Mechanics of tectogenesis in plate collision zones

Abstract

Although continental parts of tectonic plates can be stretched, fractured and rifted, it appears that orogenic belts only form on continental margins or in previously stretched and thinned regions of continents and cratons. This is because continental crust and lithosphere is much weaker under the action of extensional forces than it is under contractional forces. The stretching and shortening of crust and lithosphere is discussed using McKenzie's (1978) approach and the processes by which thinned or thickened lithosphere is restored to normal thickness are discussed in some detail. It is shown that the expressions for the initial and final changes of surface elevation are the same, apart from a difference in sign, for the cases of stretching and shortening when no material is added, or removed (by erosion). It is also shown that there is a critical value of the initial crustal thickness (~ 17 km in McKenzie's (1978) model) which must be exceeded if stretching is to cause crustal subsidence and shortening is to cause crustal elevation. Thinner crust, when shortened, will subside. This may be important in shortening processes at continental margins, where the thicker continental crust will rise and oceanward, the thinner crust will subside. The thermal and metamorphic changes associated with stretching (and thinning) and shortening (and thickening) are discussed. In the deeper parts of shortened and thickened crust prograde metamorphism will occur, possibly leading to anatexis. The strength and deformation mechanisms of crust and lithosphere are summarized. Finally, a collision tectonics model is presented based on the concept of shortening (with concomitant thickening) of the colliding passive and active margins, in which the important role of differential elevation changes across strike is emphasized. In the heart of the orogen will be a thickened crust consisting of thickened basement, a thick deformed sediment pile and nappes thrust from the margin. On a time scale of some tens of Ma, a thick metamorphosed and granitized lower crust will form after sufficient shortening has taken place.

Two layer model of lithospheric compression and uplift/exhumation in an intracratonic setting: an example from the Cooper–Eromanga Basins, Australia

“…In areas where there is evidence of crustal compression and hence crustal thickening, tectonic uplift is readily explained, indeed required, by the isostatic response to crustal thickening (Chadwick 1985;Murrell 1986). However, the origin of the tectonic force driving the regional component of 0.18 km uplift, where there is no evidence of crustal compression and thickening, is more enigmatic.…”

Subsidence and uplift by slab-related mantle dynamics: a driving mechanism for the Late Cretaceous and Cenozoic evolution of continental SE Asia?

“…The size of the indentor, rate of convergence and pre-existing structural trends are all important factors that may modify styles of deformation (e.g. Murrell 1986;Ellis 1996;Willingshofer & Sokoutis 2009), uplift and the extent of the resulting unconformity. Even major orogens such as the European Alps and New Zealand's Southern Alps show topographic profiles that rarely exceed several hundred kilometres in width ( Fig.…”

Tectonic implications of an 1846±1 Ma old migmatitic granite in south‐central Sweden

“…The heat required to induce melting originates either from increased mantle heat flow due to crustal extension (e.g., Murrell 1986) or from increased heat production in an orogenically thickened crust (e.g., England & Thompson 1984;England & Houseman 1989). Crustal thickening is confined to areas of continent-continent collision, as the accretion of a magmatic arc in a setting of continued crustal destruction results in the initiation of a new subduction zone farther away from the old arc rather than thickening of old continental crust (e.g., Hamilton 1981Hamilton , 1988.…”

“…Crustal thickening is confined to areas of continent-continent collision, as the accretion of a magmatic arc in a setting of continued crustal destruction results in the initiation of a new subduction zone farther away from the old arc rather than thickening of old continental crust (e.g., Hamilton 1981Hamilton , 1988. Considerable crustal thickening only occurs if there is no additional subductible crust available (e.g., Murrell 1986), and compressional forces have to be absorbed through internal deformation of the crustal blocks. Therefore, the age of anatectic crustal melts in collision settings provides a minimum estimate for the cessation of subduction (e.g., Harris et al 1990), the initiation of orogenic crustal thickening, and the development of thermal conditions favourable to generate melts in the thickened crust (e.g., Houseman et al 1981;England & Thompson 1984;Vielzeuf & Holloway 1988;LeBreton & Thompson 1988).…”