摘要:

A model for the origin of the outer rise is proposed which does not require multi‐kilobar deviatoric stresses in the lithosphere. The model includes stresses developed by viscous flow of the lower part of the lithosphere as it is subducted. Besides the outer rise, features similar to an oceanic trench and island arc develop in the model. The elastic upper part of the lithosphere, treated approximately, is subject to extensional stresses on the seaward side of the trench axis. The observed topography of an oceanic trench and outer rise can be produced by a 90 km thick lithosphere subducting at 60 mm/yr if the average viscosity of the lower lithosphere is about 1023pois

ISSN:0094-8276    

DOI:10.1029/GL005i005p00321

年代:1978

数据来源: WILEY

摘要:

It is observed that active inter‐arc basins are found only where the subducted plate can interact with the plate behind the trench. This condition exists where trenches are terminated or offset by transform faults or where large variations in subduction rates occur. Shear coupling between the two juxtaposed plates across a transform or strike‐slip fault creates a tensional regime behind the island arc. Differential subduction velocities will couple the plate motions across both the more slowly subducting trench and across the intervening fracture zone. If the trench axis is assumed to move more slowly than a plate, inter‐arc basin spreading may be initiated to conserve

ISSN:0094-8276    

DOI:10.1029/GL005i005p00325

年代:1978

数据来源: WILEY

摘要:

We report data on the curvature RC, rate of subduction vcand slab dip α for 28 convergent boundary segments of oceanic plates. Slowly converging plates (vc<5 cm/yr) are associated with arcs having RC<10°, while more rapidly converging plates produce arcs with RC ranging from 10° to greater than 90°. This provides a way of estimating former convergence rates of extinct arcs. Slab dip α is independent of vcfor vc<10 cm/yr; the inverse relation between α and vcproposed byLuyendyk(1970) is not substantiated by our larger data set. Slab dip and arc curvature are not corre

ISSN:0094-8276    

DOI:10.1029/GL005i005p00329

年代:1978

数据来源: WILEY

摘要:

The major problem in scale modeling of crustal tectonic processes, namely, the requirement for a brittle modeling material of extremely low strength (∼0.1 bar) can be overcome by doing model tests under artificial gravity in a centrifuge. When conditions of dynamic similarity are observed, scale modeling, because of its controlled nature, can be an important tool supplementing field investigation, theoretical study, and numerical simulation of crustal tectonic processes. Fracture events by simulated tectonic stress loading in a model thrust fault (model dimensions: 20 cm depth × 25 cm × 27 cm) have been generated when the model is subject to 50 g in a centrifuge of 1.53 m radius. Measurements obtained are: the total loading force, the stress change at one location inside the fault zone, and model seismic signals recorded on the model top surface. With use of a scaled brittle model material, the model scales up to a prototype approximately 2.2 km depth × 2.8 km × 3.0 km in dimen

ISSN:0094-8276    

DOI:10.1029/GL005i005p00333

年代:1978

数据来源: WILEY

摘要:

Experimental work on nickel indicates the existence of a stress below which dynamic recrystallization does not occur. The limiting condition for dynamic recrystallization is that the recrystallized grain size must exceed the minimum size for the stability of a nucleus. Applying this condition to olivine indicates that the maximum possible dynamically recrystallized grain size probably exceeds the grain sizes commonly observed in mantle xenoliths.

ISSN:0094-8276    

DOI:10.1029/GL005i005p00337

年代:1978

数据来源: WILEY

摘要:

We have demonstrated that a seismic solution to a set of ocean crustal P and S wave data from the Guadalupe Island area is consistent with measured P and S velocity samples from the Bay of Islands Ophiolite Suite and the observed stratigraphy. The seismic model (SOD‐1), derived separately for the P and S wave propagation, contains no major interfaces in velocity between the sea floor and the upper mantle. Although the observations do not prove the Bay of Islands Ophiolite Suite is obducted oceanic crust they do lend considerable support to this hypothesis. These observations also demonstrate that a layered sequence of rock types is not incompatible with velocity models in which the velocity changes smoothly rather than abruptly with depth. A new method for determining lithology as a function of depth, which is based on Vpand Vs, is presente

ISSN:0094-8276    

DOI:10.1029/GL005i005p00341

年代:1978

数据来源: WILEY

摘要:

The electrical conductivity of 7 dunites (Addie, Åheim, Balsam Gap, Corundum Hill, Dun Mountain, Mooihoek and Twin Sisters) in the pressure range 12.5 ‐ 45 GPa has been studied using the shock wave technique. In this pressure range the measured conductivity varies from 2.8·10−5to 2.6·10−2Ω−1cm−1. Differences in the total olivine content, Fe‐content of the olivines, Fe2O3−and chromite content and grain sizes of the dunites lead to differences in their conductivity. All dunites show an increase of about 105Ω−1cm−1of the electrical conductivity in the pressure range 0 ‐ 40 GPa, thus approaching semiconductor behavior. This increase is due to both temperature and pressure effects and possibly also to a partial pha

ISSN:0094-8276    

DOI:10.1029/GL005i005p00345

年代:1978

数据来源: WILEY

摘要:

As the CO2produced by the combustion of fossil fuels reaches the deep sea it will attack the calcite stored in abyssal sediments. This reaction will significantly augment the ocean's capacity for this combustion product. Hence it is of interest to define the kinetics of this dissolution process. One aspect, the role of bioturbation, is dealt with in this paper. We show that the bioturbation rates obtained from the core top210Pb and14C distributions are sufficiently rapid so that the turbated zone can be treated as well mixed in dissolution models. No significant buildup of the non‐calcite residue will occur in the upper few millimeters of sediment where dissolution takes place. Rather it will be "stirred" into the mixed layer with sufficient rapidity that its influence will not become significant until the mixed layer as a whole drops in calcite conten

ISSN:0094-8276    

DOI:10.1029/GL005i005p00349

年代:1978

数据来源: WILEY

摘要:

We conducted an intercalibration program among eleven laboratories making measurements of N2O in the atmosphere in December 1976. The laboratories responding to the intercalibration effort included five in the United States, one in Canada, two in Great Britain, and two in West Germany. The laboratories were in good agreement on the atmospheric concentration of nitrous oxide, with one exception. Excluding the one result which showed an anomalously low value, the other ten laboratories show a mean concentration of 323.5 ± 8.7 ppb v/v N2O for the Northern Hemisphere tropospheric background level for mid‐1976. These results are in agreement with most recent atmospheric measurements of N2O, although some groups have reported values approximately 10% lower. However, the preponderance of recent evidence suggests very strongly that the absolute concentration of nitrous oxide in the troposphere is between 315 and 330 ppb v

ISSN:0094-8276    

DOI:10.1029/GL005i005p00353

年代:1978

数据来源: WILEY

摘要:

Estimates are made for received power due to partial reflection and turbulence scattering of VHF radar echoes from the clear atmosphere. We show that, under rather general conditions, partial reflections from stratified layers in the atmosphere can contribute significantly to the received echo power and therefore should be taken into account in data interpretation. Possible experimental techniques to investigate the partial reflection are discussed. Some results from tropospheric observations will be presented indicating high echo power from thin layers having a long correlation time.

ISSN:0094-8276    

DOI:10.1029/GL005i005p00357

年代:1978

数据来源: WILEY