Boulder, CO, USA - Highlights for Lithosphere articles published online 2 September 2011 are provided below. Lithosphere is regularly posting pre-issue publication content -- finalized papers ready to go to press and not under embargo. GSA invites you to sign up for e-alerts or RSS feeds for first access to new journal content. Sign up at http://lithosphere.gsapubs.org/content/by/year.
Keywords: Bandelier Tuff, Jemez Mountains, Rio Grande Rift, Jemez-Embudo Accommodation Zone, Australia, geodynamic models, Melanesia, Tennessee Salient, Appalachians, Blue Ridge terrane, curved mountain belts
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Paleomagnetism of the Quaternary Bandelier Tuff: Implications for the tectonic evolution of the Española Basin, Rio Grande rift
Aviva J. Sussman et al., Earth and Environmental Sciences Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA; doi: 10.1130/L128.1.
Aviva J. Sussman of Los Alamos National Laboratory and colleagues present newly acquired paleomagnetic data from Bandelier Tuff exposures in the Jemez Mountains (New Mexico) of the Rio Grande Rift that show no statistically significant tectonic rotation over Quaternary time. In this part of the rift, where Proterozoic and Laramide age faults have preconditioned the crust, idealized relay ramps, prevalent locally, do not occur at the regional scale. Instead, transfer fault zones developed between half-grabens, dominated by preexisting faults. The pattern of faulting and accommodation of strain in the right-relayed step-over of the rift has been more or less invariant since the onset of rifting. From a global perspective, the difference between areas of modest crustal extension dominated by distributed deformation and those regions that develop transfer fault zones may ultimately be diagnostic of crustal conditioning and fault strength such that weak fault systems focus strain within narrow zones. Sussman et al. propose the name "Jemez-Embudo Accommodation Zone" (JEAZ) for the composite of structural and volcanic features that appear in this region in recognition of the importance they played in the evolution of the Rio Grande rift and its impact on the understanding of rift systems worldwide.
Mantle dynamics of continent-wide Cenozoic subsidence and tilting of Australia
Lydia DiCaprio et al., EarthByte Group, School of Geosciences, Madsen Building F09, The University of Sydney, Sydney, NSW 2006, Australia; doi: 10.1130/L140.1.
Australia is generally a stable continent with distal plate boundaries; however, since the Cenozoic, the whole Australian continent has undergone both a bulk subsidence of 100 meters and an additional 200 meters of tilting down toward the northeast. This paper by Lydia DiCaprio of the University of Sydney and colleagues uses geodynamic models to show how the tilting and subsidence is related to mantle flow and the continent's motion away from Antarctica and towards the subduction realm in Melanesia.
Foreland signature of indenter tectonics: Insights from calcite twinning analysis in the Tennessee salient of the Southern Appalachians, USA
James S. Hnat and Ben A. van der Pluijm, Dept. of Geological Sciences, University of Michigan, 1100 N. University Ave., Ann Arbor, Michigan 48109-1005, USA; doi: 10.1130/L151.1.
A remarkable feature of most mountain belts around the world is their curved shape, which is readily visible in such ranges as the Appalachians and Himalayas. The origin of this curvature remains highly debated. James S. Hnat and Ben A. van der Pluijm of the University of Michigan use a sensitive gauge of past stress orientations, as preserved in the mineral calcite, to determine the origin of curvature in a classic location, the Tennessee Salient of the U.S. Appalachians. The results of this study show that curvature occurred very early in the area's history in response to collision (or indentation) of the ancient continental margin of North America with a tectonic block that is today preserved as the Blue Ridge terrane. Using a simple sandbox model we can nicely illustrate this region's history and its curvature. Surprisingly, the Pennsylvania Salient to the north is similar in appearance to the Tennessee Salient, but, using the same analytical method, was earlier shown to have a different origin for curvature that reflects the irregular shape of the North American margin at that time; no indenter was involved. Thus, curved mountain belts are not formed by a single mechanism, nor at the same time in the orogen's history, but involve various scenarios that can be constrained by analysis of natural minerals that act as an ancient stress gauge.
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Lithosphere