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Takaya Iwasaki - One of the best experts on this subject based on the ideXlab platform.
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Crustal structure of southwest japan revealed by the integrated seismic experiment southwest japan 2002
Tectonophysics, 2009Co-Authors: Tanio Ito, Yuji Kojima, Shuichi Kodaira, Hiroshi Sato, Yoshiyuki Kaneda, Takaya Iwasaki, Eiji Kurashimo, Noriko Tsumura, Akira Fujiwara, Takahiro MiyauchiAbstract:Abstract A multi-purpose seismic experiment named the 2002 integrated seismic experiment Southwest Japan was conducted in 2002 along a more-than-240-km-long line across southwest Japan from the Pacific coast to the Japan Sea coast. Its profile provides the first Crustal-scale cross section across the Japanese island arc, which highlights a number of significant points related to the structural development of the arc. Major outstanding points are that the Japanese island arc is composed of two completely different crusts juxtaposed by the Median Tectonic Line (MTL), and that the MTL started its activity associated with lower Crustal Thinning and formation of an upper Crustal-scale half-graben in Late Cretaceous.
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extensional structure in northern honshu arc as inferred from seismic refraction wide angle reflection profiling
Geophysical Research Letters, 2001Co-Authors: Takaya Iwasaki, Wataru Kato, Takeo Moriya, Akiko Hasemi, Norihito Umino, Tomomi Okada, Kaoru Miyashita, Tomoko Mizogami, Tetsuya Takeda, Shutaro SekineAbstract:A recent extensive seismic wide-angle experiment revealed a new image of Crustal and uppermantle structure across Northern Honshu Arc, Japan. The western part of the arc recorded the Crustal deformation by the Miocene back arc spreading of the Sea of Japan. The crust is composed of highly deformed Tertiary sedimentary layers, a relatively low velocity (5.75–5.9 km/s) crystalline basement and a 15-km thick lower crust with a velocity of 6.6–7.0 km/s. Clear westward Crustal Thinning from 32 to 27 km represents the extensional deformation by the backarc spreading. The crust attains the maximum thickness (32–35km) east of the backbone range for which the magmatic intrusion/underplating since 10–15 Ma is a predominant factor. The eastern part of the arc has a less deformed upper crust and a reflective middle/lower crust, probably remaining a stable block since the time of the backarc spreading.
Stefan Moeller - One of the best experts on this subject based on the ideXlab platform.
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Crustal Thinning in the northern tyrrhenian rift insights from multichannel and wide angle seismic data across the basin
Journal of Geophysical Research, 2014Co-Authors: Stefan Moeller, Ingo Grevemeyer, Cesar R Ranero, Christian Berndt, Dirk Klaeschen, Valenti Sallares, Nevio Zitellini, R De FrancoAbstract:Extension of the continental lithosphere leads to the formation of rift basins or rifted continental margins if breakup occurs. Seismic investigations have repeatedly shown that conjugate margins have asymmetric tectonic structures and different amount of extension and Crustal Thinning. Here we compare two coincident wide-angle and multichannel seismic profiles across the northern Tyrrhenian rift system sampling crust that underwent different stages of extension from north to south and from the flanks to the basin center. Tomographic inversion reveals that the crust has thinned homogeneously from ~24 km to ~17 km between the Corsica Margin and the Latium Margin implying a β factor of ~1.3–1.5. On the transect 80 km to the south, the crust thinned from ~24 km beneath Sardinia to a maximum of ~11 km in the eastern region near the Campania Margin (β factor of ~2.2). The increased Crustal Thinning is accompanied by a zone of reduced velocities in the upper crust that expands progressively toward the southeast. We interpret that the velocity reduction is related to rock fracturing caused by a higher degree of brittle faulting, as observed on multichannel seismic images. Locally, basalt flows are imaged intruding sediment in this zone, and heat flow values locally exceed 100 mW/m2. Velocities within the entire crust range 4.0–6.7 km/s, which are typical for continental rocks and indicate that significant rift-related magmatic underplating may not be present. The characteristics of the pre-tectonic, syn-tectonic and post-tectonic sedimentary units allow us to infer the spatial and temporal evolution of active rifting. In the western part of the southern transect, thick postrift sediments were deposited in half grabens that are bounded by large fault blocks. Fault spacing and block size diminish to the east as Crustal Thinning increases. Recent tectonic activity is expressed by faults cutting the seafloor in the east, near the mainland of Italy. The two transects show the evolution from the less extended rift in the north with a fairly symmetric conjugate structure to the asymmetric margins farther south. This structural evolution is consistent with W-E rift propagation and southward increasing extension rates.
Jordi Diaz - One of the best experts on this subject based on the ideXlab platform.
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deep reflection seismic images of the Crustal Thinning in the eastern pyrenees and western gulf of lion
Journal of Geodynamics, 2001Co-Authors: Alexandre Nercessian, A Mauffret, A Dos T Reis, R Vidal, J Gallart, Jordi DiazAbstract:Abstract The results of the MCS LISA seismic survey in the Mediterranean Sea and the wide angle data recorded by the onland stations during this experiment are merged and compared with the ray tracing modeling and the deep structure known from previous refraction studies. The results are very good, arriving at a new deep seismic image of the Crustal structure. The LISA seismic profile 26, shown is this publication, crosses in strike line a deep basin close to the eastern Pyrenees. The shallow part of the seismic profile is poorly imaged but, thanks to the very good ELF seismic profiles crossing the LISA survey, the acoustic basement and a decollement level can be drawn. The deep part of the LISA profile data has a much better quality than the shallow part and reveals a high velocity (7.1 km/s) lower crust, overlying a shallow Moho interpreted at 8 s TWTT. The wide angle reflections enable the comparison between the ray tracing measured by distance and the seismic image measured by time thereby making the relationship between the continent and the continental shelf clearly delineated for the first time. The Thinning of the thickened crust of the eastern Pyrenees does not occur at the shore but inland at the western boundary of the Roussillon basin. However, the central part of the Gulf of Lion continental shelf forms a deep basin that overlies a thinned crust. The age of the Thinning is discussed in the general context of the convergence and divergence of the European and Iberian plates including the Sardinia-Corsica block. The geometry of the transfer faults is studied and shown as not steep and to have normal and strike-slip components.
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Crustal Thinning in the southwestern iberia margin
Geophysical Research Letters, 1996Co-Authors: Antonio Fernandez Gonzalez, Montserrat Torne, Diego Cordoba, Neus Vidal, Luis Matias, Jordi DiazAbstract:The mode of Crustal Thinning in the southwestern margin of the Iberian Peninsula is investigated along a transect that extends from onshore Iberia to the eastern end of the Horseshoe Abyssal Plain. On onshore areas, the Crustal structure has been deduced using wide-angle seismic reflection data, whereas offshore we have used coincident steep and wide-angle reflection data along a NE-SW oriented seismic profile that extends from Cape San Vicente to the Horseshoe Abyssal Plain. In addition, 2D gravity modelling has been performed to validate the Crustal structure deduced from seismic data. Our model results reveal that the crust undergoes a strong but continuous Thinning from 31 km onshore Iberia to less than 15 km in the Horseshoe Abyssal Plain and that Thinning occurs over horizontal distances of about 120 km.
Gianreto Manatschal - One of the best experts on this subject based on the ideXlab platform.
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how does the continental crust thin in a hyperextended rifted margin insights from the iberia margin
Geology, 2012Co-Authors: Emilie Sutra, Gianreto ManatschalAbstract:The discovery of hyperthinned continental crust and exhumed mantle on present-day deep-water rifted margins leads to two fundamental questions: (1) in detail, how does the crust thin in extension, and (2) what controls extreme Crustal Thinning and mantle exhumation? Reflection and refraction seismic lines across the Iberian margin show decoupling levels in the crust cut by structures that eventually transfer deformation to mantle levels. The region of decoupled extension appears to be more broadly distributed on the northern Iberian margin and more localized on the southern margin. Based on drill hole data, the transition from decoupled to coupled deformation occurred during Tithonian time (ca. 145 Ma). This evolution from decoupled to coupled deformation may help explain the Crustal architecture of the Iberian margin. An apparent delay of subsidence across the hyperextended coupled zone of the Iberian margin may indicate that Crustal Thinning had to occur simultaneously with lithospheric necking and the advection of heat related to lithospheric mantle Thinning.
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extreme Crustal Thinning in the bay of biscay and the western pyrenees from observations to modeling
Geochemistry Geophysics Geosystems, 2010Co-Authors: Suzon Jammes, L L Lavier, Gianreto ManatschalAbstract:Recent observations and models of continental rifting in magma-poor environments have led to the concept of multiphase stages of lithospheric extension. In these concepts it is shown that extreme Crustal Thinning of the crust predates exhumation of lower Crustal and subcontinental mantle rocks during final rifting. The Bay of Biscay is a V-shaped ocean basin that opened in Aptian-Albian time. In front of this propagating ocean, several rift basins formed that show evidence for extreme Crustal Thinning and locally also mantle exhumation (the Parentis, Arzacq-Mauleon, and Cantabrian basins). In this paper we propose, based on geological and geophysical observations and using numerical modeling, a model that can explain the extreme Crustal Thinning observed in the Arzacq-Mauleon and Parentis basins. Our results show that rifting in the Bay of Biscay was initiated by distributed oblique stretching (latest Jurassic to Early Aptian) before it underwent an more orthogonal asymmetric Thinning and exhumation phase from Late Aptian to Albian time. These last two stages of deformation are similar to those observed in orthogonal rift systems. We show that Thinning is accomplished by the formation of a semibrittle shear zone that allows for the transfer of middle to lower Crustal material from the side of the rift collocated with the hanging wall to the side of the rift collocated with the footwall of the detachment system. The main difference with an orthogonal rift system appears to be generated by the formation of flower structures during the distributed oblique phase and the capacity of localizing the deformation in the subsequent stages. These oblique slip faults form very steep normal faults that induce the development of strongly localized, compartmentalized, and asymmetric rift basins. In the case of the Parentis and Arzacq-Mauleon basins, these strike-slip faults separate upper plate sag basins to the north from lower plate sag basins to the south. While the northern sag basins do not show any evidence for exhumation, the southern ones are more complex and floored by detachment faults, as indicated by the occurrence of syntectonic and posttectonic sediments onlapping directly onto exhumed lower Crustal and mantle rocks.
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tectonosedimentary evolution related to extreme Crustal Thinning ahead of a propagating ocean example of the western pyrenees
Tectonics, 2009Co-Authors: Suzon Jammes, Luc L Lavier, Gianreto Manatschal, Emmanuel MasiniAbstract:[1] In this paper we describe the tectonosedimentary evolution and its subsequent inversion of a basin that underwent extreme Crustal Thinning in a transtensional setting ahead of a propagating ocean in the western Pyrenees. The Labourd-Mauleon area situated in the western Pyrenees, at the termination of the V-shaped Bay of Biscay, is an ideal natural laboratory to study how such complex basins evolve in time and space. Because of a mild inversion of the basin during Pyrenean compression, the rift structures and their relations to basement rocks and sediments are exposed and can be directly studied in the field. The basin shows a complex polyphase evolution that starts with left-lateral dominated transtension in latest Jurassic–early Aptian time. This event is overprinted by a late Aptian–early Albian extension that is related to the counterclockwise rotation of Iberia away from Europe leading to the opening of the Bay of Biscay. During this stage, the Late Triassic to Jurassic carbonate platform was stretched, salt migrated, and detachment faults exhumed upper and lower Crustal and mantle rocks to the seafloor. The final structure of the basin resembles a sag basin floored by exhumed rocks overlain by extensional allochthons and compartmentalized by N40° to N60° transfer faults. The sedimentary architecture is characterized by late Aptian synrift sediments (e.g., Urgonian limestones) that were deposited in fault-bounded basins and are overlain by thick latest Aptian to Albo-Cenomanian sediments (e.g., Flysch noir) that define a sag sequence. The complex tectonosedimentary evolution of the basin is associated with salt tectonics and overprinted by a major magmatic/thermal event that postdates mantle exhumation.
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evidence for extreme Crustal Thinning and mantle exhumation in the western pyrenees bay of biscay
EGU General Assembly Conference Abstracts, 2009Co-Authors: Suzon Jammes, Gianreto Manatschal, L L LavierAbstract:The Bay of Biscay represents a V-shaped oceanic basin that opened in Aptian-Albian time within a transtensional setting. During the opening of the Bay of Biscay, several rift basins (e.g. Parentis, Mauleon, Cantabrian basins) formed in front of this propagating ocean. During the subsequent Pyrenean compression in Late Cretaceous to Oligocene time, the basins to the south (e.g. Mauleon and Cantabrian) were strongly reactivated while to the north (e.g. Parentis) the reactivation was minor. Our investigations in two of these basins, the offshore Parentis basin and the onshore Mauleon basin, show evidence for extreme Crustal Thinning and local exhumation of lower Crustal or mantle rocks associated with the formation of these basins.
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a mechanism to thin the continental lithosphere at magma poor margins
Nature, 2006Co-Authors: Luc L Lavier, Gianreto ManatschalAbstract:Crustal Thinning where continental plates break apart can be accomplished by a system of conjugate concave downward faults, instead of multiple normal faults, through exhumation of mid-Crustal and mantle material. Where continental plates break apart, slip along multiple normal faults provides the required space for the Earth's crust to thin and subside1. After initial rifting, however, the displacement on normal faults observed at the sea floor seems not to match the inferred extension2. Here we show that Crustal Thinning can be accomplished in such extensional environments by a system of conjugate concave downward faults instead of multiple normal faults. Our model predicts that these concave faults accumulate large amounts of extension and form a very thin crust (< 10 km) by exhumation of mid-Crustal and mantle material. This transitional crust is capped by sub-horizontal detachment surfaces over distances exceeding 100 km with little visible deformation. Our rift model is based on numerical experiments constrained by geological and geophysical observations from the Alpine Tethys and Iberia/Newfoundland margins3,4,5,6,7,8,9. Furthermore, we suggest that the observed transition from broadly distributed and symmetric extension to localized and asymmetric rifting is directly controlled by the existence of a strong gabbroic lower crust. The presence of such lower Crustal gabbros is well constrained for the Alpine Tethys system4,9. Initial decoupling of upper Crustal deformation from lower Crustal and mantle deformation by progressive weakening of the middle crust is an essential requirement to reproduce the observed rift evolution. This is achieved in our models by the formation of weak ductile shear zones.
J Gallart - One of the best experts on this subject based on the ideXlab platform.
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deep reflection seismic images of the Crustal Thinning in the eastern pyrenees and western gulf of lion
Journal of Geodynamics, 2001Co-Authors: Alexandre Nercessian, A Mauffret, A Dos T Reis, R Vidal, J Gallart, Jordi DiazAbstract:Abstract The results of the MCS LISA seismic survey in the Mediterranean Sea and the wide angle data recorded by the onland stations during this experiment are merged and compared with the ray tracing modeling and the deep structure known from previous refraction studies. The results are very good, arriving at a new deep seismic image of the Crustal structure. The LISA seismic profile 26, shown is this publication, crosses in strike line a deep basin close to the eastern Pyrenees. The shallow part of the seismic profile is poorly imaged but, thanks to the very good ELF seismic profiles crossing the LISA survey, the acoustic basement and a decollement level can be drawn. The deep part of the LISA profile data has a much better quality than the shallow part and reveals a high velocity (7.1 km/s) lower crust, overlying a shallow Moho interpreted at 8 s TWTT. The wide angle reflections enable the comparison between the ray tracing measured by distance and the seismic image measured by time thereby making the relationship between the continent and the continental shelf clearly delineated for the first time. The Thinning of the thickened crust of the eastern Pyrenees does not occur at the shore but inland at the western boundary of the Roussillon basin. However, the central part of the Gulf of Lion continental shelf forms a deep basin that overlies a thinned crust. The age of the Thinning is discussed in the general context of the convergence and divergence of the European and Iberian plates including the Sardinia-Corsica block. The geometry of the transfer faults is studied and shown as not steep and to have normal and strike-slip components.
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multichannel seismic image of the Crustal Thinning at the ne iberian margin combining normal and wide angle reflection data
Geophysical Research Letters, 1995Co-Authors: J Gallart, N Vidal, Juanjo DanobeitiaAbstract:The seismic image of the Moho at the transition from the NE Iberian Peninsula to the Western Mediterranean Sea is investigated using coincident steep and wide-angle reflection data merged into a single stacked and migrated section. The multichannel analysis of onshore/offshore large-aperture data provides new insight on the deep structure in areas where the steep sections lack penetration, and reveals that the crust undergoes a strong but continuous Thinning along the flanks of the Valencia trough. The combined seismic image indicates that almost half of the continental crust (14–15 km) is lost in less than 60 km horizontal distance.