for Geophysic

Set of Experiments on Steel Balls Under Extension: A Slide Show

Boerner, (1989) carried out the original set of experiments on steel balls under extension for his Master's Thesis at the University of Texas at Austin. These experiments initially consisted of an examination of the dilation and then faulting of steel balls of uniform size in an apparatus one row thick where he could vary the number of layers. This apparatus approximated the behavior of steel balls in two dimensions. By modifying the apparatus to increase the number of rows he completed a similar set of experiments in the three dimensions. For these experiments, which were meant to be analogues of the behavior of sand in sand boxes, he varied the size of the balls. Boerner (1989) describes each experiment in detail. Boerner and Sclater (in preparation) are about to submit a summary of these experiments including an explanation of the main findings to the Journal of Geophysical Research. We present, with this set of slides, an overview of the experiments carried out by Boerner (1989) and some slides illustrating different packing geometries.Institute for Geophysic

Comment on "mantle flow drives the subsidence of oceanic plates"

Adam and Vidal (Reports, 2 April 2010, p. 83) reported sea-floor depth increasing as the square root of distance from the ridge along "mantle flow lines." However, their data actually support a depth-age relationship and "flattening" at older ages. We argue that no plausible physical mechanism supports their proposal that mantle flow drives subsidence

'Working out’ identity: distance runners and the management of disrupted identity

This article contributes fresh perspectives to the empirical literature on the sociology of the body, and of leisure and identity, by analysing the impact of long-term injury on the identities of two amateur but serious middle/long-distance runners. Employing a symbolic interactionist framework,and utilising data derived from a collaborative autoethnographic project, it explores the role of ‘identity work’ in providing continuity of identity during the liminality of long-term injury and rehabilitation, which poses a fundamental challenge to athletic identity. Specifically, the analysis applies Snow and Anderson’s (1995) and Perinbanayagam’s (2000) theoretical conceptualisations in order to examine the various forms of identity work undertaken by the injured participants, along the dimensions of materialistic, associative and vocabularic identifications. Such identity work was found to be crucial in sustaining a credible sporting identity in the face of disruption to the running self, and in generating momentum towards the goal of restitution to full running fitness and reengagement with a cherished form of leisure. KEYWORDS: identity work, symbolic interactionism, distance running, disrupted identit