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1.
R.L.M. Vissers  P.Th. Meijer 《Earth》2012,110(1-4):93-110
Following on paleomagnetic studies in the sixties showing ~ 35° counterclockwise rotation of Iberia during the Mesozoic, two classes of scenarios have been proposed for the motion history of Iberia which are currently competing. One class infers convergence in the Pyrenees in response to a scissor-type opening of the Bay of Biscay, described by a pole of rotation for Iberia with respect to Europe located within the Bay. The other class of scenarios assumes extensional or transtensional motions in the Pyrenees, compatible with opening of the Bay of Biscay described by a pole of rotation located in northern France. Although plate-kinematic studies over the last decade increasingly support the scissor-type model, geological studies in the Pyrenees have accumulated arguments in favour of an extensional or transtensional regime in the Pyrenean realm.We perform a detailed plate-kinematic analysis of the Late Jurassic and Cretaceous motion history of Iberia and surrounding plates with respect to Europe. A total of six sea-floor reconstructions in combination with paleomagnetic studies onland allow to recognize four distinct stages. (1) Early rifting and ultraslow spreading since the Kimmeridgean led to the development of an oceanic Neotethys domain north of Iberia. (2) This was followed by ~ 35° CCW rotation of Iberia during the Aptian, kinematically linked to progressive opening of the Bay of Biscay. (3) Motions in the Bay became stagnant during the Albian till Santonian, followed by the latest stages of spreading in the Bay, and (4) onset of largely Tertiary continental collision between Iberia and Europe eventually leading to the present day structure of the belt.Our analysis confirms the results of previous studies indicating that extensional or transtensional motions in the Pyrenean realm during opening of the Bay of Biscay and concurrent rotation of Iberia are incompatible with plate-kinematic reconstructions based on sea-floor anomalies. This invites a reappraisal of the geological data. Convergence in the Pyrenean realm during opening of the Bay and rotation of Iberia was accommodated by up to 300 km of subduction of mantle-dominated ocean floor exhumed during the late Jurassic and early Cretaceous. The stagnant stage in the progressive opening of the Bay indicates that convergence in the Pyrenean realm virtually came to a halt during the Albian. We hypothesize that the lithosphere previously subducted during Aptian convergence became gravitationally unstable, leading to asthenospheric upwelling and consequent magmatism and high temperature metamorphism in the overlying European margin now exposed in the North Pyrenean Zone. Aside from these magmatic and thermal effects, an enhanced gravitational potential energy of the remaining lithosphere column underlain by shallow asthenosphere may have led to a stress state allowing belt-parallel extensional deformation. Such a detachment scenario, inspired by plate-kinematic results, may provide an alternative to explain many of the geological data commonly quoted to infer a transtensional or extensional tectonic regime in the Pyrenees during the rotation of Iberia.  相似文献   

2.
New U–Pb zircon data from metagranites and metavolcanic rocks of the Schist-Graywacke Complex Domain and the Schistose Domain of Galicia Tras-os-Montes Zone from central and NW Iberia contribute to constrain the timing of the Cambro-Ordovician magmatism from Central Iberian and Galicia Tras-os-Montes Zones which occurred between 498 and 462 Ma. The crystallization ages of the metagranites and metavolcanic rocks from the northern Schist-Graywacke Complex Domain are as follows: (a) in west Salamanca, 489 ± 5 Ma for Vitigudino, 486 ± 6 Ma for Fermoselle and 471 ± 7 Ma for Ledesma; (b) in northern Gredos, 498 ± 4 Ma for Castellanos, 492 ± 4 Ma for San Pelayo and 488 ± 3 Ma for Bercimuelle; (c) in Guadarrama, 490 ± 5 Ma for La Estación I, 489 ± 9 Ma for La Cañada, 484 ± 6 Ma for Vegas de Matute (leucocratic), 483 ± 6 Ma for El Cardoso, 482 ± 8 Ma for La Morcuera, 481 ± 9 Ma for Buitrago de Lozoya, 478 ± 7 Ma for La Hoya, 476 ± 5 Ma for Vegas de Matute (melanocratic), 475 ± 5 Ma for Riaza, 473 ± 8 Ma for La Estación II and 462 ± 11 Ma for La Berzosa; and (d) in Toledo, 489 ± 7 Ma for Mohares and 480 ± 8 Ma for Polán. The crystallization ages of the metagranites from the Schistose Domain of Galicia Tras-os-Montes Zone are 497 ± 6 Ma for Laxe, 486 ± 8 Ma for San Mamede, 482 ± 7 Ma for Bangueses, 481 ± 5 Ma for Noia, 480 ± 10 for Rial de Sabucedo, 476 ± 9 Ma for Vilanova, 475 ± 6 Ma for Pontevedra, 470 ± 6 Ma for Cherpa and 462 ± 8 Ma for Bande. This magmatism is characterized by an average isotopic composition of (87Sr/86Sr)485Ma ≈ 0.712, (εNd)485Ma ≈ ?4.1 and (TDM) ≈ 1.62 Ga, and a high zircon inheritance, composed of Ediacaran–Early Cambrian (65 %) and, to a lesser extent, Cryogenian, Tonian, Mesoproterozoic, Orosirian and Archean pre-magmatic cores. Combining our geochronological and isotopic data with others of similar rocks from the European Variscan Belt, it may be deduced that Cambro-Ordovician magmas from this belt were mainly generated by partial melting of Ediacaran–Early Cambrian igneous rocks.  相似文献   

3.
The further development of Peyve’s concept of deep faults in the Earth’s crust and brittle part of the lithosphere is discussed. Three aspects are accentuated in this paper: (1) the modern definition of the term deep fault; (2) the parameters of deep faults as ruptures of the geological medium and three-dimensional, often boundary, geological bodies; and (3) reactivation of deep faults, including the development of this process in real time. Peyve’s idea of deep faults readily fitted into the concept of new global tectonics (plate tectonics). This was facilitated, first of all, by the extensive efforts made to elaborate Peyve’s ideas by a large group of researchers at the Geological Institute of the Russian Academy of Sciences (GIN RAS) and other scientists. At present, the term deep fault has been extended and transformed to cover three-dimensional geological bodies; the geological and geophysical properties and parameters of these bodies, as well as their reactivation (recurrent activation) in real time, have been studied.  相似文献   

4.
《地质学报》1932,11(2):101-105
In opening the meeting, the chairman made the following address: "It is my agreable duty to announce and make the award of the Grabau Medal to two members of our Society, Drs. J. S. Lee and Davidson Black. "The Grabau Medal was founded in 1925 by Mr. C. Y. Wang. the then President of the Geological Society. It was so named in honor of Dr. Grabau  相似文献   

5.
《Journal of Structural Geology》2001,23(6-7):1015-1030
The Malpica–Lamego Line (MLL) is a deformation zone in the Variscan belt of NW Iberia (NW Spain and N Portugal) that runs parallel to the chain for at least 275 km, bearing I-type granodiorite plutons along most of its length. The MLL affects previous structures by which high pressure and ophiolitic rocks were exhumed and emplaced on the Iberian plate during earlier deformation phases. Correlation and reconstruction of the stratigraphy of these sheets or tectonic units at both sides of the shear zone allows a preliminary estimate of the accumulated vertical and horizontal offsets after the tectonic activity of the fault. The value of the separations, of crustal-scale proportions, reaches a maximum 15 km of vertical offset that decreases gradually to the south. The structural record found in the rocks indicates a strike-slip regime that, in general, does not fit the geometry of the offsets. We suggest that the MLL went through two different stages during the same orogenic cycle: a first dip-slip episode, a reverse faulting event, overprinted by a later strike-slip reactivation.  相似文献   

6.
The Esla tectonic unit lies along the southern boundary of the Cantabrian–Asturian Arc, a highly curved foreland fold-thrust belt that was deformed during the final amalgamation of the Pangea supercontinent. Previous structural and paleomagnetic analyses of the Cantabrian–Asturian Arc suggest a two-stage tectonic history in which an originally linear belt was bent into its present configuration, creating an orocline. The Esla tectonic unit is a particularly complex region due to the interaction of rotating thrust sheets from the southern limb of the arc and the southward-directed thrusts of the Picos de Europa tectonic domain during late-stage north–south shortening and oroclinal bending. These structural interactions resulted in intense modification of early-phase thin-skinned tectonic structures that were previously affected by a deeper out-of-sequence antiformal stack that passively deformed the early thrust stack. A total of 75 paleomagnetic sites were collected from the Portilla and Santa Lucia formations, two carbonate passive-margin reef platform units from the middle Devonian. Similar to other regions of the Cantabrian–Asturian Arc, Esla Unit samples carry a secondary remanent magnetization that was acquired after initial thrusting and folding of Variscan deformation in the late Carboniferous. Protracted deformation during late-stage oroclinal bending caused reactivation of existing thrust sheets that include the Esla and younger Corniero and Valbuena thrusts. When combined with existing structural data and interpretations, these data indicate that the present-day sinuosity of the Esla Unit is the consequence of both secondary rotation of originally linear features in the western Esla exposures (e.g., frontal thrusts), and secondary modification and tightening of originally curvilinear features in the eastern Esla exposures (e.g., hanging-wall lateral/oblique ramps). Differences in structural style between the Esla and other tectonic units of the arc highlight the complex kinematics of oroclinal bending, which at the orogen-scale buckled an originally linear, north–south (in present-day coordinates) trending Cantabrian–Asturian thrust belt during the final stages of Pangea amalgamation.  相似文献   

7.
U–Pb SHRIMP ages obtained in zircons from the Sotosalbos and Toledo anatectic complexes in Central Spain give new constraints to the evolution of the inner part of the Hercynian Iberian belt. Pre-Hercynian ages in zircons from the Sotosalbos complex (∼464 Ma) are well preserved and reveal that an age diversity of the Lower Paleozoic magmatism in the area exists, as previous data on westernmost orthogneisses yield significant older ages. Zircon ages in the pelite-derived granites from the Toledo complex also show an important Neoproterozoic age component which points to a metasedimentary protolith deposited maximally 560 Ma ago. Younger zircon populations in both complexes at ∼330 Ma in the Sotosalbos region and ∼317 Ma in the Toledo complex indicate an important diachronism between the anatectic processes in both areas but also that these processes are mainly unrelated to the generation of the later Hercynian granite batholith of Central Spain, which could be of deeper crustal derivation. In addition, as migmatization occurred late in the metamorphic cycle, after peak conditions were attained, the age of anatexis is younger than the age of the main Hercynian metamorphic event, which still is not well constrained. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

8.
Extant Asplenium is one of the most widespread fern groups and occurs in the temperate and tropical regions. However, the fossil records of this genus are poorly documented, especially in the low latitudes. Here, a new species, Asplenium sanshuiense sp. nov. is described from the early Eocene of Sanshui Basin, Guangdong Province, South China. This is the lowest modern latitude fossil record of Asplenium and the first fossil assignment of A. section Darea (Jussieu) Bak., as well as the first fossil record of Asplenium reported from South China. This new species shows that Asplenium had already spread into South China by the early Eocene and the section Darea (Jussieu) Bak. was identifiable within the genus Asplenium during that time. This new species, combined with previous fossil spore-pollen records indicates a warm and humid climate in the Sanshui Basin of the early Eocene.  相似文献   

9.
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10.
Following the recommendation of the International Commission on Stratigraphy (16 votes Yes [94%], 1 abstention, 2 votes not received), the Global boundary Stratotype Section and Point (GSSP) for the base of the Turonian Stage of the Cretaceous System is defined as the base of bed 86 of the Bridge Creek Limestone Member of the Greenhorn Limestone Formation at the western end of the Denver and Rio Grande Railroad cut near the north boundary of the Pueblo Reservoir State Park Recreation Area, west of Pueblo, Colorado, USA. This GSSP horizon is also exposed and protected in the adjacent state recreation area. It coincides with the first occurrence of the ammonite Watinoceras devonense, is in the middle of a global positive excursion in Carbon-13 isotopes, and is bracketed by widespread bentonites that have yield edages of 93 to 93.5 Ma.  相似文献   

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