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  • 更新日期:2020-01-16
  • Love-to-Rayleigh scattering across the eastern North American passive margin
    Tectonophysics (IF 2.764) Pub Date : 2020-01-15
    Andrea Servali; Maureen D. Long; Jeffrey Park; Margaret H. Benoit; John C. Aragon

    This study presents observations of Love-to-Rayleigh scattering beneath the eastern North American passive margin that place new constraints on seismic anisotropy in the upper mantle. The scattering of Love-wave energy to Rayleigh waves is generated via sharp lateral gradients in anisotropic structure along the source-receiver path. The scattered phases, known as quasi-Love (QL) waves, exhibit amplitude behavior that depends on the strength of the anisotropic contrast as well as the geometrical relationship between the propagation azimuth and the anisotropic symmetry axis. Previous studies of seismic anisotropy in the upper mantle beneath eastern North America have revealed evidence for a mix of lithospheric and asthenospheric contributions, but the interpretation of indicators such as SKS splitting is hampered by a lack of vertical resolution. Complementary constraints on the depth distribution of anisotropy can be provided by surface waves, which have the additional advantage of sampling portions of the margin that lie offshore. Here we present measurements of QL phases using data from several hundred broadband seismic stations in eastern North America, including stations of the USArray Transportable Array, the Central and Eastern U.S. Network, and the MAGIC experiment in the central Appalachians. We find evidence for clear QL arrivals at stations in eastern North America, consistent with a region of particularly strong and coherent scattering inferred just offshore the central portion of the margin. The coherent scattering near the Eastern North American Margin likely reflects lateral transitions in seismic anisotropy in the asthenospheric mantle, associated with locally complex three-dimensional flow, with possible additional contributions from anisotropy in the mantle lithosphere. A second region of strong QL scattering near the southern coast of Greenland is enigmatic in origin, but may be due to pre-existing lithospheric fabric.

    更新日期:2020-01-15
  • Geodynamic nature of the Okhotsk Sea lithosphere. An overview of seismic constraints
    Tectonophysics (IF 2.764) Pub Date : 2020-01-10
    Nina I. Pavlenkova; Sergey N. Kashubin; Tamara S. Sakoulina; Galina A. Pavlenkova

    A combined interpretation of the geological, seismological and active-source seismic data in the Okhotsk Sea (Sea of Okhotsk) region allows describing the structure and geodynamics of this transition zone between the continent and the ocean. The interpreted data on the crust and uppermost mantle structure of this region are based on the recent seismic profiles with detailed system of observation carried out during the last decades in the Okhotsk Sea. Large air guns and 119 ocean bottom stations were used to study the lithosphere structure of beneath the sea down to 70 km depth. Detailed P- and S-waves interpretation methods were applied for these profiles. The study shows the Okhotsk Sea crust to be of the continental type composed mainly of the felsic rocks. Only within the elongated basin along the Kuril island arc, the crust thickness is reduced and the velocities increased to the values typical for the oceanic crust. The new seismic data are also obtained on the upper mantle structure. The detailed mathematical modeling of the observed mantle waves revealed unusual type of the wide angle reflections recorded at the first arrivals which previously interpreted as refractions. As a result, two reflective boundaries M and M1 are revealed beneath the sea depression, with velocities of 7.9 and 8.0 km/s. Along the Sakhalin Island a deep mantle fault was traced down to the depth of 70 km. This deep fault is traced in the north-south direction far into the Pacific ocean and into the east Asia. The seismological data show the Okhotsk Sea to be surrounded by deep faults of global nature. In addition to the Kuril arc zone limiting the sea depression in the eastern part, the deep Magadan fault separates the depression from the continent. These data suggest the Okhotsk Sea region as a separate micro-plate of the continental type.

    更新日期:2020-01-11
  • Volcanic edifice slip events recorded on the fault plane of the San Andrés Landslide, El Hierro, Canary Islands
    Tectonophysics (IF 2.764) Pub Date : 2020-01-09
    Jan Blahůt; Ivanka Mitrovic-Woodell; Ivo Baroň; Miloš René; Matt Rowberry; Pierre-Henri Blard; Filip Hartvich; Jan Balek; Stavros Meletlidis

    Volcanic flank collapses often result in giant debris avalanches that are capable of travelling tens of kilometres across the ocean floor and generating tsunamis that devastate distant communities. The San Andrés Landslide on El Hierro, Canary Islands, represents one of the few places in the world where it is possible to investigate the landslide mass and fault planes of a volcanic collapse structure. In this study, a new conceptual model for the development of this enormous slump is presented on the basis of structural geological and geomorphological measurements, petrological and microstructural analyses, and cosmogenic radionuclide dating. Structural geological and geomorphological measurements indicate that the fault plane records two distinct events. Petrological and microstructural analyses demonstrate that a thin layer of frictionite covers the surface of the fault in contact with an oxidised tectonic breccia that transitions into the underlying undeformed basanite host rock. This frictionite comprises a heterogeneous cataclastic layer and a translucent silica layer that are interpreted to represent two separate slip events on the basis of their architecture and crosscutting relationships. Cosmogenic 3He dating reveals a maximum exposure age of 183 ± 17 ka to 52 ± 17 ka. Arguments are presented in support of the idea that the first slip event took place between 545 ka and 430 ka, prior to significant clockwise rotation of El Hierro, and the second slip event took place between 183 ka and 52 ka, perhaps in association with one of the giant debris avalanches that occurred around that time. This is the first time that more than one slip event has been recognised from the fault plane of the San Andrés Landslide. It is also believed to be the first time a silica layer resulting from frictional melt has been described in a volcanic setting.

    更新日期:2020-01-09
  • Crustal structure and erosion of the Lofoten/Vesterålen shelf, northern Norwegian margin
    Tectonophysics (IF 2.764) Pub Date : 2020-01-08
    Asbjørn Johan Breivik; Jan Inge Faleide; Rolf Mjelde; Ernst R. Flueh; Yoshio Murai

    The Norwegian continental shelf has been through several rift phases since the Caledonian orogeny. Early Cretaceous rifting created the largest sedimentary basins, and Early Cenozoic continental breakup between East Greenland and Europe affected the continental shelf to various degrees. The Lofoten/Vesterålen shelf is located off Northern Norway, bordering the epicontinental Barents Sea to the northeast, and the deep-water Lofoten Basin to the west. An ocean bottom seismometer/hydrophone (OBS) survey was conducted over the shelf and margin areas in 2003 to constrain crustal structure and margin development. This study presents Profile 8-03, located between the islands of Lofoten/Vesterålen and the shelf edge. The wide-angle seismic data were modeled using forward raytracing to build a crustal velocity-depth transect. Gravity modeling was used to resolve an ambiguity in seismic Moho identification in the southwestern part. Results show a crustal thickness of ∼31 km, significantly thicker than what a vintage land station based study suggested. Profile 8-03 and other OBS profiles to the southwest show high sedimentary velocities at or near the seafloor, increasing rapidly with depth. Sedimentary velocities were compared to the velocity-depth function derived from an OBS profile at the Barents Sea margin, tied to a coincident well log, where there is little erosion. Results from this profile and the crossing Profile 6-03 (Breivik et al. 2017) indicate three major erosion episodes; Late Triassic-Early Jurassic, tentatively mid-Cretaceous, Late Cretaceous-early Cenozoic, and a minor late glacial erosion episode off Vesterålen.

    更新日期:2020-01-09
  • Age of metamorphism and deformation in the Montagne Noire dome (French Massif Central): Tapping into the memory of fine-grained gneisses using monazite U-Th-Pb geochronology
    Tectonophysics (IF 2.764) Pub Date : 2020-01-08
    Françoise Roger; Christian Teyssier; Donna L. Whitney; Jean-Patrick Respaut; Jean-Louis Paquette; Patrice F. Rey
    更新日期:2020-01-09
  • Fast dismantling of a mountain belt by mantle flow: Late-orogenic evolution of Pyrenees and Liguro-Provençal rifting
    Tectonophysics (IF 2.764) Pub Date : 2019-12-24
    Laurent Jolivet; Adrien Romagny; Christian Gorini; Agnès Maillard; Isabelle Thinon; Renaud Couëffé; Maxime Ducoux; Michel Séranne

    The Pyrenean Belt ends against the Gulf of Lion passive margin. The mechanism responsible for dismantling the mountain belt during Oligocene rifting has not yet found a proper explanation. The Late Eocene and Oligocene period is characterized by a first order change in subduction dynamics in the Mediterranean and the subduction zones started to retreat with back-arc basins forming at the expense of mountain belts build earlier. The slab subducting below Provence and Sardinia-Corsica started a fast south-eastward retreat, forming the Liguro-Provençal Basin. This syn-rift period in the Gulf of Lion margin is coeval with exhumation of the eastern Pyrenean basement, while underthrusting of Iberia continued until Early Miocene. Based on interpretation of seismic lines, we propose a tentative model in which the mantle flow related with Apennine slab retreat has (1) exhumed and thinned the continental mantle below the Gulf of Lion and the eastern Pyrenees and (2) exhumed the lower crust, leading to crustal thinning and subsidence of the Gulf of Lion margin. The wide distribution of syn-rift volcanism in the transition between the Gulf of Lion and Valencia Basin is in line with the geometry observed in the margin suggesting ductile deformation of a weak continental crust, typical of volcanic margins. The direction of SKS-waves seismic anisotropy below the Pyrenees and the observed migration of exhumation toward the west fit this simple model. The concentration of syn-rift magmatism and the ductile behaviour of the crust during rifting can be explained by the high heat flow above the slab tear that separates the future Apennines and Maghreb branches of the West Mediterranean subduction zone. Finally, removal of upper mantle, inducing uplift and an increase of potential energy, may explain why thrusting continued in the Pyrenees while rifting was still active nearby along strike.

    更新日期:2020-01-04
  • Mesozoic intraplate deformation in the southern part of the Central European Basin - Results from large-scale 3D modelling
    Tectonophysics (IF 2.764) Pub Date : 2020-01-02
    Alexander Malz; Christoph Nachtweide; Sophie Emmerlich; Lars Schimpf

    The Central European Basin is an intracontinental basin that initially formed due to long-lasting thermal subsidence accompanied with several tectonic phases of extension during Mesozoic times. Locally, thick evaporites were incorporated in the deformation and led to the formation of detached structures, salt pillows and diapirs. At the end of the Late Cretaceous, the formation of (sub-) basins and (half-) grabens became interrupted by a short-term event of contraction. Especially along the northern and southern edges of the basin, lithospheric shortening resulted in basin inversion and the uplift of large basement blocks. Hence, the present day's structural framework shows a complex pattern of kinematically and chronologically variable structures. Herein, we unravelled these structures for the Altmark region in northern Saxony-Anhalt (Central Germany). We used regional depth maps, reflection seismics and borehole data analysed by use of large-scale subsurface mapping and 3D modelling techniques to completely re-evaluate the structures in the Late Palaeozoic to Cenozoic sedimentary basin succession. Our results show a high variability of tectonic structures: narrow and distributed, in parts reactivated normal fault zones, huge inverted basins, thin-skinned thrust faults, detachment folds and large basement thrusts. The style of deformation significantly changed during the region's evolution. This is indicated by particular structural, kinematic, thermal and rheological conditions, which existed for the individual phases of basin formation and inversion and probably persist until today.

    更新日期:2020-01-04
  • Deep structure of the western coast of the Makran subduction zone, SE Iran
    Tectonophysics (IF 2.764) Pub Date : 2019-12-26
    K. Motaghi; E. Shabanian; T. Nozad-Khalil
    更新日期:2020-01-04
  • Episodic out-of-sequence deformation promoted by Cenozoic fault reactivation in NW Argentina
    Tectonophysics (IF 2.764) Pub Date : 2019-12-23
    Patricio Payrola; Cecilia del Papa; Alejandro Aramayo; Heiko Pingel; Fernando Hongn; Edward R. Sobel; Gerold Zeilinger; Manfred R. Strecker; Sebastian Zapata; John Cottle; Natalia Salado Paz; Johannes Glodny

    The Central Andes are the product of contractional deformation related to subduction of the Nazca plate beneath the South American continent. In this geodynamic setting, thrust belt propagation in the Central Andean retroarc in NW Argentina and southern Bolivia has been linked with the critical wedge model implying progressive eastward migration of the deformation front during the Cenozoic. However, Eocene unconformities and growth strata within the orogenic hinterland of the Eastern Cordillera and Puna Plateau suggest selective reactivation of pre-Andean and Andean faults revealing a pattern of diachronous and spatially disparate range uplifts. The Calchaquí Valley in NW Argentina is characterized by basin-and-range morphology, which is intimately linked with the heterogeneous Neoproterozoic basement, Cretaceous rift structures, and the Cenozoic foreland. In this study, we analyze this complex deformation by reconstructing Cenozoic fault reactivation and sedimentation patterns in the Eastern Cordillera. Detailed structural mapping along the eastern Calchaquí border (Tonco area) reveals five Cenozoic unconformities in the former foreland deposits related to multiple episodes of fault reactivation during the Eocene-to-Pleistocene. A refined chronostratigraphy (U-Pb zircon), new AHe thermochronological data (apatite U-Th-Sm/He), and existing evidence for deformation indicate episodic out-of-sequence deformation and increased Eo-Oligocene (Puna Plateau) to Miocene (Eastern Cordillera) fault displacement apparently controlled by pre-Cenozoic heterogeneities. The coeval eastward propagation of deformation and continuing deformation in the west generally challenge the applicability of the critical wedge model.

    更新日期:2020-01-04
  • Fault development in transtension, McCully gas field, New Brunswick, Canada
    Tectonophysics (IF 2.764) Pub Date : 2019-12-17
    Jared Kugler; John W.F. Waldron; Paul W. Durling

    In the Mississippian Moncton Sub-basin, New Brunswick, Canada, 3D seismic data reveal structure within the Mississippian McCully gas field. The asymmetric basin, elongated NE–SW, is bounded to the SE and NW by major dextral fault zones. Curved en-echelon extensional faults strike ESE–WNW. Gentle folds trend NE–SW. Contractional faults show varied orientations. These features are all consistent with deformation of the basin in an environment of dextral transtension. Analogous faults in outcrops, ~13 km to the SW, constrain sub-seismic deformation, and show that deformation occurred soon after deposition, before complete lithification. Strike-slip basins undergo concurrent extension, contraction, and rotation producing complex kinematic history which can be unraveled using the heaves and orientations of fault arrays. Based on measurements from the 3D data set, a horizon in the gas field displays an apparent stretch of ~1.14, and a perpendicular apparent shortening of ~0.976. Faults are oriented, on average, at ~40° to the shear zone boundary. These values show that the basin was deformed in transtension with overall angle of transtension alpha ≈47° to 50°. However, part of this deformation post-dated the overlying Sussex Group; removal of this component suggests alpha was in the range 62–65° during deposition of the Horton Group. Variations across the shear zone indicate that deformation was heterogeneous in space and time; an initial large strike-slip component transitioned to more divergent deformation as the deformation zone widened. Fault curvature likely reflects propagation during development of these heterogeneities. Overall, the deformation reflects an oblique-rift environment with ~N–S extension, that developed between major dextral strike-slip faults. These results show that with 3D seismic data sets it is possible to reconstruct details of strain history in transtensional basins that are potentially useful for understanding basin compartmentalization and fluid flow over time.

    更新日期:2020-01-04
  • The 2017 ML 5.4 Pohang earthquake sequence, Korea, recorded by a dense seismic network
    Tectonophysics (IF 2.764) Pub Date : 2019-12-10
    Kwang-Hee Kim; Wooseok Seo; Jongwon Han; Joa Kwon; Su Young Kang; Jin-Han Ree; Sungshil Kim; Kang Liu

    The 2017 ML 5.4 Pohang Earthquake in southeastern Korea, which was induced by fluid injection from an enhanced geothermal system, and its foreshock–aftershock sequence has been recorded by a dense and portable temporary seismic array. The hypocentral distribution of the earthquake sequence reveals the reactivation of a complex subsurface fault system that was previously unmapped. Aftershock seismicity propagated to the southwest and revealed previously unknown fault segments. The aftershocks tend to concentrate along the tips of the main rupture, with a lack of aftershocks around the mainshock hypocenter. This pattern suggests that the stress in the mainshock area was almost completely released during the mainshock and early aftershock phase, and that the recurrence of moderate to large earthquakes in the hypocentral area is unlikely compared with the marginal areas. A new rupture occurred along the southwestern margin of the main rupture after the largest aftershock (ML 4.6).

    更新日期:2020-01-04
  • Cretaceous intracontinental rifting at the southern Chatham Rise margin and initialisation of seafloor spreading between Zealandia and Antarctica
    Tectonophysics (IF 2.764) Pub Date : 2019-11-27
    Florian Riefstahl; Karsten Gohl; Bryan Davy; Kaj Hoernle; Nick Mortimer; Christian Timm; Reinhard Werner; Katharina Hochmuth

    Passive continental margins are commonly classified as magma-poor and magma-rich types. Related breakup processes are often associated with far-field tectonic stresses or upwelling mantle plumes. The Chatham Rise east off New Zealand records a sequence of Late Cretaceous tectonic events, which include subduction and collision of the oceanic Hikurangi Plateau to subsequent continental rifting and breakup. The mechanisms triggering the change in tectonic forces are poorly understood but address open questions regarding the formation of passive margins. We acquired wide-angle seismic reflection/refraction, multi-channel seismic and potential field data along three profiles crossing the southern Chatham Rise margin and SE Chatham Terrace to the oceanic crust in order to image and understand the crustal structure and breakup mechanisms. Variations in crustal thickness along the highly faulted Chatham Rise are most likely related to the collision with the Hikurangi Plateau. Our data indicate that the SE Chatham Terrace represents a broad continent-ocean transition zone (COTZ), which we interpret to consist of very thin continental crust affected by magmatic activity. Along the southern Chatham Rise margin, features of both, magma-poor and magma-rich rifted margins are present. We suggest that passive rifting initiated at 105–100 Ma related to slab dynamics after the Hikurangi Plateau collision. We revise the onset of seafloor spreading south of the eastern Chatham Rise to ~88 Ma from the extent of our inferred COTZ. Geographically extensive, but low-volume intraplate magmatism affected the margin at 85–79 Ma. We suggest that this magmatism and the onset of seafloor spreading are a response to upwelling mantle through a slab window after 90 Ma. After 85 Ma, spreading segments became connected leading to the final separation of Zealandia from Antarctica. We interpret the southern Chatham Rise margin as a unique hybrid margin whose tectonic history was influenced by passive continental rifting and mantle upwelling.

    更新日期:2020-01-04
  • The relationship between crust-lithosphere structures and seismicity on the southeastern edge of the Tibetan Plateau
    Tectonophysics (IF 2.764) Pub Date : 2019-11-22
    Xingqian Xu; Lijun Su; Junzhe Liu; Wanhuan Zhou; Xin Qu

    The crust-lithosphere structure, especially the discontinuities such as Moho and lithosphere-asthenosphere boundary (LAB), is important in the investigation of geodynamic process implications and tectonic evolution of the lithosphere and regional seismic activity. We stacked the S receiver functions from 51 permanent broad-band stations to investigate the crust-lithosphere structures beneath the southeastern edge of the Tibetan Plateau and further discussed the mechanism of lower-crust earthquakes, the regional tectonics deformation characteristics, and the relationship between the two discontinuities and seismicity in this region. The results show that the Moho depth increases from 40–52 km beneath the Sichuan Basin to 56–74 km on the both western side of the Longmenshan (LMS) fault and Anninhe-Zemuhe fault. The LAB depth ranges from 130 to 170 km beneath the Sichuan Basin, and a shallow belt ranges from 100 km to 130 km around the Sichuan Basin. On the Moho depth contour map, 374 moderate earthquakes that accounted for 72.2%, corresponding to the depth range of 44–52 km and 60–68 km on the both sides of a narrow strip (longitude 102°~104°). On the LAB depth contour map, 321 earthquakes accounted for 62.15% in the depth range of 130–150 km. The variation of LAB corresponds to the increasing crustal thickness, intensive lower crustal earthquakes (hypocenters about 60 km and magnitude 4.0 ≤ Ms. ≤ 4.9) and surface abrupt elevations. It implied that Normal strong earthquakes generate the lower crustal earthquakes or aftershocks that resulted in the shear zones where fluid-induced metamorphic transformations, the eclogitization of dry granulite, and further affect the crustal thickness and deformation to control the spatial distribution of deep faults and seismicity. Key points • The escape flow of hot asthenospheric material beneath the plateau moving roughly eastward is blocked by the thick Sichuan Basin. • Seismicity have a good consistency with crust-lithosphere deformation. • Discontinuities in the lithosphere could be used as a reference parameter for seismic hazard analysis and long-term earthquake prediction.

    更新日期:2020-01-04
  • Elastic thickness of the Iranian lithosphere from gravity and seismic data
    Tectonophysics (IF 2.764) Pub Date : 2019-09-05
    Mehdi Eshagh; Robert Tenzer; Mehrdad Eshagh

    We estimate the (effective) elastic thickness of the Iranian lithosphere (and adjoining tectonic plates) by using the approach that combines the Vening Meinesz-Moritz's (VMM) regional isostatic principle with the isostatic flexural model formulated based on solving a flexural differential equation for a thin elastic shell. To model the response on a load more realistically, we also consider the lithospheric density structure. The resulting expression describes a functional relation that links gravity field and mechanical properties of the lithosphere. The Young modulus and the Poisson ratio are computed from seismic velocity data in prior of estimating the lithospheric elastic thickness. The presented results reveal that the estimated elastic thickness closely resembles a regional tectonic configuration associated with the extensional tectonism along the Red Sea-Gulf Rift System, the continental collision of the Arabian and Eurasian plates, and the subduction along the Makran Subduction Zone. Seismically and volcanically active convergent tectonic margins of the Zagros and Kopeh Dagh Fold and Thrust Belts further extending along the Makran Accretionary Complex are characterised by a low lithospheric strength, with the elastic thickness typically less than ~30 km. These small values of the elastic thickness are in a striking contrast to much larger values within most of the Central Iranian Blocks. According to our estimate, local maxima there reach ~70 km in the Tabas micro-block. The elastic thickness of the Turan and Arabian Platforms reaches maxima of ~100 km. These results generally support the hypothesis that tectonically active zones and orogens have a relatively low strength, resulting in a significant response of the lithosphere on various tectonic loads, compared to a significant strength of old cratonic formations. Interestingly, however, we observe a striking contrast between a low strength of the Arabian Shield compared to a high strength of the Arabian Platform. A possible explanation of this finding could be given by a different thermal regime of the Arabian lithosphere, controlled mainly by a mantle upwelling and a consequent extensional tectonism along the Red Sea-Gulf Rift System.

    更新日期:2020-01-04
  • The Haselgebirge evaporitic mélange in central Northern Calcareous Alps (Austria): Part of the Permian to Lower Triassic rift of the Meliata ocean?
    Tectonophysics (IF 2.764) Pub Date : 2013-01-11
    Anja Schorn,Franz Neubauer,Johann Genser,Manfred Bernroider

    For the reconstruction of Alpine tectonics of the Eastern Alps, the evaporitic Permian to Lower Triassic Haselgebirge Formation plays a key role in (1) the origin of Haselgebirge bearing nappes, (2) the inclusion of magmatic and metamorphic rocks revealing tectonic processes not preserved in other units, and (3) the debated mode of emplacement of the nappes, namely gravity-driven or tectonic. Within the Moosegg quarry of the central Northern Calcareous Alps gypsum/anhydrite bodies are tectonically mixed with lenses of sedimentary rocks and decimeter- to meter-sized tectonic clasts of plutonic and subvolcanic rocks and rare metamorphics. We examined various types of (1) widespread biotite-diorite, meta-syenite, (2) meta-dolerite and rare ultramafic rocks (serpentinite, pyroxenite) as well as (3) rare metamorphic banded meta-psammitic schists and meta-doleritic blueschists. The apparent 40Ar/39Ar biotite ages from three biotite-diorite, meta-dolerite and meta-doleritic blueschist samples with variable composition and fabrics range from 248 to 270 Ma (e.g., 251.2 ± 1.1 Ma) indicating a Permian age of cooling after magma crystallisation or metamorphism. The chemical composition of biotite-diorite and meta-syenite indicates an alkaline trend interpreted to represent a rift-related magmatic suite. These, as well as Permian to Jurassic sedimentary rocks, were incorporated during Cretaceous nappe emplacement forming the sulphatic Haselgebirge mélange. The scattered 40Ar/39Ar white mica ages of a meta-doleritic blueschist (of N-MORB origin) and banded meta-psammitic schist are ca. 349 and 378 Ma, respectively, proving the Variscan age of pressure-dominated metamorphism. These ages are similar to detrital white mica ages reported from the underlying Rossfeld Formations, indicating a close source-sink relationship. According to our new data, the Haselgebirge bearing nappe was transported over the Lower Cretaceous Rossfeld Formations, which include many clasts derived from the Haselgebirge Formation and its exotic blocks deposited in front of the incoming nappe comprising the Haselgebirge Formation.

    更新日期:2019-11-01
  • Polyphase exhumation in the western Qinling Mountains, China: Rapid Early Cretaceous cooling along a lithospheric-scale tear fault and pulsed Cenozoic uplift.
    Tectonophysics (IF 2.764) Pub Date : 2014-03-17
    Bianca Heberer,Thomas Anzenbacher,Franz Neubauer,Johann Genser,Yunpeng Dong,István Dunkl

    The western sector of the Qinling-Dabie orogenic belt plays a key role in both Late Jurassic to Early Cretaceous "Yanshanian" intracontinental tectonics and Cenozoic lateral escape triggered by India-Asia collision. The Taibai granite in the northern Qinling Mountains is located at the westernmost tip of a Yanshanian granite belt. It consists of multiple intrusions, constrained by new Late Jurassic and Early Cretaceous U-Pb zircon ages (156 ± 3 Ma and 124 ± 1 Ma). Applying various geochronometers (40Ar/39Ar on hornblende, biotite and K-feldspar, apatite fission-track, apatite [U-Th-Sm]/He) along a vertical profile of the Taibai Mountain refines the cooling and exhumation history. The new age constraints record the prolonged pre-Cenozoic intracontinental deformation as well as the cooling history mostly related to India-Asia collision. We detected rapid cooling for the Taibai granite from ca. 800 to 100 °C during Early Cretaceous (ca. 123 to 100 Ma) followed by a period of slow cooling from ca. 100 Ma to ca. 25 Ma, and pulsed exhumation of the low-relief Cretaceous peneplain during Cenozoic times. We interpret the Early Cretaceous rapid cooling and exhumation as a result from activity along the southern sinistral lithospheric scale tear fault of the recently postulated intracontinental subduction of the Archean/Palaeoproterozoic North China Block beneath the Alashan Block. A Late Oligocene to Early Miocene cooling phase might be triggered either by the lateral motion during India-Asia collision and/or the Pacific subduction zone. Late Miocene intensified cooling is ascribed to uplift of the Tibetan Plateau.

    更新日期:2019-11-01
  • Structures, microfabrics and textures of the Cordilleran-type Rechnitz metamorphic core complex, Eastern Alps.
    Tectonophysics (IF 2.764) Pub Date : 2013-11-26
    Shuyun Cao,Franz Neubauer,Manfred Bernroider,Junlai Liu,Johann Genser

    Rechnitz window group represents a Cordilleran-style metamorphic core complex, which is almost entirely located within nearly contemporaneous Neogene sediments at the transition zone between the Eastern Alps and the Neogene Pannonian basin. Two tectonic units are distinguished within the Rechnitz metamorphic core complex (RMCC): (1) a lower unit mainly composed of Mesozoic metasediments, and (2) an upper unit mainly composed of ophiolite remnants. Both units are metamorphosed within greenschist facies conditions during earliest Miocene followed by exhumation and cooling. The internal structure of the RMCC is characterized by the following succession of structure-forming events: (1) blueschist relics of Paleocene/Eocene age formed as a result of subduction (D1), (2) ductile nappe stacking (D2) of an ophiolite nappe over a distant passive margin succession (ca. E-W to WNW-ESE oriented stretching lineation), (3) greenschist facies-grade metamorphism annealing dominant in the lower unit, and (4) ductile low-angle normal faulting (D3) (with mainly NE-SW oriented stretching lineation), and (5) ca. E to NE-vergent folding (D4). The microfabrics are related to mostly ductile nappe stacking to ductile low-angle normal faulting. Paleopiezometry in conjunction with P-T estimates yield high strain rates of 10- 11 to 10- 13 s- 1, depending on the temperature (400-350 °C) and choice of piezometer and flow law calibration. Progressive microstructures and texture analysis indicate an overprint of the high-temperature fabrics (D2) by the low-temperature deformation (D3). Phengitic mica from the Paleocene/Eocene high-pressure metamorphism remained stable during D2 ductile deformation as well as preserved within late stages of final sub-greenschist facies shearing. Chlorite geothermometry yields two temperature groups, 376-328 °C, and 306-132 °C. Chlorite is seemingly accessible to late-stage resetting. The RMCC underwent an earlier large-scale coaxial deformation accommodated by a late non-coaxial shear with ductile low-angle normal faulting, resulting in subvertical thinning in the extensional deformation regime. The RMCC was rapidly exhumed during ca. 23-18 Ma.

    更新日期:2019-11-01
  • Low temperature thermochronology in the Eastern Alps: Implications for structural and topographic evolution.
    Tectonophysics (IF 2.764) Pub Date : 2012-05-14
    Andreas Wölfler,Kurt Stüwe,Martin Danišík,Noreen J Evans

    According to new apatite fission track, zircon- and apatite (U-Th)/He data, we constrain the near-surface history of the southeastern Tauern Window and adjacent Austrolapine units. The multi-system thermochronological data demonstrate that age-elevation correlations may lead to false implications about exhumation and cooling in the upper crust. We suggest that isothermal warping in the Penninic units that are in the position of a footwall, is due to uplift, erosion and the buildup of topography. Additionally we propose that exhumation rates in the Penninic units did not increase during the Middle Miocene, thus during the time of lateral extrusion. In contrast, exhumation rates of the Austroalpine hangingwall did increase from the Paleogene to the Neogene and the isotherms in this unit were not warped. The new zircon (U-Th)/He ages as well as zircon fission track ages from the literature document a Middle Miocene exhumation pulse which correlates with a period of enhanced sediment accumulation during that time. However, enhanced sedimentation- and exhumation rates at the Miocene/Pliocene boundary, as observed in the Western- and Central Alps, cannot be observed in the Eastern Alps. This contradicts a climatic trigger for surface uplift, and makes a tectonic trigger and/or deep-seated mechanism more obvious to explain surface uplift in the Eastern Alps. In combination with already published geochronological ages, our new data demonstrate Oligocene to Late Miocene fault activity along the Möll valley fault that constitutes a major shear zone in the Eastern Alps. In this context we suggest a geometrical and temporal relationship of the Katschberg-, Polinik-Möll valley- and Mur-Mürz faults that define the extruding wedge in the eastern part of the Eastern Alps. Equal deformation- and fission track cooling ages along the Katschberg-Brenner- and Simplon normal faults demonstrate overall Middle Miocene extension in the whole alpine arc.

    更新日期:2019-11-01
  • Paleomagnetic and geochronologic constraints on the geodynamic evolution of the Central Dinarides.
    Tectonophysics (IF 2.764) Pub Date : 2012-03-20
    Arjan de Leeuw,Oleg Mandic,Wout Krijgsman,Klaudia Kuiper,Hazim Hrvatović

    The geodynamic evolution of the Dinaride Mountains of southeastern Europe is relatively poorly understood, especially in comparison with the neighboring Alps and Carpathians. Here, we construct a new chronostratigraphy for the post-orogenic intra-montane basins of the Central Dinarides based on paleomagnetic and 40Ar/39Ar age data. A first phase of basin formation occurred in the late Oligocene. A second phase of basin formation took place between 18 and 13 Ma, concurrent with profound extension in the neighboring Pannonian Basin. Our paleomagnetic results further indicate that the Dinarides have not experienced any significant tectonic rotation since the late Oligocene. This implies that the Dinarides were decoupled from the adjacent Adria and the Tisza-Dacia Mega-Units that both underwent major rotation during the Miocene. The Dinaride orogen must consequently have accommodated significant shortening. This is corroborated by our AMS data that indicate post-Middle Miocene shortening in the frontal zone, wrenching in the central part of the orogen, and compression in the hinterland. A review of paleomagnetic data from the Adria plate, which plays a major role in the evolution of the Dinarides as well as the Alps, constrains rotation since the Early Cretaceous to 48 ± 10° counterclockwise and indicates 20° of this rotation took place since the Miocene. It also shows that Adria behaved as an independent plate from the Late Jurassic to the Eocene. From the Eocene onwards, coupling between Adria and Africa was stronger than between Adria and Europe. Adria continued to behave as an independent plate. The amount of rotation within the Adria-Dinarides collision zone increases with age and proximity of the sampled sediments to undeformed Adria. These results significantly improve our insight in the post-orogenic evolution of the Dinarides and resolve an apparent controversy between structural geological and paleomagnetic rotation estimates for the Dinarides as well as Adria.

    更新日期:2019-11-01
  • States of paleostress north and south of the Periadriatic fault: Comparison of the Drau Range and the Friuli Southalpine wedge.
    Tectonophysics (IF 2.764) Pub Date : 2014-12-10
    Esther Maria Bartel,Franz Neubauer,Johann Genser,Bianca Heberer

    This study focuses on the analysis of structures and kinematics of a N-S profile along the axis of maximum shortening of the European Eastern Alps. The area includes the southern Austroalpine unit in the north and the Southalpine unit, which is a part of the Adriatic indenter. The stratigraphically different units are separated by the Periadriatic fault, the major strike-slip fault within the Alps. In order to assess the kinematics of these units, mainly fault-slip data from north and south of the Periadriatic fault were analyzed. We distinguish a succession of five main kinematic groups in both units: (1) N-S compression; (2) NW-SE compression; (3) NE-SW compression, σ3 changes gradually from subvertical to subhorizontal; (4) N-S compression; and (5) NW-SE compression. Our study reveals that the deformation sequence on either sides of the PAF is similar. The mean orientations of the principal stress axes, however, show small, but consistent differences: The subhorizontal axes north of the Periadriatic fault plunge northward, in the south southward. A counterclockwise (CCW) rotation of the southern part in respect to the north is evident and in line with the well-known counterclockwise rotation of the Adriatic indenter as well as dextral displacement of the N-fanning stress-field along the Periadriatic fault. Opposing plunge directions are interpreted as a primary feature of the internal stress-field within an orogenic wedge further increased during ongoing compression.

    更新日期:2019-11-01
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