Pseudotachylytes generated in granulite facies rocks are found in the Woodroffe thrust, central Australia. Petrologic evidence
and structural and textural features show that these pseudotachylytes contain typical melting-origin features including injection
occurrence, rounded and embayed clasts, and microlites within the fine-grained matrix, which formed contemporaneously with
the wall granulite facies rocks under conditions of ~8 kbar and ~650–700°C. These granulite-related pseudotachylyte (G-Pt)
veins are overprinted in subsequent deformation stages by three other types of pseudotachylytes including mylonite-related
(M-Pt) and ultramylonite-related (Um-Pt) pseudotachylytes that are then transcut by cataclasite-related pseudotachylytes (C-Pt).
The overprinting occurred following uplift of the lower crust where the G-Pt veins formed through the brittle-plastic transition
zone where the M-Pt and Um-Pt veins occurred within the brittle-dominated regime of the C-Pt generation zone in the upper
crust. The coexistence of multiple generations of large voluminous C-Pt, M-Pt, Um-Pt, and G-Pt veins indicates that numerous
large earthquakes accompanying distinct seismic slip which produced the pseudotachylytes occurred over an extended period
of seismicity and various depths of the crust within the Woodroffe thrust zone. The spatial distribution and structural features
of the multiple-stage pseudotachylytes suggest that coseismic slipping caused by large earthquakes which nucleated in the
brittle-dominated seismogenic zone propagated downward through the brittle-plastic transition zone into the plastic-dominated
granulite facies depth from the upper to lower crust. 相似文献
We have developed a generic dynamic model of extension of the lithosphere, which predicts major element composition and volume of melt generated from initial extension to steady state seafloor spreading. Stokes equations for non-Newtonian flow are solved and the mantle melts by decompression. Strengthening of the mantle due to dehydration as melting progresses is included. The composition is then empirically related to depletion. Using a crystallisation algorithm, the predicted primary melt composition was compared with mean North Atlantic mid-ocean ridge basalt (MORB). At steady state, using half spreading rates from 10 to 20 mm yr− 1 and mantle potential temperatures of 1300 to 1325 °C we predict a major element composition that is within the variation in the mean of North Atlantic MORB.
This model is applied to the Southeast Greenland margin, which has extensive coverage of seismic and ODP core data. These data have been interpreted to indicate an initial pulse of magmatism on rifting that rapidly decayed to leave oceanic crustal thickness of 8 to 11 km. This pattern of melt production can be recreated by introducing an initial hot layer of asthenosphere beneath the continental lithosphere and by having a period of fast spreading during early opening. The hot layer was convected through the melt region giving a pulse of high magnesian and low silica melt during the early rifting process. The predicted major element composition of primary melts generated are in close agreement with primary melts from the Southeast Greenland margin. The observed variations in major element composition are reproduced without a mantle source composition anomaly. 相似文献
The processes underlying the development of the Kuroshio large meanders that occurred in 1986 and 1989 are investigated using
a satellite SST data set and hydrographic data. In both processes visible on the satellite SST images, a round-shaped, lower
SST region with a diameter of about 200 km is found to the east of the Kuroshio small “trigger” meander (Solomon, 1978) until
the region became extinguished near theEnshu Nada. The lower SST region can be interpreted as an anti cyclonic eddy, mainly because of the existence of a warm water mass in
the subsurface layer of this region. The warm water mass is characterized by a constant temperature of 18–19°C, the maximum
thickness of which is about 400 m. The satellite images show that the eddy is closely related to the Kuroshio path transforming
into a shape like the letter “S”. This means that the eddy plays an important role in the development of the Kuroshio large
meander since this, too, tends to follow an “S”-shaped path. Added to this, the subsurface layer structure of the eddy is
similar to that of the warm water mass offShikoku. This similarity, together with the eddy behavior visible on the satellite SST images, implies that the examined eddy corresponds
to the warm water mass offShikoku. In other words, the warm water mass offShikoku can be advected near to theEnshu Nada when the Kuroshio large meander occurs. 相似文献
A three-step finite element method(FEM)together with Large Eddy Simulation(LES)is ap-plied to incompressible turbulent flow around seabed pipelines at relatively high Reynolds numbers.Bothtwo-dimensional and three-dimensional numerical simulation is carried out to determine thethree-dimensional effect.The results of numerical simulation agree quite well with the wave forces actingon pipeline models measured in physical model test. 相似文献