Consequences of progressive eclogitization on crustal exhumation, a mechanical study     

Hugues Raimbourg  Laurent Jolivet  Yves Leroy 《Geophysical Journal International》2007,168(1):379-401

  相似文献   

Do flexural stresses explain the mantle fault zone beneath Kilauea volcano?     

M. E. Pritchard  A. M. Rubin  C. J. Wolfe 《Geophysical Journal International》2007,168(1):419-430

  相似文献   

Shear wave birefringence in wedge-shaped anisotropic regions     

Vadim Levin  David Okaya  Jeffrey Park 《Geophysical Journal International》2007,168(1):275-286

  相似文献   

Two-dimensional modelling of subduction zone anisotropy with application to southwestern Japan     

Maureen D. Long  Bradford H. Hager  Maarten V. de Hoop  Rob D. van der Hilst 《Geophysical Journal International》2007,170(2):839-856

We present a series of 2-D numerical models of viscous flow in the mantle wedge induced by a subducting lithospheric plate. We use a kinematically defined slab geometry approximating the subduction of the Philippine Sea plate beneath Eurasia. Through finite element modelling we explore the effects of different rheological and thermal constraints (e.g. a low-viscosity region in the wedge corner, power law versus Newtonian rheology, the inclusion of thermal buoyancy forces and a temperature-dependent viscosity law) on the velocity and finite strain field in the mantle wedge. From the numerical flow models we construct models of anisotropy in the wedge by calculating the evolution of the finite strain ellipse and combining its geometry with appropriate elastic constants for effective transversely isotropic mantle material. We then predict shear wave splitting for stations located above the model domain using expressions derived from anisotropic perturbation theory, and compare the predictions to ∼500 previously published shear wave splitting measurements from seventeen stations of the broad-band F-net array located in southwestern Japan. Although the use of different model parameters can have a substantial effect on the character of the finite strain field, the effect on the average predicted splitting parameters is small. However, the variations with backazimuth and ray parameter of individual splitting intensity measurements at a given station for different models are often different, and rigorous analysis of details in the splitting patterns allows us to discriminate among different rheological models for flow in the mantle wedge. The splitting observed in southwestern Japan agrees well with the predictions of trench-perpendicular flow in the mantle wedge along with B-type olivine fabric dominating in a region from the wedge corner to about 125 km from the trench.  相似文献   

Geometry and brittle deformation of the subducting Nazca Plate, Central Chile and Argentina     

Megan Anderson  Patricia Alvarado †  George Zandt  Susan Beck 《Geophysical Journal International》2007,171(1):419-434

We use data from the Chile Argentina Geophysical Experiment (CHARGE) broad-band seismic deployment to refine past observations of the geometry and deformation within the subducting slab in the South American subduction zone between 30°S and 36°S. This region contains a zone of flat slab subduction where the subducting Nazca Plate flattens at a depth of ∼100 km and extends ∼300 km eastward before continuing its descent into the mantle. We use a grid-search multiple-event earthquake relocation technique to relocate 1098 events within the subducting slab and generate contours of the Wadati-Benioff zone. These contours reflect slab geometries from previous studies of intermediate-depth seismicity in this region with some small but important deviations. Our hypocentres indicate that the shallowest portion of the flat slab is associated with the inferred location of the subducting Juan Fernández Ridge at 31°S and that the slab deepens both to the south and the north of this region. We have also determined first motion focal mechanisms for ∼180 of the slab earthquakes. The subhorizontal T -axis solutions for these events are almost entirely consistent with a slab pull interpretation, especially when compared to our newly inferred slab geometry. Deviations of T -axes from the direction of slab dip may be explained with a gap within the subducting slab below 150 km in the vicinity of the transition from flat to normal subducting geometry around 33°S.  相似文献   

Numerical comparison of different convergent plate contacts: subduction channel and subduction fault   总被引：2，自引：0，他引：2  

Roberta De Franco  Rob Govers  Rinus Wortel 《Geophysical Journal International》2007,171(1):435-450

At convergent plate boundaries, the properties of the actual plate contact are important for the overall dynamics. Convergent plate boundaries both mechanically decouple and link tectonic plates and accommodate large amounts of strain. We investigate two fundamental physical states of the subduction contact: one based on a fault and the other based on a subduction channel. Using a finite element method, we determine the specific signatures of both states of the subduction contact. We pay particular attention to the overriding plate. In a tectonic setting of converging plates, where the subducting plate is freely moving, the subduction channel reduces compression relative to the fault model. In a land-locked basin setting, where the relative motion between the far field of the plates is zero, the subduction channel model produces tensile stress regime in the overriding plate, even though the amount of slab roll-back is small. The fault model shows a stronger development of slab roll-back and a compressive stress regime in the upper plate. Based on a consistent comparison of fault and channel numerical models, we find that the nature of the plate contact is one of the controlling factors in developing or not of backarc extension. We conclude that, the type of plate contact plays a decisive role in controlling the backarc state of stress. To obtain backarc extension, roll-back is required as an underling geodynamic process, but it is not always a sufficient condition.  相似文献   

A Characteristic Analysis of the Dynamic Evolution of Preseismic- Coseismic-Postseismic Interferometric Deformation Fields Associated with the M 7.9 Earthquake of Mani, Tibet in 1997   总被引：1，自引：0，他引：1       下载免费PDF全文

SHAN Xinjian ZHANG Guohong 《《地质学报》英文版》2007,81(4):587-592

By using the D-InSAR technique,we have acquired the temporal-spatial evolution images of preseismic-cosesimci-postseismic interferometric deformation fields associated with the M 7.9 earthquake of Mani,Tibet on 8 November 1997.The analysis of these images reveals the relationships between the temporal-spatial evolution features of the interferometric deformation fields and locking, rupturing,and elastic restoring of the source rupture plane,which represent the processes of strain accumulation,strain release,and postseismic restoration.The result shows that 10 months prior to the Mani event,a left-lateral shear trend appeared in the seismic area,which was in accordance with the earthquake fault in nature.The quantity of local deformation on the north wall was slightly larger than that on the south wall,and the deformation distribution area of the north wall was relatively large.With the event impending,the deformation of the south wall varied increasingly,and the deformation center shifted eastward.Two and half monthd before the event,the west side of the fault was still locked while the east side began to slide,implying that the whole fault would rupture at any moment.These features can be regarded as short-term precursors to this earthquake.Within the period from 16 April 1996 to two and half months before the earthquake,the most remarkable deformation zones appeared in the north and south walls,which were parallel to and about 40 km apart from the fault,with accumulated local displacements of 344 mm and 251 mm on the north and south walls,respectively.The south wall was the active one with larger displacements.Five months after the earthquake,the distribution feature of interferometric fringes was just opposite to that prior to the event,expressing evident right-lateral shear.The recovered displacements are～179 mm on the north wall and～79 mm on the south wall,close to the east side of the fault.However,in the area of the south wall far from the fault there still existed a trend of sinistral motion.The deformation of the north wall was small but recovered fast in a larger area,while the active south wall began to recover from the east section of the fault toward the WSW.  相似文献   

洋壳深俯冲超高压变质作用研究及其地质意义   总被引：1，自引：0，他引：1  

张立飞 《地质通报》2007,26(9):1079-1085

洋壳深俯冲经历超高压变质作用的岩石比较稀少,是目前超高压变质作用研究的重要前沿领域,有关这方面的研究对于建立新的冷俯冲带变质作用类型、探讨地幔水流体的成因、建立更广泛的超高压变质岩石的抬升机制具有重要意义。另外,洋壳深俯冲高压变质带往往与低压高温变质带组成双变质带,对双变质带的深入研究对于完整地重塑俯冲碰撞造山带的形成演化过程具有重要意义。简要地介绍了新疆西天山洋壳深俯冲超高压变质带的研究现状和存在的问题。  相似文献   

Attenuation studies based on local earthquake Coda waves in the southern Indian peninsular shield     

C. H. Patanjali Kumar  C. S. P. Sarma  M. Shekar  R. K. Chadha 《Natural Hazards》2007,40(3):527-536

The Dharwar craton, Cuddapah basin and the Godavari graben characterise three diverse geological and tectonic settings in the peninsular shield of India. Owing to their contiguous proximity, they offer a unique opportunity to document differences, if any, in their seismic wave attenuation characteristics that might have a bearing on the seismogenic nature of the crust in a craton, basin and a rift-like graben structure. An attempt is made here to bring out these differences using constraints from coda-Q. We considered local earthquakes with epicentral distances ranging from␣14 to 150 km recorded at the digital broadband stations at Dharwar (DHD), Cuddapah (CUD) and Kothagudem (KGD) regions to derive the frequency-dependent coda-Q relations. Using the single scattering method, we obtained the frequency-dependent Q _C relationship (Q _C = Q ₀ f ⁿ )for each of the three geological units separately: DHD: Q _C = (730.62 ± 0.09)f ^{(0.54 ± 0.01)}; CUD: Q _C = (535.06 ± 0.13)f ^{(0.59 ± 0.01)} and KGD: Q _C = (150.56 ± 0.08)f ^{(0.91 ± 0.01)}. The Q _C values obtained for all the three sub-regions show moderate to strong frequency dependence and essentially reflect the level of crustal heterogeneities to varying degrees.  相似文献   

Temporal Geochemical Evolution of Neogene Magmatism in the Baguio Gold–Copper Mining District (Northern Luzon, Philippines)     

Mireille Polve    Rene C. Maury    Sebastien Jego    Herve Bellon    Ahmed Margoum    Graciano P. Yumul  Jr  Betchaida D. Payot    Rodolfo A. Tamayo  Jr Joseph Cotten 《Resource Geology》2007,57(2):197-218

Baguio, in the Central Cordillera of Northern Luzon, is a district that displays porphyry copper and epithermal gold mineralization, associated with Early Miocene–Pliocene–Quaternary calc‐alkaline and adakitic intrusions. Systematic sampling, K‐Ar dating, major and trace elements, and Sr, Nd, Pb isotopic analyses of fresh magmatic rocks indicate three magmatic pulses: an Early Miocene phase (21.2–18.7 Ma), a Middle–Late Miocene phase (15.3–8 Ma) and finally a Pliocene–Quaternary event (3–1 Ma). The first phase emplaced evolved calc‐alkaline magmas, essentially within the Agno Batholith complex, and is thought to be related to the westward‐dipping subduction of the West Philippine Basin. After a quiescence period during which the Kennon limestone was deposited, magmatic activity resumed at 15.3 Ma, in connection with the start of the subduction of the South China Sea along the Manila Trench. It emplaced first petrogenetically related and relatively unradiogenic low‐K calc‐alkaline lavas and intermediate adakites. Temporal geochemical patterns observed from 15.3 to 1 Ma include progressive enrichment in K and other large ion lithophile elements, increase in radiogenic Sr and Pb and corresponding decrease in radiogenic Nd. These features are thought to reflect the progressive addition to the Luzon arc mantle wedge of incompatible elements largely inherited from South China Sea sediments. The origin of the long quiescence period, from 8 to 3 Ma, remains problematic. It might represent a local consequence of the docking of the Zambales ophiolitic terrane to Northern Luzon. Then, magmatic activity resumed at 3 Ma, emplacing chemically diversified rocks ranging from low K to high K and including a large proportion of adakites, especially during the Quaternary (dacitic plugs). The authors tentatively relate this diversity to the development of a slab tear linked with the subduction of the fossil South China Sea ridge beneath the Baguio area.  相似文献