Boulder, Colo., USA - The faulted alluvial fans near Badwater in Death Valley are amongst the most visited and classic landforms in the U.S. New mapping and dating of these landforms, presented in this open-access study by Kurt Frankel and colleagues, help to determine the timing of past earthquakes and how tectonic deformation is distributed across the western U.S. This in turn provides important data for seismic hazard mitigation and for understanding how the great landscapes of the western U.S. have evolved over recent geologic time.
Death Valley constitutes one of the most dramatic landscapes in North America, and it is famous for its faulted mountain fronts, spectacular alluvial fans, and extensive saline playa. Moreover, the valley is the type example of a pull-apart basin, which is controlled by the northern Death Valley-Fish Lake Valley fault zone, the Black Mountains fault zone, and the southern Death Valley fault zone. These three fault zones make up the Holocene fault zones of the Death Valley fault system. This Death Valley pull-apart often provides an analog for the evolution, including stress transfer and depositional systems, in other tectonically active transtensional regimes, such as the Dead Sea, East Africa, and Alpine fault of New Zealand.
Timing and rates of Holocene normal faulting along the Black Mountains fault zone, Death Valley, USA
K.L. Frankel et al., School of Earth And Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia 30332, USA. This article is OPEN ACCESS online at http://dx.
Other recently published Lithosphere articles are highlighted below:
Precollisional development and Cenozoic evolution of the Southalpine retrobelt (European Alps)
S. Zanchetta et al., Dipartimento di Scienze dell'Ambiente e del Territorio e di Scienze della Terra, Università degli Studi di Milano Bicocca, Piazza della Scienza 1, Milano 20126, Italy. This paper is online at http://dx.
Most of the orogenic belts worldwide display a doubly vergent structure. The retrobelts of these collisional orogens are classically interpreted as late-stage features that formed after the continent-continent collision. However this does not hold true for any case. In this work we demonstrate that the south-vergent retrobelt of the European Alps formed before the collision between Africa and Europe. Structural analysis and low temperature thermochronological data (apatite fission track) indicate that the central part of the Southern Alps was largely structured and already exhumed in pre-late Eocene times, when the European plate eventually collided with Africa after the subduction of the Alpine Tethys ocean.
Unzipping the Patagonian Andes--Long-Lived Influence of Rifting History on Foreland Basin Evolution
M.A. Malkowski et al., Department of Geological Sciences, Stanford University, Stanford California 94305, USA. This article is online at http://dx.
The Patagonian Andes preserve a multi-phase history of active tectonism since this region was a part of the Gondwanan margin in the Early Jurassic. Evolution of southern Patagonia includes regional rifting and ocean spreading during the opening of a backarc ocean basin (the Rocas Verdes Basin), followed by the development of a foreland fold-thrust belt (Magallanes-Austral Basin). This study presents new and previously published geochronology data that suggests the Rocas Verdes Basin opened by rifting progressively from south to north. Subsequent development of the successor foreland fold-thrust belt mirrors this pattern in the progressive initiation of coarse-clastic deposition from north to south. We suggest that the tectonic fabric emplaced by the earlier diachronous rifting was a fundamental control on the timing of mountain building and basin development along the southernmost Andes.
Polyphase deformation, dynamic metamorphism and metasomatism of Mount Everest's summit limestone, east central Himalaya, Nepal/Tibet
T.L. Corthouts et al., Earth Science Department, Montana State University, Bozeman, Montana 59715, USA. This paper is online at http://dx.
This paper provides the most detailed geologic description of Mount Everest's summit limestone (Qomolangma Formation) to date. Results presented herein show that the Qomolangma Formation has evolved through multiple phases of deformation associated with discrete episodes in Himalayan orogenesis. Rock samples from the top of the formation record Eohimalayan deformation and low-grade metamorphism associated with initial thrust faulting, folding and crustal thickening of the Tethyan Sedimentary Sequence in the Eocene. In contrast, samples from the base of the formation record events that occurred in the Late Oligocene and Early Miocene, including metasomatism associated with Neohimalayan metamorphism and normal faulting on the South Tibetan Detachment. This means that a wide range of significant tectonic events in Himalayan orogenesis are preserved in the Qomolangma Formation, a ~150 m thick succession of deformed Ordovician limestone that now comprises the top of Mount Everest.
Visualizing the sedimentary response through the orogenic cycle: A multi-dimensional scaling approach
C.J. Spencer and C.L. Kirkland, Department of Applied Geology, Curtin University, Perth WA 6845, Australia. This paper is online at http://dx.
Spencer and Kirkland apply a new statistical technique known as multi-dimensional scaling to three orogenic events associated with the assembly of Rodinia. These three case studies have long been argued to represent idealized examples of the orogenic cycle. Multi-dimensional scaling provides a way to visualize the dissimilarity of detrital zircon age spectra from a wide array of samples. Their statistical analysis of the Grenville Orogeny (sensu stricto) and Albany-Fraser Orogeny show a very clear progression of dissimilarity of age spectra with time through the orogenic cycle. On the contrary, the sediments generally associated with the assembly of Rodinia in the North Atlantic Region do not show the same pattern. They argue that the geodynamic situation in this region differs significantly from that of the other case studies presented and propose this is due to a distal position from an orogenic front, oblique translation of terranes, and complexity of the continental margin. From these case studies they propose that multi-dimensional scaling can be used to elucidate orogenic processes.
U-Pb and Hf isotope analysis of detrital zircons from Paleozoic strata of the southern Alexander terrane (southeast Alaska)
C. White et al., Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA. This paper is online at http://dx.
The Alexander terrane is a crustal fragment that underlies much of SE Alaska, NE British Columbia, and SW Yukon, but various lines of evidence suggest that it originated in the paleo-Arctic ocean basin during early Paleozoic time. The current study utilizes U-Pb ages and Hf isotope signatures of detrital zircons from the southern Alexander terrane to show that it may have been located along the Arctic margin of Baltica, as a northern extension of the Caledonian orogen, during Silurian time. The terrane remained in proximity to the Caledonides or a related orogen in the paleo-Arctic through Early Devonian time, and then began its migration westward into the Pacific realm.
Growth of the Qaidam Basin during Cenozoic exhumation in the northern Tibetan Plateau: Inferences from depositional patterns and multi-proxy detrital provenance signatures
M.A. Bush et al., Department of Geological Sciences, Jackson School of Geosciences, University of Texas at Austin, Austin, TX 78712, USA; and Department of Earth and Atmospheric Sciences, University of Houston, Houston TX 77204-5007, USA. This article is online at http://dx.
This study uses the provenance record from Qaidam Basin in the northern Tibetan Plateau over the last 50 million years to address questions about the geodynamics of collisional orogens as well as the interactions between climate/environment and the growth of high topography. The sedimentary record presented here indicates that during the Paleogene the unified Qaidam-Tarim Basin was partitioned and uplifted as it was incorporated into the growing Tibetan Plateau. Comparison with basins on and surrounding the Tibetan Plateau suggests that basement strength and lateral homogeneity, and formation of syndepositional structural dams are among the primary controls on formation of giant sedimentary basins.
Late Triassic tectonic framework and evolution of Central Qiangtang, Tibet, SW China
Wu, H., et al., College of Earth Sciences, Jilin University, Changchun 130061, People's Republic of China. This paper is online at http://dx.
From the abstract: The Late Triassic Longmu Co-Shuanghu suture zone is a metamorphic belt in Central Qiangtang, SW China, that is interpreted to have formed at the boundary between a Gondwana-derived block and Laurasia during the subduction of Paleo-Tethyan oceanic crust. Recent research has suggested that a Late Triassic (ca. 225-205 Ma) magmatic "flare-up" event took place on both sides of the metamorphic belt within Central Qiangtang coeval with exhumation of the metamorphic rocks. The age-equivalent Gangmari metamorphic belt and Riwanchaka Yangtze-type deposits of the South Qiangtang terrane are located ?70 km from the Longmu Co-Shuanghu suture zone and the North Qiangtang terrane. We propose that Central Qiangtang underwent postcollisional extension in the Late Triassic. By integrating the geological features described here, we suggest that these complex geological phenomena were triggered by slab breakoff of the northward-subducting lithosphere of the Paleo-Tethys Ocean. Central Qiangtang is therefore an ideal area in which to verify the process of slab breakoff by geological observations.
Open-access abstracts for LITHOSPHERE papers are online at http://lithosphere.