Lithospheric stretching

Lithospheric stretching, passive upwelling of asthenosphere and variable degrees of decompression melting at various mantle levels in an intracontinental rifting setting ... 

Figure 27 Occurrences of isoclinally folded and boudinaged mafic layers in the Beni Bousera otogenic peridotite, northern Morocco, after Allegre and Turcotte, 1986 reproduced by permission of Nature Publishing Group from Nature, 1986, 323, 123-127. In their marhle cake model, Allegre and Turcotte interpret these mafic layers as subducted oceanic lithosphere—modified by partial melting and metamorphism—that was stirred, stretched, and thinned by mantle convection (see, also, Kornprobst et al., 1990 Blichert-Toft et al., 1999). For Pearson et al. (1993), these pyroxenites would rather derive from crystallization products of partial melts from subducted crust. They would have been emplaced as dikes in the hanging wall of a subduction zone and deformed during the exhumation of the...

Fig. 6.3. Numerical modeling of the thermal regime in the lithosphere of the Oued el-Mya Basin, Takhoukht region. Solid line ist the base of the lithosphere as determined by intersection of the current geotherm with solidus curve for peridotite (shown in Fig. 6.4). Long dashed lines are isotherms Moho = base of the crust comp, transition = location of pyroxene peridotite-garnet peridotite compositional transition in the mantle. The considerable rise of isotherms is related to periods of thermal activation in the lithosphere in the Permian-Tfiassic and Cretaceous, Reduction of the crust thickness occurred during basement stretching (in the Ordovician-Devonian and Cretaceous) and during Permian erosion...

We note a slight rise of the isotherms during stretching of the lithosphere and a sharp rise of the isotherms during thermal activation. As a result of the two stretch-... 

This isostatic approach assumes a local isostatic response of the lithosphere to the load. The stretching of the lithosphere or its cooling from a warmer state is believed to account for the subsidence of the basement surface, whereas the thermal activation of the basement is assumed to result in raising of the basement surface. The high relief near the Red Sea is an example of a thermal activity action the Afar region is a result of simultaneous action of stretching and thermal activation of the basement. 

The sequence of tectonic events in the Akfadou area is derived from an analysis of the tectonic subsidence of the basement surface. The sequence basically repeats the sequence determined for the Takhoukht area stretching through the Ordovician-Devonian, thermal activation during the Permian, and basement stretching in the Early Cretaceous, with thermal activation of the lithosphere from the beginning of the Cretaceous until the present. A high maturation level of organic matter is observed in the lower horizons of the sedimentary section = 1.00-1.19% at depths of 3.0 3.9 km. 

Fig. 15.6 The subduction of a lithospheric plate during the Mesozoic Era caused the eruption of felsic and mafic lavas in the Antarctic Peninsula and in Marie Byrd Land. The crust of Gondwana in the back-arc basin was stretched which caused block-faulting and subsidence of the Byrd Subglacial Basin. Crustal extension of the back-arc basin may also have caused rifts to form in the Ross orogen and in the overlying rocks of...

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