Orocimales y delaminación: relaciones y efectos

Late- to post-orogenic oroclinal bending in conjunction with thinning of the lithospheric mantle is potentially an important component of the waning stages of plate convergence in collisional orogenies. This paper addresses possible and hitherto unexplored cause-effect relationships between oroclinal bending of an originally linear orogenic belt and lithospheric thinning and delamination based on an example from the Western European Variscan Belt (WEVB). We suggest that late- to post-orogenic bending of the lithosphere around a vertical axis may cause thickening and eventual detachment of the lithospheric root of orogenic belts such as the WEVB. The proposed hypothesis is consistent with the chronology of tectonic, metamorphic, magmatic and hydrothermal events recorded in the WEVB

Self-subduction of the Pangaean global plate

One of the most striking and rare occurrences in the Earth's history is the amalgamation of most of the continental lithosphere into one supercontinent. The most recent supercontinent, Pangaea, lasted from 320 to 200 million years ago. Here, we show that after the continental collisions that led to the formation of Pangaea, plate convergence continued in a large, wedge-shaped oceanic tract. We súggest that plate strain at the periphery of the supercontinent eventually resulted in self-subduction of the Pangaean global plate, when the ocean margin of the continent subducted beneath the continental edge at the other end of the same plate. Our scenario results in a stress regime within Pangaea that explains the development of a large fold structure near the apex of the Palaeotethys Ocean, extensive lower crustal heating and continental magmatism at the core of the continent as well as the development of radially arranged continental rifts in more peripheral regions of the plate

Buckling an orogen: The Cantabrian Orocline

The Paleozoic Variscan orogeny was a large-scale collisional event that involved amalgamation of multiple continents and micro-continents. Available structural, geological, geochemical, and geophysical data from Iberia are consistent with a model of oroclinal bending at the lithospheric scale of an originally near-linear convergent margin during the last stages of Variscan deformation in the late Paleozoic. Closure of the Rheic Ocean resulted in E-W shortening (in present-day coordinates) in the Carboniferous, producing a near linear N-S–trending, east-verging orogenic belt. Subsequent N-S shortening near the Carboniferous-Permian boundary resulted in oroclinal bending, highlighted by the formation of the Cantabrian Orocline. Together, these data constrain oroclinal bending in Iberia to have occurred during the latest Carboniferous over about a 10-million-year time window, which agrees well with recent geodynamical models and structural data that relate oroclinal bending with lithospheric delamination in the Variscan. This late-stage orogenic event remains an enigmatic part of final Pangaea amalgamation

Lithospheric delamination in the core of Pangea: Sm-Nd insights from the Iberian mantle

Delamination of continental lithosphere in the core of active collisional orogens is a wellestablished process; however, evidence for its occurrence in ancient orogenic belts is less obvious. The contrasting Sm-Nd isotopic signature between pre– and post–Middle Permian mantle-derived mafi c rocks from under the Iberian Massif suggests that most, but not all, of the subcontinental lithospheric mantle (SCLM) was replaced in latest Carboniferous to Permian time. Mantle replacement happened during and after the bending of the Variscan orogenic belt into the horseshoe-shaped Iberian-Armorican orocline. Delamination of thickened continental lithosphere in the core of the orocline triggered replacement of the ancient SCLM, thereby providing an explanation for the contrasting Sm-Nd isotopic characteristics of pre– and post–Middle Permian mafic rocks

Insights into the Mechanism for Orogen-Related Carbonate Remagnetization from Growth of Authigenic Fe-Oxide: A Scanning Electron Microscopy and Rock Magnetic Study of Devonian Carbonates from Northern Spain

A rock magnetic and SEM study of Devonian carbonates from the Cantabria-Asturias Region, northern Spain, was undertaken to further our understanding of the pervasive remagnetization of carbonate rocks during the Late Paleozoic, and the mechanism by which these remagnetizations occur. These rocks contain three ancient Late Paleozoic magnetizations. The rock magnetic properties of mineral extracts were compared with those of whole rock chips and nonmagnetic\u27\u27 residue to deduce magnetic carrier(s) and grain sizes. Hysteresis measurements for rock chips show typical\u27\u27 wasp-waisted loops, whereas extract shows typical pseudosingle-domain-like (PSD) unrestricted loops. Within all sites, there is a noticeable contribution of superparamagnetic (SP) grains seen in hysteresis properties and low-temperature magnetization measurements of whole rock chips, whereas a trend away from a strong SP contribution is seen when hysteresis properties of whole rock are compared with those of residue and extract. Consequently, our extraction process (predictably) removes SP grains, while preserving the characteristic fraction of remanence-carrying material, which behaves like a typical mixture of single-domain (SD) and PSD magnetite. Paradoxically, the typical fingerprint\u27\u27 of remagnetized carbonates, as seen in the whole rock data, seems to be a response to abundant SP grains associated with the acquisition of chemical remanent magnetizations (CRM), and not the actual remanence carrying population itself. Scanning electron microscopy (SEM) observations of magnetic extract reveal abundant authigenic Fe-oxides, characterized as either 10-100 mum Ni-free spherules or individual 0.1-10 mum euhedral grains. SEM observations of thin sections reveal abundant evidence of fluid flow driven chemical reactions that resulted in formation of new Fe oxide. Such reactions occurred along cracks and grain boundaries and within void space, and are associated with Fe-rich clay and calcite-dolomite reactions or as oxidation of Fe-sulfide framboids. Together, the SEM observations and rock magnetic experiments reveal that the three Late Paleozoic remagnetizations experienced by Cantabria-Asturias Paleozoic carbonates are CRMs facilitated by the presence of fluids activated during Late Paleozoic Variscan deformation

Insights into the mechanism for orogen‐related carbonate remagnetization from growth of authigenic Fe‐oxide: A scanning electron microscopy and rock magnetic study of Devonian carbonates from northern Spain

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95596/1/jgrb12919.pd

The impact of vertical-axis rotations on shortening estimates

The total amount of deformation between two converging bodies is described by the three components of the displacement fi eld: translation, rotation, and strain. Translations along faults and folding strain are the most common elements of the displacement field incorporated into estimates of tectonic shortening across orogenic systems. Determinations of vertical-axis rotations through paleomagnetic and structural analyses are keys for deciphering the rotational component of shortening within an orogenic system, and they can have a substantial effect on the amount of tectonic shortening in such systems. Accommodation structures observed in orogenic systems are typically noncoaxial and/or noncylindrical geometries (e.g., oblique and lateral ramps, superposed folding). These structures suggest that vertical-axis rotations have taken place, can aid in determining the relative timing of rotation with respect to translation, and may help constrain the location of the rotation axis. In this paper, we defi ne the components of the total displacement fi eld, describe the diagnostic and suggestive features associated with vertical-axis rotations, and apply trigonometric map-view calculations to estimate the amount of shortening contributed by such rotations. An error function relating shortening with vertical-axis rotation has been calculated and predicts values up to 50% for a 60° rotation if the rotation is not taken into account. Finally, we apply our approach to the Wyoming salient and show that previous estimates of shortening there may contain up to 14% errorEarth and Environmental Sciences Divison, Los Alamos National Laboratory, MéxicoUnidad de Zaragoza, Instituto Geológico y Minero de España, EspañaDepartment of Geosciences, University of Arizona, Estados UnidosDepartment of Earth and Environmental Sciences, University of Rochester, Estados UnidosDepartment of Geology, Bryn Mawr College, Estados Unido

A virtual tour of the Ibero-Armorican orocline

Dynamic content features, such as animations, videos or 3D representations are useful tools to explain dynamic geological processes. Modern technologies permit development of animations that are more illustrative and instructive than the classic static figures traditionally used in scientific papers. In addition, the use of supplemental files in traditional journals, and especially within new electronic journals, permit inclusion of interactive content as an analogue to the dynamic nature of geological processes. We present a collection of dynamic animations based on previous data. These animations are used to deliver ideas about the kinematic and mechanical development of the Ibero-Armorican orocline and to illustrate the complex evolution and timing of orocline formation, its tectonic setting on a regional and global-scale, and its implications for the modification of the lithosphere during orogeny

Chuar Group of the Grand Canyon: Record of Breakup of Rodinia, Associated Change in the Global Carbon Cycle, and Ecosystem Expansion by 740 Ma

The Chuar Group (similar to 1.600 m thick) preserves a record of extensional tectonism, ocean-chemistry fluctuations, and biological diversification during the late Neoproterozoic Era. An ash layer from the top of the section has a U-Pb zircon age of 742 +/- 6 Ma. The Chuar Group was deposited at low latitudes during extension on the north-trending Butte fault system and is inferred to record rifting during the breakup of Rodinia. Shallow-marine deposition is documented by tide- and wave-generated sedimentary structures, facies associations, and fossils. C isotopes in organic carbon show large stratigraphic variations, apparently recording incipient stages of the marked C isotopic fluctuations that characterize later Neoproterozoic time. Upper Chuar rocks preserve a rich biota that includes not only cyanobacteria and algae, but also heterotrophic protists that document increased food web complexity in Neoproterozoic ecosystems, The Chuar Group thus provides a well-dated, high-resolution record of early events in the sequence of linked tectonic, biogeochemical, environmental and biological changes that collectively ushered in the Phanerozoic Eon.Organismic and Evolutionary Biolog