ISSN:0278-7407    

DOI:10.1029/TC001i001p00001

年代:1982

数据来源: WILEY

摘要:

The evolution of West (Lesser) Antarctica and its relation to East (Greater) Antarctica have major implications for global plate interactions, paleoclimate, and paleobiogeography, as well as Gondwanaland reconstruction. Analyses of marine geophysical data still lead to seemingly unacceptable overlap between the Antarctic Peninsula and the South American continent or else to geologically questionable relationships. A review of the relevant geological and geophysical data indicates that the problem lies in microplate movement and crustal thinning within West Antarctica during Gondwanaland breakup in the late Mesozoic and Cenozoic. The available data allow a range of possible reconstructions with West Antarctica subdivided into several discrete or semidiscrete microplates. Final solution of this problem requires additional geological and, particularly, geophysical data from West Antarctica as a whole, and the Weddell Sea‐Ross Sea embayment in particular. Meantime, it seems inadvisable to use the present continental outline of Antarctica on the Pacific side of the Transantarctic Mountains in reconstructing Gondwanalan

ISSN:0278-7407    

DOI:10.1029/TC001i001p00003

年代:1982

数据来源: WILEY

摘要:

The purpose of this paper is to clarify the dynamic role of lithospheric density heterogeneities, in particular with respect to mountain building and other processes of intraplate deformation. Density anomalies within or just beneath the lithosphere constitute major sources for tectonic stress fields: the product of their magnitude by their depth is shown to characterize their ability to induce deformation. This rule of the density moment directly yields the lithospheric thickening or thinning rate when applied to structures of large lateral extent. For anomalies of lateral extent that is small in comparison with their depth, the deformation is vertically inhomogeneous and has been computed with the help of simple physical models of a stratified viscous Newtonian lithosphere. The analytical treatment is based on Fourier transform. Continent‐continent collision thickens not only the crust but the entire lithosphere. The cold root underlying a mountain chain induces strong regional compressive stresses able to sustain the mountain bulding process without further help from forces transmitted from far away. Thus the continental lithosphere is in a somewhat metastable mechanical state. Adiabatic, i.e. rapid, thickening (or thinning) tends to grow further once initiated. Tectonic phases of strong compression correspond to the climax of such instabilities. The response of models with cold lithospheric roots of various intensities has been computed both in two and three dimensions. They yield velocity distributions and stress fields. Instructive comparisons are made with earthquake focal mechanisms and in situ stress measurements in the Alpine and Appalachian regions. In the presence of lateral variations of the mechanical properties of the lithosphere, the tectonic style is not only function of the local topography and of the nature of its compensation. Deformations in neighbouring provinces are coupled as shown by 3‐dimensional models. For example, thickening sustained by a cold lithospheric root may generate extension in peripheral zones of weakness. These last results illustrate the point that the computation of regional tectonic stresses requires the knowledge of the density anomalies within the lithosphere on the one hand, and of geometrical constraints related to lateral mechanical heterogeneities on the ot

ISSN:0278-7407    

DOI:10.1029/TC001i001p00021

年代:1982

数据来源: WILEY

摘要:

Strain distribution across the high‐pressure‐type Sambagawa regional metamorphic belt was measured by studies of shape change of initially spherical radiolaria. Strains change from 5 to 2000% with increasing metamorphic temperatures. Aburpt strain increase apparently occurs in the intermediate metamorphic grades of the terrane. Deformation stresses during metamorphism were inferred using the grain‐sized quartz piezometer method, which is applicable to dynamically recrystallized quartzose rocks. Stress distribution across the terrane was composed of two levels; the stress level in the lower‐grade zones was about 130 MPa but in the higher‐grade zones was about 50 MPa. Combining stress distribution, strain distribution, and temperatures of the studied metamorphic terrane, the activation energy of the deformation of these quartzose rocks is estimated to have been about 80–90 kJ/mol. The huge amount of deformation of the deep‐seated Sambagawa metamorphic terrane, which was formed probably at the lower crustal to uppermost mantle levels over the subducting lithosphere, was sufficient to bring about the uplift of parts of the terrane to the ea

ISSN:0278-7407    

DOI:10.1029/TC001i001p00057

年代:1982

数据来源: WILEY

摘要:

Based on published results of experiments on low‐temperature, low‐pressure frictional sliding and creep at higher temperature and pressure, theoretical curves of yield strength versus depth corresponding to maximum crustal stresses (STRESSMAX) are calculated. These curves are compared to the frequency‐depth distribution of earthquakes (DEFREQ) in several tectonic areas. Both sets of curves have a very similar form and show a prominent peak. From the similarity it is concluded that it is basically the temperature and the water content of the entire crust, not the properties of a particular layer, which determine the shape of maxima of the DEFREQ curves. The peaks of DEFREQ curves are generally at 5‐ to l0‐km depth and agree with STRESSMAX peaks of wet upper crust only. At this depth range the high stresses provide an increased ‘cracking potential’, resulting in an increased number and an increased stress drop of earthquakes. More and stronger barriers/asperities seem to exist at these depths, causing large earthquakes to nucleate in this high‐strength region. The stresses required to overcome the strength maximum are built up from below by ductile creep. The lower crust is considered to be a stress and viscosity minimum; in orogenic zones, strong interaction with plumes from the mantle may take place, and lateral movemen

ISSN:0278-7407    

DOI:10.1029/TC001i001p00073

年代:1982

数据来源: WILEY

摘要:

Pull‐apart basins or rhomb grabens and horsts along major strike‐slip fault systems in the world are generally associated with horizontal slip along faults. A simple model suggests that the width of the rhombs is controlled by the initial fault geometry, whereas the length increases with increasing fault displacement. We have tested this model by analyzing the shapes of 70 well‐defined rhomb‐like pull‐apart basins and pressure ridges, ranging from tens of meters to tens of kilometers in length, associated with several major strike‐slip faults in the western United States, Israel, Turkey, Iran, Guatemala, Venezuela, and New Zealand. In conflict with the model, we find that the length to width ratio of these basins is a constant value of approximately 3; these basins become wider as they grow longer with increasing fault offset. Two possible mechanisms responsible for the increase in width are suggested: (1) coalescence of neighboring rhomb grabens as each graben increases its length and (2) formation of fault strands parallel to the existing ones when large displacements need to be accommodated. The processes of formation and growth of new fault strands promote interaction among the new faults and between the new and preexisting faults on a larger scale. Increased displacement causes the width of the fault zone to increase resulting in wider pull

ISSN:0278-7407    

DOI:10.1029/TC001i001p00091

年代:1982

数据来源: WILEY

摘要:

During the interval between continental collision in the Devonian and continental breakup in the Triassic the northern Appalachians became the site of a wide plate boundary zone of dominantly right‐lateral strike slip. As is typical of intracontinental transforms, tectonism was both diachronous and rapidly variable along strike through regimes of ‘pure’ strike slip, transpressional deformation, and rapid subsidence of extensional basins. Up to 9 km of mainly nonmarine, clastic sediments accumulated in these local depocenters, which subsided episodically in two stages: (1) an initial phase of stretching and thinning of the lithosphere, when subsidence was rapid, fault controlled, and often accompanied by volcanism and (2) a subsequent phase of gradual thermal subsidence, during which the depositional basins expanded to bury the earlier border faults and progressively younger sedimentary units onlapped basement. The largest depocenter, the Magdalen Basin, opened as a pull‐apart between strike slip faults in Newfoundland and New Brunswick from late Devonian to early Carboniferous. Subsequent thermal subsidence affected a large area during medial and late Carboniferous, a phenomenon that is well recorded to the north and west, where no later tectonism occurred. In areas to the south and east of the basin, strike slip on other faults continued into the time of thermal subsidence, introducing complications such as localized transpressional deformation and rapid subsidence in smaller pull

ISSN:0278-7407    

DOI:10.1029/TC001i001p00107

年代:1982

数据来源: WILEY